Determination and Geological significance of the Paleoproterozoic Geochronological Framework in Aqtashtagh Area in Southeast of Tarim, China
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    Abstract:

    A significant quantity of Paleoproterozoic granite and Khondalites in Dunhuang Group were identified from the Archean base metamorphic rocks in Agetashtag area, southeastern margin of the Tarim basin. The Paleoproterozoic granite differed from Neoarchean TTG rocks by their amphibolite facies metamorphism, non-sodium migmatization and had clear boundary with Milan Group. These large-scaled intrusions contained dioritic gneiss, gneissic quartz diorite, amphibole quartz syenite and carbonatite, with syenite and monzonite mafic rocks appeared as veins or dykes. In this paper, we did zircon SHRIMP U-Pb dating on all the following rocks: gneissic diorite, gneissic quartz diorite, gray felsic veins (felsic migmatization) and quartz syenite, and yielded their age of 2135±110Ma, 2051.9±9.9Ma, 2050±16Ma and 1873.4±9.6Ma respectively. In addition, we dated the Dunhuang Group volcanic rocks with the same method and got 1873.4 ± 9.6Ma as a result. We also found that, without exception, all Neoarchean metamorphic rocks had group metamorphic ages of either 2.27~2.38Ga or 1.9~2.05Ga. From these and some existing geochronological data by other researchers for the same study area, we can establish a fine geochronological framework as follow: (a)The formation of Khondalites and the emplacement of calc-alkaline island arc quartz diorite indicated an early subduction environment in the middle of Paleoproterozoic (2.10~2.15Ga) era, (b)Late Paleoproterozoic (1.93~2.05Ga), this area went through a syn-collisional orogenesis stage, during which, igneous carbonatite, quartz diorite and potassium migmatite were formed due to intense anatexis of crustal derived rocks and pre-existing rock underwent amphibolite facies metamorphism and intense ductile shear deformation. (c) In the post-orogenic stage (1.85~1.87Ga) in last Paleoproterozoic era, when post-orogenic ganite such as quartz monzonite, quartz syenite were formed. NW-trending mafic dyke swarms were well developed, indicating continental breakup of the Tarim craton in early Mesoproterozoic. The sedimentary strata of Suoerkuli Group (Annanba Group,conglomerate and quartzite) were widely developed giving further evidence for breakup in Mesoproterozoic. In summary, this geochronology framework provides not only a scientific basis for the discussion of early crustal evolution of the Tarim craton but also a comparison framework for the study of early Precambrian metamorphic base of North China craton. Moreover it provides data for the further study of the Columbia super continent assembly.

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XIN Houtian, ZHAO Fengqing, LUO Zhaohua, LIU Yongshun, WAN Yusheng, WANG Shuqing.2011. Determination and Geological significance of the Paleoproterozoic Geochronological Framework in Aqtashtagh Area in Southeast of Tarim, China[J]. Acta Geologica Sinica,85(12):1977-1993

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History
  • Received:July 14,2011
  • Revised:September 16,2011
  • Adopted:September 27,2011
  • Online: December 09,2011
  • Published: