Geochemistry and Genesis of Craton-derived Sediments from Active Continental Margins: Insights from the Mizoram Foreland Basin, NE India

Accepted Manuscript Geochemistry and Genesis of Craton-derived Sediments from Active Continental Margins: Insights from the Mizoram Foreland Basin, NE India

Sariput S. Sawant, K. Vijaya Kumar, V. Balaram, D.V. Subba Rao, K.S. Rao, R.P. Tiwari PII: DOI: Reference:

S0009-2541(17)30471-0 doi: 10.1016/j.chemgeo.2017.08.020 CHEMGE 18448

To appear in:

Chemical Geology

Received date: Revised date: Accepted date:

19 December 2016 30 July 2017 22 August 2017

Please cite this article as: Sariput S. Sawant, K. Vijaya Kumar, V. Balaram, D.V. Subba Rao, K.S. Rao, R.P. Tiwari , Geochemistry and Genesis of Craton-derived Sediments from Active Continental Margins: Insights from the Mizoram Foreland Basin, NE India, Chemical Geology (2017), doi: 10.1016/j.chemgeo.2017.08.020

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ACCEPTED MANUSCRIPT Geochemistry and Genesis of Craton-derived Sediments from Active Continental Margins: Insights from the Mizoram Foreland Basin, NE India

Geochemistry Division, CSIR-National Geophysical Research Institute, Uppal Road, Hyderabad – 500007, Telangana, India b School of Earth Sciences, SRTM University, Nanded – 431606, Maharashtra, India c Department of Geology, Mizoram University, Aizawl – 796004, Mizoram, India

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Sariput S. Sawanta, K. Vijaya Kumarb*, V. Balarama, D.V. Subba Raoa, K.S. Raoc, and R.P. Tiwaric

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*(Corresponding Author: K. Vijaya Kumar, E mail: [email protected]) Abstract

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This study investigates relative controls of source compositions and sedimentary processes (weathering + mineral sorting) on the bulk-rock geochemistry of clastic rocks

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deposited along an active continental margin setting by considering the Miocene Mizoram basin

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of NE India. It is a classic foreland accretionary sedimentary basin related to Himalaya orogeny and is ideally located to understand tectonic evolution of the Eastern Himalayas, Indo-Burmese arc, and Indian cratonic margin [the Meghalaya Plateau (also known as Shillong Plateau)]. These

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three tectonic domains represent potential suppliers of clastic sediments to the basin. The

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Mizoram basin comprises sandstone, siltstone and shale deposited under shallow marine conditions. Depletions in Ca and Sr indicate plagioclase-dominated weathering of the sources. The Mizoram strata are first-cycle sediments; however, quartz dilution has resulted in the

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decrease of both major (except SiO2) and trace elements, carbonate dilution has increased Ca and Sr, and heavy minerals have influenced Zr, HREE, Hf, U and Y abundances in a few of the studied Mizoram sediments. Newly formulated Rb/V-Zr/Zn-Sc/Nb and Rb/V-Zr/Zn-Eu/Eu* ternary plots distinguish sediments derived from mafic versus felsic sources, and allow the estimation of mafic:felsic proportions in the sedimentary provenances. We thus suggest an average tonalite-granodiorite source terrain for the Mizoram sediments. The geochemical evidences, including TiO2 (>0.7), Cr/Cr* (>1), V/V* (>1), Th/U (10.23), Nb/U (9.01) and Th/Rb (0.124) values, indicate that the Mizoram sediments were derived chiefly from old cratonic crust 1

ACCEPTED MANUSCRIPT of the Meghalaya Plateau. The source for the Miocene Mizoram sediments is slightly mafic than that supplying the modern Brahmaputra and Ganga sediments (dominated by the juvenile Himalayas). The Mizoram clastics provide indirect evidence for rise of the Meghalaya Plateau and a possible change in the Brahmaputra drainage as controlled by the uplift. We suggest that the Mizoram sediments are archives of the cratonic provenance in a foreland basin dominated by

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orogeny-derived detritus.

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Keywords: Foreland sediments; Mizoram basin; Meghalaya Plateau; Geochemistry; Cratonic

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provenance

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1. Introduction

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Source compositions, silicate weathering, sedimentary sorting and physico-chemical conditions at the sites of weathering, transportation, and deposition are fundamental controls on

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the geochemistry of sediments (Nesbitt and Young, 1982; Nesbitt and Young, 1984; Johnson, 1993; Taylor and McLennan, 1995; Roser, 2000; Garzanti et al., 2009; Bloemsma et al., 2012;

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Garzanti and Resentini, 2016). However, assessment of relative influence of source versus process on the geochemistry of sediments deposited in different tectonic environments is not yet

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fully understood. In general, the source composition plays a dominant role on the sediment geochemistry in active continental margin settings (Nesbitt, 1979; McLennan et al., 1990;

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Garzanti et al., 2004; Goodbred et al., 2014); in contrast, the contributions of weathering and sedimentary differentiation processes are significant in the geochemical variation of passive

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continental margin sediments (McLennan, 1989; Garzanti et al., 2014). Similarly, relative control of clastic and non-clastic materials responsible for chemical variability in the sediments depends on the depositional environments. The trace element budget of sediments deposited near continental margins is controlled by clastic material mixed with organic matter (Plank and Langmuir, 1998; Carpentier et al., 2009). Whereas, trace element contents in sediments deposited slowly, away from the continental margins are influenced by sea-water, hydrothermal solutions and organic matter in addition to the detrital material (Plank and Langmuir, 1998; Plank et al., 2007; Chauvel et al., 2009).

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ACCEPTED MANUSCRIPT Identifying the sources for sediments in the accretionary belts of active continental margins is one of the fundamental problems of sedimentary geochemistry (see Garzanti, 2016 for a review). In general, foreland basins are dominated by sediments derived from parental orogenic belts; however, ancient and recent foreland basins containing sediments derived from cratons are not uncommon (Cowan, 1993; Gupta and Allen, 2000; Najman et al., 2000; Robinson et al., 2001; Miall and Jones, 2003; DeCelles and Horton, 2003; Jain et al., 2009; Rengarajan et al.,

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2009; Sinha et al., 2009; Cawood et al., 2012; Lupker et al., 2012; Tripathi et al., 2013; Garzanti,

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2016 and references therein). Because sediments in foreland basin originate from fold-thrust belt,

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forebulge and craton (Schwab, 1986; McLennan et al., 1990; DeCelles and Hertel, 1989; Critelli and Ingersoll, 1994), they are ideally suited to assess relative contributions from old, matured

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cratonic sources and young, juvenile arc/collisional sources as well as differences in the style and intensity of source terrain weathering. Thus, sedimentary sequences in the foreland basins record

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spatio-temporal evolution of their provenances (DeCelles and Giles, 1996; Nie et al., 2012; Yang

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et al., 2012).

Trace element ratios such as Ni/Co, Th/Sc, Cr/Th, Sc/Nb, Rb/V and Eu/Eu*, considered

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to be independent from weathering and hydraulic sorting effects, are extensively utilized to characterize sedimentary provenances and mixing between different sources (Taylor and

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McLennan, 1985; Bhatia and Crook, 1986; Cullers, 1994, 1995, 2000; von Eynatten et al., 2016; Tang et al., 2016). Mineral sorting during transportation is the main complicating factor in

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quantitative estimation of contributions from different sources. Small proportions of accessory phases in sediments have dramatic effects on the trace element geochemistry and may lead to

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erroneous interpretations in the identification of sources and tectonic environments (Garzanti et al., 2010, 2011; Lupker et al., 2012; Garcon et al., 2013, 2014; Riboulleau et al., 2014).

In the present study, we have investigated the geochemical characteristics of the sediments from the Mizoram basin of NE India with an aim to understand the sedimentary provenances for foreland basins. It is a classic accretionary sedimentary basin of Miocene age related to Himalaya orogeny (Nandy, 2001). The Mizoram basin therefore is ideally located to understand tectonic evolution of the Eastern Himalayas, the Indo-Burmese arc, and Indian cratonic margin as these three tectonic domains stand as potential suppliers of foreland 3

ACCEPTED MANUSCRIPT sediments. The main objective of the present study is to assess the contributions from cratonic and juvenile sources and evaluate relative controls of source composition and sedimentary differentiation processes (weathering + hydraulic sorting) on the geochemistry of the Mizoram foreland basin sedimentary rocks in particular, and active continental margin clastic sediments in general.

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2. Geology, Depositional Environment and Tectonics

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The geology and distribution of sediments in the Mizoram basin, flanking the eastern and southeastern margin of the Meghalaya Plateau (also known as Shillong Plateau), are depicted in

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Figures 1A and B (modified after GSI, 1974) and Figure 2. A sketch of the lithologic units of the Mizoram basin in and around Aizawl town along with sample locations is shown in Figure 1C

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(modified after Malsawma et al., 2010). The stratigraphic succession with lithology, thickness and deposition environments are presented in Fig. 1D. Samples for the present study were

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collected from the Middle and Upper Bhuban formations (shown with an arrow in Fig. 1D) in and around Aizawl (Bawkwan-Durtlang and Bombay-Zebra sections) within the Mizoram basin.

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Samples were collected from laminated, massive and fissile shales and inter-bedded sandstones and siltstones. Three to five kilograms of in situ fresh samples were collected from road cuts and

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exposed outcrops; weathered parts of the rock had been carefully avoided or chipped out. Sampling was intended to cover different grain-size spectrum from sandstone to shale so that we

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can better evaluate the effects of mineral sorting on the chemical composition and grain-size

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related provenance.

The Disang, Barail and Surma groups of sediments, from bottom to top, constitute the Mizoram foreland basin, which is a sub-basin of the Surma basin (Fig. 2). These formations are overlain by Tipam sandstone, and Dupitila and Dihing formations. In the study area, the Surma Group represents a major cycle of sedimentation essentially during Miocene. The Surma Group is divided into Bhuban and Bokabil formations (Mathur and Evans, 1964; Ganguly, 1975; Nandy, 2001). The ~ 5000 m thick Bhuban Formation, focus of the present study, is further divided into Lower, Middle and Upper (Ganguly, 1975; Dasgupta, 1984; Jokhan Ram and Venkataraman, 1984; Nandy, 2001; Tiwari et al., 2006) based on the lithologic assemblages and 4

ACCEPTED MANUSCRIPT fossil content. The Lower Bhuban Formation comprises alternating shale and sandstone layers; the Middle Bhuban predominantly contains an argillaceous sequence with subordinate sandstones whereas the Upper Bhuban is constituted by alternating sequence of arenaceous and argillaceous clastics in almost equal proportions. Field features of the Mizoram sediments are shown in the supplementary figure SF1.

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The Paleogene Disang and Barail group sediments in the Surma basin are considered to

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have deposited under marine conditions whereas the Neogene Bhuban and Bokabil were

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deposited in shallow marine to transitional conditions (Holtrop and Keizer, 1970; Gopendra Kumar, 1997; Tiwari and Mehrotra, 2002; Ralte et al., 2011; Fig. 1D). The overlying Tipam

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formation represents Pliocene estuarine/fluvial sediments (Sinha and Sastri, 1973; Ganju, 1975; Karunakaran and Ranga Rao, 1979). Magnetostratigraphic studies have suggested that the

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Bhuban Formation of the Mizoram basin was deposited between 12.5 and 8 Ma with a significant increase in the rate of sedimentation at ~ 9.5 Ma where a facies change occurred from

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a shallow marine to a pro-delta depositional environment (Malsawma et al., 2010).

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Tectonic map of the NE India and adjoining regions is shown in Figure 2. The India plate was thrust beneath the Eurasian plate along its northern margin, resulting in creation of the

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Himalayas and subducted beneath the Burmese plate to produce Indo-Burmese arc and the outer arc Surma basin (Sarkar and Nandy, 1977; Shrivastava et al., 1979; Figure 2). The Mizoram

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foreland basin is considered to have formed by lithospheric flexure due to thrust loading in the Indo-Burmese arc. The Mizoram basin represents the continental part of the Indian plate nearer

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the junction where the oceanic part of the Indian plate subducted beneath the Burmese continental plate (Dasgupta and Nandy, 1995; Figure 2B).

3. Potential Sources and Significance of the Study

The Mizoram foreland basin is located in a complex active continental margin setting with cratonic (Meghalaya Plateau), Himalayan fold belt [Trans-Himalayan Sequence (THS), High Himalayan Crystallines (HHC) and Lower Himalaya Sequence (LHS)] and arc [IndoBurma Ranges (IBR)] sources being potential contributors to the sediments (Najman et al., 2010; 5

ACCEPTED MANUSCRIPT Bouilhol et al., 2013; Wu et al., 2014; Vadlamani et al., 2015; Li et al., 2017; Fig. 2). The Meghalaya Plateau is dominated by Paleo-Mesoproterozoic tonalitic gneisses, metagabbonorites and amphibolites + Neoproterozoic granites + Cretaceous basalts (Sylhet traps) + Tertiary shelf sediments (Chatterjee et al., 2007; Yin et al., 2010). The THS of the Himalayas is of NeoProterozoic and Cambrian age and comprises essentially the Indian passive margin sediments and voluminous Cambrian-Ordovician granitoids (Gansser, 1983; Yin, 2006); the HHC is of

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Neo-Proterozoic to Cambrian + Miocene age and contains orthogneisses and two-mica granites

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(Gopendra Kumar, 1997; Yin, 2006); the LHS is considered as a Paleo-Mesoproterozoic arc

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(Kohn et al., 2010) and is dominated by granitoids, schists, gneisses, quartzites and low-grade sediments (Webb et al., 2013). The Indo-Burmese ranges consist of a complex lithologic package

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including magma arc-related andesitic rocks with local basalt and rhyolite and fore arc-related thick turbiditic sequences of Cretaceous to Upper Eocene shales and sandstones, along with

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slices of underlying oceanic crust, and local ophiolites (Mitchell and McKerrow, 1975). The uplifted Meghalaya Plateau and the Indo-Burmese arc represent proximal sources whereas the

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Himalayas could be distal sources for the Mizoram sediments.

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The Surma basin in the Eastern Himalayas considered to have recorded dynamic changes in sedimentation controlled by tectonic evolution of the adjoining craton, arc and orogenic belt

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(Gani and Alam, 1999, 2003; Acharya, 2007). A major change from cratonic to Himalayan provenance was proposed at 38 Ma—the boundary between the Disang Group and the Barail

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Group (Najman et al., 2008; Vadlamani et al., 2015). The distal Bengal Fan sediments further record a sudden change in the Himalayan provenance from dominantly THS sources to HHC

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sources at around 12 Ma (Galy et al., 2010). This shift is correlated with the tectonic uplift of HHC along the Main Central Thrust (Kellet et al., 2015). Exhumation of the HHC between 16 and 12 Ma (Kellet et al., 2015) coincides with the uplift of the Meghalaya Plateau at ~ 15 to 8 Ma (Biswas et al., 2007; Clark and Bilham, 2008) and a possible change in the Brahmaputra drainage during 12 to 8 Ma period (Chirouze et al., 2013). Post 12 Ma, the composition, consequently the sources (dominated by the HHC), remained constant for sediments drained by the Brahmaputra system (Galy et al., 2010).

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ACCEPTED MANUSCRIPT It is evident that several tectonic changes took place in the Eastern Himalayan system during deposition of the Surma foreland basin sediments including tectonic exhumation of the HHC, elevation of the Meghalaya Plateau, possible change in the Brahmaputra drainage system (see Chirouze et al., 2013) and a change of main source for the detrital sediments. Among the three potential provenances, it is argued that the Surma Group sediments derived mostly from the tectonically rising Himalayas (Alam, 1989; Uddin and Lundberg, 1998, 2004; Rahman and

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Faupl, 2003). However, most of these propositions are based on studies focused on Surma basin

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sediments deposited far from the Meghalaya Plateau, hence where the cratonic provenance signal

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is more difficult to identify. In the present study, we considered sediments proximal to the

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Meghalaya Plateau, with the aim of identifying cratonic provenance in the Mizoram basin.

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4. Analytical Methods

Petrographic studies, including mineral identification and description of textural features,

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were carried out on Lietz Research Microscope (DM 2500 P). Geochemical analyses of Mizoram clastic rock samples were carried out in the chemical laboratories of National Geophysical

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Research Institute (NGRI), Hyderabad, employing an X-Ray Fluorescence Spectrometry (XRF) and an Inductively Coupled Plasma Mass Spectrometer (ICP-MS). For geochemical analysis, 2-3

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kg samples were rinsed thoroughly with distilled water. Pressed pellets were used for major and minor element XRF analysis. For the preparation of pressed pellets, collapsible aluminum cups

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were filled with nine grams of boric acid which acts as a binding material. One gram of ~230 mesh rock powder was sprayed uniformly on each pellet. Twenty tons of pressure was applied

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using Herzog hydraulic press (TP2d, Germany) to obtain ~40 mm diameter pellets. A Philips PW 1400 microprocessor controlled wavelength dispersive sequential X-ray Fluorescence Spectrometer (Philips, Holland) was employed to measure different peaks and background counts for the major and minor elements. International sandstone (GSR-4) and shale (GSR-5) reference samples (Institute of Geophysical and Geochemical Prospecting, IGGE, China) were used for calibration. Details of XRF analysis, precisions and accuracies achieved are given by Krishna et al. (2007).

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ACCEPTED MANUSCRIPT For trace and REE analysis on ICP-MS, a 10 mL acid mixture of HF + HNO3 + HCl (in 6:2:1 proportions) was added to a 50 milligram sample in a microwave vessel. Rh (0.5 mL of 10 mg/mL) was also added to the sample to act as an internal standard (for operating parameters see Balaram and Rao, 2003 and Roy et al., 2007). The acid treatment was repeated to ensure total dissolution. After adding 1 mL of HClO4, the solution was evaporated to incipient dryness. The residue was dissolved in 20 mL of 1:1 HNO3 and brought to a final volume of 250 mL by adding

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ultra-distilled water. A procedural blank solution was also prepared. Sample solutions were

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introduced into the ICP-MS (Perkin Elmer SCIEX, Model ELAN® DRC II ICP-Mass

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Spectrometer; Toronto, Ontario, Canada) and the selected ions were separated on the basis of their mass–to–charge ratio by quadrupole mass analyzer. To determine accuracy and precision of

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the instrument, replicate analysis of the standards and a shale sample were carried out. International sandstone (GSR-4) and shale (GSR-5) reference samples (as above) were used for

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calibration. The precisions for all trace and REE analyzed here were determined to be < 5% RSD (relative standard deviation) with comparable accuracy. Data for reference standards used for

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calibration and estimation of accuracy and precision are given in supplementary Table ST1.

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5. Results

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5.1 Petrography

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The Upper and Middle Bhuban formation clastics from the Mizoram basin are composed chiefly of quartz, feldspar, clinochlore, and muscovite in variable sizes and proportions. The

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sediments show poor to moderate sorting over a range of textures (see supplementary figure SF2). Carbonate matrix is predominant in the coarse-grained sediments but almost absent in the clay-rich ones. Sand- and silt-stones contain sub-angular quartz and plagioclase + K-feldspar + mica ± calcite with substantial clay (clinochlore) matrix. Quartz is monocrystalline and shows normal to oscillatory extinctions. Polysynthetic twinning is retained in a few plagioclase grains; zoning is intact in some alkali feldspars/plagioclases. K-feldspar (microcline + perthitic feldspar) is the main feldspar; however, in some of the sandstones, plagioclase dominates. Rarely feldspars show sericitization and are locally replaced by carbonate cement. In the sand-clay mixed sediments, calcite cement is restricted to the sandy portion. Plate-shaped muscovite is dominant 8

ACCEPTED MANUSCRIPT in coarse-grained rocks.

The shales consist mainly of quartz, clinochlore, albite, muscovite and K-feldspar. The shales are characterized by the presence of well preserved monocrystalline silt-size sub-angular quartz admixed with micaceous and ferruginous material. The shales show massive to layered structures, with some exhibiting graded layering. Iron oxide coatings are predominant on the clay

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matrix, which imparted dark brown/black colour to the shales. Some clasts containing quartz +

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may represent preserved fragment of weathered felsic protolith.

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feldspar + kaolinite + muscovite are connected by intergranular iron oxides (Fig. SF2), which

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Zircon, monazite, rutile and Fe-oxides are heavy minerals recorded in the Mizoram sediments, especially in the sandstones (Fig. SF3); Zircon is generally associated with Fe-oxides

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and rarely rimmed by magnetite. Some zircons show zoning (Fig. SF3); rare doubly tapering

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micro-zircon within zoned feldspar is also present (Fig. SF3).

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5.2 Geochemistry

Major and trace element compositions of the Mizoram clastic rocks are given in Table 1

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and illustrated in Figs. 3 and 4. Relevant petrogenetic ratios are presented in Table 2. In the Log (SiO2/Al2O3) vs. Log (Fe2O3/K2O) figure (after Herron, 1988; see Table 2) the Mizoram

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sedimentary rocks plot in the fields for shale, greywacke and litharenite (diagram not shown).

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5.2.1. Major elements

Representative binary plots of Fig. 3 illustrate the major element variations and interelement relationships. SiO2 exhibits a negative correlation with Fe2O3 (Fig. 3A); two carbonaterich sandstones show lower SiO2 and Fe2O3 due to dilution effect. Similar SiO2 contents for different grain-sized sediments suggest that quartz is the main detritus in the Mizoram sediments. A positive correlation between Al2O3 and Fe2O3 indicates the importance of clinochlore + mica in the Mizoram rocks; however, shales among themselves show a gentle negative trend (Fig. 3B). The Fe2O3-SiO2 and Fe2O3-Al2O3 relationships suggest that alumina is hosted in at least two 9

ACCEPTED MANUSCRIPT distinct phases: clay (+ mica) and feldspar; the former is richer in Fe and Al whereas feldspar contributes only Al to the bulk sediment. Similarly, iron is hosted in both silicate and oxide phases [clay (+ mica) / oxides (+ oxyhydroxides)]. A positive correlation between Fe and Ti (Fig. 3C) suggests either both the elements are hosted in a single mineral or resulted from hydrodynamic association of Fe-bearing and Ti-bearing heavy minerals. A good correlation between Al, Fe, K and Ti (Table 1) indicate that these elements are detrital in origin (see Taylor

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and McLennan, 1985). The importance of clinochlore + mica in the Mizoram sediments is

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indicated by the strong negative correlation between Al2O3 vs. K2O/Al2O3, Na2O/Al2O3 and

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SiO2/Al2O3 (Tables 1 and 2). Except for the two carbonate-rich sandstones, the CaO content in the Mizoram sediments (0.35 – 3.06 wt.%) is restricted. P2O5 and CaO do not share a collinear

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relationship. The Na2O content is independent of sediment grain-size; however, K2O is

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consistently lower in the sandstones.

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5.2.2. Trace elements

Analyzed Mizoram samples clearly show quartz and carbonate dilution effects in the

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trace element plots (Figs. 3D-F). Carbonate-rich sandstones (samples AZS-8 and AZS-6) are richer in Sr (Fig. 3D; Table 1); however quartz and carbonate dilution resulted in the decrease of

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all other trace elements (Figs 3E and F; Table 1). In the studied sediments, K is well correlated with Rb, Cs – trace elements accommodated in muscovite and Ba – trace element hosted by K-

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feldspar (Alfonso et al., 2003; Table 1) suggesting that bulk-rock K contents appear to be controlled by both clay/mica as well as K-feldspar. Most of the HFSE share a positive

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relationship with Zr, indicating the importance of zircon in the Mizoram sediments. The Ni, Co and Cu concentrations of the Mizoram sediments, especially in the sandstones, are positively correlated with MgO.

We illustrate variations in rare earth element abundances among the Mizoram sediments in the Chondrite-normalized plots (Fig. 4). The Chondrite-normalized REE patterns of the Mizoram sedimentary rocks display fractionated REE patterns with negative Eu anomalies (Figs. 4A to C). The REE patterns of the sandstones, siltstones and shales are almost sub-parallel with fractionated LREE, moderate negative Eu anomalies and flat (in sandstone) to dipping (in 10

ACCEPTED MANUSCRIPT siltstone and shale) HREE. The shales show higher REE spreads and also have higher (La/Yb)N ratios than the sandstones (Table 2 and Fig. 4). The sandstones have higher HREE than siltstones and shales, and PAAS; the siltstones and shales have lower HREE values compared to the PAAS (Fig. 4). The (La/Yb)N ratios are variable (7.07 to 17.5) and the average (La/Yb)N ratio for the Mizoram sediments (12.92) is higher than that in the PAAS (9.2; Taylor and McLennan 1985; Fig. 4). The shale with lowest REE has also lower abundance of all other trace elements (sample

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AZS-32; Table 1).

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6. Discussion

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In this section we evaluate the geochemical characteristics of the Mizoram clastic sediments to infer parent rock compositions, weathering + hydraulic sorting controls, and

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propose a model for Mizoram sedimentation.

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6.1. Weathering

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The mineralogic constitution of the Mizoram sedimentary rocks (quartz + feldspar + clinochlore + muscovite) is similar to phase assemblages of weathering profiles and recent flood-

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plain sediments from the Archaean basement of Southern India (Sharma and Rajamani, 2000; Singh and Rajamani, 2001), which the authors attributed to rapid neotectonic uplift and physical

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erosion of the terrains. Preservation of fragments of weathered protoliths, zoning in zircon and feldspars, zircon inclusions within feldspar, sub-angular shapes and poor sorting suggest that the

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sources for the Mizoram clastic sediments were proximal to the depositional basin.

The Chemical Index of Alteration (CIA = 100*Al2O3/Al2O3+CaO*+Na2O+K2O in molecular proportions, with CaO* representing the calcium present in silicate minerals only) is a good measure of weathering intensity (Nesbitt and Young, 1982). Low CIA values in two sandstones (AZS-8 and AZS-6; Table 2) is an artifact of presence of carbonates. The CIA values between 50 and 60 suggest low, 60 and 80 moderate and > 80 advanced stages of chemical weathering of parent rocks (Teng et al., 2004). The CIA values of Mizoram sediments, excluding sandstones with carbonate, (65-77; Table 2) suggest moderate chemical weathering of the 11

ACCEPTED MANUSCRIPT bedrock sources. As the upper continental crust is dominated by plagioclase– and K-feldspar– rich rocks and clay minerals, progressively weathered products plot parallel to the CN-A join in the CN (CaO + Na2O molar) - A (Al2O3 molar) - K (K2O molar) diagram (Nesbitt and Young, 1984, 1989; supplement figure SF4). Where sediments contain more potassium than the predicted trend, it is generally interpreted as an outcome of ‗K‘ metasomatism (Fedo et al., 1995). The CIA values for sand- and silt-stones tend to be lower than shale and plot towards the

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source rocks in the CN-Al-K plot (Fig. SF4). This difference in the CIA values for coarse- and

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fine-grained sediments supposedly derived from the same weathering profile is due to the fact

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that the sandstones contain less weathered mineral assemblages (quartz + feldspar), whereas shales contain more weathered phases (clay minerals) (see von Eynatten et al., 2016). The

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weathering trend of the Mizoram rocks, as illustrated in the CN-A-K diagram, suggest a likely

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granodioritic provenance (Fig. SF4).

Plagioclase-dominated weathering in the sources for the Mizoram sediments is clearly

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documented when the trace and REE abundances are double-normalized to the UCC composition (Fig. 5; Gaschnig et al., 2014). In the first normalization, the elemental concentrations are

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multiplied with Ysample/YUCC ratio and the obtained data is further normalized to the average UCC (Rudnick and Gao, 2003). The double-normalization minimizes the effects of silica and

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carbonate dilution; therefore the data reflect the control of sources. The elements are arranged on the basis of relative compatibilities (e.g., Gaschnig et al., 2014). For example, Sr and Nd

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partition similarly during magmatic processes (McDonough and Sun, 1995) therefore any differential variation between the two is due to post-magmatic processes. The Mizoram

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sediments show large depletion in Sr compared to the juxtaposed elements (Fig. 5A-C). Bulkrock Sr depletions of the Mizoram sediments are independent of grain-size (Fig. 5; see Garzanti et al., 2010; Lupker et al., 2012). Strong depletion in Sr is characteristic of sub-aerial weathering, especially when plagioclase is the dominant weathering phase (Garzanti et al., 2004). It is also been suggested that dissolution of hydrothermal phases and carbonate veins contribute to Sr depletion in the sediments (White et al., 1999; Jacobson and Blum, 2000). Large troughs for Sr in the double-normalized plots suggest that the sources to the Mizoram sediments have experienced predominant plagioclase weathering.

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ACCEPTED MANUSCRIPT 6.2. Discriminating weathering and recycling effects

We argue that the Mizoram sediments represent first-cycle sediments rather than recycled earlier-deposited sediments (i.e., recycled quartzose sources). Presence of a variety of original silicate minerals, lithic fragments and lack of compositional maturity in the Mizoram clastics is typical of first-cycle sediments (Dickinson and Suczek, 1979; Dickinson et al., 1983; Cox and

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Lowe, 1995). First-cycle sediments tend to be richer in Fe, Mg, Na and low in K relative to

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average upper crustal composition (Cox and Lowe, 1995). Such features also are exhibited by the

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Mizoram sediments (Table 1). Garzanti et al. (2014) suggested that the Weathering Index of Plagioclase-Chemical Index of Alteration (WIP-CIA) relationship is a good discriminator

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between first-cycle and recycled sediments (Fig. 6). First-cycle sediments show a linear inverse relationship between WIP and CIA with progressive weathering of a source of UCC composition

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(CIA/WIP = 0.6; Fig. 6). With continuous weathering the CIA/WIP ratio linearly increases. The CIA/WIP values generally range between 1 and 2 for first-cycle sediments and fall in the zone

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defined in Fig. 6 (Garzanti et al., 2014). Recycling essentially increases both carbonate and silica proportions in the sediments. Carbonate dilution increases WIP but decreases CIA values

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whereas silica dilution decreases WIP but almost does not affect CIA values (Garzanti et al., 2014; see Fig. 6). Our analyzed carbonate-rich (2 samples) and silica-rich (5 samples) do exhibit

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these predicted trends. Except for rocks affected by silica- and carbonate-dilution, all other Mizoram sediments have CIA/WIP values between 1.33 and 1.82, and plot close to the PAAS

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(post-Archaean Australian Shale) composition within the first-cycle sediment field. Variations in CIA and WIP values for the Mizoram clastics illustrate their first-cycle sediment characteristics

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with limited influence of quartz- and carbonate-dilution.

6.3. Hydraulic sorting

Hydrodynamic processes induce segregation of material based on grain-size, shape and density, which in turn strongly controls the chemical composition of detrital sedimentary rocks (McLennan et al., 1993; Singh and Rajamani, 2001; Ohta, 2004; Garzanti et al., 2010, 2011; von Eynatten et al., 2016). Sedimentary differentiation through mineral sorting and heavy mineral concentration during transportation needs to be considered to model source characteristics and to 13

ACCEPTED MANUSCRIPT accurately identify tectonic settings (Garzanti et al., 2010, 2011; Lupker et al., 2012; Riboulleau et al., 2014). Mineral sorting results in selective enrichment of elements accommodated in clay minerals such as Al, Cs, Rb, Th and LREE especially in fine-grained sediments (Riboulleau et al., 2014). Of course, quartz enrichment has a dilution effect on all major and trace elements excepting Si; carbonate enrichment results in the increase of Ca and Sr contents.

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The Mizoram sediments rich in silica or calcium (5 sandstones + 2 siltstones) show grain-

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size based distinction in the major element plots (Fig. 3). The sandstones are richer in Y, Zr, Hf,

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Pb, U and HREE (elements that partition into the zircon structure; Fujimaki, 1986; McLennan, 1989; McLennan et al., 1993; Carpentier et al., 2009) than those in shales and siltstones (Fig. 7;

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Table 1). Two sandstones have elevated La abundances, and thus plot away from the array, possibly due to monazite presence (Fig. 7B). Two of the sandstones contain relatively higher Y

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concentrations (Fig. 7C), which we suggest could be due to presence of monazite in addition to zircon. Two sandstones possessing higher Sr concentrations (Fig. 7D) also have high CaO

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contents (Table 1). Further evidence for the grain-size based geochemical distinction within the Mizoram sediments comes from Nb/Yb, Nb/Y, Nb/Ta, Zn/Zr, Cu/Zr and V/Lu ratios (Table 2),

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with sandstone having consistently lower ratios than the siltstones and shales. This distinction is due to partition of Yb, Y, Zr and Lu into zircon, which is enriched in sandstones. PAAS-

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normalized Ce/Ce* values and UCC-normalized V/V* values also distinguish the Mizoram

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6.4. Sources

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clastic sediments based on grain-size (Table 2).

In general, sediment chemistry is compared with that of potential sources of known composition to evaluate the provenance (Latimer et al., 2006; Monien et al., 2012). Pinpointing a specific source becomes difficult if possible sources exhibit similar geochemical characteristics (Pe-Piper et al., 2008). We have utilized major and trace elements including Al, Fe3+, HFSE and transition elements, which are considered to be geochemically immobile and independent of sedimentary differentiation processes (Taylor and McLennan, 1985; Bhatia and Crook, 1986; McLennan et al., 1990; Fedo et al., 1995; Young and Nesbitt, 1999; Cullers, 1994, 1995, 2000), thereby reflecting the characteristics of the original protoliths for the Mizoram sediments. 14

ACCEPTED MANUSCRIPT 6.4.1. Source Lithology

Trace element ratios such as La/Co, Th/Sc, Eu/Eu* and Rb/V are utilized to distinguish sediments derived from mafic versus felsic sources (Bhatia and Crook, 1986; Cullers et al., 1988; von Eynatten et al., 2016). We have formulated a new Rb/V-Zr/Zn-Sc/Nb ternary plot to discriminate among the possible sources for the Mizoram clastics (Fig. 8). Rb/V ratio effectively

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discriminate sediments derived from basalts and granites. Rb is higher in sediments sourced from

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granitic protoliths whereas V is higher in sediments derived from basaltic sources (von Eynatten

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et al., 2016). Sc is enriched in the sediments derived from mafic sources as a result Sc/Nb ratio defines mafic end member in the Rb/V-Zr/Zn-Sc/Nb ternary plot. Both Sc/Nb and Rb/V ratios

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are not affected by grain-size distributions. Zn is enriched in fine-grained sediments independent of source lithology. Zr is more abundant in the coarser fraction. Therefore, Zr/Zn ratio reflects

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the grain-size control on sediment geochemistry, and shares a positive relationship with increasing grain-size of the sediments from clay to coarse sand (von Eynatten et al., 2016; Fig.

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8).

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When plotted in the Rb/V-Zr/Zn-Sc/Nb ternary diagram, basalts and rhyolites have distinct behavior (Fig. SF5). The basalts plot parallel to the Sc/Nb-Zr/Zn segment; in contrast,

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rhyolites plot parallel to the Rb/V-Zr/Zn segment (Fig. SF5). Sediments derived from the basalts and rhyolites plot similar to their protoliths. Sediments derived from the basaltic source plot

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parallel and close to the Sc/Nb-Zr/Zn segment (Fig. 8). Sediments having granitic provenance plot parallel and close to the Rb/V and Zr/Zn line, and with increasing mafic content, the point of

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intersection would show an anti-clockwise rotation from Rb/V towards Sc/Nb axis (Fig. 8). Therefore, the Rb/V and Sc/Nb axes represent the felsic and mafic end member provenances respectively and the intersection point on the Sc/Nb-Rb/V line gives approximate mafic:felsic proportion in the sedimentary provenance. Different grain-sized sediments derived from a single provenance or grain-size separates from single sediment plot in a linear array between Zr/Zn axis and some point on the Rb/V-Sc/Nb line (Fig. 8). If the sediments are homogenized by mixing then the sediments derived from multiple provenances also plot in a linear array from Zr/Zn axis towards Rb/V-Sc/Nb segment. The intercepting point on the Rb/V and Sc/Nb axis defines the average composition of the multiple provenances contributed to the sediments. The Mizoram 15

ACCEPTED MANUSCRIPT clastics define an array from Zr/Zn axis towards Rb/V-Sc/Nb line and fall in the field defined by sediments derived from tonalite-granodiorite sources (Fig. 8). Note that the sandstones plot towards the Zr/Zn axis and shales plot away from it. We found similar relationships when Eu/Eu* was substituted for Sc/Nb in the Rb/V-Zr/Zn-Sc/Nb ternary plot as similar to Sc/Nb ratio, Eu/Eu* in the sediments also distinguishes mafic and felsic sources (Taylor and

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McLennan, 1985).

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6.4.2. Evidence for Cratonic Provenance

The UCC double-normalized patterns of HREE and first-row transition metals (i.e.

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compatible elements) are strongly controlled by the nature of the source terrain feeding the sediments. Positive slope for compatible elements in the double-normalized plots is characteristic

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of a provenance that is more mafic-rich than the Phanerozoic orogen-derived sediments (Gaschnig et al., 2014). Clasts derived from relatively mafic-rich sources show elevated

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abundances and peaks for V (V/V*>1) and Cr (Cr/Cr*>1) (Fig. 9; Table 2) whereas sediments derived from Phanerozoic orogen (felsic-rich) sources show lower abundances and depleted

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levels for the transition metals (Gaschnig et al., 2014). Flat HREE and peaks for V and Cr are present in all analyzed Mizoram sediments. The UCC double-normalized patterns of HREE and

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first-row transition metals for the Miocene Mizoram sediments suggest that they were derived from a relatively mafic crust than the average Phanerozoic orogenic sources. Three possible

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sources that can supply the Mizoram sediments with observed geochemical characteristics include the Archaean-Proterozoic Meghalaya Plateau, Archaean-Proterozoic Lower Himalayan

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Sequence (LHS) and the juvenile Indo-Burmese subduction-related arc crust.

Evidences for Archaean/Proterozoic sources for the Mizoram strata come from U and Rb behavior (Carpentier et al., 2013). Fundamental geochemical differences exist in the detritus derived from old cratonic versus young juvenile sources. Extensive loss of U and Rb is due to leaching by surface waters during continuous weathering of exposed cratonic weathered profiles tend to create a slow but systematic increase in Th/U and Th/Rb ratios with exposure time. Since the cratonic sources exposure time far exceeds that of the juvenile sources, the former tend to lose large amounts of U and Rb (Carpentier et al., 2013). Additionally, decay of these two 16

ACCEPTED MANUSCRIPT radioactive parents results in decrease of their abundances in the Archaean crust but not in juvenile sources. As a result, cratonic sediments contain much lower U and Rb contents compared to juvenile sediments for any given Th abundances (Fig. 10; Carpentier et al., 2013 and references therein). Low organic carbon in the Mizoram rocks (0.06 to 0.35%) allowed us to explore the Th-U relationship; a higher proportion of TOC in the sediments would make the ThU relationship difficult to interpret as organic-rich sediments are sinks for seawater uranium.

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Average Th/U (10.23), Nb/U (9.01) and Th/Rb (0.124) ratios for the Mizoram sediments suggest

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their cratonic derivation (6.87±3.38, 7.95±4.37 and 0.139±0.038 respectively) and substantially

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exceed those in juvenile sediments (3.05±0.80, 5.09±1.27 and 0.089±0.026 respectively; Carpentier et al., 2013). The present study shows that the trace element budget of the Mizoram

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foreland basin sedimentary rocks was dominated by cratonic sources but not juvenile arc crust. Foreland sedimentary basins occurring adjacent to the uplifted cratonic blocks tend to contain

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craton-derived first-cycle sediments (Cox and Lowe, 1995) as clearly illustrated by the Mizoram rocks (Fig. 5). Two potential cratonic provenances capable of supplying sediments to the

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Mizoram basin include the proximal Meghalaya Plateau and distal LHS of Himalayas. The Meghalaya Plateau contains abundant mafic rocks (amphibolites and meta-gabbro-norites +

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Sylhet basalts) and basement tonalities/granites. The LHS is dominated by Archaean and Proterozoic granitoids equivalent to Aravalli and Bundelkhand granites (Sharma, 1998; DeCelles

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et al., 2000), schists, gneisses, quartzites and low-grade sediments (Webb et al., 2013). The available data set cannot distinguish whether the sediments were derived from cratonic crust of

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the Meghalaya Plateau or Himalayan Sequences. However, the fact that the present-day Brahmaputra and Ganga sediments derived from multiple litho-terrains of Himalayas (consisting

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cratonic + juvenile + recycled components) broadly define a homogeneous felsic provenance (see discussion below), we prefer a proximal provenance for the Mizoram sediments to retain the relatively mafic-rich nature of the source. The readily available mafic-rich (cratonic) proximal source is the Meghalaya Plateau (see Fig. 2C). It is to be noted that basaltic to diabase grains and laterite soil clasts occur locally in the Meghalaya tributaries (Garzanti et al., 2004). Apparently, up to 80% plagioclase + lithic fragments and 40-45% orthoclase perthite were selectively dissolved from detritus in the Meghalaya rivers; quartz and microcline are stable phases (Garzanti et al., 2004). Mizoram sandstones contain high feldspar/plagioclase ratios, conspicuous microcline, clinochlore and laterite clasts – all typical of sediments derived from cratonic sources 17

ACCEPTED MANUSCRIPT (Nesbitt et al., 1997). Mizoram sediments also show the geochemical signatures of selective plagioclase weathering (strong depletions in Ca and Sr; Fig. 5). We suggest that the Meghalaya Plateau is the most geologically likely source of the sediments supplied to the Mizoram basin.

6.5. A Model for Mizoram Sedimentation

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The Mizoram samples compared with Surma basin sediments and modern Brahmaputra-

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Ganga river sediments (Figs. 11 and 12) allow us to propose a model for sedimentation in the

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Mizoram basin as controlled by tectonics in an active continental margin setting.

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Grain-size controlled geochemical proxies like Si/Al and Zr/Zn show distinctly different distributions for sediments from the Surma and Mizoram basins (Figs. 11A and B). It is evident

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that matured coarse-grained sediments (sandstones) dominate data sets from other sub-basins of the Surma basin (Rahman and Suzuki, 2007a and b; Ranjeeta Devi and Mondal, 2008; Rahman

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et al., 2014). However, the Surma basin and Mizoram basin sediments show similar geochemical characteristics when grain-size independent geochemical proxies (Rb/V and Eu/Eu*) are

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compared (Figs. 11C and D). The Cr/Th and Eu/Eu* values are higher in sediments sourced from mafic-rich sources and lower in the sediments derived from felsic-rock dominated provenances

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(Taylor and McLennan, 1985; Condie and Wronkiewicz, 1990). Similarly, Rb/V in the sediments is positively correlated with felsic component in the sources (von Eynatten et al., 2016). Both

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Mizoram and Surma basin sediments require more mafic provenance than the UCC (Fig. 11). However, the Surma basin average sediment composition suggests slightly less mafic component

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in the provenance than the one that contributed to the Mizoram basin. Both recycled orogen and cratonic interior are considered to be the provenances for the Surma basin sediments (Rahman and Suzuki, 2007a and b; Ranjeeta Devi and Mondal, 2008; Malsawma et al., 2010; Rahman et al., 2014). Contributions from both orogenic (felsic-rich) and cratonic (mafic-rich) sources possibly resulted in relatively lower Cr/Th ratios in the Surma basin sediments (Fig. 11). In comparison, the Mizoram basin sediments retain the mafic-rich nature of the provenance as it was considered to have dominantly fed by the Meghalaya Plateau cratonic crust.

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ACCEPTED MANUSCRIPT Geochemical characteristics of the Mizoram and Brahmaputra-Ganga clastic sediments are illustrated in Figure 12. The Ganga sediments are low in Cr/Th and Eu/Eu* (Fig. 11A) and high in Rb/V (Fig. 11B); in contrast, the Mizoram sediments are high in Cr/Th and Eu/Eu* and low in Rb/V compared to the Ganga and Brahmaputra sediments. The Brahmaputra sediments show intermediate values between Mizoram and Ganga sediments. The low-Cr/Th sediments, sourced from Ganges drainage, were derived dominantly from felsic provenances of LHS and

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HHC (Garcon et al., 2013; Goodbred et al., 2014 and references therein). Contribution from the

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THS in addition to the HHC to the Brahmaputra sediments (Galy and France-Lanord, 2001;

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Singh and France-Lanord, 2002; Garzanti et al., 2004, 2010 and 2011) resulted in relatively higher Cr/Th and Eu/Eu* and lower Rb/V in the Brahmaputra sediments compared to those of

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Ganga (Fig. 12) The Mizoram sediments inferred to be derived from the cratonic crust of Meghalaya Plateau with more mafic component than the Himalayas resulted in elevated Cr/Th

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and Eu/Eu* and depleted Rb/V values compared to the modern Brahmaputra and Ganga sediments (Fig. 12). Average compositions of Mizoram (Cr/Th = 8.50; Eu/Eu* = 0.67; Rb/V =

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1.40), Brahmaputra (Cr/Th = 5.36; Eu/Eu* = 0.63; Rb/V = 1.56) and Ganga (Cr/Th = 2.66; Eu/Eu* = 0.54; Rb/V = 2.43) sediments suggest decreasing mafic component in the provenances

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from the former to the latter. Therefore, the geochemical differences between the Mizoram, Brahmaputra and Ganga sediments are linked to the input of different sources. We argue that

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provenance for the Mizoram sediments is slightly more mafic than that for the present-day

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Brahmaputra-Ganga deltaic system.

We suggest that it may be possible for sediments of the exposed upper continental crust

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to retain geochemical characteristics, albeit locally, of a single geologic terrain, if the chemical weathering of the sources is moderate and sediments are derived by focused erosion. The Meghalaya Plateau and the Mizoram basin offered such a scenario during the Miocene. Apatite He (U/Th/Sm) ages indicate that the Meghalaya Plateau has undergone rapid elevation between 14 and 8 Ma (Clark and Bilham, 2008). During this time interval, there is a significant increase in the rate of sedimentation within the Mizoram basin (Malsawma et al., 2010). Thus the accelerated erosion rates of the Meghalaya Plateau were temporally associated with rapid sedimentation and accretion leading to shallower deposits in the Surma basin, or at least in subbasins proximal to the Plateau as demonstrated in the present study. Mizoram clastics retain 19

ACCEPTED MANUSCRIPT geochemical characteristics of this rapidly elevated and eroded cratonic lithology (Figs. 10, 11 and 12).

Chirouze et al. (2013 and references therein) suggested that the Brahmaputra River changed its drainage over time. Figure 13A illustrates the inferred Miocene (between 12 and 8 Ma; Chirouze et al., 2013) drainage of the Brahmaputra cutting across the Meghalaya Plateau,

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and the present-day Brahmaputra valley, which may be a piggyback basin of the Meghalaya

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uplift (Yin et al., 2010). If this change in the course of Brahmaputra from cutting across to

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circumventing the Meghalaya Plateau is valid, then a decrease in the mafic component contributed by the Meghalaya Plateau has to have occurred in the Brahmaputra-sourced

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sediments. The modern Brahmaputra sediments are primarily derived from Himalayan felsic sources (Galy and France-Lanord, 2001; Singh and France-Lanord, 2002; Garzanti et al., 2010,

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2011) with the Namcha Barwa massif, composed of High Himalayan Crystalline rocks, contributing ~40% of the Brahmaputra sediment flux (Garzanti et al., 2004; Cina et al., 2009).

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Miocene Mizoram rocks contain higher proportions of mafic components than do modern Brahmaputra sediments (Figs. 12 and 13B), suggesting that felsic components increased in the

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Brahmaputra sediments with decreasing Meghalaya and increasing Himalayan contribution. The sources for Ganga sediments are far more felsic than the Mizoram and Brahmaputra sediments

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(Figs. 12 and 13B). At present Meghalaya Plateau tributaries contribute 11±5% to the Brahmaputra drainage (Garzanti et al., 2004). However, Mizoram sediment compositions

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indicate that the contribution would have been much more when the Meghalaya Plateau was

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rising.

In summary, bulk compositions of the Mizoram clastics record the Meghalaya Plateau uplift and a dominant cratonic provenance. It is evident that sediment evolution in a tectonically controlled foreland basin records the tectonic histories of juxtaposed geologic terrains. It is also possible that different domains in a single large sedimentary basin may receive sediments from distinctly different sources. The present study illustrates that elevated craton margins are important sources for sediments in accretionary sedimentary basins of active continental margins.

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ACCEPTED MANUSCRIPT 7. Conclusions

We have investigated sediments from the Mizoram basin of NE India with a two-fold aim: 1) to assess contributions from cratonic and juvenile sources and 2) to evaluate relative controls of source composition and sedimentary differentiation processes (hydraulic sorting) on the bulk-rock geochemistry of sediments deposited in an active continental margin. We show

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that weathering and mineral dilution effects are detectable but relatively less important than

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parent terrain chemistry in producing the sedimentary geochemical variations. Mizoram strata

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are first-cycle sediments derived from exposed sources that were subjected to plagioclasedominated sub-aerial weathering. Dilution by quartz resulted in the decrease of both major

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(except SiO2) and trace elements, whereas carbonate dilution increased CaO and Sr, and heavy minerals influenced Zr, HREE, Hf, U and Y abundances in only a few of the studied Mizoram

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sediments.

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To assess contribution from different sources, we have constructed new Rb/V-Zr/ZnSc/Nb and Rb/V-Zr/Zn-Eu/Eu* ternary plots, which clearly separate sediments derived from

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mafic versus felsic sources and estimate the mafic:felsic proportions in sedimentary provenances. The geochemical variations in the Mizoram clastics correspond to tonalite-granodirite source

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terrains. Based on geochemical evidence, we propose that the Miocene Mizoram sediments were derived from a cratonic source (the Meghalaya Plateau). Mizoram strata provide indirect

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evidence for the uplift of the Meghalaya Plateau and possible change in the Brahmaputra drainage as controlled by Plateau uplift. The source of the Miocene sediments is slightly more

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mafic than those of modern Brahmaputra and Ganga sediments. It is possible that the Brahmaputra sediments became relatively more felsic post-Meghalaya uplift due to increased contribution from orogenic provenances and decreased inputs from the ancient craton. In spite of the availability of multiple sources, sedimentary basins may derive their detritus from a localized geologic terrain through focused erosion under favorable conditions. The subsiding Mizoram basin and dynamically uplifting Meghalaya Plateau offer such a scenario during the Miocene (15 to 8 Ma) in NE India. Such sediments inform in our understanding of the evolution of foreland basins, especially when a rising cratonic landmass temporarily dominates sediment supply over more formidable orogenic sources. 21

ACCEPTED MANUSCRIPT Acknowledgements

The research results presented in this paper are a part of the Ph.D. thesis of SSS. Microscopic facility at the SRTM University is funded by FIST-DST program. Gary Ernst (Stanford University), Bob Cullers (Kansas State University) and two anonymous journal reviewers provided constructive comments on an earlier version of the manuscript. Catherine

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Chauvel (executive editor) made significant editorial comments. The Director of NGRI permitted

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SSS to publish this paper. We thank the above said institutions and individuals for help and

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support.

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Explanation to Figures

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Figure 1. Geological framework of the Mizoram basin, NE India (A and B; after GSI, 1974) and sketch lithologic map of the Mizoram basin in and around Aizawl town (C; after Malsawma et

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al., 2010). Stratigraphy of the Mizoram basin along with lithology, thickness and deposition environments is shown in D (compiled from Karunakaran, 1974; Ganju, 1975; Mandaokar, 2000;

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Tiwari and Kachchra, 2003; Tiwari et al., 2006; Vaidyanadhan and Ramakrishnan, 2010 and references therein). Samples for the present study come from the Middle and Upper Bhuban

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formations (shown with an arrow in D). Four samples are not shown as they fall further west of

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area shown in the map. See the web version of article for colour figure.

Figure 2. Tectonic map of the NE India and adjoining regions (A and B; modified after Evans

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1964). The India plate was thrusted beneath the Eurasian plate in the northern margin resulting in the creation of Himalayas and subducted beneath the Burmese plate to produce Indo-Burmese arc. The Surma basin is an outer arc basin within the greater Bengal basin (Sarkar and Nandy, 1977) linked to the Indo-Burmese collision. Study area is shown within the Surma basin. Figure 2C schematically illustrates the possible sources for the Mizoram sediments (Mizoram is a subbasin within the Surma basin). The uplifted Meghalaya Plateau and the Indo-Burmese arc form proximal sources whereas the Himalayas form the distal sources for the Mizoram sediments. Axial and transverse rivers are schematically shown. See the web version of article for colour figure. 22

ACCEPTED MANUSCRIPT Figure 3. Major and trace element binary variation plots for sediments from the Mizoram basin, NE India. The elemental distribution in some of the samples is controlled by silica- and carbonate-dilution. See the web version of article for colour figure.

Figure 4. Chondrite-normalized rare earth element plots for sandstone (A), siltstone (B) and shale (C) from the Mizoram basin, NE India. The REE pattern of PAAS is shown for

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(1980) respectively. See the web version of article for colour figure.

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comparison. The PAAS and Chondrite values are after Taylor and McLennan (1985) and Hanson

Figure 5. Normalized abundance diagrams showing the light rare earth elements (LREEs) and Sr

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for the sediments from the Mizoram basin, NE India. Elemental abundances are multiplied by the ratio of the measures sample Y concentration to average Y content of the upper continental crust

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(UCC) to minimize the effects of quartz and carbonate dilution, and then these abundances are normalized to the average UCC (Rudnick and Gao, 2003). For discussion see the text. See the

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web version of article for colour figure.

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Figure 6. WIP vs. CIA variation in the sediments from the Mizoram basin, NE India depicting the influence of recycling on the chemical indices. Quartz dilution affects WIP strongly but not

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CIA and carbonate dilution drastically decreases CIA and increases WIP. Field for first-cycle sediments is after Garzanti et al. (2014). The UCC (upper continental crust) and PAAS (post-

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Archaean Australian Shale) compositions are after Rudnick and Gao (2003) and Taylor and McLennan (1985) respectively. Majority of the Mizoram sediments represent first-cycle

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sediments. CIA = Chemical Index of Alteration (100*Al2O3/Al2O3+CaO*+Na2O+K2O in molecular proportions, with CaO* representing the calcium present in silicate minerals only; Nesbitt and Young, 1982); WIP = Weathering Index (WIP = 100 x [CaO*/0.7 + 2Na 2O/0.35+ 2K2O/0.25 + MgO/0.9] in molecular proportions, with CaO* representing the calcium present in silicate minerals only; Parkar, 1970). For discussion see the text. See the web version of article for colour figure.

Figure 7. Trace element vs. Nb variation plots for the sediments from the Mizoram basin, NE India. Geochemical effects of detrital zircon and other heavy minerals are clearly identified in 23

ACCEPTED MANUSCRIPT these plots. See the web version of article for colour figure.

Figure 8. Rb/V-Zr/Zn-Sc/Nb ternary diagram for discrimination of provenance for the sediments from the Mizoram basin, NE India. Rb/V and Sc/Nb axes represent the felsic and mafic end members respectively. Sediments derived from the granitic source would plot parallel to the Rb/V-Zr/Zn line whereas the ones derived from basaltic source plot parallel to the Sc/Nb-Zr/Zn

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line. The Mizoram sediments plot in the field defined by sediments derived from tonalite-

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granodiorite sources. Data for gabbro-diorite, tonalite-granodiorite and monzogranite

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provenances are after von Eynatten et al. (2016). For discussion see the text. See the web version

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of article for colour figure.

Figure 9. Normalized abundance diagrams showing heavy rare earth elements (HREEs) and

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transition metals for the sediments from the Mizoram basin, NE India. Normalization scheme is as in Fig. 5. The Mizoram sediments show enrichment in V and Cr indicating a provenance with

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more mafic component than the present UCC. For discussion see the text. See the web version of

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article for colour figure.

Figure 10. U vs. Th (A) and Rb vs.Th (B) variation plots for the sediments from the Mizoram

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basin, NE India. Fields for juvenile and craton sediments are constructed using the data from Carpentier et al. (2009). Anomalous data points (up to 10-15% of the total data) are not

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considered while constructing the fields. Note that the Mizoram sediments are restricted to the fields for craton-derived sediments. For discussion see the text. See the web version of article for

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colour figure.

Figure 11. SiO2/Al2O3 vs. Cr/Th (A), Zr/Zn vs. Cr/Th (B), Eu/Eu* vs. Cr/Th (C) and Rb/V vs. Cr/Th (D) variation plots for the sediments from the Mizoram and Surma basins. The Surma sediments show much larger hydraulic sorting effects as indicated by higher SiO2/Al2O3 and Zr/Zn values. However, the sorting independent parameters like Eu/Eu* and Rb/V almost have similar values for the Mizoram and Surma basin sediments; the Surma basin additionally contains sediments with slightly higher Rb/V values. The average Mizoram sediment has higher Cr/Th and lower Rb/V values than the average Surma basin sediment. Data for Surma basin 24

ACCEPTED MANUSCRIPT sediments are after Rahman and Suzuki (2007a and b) and Rahman et el. (2014); UCC values are after Rudnick and Gao (2003). For discussion see the text. See the web version of article for colour figure.

Figure 12. Eu/Eu* vs. Cr/Th (A) and Rb/V vs. Cr/Th (B) variation plots for the sediments from the Mizoram basin, Brahmaputra and Ganga rivers. The Mizoram sediments with higher Cr/Th

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and Eu/Eu*, and lower Rb/V values than the modern Brahmaputra-Ganga deltaic system are

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interpreted to have sourced from the relatively mafic-rich (cratonic) provenance. Anomalous data

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points (1 sample from Ganga and 2 samples from Brahmaputra) are not considered while constructing the fields; however all the samples are considered while computing averages. Data

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for modern Brahmaputra and Ganga sediments are after Garzanti et el. (2010, 2011) and Garcon et al. (2013) respectively; UCC values are after Rudnick and Gao (2003). For discussion see the

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text. See the web version of article for colour figure.

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Figure 13. Modern and inferred mid-Miocene (between 12 and 8 Ma) drainage of Brahmaputra River (A; modified after Chirouze et al., 2013). It is possible that the Brahmaputra changed its

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drainage due to elevation of Meghalaya Plateau between 15 and 8 Ma. Rb/V-Zr/Zn-Eu/Eu* plot for the sediments from the Mizoram basin and the modern Brahmaputra and Ganga sediments

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(B). Rb/V and Eu/Eu* represent the felsic and mafic end members respectively. Sediments derived from the basalts will plot parallel to the Eu/Eu*-Zr/Zn segment whereas the ones derived

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from granitic source plot parallel to the Rb/V-Zr/Zn segment. The Mizoram sediments seem to have derived from provenances more mafic-rich than those for Brahmaputra and Ganga

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sediments. Data for modern Brahmaputra and Ganga sediments are after Garzanti et el. (2010, 2011) and Garcon et al. (2013) respectively. For discussion see the text. See the web version of article for colour figure.

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Uddin, A., Lundberg, N., 2004. Miocene sedimentation and subsidence during continent-continent collision, Bengal Basin, Bangladesh. Sedimentary Geology 164, 131–146. Vadlamani, R., Wu, Fu-W., Ji, Wei-Q., 2015. Detrital zircon U-Pb age and Hf isotopic composition from foreland sediments of the Assam basin, NE India: constraints on sediment provenance and tectonics of the eastern Himalaya. Journal of Asian Earth Sciences 111, 254–267. Vaidyanadhan, R., Ramakrishnan, M., 2010. Geology of India. Geological Society of India 2, 997p. von Eynatten, H., Tolosana-Delgado, R., Karius, V., Bachmann, K., Caracciolo, L., 2016. Sediment generation in humid Mediterranean setting: grain-size and source-rock control on sediment geochemistry and mineralogy (Sila Massif, Calabria). Sedimentary Geology 336, 68–80. Webb, A.A.G., Yin, A., Dubey, C.S., 2013. U–Pb zircon geochronology of major lithologic units in the eastern Himalaya: implications for the origin and assembly of Himalayan rocks. Geological Society of America Bulletin 125, 499–522. White, A.F., Bullen, T.D., Vivit, D.V., Schulz, M.S., Clow, D.W., 1999. The role of disseminated calcite in the chemical weathering of granitoid rocks. Geochimica et Cosmochimica Acta 63, 1939–1953. Wu, F.Y., Ji, W.Q., Wang, J.G., Liu, C.-Z., Chung, S.L., Clift, P.D., 2014. Zircon U–Pb and Hf isotope constraints on the onset time of the India-Asia collision. American Journal of Science 314. http://dx.doi.org/10.2475/04.2014.00. Yang, X., He, D., Wang, Q., Tang, Y., Tao, H., Li, D., 2012. Provenance and tectonic setting of the carboniferous sedimentary rocks of the East Junggar basin, China: Evidence from geochemistry and U-Pb zircon geochronology. Gondwana Research 22, 567–584. Yin, A., 2006. Cenozoic tectonic evolution of the Himalayan orogeny as constrained by along-strike variation of structural geometry, exhumation history, and foreland sedimentation. Earth Science Reviews 76, 1–131. Yin, A., Dubey, C.S., Webb, A.A.G., Kelty, T.K., Grove, M., Gehrels, G.E., Burgess, W.P., 2010. Geologic correlation of the Himalayan orogen and Indian craton. Part 1. Structural geology, U-Pb zircon geochronology, and tectonic evolution of the Shillong plateau and its neighbouring regions in NE India. The Geological Society of America 122, 336–359. Young, G.M., Nesbitt, W.H., 1999. Paleoclimatology and provenance of the glaciogenic Gowganda Formation (Paleoproterozoic), Ontario, Canada: a chemostratigraphic approach. Geological Society of America Bulletin 111, 264–274.

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ACCEPTED MANUSCRIPT Table 1. Whole-rock major and trace element composition of sediments from the Mizoram basin, NE India Sandstone

T

AZS AZS AZS AZS AZS AZS AZS AZS AZS AZS AZS AZS AZS AZS AZS AZS -57 -51 -4 -6 -8 -20 -21 -22 -14 -36 -52 -54 -48 -3 -11 -26

IP

23.8 23.8 23.7 23.7 23.7 23.6 23.6 23.6 23.7 23.7 23.8 23.8 23.7 23.7 23.7 23.7 095 064 344 344 501 819 819 819 016 692 062 095 828 376 055 651

CR

92.6 92.6 92.6 92.6 92.6 92.7 92.7 92.7 92.7 92.7 92.6 92.6 92.6 92.6 92.7 92.7 235 612 699 699 778 161 161 161 195 355 298 235 754 820 175 346

278

US

Sampl e No.: Latitut de (oN) Longit ude (oE) Elevat ion (m)

315 858 858 865 1047 1047 1047 1062 1251 206 278 436 827 1064 1189

M

AN

Major eleme nts (wt.%)

61.8 75.2 67.6 63.2 60.6 80.6 64.8 74.1 63.6 67.9 61.8 69.1 65.4 62.5 4 6 2 2 8 4 4 3 3 9 1 60.9 9 71.3 4 6

ED

SiO2

Siltstone

1.00 0.58 0.84 0.61 0.44 0.8 0.88 0.85 0.94 0.88 0.97 1.1 0.79 0.74 0.91 0.93 18.4 12.1 14.5 12.4 10.4 15.7 12.5 18.0 16.0 18.5 18.7 14.9 13.6 17.0 19.0 9 1 2 3 3 9.55 9 6 4 3 1 5 2 8 7 4

MnO

0.09 0.07 0.07 0.28 0.63 0.02 0.16 0.05 0.09 0.03 0.05 0.07 0.05 0.05 0.07 0.05

MgO CaO

2.71 1.56 2.65 1.94 1.42 1.09 2.23 1.66 2.3 2.18 3 2.98 2.65 2.59 2.35 2.05 12.5 18.4 0.64 0.71 2.21 9 4 0.27 3.6 0.75 0.68 0.56 1.06 1.00 1.45 1.31 0.60 0.36

Na2O

1.14 1.43 1.34 1.17 0.95 1.18 1.12 1.3 1.18 1.31 0.86 1.04 1.48 1.5 1.14 1.14

K2O

3.59 2.2 2.77 2.33 2.2 1.54 2.94 2.29 3.56 2.76

P2O5

0.12 0.12 0.12 0.12 0.13 0.1 0.12 0.11 0.13 0.14 0.12 0.12 0.13 0.11 0.14 0.09 98.0 98.8 98.7 98.8 98.3 98.3 98.7 98.7 98.6 98.3 98.3 98.9 98.2 98.4 98.5 4 5 1 9 4 4 1 2 2 1 8 4 2 98.9 6 3

Total

CE

PT

TiO2 Al2O 3 Fe2O 3#

8.2 9.29 4.90 5.05 7.52 7.86

AC

8.42 4.81 6.57 4.2 3.02 3.15 7.03 5.02 8.07 6.43

47

3.8 3.69 2.66 2.57 3.22 4.45

ACCEPTED MANUSCRIPT LFSE (ppm) 11.3 10.7 10.3 2 7.92 2 2 11.9

15.3 3.79 7.21 5.24 4.78 2.28 7.88 4.46 11.1 6.93 5.43

Rb

184 79.1 117 91.9 83.0 56.3 128 89.1 160 115 103 160 133 188 179 194

Ba

550 339 389 339 359 258 451 366 533 422 402 483 479 621 585 610

Sr

124 109 125 170 249 54.0 130 87.0 101 122 102 104 110 110 116 121

Ga

26.7

13 11.6 9.09 19.1 13.6 23.7 19.1

CR

HFSE (ppm)

14 24.0 20.0 26.5 24.4 26.8

IP

12 16.7

T

Cs

18.3 11.2 14.6 11.7 9.8 16.0 18.0 16.9 16.8 14.4 15.1 17.9 15.6 19.4 17.0 17.6

U

2.16 2.45 2.08 2.47 2.05 2.30 1.95 2.15 2.29 2.19 1.30 1.40 1.09 1.32 1.24 1.28

Nb

18.3 7.26 12.3 8.56 9.17 9.61 14.6 11.4 16.1 13.4 10.1 17.2 14.3 17.2 15.8 16.1

Ta

1.51 0.65 1.08 0.70 0.71 0.85 1.16 0.93 1.35 1.13 0.68 1.03 0.87 1.03 0.95 0.96

Pb

21.4 18.7 17.6 16.8 16.7 17.2 27.1 16.8 21.8 16.1 7.98 14.0 12.7 13.8 12.8 15.3

Zr

249 90.7 124 72.9 92.8 138 204 166 238 182 33.1 78.2 59.6 82.5 67.4 70.9

Hf

7.19 3.03 4.03 2.51 3.10 4.50 6.15 5.09 6.92 5.80 1.03 2.33 1.86 2.62 2.11 2.14

Y

36.9 25.7 29.5 36.4 66.1 27.3 32.1 28.9 33.3 33.2 18.2 21.0 21.8 18.1 20.4 24.6

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PT CE

Trans ition metals (ppm)

US

Th

127 150 136 178 121 250 139 191 120 157 107 125 113 119 101 118

Co

22.3 12.2 16.8 12.5 10.2 8.3 16.7 12.7 18.3 15.3 11.3 26.6 17.0 16.4 17.7 19.7

Ni

62.7 38.4 50.3 47.7 41.7 24.5 47.6 38.0 48.2 57.8 34.8 73.4 53.4 38.1 41.2 51.8

Sc

17.0 7.75 11.1 8.40 7.43 6.67 12.7 8.98 15.0 12.7 9.06 15.7 13.1 16.0 14.8 17.7

V

123 61.9 74.4 60.0 51.3 48.2 91.9 70.0 105 91.6 68.0 127 109 117 116 136

Cu

30.5 10.3 12.8 19.1 22.8 10.4 31.4 19.9 27.0 18.4 16.7 37.1 27.2 29.9 27.6 43.4

Zn

60.0 34.4 45.0 56.8 49.4 34.8 63.4 46.3 58.6 48.5 50.0 84.7 78.6 73.1 73.1 81.3

AC

Cr

REE (ppm) 48

ACCEPTED MANUSCRIPT

43.0 30.0 34.5 30.3 32.2 46.8 46.2 46.5 42.0 38.9 39.3 43.7 42.8 50.5 45.5 43.9

Ce

86.8 59.9 68.5 59.3 57.3 94.3 90.8 93.8 83.7 78.2 74.7 82.2 82.7 92.2 85.3 84.3

Pr

10.4 7.28 8.38 7.15 7.22 11.4 11.1 11.4 10.1 9.57 9.27 10.0 10.2 11.2 10.5 10.5

Nd

37.8 26.3 29.9 26.1 27.1 40.5 39.4 40.8 36.8 34.4 33.2 36.0 37.4 40.4 38.2 38.8

Sm

7.59 5.38 6.04 5.66 5.81 8.01 7.93 8.26 7.48 7.15 6.57 7.21 7.63 7.58 7.67 8.25

Eu

1.67 1.23 1.24 1.22 1.32 1.42 1.59 1.48 1.63 1.53 1.27 1.45 1.57 1.35 1.48 1.73

Gd

7.14 5.20 5.79 5.53 6.46 7.05 7.30 7.07 6.91 6.68 5.17 5.46 6.06 5.50 5.88 6.47

Tb

1.28 0.96 1.02 1.04 1.26 1.13 1.29 1.26 1.22 1.20 0.86 0.95 1.03 0.87 0.96 1.13

Dy

6.91 4.83 5.65 5.83 7.80 5.64 6.64 6.05 6.52 6.46 4.18 4.81 5.01 4.24 4.60 5.50

Ho

1.31 0.90 1.03 1.15 1.59 1.00 1.17 1.04 1.20 1.20 0.74 0.85 0.89 0.78 0.83 0.97

Er

3.85 2.49 2.79 3.19 4.23 2.71 3.30 2.88 3.28 3.32 1.91 2.41 2.28 2.21 2.22 2.54

Tm

0.57 0.36 0.43 0.49 0.63 0.38 0.52 0.44 0.51 0.45 0.29 0.37 0.34 0.35 0.36 0.38

Yb

3.70 2.49 2.73 2.98 3.44 2.32 3.16 2.63 3.22 3.04 1.70 2.21 2.02 2.17 2.06 2.30

Lu

0.54 0.36 0.38 0.45 0.51 0.35 0.48 0.38 0.48 0.43 0.23 0.33 0.29 0.32 0.30 0.34

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Table 1. Contd… …..

Shale

AC

CE

PT

Sample AZS- AZS- AZS- AZS- AZS- AZS- AZS- AZS- AZS- AZS- AZS- AZS- AZS- AZSNo.: 50 56 16 17 43 44 39 24 25 40 31 32 33 35 Latitude 23.79 23.80 23.69 23.69 23.74 23.74 23.74 23.76 23.76 23.74 23.76 23.76 23.76 23.76 (oN) 47 95 34 34 77 77 96 40 40 77 52 69 69 96 Longitu 92.66 92.62 92.71 92.71 92.73 92.73 92.73 92.73 92.73 92.73 92.73 92.73 92.73 92.73 de (oE) 50 35 90 90 54 54 47 37 37 54 45 60 60 58 Elevatio n (m) 393 393 1024 1024 1033 1033 1034 1169 1169 1181 1192 1219 1219 1250 Major element s (wt.%) SiO2

62.44 61.46 63.05 62.01 63.28 65.22 62.11 65.22 63.33 63.14 62.05 64.22 62.98 60.23

TiO2

0.87 1.10 0.95 1.03 0.92 0.76 0.89 0.98 0.88 0.98 0.99 0.93 0.90 0.93

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ACCEPTED MANUSCRIPT Al2O3

16.55 15.02 15.68 16.01 15.66 16.58 16.22 16.03 19.9 15.95 15.88 17.03 16.22 15.77 7.07 0.07 2.94 1.28

9.51 0.12 2.57 0.86

6.58 8.4 7.87 6.30 0.10 0.07 0.07 0.06 2.62 2.61 2.46 1.92 0.40 0.58 0.63 0.45

7.44 0.09 2.25 0.40

Na2O

1.17 1.03 1.01 1.29 1.08 1.31 0.99 1.28 1.08 1.11 1.05 1.18 1.02 1.00

K2O

3.50 3.43 3.50 3.26 3.78 2.64 3.98 3.61 4.25 3.70 4.00 3.41 4.03 4.29

P2O5 Total

0.12 0.14 0.09 0.13 0.10 0.09 0.12 0.09 0.09 0.10 0.11 0.09 0.10 0.16 96.01 95.24 93.98 95.39 95.85 95.33 94.49 97.28 99.00 95.72 95.51 95.91 95.43 95.35

7.89 0.06 2.39 0.40

8.58 0.10 2.32 0.43

6.65 0.06 1.96 0.38

7.62 0.08 2.09 0.39

9.85 0.16 2.27 0.69

IP

CR

ED

M

AN

9.30 11.5 6.61 7.50 10.3 10.6 10.4 9.43 8.75 5.25 5.30 3.82 7.78 9.23 155 157 141 132 159 175 178 177 143 102 102 71.1 119 151 500 482 433 462 479 550 566 601 445 404 404 247 400 498 93.8 160 117 104 112 90.9 109 99.5 98.1 110 74.3 57.5 123 88.6 21.9 24.4 28.8 21.1 22.9 24.1 24.9 25.6 19.6 14.6 15.9 10.2 17.5 22.6

18.1 2.26 17.1 1.25 9.18 114 3.02 28.3

CE

17.0 1.04 16.1 1.00 14.4 77.0 2.43 24.2

AC

16.2 1.27 15.3 0.93 12.5 170 1.91 17.5

PT

HFSE (ppm) Th U Nb Ta Pb Zr Hf Y

7.00 0.04 2.08 0.35

US

LFSE (ppm) Cs Rb Ba Sr Ga

7.65 0.06 1.96 0.40

T

Fe2O3# MnO MgO CaO

15.7 1.28 14.9 0.89 11.2 61.7 1.85 20.0

17.1 1.52 15.3 0.95 12.8 62.1 1.91 20.1

18.7 1.29 16.4 1.01 13.2 74.2 2.39 22.2

17.5 1.35 16.2 0.97 14.3 74.9 2.17 18.2

Transiti on metals (ppm)

50

19.1 3.30 16.5 1.22 10.8 154 4.82 28.7

16.9 1.27 13.9 0.93 11.3 53.4 1.75 19.8

14.0 1.21 9.68 0.66 9.02 30.8 0.96 14.8

13.0 1.44 11.4 0.70 10.0 45.1 1.31 15.0

8.84 0.68 7.23 0.45 5.75 30.1 0.96 9.53

13.8 1.22 11.1 0.71 11.4 43.1 1.34 19.2

16.7 1.33 16.1 1.00 11.0 70.7 2.19 19.4

ACCEPTED MANUSCRIPT 117 17.7 53.7 14.3 113 28.9 86.7

125 21.3 72.0 16.5 128 37.5 82.4

83.4 17.4 47.2 14.5 115 37.0 58.9

116 17.9 53.8 13.8 116 32.1 78.7

124 15.6 57.3 15.4 123 31.2 74.2

114 18.6 52.3 15.0 112 30.5 79.4

111 19.4 55.6 15.4 116 29.7 79.2

273 17.4 59.5 15.4 120 61.2 89.3

42.7 80.8 9.94 36.0 6.89 1.32 5.25 0.87 4.00 0.72 1.93 0.29 1.77 0.27

41.9 80.5 9.93 36.8 7.66 1.57 6.03 1.06 5.28 0.99 2.66 0.42 2.49 0.37

45.9 86.3 10.6 38.3 7.66 1.47 5.90 1.01 5.03 0.95 2.55 0.43 2.38 0.37

43.8 82.5 10.2 37.2 7.39 1.45 5.62 0.93 4.45 0.81 2.24 0.32 1.89 0.29

42.8 78.9 9.49 34.0 6.49 1.38 5.17 0.87 4.28 0.80 2.24 0.35 2.19 0.33

47.6 90.8 11.2 40.9 8.02 1.55 6.15 1.03 5.03 0.94 2.48 0.38 2.44 0.33

45.7 84.8 10.5 37.9 7.25 1.35 5.37 0.90 4.09 0.74 2.09 0.32 1.98 0.29

44.0 89.0 10.4 38.2 7.49 1.42 6.08 1.04 5.59 1.09 2.98 0.51 3.13 0.47

122 16.7 57.7 11.9 92.9 25.4 70.1

103 13.0 36.2 9.65 72.1 17.6 60.8

61.7 8.24 18.8 6.27 47.9 11.3 32.6

143 13.4 54.4 11.4 88.3 22.0 61.1

117 18.3 55.4 14.5 118 27.5 80.4

23.5 44.3 5.43 19.9 3.97 0.75 2.95 0.47 2.29 0.41 1.06 0.17 0.98 0.15

35.1 66.6 8.19 30.5 6.15 1.26 4.80 0.85 4.12 0.78 2.03 0.31 1.88 0.28

44.8 84.8 10.4 37.6 7.56 1.42 5.64 0.93 4.46 0.81 2.23 0.33 2.10 0.29

39.1 74.3 9.12 33.1 6.67 1.32 5.15 0.88 4.48 0.82 2.15 0.33 1.97 0.30

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PT

CE

CR

IP

REE (ppm) La Ce Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yb Lu

68 13.1 45.0 9.13 70.5 15.6 84.9

T

Cr Co Ni Sc V Cu Zn

AC

# = Total Fe as Fe2O3

51

37.2 70.0 8.51 30.7 5.99 1.16 4.80 0.74 3.59 0.61 1.59 0.26 1.35 0.21

36.5 70.4 8.69 31.3 6.39 1.18 4.73 0.79 3.66 0.60 1.63 0.24 1.44 0.20

ACCEPTED MANUSCRIPT Table 2. Petrogenetic ratios for sediments from the Mizoram basin, NE India Sandstone

Siltstone

T

AZ AZ AZ AZ AZ S- S- S- AZ S- S52 54 48 S-3 11 26 23.8 23.8 23.7 23.7 23.7 23.7 062 095 828 376 055 651 92.6 92.6 92.6 92.6 92.7 92.7 298 235 754 820 175 346 106 118 206 278 436 827 4 9

US

CR

IP

AZ AZ AZ AZ AZ AZ AZ SS- AZ AZ AZ S- SS- SSSample No.: 57 51 S-4 S-6 S-8 20 21 22 14 36 23.8 23.8 23.7 23.7 23.7 23.6 23.6 23.6 23.7 23.7 Latitutde (oN) 095 064 344 344 501 819 819 819 016 692 Longitude 92.6 92.6 92.6 92.6 92.6 92.7 92.7 92.7 92.7 92.7 (oE) 235 612 699 699 778 161 161 161 195 355 104 104 104 106 125 Elevation (m) 278 315 858 858 865 7 7 7 2 1

M

73.6 67.9 67.1 31.5 21.9 71.2 72.6 68.7 72.9 73.3 73.5 72.4 66.7 65.0 73.6 72.8 49.7 37.6 48.4 67.6 77.9 27.3 50.2 37.5 48.7 42.5 50.8 51.3 46.8 45.8 45.4 54.6 1.48 1.81 1.39 0.47 0.28 2.61 1.45 1.83 1.49 1.73 1.45 1.41 1.43 1.42 1.62 1.33

ED

0.37 0.34 0.38 0.26 0.14 0.31 0.38 0.34 0.36 0.37 0.33 0.40 0.27 0.29 0.37 0.25

PT

0.52 0.79 0.67 0.71 0.76 0.93 0.61 0.77 0.55 0.63 0.52 0.51 0.67 0.72 0.58 0.52 0.15 0.13 0.18 0.16 0.14 0.11 0.14 0.13 0.13 0.14 0.16 0.16 0.18 0.19 0.14 0.11

CE

0.06 0.12 0.09 0.09 0.09 0.12 0.07 0.10 0.07 0.08 0.05 0.06 0.10 0.11 0.07 0.06 3.15 1.54 2.07 1.99 2.32 1.31 2.63 1.76 3.02 2.11 4.42 3.55 1.80 1.71 2.82 3.90

AC

CIA WIP CIA/WIP Log(Fe2O3/K 2O) Log(SiO2/Al2 O3) MgO/Al2O3M gO/Al2O3 Na2O/Al2O3 Na2O/Al2O3 K2O/Na2OK2 O/Na2O Al2O3/SiO2A l2O3/SiO2 K2O/Al2O3K 2O/Al2O3 Fe2O3/SiO2F e2O3/SiO2

AN

Bulk-rock ratios

Cr/Ni Ni/Co Cr/Zn Cr/Th

0.30 0.16 0.21 0.20 0.17 0.12 0.24 0.17 0.28 0.24 0.30 0.31 0.22 0.19 0.26 0.30 0.19 0.18 0.19 0.19 0.21 0.16 0.19 0.18 0.20 0.17 0.21 0.20 0.18 0.19 0.19 0.23 0.14 0.06 0.10 0.07 0.05 0.04 0.11 0.07 0.13 0.09 10.2 2.03 3.91 2.70 3.73 2.90 3 2.93 5.02 2.50 2.72 2.82 3.14 2.99 3.82 4.08 2.96 2.86 3.00 2.64 3.79 2.12 4.37 3.02 3.13 2.44 7.18 2.20 4.12 2.06 3.24 6.95 13.4 9.34 15.2 12.3 15.6 7.77 11.2 7.16 10.9 52

0.13 0.15 0.07 0.07 0.11 0.13 3.07 1.70 2.12 3.12 2.45 2.27 3.08 2.76 3.14 2.32 2.33 2.63 2.14 1.47 1.44 1.62 1.38 1.45 8.52 9.09 8.56 8.52 9.05 8.93

ACCEPTED MANUSCRIPT 7 Th/Sc Th/Rb

4

2

1

9

1

1.08 1.44 1.31 1.39 1.32 2.40 1.41 1.88 1.12 1.13 1.66 1.14 1.19 1.21 1.14 0.99 0.10 0.14 0.12 0.13 0.12 0.28 0.14 0.19 0.11 0.13 0.15 0.11 0.12 0.10 0.09 0.09 11.6 12.7 14.3 14.7 13.6 13.6 8.46 4.55 6.99 4.73 4.78 6.97 9.22 7.89 7.36 6.58 2 8 5 2 4 8 0.24 0.38 0.36 0.78 0.53 0.25 0.31 0.28 0.25 0.27 1.51 1.08 1.32 0.89 1.08 1.15 0.12 0.11 0.10 0.26 0.25 0.08 0.15 0.12 0.11 0.10 0.50 0.47 0.46 0.36 0.41 0.61 32.7 16.8 20.4 12.8 15.9 17.2 25.7 20.1 31.7 25.4 10.8 10.8 8 5 7 8 7 9 3 1 8 9 5.04 5 7.81 8 8.79 8.60 12.0 11.2 11.3 12.3 12.8 11.2 12.5 12.2 11.9 11.8 14.9 16.7 16.4 16.6 16.7 16.8 9 0 6 1 9 9 3 6 2 9 4 1 1 5 6 4 12.2 13.1 13.0 12.7 12.5 8.46 2.96 5.89 3.46 4.47 4.18 7.49 5.30 7.05 6.14 7.79 7 8 4 3 5 0.49 0.28 0.42 0.24 0.14 0.35 0.45 0.39 0.48 0.41 0.56 0.82 0.66 0.95 0.77 0.66 4.94 2.91 4.50 2.88 2.66 4.14 4.61 4.32 5.00 4.42 5.94 7.78 7.10 7.93 7.68 7.01 10.3 32.2 15.4 20.1 15.4 18.1 18.1 5.26 8.67 7.43 9 8.73 9.01 6.40 8.01 5.31 5.93 7 5 0 2 5 4 1.50 1.28 1.57 1.53 1.62 1.17 1.39 1.27 1.52 1.26 1.51 1.26 1.22 1.60 1.54 1.42 1.49 0.73 0.93 0.54 0.33 1.04 0.99 1.02 1.58 0.94 1.01 1.54 1.21 1.71 1.54 1.60 4.87 3.01 3.91 3.52 3.07 1.39 3.25 2.19 4.35 3.35 3.09 4.44 3.56 4.66 4.68 4.99 6.91 6.67 7.00 7.16 7.18 6.19 6.69 6.54 6.74 6.04 7.12 6.65 6.66 7.10 7.32 7.23 0.93 1.07 0.90 0.98 0.81 0.69 0.87 0.79 0.93 0.95 0.90 0.91 0.92 0.93 0.94 1.10 1.57 1.53 1.51 1.53 1.55 1.36 1.50 1.52 1.58 1.50 1.59 1.53 1.53 1.65 1.65 1.51 2.53 3.87 3.11 3.61 4.33 7.02 3.63 5.18 2.80 3.06 4.33 2.79 3.26 3.16 3.07 2.48 24.7 27.7 23.1 27.1 35.2 31.2 27.0 28.9 29.1 27.6 35.6 18.1 28.1 37.9 33.1 30.9 2 4 1 5 0 6 8 2 4 5 1 7 6 0 3 5 1.93 2.45 2.05 2.43 3.15 5.66 2.77 3.67 2.29 2.55 3.47 1.64 2.51 3.08 2.58 2.23 228 174 198 134 100 137 193 186 222 213 295 381 373 362 388 402

T

Th/U Zn/Zr Cu/Zr

IP

Zr/Sm

CR

Nb/Ta

US

Nb/U Nb/Y Nb/Yb

PT

ED

M

AN

Nd/Hf Rb/V Rb/Sr Rb/Nd Rb/Ga Sc/Nb Ga/Sc La/Sc

AC

CE

Ba/Co La/Co V/Lu Chondritenormalized ratios

13.9 10.1 12.2 16.0 13.7 14.7 16.1 15.3 13.2 8 4 6 9.04 8.88 0 0 0 6 1 4

(La/Yb)N

8.06 8.34 8.77 7.07 6.49

(Dy/Yb)N Eu/Eu*

1.25 1.30 1.39 1.31 1.52 1.63 1.41 1.54 1.36 1.42 1.65 1.46 1.66 1.31 1.50 1.60 0.69 0.70 0.64 0.66 0.65 0.57 0.63 0.59 0.69 0.67 0.66 0.70 0.70 0.64 0.67 0.72

PAAS53

ACCEPTED MANUSCRIPT normalized ratios MREE/MREE * 1.20 1.28 1.21 1.21 1.19 1.27 1.25 1.28 1.25 1.25 1.31 1.26 1.36 1.21 1.32 1.39 Eu/Eu* 1.06 1.08 0.98 1.02 1.00 0.88 0.97 0.90 1.05 1.03 1.01 1.07 1.08 0.98 1.03 1.10

CR

IP

T

UCC doublenormalized ratios

0.24 0.30 0.31 0.48 0.69 0.10 0.24 0.16 0.20 0.26 1.27 1.16 1.14 0.97 0.82 0.99 1.17 1.19 1.24 1.22 10.1 1.96 4.62 2.98 5.21 4.15 0 2.87 5.37 2.18 3.38 0.93 0.92 0.91 0.91 0.85 0.93 0.91 0.92 0.92 0.92

Cr/Cr* Ce/Ce*

ED

M

Table 2. Contd……

CE

AC

Longitude (oE) Elevation (m)

AZ S50 23. 794 7 92. 665 0

AZ S56 23. 809 5 92. 623 5

AZ S16 23. 693 4 92. 719 0 102 393 393 4

PT

Sample No.:

Latitude (oN)

0.22 0.21 0.22 0.20 0.22 0.23 1.47 1.74 1.74 1.61 1.72 1.74 3.16 1.83 2.27 2.19 1.87 1.89 0.89 0.89 0.90 0.88 0.88 0.89

AN

US

Sr/Sr* V/V*

AZ S17 23. 693 4 92. 719 0 102 4

Shale AZ S43 23. 747 7 92. 735 4 103 3

AZ S44 23. 747 7 92. 735 4 103 3

AZ S39 23. 749 6 92. 734 7 103 4

AZ S24 23. 764 0 92. 733 7 116 9

AZ S25 23. 764 0 92. 733 7 116 9

AZ S40 23. 747 7 92. 735 4 118 1

AZ S31 23. 765 2 92. 734 5 119 2

AZ S32 23. 766 9 92. 736 0 121 9

AZ S33 23. 766 9 92. 736 0 121 9

AZ S35 23. 769 6 92. 735 8 125 0

Bulk-rock ratios

CIA WIP CIA/WIP

69. 69. 72. 71. 69. 74. 71. 71. 74. 71. 70. 73. 71. 68. 2 4 5 5 8 7 8 1 5 6 7 6 4 8 51. 47. 47. 47. 50. 40. 49. 48. 52. 48. 50. 45. 50. 53. 5 4 0 8 1 6 7 6 4 9 8 9 0 1 1.3 1.4 1.5 1.4 1.3 1.8 1.4 1.4 1.4 1.4 1.3 1.6 1.4 1.2 5 6 4 9 9 4 4 6 2 6 9 0 3 9 54

ACCEPTED MANUSCRIPT

Ni/Co

Cr/Th

PT

Th/Sc

Cu/Zr Zr/Sm Nb/Ta Nb/U Nb/Y

AC

Zn/Zr

CE

Th/Rb Th/U

55

0.2 7 0.5 8 0.1 4 0.0 6 4.0 2 0.2 6 0.2 5 0.1 2 1.9 9 2.8 6 1.4 0 6.3 1 1.1 4 0.1 0 12. 98 1.0 6 0.4 0 10. 34 16. 71 12. 01 0.8 9

0.3 3 0.6 1 0.1 2 0.0 8 2.8 2 0.2 5 0.2 3 0.1 2 4.5 9 3.4 2 3.0 6 14. 29 1.2 4 0.1 1 5.7 8 0.5 8 0.4 0 20. 54 13. 56 4.9 9 0.5 7

0.2 2 0.5 0 0.1 0 0.0 5 3.9 4 0.3 1 0.2 1 0.1 1 2.1 2 3.4 5 1.7 4 7.2 3 1.4 2 0.1 2 13. 31 1.3 1 0.4 8 8.0 0 14. 99 10. 98 0.7 0

0.3 3 0.6 0 0.1 5 0.0 7 3.3 3 0.2 5 0.2 3 0.1 2 1.5 0 3.4 3 0.8 0 4.8 4 1.5 3 0.1 4 11. 55 2.7 6 0.5 1 5.1 4 14. 77 7.9 9 0.6 5

T

0.3 8 0.5 9 0.1 2 0.0 8 2.0 2 0.2 5 0.1 6 0.1 0 2.1 8 2.8 0 1.4 3 6.0 8 1.2 5 0.1 1 14. 52 1.0 7 0.4 1 9.2 5 16. 17 12. 72 0.7 4

IP

0.3 2 0.6 1 0.1 6 0.0 7 3.5 0 0.2 5 0.2 4 0.1 2 2.1 6 3.6 6 1.6 7 7.2 2 1.1 1 0.1 1 11. 30 1.2 0 0.5 0 9.5 7 16. 14 10. 11 0.7 6

CR

0.4 1 0.5 9 0.1 6 0.0 8 2.5 3 0.2 6 0.2 0 0.1 4 2.1 6 3.0 1 1.4 8 7.4 0 1.1 4 0.1 2 12. 26 1.2 7 0.5 2 8.3 5 16. 69 11. 60 0.7 4

US

0.2 7 0.6 0 0.1 7 0.0 6 3.4 7 0.2 5 0.2 2 0.1 0 1.7 7 2.7 1 1.4 2 4.6 1 1.2 4 0.1 3 7.9 9 0.5 1 0.3 2 14. 94 13. 67 7.5 6 0.6 0

ED

Cr/Zn

0.4 4 0.6 1 0.1 7 0.0 7 3.3 3 0.2 4 0.2 3 0.1 5 1.7 4 3.3 8 1.5 2 7.3 7 1.0 3 0.1 1 16. 41 1.0 7 0.4 9 10. 06 16. 06 15. 54 0.6 6

AN

Cr/Ni

0.3 1 0.5 8 0.1 8 0.0 7 2.9 9 0.2 7 0.2 1 0.1 1 2.1 9 3.0 3 1.3 5 7.2 4 1.1 3 0.1 0 12. 79 0.5 1 0.1 7 24. 65 16. 37 12. 04 0.8 7

M

Log(Fe2O3/K2O)Log(Fe2O 3/K2O)Log(Fe2O3/K2O) Log(SiO2/Al2O3)Log(SiO2/ Al2O3)Log(SiO2/Al2O3) MgO/Al2O3MgO/Al2O3Mg O/Al2O3 Na2O/Al2O3Na2O/Al2O3N a2O/Al2O3 K2O/Na2OK2O/Na2OK2O/ Na2O Al2O3/SiO2Al2O3/SiO2Al2 O3/SiO2 K2O/Al2O3K2O/Al2O3K2 O/Al2O3 Fe2O3/SiO2Fe2O3/SiO2Fe2 O3/SiO2

0.3 3 0.5 9 0.1 5 0.0 7 3.8 1 0.2 6 0.2 5 0.1 4 2.8 4 2.7 8 1.6 9 7.9 0 1.3 5 0.1 3 9.0 6 1.3 5 0.3 9 7.0 5 16. 33 7.9 6 0.7 6

0.2 9 0.5 8 0.1 2 0.0 7 2.8 9 0.2 7 0.2 0 0.1 0 3.2 8 2.2 8 1.8 9 6.9 8 1.4 1 0.1 2 12. 96 1.0 8 0.3 7 7.6 0 16. 03 10. 60 0.7 6

0.2 8 0.5 9 0.1 3 0.0 6 3.9 5 0.2 6 0.2 5 0.1 2 2.6 4 4.0 7 2.3 5 10. 38 1.2 1 0.1 2 11. 31 1.4 2 0.5 1 7.0 1 15. 60 9.1 1 0.5 8

0.3 6 0.5 8 0.1 4 0.0 6 4.2 9 0.2 6 0.2 7 0.1 6 2.1 1 3.0 2 1.4 5 6.9 8 1.1 5 0.1 1 12. 56 1.1 4 0.3 9 9.3 6 16. 16 12. 10 0.8 3

ACCEPTED MANUSCRIPT

Rb/Ga Sc/Nb Ga/Sc La/Sc Ba/Co

(La/Yb)N

AC

(Dy/Yb)N Eu/Eu*

PT

CE

Chondrite-normalized ratios

ED

La/Co V/Lu

16. 72 1.4 9 0.6 7

11. 64 1.4 1 0.7 0

13. 36 1.3 5 0.6 7

16. 06 1.5 1 0.6 9

13. 59 1.3 0 0.7 3

13. 54 1.4 9 0.6 7

8.1 9 17. 46 1.5 3 1.6 3 4.7 1 7.1 6 0.9 5 1.6 2 2.9 7 29. 13 2.3 5 407

5.2 6 7.9 1 1.4 8 1.7 8 4.6 4 6.9 1 0.9 4 1.6 6 2.8 5 34. 53 2.5 3 253

7.0 8 18. 92 1.5 3 1.4 5 4.3 1 7.2 8 0.8 5 1.6 5 3.3 0 26. 63 2.3 4 310

7.1 8 31. 93 1.4 5 0.9 2 3.3 3 6.9 8 0.9 4 1.6 0 4.0 7 30. 77 2.8 3 342

7.9 3 23. 93 1.4 1 1.3 7 3.2 6 6.4 1 0.8 4 1.6 5 3.7 8 31. 05 2.8 0 362

7.3 5 20. 71 1.4 9 1.2 4 3.5 8 6.9 5 0.8 7 1.6 3 3.7 5 29. 99 2.8 5 321

5.9 3 22. 87 1.3 5 0.9 6 3.9 0 6.8 0 1.0 2 1.5 4 3.0 9 29. 95 2.6 3 315

7.6 7 17. 17 1.2 8 1.7 0 4.0 1 6.6 7 0.9 0 1.5 6 3.0 8 27. 20 2.4 5 403

15. 9.7 13. 19. 17. 99 4 78 16 52 1.4 1.1 1.4 1.7 1.8 1 7 7 2 2 0.6 0.6 0.6 0.6 0.6 6 4 8 6 5

16. 55 1.5 2 0.6 7

12. 99 1.4 5 0.7 1

14. 77 1.5 1 0.6 6

T

6.7 3 17. 08 1.5 6 1.9 3 4.2 9 7.2 6 0.9 2 1.6 0 3.1 7 29. 51 2.5 5 337

IP

Rb/Nd

7.0 1 17. 77 1.2 9 1.4 2 4.6 7 6.9 4 1.0 1 1.4 8 2.7 8 30. 58 2.7 4 378

CR

Rb/Sr

7.8 6 20. 07 1.1 3 1.2 7 3.5 4 6.2 3 0.9 3 1.5 3 3.1 7 25. 81 2.4 5 400

US

Rb/V

7.1 8 12. 71 1.2 2 1.2 1 3.6 8 4.8 9 0.8 5 1.9 8 3.1 5 24. 85 2.6 3 312

AN

Nd/Hf

6.4 5 15. 17 1.2 3 0.9 8 4.2 5 6.4 0 1.0 3 1.4 8 2.5 3 22. 59 1.9 6 344

M

8.6 2 18. 79 1.3 7 1.6 5 4.3 1 7.0 7 0.9 4 1.5 3 2.9 9 28. 20 2.4 1 424

Nb/Yb

PAAS-normalized ratios

MREE/MREE* Eu/Eu*

1.3 1.3 1.2 1.3 1.2 1.2 1.2 1.1 1.2 1.3 1.3 1.3 1.3 1.2 1 0 5 2 4 7 8 5 8 5 8 3 3 9 1.0 1.0 1.0 1.0 1.1 1.0 1.0 0.9 1.0 1.0 1.0 1.0 1.0 1.0 2 8 2 5 1 3 1 8 5 1 0 3 3 2

56

ACCEPTED MANUSCRIPT UCC double-normalized ratios

Cr/Cr*

0.2 0 1.8 2 2.2 2 0.8 8

0.2 4 1.7 2 2.3 8 0.8 9

0.1 6 1.5 7 2.0 4 0.8 9

0.2 1 1.7 3 1.9 2 0.8 8

0.1 9 1.3 9 4.9 9 0.9 4

0.2 2 1.5 4 2.6 0 0.8 9

AC

CE

PT

ED

M

AN

US

CR

Ce/Ce*

0.2 2 1.5 6 1.5 7 0.8 9

57

0.2 6 1.6 1 1.8 5 0.8 9

T

V/V*

0.3 2 1.6 1 2.0 0 0.8 9

IP

0.1 9 1.8 1 2.2 1 0.8 9

Sr/Sr*

0.1 7 1.6 3 2.7 5 0.9 0

0.2 1 1.5 5 2.5 7 0.8 9

0.3 0 1.5 5 3.4 8 0.8 9

0.1 7 1.7 9 2.1 5 0.8 9