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Petrogenesis and mineral characteristics of the oldest volcanogenic breccia unit from the Himalayan foreland basin, India
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Petrogenesis and mineral characteristics of the oldest volcanogenic breccia unit from the Himalayan Foreland Basin, India M.K. Shukla , Anupam Sharma PII: DOI: Reference:
S2214-2428(16)30085-7 10.1016/j.grj.2017.01.001 GRJ 62
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GeoResJ
Received date: Revised date: Accepted date:
2 December 2016 21 January 2017 27 January 2017
Please cite this article as: M.K. Shukla , Anupam Sharma , Petrogenesis and mineral characteristics of the oldest volcanogenic breccia unit from the Himalayan Foreland Basin, India, GeoResJ (2017), doi: 10.1016/j.grj.2017.01.001
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Petrogenesis and mineral characteristics of the oldest volcanogenic breccia unit from the Himalayan Foreland Basin, India M.K.Shukla* and Anupam Sharma Birbal Sahni Institute of Palaeosciences, 53 University Road, Lucknow-226 007, U.P, India * Email: [email protected]
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ABSTRACT
Jangalgali breccia unit (JBU), the oldest volcanogenic rock unit in the Himalayan foreland basin, has been studied from five different, however, stratigraphically equivalent localities of Jammu region in NW India. The field and thin section slides of JBU reveal that quartz and plagioclase are the two most common minerals and sanidine, magmatic
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zircon, rutile, hornblende and biotite are present as accessory phases. Petrographic signatures show that quartz and K-feldspar are set in a fine-grained cryptocrystalline glassy matrix and do not represent any preferred orientation. The euhedral hexagonal dipyramidal quartz phenocrysts, irregularly shaped inclusions having high volatile contents and no signatures of transport/reworking in phenocrysts prior to deposition are
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the prominent petrographic features of JBU. The mineral grains arrangement varies between tight-fitted fabric geometry to more open-chaotic packing. Overall, the field
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relationship, texture, mineralogy along with mineral chemistry, and presence of high gas and silica content in the host magma, support the volcanic origin of the JBU litho unit,
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which has wider implications towards understanding the timing of India-Asia collision as well as geodynamic evolution of the Himalayas.
1.
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Keywords: JBU, Jangalgali Formation, Northwest Himalaya, Quartz Introduction
Breccia, in common terms, consists of broken fragments of rocks or different types of
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minerals cemented together by a fine grain matrix, some time glassy matrix, which may or may not be similar to the composition of those broken fragments (Glossary of meteoritical terms). Breccias have diverse origin and can be formed in variety of ways and accordingly defined as volcanic breccia, chert breccia, collapse breccia, fault breccia, impact breccia and seismic breccia. However, to establish the origin of a particular breccia extensive field study along with its relationship with other litho-units and subsequent laboratory analyses is required. The breccias of a specific type provide 1
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important information about the depositional setting of a given time interval, which may be proved helpful in ascertaining major tectonic events as well as geodynamic evolution of that region (Blount and Moore, 1969). The study of breccia also plays a significant role in exploring valuable economic ore deposits, as it is being associated with different metallic ore accumulations (Laznicka, 1988; Hedenquist and Lowenstern, 1994). The
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breccias have also been used as a marker horizon in various geological settings across the world and the present study is an addition to it (Singh, 1980; Singh and Andotra 2000; Singh, 2003).
In Northwest Sub-Himalaya, a lithosequence known as the Jangalgali Formation is situated ~120 Km North West from Jammu City, in Jammu and Kashmir State of India.
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This formation is lying unconformably over the Neoproterozoic Sirban limestone and is comprised of a siliceous breccia unit (Jangalgali Breccia Unit - JBU) at the bottom, and overlain by bauxite and/or laterite layers towards the top. The breccia is one of the important lithounit of Jangalgali Formation, however, not much is known about its mode of origin. Also there is no absolute age, yet available, for this unit and therefore, its
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stratigraphic position is bracketed between Neoproterozoic to Late Paleocene age (Siddaiah, 2011). Medlicott (1876) was probably the first who discussed the siliceous
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breccia overlying the carbonate rocks, based on their field characteristics. Presence of rhyolitic clasts has been recorded from the bauxite unit of lower Subathu sequence of the NW Himalayan frontal belt (Anon, 1979; Acharyya, 1999a, 1999b and 2000), but no in-
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depth study was carried out on this lithounit. Singh (2003) proposed a model for the origin of breccia unit, wherein he advocated that breccias are the silicified products of the
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underlying dolomitic limestone formed during India-Asia collision. However, based on preliminary evidences, it was later discarded and established as a high-silica rhyolitic tuff
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breccia (Siddaiah, 2011; Shukla and Siddaiah, 2011; Siddaiah and Shukla, 2012), which is in support of earlier works (Anon, 1979; Acharyya, 1999a, 1999b and 2000). It has now considered as the oldest volcanogenic rock unit in the Himalayan foreland basin (Acharyya, 2008; Siddaiah and Kumar, 2007, 2008), however, the volcanogenic hypothesis is also not unanimously accepted. In our opinion also, the relationship between the breccia and rhyolitic magmatism is not consensual and need further
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investigation to resolve the issues related to its origin. It cannot be said that the other types of models have been discarded. In this study, field and petrogenetic data on JBU from five localities i.e. Kalakot, Beragua, Khargala, Tattapani and Kanthan is discussed. Adequate emphasis has been given to the textural characteristics of the breccia constituents including rock fragments
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and cement/matrices types and chemical characteristics of individual minerals present in this unit. The inferences drawn from the study not only helps in understanding the geological characteristics of the JBU but also provide clues for its possible mode of origin, which has wider implications towards understanding the meaning of the unconformity gap existing between Neoproterozoic Sirban Limestone and Subathu Group
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of rocks (late Palaeocene to middle Eocene) as well as help in building a future model for the geodynamic evolution of the NW Sub-Himalaya. 2. Geological setting
In general, the foreland succession of the Jammu region comprises of the Subathu, Murree and Siwalik groups of rocks, where the Subathu is placed at the bottom. In the
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study area, the exposed lithounits mainly belong to the Murree Group (late Eocene to Early Miocene) and Subathu Group of rocks (late Palaeocene to middle Eocene) (Fig.1a;
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Table.1a). The major rock types found in this part of the study area are shales and limestones. The Neoproterozoic Sirban Limestone is the basement rock (not exposed in the study area) on which the Jangalgali Formation, comprising the breccia unit and the
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overlying bauxites/laterites, was deposited. The whole Jangalgali Formation lies south of the Main Boundary Thrust (MBT) and is sandwiched between Neoproterozoic Sirban
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Limestone (Raha et. al., 1978; Rao and Rao, 1979; Raha, 1984; Venkatachala and Kumar, 1997, 1998) and basal part of Thanetian Subathu Formation (Singh, 1970, 1973, 1980;
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Singh and Andotra 2000) and the contact between JBU and Subathu is also unconformable (Fig.1b). The Jangalgali Formation was earlier included within the Subathu Group along with its two members i.e. Khargala Chert breccia and Lain Bauxite (Singh, 1973). But, since the Jangalgali Formation is represented by entirely different lithotypes, it has been later designated as a separate lithounit (Singh, 1973 and 1980; Bhat et. al., 2008, 2009). The Lain Bauxite, which conformably overlies Khargala Chert Breccia, is named after the village Lain and it is represented by pisolitic and massive 3
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varieties of bauxite, however, at few places, where it has not attained to bauxite level laterites are also noticed (Nanda and Kumar, 1999; Singh, 1980). The JBU is ~ 10 m thick and its thickness varies in different localities (Fig.1c). The breccia accompanied with the overlying bauxite/laterite unit, which is non fossiliferous, lie unconformably over the Precambrian basement (Singh, 1973, 1980; Singh, 2003). As
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such, the JBU represents an unconformity zone and is acting as a marker horizon in the study area. The upper contact of Jangalgali Formation with carbonaceous shale of Subathu Formation is sharp and is distinctly observed (Fig.2 & 3) in the study area; the latter is followed up by the overlying Murree Group of rocks (Raha et. al., 1978; Singh, 1980; Najman and Garzanti, 2000). The exposures of the brecciated unit can be followed
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for more than 100 km in the northwestern part of the Indian Himalaya, which include the five studied localities (Table.1b). The whole sequence of Jangalgali Formation, i.e. breccia at the bottom overlain by bauxite/laterite units, is found only in Kanthan area; whereas in other localities breccia unit is placed unconformably just below the Subathu shales.
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3. Analytical methods
Twelve lithological sections were investigated to establish the field relationship and
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geological characters of the JBU from five different localities of Jammu region of India. Representative samples were collected from the fresh exposures at the interval of 1 m, where it is exposed or cut across. A total 127 thin sections from various representative
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samples of JBU were prepared for petrography and other studies, using balsam and araldite (for EPMA study) and coated with carbon for EPMA and SEM-EDX analyses.
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Detailed scanning electron microscopic (SEM) investigations were carried out for the groundmass as well as quartz phenocrysts of all thin sections of JBU. Carl Zeiss SMT
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EVO 40 instrument, equipped with EDX, was used for the SEM study. The data was generated at the operating conditions (in most cases): WD 8 mm; HV 25 kV; Image size: 1000 x 750; Magnification: 846 xs. For Raman spectroscopy, Horiba JY-Lab RAM HR instrument equipped with Ar- laser
(514.57 nm) and Lab spec software was used. The other specifications for most of the observations are: Power 20 MW; Accumulation 1; Exposure time 2 seconds. The Cathodo-Luminescence (CL) microscopic study was also carried out on various zircon 4
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grains with the help of GATAN CHROMA CL2 UV model 788, at the operating conditions for most of the cases: Probe current- 5 n A; Beam current- 100 µA and voltage- 20 kV. CAMECA SX-100 electron microprobe analyser (EPMA) was used for the study of individual mineral chemistry with the operating conditions such as voltage: 15 kV;
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current: 20 n A with a beam diameter of 1 μm. Following mineral standards were used during elemental analysis - Kyanite for Si & Al; Orthoclase for K; Jadeite for Na; Wollastonite for Ca; Diopside for Mg; Almandine for Fe; Rhodonite for Mn; Apatite for P; Chromite for Cr; Barite for Ba; Zircon for Zr and Rutile for Ti. The precision was better than 2% for major elements and better than 5 and 10% for minor and trace
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elements respectively.
All analyses have been done at Wadia Institute of Himalayan Geology, Dehradun. 4. Results 4.1 Field observations
The JBU show distinct porphyritic texture (~25-45 volume % phenocrysts at few
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horizons) with quartz as the dominant component. The different types of angular clasts and phenocrysts of quartz and K-feldspar are set in a fine-grained siliceous matrix
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without any preferred orientations. Freshly exposed outcrop surfaces appear glassy and break through conchoidal fracture. The average fragment size of breccia ranges from approximately 2-30 cm in diameter. However, in all five localities, the fragments size
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vary from few millimeters to meter-size. It is interesting to notice that the larger fragments occur more frequently and angular to sub angular fragments are in contact with
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each other, which can often be refitted into each other (Fig.4). The flow-like pattern (lava flow), a feature of the whole rock is commonly observed at all localities. In few breccia
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fragments, vesicles of 0.5-1.5 cm size have also been noticed (Fig.5). In spatial distribution, the Jangalgali breccia clasts show massive to highly fractured character. Similarly, there is no credible evidence of transport or reworking of phenocrysts prior to deposition. The entire JBU unit is relatively impermeable and largely barren. However, careful examination of the fragments as well as matrix indicate that many of the displaced fragments have no preferred relative orientation with respect to each other and also have no or very little proportion of calcareous materials. 5
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4.2. Petrography and Mineral Characteristics The microscopic study of JBU reveals cryptocrystalline nature of matrices consisting of random aggregates of light and dark gray crystallites exhibiting weak pleochroism. In the JBU, quartz is the dominant mineral phase, which occurs in various form (Hexagonal, dipyramidal, angular, rounded to sub rounded, skeletal and as mosaic interlocking), of
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which the euhedral hexagonal dipyramids and angular crystals of quartz are more common among all phenocrysts. The texture and other characteristic features of quartz is presented in detail in the following section. 4.2.1Quartz textures
In thin section petrography, quartz grain exhibits diverse textures such as packet of
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hexagonal phenocryst occur in a fine grain matrix, pair of quartz phenocrysts resemble like twins, hexagonal quartz crystal placed within quartz phenocrysts, euhedral hexagonal quartz phenocrysts arranged in identical orientation, negative crystals and mosaic of quartz eyes in a fine grain glassy matrix, mosaic of tiny quartz crystals (50 - 100 µm) lying within the hexagonal quartz phenocrysts (Fig.6a-h).
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The phenocrysts of quartz having euhedral hexagonal dipyramidal texture represent the basal section; however, few of them occur within euhedral hexagonal quartz (Fig.6c),
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probably indicating slow crystallization. Most of the individual euhedral quartz phenocryst (200-600 μm) is arranged in the groundmass without any preferred orientation and the crystal faces of phenocrysts are very sharp. Paired crystals of quartz (200-500
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μm) formed in a fine grain groundmass showing parallel extinction (Fig.6b). Few anhedral phenocrysts of quartz grains of 0.5-1.0 mm size occur in different shapes such
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as triangular, multifaceted angular, zigzag, nib or needle type etc. The Secondary Electron (SE) imaging show few tiny quartz crystals (10-30 μm) with
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euhedral hexagonal texture lying in the fine grain ground mass (Fig.7a). Crystal inclusions (<1 μm) in angular shape were also noticed in these euhedral hexagonal quartz, which may be either formed during its crystallization or rapid cooling (Gotze, 2009; Maclellan and Trembath, 1991). The size of inclusion ranges between 10 to 125 μm and noticed in both phenocryst as well as fine grained siliceous ground mass. A few glass shards of irregular and curvilinear shape were found in the matrix of JBU (Fig.7b). It has been analyzed through SEM-EDX (Table.2), at two points (1 and 2) and 6
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found rich in volatiles (Cl: 2.17-2.21 wt %; S: 0.11-0.21 wt % and Cr: 0.45-2.17 wt %). The analyses of EPMA data of majority of quartz crystals indicate its pristine character, however variable amount of Al, Ti and Fe were also observed in few quartz phenocrysts (Table-3a), revealing the oxygen rich environment during post crystallization or depositional period (Manley, 1996; Gotze, 2009).
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4.2.2 Accessory minerals The JBU has very small amount of accessory minerals (<2 vol %), of which feldspar (orthoclase, sanidine), zircon, rutile, ilmenite, hematite, biotite and hornblende are the most abundant once (Fig.8); besides, ilmenite, tourmaline and pyrite are also noticed occasionally. The microphenocrysts of plagioclase (~80-400 µm) invariably show
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multiple (polysynthetic) twinning, which appears as dark and light bands in crystals observed under the crossed polar condition; microlithic texture of plagioclase grains with quartz eyes in fine grained matrix is also observed. The EPMA studies on crystals of orthoclase feldspar (Table-3b) show variable amounts of alkaline earth metals (Mg, Ca, and Ba) along with trace elements (e.g. Cr, Ti, and Zr) as well as significant content of
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iron oxide (~4%).
Several zircon grains were observed in thin sections, exhibiting varied habits such as
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euhedral, prismatic to sub rounded. The grain size ranges between 40–180 µm; however majority of crystals are between 40-70 µm. These usually show light yellow to reddish brown color having rainbow shades while observed under crossed polars. The
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Cathodoluminescence (CL) images of zircon display various growth patterns and resorbed textures; few inherited zircon crystals (or inherited cores) have also been noticed
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(Fig.9a). The Raman spectra of zircons show the overall decreasing pattern in terms of wavenumber (cm−1) from 353.45 to 1002.75, which exhibit a magmatic trend (Shukla,
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2014; Bao, 1995; Bao et. al. 1998). The energy dispersive x-ray (EDX) spectrum of zircon shows minor proportions of trace elements such as Hf and Sc, an obvious character of zircons. The chemical characteristics of zircons analysed through EPMA suggest its pristine nature. However, variable amount of Fe and Mn (0.1 -0.3 wt %), Ca and K (< 0.1 wt %) were also observed in some crystals (Table-3c), which may have incorporated later due to surface interaction during deposition or post depositional conditions.
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Rutile grains are of various shapes varying from sub-rounded to rounded, ellipsoidal to euhedral. These are largely equidimensional varying between 30 to 200 µm sizes and showing halos at their outer rim like zircon, rutile crystals are also enclosed by fine to medium grain siliceous matrix and coarse-grained quartz phenocrysts. Raman analysis of various rutile crystals (graph not shown) were identified by four bands at wavenumbers
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145, 257, 454 and 627.784 cm-1 (maximum peak), which confirmed its diagnostic peak pattern of igneous rutile as explained by Meinhold (2010). The EDX study of rutile grains shows the presence of Ti and O as primary elements along with minor amounts of Fe, Al and Rb (Fig.9b), supporting its igneous source (Meinhold, 2010). The EPMA data reveal that various rutile grains exhibit measurable amounts of various trace elements (e.g. Al,
in oxygen rich environment (Table-3d).
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Si, Ca, Fe and Zr), which is probably due to the result of replacement of primary elements
Few crystals of hematite (~200 µm) with brown color in thin section enclosed by fine to medium grain quartz phenocrysts were found and analyzed through EPMA and Raman spectroscopy for its chemical characteristics. Two different types of hematite crystals,
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reddish gray to dark brown in color have been noticed; one is elliptical (~210 µm) while another is of pentagonal (~100 µm) shape, surrounded by medium grain quartz
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phenocryst. Raman spectroscopic analysis of hematite confirmed its diagnostic peak pattern (data not shown). The EPMA data on hematite crystals indicates the presence of other elements besides Fe and O (such as Na, Mg, Al, Si, P, K, Ca, Ti) in various
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proportions (Table-3e), revealing highly oxidized environment. Anhedral grains consisting of altered biotite in a matrix of fine-grained authigenic quartz were found in
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many samples. Although few opaque crystals of pyrite (~210 µm) were noticed, however, their presence is sporadic in most of samples and therefore may be considered as
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secondary product, i.e. not contemporary with host rock and formed due to the result of hydrothermal alteration. 5. Discussion The Jangalgali breccia unit occupies an important stratigraphic position in the archive of Northwestern Himalayan foreland basin. As it lies between a huge unconformity zone (~500 Ma), it holds key information about such a large geological period that may fill this gap at least to some extent. The breccia unit acts as an important proxy for India-Eurasia 8
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collision in the foreland basin and also being used as a marker horizon in the unconformity zone that lies between Neoproterozoic Sirban Limestone and Palaeocene to Mid Eocene Subathu Formation (Singh 2003; Singh et al 2005, 2009). The detailed study of this litho-unit particularly petro-genesis, mineralogy and geochemical characteristics may provide insights towards its origin, which is still a topic of debate. There are
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different opinions put forth by earlier workers regarding the origin of these units (Anon 1979; Acharyya 1999a, b and 2000; Singh 2003 & 2012; Bhat et. al 2008; Siddaiah 2011). Anon (1979) reported this unit, as a rhyolitic origin, later supported by Acharyya (1999a, b, 2000, 2008). Singh (2003 & 2012) proposed a sedimentary model, supported by Bhat et al. (2008), for the origin of this breccia and suggested that it is formed by the
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silicification of Sirban Limestone and is entirely composed of basement-derived sediments. Further, it has been suggested as high-silica rhyolitic tuff breccia (Siddaiah 2011) based on preliminary geochemical study. The present study constrains using mineral assemblages, mineral morphology, textures, mineral chemistry and field relationships as tools to suggest its volcanic origin.
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The field characteristics of Jangalgali breccia unit depicts that it consists of angular fragments with fine-grained matrix between them, tightly fitted fabric geometry and
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chaotic packing i.e. lacking a visible order or organization; the textural pattern is more or less similar as described by Woodcock et al (2006). Euhedral quartz phenocrysts described as ‘quartz eyes’ by Williams and Burr (1994) are observed in all thin sections
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of JBU; usually such types of euhedral crystals of quartz develop with small amounts of degree of under cooling i.e. ∆T< 55o C (Swanson and Fenn, 1986). Hexagonal
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dipyramids, as in the present case, crystallizes at small degree of initial under cooling and are replaced by skeletal quartz at moderate to large degree of initial under cooling
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(Maclellan and Trembath, 1991). In this case, the presence of hexagonal dipyramidal quartz, a typical habit of high temperature quartz, indicates a volcanic source of origin under slow cooling and also, the presence of irregularly shaped volatile rich inclusions in fine grained silicic matrix of JBU thin sections may results due to magma trapping just before the eruption (Manley, 1986). Such type of interrelation between quartz genesis and the specific properties developed during their formation can be useful for the reconstruction of geological processes as described by Gotze (2009). 9
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In the Jangalgali Formation, JBU is overlain by the bauxite/laterite units although it is not yet confirmed whether any correlation exists between them or not. However, volcanic source is suggested for both units i.e. for the precursor bauxite (Singh et al., 2005, 2009) as well as for the Kanthan breccia (Anon, 1979; Acharyya, 199a, 1999b, 2000; Bhat et al. 2008) in the Jammu region of India. In the present study, the stratigraphic position and
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the chemical and mineral characteristics of the breccias at Kanthan and breccias at Khargala and its surrounding areas (Kalakot, Beragua, and Tattapani) have been studied thoroughly and found with similar characteristics.
The study of chemical characteristics of the bulk rock unit revealed that silica content in the JBU is very high which is generally uncommon and indicating its high siliceous
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granitic magma source (supplementary data); however, similar kind of high silica is also reported from Proterozoic Singhora tuff in Chattisgarh (Das et al., 2009). Presence of such high silica concentration indicates a nearby source as viscosity increases with increasing SiO2 concentration in the magma. Zircons in JBU are chemically homogenous and Raman analyses indicate its magmatic origin (Shukla, 2014). Rutile chemistry
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suggests involvement of low degree of alteration in their formation. The presence of ilmenite rim on the margin of rutile crystal indicates that it is a secondary igneous rutile
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formed by the oxidation of ilmenite (Meinhold, 2010). The morphology, textures and microstructures, present in zircons and rutiles (e.g. hollows or incompletely grown crystals) indicate rapid growth from a vapor phase. Irregular fractures and scratches in the
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crystals are due to long-term corrosion, metamictization and alteration (Bao, 1995; Bao et al 1998; Meinhold, 2010).
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Overall the JBU is made up primarily of quartz, plagioclase with minor amounts of sanidine, zircon, rutile, hornblende and biotite, all occurring in a glassy material. It also
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contains vesicles, produced due to trapped gases in the rock. It is probably formed from a granitic magma source that has partially cooled in the subsurface and responsible for the formation of the phenocrysts of JBU, while the fine and tiny crystals that made the matrix of JBU are formed later as a result of rapid cooling at the surface. These granitic magmas were very rich in silica and may contain gas up to several percentages by weight. Further, as these magmas cool down, the silica transforms into complex molecules and eventually gives the magma a high viscosity which causes it to move very sluggishly. The sluggish 10
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rhyolitic lava can slowly exude from a volcano and piles up around the vent which later collapsed due to sudden lowering of pressure released through cracks and fractures developed due to the additional magma extrudes. The presence of high gas content and high viscosity (due to high silica) in the host magma, indicate an explosive eruption, as the viscosity was so high that the gas can only escape by blasting the magma from the
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vent; As a result of it, the volcanic debrises in the form of breccias were formed (Blount and Moore, 1969; Laznicka, 1998; Kueppers et. al. 2006; Koyaguchi et. al. 2008) (Fig.10a&b).
Rhyolite usually forms where granitic magma reaches the surface either within continent or at continental margins (Hedenquist and Lowenstern, 1994; Tamura and Tatsumi, 2002;
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Elders et al, 2011), so it strengthens the case that JBU may have formed when granitic magma was erupting at the surface along the Indian plate margin during the initial phase of India-Asia collision. If it is so, then Jangalgali breccia unit may portray the crucial episodes of the geodynamic evolution of the North-western Himalaya. 6. Concluding remarks
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Based on field, petrography and geochemical characteristics of JBU lithounit the following inferences can be drawn with:
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1. The presence of various textures in quartz (e.g. hexagonal dipyramidal quartz, quartz eyes, mosaic of euhedral quartz phenocryst), the accessory mineral assemblages (i.e. euhedral magmatic zircons, rutile, sanidine, hematite and biotite etc) and irregularly
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shaped volatile rich melt inclusions, support a volcanic origin. Absence of calcareous materials and micro-fossils in the matrix, lack of visible order of orientation of clast
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and no significant evidence of transport or reworking (prior to deposition) also support its volcanic origin.
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2. The various mineral textures as well as its mineral chemistry (e.g. quartz, orthoclase, zircon, rutile and hematite) studied by EPMA and EDX are pointing towards its primary origin from highly siliceous granitic magma, deposited in an oxygen rich environment.
3. The brecciated units from all five localities occur at same stratigraphic level and exhibits similar characteristics i.e. rhyolitic and agglomeratic. Therefore the whole
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JBU can be considered as the oldest volcanogenic rocks reported in the Himalayan Foreland Basin. 4. The JBU was probably formed as a result of explosive eruptions. However, the source of granitic magma is still not confirmed, but it is definitely a nearby source owing to higher SiO2 content and eventually a higher viscosity of the magma.
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Acknowledgements MKS is grateful to Dr. N.S. Siddaiah for introducing him to this problem (for Ph.D work) and also for his valuable suggestions. Prof S.K. Pandita is thanked for his help during field work. We are grateful to Drs. N. K. Saini, P.P. Khanna, Rajesh Sharma, S.S Thakur, D.R Rao and Shri N.K. Juyal for their kind support in laboratory work. We are also
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thankful to the two anonymous reviewers and the editor (Vasile Ersek) for their constructive remarks. We are highly thankful to the Director BSIP, Lucknow for providing us fruitful environment for the study. References
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Woodcock NH, Omma JE, Dickson J A D. Chaotic breccia along the Dent Fault, NW England: implosion or collapse of a fault void. Journal of the Geological Society
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Fig.1a) Geological map of the study area showing the locations of the exposure of JBU (modified after Singh, 2003; JBU is not map able on larger scale); MBT-Main Boundary Thrust b) Generalized Litho-log of the study area showing the stratigraphic position of the Jangalgali breccia unit (after Singh, P. 1980) c) Litho-logs from five different localities of the study area.
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Fig.2. Lithological contacts of breccia unit with overlying Subathu shale at, A) Kalakot, B) Beragua, C) Khargala, and D) Tattapani; black arrows are showing the points,
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from where samples have been taken.
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Fig.3. A) Field photograph, showing a synoptic view of JBU exposed at Kanthan, B) a close-up view of field photograph showing the well exposed upper contact of JBU with Subathu shale.
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Fig.4. Field photographs of JBU showingA) A massive fine grained block of rhyolite clast of gray to pink gray in color (at
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Beragua), B) Gray monomictic breccia with angular to sub angular rhyolite clasts in rock-flour matrix (at Kanthan), C) Breccia with angular to sub angular rhyolite
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porphyry clasts (at Tattapani), D) Rhyolite clast (~15 cm length of pen) in fine grain
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with gray to light gray matrix (at Tattapani); (~35 cm length of hammer for scale).
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Fig.5. Photographs of hand specimen of JBU- A) samples showing the angular clast arrangement in fine grain matrix (~15 cm length of pen for scale), B) sample having vesicles in clast matrix.
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Fig.6. Photomicrographs of quartz from JBU- A) packet of hexagonal quartz phenocrysts occurring in a fine grained matrix, (xpl; x 2),
B) Pair of quartz phenocrysts
resembling as twin, (xpl; x 5), C) Hexagonal quartz crystal occurred within quartz phenocrysts, (xpl; x 2), D) Euhedral hexagonal quartz phenocrysts, arranged in similar orientation, (xpl; x 5), E) Negative crystals of quartz in a fine grain glassy 24
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matrix, (xpl; x 2), F) Mosaic of quartz eyes associated with fine-grained aggregates of quartz, (xpl; x 5), G) Mosaic of quartz within a phenocryst (xpl; x 2), H) Mosaic of
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hexagonal quartz phenocrysts (xpl; x 2)
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Fig.7 (a). Secondary electron (SE) image of euhedral hexagonal quartz from JBU (sample no. KDL-2, from Kalakot). (b). SEM image of a thin section showing glass shards in fine grained quartz matrix (1 & 2 are the EDX analysis point; sample no. KDR3 from Kalakot).
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Fig.8. Photomicrographs of accessary minerals present in JBU A) microphenocryst of
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plagioclase (plg) crystals in plane-polarized light (x20), B) Plagioclase and quartz eyes within fine grained groundmass (xpl; x5) , C) microlithic texture of plagioclase
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grains in fine grained matrix (ppl; x2), D) a euhedral zircon (Zr) crystal (ppl; x 20), E) twin crystal of rutile (Rt) (ppl; x 10), F) two different types of hematite (Hm) crystals
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taken with crossed polars (x 10), G) hornblende (Hb) in fine grained quartz matrix (xpl; x10), H) altered biotite (Bt) grains (ppl; x20), I) Pyrite (Py) crystal in fine grain groundmass (ppl; x10).
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Fig.9 (a) Cathodoluminescence (CL) images of zircon showing various growth patterns along with inherited cores. (b) Energy dispersive x-ray spectra of rutile with SEM image.
Fig.10 a)
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Fig.10a. Sketch model of JBU formation, based on field and petrographic observations (photo is from Kalakot section) (b). Sketch model of JBU formation, based on field and petrographic observations
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Table-1a Geological sequence of the Subathu and Jangalgali Groups in Jammu Himalaya (Modified after Singh, 1973 and 1980) Group
Middle Eocene
Formation
Member
Arnas Limestone
Chinab Limestone
Lithology
Chinkah Limestone Early Eocene
Subathu Ans Limestone
2-5
Grey shelly Limestone
4-6
Grey fossiliferous Limestone
5-20
Olive, green, grey or khaki needle shales interbedded with dark grey fossiliferous Limestone bands, lenticular to nodular limestones, and marls containing pyrite and phosphatic nodules. Shales contain thin bands of siltstones, clay and lenses of red / purple shales.
10-85
Quartz-wacke, quartzarenite, carbonaceous shales, coal seams, pyrite concretions and ferruginous shales.
6-54
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Beragua
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Late Palaeocene
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Kalakot
Thickness (m)
Greenish grey Limestone
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Age
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----------------------------------UNCONFORMITY -------------------------------Lain- Bauxite (Bauxite pisolitic and massive) (?) JANGALGALI FORMATION Jangalgali Breccia unit (JBU) ----------------------------------UNCONFORMITY --------------------------------
Precambrian (NeoProterozoic)
SIRBAN LIMESTONE
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Dolomitic Limestone cherty with Stromatolites and Quartzite
1.8-2
2-5
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Table-1b Location of samples of Jangalgali breccia unit Co-ordinates Lat/Long Elevation (m)
Sample name KDR & KDL
33° 12’ 58” N; 74° 24’ 58” E
625
Beragua
BG & BGB
33° 12 55 N; 74° 24 04 E
825.5
Khargala
KH
33° 14 10 N; 74° 23 48 E
900
Tattapani
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33° 14 25 N; 74° 24 41 E
798
Kanthan
KN & KO
33° 10 14 N; 74° 51 04 E
525.5
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Location Kalakot
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Series Concentration Atom. C (Wt. %) (at.%) K 2.21 1.03 K 2.17 0.69 K 0.44 0.26 K 0.16 0.07 K 0.11 0.06 K 94.92 97.91 100.01 100.02
Error (%) 0.1 0.0 0.0 0.0 0.0 4.5
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Elements (AN) Cl (17) Cr (24) Si (14) Ca (20) S (16) O (8) Total
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Table-2a EDX data of melt in fine grain quartz matrix (sample no. KDL-3a from Kalakot) at point-1
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Table-2b EDX data of melt in fine grain quartz matrix (sample no. KDL-3a from Kalakot) at Point-2
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Elements (AN) Cl (17) Cr (24) Si (14) S (16) O (8) Total
Series Concentration Atom. C (Wt. %) (at.%) K 2.17 1.00 K 0.45 0.14 K 0.13 0.07 K 0.21 0.10 K 97.05 98.69 100.01 100.00
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Error (%) 0.1 0.0 0.0 0.0 23.6
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Table-3a Electron microprobe analysis data (major oxides wt. %) of quartz Sample No. 0 0.10 0.03 98.66 0 0 0.15 0.04 0.05 0.03 0.11 0 0 99.17
KH7-2
BG-9A 1
BG-9A 2
BG-9A 1
BG-9A 2
0.01 0 0.01 100.41 0.01 0 0.01 0.01 0 0 0.04 0.03 0 100.54
0.03 0.11 0.76 97.11 0.08 0.07 0 0.01 0.05 0.05 0.49 0 0.31 99.07
0 0 0 98.61 0 0.01 0 0.08 0 0 0 0 0.01 98.71
0.03 0.06 0.59 95.53 0 0.02 0.02 0.03 0 0.03 5.82 0.03 0 102.17
0.03 0 0.39 95.28 0 0 0 0.19 0 0 3.96 0.12 0 99.97
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KH7-1
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Oxide Na2O MgO Al2O3 SiO2 P2O5 K2O CaO TiO2 Cr2O3 MnO FeO BaO ZrO2 Total
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KO4A2
Sample No. KO4A3 KO4A4
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KO4A1
0.08 2.99 26.21 54.18 0 9.69 0.18 0.07 0.07 0 4.40 0.15 0 98.03
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0.10 3.00 26.43 55.01 0.01 9.7 0.18 0.03 0.04 0 4.36 0.14 0.07 99.07
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Oxide Na2O MgO Al2O3 SiO2 P2O5 K2O CaO TiO2 Cr2O3 MnO FeO BaO ZrO2 *Total
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Table-3b Electron microprobe analysis data (major oxides wt. %) of feldspar
0.12 2.69 27.58 53.62 0.04 9.51 0.15 0.08 0.02 0 3.40 0.05 0 97.27
0.11 2.8 27.08 53.68 0.06 9.53 0.21 0.07 0 0.07 3.50 0.05 0.04 97.18
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KO4A5
KO4A6
KO4A7
0.06 2.91 26.31 54.96 0.03 9.68 0.13 0.10 0.10 0.10 4.45 0.13 0 98.97
0.10 2.98 26.51 54.88 0 9.55 0.20 0.10 0 0 4.00 0.12 0.01 98.47
0.08 2.86 26.41 54.53 0.07 9.42 0.22 0.10 0.04 0 4.05 0.11 0.09 97.97
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Table-3c Electron microprobe analysis data (major oxides wt. %) of zircon Sample No.
*Total
BG9A1
BG9A2
BG9A2
BG9A3
BG9A4
BG9A4
KO4A 1
KO4A 2
KO4A 3
0 0.01 0 31.39 0 0 0.04 0 0.02 0.08 0.04 0 66.31
KH7-2
0 0.01 0 32.11 0 0 0.03 0 0 0.08 0.15 0 64.65
0 0.02 0.03 30.45 0.01 0.02 0.03 0 0 0.02 0.33 0.04 64.58
0 0 0 30.92 0 0.01 0.01 0.02 0.01 0.01 0.17 0 66.49
0 0.01 0 31.32 0 0.01 0 0.06 0 0 0.1 0 66.39
0 0.01 0 30.99 0 0 0 0 0.01 0.09 0.08 0 67.13
0 0.01 0 31.03 0 0.01 0.03 0 0.01 0.01 0.15 0 65.94
0 0.01 0 31.35 0 0.02 0 0 0.11 0.02 0.03 0 65.87
0 0 0 31.58 0 0 0.03 0.04 0 0 0.09 0.1 66.91
0 0.01 0 31.39 0 0.01 0 0 0 0 0.02 0 65.76
0 0.01 0.16 30.28 0.02 0.02 0.13 0 0 0.1 0.24 0 65.02
97.88
97.02
95.51
97.62
97.89
98.3
97.19
97.4
98.74
97.19
95.98
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KH7-1
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Table-3d Electron microprobe analysis data (major oxides wt. %) of rutile
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Sample No. KH7-1 KH7-2 0.01 0.01 0.03 0.01 2.61 3.2 0.5 0.65 0.03 0 0.02 0 0.13 0.14 84.55 78.02 1.62 1.97 0 0 5.68 10.2 0 0 0.43 0.36 95.62 94.57
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BG9c 2 0 0.01 0.08 0.03 0.01 0.01 0.02 94.88 0 0.02 0.87 0 0.14 96.08
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BG9c 1 0.03 0 0.17 0.06 0 0 0.03 93.39 0.02 0 2.22 0 0.14 96.06
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Oxide Na2O MgO Al2O3 SiO2 P2O5 K2O CaO TiO2 Cr2O3 MnO FeO BaO ZrO2 *Total
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BG9A 1 0.05 0.09 0.81 0.75 0.05 0 0.38 91.04 0.44 0.09 1.96 0 0.43 96.08
BG9A 2 0.08 0.13 0.94 0.78 0.04 0 0.32 89.34 0.55 0 2.86 0 0.56 95.6
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Table-3e Electron microprobe analysis data (major oxides wt. %) of hematite
KO4A 2 0.07 0 0.57 1.18 0.06 0.05 0.05 0.21 0.16 0.01 83.17 0 0.06 85.58
KO4A 5 0.07 1.41 4.43 6.48 0.15 0.22 0.1 0.14 0.03 0.07 74.66 0.01 0.04 87.81
KO4A 6 0.12 1.25 4.62 6.54 0.16 0.25 0.2 0.25 0.07 0 72.7 0.01 0 86.17
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KO4A 1 0.17 2.23 7.13 11.6 0.09 0.98 0.26 0.38 0.2 0 64.82 0 0 87.84
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Oxide Na2O MgO Al2O3 SiO2 P2O5 K2O CaO TiO2 Cr2O3 MnO FeO BaO ZrO2 *Total
Sample No. KO4A 3 KO4A 4 0.12 0.08 1.34 0.05 4.14 0.63 7.95 1.98 0.05 0.06 0.47 0.02 0.17 0.07 0.21 0.44 0.28 0.06 0.06 0.04 70.87 82.07 0.06 0.03 0.04 0 85.79 85.54
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Petrogenesis and mineral characteristics of the oldest volcanogenic breccia unit from the Himalayan Foreland Basin, India M.K. Shukla , Anupam Sharma PII: DOI: Reference:
S2214-2428(16)30085-7 10.1016/j.grj.2017.01.001 GRJ 62
To appear in:
GeoResJ
Received date: Revised date: Accepted date:
2 December 2016 21 January 2017 27 January 2017
Please cite this article as: M.K. Shukla , Anupam Sharma , Petrogenesis and mineral characteristics of the oldest volcanogenic breccia unit from the Himalayan Foreland Basin, India, GeoResJ (2017), doi: 10.1016/j.grj.2017.01.001
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Petrogenesis and mineral characteristics of the oldest volcanogenic breccia unit from the Himalayan Foreland Basin, India M.K.Shukla* and Anupam Sharma Birbal Sahni Institute of Palaeosciences, 53 University Road, Lucknow-226 007, U.P, India * Email: [email protected]
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ABSTRACT
Jangalgali breccia unit (JBU), the oldest volcanogenic rock unit in the Himalayan foreland basin, has been studied from five different, however, stratigraphically equivalent localities of Jammu region in NW India. The field and thin section slides of JBU reveal that quartz and plagioclase are the two most common minerals and sanidine, magmatic
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zircon, rutile, hornblende and biotite are present as accessory phases. Petrographic signatures show that quartz and K-feldspar are set in a fine-grained cryptocrystalline glassy matrix and do not represent any preferred orientation. The euhedral hexagonal dipyramidal quartz phenocrysts, irregularly shaped inclusions having high volatile contents and no signatures of transport/reworking in phenocrysts prior to deposition are
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the prominent petrographic features of JBU. The mineral grains arrangement varies between tight-fitted fabric geometry to more open-chaotic packing. Overall, the field
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relationship, texture, mineralogy along with mineral chemistry, and presence of high gas and silica content in the host magma, support the volcanic origin of the JBU litho unit,
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which has wider implications towards understanding the timing of India-Asia collision as well as geodynamic evolution of the Himalayas.
1.
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Keywords: JBU, Jangalgali Formation, Northwest Himalaya, Quartz Introduction
Breccia, in common terms, consists of broken fragments of rocks or different types of
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minerals cemented together by a fine grain matrix, some time glassy matrix, which may or may not be similar to the composition of those broken fragments (Glossary of meteoritical terms). Breccias have diverse origin and can be formed in variety of ways and accordingly defined as volcanic breccia, chert breccia, collapse breccia, fault breccia, impact breccia and seismic breccia. However, to establish the origin of a particular breccia extensive field study along with its relationship with other litho-units and subsequent laboratory analyses is required. The breccias of a specific type provide 1
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important information about the depositional setting of a given time interval, which may be proved helpful in ascertaining major tectonic events as well as geodynamic evolution of that region (Blount and Moore, 1969). The study of breccia also plays a significant role in exploring valuable economic ore deposits, as it is being associated with different metallic ore accumulations (Laznicka, 1988; Hedenquist and Lowenstern, 1994). The
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breccias have also been used as a marker horizon in various geological settings across the world and the present study is an addition to it (Singh, 1980; Singh and Andotra 2000; Singh, 2003).
In Northwest Sub-Himalaya, a lithosequence known as the Jangalgali Formation is situated ~120 Km North West from Jammu City, in Jammu and Kashmir State of India.
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This formation is lying unconformably over the Neoproterozoic Sirban limestone and is comprised of a siliceous breccia unit (Jangalgali Breccia Unit - JBU) at the bottom, and overlain by bauxite and/or laterite layers towards the top. The breccia is one of the important lithounit of Jangalgali Formation, however, not much is known about its mode of origin. Also there is no absolute age, yet available, for this unit and therefore, its
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stratigraphic position is bracketed between Neoproterozoic to Late Paleocene age (Siddaiah, 2011). Medlicott (1876) was probably the first who discussed the siliceous
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breccia overlying the carbonate rocks, based on their field characteristics. Presence of rhyolitic clasts has been recorded from the bauxite unit of lower Subathu sequence of the NW Himalayan frontal belt (Anon, 1979; Acharyya, 1999a, 1999b and 2000), but no in-
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depth study was carried out on this lithounit. Singh (2003) proposed a model for the origin of breccia unit, wherein he advocated that breccias are the silicified products of the
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underlying dolomitic limestone formed during India-Asia collision. However, based on preliminary evidences, it was later discarded and established as a high-silica rhyolitic tuff
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breccia (Siddaiah, 2011; Shukla and Siddaiah, 2011; Siddaiah and Shukla, 2012), which is in support of earlier works (Anon, 1979; Acharyya, 1999a, 1999b and 2000). It has now considered as the oldest volcanogenic rock unit in the Himalayan foreland basin (Acharyya, 2008; Siddaiah and Kumar, 2007, 2008), however, the volcanogenic hypothesis is also not unanimously accepted. In our opinion also, the relationship between the breccia and rhyolitic magmatism is not consensual and need further
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investigation to resolve the issues related to its origin. It cannot be said that the other types of models have been discarded. In this study, field and petrogenetic data on JBU from five localities i.e. Kalakot, Beragua, Khargala, Tattapani and Kanthan is discussed. Adequate emphasis has been given to the textural characteristics of the breccia constituents including rock fragments
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and cement/matrices types and chemical characteristics of individual minerals present in this unit. The inferences drawn from the study not only helps in understanding the geological characteristics of the JBU but also provide clues for its possible mode of origin, which has wider implications towards understanding the meaning of the unconformity gap existing between Neoproterozoic Sirban Limestone and Subathu Group
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of rocks (late Palaeocene to middle Eocene) as well as help in building a future model for the geodynamic evolution of the NW Sub-Himalaya. 2. Geological setting
In general, the foreland succession of the Jammu region comprises of the Subathu, Murree and Siwalik groups of rocks, where the Subathu is placed at the bottom. In the
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study area, the exposed lithounits mainly belong to the Murree Group (late Eocene to Early Miocene) and Subathu Group of rocks (late Palaeocene to middle Eocene) (Fig.1a;
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Table.1a). The major rock types found in this part of the study area are shales and limestones. The Neoproterozoic Sirban Limestone is the basement rock (not exposed in the study area) on which the Jangalgali Formation, comprising the breccia unit and the
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overlying bauxites/laterites, was deposited. The whole Jangalgali Formation lies south of the Main Boundary Thrust (MBT) and is sandwiched between Neoproterozoic Sirban
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Limestone (Raha et. al., 1978; Rao and Rao, 1979; Raha, 1984; Venkatachala and Kumar, 1997, 1998) and basal part of Thanetian Subathu Formation (Singh, 1970, 1973, 1980;
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Singh and Andotra 2000) and the contact between JBU and Subathu is also unconformable (Fig.1b). The Jangalgali Formation was earlier included within the Subathu Group along with its two members i.e. Khargala Chert breccia and Lain Bauxite (Singh, 1973). But, since the Jangalgali Formation is represented by entirely different lithotypes, it has been later designated as a separate lithounit (Singh, 1973 and 1980; Bhat et. al., 2008, 2009). The Lain Bauxite, which conformably overlies Khargala Chert Breccia, is named after the village Lain and it is represented by pisolitic and massive 3
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varieties of bauxite, however, at few places, where it has not attained to bauxite level laterites are also noticed (Nanda and Kumar, 1999; Singh, 1980). The JBU is ~ 10 m thick and its thickness varies in different localities (Fig.1c). The breccia accompanied with the overlying bauxite/laterite unit, which is non fossiliferous, lie unconformably over the Precambrian basement (Singh, 1973, 1980; Singh, 2003). As
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such, the JBU represents an unconformity zone and is acting as a marker horizon in the study area. The upper contact of Jangalgali Formation with carbonaceous shale of Subathu Formation is sharp and is distinctly observed (Fig.2 & 3) in the study area; the latter is followed up by the overlying Murree Group of rocks (Raha et. al., 1978; Singh, 1980; Najman and Garzanti, 2000). The exposures of the brecciated unit can be followed
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for more than 100 km in the northwestern part of the Indian Himalaya, which include the five studied localities (Table.1b). The whole sequence of Jangalgali Formation, i.e. breccia at the bottom overlain by bauxite/laterite units, is found only in Kanthan area; whereas in other localities breccia unit is placed unconformably just below the Subathu shales.
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3. Analytical methods
Twelve lithological sections were investigated to establish the field relationship and
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geological characters of the JBU from five different localities of Jammu region of India. Representative samples were collected from the fresh exposures at the interval of 1 m, where it is exposed or cut across. A total 127 thin sections from various representative
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samples of JBU were prepared for petrography and other studies, using balsam and araldite (for EPMA study) and coated with carbon for EPMA and SEM-EDX analyses.
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Detailed scanning electron microscopic (SEM) investigations were carried out for the groundmass as well as quartz phenocrysts of all thin sections of JBU. Carl Zeiss SMT
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EVO 40 instrument, equipped with EDX, was used for the SEM study. The data was generated at the operating conditions (in most cases): WD 8 mm; HV 25 kV; Image size: 1000 x 750; Magnification: 846 xs. For Raman spectroscopy, Horiba JY-Lab RAM HR instrument equipped with Ar- laser
(514.57 nm) and Lab spec software was used. The other specifications for most of the observations are: Power 20 MW; Accumulation 1; Exposure time 2 seconds. The Cathodo-Luminescence (CL) microscopic study was also carried out on various zircon 4
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grains with the help of GATAN CHROMA CL2 UV model 788, at the operating conditions for most of the cases: Probe current- 5 n A; Beam current- 100 µA and voltage- 20 kV. CAMECA SX-100 electron microprobe analyser (EPMA) was used for the study of individual mineral chemistry with the operating conditions such as voltage: 15 kV;
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current: 20 n A with a beam diameter of 1 μm. Following mineral standards were used during elemental analysis - Kyanite for Si & Al; Orthoclase for K; Jadeite for Na; Wollastonite for Ca; Diopside for Mg; Almandine for Fe; Rhodonite for Mn; Apatite for P; Chromite for Cr; Barite for Ba; Zircon for Zr and Rutile for Ti. The precision was better than 2% for major elements and better than 5 and 10% for minor and trace
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elements respectively.
All analyses have been done at Wadia Institute of Himalayan Geology, Dehradun. 4. Results 4.1 Field observations
The JBU show distinct porphyritic texture (~25-45 volume % phenocrysts at few
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horizons) with quartz as the dominant component. The different types of angular clasts and phenocrysts of quartz and K-feldspar are set in a fine-grained siliceous matrix
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without any preferred orientations. Freshly exposed outcrop surfaces appear glassy and break through conchoidal fracture. The average fragment size of breccia ranges from approximately 2-30 cm in diameter. However, in all five localities, the fragments size
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vary from few millimeters to meter-size. It is interesting to notice that the larger fragments occur more frequently and angular to sub angular fragments are in contact with
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each other, which can often be refitted into each other (Fig.4). The flow-like pattern (lava flow), a feature of the whole rock is commonly observed at all localities. In few breccia
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fragments, vesicles of 0.5-1.5 cm size have also been noticed (Fig.5). In spatial distribution, the Jangalgali breccia clasts show massive to highly fractured character. Similarly, there is no credible evidence of transport or reworking of phenocrysts prior to deposition. The entire JBU unit is relatively impermeable and largely barren. However, careful examination of the fragments as well as matrix indicate that many of the displaced fragments have no preferred relative orientation with respect to each other and also have no or very little proportion of calcareous materials. 5
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4.2. Petrography and Mineral Characteristics The microscopic study of JBU reveals cryptocrystalline nature of matrices consisting of random aggregates of light and dark gray crystallites exhibiting weak pleochroism. In the JBU, quartz is the dominant mineral phase, which occurs in various form (Hexagonal, dipyramidal, angular, rounded to sub rounded, skeletal and as mosaic interlocking), of
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which the euhedral hexagonal dipyramids and angular crystals of quartz are more common among all phenocrysts. The texture and other characteristic features of quartz is presented in detail in the following section. 4.2.1Quartz textures
In thin section petrography, quartz grain exhibits diverse textures such as packet of
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hexagonal phenocryst occur in a fine grain matrix, pair of quartz phenocrysts resemble like twins, hexagonal quartz crystal placed within quartz phenocrysts, euhedral hexagonal quartz phenocrysts arranged in identical orientation, negative crystals and mosaic of quartz eyes in a fine grain glassy matrix, mosaic of tiny quartz crystals (50 - 100 µm) lying within the hexagonal quartz phenocrysts (Fig.6a-h).
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The phenocrysts of quartz having euhedral hexagonal dipyramidal texture represent the basal section; however, few of them occur within euhedral hexagonal quartz (Fig.6c),
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probably indicating slow crystallization. Most of the individual euhedral quartz phenocryst (200-600 μm) is arranged in the groundmass without any preferred orientation and the crystal faces of phenocrysts are very sharp. Paired crystals of quartz (200-500
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μm) formed in a fine grain groundmass showing parallel extinction (Fig.6b). Few anhedral phenocrysts of quartz grains of 0.5-1.0 mm size occur in different shapes such
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as triangular, multifaceted angular, zigzag, nib or needle type etc. The Secondary Electron (SE) imaging show few tiny quartz crystals (10-30 μm) with
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euhedral hexagonal texture lying in the fine grain ground mass (Fig.7a). Crystal inclusions (<1 μm) in angular shape were also noticed in these euhedral hexagonal quartz, which may be either formed during its crystallization or rapid cooling (Gotze, 2009; Maclellan and Trembath, 1991). The size of inclusion ranges between 10 to 125 μm and noticed in both phenocryst as well as fine grained siliceous ground mass. A few glass shards of irregular and curvilinear shape were found in the matrix of JBU (Fig.7b). It has been analyzed through SEM-EDX (Table.2), at two points (1 and 2) and 6
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found rich in volatiles (Cl: 2.17-2.21 wt %; S: 0.11-0.21 wt % and Cr: 0.45-2.17 wt %). The analyses of EPMA data of majority of quartz crystals indicate its pristine character, however variable amount of Al, Ti and Fe were also observed in few quartz phenocrysts (Table-3a), revealing the oxygen rich environment during post crystallization or depositional period (Manley, 1996; Gotze, 2009).
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4.2.2 Accessory minerals The JBU has very small amount of accessory minerals (<2 vol %), of which feldspar (orthoclase, sanidine), zircon, rutile, ilmenite, hematite, biotite and hornblende are the most abundant once (Fig.8); besides, ilmenite, tourmaline and pyrite are also noticed occasionally. The microphenocrysts of plagioclase (~80-400 µm) invariably show
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multiple (polysynthetic) twinning, which appears as dark and light bands in crystals observed under the crossed polar condition; microlithic texture of plagioclase grains with quartz eyes in fine grained matrix is also observed. The EPMA studies on crystals of orthoclase feldspar (Table-3b) show variable amounts of alkaline earth metals (Mg, Ca, and Ba) along with trace elements (e.g. Cr, Ti, and Zr) as well as significant content of
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iron oxide (~4%).
Several zircon grains were observed in thin sections, exhibiting varied habits such as
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euhedral, prismatic to sub rounded. The grain size ranges between 40–180 µm; however majority of crystals are between 40-70 µm. These usually show light yellow to reddish brown color having rainbow shades while observed under crossed polars. The
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Cathodoluminescence (CL) images of zircon display various growth patterns and resorbed textures; few inherited zircon crystals (or inherited cores) have also been noticed
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(Fig.9a). The Raman spectra of zircons show the overall decreasing pattern in terms of wavenumber (cm−1) from 353.45 to 1002.75, which exhibit a magmatic trend (Shukla,
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2014; Bao, 1995; Bao et. al. 1998). The energy dispersive x-ray (EDX) spectrum of zircon shows minor proportions of trace elements such as Hf and Sc, an obvious character of zircons. The chemical characteristics of zircons analysed through EPMA suggest its pristine nature. However, variable amount of Fe and Mn (0.1 -0.3 wt %), Ca and K (< 0.1 wt %) were also observed in some crystals (Table-3c), which may have incorporated later due to surface interaction during deposition or post depositional conditions.
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Rutile grains are of various shapes varying from sub-rounded to rounded, ellipsoidal to euhedral. These are largely equidimensional varying between 30 to 200 µm sizes and showing halos at their outer rim like zircon, rutile crystals are also enclosed by fine to medium grain siliceous matrix and coarse-grained quartz phenocrysts. Raman analysis of various rutile crystals (graph not shown) were identified by four bands at wavenumbers
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145, 257, 454 and 627.784 cm-1 (maximum peak), which confirmed its diagnostic peak pattern of igneous rutile as explained by Meinhold (2010). The EDX study of rutile grains shows the presence of Ti and O as primary elements along with minor amounts of Fe, Al and Rb (Fig.9b), supporting its igneous source (Meinhold, 2010). The EPMA data reveal that various rutile grains exhibit measurable amounts of various trace elements (e.g. Al,
in oxygen rich environment (Table-3d).
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Si, Ca, Fe and Zr), which is probably due to the result of replacement of primary elements
Few crystals of hematite (~200 µm) with brown color in thin section enclosed by fine to medium grain quartz phenocrysts were found and analyzed through EPMA and Raman spectroscopy for its chemical characteristics. Two different types of hematite crystals,
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reddish gray to dark brown in color have been noticed; one is elliptical (~210 µm) while another is of pentagonal (~100 µm) shape, surrounded by medium grain quartz
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phenocryst. Raman spectroscopic analysis of hematite confirmed its diagnostic peak pattern (data not shown). The EPMA data on hematite crystals indicates the presence of other elements besides Fe and O (such as Na, Mg, Al, Si, P, K, Ca, Ti) in various
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proportions (Table-3e), revealing highly oxidized environment. Anhedral grains consisting of altered biotite in a matrix of fine-grained authigenic quartz were found in
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many samples. Although few opaque crystals of pyrite (~210 µm) were noticed, however, their presence is sporadic in most of samples and therefore may be considered as
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secondary product, i.e. not contemporary with host rock and formed due to the result of hydrothermal alteration. 5. Discussion The Jangalgali breccia unit occupies an important stratigraphic position in the archive of Northwestern Himalayan foreland basin. As it lies between a huge unconformity zone (~500 Ma), it holds key information about such a large geological period that may fill this gap at least to some extent. The breccia unit acts as an important proxy for India-Eurasia 8
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collision in the foreland basin and also being used as a marker horizon in the unconformity zone that lies between Neoproterozoic Sirban Limestone and Palaeocene to Mid Eocene Subathu Formation (Singh 2003; Singh et al 2005, 2009). The detailed study of this litho-unit particularly petro-genesis, mineralogy and geochemical characteristics may provide insights towards its origin, which is still a topic of debate. There are
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different opinions put forth by earlier workers regarding the origin of these units (Anon 1979; Acharyya 1999a, b and 2000; Singh 2003 & 2012; Bhat et. al 2008; Siddaiah 2011). Anon (1979) reported this unit, as a rhyolitic origin, later supported by Acharyya (1999a, b, 2000, 2008). Singh (2003 & 2012) proposed a sedimentary model, supported by Bhat et al. (2008), for the origin of this breccia and suggested that it is formed by the
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silicification of Sirban Limestone and is entirely composed of basement-derived sediments. Further, it has been suggested as high-silica rhyolitic tuff breccia (Siddaiah 2011) based on preliminary geochemical study. The present study constrains using mineral assemblages, mineral morphology, textures, mineral chemistry and field relationships as tools to suggest its volcanic origin.
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The field characteristics of Jangalgali breccia unit depicts that it consists of angular fragments with fine-grained matrix between them, tightly fitted fabric geometry and
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chaotic packing i.e. lacking a visible order or organization; the textural pattern is more or less similar as described by Woodcock et al (2006). Euhedral quartz phenocrysts described as ‘quartz eyes’ by Williams and Burr (1994) are observed in all thin sections
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of JBU; usually such types of euhedral crystals of quartz develop with small amounts of degree of under cooling i.e. ∆T< 55o C (Swanson and Fenn, 1986). Hexagonal
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dipyramids, as in the present case, crystallizes at small degree of initial under cooling and are replaced by skeletal quartz at moderate to large degree of initial under cooling
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(Maclellan and Trembath, 1991). In this case, the presence of hexagonal dipyramidal quartz, a typical habit of high temperature quartz, indicates a volcanic source of origin under slow cooling and also, the presence of irregularly shaped volatile rich inclusions in fine grained silicic matrix of JBU thin sections may results due to magma trapping just before the eruption (Manley, 1986). Such type of interrelation between quartz genesis and the specific properties developed during their formation can be useful for the reconstruction of geological processes as described by Gotze (2009). 9
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In the Jangalgali Formation, JBU is overlain by the bauxite/laterite units although it is not yet confirmed whether any correlation exists between them or not. However, volcanic source is suggested for both units i.e. for the precursor bauxite (Singh et al., 2005, 2009) as well as for the Kanthan breccia (Anon, 1979; Acharyya, 199a, 1999b, 2000; Bhat et al. 2008) in the Jammu region of India. In the present study, the stratigraphic position and
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the chemical and mineral characteristics of the breccias at Kanthan and breccias at Khargala and its surrounding areas (Kalakot, Beragua, and Tattapani) have been studied thoroughly and found with similar characteristics.
The study of chemical characteristics of the bulk rock unit revealed that silica content in the JBU is very high which is generally uncommon and indicating its high siliceous
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granitic magma source (supplementary data); however, similar kind of high silica is also reported from Proterozoic Singhora tuff in Chattisgarh (Das et al., 2009). Presence of such high silica concentration indicates a nearby source as viscosity increases with increasing SiO2 concentration in the magma. Zircons in JBU are chemically homogenous and Raman analyses indicate its magmatic origin (Shukla, 2014). Rutile chemistry
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suggests involvement of low degree of alteration in their formation. The presence of ilmenite rim on the margin of rutile crystal indicates that it is a secondary igneous rutile
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formed by the oxidation of ilmenite (Meinhold, 2010). The morphology, textures and microstructures, present in zircons and rutiles (e.g. hollows or incompletely grown crystals) indicate rapid growth from a vapor phase. Irregular fractures and scratches in the
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crystals are due to long-term corrosion, metamictization and alteration (Bao, 1995; Bao et al 1998; Meinhold, 2010).
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Overall the JBU is made up primarily of quartz, plagioclase with minor amounts of sanidine, zircon, rutile, hornblende and biotite, all occurring in a glassy material. It also
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contains vesicles, produced due to trapped gases in the rock. It is probably formed from a granitic magma source that has partially cooled in the subsurface and responsible for the formation of the phenocrysts of JBU, while the fine and tiny crystals that made the matrix of JBU are formed later as a result of rapid cooling at the surface. These granitic magmas were very rich in silica and may contain gas up to several percentages by weight. Further, as these magmas cool down, the silica transforms into complex molecules and eventually gives the magma a high viscosity which causes it to move very sluggishly. The sluggish 10
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rhyolitic lava can slowly exude from a volcano and piles up around the vent which later collapsed due to sudden lowering of pressure released through cracks and fractures developed due to the additional magma extrudes. The presence of high gas content and high viscosity (due to high silica) in the host magma, indicate an explosive eruption, as the viscosity was so high that the gas can only escape by blasting the magma from the
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vent; As a result of it, the volcanic debrises in the form of breccias were formed (Blount and Moore, 1969; Laznicka, 1998; Kueppers et. al. 2006; Koyaguchi et. al. 2008) (Fig.10a&b).
Rhyolite usually forms where granitic magma reaches the surface either within continent or at continental margins (Hedenquist and Lowenstern, 1994; Tamura and Tatsumi, 2002;
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Elders et al, 2011), so it strengthens the case that JBU may have formed when granitic magma was erupting at the surface along the Indian plate margin during the initial phase of India-Asia collision. If it is so, then Jangalgali breccia unit may portray the crucial episodes of the geodynamic evolution of the North-western Himalaya. 6. Concluding remarks
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Based on field, petrography and geochemical characteristics of JBU lithounit the following inferences can be drawn with:
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1. The presence of various textures in quartz (e.g. hexagonal dipyramidal quartz, quartz eyes, mosaic of euhedral quartz phenocryst), the accessory mineral assemblages (i.e. euhedral magmatic zircons, rutile, sanidine, hematite and biotite etc) and irregularly
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shaped volatile rich melt inclusions, support a volcanic origin. Absence of calcareous materials and micro-fossils in the matrix, lack of visible order of orientation of clast
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and no significant evidence of transport or reworking (prior to deposition) also support its volcanic origin.
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2. The various mineral textures as well as its mineral chemistry (e.g. quartz, orthoclase, zircon, rutile and hematite) studied by EPMA and EDX are pointing towards its primary origin from highly siliceous granitic magma, deposited in an oxygen rich environment.
3. The brecciated units from all five localities occur at same stratigraphic level and exhibits similar characteristics i.e. rhyolitic and agglomeratic. Therefore the whole
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JBU can be considered as the oldest volcanogenic rocks reported in the Himalayan Foreland Basin. 4. The JBU was probably formed as a result of explosive eruptions. However, the source of granitic magma is still not confirmed, but it is definitely a nearby source owing to higher SiO2 content and eventually a higher viscosity of the magma.
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Acknowledgements MKS is grateful to Dr. N.S. Siddaiah for introducing him to this problem (for Ph.D work) and also for his valuable suggestions. Prof S.K. Pandita is thanked for his help during field work. We are grateful to Drs. N. K. Saini, P.P. Khanna, Rajesh Sharma, S.S Thakur, D.R Rao and Shri N.K. Juyal for their kind support in laboratory work. We are also
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thankful to the two anonymous reviewers and the editor (Vasile Ersek) for their constructive remarks. We are highly thankful to the Director BSIP, Lucknow for providing us fruitful environment for the study. References
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Fig.1a) Geological map of the study area showing the locations of the exposure of JBU (modified after Singh, 2003; JBU is not map able on larger scale); MBT-Main Boundary Thrust b) Generalized Litho-log of the study area showing the stratigraphic position of the Jangalgali breccia unit (after Singh, P. 1980) c) Litho-logs from five different localities of the study area.
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Fig.2. Lithological contacts of breccia unit with overlying Subathu shale at, A) Kalakot, B) Beragua, C) Khargala, and D) Tattapani; black arrows are showing the points,
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from where samples have been taken.
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Fig.3. A) Field photograph, showing a synoptic view of JBU exposed at Kanthan, B) a close-up view of field photograph showing the well exposed upper contact of JBU with Subathu shale.
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Fig.4. Field photographs of JBU showingA) A massive fine grained block of rhyolite clast of gray to pink gray in color (at
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Beragua), B) Gray monomictic breccia with angular to sub angular rhyolite clasts in rock-flour matrix (at Kanthan), C) Breccia with angular to sub angular rhyolite
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porphyry clasts (at Tattapani), D) Rhyolite clast (~15 cm length of pen) in fine grain
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with gray to light gray matrix (at Tattapani); (~35 cm length of hammer for scale).
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Fig.5. Photographs of hand specimen of JBU- A) samples showing the angular clast arrangement in fine grain matrix (~15 cm length of pen for scale), B) sample having vesicles in clast matrix.
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Fig.6. Photomicrographs of quartz from JBU- A) packet of hexagonal quartz phenocrysts occurring in a fine grained matrix, (xpl; x 2),
B) Pair of quartz phenocrysts
resembling as twin, (xpl; x 5), C) Hexagonal quartz crystal occurred within quartz phenocrysts, (xpl; x 2), D) Euhedral hexagonal quartz phenocrysts, arranged in similar orientation, (xpl; x 5), E) Negative crystals of quartz in a fine grain glassy 24
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matrix, (xpl; x 2), F) Mosaic of quartz eyes associated with fine-grained aggregates of quartz, (xpl; x 5), G) Mosaic of quartz within a phenocryst (xpl; x 2), H) Mosaic of
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hexagonal quartz phenocrysts (xpl; x 2)
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Fig.7 (a). Secondary electron (SE) image of euhedral hexagonal quartz from JBU (sample no. KDL-2, from Kalakot). (b). SEM image of a thin section showing glass shards in fine grained quartz matrix (1 & 2 are the EDX analysis point; sample no. KDR3 from Kalakot).
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Fig.8. Photomicrographs of accessary minerals present in JBU A) microphenocryst of
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plagioclase (plg) crystals in plane-polarized light (x20), B) Plagioclase and quartz eyes within fine grained groundmass (xpl; x5) , C) microlithic texture of plagioclase
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grains in fine grained matrix (ppl; x2), D) a euhedral zircon (Zr) crystal (ppl; x 20), E) twin crystal of rutile (Rt) (ppl; x 10), F) two different types of hematite (Hm) crystals
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taken with crossed polars (x 10), G) hornblende (Hb) in fine grained quartz matrix (xpl; x10), H) altered biotite (Bt) grains (ppl; x20), I) Pyrite (Py) crystal in fine grain groundmass (ppl; x10).
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Fig.9 (a) Cathodoluminescence (CL) images of zircon showing various growth patterns along with inherited cores. (b) Energy dispersive x-ray spectra of rutile with SEM image.
Fig.10 a)
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b)
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Fig.10a. Sketch model of JBU formation, based on field and petrographic observations (photo is from Kalakot section) (b). Sketch model of JBU formation, based on field and petrographic observations
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Table-1a Geological sequence of the Subathu and Jangalgali Groups in Jammu Himalaya (Modified after Singh, 1973 and 1980) Group
Middle Eocene
Formation
Member
Arnas Limestone
Chinab Limestone
Lithology
Chinkah Limestone Early Eocene
Subathu Ans Limestone
2-5
Grey shelly Limestone
4-6
Grey fossiliferous Limestone
5-20
Olive, green, grey or khaki needle shales interbedded with dark grey fossiliferous Limestone bands, lenticular to nodular limestones, and marls containing pyrite and phosphatic nodules. Shales contain thin bands of siltstones, clay and lenses of red / purple shales.
10-85
Quartz-wacke, quartzarenite, carbonaceous shales, coal seams, pyrite concretions and ferruginous shales.
6-54
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Beragua
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Late Palaeocene
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Kalakot
Thickness (m)
Greenish grey Limestone
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Age
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----------------------------------UNCONFORMITY -------------------------------Lain- Bauxite (Bauxite pisolitic and massive) (?) JANGALGALI FORMATION Jangalgali Breccia unit (JBU) ----------------------------------UNCONFORMITY --------------------------------
Precambrian (NeoProterozoic)
SIRBAN LIMESTONE
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Dolomitic Limestone cherty with Stromatolites and Quartzite
1.8-2
2-5
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Table-1b Location of samples of Jangalgali breccia unit Co-ordinates Lat/Long Elevation (m)
Sample name KDR & KDL
33° 12’ 58” N; 74° 24’ 58” E
625
Beragua
BG & BGB
33° 12 55 N; 74° 24 04 E
825.5
Khargala
KH
33° 14 10 N; 74° 23 48 E
900
Tattapani
TP
33° 14 25 N; 74° 24 41 E
798
Kanthan
KN & KO
33° 10 14 N; 74° 51 04 E
525.5
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Location Kalakot
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Series Concentration Atom. C (Wt. %) (at.%) K 2.21 1.03 K 2.17 0.69 K 0.44 0.26 K 0.16 0.07 K 0.11 0.06 K 94.92 97.91 100.01 100.02
Error (%) 0.1 0.0 0.0 0.0 0.0 4.5
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Elements (AN) Cl (17) Cr (24) Si (14) Ca (20) S (16) O (8) Total
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Table-2a EDX data of melt in fine grain quartz matrix (sample no. KDL-3a from Kalakot) at point-1
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Table-2b EDX data of melt in fine grain quartz matrix (sample no. KDL-3a from Kalakot) at Point-2
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Elements (AN) Cl (17) Cr (24) Si (14) S (16) O (8) Total
Series Concentration Atom. C (Wt. %) (at.%) K 2.17 1.00 K 0.45 0.14 K 0.13 0.07 K 0.21 0.10 K 97.05 98.69 100.01 100.00
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Error (%) 0.1 0.0 0.0 0.0 23.6
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Table-3a Electron microprobe analysis data (major oxides wt. %) of quartz Sample No. 0 0.10 0.03 98.66 0 0 0.15 0.04 0.05 0.03 0.11 0 0 99.17
KH7-2
BG-9A 1
BG-9A 2
BG-9A 1
BG-9A 2
0.01 0 0.01 100.41 0.01 0 0.01 0.01 0 0 0.04 0.03 0 100.54
0.03 0.11 0.76 97.11 0.08 0.07 0 0.01 0.05 0.05 0.49 0 0.31 99.07
0 0 0 98.61 0 0.01 0 0.08 0 0 0 0 0.01 98.71
0.03 0.06 0.59 95.53 0 0.02 0.02 0.03 0 0.03 5.82 0.03 0 102.17
0.03 0 0.39 95.28 0 0 0 0.19 0 0 3.96 0.12 0 99.97
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KH7-1
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Oxide Na2O MgO Al2O3 SiO2 P2O5 K2O CaO TiO2 Cr2O3 MnO FeO BaO ZrO2 Total
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KO4A2
Sample No. KO4A3 KO4A4
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KO4A1
0.08 2.99 26.21 54.18 0 9.69 0.18 0.07 0.07 0 4.40 0.15 0 98.03
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0.10 3.00 26.43 55.01 0.01 9.7 0.18 0.03 0.04 0 4.36 0.14 0.07 99.07
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Table-3b Electron microprobe analysis data (major oxides wt. %) of feldspar
0.12 2.69 27.58 53.62 0.04 9.51 0.15 0.08 0.02 0 3.40 0.05 0 97.27
0.11 2.8 27.08 53.68 0.06 9.53 0.21 0.07 0 0.07 3.50 0.05 0.04 97.18
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KO4A5
KO4A6
KO4A7
0.06 2.91 26.31 54.96 0.03 9.68 0.13 0.10 0.10 0.10 4.45 0.13 0 98.97
0.10 2.98 26.51 54.88 0 9.55 0.20 0.10 0 0 4.00 0.12 0.01 98.47
0.08 2.86 26.41 54.53 0.07 9.42 0.22 0.10 0.04 0 4.05 0.11 0.09 97.97
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Table-3c Electron microprobe analysis data (major oxides wt. %) of zircon Sample No.
*Total
BG9A1
BG9A2
BG9A2
BG9A3
BG9A4
BG9A4
KO4A 1
KO4A 2
KO4A 3
0 0.01 0 31.39 0 0 0.04 0 0.02 0.08 0.04 0 66.31
KH7-2
0 0.01 0 32.11 0 0 0.03 0 0 0.08 0.15 0 64.65
0 0.02 0.03 30.45 0.01 0.02 0.03 0 0 0.02 0.33 0.04 64.58
0 0 0 30.92 0 0.01 0.01 0.02 0.01 0.01 0.17 0 66.49
0 0.01 0 31.32 0 0.01 0 0.06 0 0 0.1 0 66.39
0 0.01 0 30.99 0 0 0 0 0.01 0.09 0.08 0 67.13
0 0.01 0 31.03 0 0.01 0.03 0 0.01 0.01 0.15 0 65.94
0 0.01 0 31.35 0 0.02 0 0 0.11 0.02 0.03 0 65.87
0 0 0 31.58 0 0 0.03 0.04 0 0 0.09 0.1 66.91
0 0.01 0 31.39 0 0.01 0 0 0 0 0.02 0 65.76
0 0.01 0.16 30.28 0.02 0.02 0.13 0 0 0.1 0.24 0 65.02
97.88
97.02
95.51
97.62
97.89
98.3
97.19
97.4
98.74
97.19
95.98
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Table-3d Electron microprobe analysis data (major oxides wt. %) of rutile
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Sample No. KH7-1 KH7-2 0.01 0.01 0.03 0.01 2.61 3.2 0.5 0.65 0.03 0 0.02 0 0.13 0.14 84.55 78.02 1.62 1.97 0 0 5.68 10.2 0 0 0.43 0.36 95.62 94.57
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BG9c 2 0 0.01 0.08 0.03 0.01 0.01 0.02 94.88 0 0.02 0.87 0 0.14 96.08
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BG9c 1 0.03 0 0.17 0.06 0 0 0.03 93.39 0.02 0 2.22 0 0.14 96.06
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BG9A 1 0.05 0.09 0.81 0.75 0.05 0 0.38 91.04 0.44 0.09 1.96 0 0.43 96.08
BG9A 2 0.08 0.13 0.94 0.78 0.04 0 0.32 89.34 0.55 0 2.86 0 0.56 95.6
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Table-3e Electron microprobe analysis data (major oxides wt. %) of hematite
KO4A 2 0.07 0 0.57 1.18 0.06 0.05 0.05 0.21 0.16 0.01 83.17 0 0.06 85.58
KO4A 5 0.07 1.41 4.43 6.48 0.15 0.22 0.1 0.14 0.03 0.07 74.66 0.01 0.04 87.81
KO4A 6 0.12 1.25 4.62 6.54 0.16 0.25 0.2 0.25 0.07 0 72.7 0.01 0 86.17
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KO4A 1 0.17 2.23 7.13 11.6 0.09 0.98 0.26 0.38 0.2 0 64.82 0 0 87.84
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Sample No. KO4A 3 KO4A 4 0.12 0.08 1.34 0.05 4.14 0.63 7.95 1.98 0.05 0.06 0.47 0.02 0.17 0.07 0.21 0.44 0.28 0.06 0.06 0.04 70.87 82.07 0.06 0.03 0.04 0 85.79 85.54
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[*Note- Total is not up to 100 in Tables 3b-3e due to the incorporation of other trace elements]
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