祁连山西段玉石沟地区上二叠统砂岩碎屑锆石年代学及其地质意义
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摘要
玉石沟地区位于青藏高原东北缘,大地构造属于北祁连造山带南缘,其石炭纪—三叠纪是上叠盆地发育时期,表现为浅海相、海陆交互相至陆相稳定型沉积建造。对玉石沟北部紫红色粗砂岩样品进行LA-ICP-MS碎屑锆石U-Pb测年,其年龄结果主要分布在4个区间:260～350 Ma(峰值314 Ma)、400～500 Ma(峰值445 Ma)、1 700～2 000 Ma、2 200～2 600 Ma,800～1 000 Ma锆石数仅有2颗,另有1颗锆石为2 056 Ma。锆石CL图像显示:260～350 Ma锆石中既有变质锆石也有岩浆锆石,可能响应南祁连地区石炭纪—早二叠世的热事件。400～500 Ma锆石以岩浆锆石为主,表明北祁连造山带和中祁连地块广泛发育的弧岩浆岩和同碰撞花岗岩提供了物源。1 700～2 000 Ma和2 200～2 600 Ma锆石主要为变质锆石,反映了祁连地块基底变质岩的年龄信息,推测来源于基底变质岩的剥露。800～1 000 Ma年龄区间的锆石数量稀少,可能反映新元古代侵入体在该组沉积时期尚未大规模剥露。砂岩中最年轻的锆石年龄为(289±2)Ma,限定了其沉积时代的下限为早二叠世,结合实测地层剖面上的岩石组合和层序变化,将之归属于上二叠统红泉组。碎屑锆石年龄结构表明玉石沟地区红泉组兼具北祁连造山带和中—南祁连地块的年龄信息,红泉组沉积物可能具有南、北两个物源区。
Yushigou area is located in the northeastern margin of the Qinghai-Tibetan plateau,and lies tectonically on the southern margin of the North Qilian orogenic belt. We conducted LA-ICP-MS detrital zircon U-Pb dating on the red sandstones from Yushigou. The results yielded four age groups at 260-350 Ma( peak at 314 Ma),400-500 Ma( peak at 445 Ma),1,700-2,000 Ma,and 2,200-2,600 Ma. Besides,two zircon grains were dated to be 800-1,000 Ma and another zircon to be 2,056 Ma. Zircons of 260-350 Ma show mainly magmatic( and minor metamorphic) features in CL imaging,reflecting the occurrence of Carboniferous to Early Permian magmatic-metamorphic events. Zircons of 400-500 Ma have mainly a magmatic origin,sug-gesting that the detrital provenance of the Yushigou sandstones were from arc magmatic rocks and syn-collisional felsic rocks. Zircons of 1,700-2,000 Ma and 2,200-2,600 Ma are dominantly metamorphic with old age information,indicating that the highly metamorphosed basement rocks were the detrital provenance of the sandstones. The few 800-1,000 Ma zircons indicate that the Neoproterozoic batholith had not been significantly exhumed. The youngest detrital zircon age from these sandstones( 289 ± 2 Ma) constrains the maximum deposition age of the Yaogou Group to the Early Permian. Comparing the rock features along the geological section,the strata likely belong to the Upper Permian Hongquan Formation. The broad age spectrum reflects the tectonomagmatic events in both the North Qilian orogenic belt and the South-Central Qilian block,and indicates that the Hongquan Formation has two detrital provenances.
Yushigou area is located in the northeastern margin of the Qinghai-Tibetan plateau,and lies tectonically on the southern margin of the North Qilian orogenic belt. We conducted LA-ICP-MS detrital zircon U-Pb dating on the red sandstones from Yushigou. The results yielded four age groups at 260-350 Ma( peak at 314 Ma),400-500 Ma( peak at 445 Ma),1,700-2,000 Ma,and 2,200-2,600 Ma. Besides,two zircon grains were dated to be 800-1,000 Ma and another zircon to be 2,056 Ma. Zircons of 260-350 Ma show mainly magmatic( and minor metamorphic) features in CL imaging,reflecting the occurrence of Carboniferous to Early Permian magmatic-metamorphic events. Zircons of 400-500 Ma have mainly a magmatic origin,sug-gesting that the detrital provenance of the Yushigou sandstones were from arc magmatic rocks and syn-collisional felsic rocks. Zircons of 1,700-2,000 Ma and 2,200-2,600 Ma are dominantly metamorphic with old age information,indicating that the highly metamorphosed basement rocks were the detrital provenance of the sandstones. The few 800-1,000 Ma zircons indicate that the Neoproterozoic batholith had not been significantly exhumed. The youngest detrital zircon age from these sandstones( 289 ± 2 Ma) constrains the maximum deposition age of the Yaogou Group to the Early Permian. Comparing the rock features along the geological section,the strata likely belong to the Upper Permian Hongquan Formation. The broad age spectrum reflects the tectonomagmatic events in both the North Qilian orogenic belt and the South-Central Qilian block,and indicates that the Hongquan Formation has two detrital provenances.
引文
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[2]BHATIA M R.Plate tectonics and geochemical composition of sandstones[J].The Journal of Geology,1983,91(6):611-627.
[3]WELTJE G J,EYNATTEN H V.Quantitative provenance analysis of sediments:Review and outlook[J].Sedimentary Geology,2004,171(1/4):1-11.
[4]王成善,李祥辉.沉积盆地分析原理与方法[M].北京:高等教育出版社,2003:86-111.
[5]ANDERSON T.Detrital zircons as tracers of sedimentary provenance:Limiting conditions from statistics and numerical simulation[J].Chemical Geology,2005,216:249-270.
[6]GEHRELS G E,DICKINSON W R,ROSS G M,et al.Detrital zircon reference for Cambrian to Triassic miogeoclinal strata of western North America[J].Geology,1995,23(9):831-834.
[7]CARTER A,MOSS S J.Combined detrital zircon fission-track and U-Pb dating:A new approach to understanding hinter-land evolution[J].Geology,1999,27(3):235-238.
[8]WEISLOGEL A L,GRAHAM S A,CHANG E Z,et al.Detrital zircon provenance of the Late Triassic Songpan-Ganzi complex:Sedimentary record of collision of the North and South China blocks[J].Geology,2006,34(2):97-100.
[9]冯益民,何世平.祁连山大地构造与造山作用[M].北京:地质出版社,1996:12-101.
[10]左国朝,吴汉泉.北祁连中段早古生代双向俯冲-碰撞造山模式剖析[J].地球科学进展,1997,12(4):315-323.
[11]夏林圻,夏祖春,徐学义.北祁连洋壳-洋脊和弧后盆地火山作用[J].地质学报,1998,72(4):301-312.
[12]XIA L Q,XIA Z C,XU X Y.Magma genesis in the Ordovician back-arc basins of the northern Qilian Mountain,China[J].Geological Society of America Bulletin,2003,115(12):1510-1522.
[13]张旗,王焰,钱青.北祁连早古生代洋盆是裂陷槽还是大洋盆:与葛肖虹讨论[J].地质科学,2000,35(1):121-128.
[14]李三忠,李涛,赵淑娟,等.东亚原特提斯洋(Ⅳ):北界西段早古生代构造变形[J].岩石学报,2017,33(6):1615-1632.
[15]XIAO W J,WINDLEY B F,YONG Y,et al.Early Paleozoic to Devonian multiple-accretionary model for the Qilian Shan,NWChina[J].Journal of Asian Earth Sciences,2009,35(3/4):323-333.
[16]潘桂棠,王立全,张万平,等.青藏高原及邻区大地构造图及说明书(1∶1 500 000)[M].北京:地质出版社,2013:37-38.
[17]SONG S G,NIU Y L,SU L,et al.Tectonics of the North Qilian orogen,NW China[J].Gondwana Research,2013,23:1378-1401.
[18]戚学祥,张建新,李海兵,等.北祁连南缘右行韧性走滑剪切带的同位素年代学及其地质意义[J].地学前缘,2004,11(4):469-479.
[19]李怀坤,耿建珍,郝爽,等.用激光烧蚀多接收器等离子体质谱仪(LA-MC-ICPMS)测定锆石U-Pb同位素年龄的研究[J].矿物学报,2009,29(S1):600-601.
[20]ANDERSON T.Correction of common lead in U-Pb analyses that do not report204Pb[J].Chemical Geology,2002,92(1/2):59-79.
[21]杨雨,范国琳,姚国金,等.甘肃省岩石地层[M].武汉:中国地质大学出版社,1997:128-177.
[22]孙崇仁,陈国隆,李璋荣,等.青海省岩石地层[M].武汉:中国地质大学出版社,1997:112-141.
[23]刘永江,FRANZ N,李伟民,等.柴北缘-南祁连地区构造热事件[J].吉林大学学报(地球科学版),2012,42(5):1317-1329.
[24]吴才来,徐学义,高前明,等.北祁连早古生代花岗质岩浆作用及构造演化[J].岩石学报,2010,26(4):1027-1044.
[25]黄增保,郑建平,李葆华,等.中祁连西段野马山岩基年代学、地球化学特征及地质意义[J].中国地质,2015,42(2):406-420.
[26]黄增保,郑建平,李葆华,等.中祁连西段晚寒武世埃达克岩的发现及地质意义[J].岩石矿物学杂志,2014,33(6):1008-1018.
[27]侯荣娜,王淑华,张翔,等.中祁连西段花岗岩类的地球化学特征及构造意义[J].地球科学进展,2015,30(9):1034-1049.
[28]齐瑞荣.中祁连西段巴嘎德尔基岩体LA-ICP-MS锆石U-Pb年龄及地质意义[J].沉积与特提斯地质,2012,32(4):86-93.
[29]贾群子,杨忠堂,肖朝阳,等.祁连山铜金钨铅锌矿床成矿规律和成矿预测[M].北京:地质出版社,2007:1-313.
[30]钱青,张旗,孙晓萌.北祁连老虎山玄武岩和硅岩的地球化学特征及形成环境[J].地质科学,2001,36(4):444-453.
[31]苏建平,胡能高,张海峰,等.中祁连西段黑沟梁子花岗岩的锆石U-Pb同位素年龄及成因[J].现代地质,2004,18(1):70-74.
[32]陈隽璐,徐学义,曾佐勋,等.中祁连东段什川杂岩基的岩石化学特征及年代学研究[J].岩石学报,2008,24(4):841-854.
[33]雍拥,肖文交,袁超,等.中祁连东段古生代花岗岩的年代学、地球化学特征及其大地构造意义[J].岩石学报,2008,24(4):855-866.
[34]陈隽璐,李好斌,王洪亮,等.秦祁结合部位王家岔石英闪长岩体锆石LA-ICP-MS定年及地质意义[J].吉林大学学报(地球科学版),2007,37(3):423-431.
[35]秦海鹏,吴才来,王次松,等.祁连东部西格拉高Sr/Y型花岗岩LA-ICP-MS锆石U-Pb定年及其地球化学特征[J].岩石学报,2014,30(12):3759-3771.
[36]何世平,王洪亮,陈隽璐,等.中祁连马衔山岩群内基性岩墙群锆石LA-ICP-MS U-Pb年代学及其构造意义[J].地球科学---中国地质大学学报,2008,33(1):35-45.
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