Hidden Eoarchean crust in the southwestern Central Asian Orogenic Belt

Journal Pre-proof Hidden Eoarchean crust in the southwestern Central Asian Orogenic Belt

Jian Wang, Yuping Su, Jianping Zheng, E.A. Belousova, W.L. Griffin, Xiang Zhou, Hongkun Dai PII:

S0024-4937(20)30074-8

DOI:

https://doi.org/10.1016/j.lithos.2020.105437

Reference:

LITHOS 105437

To appear in:

LITHOS

Received date:

7 October 2019

Revised date:

15 February 2020

Accepted date:

16 February 2020

Please cite this article as: J. Wang, Y. Su, J. Zheng, et al., Hidden Eoarchean crust in the southwestern Central Asian Orogenic Belt, LITHOS(2020), https://doi.org/10.1016/ j.lithos.2020.105437

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Hidden Eoarchean crust in the southwestern Central Asian Orogenic Belt Jian Wang a, Yuping Su a, *, Jianping Zheng a, *, E.A. Belousova b, W.L. Griffin b, Xiang a

Zhou , Hongkun Dai a

a

State Key Laboratory of Geological Processes and Mineral Resources, School of Earth

ARC Centre of Excellence for Core to Crust Fluid Systems/GEMOC, Department of

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b

f

Sciences, China University of Geosciences, Wuhan 430074, China

Corresponding author. Tel.: +86 27 67883001; Fax: +86 27 67883002; E-mail address:

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*

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Earth and Planetary Sciences, Macquarie University, Sydney, NSW 2109, Australia

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[email protected] (Y.P. Su) and [email protected] (J.P. Zheng).

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Abstract

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U-Pb and Hf-isotope analyses of zircon xenocrysts from drilling-sampled

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Carboniferous volcanic rocks suggest the presence of unexposed Eoarchean crust beneath the Junggar Basin (NW China), southwestern Central Asian Orogenic Belt (CAOB).

The oldest zircon population with U-Pb ages of 3.8 Ga shows chondritic ε Hf (t)

of -0.7 to +0.7, and Hf model ages of 3900‒3952 Ma (T DM) and 3973‒4062 Ma (Tcrust). Three slightly younger populations at 3.7, 3.62 and 3.45 Ga have ε Hf (t) of -5.7 to +2.4, T DM of 3.6‒3.9 Ga and T crust of 3.7‒4.1 Ga.

The youngest xenocrysts yield U-Pb ages

of 2.55 Ga with ε Hf (t) values of +3.7 to +8.0.

Crustal mineral inclusions and the

trace-element compositions of all these zircons show that they probably crystallized from granitic magmas.

The observation of deeply hidden Archean crust significantly older

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than the exposed Phanerozoic upper crust suggests that the juvenile origin in CAOB may be overestimated, and the study of crustal growth rates through time for young orogens will require revision.

By comparing the Hf isotopic signatures of ancient

zircons (>3.4 Ga) worldwide, we infer that there may have been a great change in early crustal evolution at the Hadean‒Archean transition (~3.9 Ga) , possibly linked to the Late

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Heavy Bombardment (LHB).

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Key words: Archean crustal evolution; Zircon U-Pb ages; Hf-isotopes; Central Asian

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Orogenic Belt

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1. Introduction

Dating the oldest rocks and minerals is of great importance in understanding the The oldest known rocks, with ages around 4.0 Ga, have

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evolution of the early Earth.

Meanwhile, a ~4.4 Ga detrital zircon discovered at Jack Hills of the

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Williams, 1999).

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been identified in the Acasta Gneiss Complex of northwestern Canada (Bowring and

western Australia represents the oldest mineral so far found on Earth (Wilde et al., 2001). Most of the earliest rocks generally suffered complicated metamorphism, and accordingly it is hard to obtain detailed information about their protolith.

However,

zircon is extremely resistant and can survive erosion or metamorphism during successive geological events, making it as an ideal object for investigations of early crustal evolution (Amelin et al., 1999).

In particular, the development of in situ U-Pb and

Lu-Hf isotopic techniques has resulted in a considerable growth of datasets on early crustal materials worldwide (e.g., Zhang et al., 2008; Byerly et al., 2018).

Identifying

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new, scarce but essential material of the primitive Earth is still a challenge (Paquette and Le Pennec, 2012). The Central Asian Orogenic Belt (CAOB), situated between the European and Siberian cratons to the north and the Tarim and North China cratons to the south (Fig. 1A), is one of the largest accretionary orogens in the world (e.g., Sengör et al., 1993; It was constructed by successive accretion of island arcs,

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Xiao et al., 2015).

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microcontinents, ophiolites, seamounts, accretionary complexes and post -collisional

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magmatic rocks during Neoproterozoic to latest Paleozoic time, accompanied by the

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opening and closure of the Paleo-Asian Ocean (e.g., Sengör et al., 1993; Buslov et al.,

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2004; Long et al., 2007; Xiao et al., 2008; Su et al., 2012; Ren et al., 2014; Yang et al., 2015; Tang et al., 2017; Zhou et al., 2018).

Many previous studies have suggested that

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more than half of the crust within the CAOB is juvenile, and thus the CAOB represents

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the world’s largest area of Phanerozoic crustal growth (e.g., Sengör et al., 1993; Han et

2019).

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al., 1997; Jahn et al., 2000; Chen and Arakawa, 2005; Tang et al., 2017; Song et al., However, increasing numbers of studies show that reworking of Precambrian

materials in the crustal generation of CAOB may be significant as well (e.g., Kröner et al., 2014, and reference therein).

In addition, more and more Proterozoic and even

Archean rocks/minerals have been identified in the CAOB, in areas such as the Tuva-Mongolia blocks and Beishan block in the central CAOB, the NE China blocks in the eastern CAOB, as well as the NW China blocks in the western CAOB (e.g., Xu et al., 2015; Zhang et al., 2017; Zhou et al., 2018, and reference therein).

Therefore, ancient

geological records in the CAOB may be more widespread than previous recognized, and

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may change our view of the models of continental generation for CAOB.

In the present

study, we report in situ U-Pb and Hf-isotopes of Archean xenocrystic zircons with ages up to 3.8 Ga identified in drilling-sampled Carboniferous volcanic rocks from the Junggar Basin (NW China), southwestern Central Asian Orogenic Belt (CAOB).

The data are

important for understanding the nature of the basin’s basement and the crustal

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generation of the CAOB, and provide new clues to crustal evolution on the early Earth.

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2. Geological background, drilling techniques and sampling

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The Junggar terrane, a key component of the southwestern CAOB, is traditionally

middle (Fig. 1B).

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divided into three parts: West Junggar, East Junggar and the Junggar Basin in the The West and East Junggar terranes are mainly covered by Paleozoic

The granitic plutons generally show positive ε Nd(t) values, and

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ophiolite belts (Fig. 1B).

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and minor Mesozoic–Cenozoic strata with extensively exposed granitic plutons and

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are interpreted to have formed by partial melting of a juvenile crust during the Late Paleozoic (e.g., Han et al., 1997; Chen and Jahn, 2004; Chen and Arakawa, 2005; Song et al., 2019).

The ophiolite belts are highly deformed with complex Paleozoic ages,

demonstrating the presence of multiple subduction-accretion processes as well as the closure of Paleo-Asian Ocean in the Junggar terrane (e.g., Xiao et al., 2008).

The

Junggar Basin (an area of ~137,000 km2) is filled with thick marine and continental sedimentary rocks with ages not older than early Permian (Zheng et al., 2007; Li et al., 2015).

Structurally, the basin can be subdivided into six units: Western uplift, Ulungur

depression, Luliang uplift, Central depression, North Tianshan thrust belt and the

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Eastern uplift (Fig. 1B). Supported by the Xinjiang Oil-field Company, we obtained several samples of volcanic rocks from drill cores JL101 and JL102 within the Western uplift (Fig. 1B).

The

drilling processes, taking JL101 as an example, can be divided into three stages .

The

first stage of shallow layer drilling (0 to ~500 m) used the Φ444.5 mm drill bit, and then The second stage of medium-deep drilling (~500

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set the Φ339.73 mm surface casing.

The last stage of deep drilling (~2900 to ~3510 m) employed the Φ215.9 mm

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casing.

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to ~2900 m) adopted the Φ311.1 mm drill bit, and then set the Φ244.48 mm technical

Well-washing was made for

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drill bit, and then set the Φ139.7 mm productive casing.

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half an hour before core extraction. The core extraction tool (Chuan 8-4) comprises a core bit, a core barrel and a core catcher.

The core catcher is self-locking.

When

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coring with the Chuan 8-4, the core catcher automatically clamps the core and cuts it.

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The drilling mud is mainly made up of bentonite and fresh water, to create a gel-like slurry. Finally,

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Sometimes, barite power can be admixed into the mud to increase its density.

the obtained core samples were carefully cleaned, recorded and saved in the Karamay city.

The borehole data show the presence of volcanic rocks beneath the thick sediments (~3000m) (Fig. 1C).

Two basaltic andesites (JL101-4 and JL102-2) sampled from drill

cores JL101 and JL102 at depth of 3282 m and 3106 m, respectively, were selected for whole-rock geochemistry and zircon analyses (Fig. 1C).

According to fossils and

comparative studies of surrounding outcropping strata, the andesites are interpreted as Carboniferous in age.

The rocks have porphyritic textures with phenocryst minerals of

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plagioclase and pyroxene, set in a groundmass of fine-grained plagioclase, pyroxene and glass as well as minor olivine and opaque minerals (Fig. 2).

3. Analytical methods Whole-rock

major element

compositions

were

done

by traditional X-ray

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fluorescence (XRF) method using a Shimadzu Sequential 1800 spectrometer at the

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State Key Laboratory of Geological Processes and Mineral Resources, China University Loss on ignition was obtained by weighing after 90 min of

calcinations at 1000 °C.

Trace element compositions were measured on an Agilent

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of Geosciences (CUG).

Whole-rock Nd isotopic analyses

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7500a ICP-MS instrument at CUG (Liu et al., 2008).

were performed on a Neptune Plus MC-ICP-MS (Thermo Fisher Scientific, Dreieich,

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(Li et al., 2012).

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Germany) at the Wuhan Sample Solution Analytical Technology Co., Ltd, Hubei, China

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Two basaltic andesites (JL101-4 and JL102-2) with a total weight of about 3 kg were carefully selected for zircon separation.

After the rocks were crushed and sieved, only

30─40 grains of zircon from each sample were separated by routine approach employing elutriation, heavy liquids and magnetic techniques.

Then the zircon grains

were carefully hand-picked under a binocular microscope, mounted in epoxy resin and polished to expose their cores.

Cathodoluminescence (CL) images of zircon grains

were obtained using panchromatic CL imaging technique on a Gatan Mono CL4 Cathode-Luminescence detector attached to Zeiss Sigma 300 field emission SEM at CUG, to reveal their external morphology and internal structure, as well as to select

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spots for zircon U-Pb and Hf-isotope analyses.

Mineral inclusions within the zircons

were identified using a Thermo Scientific DXR dispersive Raman micro-spectrometer at CUG, following method described in detail by Xiong et al. (2011). In situ U-Pb dating and trace element analyses of zircons were simultaneously performed by LA-ICP-MS at the Wuhan SampleSolution Analytical Technology Co., Ltd., Detail analytical techniques for the laser ablation system and the

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Hubei, China.

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ICP-MS instrument and data reduction procedure can be found in Zong et al. (2017).

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Laser sampling was carried out using a GeolasPro laser ablation system that consists of

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a COMPexPro 102 ArF excimer laser (wavelength of 193 nm and maximum energy of An Agilent 7700e ICP-MS instrument was

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200 mJ) and a MicroLas optical system. used to obtain ion-signal intensities.

Helium was applied as a carrier gas, and argon

A “wire” signal smoothing device is included in this laser ablation

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entering the ICP.

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was used as the make-up gas and mixed with the carrier gas via a T-connector before

In this study, the spot size and frequency of the laser were set

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system (Hu et al., 2015).

to 32 µm and 5 Hz, respectively.

Zircon 91500 and glass NIST610 were served as

external standards for U-Pb dating and trace element calibration, respectively.

An

Excel-based software ICPMSDataCal was used to perform off-line selection and integration of background and analyzed signals, time-drift correction and quantitative calibration for U-Pb dating and trace element analysis (Liu et al., 2008; Liu et al., 2010). Concordia diagrams and weighted mean calculations were Isoplot/Ex_ver4 (Ludwig, 2003).

made using the

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In situ Hf-isotope analyses of zircons were conducted using a Neptune Plus MC-ICP-MS (Thermo Fisher Scientific, Germany) in combination with a Geolas HD excimer ArF laser ablation system (Coherent, Göttingen, Germany) that was hosted at the Wuhan Sample Solution Analytical Technology Co., Ltd, Hubei, China.

Lu-Hf

isotope data were acquired on the same zircon grains that were previously analyzed for All data were obtained on zircon using a single spot ablation mode at a

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U-Pb ages.

spot size of 44 μm.

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Detailed operating conditions for the laser ablation system and the

The

Lu decay constant of 1.865×10 -11 year-1 (Scherer et al., 2001), and

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Hf/

177

Hf (0.282772) and

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Lu/

177

Hf (0.0332) ratios of the chondritic

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the present-day

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al. (2012).

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MC-ICP-MS instrument and analytical method are the same as those described by Hu et

reservoir (Blichert-Toft and Albarède, 1997) were used to calculate initial

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Hf/

177

Hf

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ratios and ε Hf (t) values. The depleted mantle (DM) model ages (T DM) were obtained

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Hf/

177

Hf ratio of 0.28325,

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Lu/

177

Hf of 0.0384, Griffin et al., 2000). The average

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DM (

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using the measured Lu/Hf of zircon and Lu-Hf isotope compositions of the present-day

crustal model ages (T crust) were calculated by assuming that the protolith of the host rock of a zircon was originally derived from the depleted mantle and then evolved as a reservoir similar to the average continental crust with

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Lu/177Hf of 0.015 (Griffin et al.,

2004).

4. Results 4.1. Whole-rock major and trace elements, and Nd isotopic results The studied two basaltic andesites have similar geochemical signatures (Appendix

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Table A).

The rocks contain SiO 2 of 52.58‒54.06 wt. %, TiO 2 of 0.92‒1.50 wt. %, Al2O3

of 14.38‒15.32 wt. %, FeO* of 9.71‒11.82 wt. %, MgO of 4.40‒5.12 wt. %, CaO of 3.87‒ 5.69 wt. % and (Na 2O + K2O) of 4.99‒5.59 wt. %.

They show arc-like trace-element

distribution patterns characterized by enrichment of LILEs (e.g., Pb) and LREEs but In addition, they have ε Nd(t=300 Ma)

depletion of HFSEs (e.g., Nb and Ta) (not shown).

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4.2. Zircon morphology, inclusions and U-Pb dating

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values from +7.67 to +7.94, with T DM model ages of 502‒639 Ma.

Zircons from sample JL101-4 are light

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The U-Pb data are summarized in Table 1.

3).

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purple to transparent, and have short, prismatic (~85%) to rounded (~15%) shapes (Fig. The crystals are 70‒160 µm in length and have length/width ratios of 1.2‒2.2.

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Pb/206Pb ages, the zircons fall into four groups (Fig.

Group 1 (four oldest concordant grains) has

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Pb/

206

Pb ages from 3794 to 3802

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5A).

Based on the

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apatite (Fig. 4).

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Raman spectroscopic studies reveal that a few zircons contain inclusions of quartz and

Ma with a weighted mean age of 3798±22 Ma (MSWD=0.02, n=5).

They show clear

oscillatory zoning and have Th/U ratios of 0.43‒0.86, typical of a magmatic origin (Hoskin and Schaltegger, 2003).

Group 2 (fifteen zircons) gives

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Pb/206Pb ages

ranging from 3671 to 3753 Ma.

They yield an upper intercept age of 3707±16 Ma

(MSWD=0.92, n=15) (Fig. 5A).

Among them, six discordant grains are generally

structureless and have high Th/U ratios (mean 1.89), whereas the concordant ones show oscillatory zoning with mean Th/U ratio of 0.75 and give a weighted mean age of 3699±21 Ma (MSWD=1.3, n=9), which is identical within analytical uncertainty of the

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upper intercept age.

Group 3 (six zircons) yields concordant ages from 3595 to 3640

Ma (mean 3622±20 Ma, MSWD=0.37).

These grains exhibit internal oscillatory to

irregular zoning and have variable Th/U ratios of 0.02‒1.00. zircons in the sample) has

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Pb/

206

Group 4 (nine youngest

Pb ages from 3383 to 3475 Ma.

Among them, two

analyses are concordant with a weighted mean age of 3455±32 Ma (MSWD=1.1, n=2), The

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consistent with the upper intercept age of 3453±40 Ma (MSWD=0.67, n=9).

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concordant grains show oscillatory zoning and have Th/U ratios of 0.10‒0.60, whereas

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the discordant ones tend to be structureless with Th/U ratios of 0.04‒0.28.

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Zircons from sample JL102-2 are light brown to translucent with long to short

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prismatic shapes (Fig. 3). They are slightly larger than those in sample JL101-4, with lengths of 90‒240 µm and length/width ratios of 1.4‒2.8.

K-feldspar, quartz and apatite The

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inclusions in these zircons were identified using Raman spectroscopy (Fig. 4).

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zircon grains mainly show oscillatory or irregular zoning and have Th/U ratios of 0.16‒

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1.49 (mean 0.77), indicative of originally igneous derivation (Hoskin and Schaltegger, 2003). They yield an upper intercept age of 2529±31 Ma (MSWD=6.6, n=35) (Fig. 5B). Among them, six concordant grains have

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Pb/206Pb ages from 2491 to 2575 Ma, giving

a weighted mean age of 2544±21 Ma (MSWD=1.4, n=6), similar to the upper intercept age. In summary, all the zircons found in the volcanic rocks are Archean in age, much older than the Carboniferous host rocks, indicating that they are xenocrystic.

The

xenocrystic origin of these zircons is also consistent with the observation that some grains are cracked and broken (e.g., JL101-4-01), and contain overgrow rims (e.g.,

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JL102-2-30) (Fig. 3).

The overgrowth rims indicate that the zircon xenocrysts interacted

with the host magma during rapid ascent. dating.

However, these rims are far too thin for U-Pb

The absence of emplacement age zircons in the studied basaltic andesites is

probably due to the fact that mantle-derived mafic magmas rarely crystallize zircons, or zircons crystallized in such magmas are commonly too small for U-Pb dating. This

It is also notable that there are

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which may hamper the crystallization of zircon crystals.

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speculation is further supported by the low Zr (64.6─81.6) contents of the volcanic rocks,

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not Proterozoic or Paleozoic zircons found in these rocks. The reason behind this could

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be related with complex differentiation processes of the mafic magmas in the crust,

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resulting in the crustal fragments that were partly entrained during magma ascent.

The

relatively young Nd model ages (502─639 Ma) of the rocks also suggest that the Therefore, we infer that the

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contamination by ancient crustal materials is limited.

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Basin.

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ancient components may be locally and incompletely preserved beneath the Junggar

4.3. Zircon trace elements

The trace element compositions (Appendix Table B) of the studied zircons are used to constrain the crystallization temperature, the provenance and composition of the protolith.

Ti-in-zircon thermometer (Watson et al., 2006) reveals that most of the

zircons crystallized at temperature range of 600─800°C (Fig. 6B).

Specially, the 3.8 Ga

grains have the lowest crystallization temperatures of 639─709°C (average of 674°C) when compared to the others.

All the studied zircons have low Yb but high U contents

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(Fig. 6C), similar to those of zircons from continental crust-forming magmas (Grimes et al., 2007).

In the Y-Yb/Sm diagram (Fig. 6D), most of the zircons are plotted in the field

of granitoids, indicative of derivation from felsic sources (Belousova et al., 2002).

4.4. Zircon Hf-isotopes In situ analyses of Hf-isotopes are presented in Table 2 and shown in Figs. 7, 8. Hf/177 Hf ratios of 0.280315‒0.280354 and chondritic ε Hf (t)

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3.8 Ga zircons have initial

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Hf/1 77 Hf ratios (0.280337‒0.280467) and ε Hf (t)

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3.7 Ga grains show variable initial

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values (-0.7 to +0.7), and Hadean T DM (3900‒3952 Ma) and T crust (3973‒4062 Ma) ages.

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values (-2.2 to +2.4), as well as T DM (3753‒3925 Ma) and T crust (3791‒4086 Ma) ages. 3.62 Ga zircons yield ε Hf (t) values from -1.6 to +0.8, and give TDM of 3744‒3831 Ma and 3.45 Ga grains have initial

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Hf/177 Hf ratios

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T crust of 3834‒3987 Ma, respectively.

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(0.280404‒0.280591) and ε Hf (t) values (-5.7 to +0.9), with Hadean‒Eoarchean T DM All the Neoarchean (2.55 Ga)

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(3596‒3842 Ma) and T crust (3695‒4119 Ma) ages.

zircons show positive ε Hf (t) values from +3.7 to +8.0, and give T DM of 2549‒2716 Ma and T crust of 2548‒2829 Ma, respectively.

5. Discussion 5.1. Provenance of the Archean zircons Zircon extracted from drill-sampled rocks is increasingly used to reveal geologic processes, yet the potential cross-contamination between the sample and the drilling mud should not be ignored (Andrews et al., 2016).

Nevertheless, we think the drilling

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mud may not affect the zircon U-Pb dating results of the volcanic rocks in this study, based on the following reasons.

(1) Well-washing was made for half an hour before

core extraction, and the obtained core samples were carefully cleaned just after the c ore extraction.

The drilling processes indicate very minor cross-contamination; (2) The

main raw material of the drilling mud (bentonite) is quarried around the Junggar Basin by

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Xinjiang Oil-field Company, ruling out the possible contamination from the other places;

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(3) The volcanic rocks selected for zircon analyses are relatively dense, with thorough

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scrubbing and washing as well as removal of their uneven surfaces during the zircon

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separation process, suggesting negligible influence of contamination of the drilling mud

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on the samples (Andrews et al., 2016); (4) The morphology of the studied zircons indicates that they have xenocrystic origin (e.g., overgrow rims for some grains, Fig. 3);

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(5) If the ~2.5 Ga and Eoarchean zircons were really from the drilling mud, these age

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data must have been reported in the previous drilling-sampled rocks from the Junggar However, the published U-Pb results for the

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Basin using the same drilling mud.

volcanic rocks rarely reveal Archean ages (e.g., Zheng et al., 2007; Su et al., 2010; Li et al., 2015; Li et al., 2020).

Given the above evidences, we suggest that the dated

zircons are unlikely to come from the drilling mud. Another key concern is whether the Archean zircons identified in this study were captured from the deep-seated crust beneath the Junggar Basin, or from the overlying supracrustal sedimentary sequences.

We would expect zircons derived from

sedimentary sources to have textures indicative of abrasion but most of the Archean zircons are euhedral to subhedral in shape (Fig. 3), arguing against their detrital origin.

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In addition, no post-Archean zircons were identified in the studied samples, inconsistent with derivation from sedimentary rocks that should contain zircons with a variety of ages. Most importantly, zircons with Eoarchean (3.8‒3.7 Ga) ages have not previously been reported in any sedimentary rocks within the basin, even the surrounding areas. Therefore, a local, deep-seated crustal source is the most likely explanation.

Laser

In addition, the similar trace element

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apatite (Fig. 4), a granitic mineral assemblage.

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Raman spectroscopy shows that the inclusions in zircons are quartz, K-feldspar and

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compositions to those from granitoids, and the low crystallized temperatures (600‒800°C)

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from Ti-in-zircon thermometer (Fig. 6), suggest that these zircons were derived from

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granitic sources.

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5.2. Hidden Archean crust

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Based on the Sr-Nd isotopes of the exposed granitoids from the east and west sides

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of the basin, Chen and Arakawa (2005) suggest that the basement is dominated by Paleozoic arc and oceanic crust, whereas Han et al. (1999) argued for underplated mantle-derived basic rocks.

Some researchers have examined the geochemical

features of volcanic rocks (e.g., arc-like trace element patterns) around or within the basin and also think that the basement is mainly composed of Paleozoic oceanic blocks (e.g., Zheng et al., 2007; Su et al., 2012).

On the other hand, studies from xenoliths and

geophysical data (e.g., P-wave tomography) suggested that the basin may represent a continental block, possibly with Precambrian basement (Zhang et al., 2013; Xu et al., 2015).

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The oldest xenocryst population at 3.8 Ga in the study shows chondritic ε Hf (t) values and Hadean T crust (3973‒4062 Ma) ages.

If the protoliths of the 3.8 Ga grains originated

from primary crust that was extracted from a mantle reservoir with nearly chondritic Hf-isotope composition (Amelin et al., 1999), the Hf model ages require crustal differentiation from the mantle as early as 4.0 Ga.

The U-Pb ages are only 0.2 Ga

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younger than the Hf model ages, suggesting rapid reworking of juvenile crust in the The three slightly younger populations with ages of

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Eoarchean and the latest Hadean.

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3.7 Ga, 3.62 Ga and 3.45 Ga have consistent Eoarchean‒Hadean Hf model ages (T DM of 3596‒3925 Ma, T crust of 3695‒4119Ma).

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These zircons roughly lie on the same crustal

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evolution lines as the 3.8 Ga grains (Fig. 7), implying that crustal reworking played an important role during the Early Archean (Belousova et al., 2010).

The youngest 2.55 Ga

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zircons in this study show εHf (t) values from +3.7 to +8.0, reflecting growth of juvenile crust This growth event coincides with

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from a depleted mantle reservoir in Neoarchean time.

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an important period of global supercontinent formation in the Neoarchean (Condie et al., 2011). The U-Pb ages and Hf-isotope analyses of these xenocrysts, therefore, suggest the presence of unexposed Archean crust beneath the Junggar Basin.

Moreover, the

distinct xenocryst ages from rocks from two neighbouring drill cores (Fig. 1B) seems to indicate that the volcanic rocks were erupted through a complex Archean basement with different age provinces, consistent with previous geochronological and geophysical data that the Junggar terrane may have a complicated Precambrian crystal basement (e.g., Zhang et al., 2013; Xu et al., 2015). It is difficult at this stage to quantitatively estimate the volume of Archean crust

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beneath the Junggar terrane as Archean rocks have never been identified.

It could be

speculated that the ancient basement, if it ever existed, might have been tectonically dismembered during the long-lived evolution of Paleo-Asian Ocean and thus ancient geologic record is only incompletely preserved, or largely hidden in the deep. Alternatively, the basement beneath the Junggar terrane may represent an ancient

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microcontinent once present in Paleo-Asian Ocean, just like the Australian block which Archean components, including dioritic xenoliths (2.52 Ga)

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now exists in Pacific Ocean.

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from Paleozoic rocks (Xu et al., 2015) and detrital zircons (one 3.6 Ga, one 3.5 Ga, few

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3.4‒2.88 Ga and major ~2.5 Ga) from sediments (Li et al., 2007; Huang et al., 2013 ; Li et One 2536 Ma zircon xenocryst has also

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al., 2020), are reported in the East Junggar.

been identified in basalts from the Karamay area, West Junggar (Zhu et al., 2007).

The

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occurrences of these Archean “windows” and the newly discovered abundant Archean

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Junggar terrane.

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zircons presented here, imply that Archean protoliths still remain to be discovered in the

The CAOB has long been regarded as an important area of continental growth during the Phanerozoic, with considerable juvenile materials added to the continents (e.g., Sengör et al., 1993; Han et al., 1997; Jahn et al., 2000; Chen and Arakawa, 2005; Tang et al., 2017).

However, this conclusion needs to be carefully assessed as it is mainly based

on the studies from surface geology.

Kröner et al. (2014) also pointed out that the

production of mantle-derived or juvenile continental crust during the accretionary history of the CAOB has been grossly overestimated.

Our findings highlight that deeply buried

Archean crust may be still preserved beneath the significantly younger Phanerozoic upper

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crust of the southwestern CAOB.

If large parts of the exposed CAOB are also underlain

by older lower crust, the study of crustal growth rates through time only from surface exposures will require revision.

This may significantly change our view of the models of

continental generation for young orogens, to rather support a higher rate of crustal growth

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in the early Earth (e.g., Belousova et al., 2010).

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5.3. Global comparisons and implications for early crustal evolution

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In order to compare the Early Archean zircons from the Junggar Basin with other

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ancient ones, we compiled a Hf-isotope and U-Pb age dataset of zircons (>3.4 Ga)

parameters described above.

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worldwide and recalculated all εHf (t) values (Appendix Table C) using the same modeling As shown in Fig. 9A, there is not a great difference in

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Hf-isotopic compositions between the Junggar Basin grains and other coeval zircons

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worldwide, implying a similar trend of global crustal evolution during the Early Archean However, the available Hadean and Eoarchean zircons

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(Belousova et al., 2010).

especially around 3.9 Ga, exhibit distinct Hf-isotopic signatures.

In detail, the zircons

with ages older than ~3.9 Ga have negative ε Hf (t) values, and the data plot on an approximate trend of falling ε Hf (t) values with decreasing ages.

This trend suggests that

the parental magmas of these zircons were derived from continued reworking of a similar juvenile source, which could be dominated by either granitic or mafic protoliths (Harrison et al., 2008; Kemp et al., 2010).

In contrast, except for: (1) minor Eoarchean zircons

(<3.9 Ga) from the North China Craton and Antarctic show extremely positive ε Hf (t) values above the DM evolution line, possibly indicative of the presence of ultra-depleted mantle

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domains (Choi et al., 2006; Wang et al., 2015); (2) part of grains (3.9─3.8 Ga) from the Australia, Wyoming Province, Canada and Africa have relatively negative εHf (t) values, suggestive of reworking of Hadean crust (e.g., Frost et al., 2017), most Eoarchean zircons are characterized by chondritic Hf isotopic compositions and plot in another separate field. The sudden appearance of abundant zircons with higher εHf (t) values at about 3.9 Ga

The transition in Lu-Hf isotope systematics may imply a great

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the Hadean crust was lost.

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signals the renewed input of juvenile materials from the mantle, and indicates that much of

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change in the nature of crustal evolution at the Hadean-Archean boundary (~3.9 Ga).

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This inference has been put forward by some previous studies (e.g., Pietranik et al., 2008;

important transition again.

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Jacobsen et al., 2010; Bell et al., 2014), and our new data and compilation emphasize this However, the mechanism triggering this change is still an

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open question.

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The period around 3.9 Ga was a time when the early Earth and other planets in the This idea was

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inner Solar System were bombarded by a heavy flux of meteorites.

named as Late Heavy Bombardment (LHB), supported by numerous geochronological studies (e.g., Rb-Sr, U-Pb, K-Ar and Ar-Ar systems) on Apollo and Luna samples which ages were reset at ca.4.0–3.8Ga (e.g., Tera et al.,1974; Ryder, 2002).

The LHB was

possibly resulted from perturbation of the asteroid belt triggered by a change in the orbits of the giant planets (Gomes et al., 2005).

Now the concept has probably been expanded

as increasingly number of Lunar zircons show older ages from 4.3-4.1 Ga (Fig. 9B), suggesting a more constant large impact flux on the early Moon (e.g., Crow et al., 2017). Although different models of impact rate vs. time have been proposed to explain the lunar

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bombardment (e.g., Zahnle et al., 2007; Hopkins and Mojzsis, 2015 and reference therein), the ~3.9 Ga may be one of the most importing periods during LHB (Fig. 9B).

If the Moon

had experienced intense flux of impactors around ~3.9 Ga, the Earth should be bombarded approximately 20 times greater than the Moon (e.g., Grieve et al.,2006). Large impacts on the early Earth at ~3.9 Ga is also supported by studies on Hadean For example, Abbott et al. (2012) presented evidence for a heating event in

f

zircons.

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3.95–3.85 detrital zircons compared to other older or younger grains, and Bell and

As a consequence, the transition at ~3.9 Ga observed

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Jack Hills zircons (3.84–3.91Ga).

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Harrison (2013) discovered a statistically anomalous population of low-T metamorphic

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from Lu-Hf isotope systematics of Earth’s zircons lead us to speculate a possible link to the LHB at~3.9 Ga (Fig. 9).

The LHB could also have strongly disrupted the Hadean We must admit that the

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crust, as a result of the nearly absence of Hadean rocks.

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transition may not be exactly correct as larger proportion of the zircon data >3.9 Ga

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coming from a single location (e.g., Jack Hills), but our speculation based on the available data provides some new insights on the early Earth evolution.

Further investigations on

the oldest rocks and minerals will shed light on this possible dramatic change during the Hadean-early Archean time (~3.9 Ga).

6. Conclusions Drilling-sampled Carboniferous volcanic rocks from the Junggar Basin (NW China), southwestern Central Asian Orogenic Belt (CAOB), have captured abundant Archean zircon xenocrysts.

The oldest population with U-Pb ages of 3.8 Ga shows chondritic ε Hf (t)

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of -0.7 to +0.7, and Hf model ages (T DM of 3900‒3952 Ma and Tcrust of 3973‒4062 Ma) that require crustal differentiation from the mantle as early as 4.0 Ga.

Three slightly

younger populations at 3.7, 3.62 and 3.45 Ga have ε Hf (t) of -5.7 to +2.4 and consistent Eoarchean-Hadean Hf model ages, indicating multi-stage reworking of Early Archean crustal materials.

A series of 2.55 Ga zircons have positive and high ε Hf (t) values of +3.7

Our results imply the potential presence of unexposed

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mantle reservoir at Neoarchean.

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to +8.0, arguing for their derivation from juvenile crust that was extracted from a depleted

The

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Archean basement beneath the Junggar Basin in the southwestern CAOB.

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observation of deeply buried Archean crust significantly older than the exposed upper The

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crust will require revision of crustal growth rates through time for young orogens.

global comparisons of Hf isotopic signatures of ancient zircons (>3.4 Ga) imply that there

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may have been a great change in early crustal evolution at the Hadean‒Archean

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transition (~3.9 Ga), possibly linked to the Late Heavy Bombardment (LHB).

Acknowledgements

We are grateful to journal Editor-in-Chief (Prof. G. Shellnutt), Prof. Shan Li and two anonymous reviewers for their critical and constructive comments which substantially improved an earlier version of the manuscript.

We also thank Xinjiang Oil-field

Company which kindly supplied borehole samples and related geological data.

This

study was financially supported by the National Natural Science Foundation of China (NSFC) (grants 41973033, 41373038, 41673034 and 41520104003), the Fundamental Research Funds for the Central Universities, China University of Geosciences (Wuhan)

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(CUGL150406 and MSF GPMR06), and the Fund for Outstanding Doctoral Dissertation of CUG (Wuhan). This is a publication 1388 from the ARC Centre of Excellence for Core to Crust Fluid Systems (http://www.ccfs.mq.edu.au) and 1351 from the GEMOC

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Key Centre (http://www.gemoc.mq.edu.au).

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Journal Pre-proof Wu, F.Y., Yang, J.H., Liu, X.M., Li, T.S., Xie, L.W., Yang, Y.H., 2005. Hf isotopes of the 3.8 Ga zircons in eastern Hebei Province, China: Implications for early crustal evolution of the North China Craton. Chinese Science Bulletin 50, 2473–2480. Wu, F.Y., Zhang, Y.B., Yang, J.H., Xie, L.W., Yang, Y.H., 2008 . Zircon U-Pb and Hf isotopic constraints on the Early Archean crustal evolution in Anshan of the North China Craton. Precambrian Research 167, 339–362. Xiao, W.J., Han, C.M., Yuan, C., Sun, M., Lin, S.F., Chen, H.L., Li, Z.L., Li, J.L., Sun, S., 2008. Middle Cambrian to Permian subduction-related accretionary orogenesis of

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Research 290, 32–48.

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Figure captions

Fig. 1. (A) Simplified tectonic map of the Central Asian Orogenic Belt (modified from Wang et al., 2019). Su et al., 2010).

(B) Simplified geological map of the Junggar terrane (modified from

The studied drill cores JL101 and JL102 are located within the western

Red stars in the stratigraphic column represent the

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JL102 within the Junggar Basin.

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part of the Junggar Basin. (C) Simplified stratigraphic column of drill cores JL101 and

Representative images (A, C) and photomicrographs (B, D, cross-polarized light)

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Fig. 2.

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sample positions.

of the basaltic andesites from drill cores JL101 and JL102 within the Junggar Basin.

207

Pb/

206

Representative cathodoluminescence (CL) images of zircons with preferred

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Fig. 3.

rn

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Mineral abbreviations: Pl—plagioclase; Px—pyroxene.

Pb ages (Ma), εHf (t) values (within parentheses) and Th/U ratios.

U-Pb dating

pits are shown by small solid circles, and Lu-Hf analysis pits are shown by large dotted circles.

Fig. 4.

Representative photographs (transmitted light) and Raman spectra of mineral

inclusions in studied zircons. The small solid circles and large dotted circles show the spot by U-Pb and Lu-Hf analyses, respectively. Qz—quartz; Ap—apatite; Kfs—K-feldspar.

Mineral abbreviations: Zrn—zircon;

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Fig. 5.

Concordia plots of U-Pb results for xenocrystic zircons within the Junggar Basin.

MSWD—mean square of weighted deviates; n—number of analyses.

Fig. 6. (A) U-Th plot for the studied zircons; (B) The plot of zircon temperatures versus The temperatures were calculated using the Ti-in-zircon thermometer (Watson et

f

ages.

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al., 2006); (C) U-Yb plot for the studied zircons (modified from Grimes et al., 2007); (D)

176

Hf/

177

Hf)i (A) and ε Hf (t) (B) versus U-Pb ages for xenocrystic zircons within DM—depleted mantle; CHUR—chondritic uniform reservoir.

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the Junggar Basin.

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Fig. 7. (

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Y-Yb/Sm plot for the studied zircons (after Belousova et al., 2002).

Probability diagram of Hf model ages for xenocrystic zircons within the Junggar

Basin.

(A) T DM denotes the single-stage model age with reference to the depleted

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Fig. 8.

mantle, and (B) T crust denotes the two-stage model age with reference to Archean crust.

Fig. 9. (A) A global comparison between Hf-isotopes and U-Pb ages of the ancient zircons (>3.4 Ga) worldwide.

All ε Hf (t) values were recalculated using CHUR

parameters from Blichert-Toft and Albarède (1997) and λ176Lu of 1.865 × 10−11 a−1 from Scherer et al. (2001).

Data sources are from: (1) Ge et al. (2018), (2) Diwu et al.

(2013), (3) Liu et al. (2008), (4) Wu et al. (2008), (5) Wang et al. (2015), (6) Zheng et al. (2004), (7) Wu et al. (2005), (8) Harrison et al. (2008), (9) Kemp et al. (2010), (10)

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Jacobsen et al. (2010), (11) Frost et al. (2017), (12) Guitreau et al. (2012), (13) Iizuka et al. (2009), (14) Amelin et al. (2000), (15) Pietranik et al. (2008), (16) Kemp et al. (2009), (17) Hiess et al. (2009), (18) Zeh et al. (2008), (19) Choi et al. (2006).

Data marked with “*” are for

used for comparison are presented in (Appendix Table C). detrital zircons.

Detailed data

(B) The columns are the age histogram for impact grown or

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recrystallized lunar zircon and zirconolite grains from Apollo missions, and these zircon

The dotted lines represent four popular concepts of the late lunar

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therein for details).

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ages provide evidence for large impacts (modified from Crow et al., 2017, and reference

over the Hadean.

The “Multiple cataclysms” scatters several cataclysms

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reference therein for details).

e-

bombardment (modified from Zahnle et al., 2007; Hopkins and Mojzsis, 2015, and

The “Unimodal cataclysm” is a schematic but quantitatively The “Sawtooth

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representative view of the “classical” late heavy bombardment.

rn

cataclysm” is quantitatively representative of a relatively weaker cataclysm with an The “Exponential decay” is calibrated to crater counts and

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upturn at ca. 4100 Ma.

surface ages from Apollo landing sites and the Imbrium impact basin.

The time around

~3.9 Ga was considered as one of the most important periods during LHB.

Journal Pre-proof No conflict of interest exits in the submission of this manuscript, and manuscript is approved by all authors for publication.

I would like to declare on behalf of my

co-authors that the work described was original research that has not been published previously, and not under consideration for publication elsewhere, in whole or in part.

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All the authors listed have approved the manuscript that is en closed.

Journal Pre-proof

Table 1. U-Pb dating results of xenocrystic zircons from the Junggar Basin, NW China. Th

U

(p

(p

p

p

m)

m)

Analyti

T h/

cal

Atomic ratios 207

U

spots

/

207

Pb

206

P

1σ

b/

Ages (Ma) 206

P

235

1σ

b/

207

P

238

1σ

/

206

1 P

σ

ra b

U

U

207

Pb

b/

b

206

P

235

1 σ

U

b/

Concord P

238

1

ance

σ

(%)

U

tio Sample JL101-4

26 3

10

18

0.0

0

1

05

17

30

4-03

7

1

0.0

21

24

4-04

1

7

0.0

25

89

7 0.0

3

4

04 36

8

1

1. JL101-

42

29

0.0

0.34 4

4-06

5

8

9

Jo u

3 0.

JL101-

42

94

0.0

0.34

4

4-07

1

3

51

0.

JL101-

15

81

4-08

6

6

1

44

73 6

4-09

8

1

81

31

52 6

4-10

4

6

JL101-

53

36

4-11

.3

8

09

31

18

0

1 0.0

2.

0.34

0.0

09

7

8

4

8

1

379

1

378

2

9

3

4

6

5

2

317

3

285

8

3

7

6

9

5

2

371

1

372

3

1

3

8

9

3

1

371

1

375

3

9

5

8

0

3

2

372

4

420

9

1

5

6

99%

99%

89%

99%

99%

0

1

361

1

362

2

8

9

5

9

8

87%

2

346

2

347

6

5

3

3

6

8

2

371

1

372

3

0

1

7

8

4

1

349

1

313

3

99%

2

99%

3698

30 0.5

8

3475

0.78 36

30.3

2

3608

47 0.6

6

369

0.0

83

522

1

3

0.71

37.6

371

5

0.6

04

2

99%

3410

58

8

4 78

07

0.0 79

0

0.0

0 0.34

0

1

0.75

783

7

5

0. 1

JL101-

30

7

05

6

0.0 01

29.2

2

3687

0.92

97

0.0 0.30

3

2

0.4

8

0. JL101-

09 92

063

379

0.0 0.78

34.3

1

2

9

03

1

0

15

0.0 0.32

379

3698

33

370 4

0. JL101-

09

1.7

05 86

9

80

38.0

2

0.0

7

0.0

0.28

99%

3383

0.78

225

3

6

93

4

9

3794

81

0.6

04

5

20

0.6

37.8

9

0.0

6

524

4

1

16

04

76

07

0.55

37.7

6

3732

90

414

3

0.0

0.8

21.8

377

7

9

0.28 2

4-05

915

1

3798

0.79

81

03 0.

JL101-

0.5 40.8

04

6

37 7

0.37 8

07

796 6

379

0.0

0.77 72

58 0.

JL101-

2

0.6 37.8

06

9

03 9

0.35 5

08

189 4

0. JL101-

0.0 0.80

76

12 5

2

0.6 41.0

2 3802

71 3

0.37 5

4-02

585 4

0. JL101-

09

f

.7

86

al

.6

06

0.0 0.79

oo

4 4-01

0.7 40.9

pr

0.0 0.37

e-

78

rn

33

Pr

0. JL101-

99%

3 0.62

0.0

3706

89%

Journal Pre-proof

2 51

0.0

59

2

04

5 0. JL101-

47

73

4-14

.3

0

0.0

JL101-

52

04 2

6

7

0.0

0.7

0.0

0.33

.4

7

91

0.0

4-16

.3

4

05

4 0. JL101-

11

51

0.0

4-17

6

9

04

2 19

11

4-18

.4

38

0.0 24 4

0. JL101-

99

10

4-19

.4

25

0.0 04

7

4

05 27

7 0.

4-01(2 )

10 72

9

6 6

14

2.

JL10145

17

0

6

4-22

07 9

10

5

2

362

2

360

5

3

5

3

2

1

2

337

2

328

2

9

2

2

2

2

369

1

373

3

3

8

9

5

6

2

362

1

360

2

1

4

5

7

4

2

345

4

344

1

0

6

1

94%

99%

97%

99%

99%

3440

1

99%

2

3

1

0.8

0.0

72

0.79

07

5

11

8

0.6

2

368

1

369

3

6

0

7

9

7

3

379

2

375

2

2

5

1

7

8

3

355

1

327

2

1

0

9

3

1

2

369

2

369

3

9

2

1

1

7

3

361

2

354

2

5

4

2

5

5

3

339

2

327

4

3

6

9

4

8

2

371

1

362

2

8

5

8

0

1

3675

51

774

3797

99%

99%

0.0

0.34

07

31.9

01

0.66

05

6

69

0

899

2

16

5

0.0

3

0

0.0

5

0.

310

4

1

0.77

40.9

0.0

1

0

5

27

0.0

0.37

29

0.6

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JL101-

8

328

2

0.0

53

134

2

99%

3628

0.70

36.5

3

5

6

0.0 0.34

3 4-20

828 1

0. 31

06

46

42 0

11

1.3

28.8

3

3671

98

5

0.29 1

JL101-

676

7

0.0

0.74 17

5

9

0.5 34.4

04

2

49 9

0.33 0

09

721 8

0. JL101-

0.0 0.78

17

19

6

9

7

0.7 37.1

3

3424

39 2

0.34 2

05

869 4

370

0.0 0.66

90

11

1

9

0.5 26.8

372

3633

85 1

0.29 0

13

120 9

0. 37

0.74 99

34 8

JL101-

34.5 04

2

3394

75

6

0 4-15

08

808

0. 61

0

0.0 0.61

48

55

2

1

0.3 24.2

7

3735

62 7

0.28 0

09

119 9

7

0.0 0.77

62

65

9

5

0.6 38.2

07

pr

4-13

57

1

0.35 6

34

e-

13

104

4

2. JL101-

04

f

97

oo

5

Pr

1

al

4

rn

4-12

0.7

3694

91%

0.0

JL10181

0

0.34

06

36.9

80

0.77

10

4

9

23

5

361

2

27

3

4-23 77

1.

0.0

0.7

3673

99%

0.0

JL10123

23

1

2

0

0.33

0

37

07

34.1

5

534

39

0.73

7

31

06

4-24 0.

0.0

0.8

7

3634

98%

0.0

JL10125

15

1

0.29

06

27.3

00

0.66

12

8

00

7

45

2

488

2

16

4

4-25 0.

0.0

0.6

3441

96%

0.0

JL10131

39

8

0.36

06

37.8

93

0.75

05

6

6

0

06

6

099

6

33

8

4-26 3753

97%

Journal Pre-proof 0.

0.0

0.5

0.0

JL10124

10

2

0.29

06

24.1

69

0.58

07

1

18

4

58

2

434

3

68

0

3

327

2

297

2

2

4

3

7

9

3

360

2

360

2

6

4

3

8

9

3

363

2

360

2

5

5

3

6

5

3

345

2

303

2

7

7

5

9

5

4-27 0.

0.0

0.7

3450

90%

0.0

JL10129

1

0.32

07

33.8

98

0.75

07

1

5

53

6

005

3

00

9

4-28 43

0.

0.0

0.8

3595

99%

0.0

JL10130

3

0.33

07

34.8

09

0.74

06

9

1

49

6

535

4

97

8

4-29 97

2.

0.0

0.7

3640

99%

0.0

JL10175

30

4

0.34

08

29.0

29

0.60

06

3

8

5

85

4

986

7

22

1

4-30 0.0

0.7

0.0

f

0.

3702

12

69

1

0.34

07

31.4

08

0.66

06

4

8

8

23

3

762

1

41

4

4-31 0.0

0.9

0.0

21

4

0.37

4

19

07

41.1

7

266

34

0.79

1

98

4-32 5

1.

0.0

0.4

JL10157

39

4

0.35

06

24.0

91

6

2

7

30

8

117

6

2.

0.0

65

30

1

0.35

07

29.8

9

3

8

01

0

792

0.

0.0

JL1012

0.29

5

0

97

58

1.

JL102-

12

11

22

40

34

17

0 2-02

54

93 3

89

42

2-03

.8

4

96

52

44

2-04

.1

39

2-05

8

1

18 8

JL102-

23

17

1.

0.0

2

3

5

3

379

2

378

3

2

8

3

9

6

2

326

2

258

2

9

9

0

1

0

3

348

2

310

2

1

3

0

5

3

4

341

2

332

2

0

4

7

0

8

6

196

2

152

1

3

3

2

6

7

2

253

1

251

1

0

5

3

0

4

2

234

1

215

1

2

4

2

4

1

2

214

2

179

3

5

9

1

8

0

2

256

1

255

1

5

7

6

2

7

2

149

1

971

9

2491

03

92%

99%

76%

88%

97%

74%

2552

99%

1 0.0 0.39 02

2509

68

91%

3 0.0 0.32 06

2502

17

82%

1

0.1

0.0 0.48

93

03

2575

56 2 0.0

4

0.0

4

3.36

3469

60

320

2

4

70

7 0.14

03

0.1

02

3707

0.47

11.5

2

0.0

8

0.0

3720

71

50

0.17

3799

0.26

19

4

2

2

7.30

43

31

36

0.1

02

1. JL102-

5

7

0.0

2

07

64

0.16

7

0.67

48

0

2

60

9.05

328

0.0

0.1

02

0. JL102-

8

11.1

0.0

1

87

408

0.16 2

5

2

0

0. JL102-

05

52

02 94

0.61

46

2

0.0

0.1

0.0

0.16

5

18

5.91

0

1.

18

584

06

7

JL102-

27.8

0.0

0.16

0

2-01

7

Jo u

Sample JL102-2

07

24

0.7

rn

29 4-35

04

al

4-34

1

0.49

0.6

JL101-

353

0.0

Pr

4-33

10

e-

94

3673

pr

0. JL101-

3

oo

JL101-

87%

99%

9 0.16

0.0

2344

57%

Journal Pre-proof

4 66

0.0

8

7

02

7 0. JL102-

47

12

2-08

1

79

0.0

JL102-

83

02 3

5

4

0.0

0.1

0.0

0.17

0

1

16

0.0

2-10

4

33

03

6 0. JL102-

10

12

0.0

2-11

81

22

02

8 95

10

2-12

4

49

0.0 61 7

0. JL102-

27

42

0.0

4

6

02

74

5

8

02 94

1

5

0. JL102-

41

74

2-15

9

8

5

Jo u 6

5

0.

JL102-

64

84

7

2-16

2

1

6

1. JL102-

96

76 2

2-17

7

7 0.

JL102-

95

23 4

2-18

JL102-

.4

84

4

.8

2

3

0.2

0.0

5

34

50

5

4 7

3

00

05 81

3

3

0

138

1

82%

1 837

50%

2

9

5

0

2

202

1

150

2

6

4

8

1

0

2

240

2

217

3

4

3

0

5

6

2

192

1

140

2

5

9

7

8

1

2

251

1

249

2

5

1

6

5

5

2

223

1

192

1

5

6

6

7

7

1

168

1

113

9

1

2

6

2

254

1

252

1

2

9

4

4

5

4

250

2

254

4

0

3

1

7

4

3

253

1

256

2

3

8

7

2

3

70%

90%

68%

99%

85%

8

61%

99%

98%

0.0 0.48

799

8

2

0.2

03

9

2491

44

11.1

37

10

8

0.0 0.16

6 2-20

639

2

2565

0.48 39

8

0. 33

03 94

10.7

193

0.0

66

03

1

2447

0.47

4

9 JL102-

0.1

0.0 0.16

230

4

1

1 2-19

01

0. 45

3

63%

0.0 27

082

0

6

3

02

1

2524

0.19

11.3

07

03

62

0.0 0.17

0

0.0

0.0

3

3

7

84

67

8

2525

0.34

4.23

92

05 25

8

02

6

91

43

0.0 0.15

4

0.0

0.1

4

127

1

0.47

98

3

2554

40

0.1

8.03

02

67

04

2

0.0

0.16

184

0.0

2

617

2

79%

2617

0.24

10.8

7

9

12

02

67

07

0.1

0.0

0.16

1

3

0.0

14

20

167

6

2616

0.40

5.68

1

8

8

0

0.0 0.16

8 2-14

07 5

0. 60

03

08

62 4

JL102-

0.2

9.66

205

4

2396

22

7

0.17 6

2-13

18

2

80%

0.0

0.26 31

9

7

0.1 6.34

02

1

87 5

0.17 9

9

3

01

91 8

0. JL102-

0.0 0.13

58

45

6

0

1

0.0 2.92

5

2672

96 1

0.15 8

04

41 3

4

0.0 0.34

74

20

1

5

0.1 8.71

169

2584

79 1

0.18 1

07

00 8

0. 25

0.21 82

28 5

JL102-

5.14 02

1

2473

63

7

0 2-09

03

78

1. 79

206

0.0 0.29

16

16

2 9

0.1 6.58

4

2457

15 5

0.16 3

03

08 3

6

0.0 0.30

17

02

6

7

0.1 6.64

01

pr

2-07

26

0

0.16 6

60

e-

44

27

3

0. JL102-

02

f

99

oo

3

Pr

37

al

22

rn

2-06

4

2495

99%

Journal Pre-proof

46

90 4

67

0.0

0 2-22

7

1

03

0. 58

65

0.0

8 2-23

1

1 0.

JL102-

46

75

0.0

6 2-24

2

8 0.

JL102-

21

31 6

2-25

0

9 1.

JL102-

16

12

2-26

JL102-

42

50

97

0

0.

0.0

0.1

0.15

93

7

0.0

4

03 6

1. 15

14

0.0 0.16

0 2-29

92

85

63

1

2-30

68

22

42

4

69

11

6

2-31

7

13

77

3 1. JL102-

12

10 1

2-32

38

47

05 8 0.

JL102-

19

62 3

2-33

4

5

22 1

54

71 7

2-34

5

6

30 6

JL102-

89

59

1.

0.0

183

2

133

1

1

0

1

3

5 68%

3

179

1

131

1

5

6

9

1

4

3

155

1

4

6

6

879

7

111

3

1 530

7

0

9

2

226

1

200

1

7

9

8

8

4

6

165

1

9

8

7

995

8

3

172

2

106

1

7

8

0

1

1

2657 52%

04

3

203

2

170

2

9

2

4

5

4

2372

27 9

82%

0.0 0.18 01

9

3

165

1

107

7

5

8

4

2487

12 0.0

4

0.0

91

4.72

96%

50%

0.30

44

7

0

0.0

6 0.17

02

5

03

7

2631

89

4.10

3

0.0

71

0.0 0.16

6

87%

0.17

82

2

4

0.1

5

0. JL102-

01

0

03

225

2500

69

6.39

2

0.0

07

0.0 0.15

233

28%

0.16

44

4

9

0.1

1

7

5

02

4

04

0

2521

55

4.48

7

0.0

87

0.0 0.18

5

44%

0.36

0.0

9

1

1

0.1

73

145

3 03

5

03

2

2644

57

4.11

195

0.0

61

0.0

0.17

3

3

2

22

0

68%

0.08

8.34

1

0.

JL102-

01

90

03

3

0.0

0.0

0.0

0.16

Jo u

10

1

2406

61

52

2

7

2

5

1. 11

02

0.14

2.00

03

7 JL102-

91

3

0.0

73

90

2

9

0.0

3.62

197

2456

55

5

0.17 7

JL102-

15 3

2

2392

0.22

09

52

4 2-28

4.86 03

0. 43

97 1

24

02

52 8

1 JL102-

27

90

12

0.0 0.22

7

222

0

9

0.1

03

4 2-27

91

5.06

3

3

05

1

0.0

2

0.0

55

0.15

0

70%

0.41 21

2

7

7

0.2

41

3

2526

36

8.97 03

6

02

2

0.0

6

0.0

11

0.15

7

88%

0.25 36

5

2

2

0.1

68

133

2450

80

5.87 03

1

04

4

0.16

2

0.0

27 1

178

71%

0.35 84

95 9

3 8

0.1

03

3

2354

04

7.92

1

54%

03

1

0.15

1

0.0

37 3

1 959

3

0.23 30

07 5

JL102-

4.80

2

3

0.1

0.15

153

2456

04 2

Pr

70

4 02

60 1

1. JL102-

93

al

9

04

0.0 0.16

f

5 2-21

0.0 3.51

oo

0.0 0.15

pr

10

rn

56

e-

0. JL102-

9

6 0.19

57%

0.0

3

177

1

115

1

7

2

8

9

9

2595 2-35

0

9

4

38

03

65

98

70

03

58%

Journal Pre-proof 7

7

6

Jo u

rn

al

Pr

e-

pr

oo

f

9

Journal Pre-proof

Table 2. Hf-isotope results of xenocrystic zircons from the Junggar Basin, NW China. Analytical

176

Hf/17

7

spots

176

1σ

Lu/17

7

Hf

(176Hf/177

Age

1σ

Hf

(Ma)

Hf)i

ε Hf(t )*

1 σ

T DM †

1σ

(Ma)

T crust §

1σ

(Ma)

Sample JL101-4 0.0000

0.0007

0.0000

0.28035 3800

08

21

35

22

0.2803

0.0000

0.0009

0.0000

86

17

34

09

0.2804

0.0000

0.0008

0.0000

4 3800

98

11

0.2803

0.0000

0.0009

0.0000

7 3800

14

03

29

0.2806

0.0000

0.0016

0.0000

5 3450

97

21

02

45

0.2805

0.0000

0.0007

0.0000

0.28046

17

17

00

04

0.2804

0.0000

0.0017

0.0000

68

17

30

50

0.2804

0.0000

0.0009

0.0000

16

05

0.2804

0.0000

0.0003

JL101-4-09

08

08

0.2805

0.0000

0.0009

0.0000

rn

10

63

34

0.2804

0.0000

64

0.0006

0.0000

43

13

12

03

0.2804

0.0000

0.0009

0.0000

13

09

15

29

0.2804

0.0000

0.0008

0.0000

07

12

30

36

0.2805

0.0000

0.0005

0.0000

JL101-4-14 78

06

78

00

0.2805

0.0000

0.0005

0.0000

JL101-4-15 10

13

16

17

0.2805

0.0000

0.0004

0.0000

28

18

16

06

0.2803

0.0000

0.0007

0.0000

98

10

17

61

0.2804

0.0000

0.0003

0.0000

JL101-4-17

3

JL101-4-18 52

14

07

15

0.2805

0.0000

0.0010

0.0000

0

23

3791

39

3921

23

4070

38

3842

21

4119

36

3831

13

3987

23

3711

46

3895

78

3842

17

3945

29

3912

12

4064

20

3911

16

4063

27

3660

7

3812

13

3744

17

3834

29

3711

24

3901

41

3912

13

4066

23

3800

19

3934

33

3753

33

3964

55

0. -1.9

7

3

0.28034

0. -1.9

8

4

0.28054

0. -0.9

0

2

0.28047

0. 0.8

4

5

0.28050

0. -2.3

0

6

0.28034

0. -1.9

7

4

0.28043

0. -0.8

1 0.28047

3753

5

0.28034

3450

48

0. 0.0

3620

3695

2

0.28040

3700

29

1. -2.2

3450

3596

4

0.28050

3620

JL101-4-16

JL101-4-19

7

3450

32

0. -1.6

3700

4062

6

0.28040

3700

19

0.

4

3700

3952

6 -5.7

3620

31

0.

0.28040

3450

06

Jo u

JL101-4-13

0.0000

29 JL101-4-10

JL101-4-12

29

al

65

4086

0.

-2.0

5

3450

18

6

0.28034

3700

JL101-4-08

JL101-4-11

7

Pr

JL101-4-07

3925

7

2.4

e-

3700

39

0.

0.9

1

JL101-4-06

4056

5

0.28059

JL101-4-05

23

0.

-0.7

pr

82

3949

5

0.28031

JL101-4-04

48

0. -2.2

oo

14

3973

6

0.28033 3700

28

0. -0.6

8

JL101-4-03

3900 7

0.28031

JL101-4-02

02

0. 0.7

f

0.2804 JL101-4-01

5 -3.3

0.

Journal Pre-proof 45

24

95

30

0.2804

0.0000

0.0008

0.0000

3 0.28042

JL101-4-20

3700 90

22

71

37

0.2813

0.0000

0.0015

0.0000

9 0. 1.0

8

3805

29

3880

50

2658

20

2728

33

2647

15

2712

24

2612

16

2654

27

2672

15

2758

25

2648

21

2712

35

2647

16

2713

28

2656

18

2730

31

2649

22

2717

37

2716

19

2829

32

2652

13

2724

22

8

Sample JL102-2 0.28130

JL102-2-01

2550 14

20

21

0.2813

0.0000

0.0010

0.0000

2 0.28130

JL102-2-02

2550 61

11

62

07

0.2813

0.0000

0.0007

0.0000

23

18

0.2813

0.0000

0.0003

0.0000

66

04

0.2813

0.0000

0.0014

0.0000

0.28130 2550

52

14

0.2813

0.0000

0.0009

0.0000 22

0.2813

0.0000

0.0005

0.0000

8 2550

12

16

0.2813

0.0000

0.0006

0.0000

JL102-2-08 70

31

0.2813

0.0000

0.0008

0.0000

00

14

57

0.2813

0.0000

0.0003

62

0.0000

26

0.2813

0.0001

0.0010

JL102-2-11 05

0.2813

0.0000

JL102-2-12 11

0.0006 93

Jo u

79

88

0.2814

0.0000

0.0007

8

0.0000

0.0008

0.0000

6

39

11

42

11

0.2813

0.0000

0.0005

0.0000

JL102-2-15 29

12

65

38

0.2813

0.0000

0.0008

0.0000

JL102-2-16

5

58

11

02

19

0.2814

0.0000

0.0004

0.0000

JL102-2-17 05

19

99

50

0.2813

0.0000

0.0002

0.0000

JL102-2-18

8

23

10

88

01

0.2813

0.0000

0.0005

0.0000

JL102-2-19 29

12

52

14

0.2813

0.0000

0.0009

0.0000

JL102-2-20

1

63

11

99

06

19

2560

31

2661

14

2737

24

2656

16

2729

26

2633

15

2690

26

2549

26

2548

44

2644

13

2711

23

2655

17

2728

28

2639

15

2700

26

0. 5.8

9

4

0.28138

0. 8.0

1

7

0.28130

0. 5.5

9

3

0.28130

0. 5.2

2

4

0.28131

0. 5.7

4

2556

4

0.28131

2550

26

0. 5.2

2550

2628

4

0.28130

2550

15

0. 5.1

2550

2596

5

0.28129

2550

1

0. 7.8

2550

4

4

0.28137

2550

24 2630

0. 6.8

2550

14 2598

7

0.28134

0.0000

0.2813

3.

5

06

26

3 6.7

2550

68

0. 5.3

0.28134

0.0000

14

5

0.28130

2550

75

13

0. 3.7

4

0.0000

rn

98

04

al

09

0. 6

0.28125

2550

19

5

5.4

7

2550

JL102-2-10

JL102-2-14

0.28130

Pr

16

JL102-2-09

JL102-2-13

1

2550

39

0.

5.2

e-

14

4

0.28130

JL102-2-07 26

0.

5.5

pr

49

5

0.28130 2550

12

0.

5.5 9

JL102-2-06 54

4

oo

15

0. 4.8

9

JL102-2-05 79

4

0.28128 2550

11

0. 6.4

4

JL102-2-04 06

4

0.28133 2550

12

0. 5.5

9

JL102-2-03 69

5

f

76

0. 5.2

4

Journal Pre-proof *ε Hf(t) = 10000×(((176Hf/177Hf)s-(176Hf/177Hf)s ×(e λt-1))/(176Hf/177Hf)CHUR-(176Lu/177Hf)CHUR×(e λt-1))-1). 176

†T DM = 1/λ×ln(1+((

Hf/

176

§T crust = 1/λ×ln(1+(( 176

(

Lu/

The

177

176

177

Hf/

176

Hf)s -(

177

Hf/

176

Hf)s -(

177

Hf/

176

Hf)DM))/((

177

Lu/

176

Hf)DM))/((

177

Lu/

176

Hf)s -(

177

Lu/

176

Hf)C-(

177

Lu/

Hf)DM)).

177

Hf)DM)) + t.

Hf)C = 0.015; t = crystallization age of zircon; s = sample; λ = 1.865×10

Hf/

177

Hf and

176

Lu/

177

-11 -1

a .

Hf ratios of chondrite (CHUR) and depleted mantle (DM) at present are 0.282772 and 0.0332,

Jo u

rn

al

Pr

e-

pr

oo

f

0.28325 and 0.0384, respectively.

Journal Pre-proof

Highlights： 1. The Junggar Basin volcanic rocks captured abundant Archean zircon xenocrysts. 2. Our results imply unexposed Eoarchean crust beneath the Junggar Basin .

Jo u

rn

al

Pr

e-

pr

oo

f

3. Global Hf isotopes reveal a great change in early crustal evolution at ~3.9 Ga.

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9