摘要
本文对出露于豫西二郎坪地区的西庄河花岗闪长岩进行了详细的岩石学、地球化学、锆石U-Pb年代学及Hf同位素研究,重点讨论其岩石成因及地质意义。西庄河花岗闪长岩主要由斜长石、石英及少量角闪石和黑云母组成。地球化学分析显示,该花岗岩具有高Si(SiO2=66.84%～71.57%)、富Al(Al2O3=14.11%～16.78%)、富Na(Na2O=3.45%～4.78%,Na2O/K2O为1.06～2.40)及低Mg(MgO=0.88%～1.0%,Mg#为0.43～0.46)的特征。微量元素方面显示高Sr(327.04×10-6～613.97×10-6)、低Y(12.30×10-6～17.17×10-6)和Yb(1.36×10-6～1.88×10-6)及高Sr/Y比值(介于24～38);稀土含量中等(∑REE=86.79×10-6～197.04×10-6),轻重稀土高度分异((La/Yb)N=12.35～23.28),无Eu异常或正Eu异常(δEu=0.97～1.34);在原始地幔标准化微量元素蛛网图上,岩石富集轻稀土和K、Rb、Ba、Th及Sr,而Nb、Ta、P及Ti具明显的负异常。锆石Hf同位素显示具有正的εHf(t)值,变化于8.37～11.13之间。以上花岗闪长岩的岩石地球化学特征及锆石Hf同位素特征与俯冲洋壳部分熔融成因的O型埃达克岩特征相似。利用锆石原位LA-ICP-MS定年方法,获得西庄河花岗闪长岩的形成年龄为461±0.9Ma。该年龄与其共生的二郎坪基性火山岩的形成年龄(460～473Ma)在误差范围内一致,结合其O型埃达克岩的地球化学特征,共同指示豫西二郎坪地区存在早古生代洋盆及洋盆的俯冲消减事件。
The Xizhuanghe granodiorite is distributed in the Erlangping area, northern Xixia County, western Henan Province. This paper studied petrography and geochemistry, and zircon U-Pb geochronology and Hf isotopic compositions, with an emphasis on its petrogenesis and geological significance. The Xizhuanghe granitoid consists mainly of plagioclase and quartz, with minor amphibole and biotite. Geochemical studies indicate that the Xizhuanghe granitoid is high in SiO2 （66. 84% - 71. 57）, A12 03 （14.11%-16.78%）, Na20 （Na2O contents vary from 3.45% to 4.78% and the ratios of Na20/K20 are between 1.06 and 2.40） and Sr （327.04）〈 10.6-613. 973（ 10-6）, but low in MgO （MgO contents range between0.88% and 1.0%, and the index of Mg#is vary from 0.43 to 0.46）. but, Y （12.30X10 6 17.17）〈10.6） and Yb （1.36 X 10 6 -1.88 X 10-G）, with high Sr/Y ratios ranging from 24 to 38）. The Xizhuanghe granitoid has relative high REE contents （86. 79 ）〈 10-6 - 197. 04 X 10-6 ） with strong fractionations between LREE and HREE （（La/Yb）N =12.35-34.89）, and noEu negative or Eu positive anomalies （0.97-1.34）. The chondrite-normalized REE diagram demonstrates enrichment of LREEs and K, RB, Ba, Th and Sr, and negative anomalies of Nb, Ta, P and Ti. Primitive mantle normalized trace element spider patterns show obvious enrichment in LILE and LREE such as Rb, Ba, Th, U, etc. and relative depletion in HSFE and HREE such as Nb, Ta, Ti, etc. , showing geochemical features of O-type adakites are related to subduction of oceanic slab. Zircon LA-ICP-MS dating yielded a formation age of 461 Ma for the Xizhuanghe granodiorite, which is consistent to that （460-473 Ma） of Erlangping basic volcanic rocks paragenetic with the granodiorite. Combined with the geochemical features of the O-type adakite, all evidence suggests existence of the oceanic basin and subduction event of the oceanic crust in the Erlangping areas of western Hennan Provience during Paleozoic of 460-470 Ma.
出处
《地质学报》
EI
CAS
CSCD
北大核心
2011年第12期1994-2002,共9页
Acta Geologica Sinica
基金
西北大学大陆动力学国家重点实验室科技部专项经费
国家基础研究规划“973”项目(编号2009CB825003)
国家自然科学基金项目(编号41072051)资助成果
