藏南泽当岛弧花岗岩成因限定——来自角闪石岩锆石U-Pb、地球化学和Sr-Nd同位素的证据
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P588.12;P597

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国家重点研发计划-深地专项(2018YFC0604106);国家自然科学基金项目(41503006);中国地质调查局二级项目(DD20190167)


Petrogenesis of the Zetang arc granite in southern Tibet: Evidence from zircon U-Pb dating, geochemistry and Sr-Nd isotopes of amphibolite
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    摘要:

    泽当岛弧位于藏南乃东县境内,主要由英云闪长岩、花岗闪长岩、奥长花岗岩和角闪石岩组成,是晚侏罗世洋壳俯冲的产物。本文对该地区出露的角闪石岩开展了野外地质调查,通过室内SHRIMP锆石U-Pb定年、全岩地球化学和Sr-Nd同位素等研究,探讨了泽当角闪石岩的成因、源区及其与花岗岩的成因关系,获得以下认识:角闪石岩成岩年龄为159.1±7.2 Ma;角闪石岩具有较低Sr含量、较高的Y含量和较低的Sr/Y值,富集MREE;角闪石岩与花岗岩Sr-Nd同位素特征一致,角闪石岩87Sr/86Sr(t)值(0.704 0~0.704 5)较低,εNd(t)值变化范围为+5.5~+6.1。结合前人研究认为,泽当岛弧的英云闪长岩、花岗闪长岩、奥长花岗岩和角闪石岩均来自地幔楔部分熔融作用。英云闪长岩为相对原始的岩浆,在角闪石分离结晶作用未结束前,先从岩浆房中分离出来;残余岩浆继续发生角闪石分离结晶作用,导致Sr/Y值进一步升高和Cr、Ni、MREE含量进一步降低。因此,角闪石的分离结晶作用是泽当岛弧高Sr/Y花岗岩形成的关键因素。

    Abstract:

    The Zetang island arc, located in Nedong County, southern Tibet, mainly consists of tonalite, trondhjemite, granodiorite and amphibolite. The Zetang island arc has been identified as a late Jurassic intra-oceanic arc. In this paper, integrated field geological survey, SHRIMP zircon U-Pb dating, whole rock geochemistry and Sr-Nd isotope study were carried out on the Zedang island arc to discuss magma source of amphibolite and its relationship with coeval granites. Some conclusions have been reached:① SHRIMP zircon 206Pb/238U dating of amphibolite shows a crystallization age of 159.1±7.2 Ma; ② Sr-Nd isotopic characteristics of amphibolite and granites are similar, with 87Sr/86Sr(t) ratios being 0.704 0~0.704 5 and εNd(t) values being +5.5~+6.1. ③ geochemical characteristics show low Sr, high Y, low Sr/Y radio, and enrichment of MREE. A comparison with other published data shows that tonalite, trondhjemite, granodiorite and amphibolite of Zetang arc were likely derived from the partial melting of the mantle wedge. Tonalite is a relatively primitive magma, and had been separated from the magma chamber before the full completion of amphibolite fractional crystallization. With the ongoing crystallization of amphibolite, the Sr/Y ratios, Cr, Ni and MREE values of residual magma increased step by step. Therefore, the fractional crystallization of amphibolite seems to have been the key factor for forming the high Sr/Y granites of Zetang island arc.

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陈翰,胡古月,郭英帅,王莉,2020,藏南泽当岛弧花岗岩成因限定——来自角闪石岩锆石U-Pb、地球化学和Sr-Nd同位素的证据[J].岩石矿物学杂志,39(5):511~524.

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  • 收稿日期:2019-10-24
  • 最后修改日期:2020-06-03
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  • 在线发布日期: 2020-09-12
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