Geochemical characteristics and age of rhyolite LA-ICP-MS Zircon U-Pb in Fengleishan area of Beishan, Inner Mongolia
CHEN Haidong1, WANG Zilong2, JING Yaozu1, GAO Yong1, HAO Zengyuan1, LU Ning1
1. Inner Mongolia Institute of Geological Survey and Mineral Exploration, Hohhot, Inner Mongolia 010010, China; 2. Chengdu University of Technology, Earth Science Institute, Cheng' du 610059, China
Abstract：There are large quantities of volcanic rocks in the south of the eastern section of Beishan area's Hongshishan-Baiheshan-Pengboshan ophiolitic belt. The age of rhyolite indicated by LA-ICP-MS zircon U-Pb is (318.5±1.2) Ma, Late Carboniferous. The rhyolite has 77.05%~77.52% of SiO2, and 6.96%~7.83% of K2O+Na2O. Large ion lithophile (Rb,K,Th,U,Zr,Hf) enrichment and high field strength elements (Ta,Nb,Ti) shortage are displayed in the primitive mantle normalized trace element spider diagram. The petrogeochemical features indicate that the rhyolite shows high potassium calc alkaline series, with the volcanic arc granite attribute. Combined with the study of regional geological characteristics, it indicates that Hongshishan-Baiheshan-Pengboshan extensional faulting formed the initial small ocean basin. Namely, it's similar to the Red Sea Type trough environment in Early Carboniferous. The oceanic crust subducted into the south and the north directions in late Early Carboniferous. And the southern edge of the consistently cleaving small ocean basin subducted into the south direction by the Late Carboniferous, so large amounts of arc volcanic rocks formed.
[1] Windley B F,Alexeiev D,Xiao W J,et al.Tectonic models for accretion of the Central Asian Orogenic Belt[J].J Geol Soc,2007,164(1):31-47. [2] 左国朝,张淑玲,何国琦,等.北山地区早古生代板块构造特征[J].地质科学,1990(4):305-314. [3] 刘雪亚,王荃.中国西部北山造山带的大地构造及其演化[J].地学研究,1995(28):37-48. [4] 龚全胜,刘明强,李海林,等.甘肃北山造山带类型及基本特征[J].西北地质,2002,35(3):28-34. [5] 何世平,周会武,任秉琛,等.甘肃内蒙古北山地区古生代地壳演化[J].西北地质,2005,38(3):6-15. [6] 杨合群,李英,赵国斌,等.北山蛇绿岩特征及构造属性[J].西北地质,2010,43(1):26-36. [7] 侯可军,李延河,田有荣.LA-MC-ICP-MS锆石微区原位U-Pb定年技术[J].矿床地质,2009,28(4):481-492. [8] 李长民.锆石成因矿物学与锆石微区定年综述[J].地质调查与研究,2009,33(3):161-174. [9] 彭智敏,耿全如,张璋,等.西藏那曲地区流纹岩LA-ICP-MS锆石U-Pb年龄和地球化学特征[J].地质通报,2011,30(7):1050-1059. [10] Barth M G,McDonough W F,Rudnick R L.Tracking the budget of Nb and Ta in the continental crust[J].Chem Geol,2000,165(3-4):197-213. [11] Sun S S,McDonough W F.Chemical and isotopic systematics of oceanic basalts:Implications for mantle composition and processes[J].Geol Soc London, Spec Publicat,1989,42(1):313-345. [12] Pearce J A,Harris N B W,Tindle A G.Trace element discrimination diagrams for the tectonic interpretation of granitic rocks[J].J Petrol,1984,25(4):956-983. [13] Pearce J A.Sources and setting of granitic rocks[J].Episodes,1996,19(4):120-125. [14] 张旗,钱青,王焰.造山带火成岩地球化学研究[J].地学前缘,1999,6(3):113-120. [15] 牛延宏,王兴,李旭东,等.黑龙江省伊春地区中寒武世细中粒二长花岗岩U-Pb定年及其地质意义[J].中国地质调查,2015,2(6):26-33. [16] 李善平,李延京,任华,等.青海三江北段拉地贡玛地区印支期花岗岩地球化学特征及地质意义[J].中国地质调查,2016,3(1):35-43. [17] 甘肃省地质局地质力学区测队.1:20万路井幅地质图及报告[Z].1977. [18] Miyashiro A.Volcanitic rock series in island and active continental margins[J].AIS,1974,274:321-335. [19] 王国强,李向民,徐学义,等.甘肃北山红石山蛇绿岩锆石U-Pb年代学研究及构造意义[J].岩石学报,2014,30(6):1685-1694.
2017, Vol. 4 
