EAGE Basin Research (2010) 22, 126–138, doi: 10.1111/j.1365-2117.2009.00440.x Detrital zircon geochronology and its provenance implications: responses to Jurassic through Neogene basin-range interactions along northern margin of the Tarim Basin, Northwest China Zhong Lin and Shoutao Pengn,w nInstitute of Geology and Geophysics, Chinese Academy of Sciences, Beijing, China wExploration & Production Research Institute, SinoPec, Beijing, China ABSTRACT Previously published research from the Kuqa Subbasin along northern margin of theTarim Basin shows ¢ve tectonic-depositional phases fromTriassic to Neogene time. In order to reveal additional detailed information on the nature of provenance terrains and tectonic attributes since late Mesozoic time, ¢ve typical sandstone samples from Jurassic^Neogene strata were collected for U^Pb dating of detrital zircons.Geochronological constitution of detrital zircons of the Middle Jurassic sample is essentially unimodal and indicates major contributions from the South Tian Shan even Yili^Central Tian Shan, wherein most 370^450 Ma zircons probably resulted from tectonic accretion events between theYili^Central Tian Shan block and SouthTian Shan Ocean during Silurian and Devonian time, with sandstone provenance tectonic attributes of passive continental margin.The Lower Cretaceous sample shows a complicated provenance detrital zircon signature, with new peak ages of 290^330 Ma as well as 370(or 350)^450 Ma showing evident arc orogenic provenance tectonic attribute, probably re£ecting a new provenance supply that resulted from denudation process whthin the SouthTian Shan and SouthTian Shan suture.There are no obvious changes within age probability spectra of detrital zircons between the Cretaceous and early Paleogene samples, which suggests that similar provenance types and basin-range framework continued from Cretaceous to Early Paleogene time. However, unlike the Cretaceous and early Paleogene samples, an age spectra of the Miocene sample is relatively unimodal and similar to that of the Pliocene sample, with peak ages ranging between 392 and 458 Ma older than the comparable provenance ages (peak ages about 370^450 Ma) of the Middle Jurassic and Lower Cretaceous samples.Therefore, we conclude that the SouthTian Shan was rapidly exhumated and the southern SouthTian Shan had become the main source of clastics for the Kuqa Subbasin since the Miocene epoch. INTRODUCTION processes(Molnar& Tapponier,1975;Tapponier &Molnar, 1979; Hendrix et al.,1992; Avouac et al., 1993; Burtman et al., The Tian Shan (Heavenly Mountains) of northwestern 1996; Yin et al., 1998; Allen et al., 1999; Burtman, 2000; China is topographically characterized by higher west and Heermance et al., 2007). The Kuqa Subbasin is located lower east, with a peak elevation of 7000 m. Resulting from within the Tarim basin, in which relatively successive multiple accretion and collisions of di¡erent blocks in depositional and structural deformation records of Meso- Late Paleozoic time (Coleman, 1989; Windley et al., 1990, zoic^Cenozoic are preserved.Therefore, the Kuqa Subba- 2007; Allen & Zhang, 1992; Carroll et al., 1995), intense sin^Tian Shan system is a key tectonic region to study intracontinental structural deformation occurred in the basin-range relationship and continental evolution. Tian Shan and adjacent areas during Mesozoic^Cenozoic, Although many advances in structural and sedimentary which controlled coeval basin-range evolution and surface geology of the Mesozoic^Cenozoic basins adjacent to the Tian Shan have been published, and its tectonic evolu- Correspondence: Z. Li, Institute of Geology and Geophysics, tion has generally documented (Hendrix et al., 1992; Chinese Academy of Sciences, PO Box 9825, Beijing100029,Chi- Graham et al., 1993; Lu et al., 1994; Hendrix, 2000; Liu na. E-mail: [email protected] etal., 2000; Li et al., 2003, 2004), the geodynamic attributes r 2009 The Authors 126 Journal Compilation r Blackwell Publishing Ltd, European Association of Geoscientists & Engineers and International Association of Sedimentologists Detrital zircon geochronology and its provenance implications and evolution of the Kuqa Subbasin^Tian Shan are still excellent opportunity for analyzing basin-range interac- ambiguous. Building upon our recently published data tions in this intracontinental tectonic setting. on Jurassic^Neogene depositional systems, this research focuses on depositional responses to Mesozoic^Cenozoic basin-range interactions, with attention on detrital SAMPLE, ANALYTICAL METHODS zircon geochronology and its provenance implications, AND DATA and further explores tectonic controls and detailed pro- cesses of the Kuqa Subbasin^Tian Shan system. Along a belt between the Kuqa Subbasin and South Tian Shan, four relatively successive depositional pro¢les of Mesozoic^Cenozoic stratawere investigatedwith systemic TECTONIC UNITS AND REGIONAL sampling at Wenquan, Kelasu River, Kuqa River and Yang- GEOLOGY OF THE TIAN SHAN^KUQA xia (Fig. 1b). For each pro¢le, we had studied depositional SUBBASIN records, sandstone framework grain compositions, detrital heavy mineral compositions and whole-rock geochemical The Tian Shan is the largest intracontinental orogenic compositions (Li et al., 2004, 2005), and ¢ve tectonic- belt in Central Asia, and the Tarim and Junggar basins depositional phases from LowerTriassic to Neogene were are located along its south and north sides, respectively primarily outlined. (Fig. 1). Previous work suggests that Tian Shan orogene- On the basis of the work mentioned above, ¢ve respec- sis terminated in late Paleozoic time (Coleman, 1989; tive sandstone samples were selected from the Kuqa River Carroll et al., 1990; Seng˛r et al., 1993; Zhou et al., 2001), pro¢le (Table1, Fig.6), and their detrital zircons were sepa- but was subsequently modi¢ed by a series of Mesozoic^ rated for U^Pb dating in order to further explore tectonic Cenozoic intracontinental deformation events, probably controls and detailed evolutional processes of the late Me- related to accretion process occurred in the far southern sozoic^Cenozoic Kuqa Subbasin^Tian Shan system. This margin of the Eurasian Plate (Dewey et al., 1988; Avouac analytical method can be described as follows. et al., 1993). Two late Paleozoic sutures, the North Tian First, detrital heavy minerals were separated from Shan Suture and the South Tian Shan Suture, had been sandstone samples by the standard procedures for mineral identi¢ed according to ophiolite melanges within the separation (Li et al., 2004), and then detrital zircons were Tian Shan area (Allen & Zhang, 1992; Gao et al., 1998). carefully identi¢ed under a binocular microscope. Clean Accordingly the Tian Shan and its adjacent area may be detrital zircons with well-formed crystal shapes were divided into ¢ve tectonic units from north to south, Jung- selected and mounted in epoxy adhesive within 1cm gar basin, North Tian Shan, Yili^Central Tian Shan diameter rings and then were polished to yield a smooth (Central Tian Shan island arc), South Tian Shan and £at surface (slice) exposing the interiors of most zircon Tarim basin (Fig. 1a). Some researchers indicated that grains. Cathodoluminescence (CL) images, obtained by a the North Tian Shan and South Tian Shan all have CAMECA SX-50 microprobe (Cameca, France), were complicated structural attributes. Generally the North used to detect internal textures related to origin and Tian Shan is considered to be a tectonic^lithofacies choose potential target sites for U^Pb dating of zircons be- belt of Devonian^Carboniferous, the Central Tian Shan fore analysis. attributed to an island arc belt with pre-Cambrian Laser ablation ICP-MS zircon U^Pb analyses were con- basement, and the South Tian Shan may be a tectonic^ ducted on an Agilent 7500a ICP-MS (Hewlett^Packard, lithofacies (me¤lange?) belt of Devonian (?)^Carboniferous USA) equippedwith a193nm laser, housed at the Key La- age (Fig.1a). boratory ofContinentalGeodynamics,NorthwestUniver- The Kuqa Subbasin, situated south of the Tian Shan, sity in Xi’an, China. Zircon 91500 (Wiedenbeck et al., 1995) is an important Mesozoic^Cenozoic tectonic unit in the was used as the standard and the standard silicate glass northern Tarim basin (Jia, 1997). The Kuqa Subbasin NISTwasusedto optimize the machine:the spotdiameter and South Tian Shan together constitute a basin-range was 30 mm. The detailed analytical technique is described system (Fig. 1b and c). The Kuqa Subbasin was developed in Yuan et al. (2004).The common-Pb correction used the by Mesozoic^Cenozoic depositional records in thickness method described byAndersen (2002), since the signal in- of 6000^8000 m, which principally show £uviolacustrine tensity of 204Pb was much lower than the other Pb isotopes and alluvial sedimentary systems. and there is a large isobaric interference from Hg. For zir- Paleocurrent measurements from Mesozoic^Cenozoic cons older than 1000 Ma, ages were calculated from their strata within the northern Kuqa Subbasin are mainly 207Pb/206Pb ratios, whereas zircon ages younger than south-directed (Hendrix et al., 1992; Graham et al., 1000Mawere based on their 206Pb/238U ratios, which pro- 1993; Hendrix, 2000; Li et al., 2004), re£ecting tectonic vides a more reliable age estimate for these younger grains compression and uplift during this time frame.Therefore, due to the low content of radioactive Pb and the uncertain- a mass of terrestrial detrital materials from theTian Shan ties in common lead correction (Sircombe, 1999).