豫西二郎坪地区O型埃达克岩的厘定及其地质意义
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The idenfication and Geological Significance of O-type Adakitic Rocks in Erlangping area of Xixia County, western of Henan Provinces
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    摘要:

    本文对出露于豫西二郎坪地区的西庄河花岗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)、Yb(1.36×10-6~1.88×10-6)和高Sr/Y比值(介于24~38);稀土含量中等(∑REE=86.79~197.04×10-6),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型埃达克岩的特征相似。利用锆石原位LA-ICP-MS定年方法,获得西庄河花岗岩的形成年龄为461±0.9Ma。该年龄与其共生的二郎坪岛弧火山岩的形成年龄在误差范围内一致(460-473Ma),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。

    Abstract:

    The Xizhuanghe granite is located in Erlangping area of Xixia County, western of Henan Provinces. This paper has studied petrographical, geochemical, zircon U-Pb geochronological and Hf isotope of this granite as well as its petrogenesis and geological significance. The Xizhuanghe granite mainly consists of plagioclase, quarts and minor amphibole, biotite. Geochemical studies indicate that the Xizhuanghe granite has high SiO2 (66.84%~71.57), Al2O3 (14.11%~16.78%) and high Na2O (3.45%~4.78%),The ratio of Na2O/K2O are between 1.06 and 2.40. but lower MgO (0.88%~1.0%, the index of Mg# is vary from 0.43 to 0.46). also high Sr (327.04×10-6~613.97×10-6) contents, low Y (12.30×10-6~17.17×10-6) and Yb (1.36×10-6~1.88×10-6) contents, with high Sr/Y ratios (24~38). The Xizhuanghe granite has relative medium REE content of(86.79~197.04×10-6)with strong fractionations between LREE and HREE ((La/Yb)N=12.35-34.89), δEu shows slightly negative-obviously positive anomaly (δEu=0.97~1.34) on the chondrite-normalized REE diagrams. Primitive mantle normalized trace element spider pattern shows 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., displaying geochemical features of O-type adakites which are related to subduction of oceanic slab. Zircon LA-ICP-MS dating yield the formation age of 460 Ma, represents its magmatic crystallization age Which is almost the same as the formation age of the basic volcanic rocks(460-473Ma) in Erlangping areas. The Xizhuanghe granite has also close relationship in space with Erlangping basic volcanics, which was consider to have been formed in the island arc and back arc-basin, and be related to subduction of oceanic-slab. Combined the geochmical characteristics of O-type adakite and symbiotic relationship between Xizhuanghe granite and erlangping basic volcanics, we conclude that the existence of ocean basin and its subduction in Erlangping areas of the western Henan Province.

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郭彩莲,陈丹玲.2011.豫西二郎坪地区O型埃达克岩的厘定及其地质意义[J].地质学报,85(12):1994-2002.
GUO Cailian, CHEN Danling.2011. The idenfication and Geological Significance of O-type Adakitic Rocks in Erlangping area of Xixia County, western of Henan Provinces[J]. Acta Geologica Sinica,85(12):1994-2002.

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  • 收稿日期:2010-12-27
  • 最后修改日期:2011-04-29
  • 录用日期:2011-05-03
  • 在线发布日期: 2011-12-09
  • 出版日期: