甘肃北山地区花岗闪长岩LA-ICP-MS锆石U-Pb年龄及地球化学特征研究
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摘要
为了研究甘肃北山地区北山幅晚古生代岩浆岩的年代学特征和地球化学特征,利用Agilent7500 a ICP-MS的方法对研究区的花岗闪长岩进行全岩地球化学分析。结果表明:(1)岩石中Na_2O/K_2O<1,里特曼指数介于2.45～2.86,铝饱和指数A/CNK为1.48,总体显示过铝质、高钾钙碱质花岗岩类;(2)富集大离子亲石元素,如Rb,Ba和Sr,损失高场强元素如Ta,Ti和Hf;(3)δEu值为0.55～0.61,平均值为0.58,呈现负Eu异常,有一定的亏损,整体属于轻稀土富集类型。通过LA-ICP-MS方法对研究区的花岗闪长岩进行锆石~(206)Pb/~(238)U年龄测试,锆石~(206)Pb/~(238)U加权平均年龄为(400.1±2.3)Ma(MSWD=0.96),代表了花岗闪长岩的结晶年龄,即该期花岗闪长岩形成的地质时期为早泥盆世。
In order to study the chronological and geochemical characteristics of Late Paleozoic magmatic rocks in Beishan area,Gansu province,the whole-rock geochemical analysis of granodiorites in the study area was carried out by Agilent 7500 a ICP-MS method. The results show that:(1)Na_2O/K_2O < 1,ritman index is between 2.45 and 2.86,Al saturation index A/CNK is 1.48,showing peraluminous and high-potassium calc-alkaline granites;(2)Large ion lithophile elements such as Rb,Ba and Sr are enriched and high field strength elements such as Ta,Ti and Hf are depleted;(3)Delta Eu value is from 0.55 to 0.61,with an average of 0.58,showing negative Eu anomaly and a certain loss. The granodiorite belongs to the light rare earth enrichment type as a whole. Zircon ~(206)Pb/~(238)U ages of granodiorites in the study area were measured by LA-ICP-MS method.The weighted average age of zircon ~(206)Pb/~(238)U is(400.1±2.3) Ma(MSWD=0.96),which represents the crystallization age of granodiorite,i.e. the geological period of granodiorite formation is Early Devonian.
In order to study the chronological and geochemical characteristics of Late Paleozoic magmatic rocks in Beishan area,Gansu province,the whole-rock geochemical analysis of granodiorites in the study area was carried out by Agilent 7500 a ICP-MS method. The results show that:(1)Na_2O/K_2O < 1,ritman index is between 2.45 and 2.86,Al saturation index A/CNK is 1.48,showing peraluminous and high-potassium calc-alkaline granites;(2)Large ion lithophile elements such as Rb,Ba and Sr are enriched and high field strength elements such as Ta,Ti and Hf are depleted;(3)Delta Eu value is from 0.55 to 0.61,with an average of 0.58,showing negative Eu anomaly and a certain loss. The granodiorite belongs to the light rare earth enrichment type as a whole. Zircon ~(206)Pb/~(238)U ages of granodiorites in the study area were measured by LA-ICP-MS method.The weighted average age of zircon ~(206)Pb/~(238)U is(400.1±2.3) Ma(MSWD=0.96),which represents the crystallization age of granodiorite,i.e. the geological period of granodiorite formation is Early Devonian.
引文
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[2] LIU X Y,WANG Q.Tectonics of orogenic belts in Beishan MTS,Western China and their evolution (in Chinese)[J].Geosci Res,1995,28:7-48.
[3] SONG D,XIAO W,HAN C,et al.Progressive accretionary tectonics of the Beishan orogenic collage,Southern Altaids:Insights from zircon U-Pb and Hf isotopic data of high-grade complexes[J].Precambrian Res,2012,227:368-388.
[4] CLEVEN N R,LIN S,XIAO W.The Hongliuhe fold-and-thrust belt:Evidence of terminal collision and suture-reactivation after the Early Permian in the Beishan orogenic collage,Northwest China [J].Gondwana Res,2015,27:796-810.
[5] TIAN Z,XIAO W,WINDLEY B F,et al.Structure,age,and tectonic development of the Huoshishan–Niujuanzi ophiolitic mélange,Beishan,southernmost Altaids [J].Gondwana Res,2014,25:820-841.
[6] 刘雪亚,王荃.中国西部北山造山带的大地构造及其演化[C]//中国地质学会.中国地质科学院地质研究所文集(28).北京:地质出版社,1995:37-47.
[7] 潘金花,郭召杰,刘畅,等.新甘交界红柳河地区二叠纪玄武岩年代学、地球化学及构造意义[J].岩石学报,2008,24(4):793-802.
[8] ZHANG Y Y,DOSTALl J,ZHAO Z H,et al.Geochronology,geochemistry and petrogenesis of mafic and ultramafic rocks from Southern Beishan area,NW China:Implications for crust mantle interaction[J].Gondwana Research,2011,20:816-830.
[9] 左国朝,何国琦.北山板块构造及成矿规律北京[M].北京:北京大学出版社,1990:45-50.
[10] 左国朝,刘义科,刘舂燕.甘新蒙北山地区构造格局及演化[J].甘肃地质学报,2003,12(1):1-14.
[11] 龚全胜,刘明强,李海明,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.
[12] 何世平,周会武,任秉深,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.
[13] 赵泽辉,郭召杰,王毅.甘肃北山柳园地区花岗岩类的年代学、地球化学特征及构造意义[J].岩石学报,2007,23(8):1847-1860.
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