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_Journal of Structural Geology 33 (2011) 362-380_ _Contents lists available at ScienceDirect_ _Journal of Structural Geology_ _journal homepage: www.elsevier.com/locate/jsg_ _Structural and geochronological evidence for Early Cretaceous orogen-parallel extension of the ductile lithosphere in the northern Dabie orogenic belt, East China_ _Yongsheng Wang a,*, Biwei Xiang b, Guang Zhu a, Dazhi Jiang c a School of Resource and Environmental Engineering, Hefei University of Technology, Hefei 230009, PR China b Faculty of Earth Sciences, China University of Geosciences, Wuhan 430074, PR China c Department of Earth Sciences, University of Western Ontario, London, Ontario N6A5B7, Canada_ _article info_ _Article history: Received 13 April 2010; Received in revised form 11 August 2010; Accepted 5 September 2010; Available online 16 September 2010_ _Keywords: Dabie orogenic belt North Dabie dome Xiaotian-Mozitan shear zone Wuhe-Shuihou shear zone 40Ar/39Ar dating orogen-parallel extension_ _abstract_ _The WNW-trending North Dabie dome (NDD) in the northern Dabie orogenic belt is bounded by the Xiaotian-Mozitan ductile shear zone (XMSZ) in the north and the Wuhe-Shuihou shear zone (WSSZ) in the south. Fabric geometries and kinematics of both the XMSZ and the WSSZ are similar. They both show a top-to-NW or WNW sense of shear and display similar microstructures which indicate that the deformation temperature was about 600-650°C. 40Ar/39Ar dating of hornblende and biotite from the mylonites of the XMSZ suggests that the shear zone was developed prior to 142 Ma. U-Pb zircon LA-ICPMS dating of undeformed granite dikes that cut the XMSZ suggests that the ductile shearing occurred before 130 Ma. The WSSZ was also developed in the Early Cretaceous. The interior of the NDD is dominated by top-to-NW or WNW sense of shear in the migmatitic gneiss and deformed plutons of the earliest Early Cretaceous ages. We suggest that the XMSZ, the WSSZ, and the interior of the NDD were involved in the same Early Cretaceous deformation. The XMSZ and the WSSZ were originally a single connected, more flat-lying zone, which we call the East Dabie Detachment Zone (EDDZ). It developed at a crustal level of over 18 km in depth. Kinematics of the EDDZ suggest that the ductile crust and possibly part of the lithospheric mantle in the eastern Dabie orogen underwent pervasive orogen-parallel and ESE-ward extension at the beginning of the Early Cretaceous. Large-scale magmatic intrusions following this deformation and the resultant increase in buoyancy led to the exhumation of the NDD and the warping of the EDDZ. Erosion separated the EDDZ into two zones (the XMSZ and the WSSZ) as observed today. Many metamorphic core complexes of Early Cretaceous were developed in the eastern North China Craton, most showing top-to-NW or WNW sense of shear. We suggest that such a widespread uniform shear sense reflects a uniform flow direction of the ductile lithosphere in East China that has also been documented in the Liaonan, Yiwulushan and Yumenshan metamorphic core complexes in the northeastern part of the North China Craton._ _© 2010 Elsevier Ltd. All rights reserved._ _1. Introduction_ _The Dabie orogenic belt (DOB) was developed by continent-continent collision between the North China Block (NCB) and the South China Block (SCB). Coesite-bearing (Okay et al., 1989; Wang et al., 1989) and microdiamond-bearing (Xu et al., 1992) eclogites from the ultra-high pressure (UHP) unit of the DOB suggest that part of the SCB crust was deeply subducted to mantle depth. In the past twenty years, detailed studies have shown that the collision took place in the Middle Triassic (ca. 240-230 Ma)._ _* Corresponding author. E-mail address: yshw9007@126.com (Y. Wang)._ _0191-8141 $ e see front matter © 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.jsg.2010.09.002_ _Proposals for the kinematics of the XMSZ include normal shear sense (e.g., Maruyama et al., 1994; Faure et al., 2003; Jiang et al., 2003a; Lin et al., 2005), normal shear sense with a sinistral component (e.g., Hacker et al., 2000; Ratschbacher et al., 2000), or sinistral shear (Wang et al., 2003). Wang et al. (2000), Suo et al. (2000), Zhang et al. (2002), and Liu et al. (2005a,b) regarded the XMSZ as being developed in the Middle Triassic, whereas others considered it to occur in the Early Cretaceous (e.g., Faure et al., 1999; Ratschbacher et al., 2000; Lin et al., 2005). No isotopic dating of mylonites has been reported from the XMSZ. Ratschbacher et al. (2000) obtained a 40Ar/39Ar biotite age of 120.5 Ma from a deformed gabbro near the XMSZ and interpreted it as the cooling age related to the development of the XMSZ._ _The timing and kinematics of the bounding shear zones, the XMSZ and the WSSZ, are also controversial. Proposals for the kinematics of the XMSZ include normal shear sense (e.g., Maruyama et al., 1994; Faure et al., 2003; Jiang et al., 2003a; Lin et al., 2005), normal shear sense with a sinistral component (e.g., Hacker et al., 2000; Ratschbacher et al., 2000), or sinistral shear (Wang et al., 2003). Wang et al. (2000), Suo et al. (2000), Zhang et al. (2002), and Liu et al. (2005a,b) regarded the XMSZ as being developed in the Middle Triassic, whereas others considered it to occur in the Early Cretaceous (e.g., Faure et al., 1999; Ratschbacher et al., 2000; Lin et al., 2005). No isotopic dating of mylonites has been reported from the XMSZ. Ratschbacher et al. (2000) obtained a 40Ar/39Ar biotite age of 120.5 Ma from a deformed gabbro near the XMSZ and interpreted it as the cooling age related to the development of the XMSZ._ _In this contribution, we present detailed structural analysis of the XMSZ, the WSSZ, and the interior of the NDD. We also present geochronological data on the XMSZ. Our data place good constraints on the timing and kinematics of the deformation._ _2. Geological setting_ _The DOB is truncated in the east by the NE-striking Tan-Lu fault zone (Fig. 1). To the west, it is separated from the Hong’an belt, the western part of the DOB, by the NE-striking Shang-Ma fault zone. To the south and north, the DOB is bounded by the Yangtze foreland fold and thrust belt and the Hefei Basin respectively. The Tan-Lu fault zone is a sinistral zone overprinted by a series of brittle normal faults (Zhu et al., 2005). The Shang-Ma fault zone is expressed by a series of_ _Fig. 1. Structural map of the North Dabie region. Geochronological data for undeformed and deformed intrusions are after Xie et al. (2006), Wang et al. (2007), Xu et al. (2007), and Zhao et al. (2005, 2007). 1: the North Huaiyang unit (NH); 2: the North Dabie Dome (NDD); 3: the UHP eclogite unit (UHP); 4: Early Cretaceous volcanic rocks; 5: Early Cretaceous intrusion (undeformed); 6: Early Cretaceous intrusion (deformed); 7: Early Cretaceous dike; 8: Lower Cretaceous deposits; 9: Ductile shear zone; 10: Brittle normal fault; 11: Zircon SHRIMP U-Pb age; 12: Sampling localities for dating in this paper; 13: Foliation attitude of metamorphic rocks; 14: Top-to-shear sense from field and microscopic observation. (a) Sketch of the Qinlinge-Dabie-Sulu orogenic belts; (b) Lower-hemisphere, equal-area stereograms of poles to the gneiss foliation and plunges of mineral elongation lineation of the NDD, (c) Cross-sections showing the North Dabie units, the Xiaotian-Mozitan shear zone, and the Wuhe-Shuihou shear zone. NH: northern Huaiyang unit; NDD: northern Dabie dome; UHP: ultra-high pressure unit. (1) The Yunfengding pluton; (2) the Egongbao pluton; (3) the Shigujian pluton; (4) the Shuntan pluton; (5) the Xiaotian Basin._ _364_ _Y. Wang et al. Journal of Structural Geology 33 (2011) 362-380_ _Fig. 2. Field photos from the Xiaotian-Mozitan shear zone. a: Brittle normal faults cut across the ductile shear zone at a small angle with mylonite foliation; b: Mylonite xenolith in an Early Cretaceous pluton; c: Undeformed granite dike in the ductile shear zone; d: A NW-striking ductile shear belt shown as a mylonite belt; e: S-C fabrics indicating top-to-NW shear sense in the shear zone; f: s-type feldspar porphyroclast indicating top-to-NW shear sense in the shear zone._ _brittle WNW-dipping normal faults. It is a common practice (e.g., Zhai et al., 1995; Suo et al., 2001; Ma et al., 2004; Zhao et al., 2005, 2007; Xu et al., 2007; Wang et al., 2007; Liu et al., 2005a,b; Wu et al., 2007) to divide the DOB, from north to south._ Ключевые слова: eddz, foliation, deformed intrusion, feldspar, hanging wall, shuntan pluton, tectonophysics, early cretaceous, mylonites, hornblende sample, tectonic, li, shear, dome, uhp slab, migmatitic gneiss, zircon, crust, feldspar hornblende, dabie orogen, zheng, chemical geology, ? bt, northern margin, closure temperature, plunge, field photo, gbm recrystallization, exhumation, xmsz suggests, gravitational collapse, yunfengding pluton, minimum axis, dodson, science, segment, orogen, sinistral sense, step released, cooling age, biotite, egongbao pluton, quartz, microscopic observation, gneiss foliation, faure, tectonics, lineation, porphyroclastic biotite, qtz, fabric, cooling, mylonitic foliation, belt, wnw sense, uniform top-to-nw, liu, deformed pluton, luotian dome, university, geophysical, mylonite, suo, west, western segment, xmsz, earlier stage, ratschbacher, age, ti ?, eastern dabie, wssz, jiang, mooney, gbm gbm, protolith age, east, east segment, biotite sample, rock, north, crustal, earth, differential rotation, liou, tullis, ductile crust, recrystallization, tga, zhao, lithos, structural, early jurassic, metamorphic rock, protomylonites mylonites, ndd, sense, kinematics, eastern segment, ductile shearing, cretaceous, blg, east china, c-axis pattern, feld, top-to-nw wnw, ultrahigh-pressure metamorphism, sgr recrystallization, gneiss, ma, intraplate deformation, ultrahigh, small angle, geology, central, normal, plateau age, ? ma, tectonic evolution, geochronology, xmsz wssz, doming, yuexi dome, dated mineral, released, structural geology, central china, shear sense, deformation, partial melting, complex, fast uplifting, area, middle segment, zircon age, wnw, pluton, yang, china, late triassic, west segment, gao, wa, zhou, uhp, principle, deformation event, biotite age, williams, deformed, bt, monoclinic symmetry, muscovite age, bulletin, journal geophysical, acta, sinistral motion, pressure, dabie, zircon sample, zone, unit, hornblende, wang, granite, step, eastern ncb, sample, mylonite foliation, hacker, high, sgr, journal structural, wang journal, middle triassic, ti, eastern, wu, mswd, nature, curved segment, oriented thin-sections, ma xu, temperature, mineral, metamorphic, ductile, ductile deformation, western, ductile lithosphere, locally ultramylonites, gbm, middle, north dabie, deformation temperature, top-to-nw, early, lin, chemical, s-c fabric, china series, granite dike, initial, shear zone, xu, ultrahigh pressure, channel, elsevier, zhang, dating result, zhong, nite strain, journal structural geology, mineralogy, plane, fault, journal, dating, geochronological, tp, orthorhombic symmetry, extension, thrust belt, stretching lineation, chen