Origin of the basal lherzolite of the Muslim Bagh Ophiolite, Pakistan, deduced from the trace element characteristics of clinopyroxene
Origin of the basal lherzolite of the Muslim Bagh Ophiolite, Pakistan, deduced from the trace element characteristics of clinopyroxene
复制标题
从单斜辉石微量元素特征推断巴基斯坦穆斯林巴格蛇绿岩基底二辉橄榄岩成因
DOI：
10.1002/gj.4269
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发表时间：
2021
影响因子：
1.8
通讯作者：
Bussolesi Micol
中科院分区：
文献类型：
--
作者：
Kakar Aminullah;Morishita Tomoaki;Khan Mehrab;Mahmood Khalid;Tamura Akihiro;Guotana Juan Miguel;Bussolesi Micol
在哈次布日峰为主的蛇绿岩的地幔部分中，基底二赫茨基的起源是一个谜。巴基斯坦穆斯林巴格蛇绿岩是特提斯蛇绿岩带中以辉橄榄岩为主的蛇绿岩之一，地幔底部出露良好。在这篇文章中，我们描述了巴基斯坦穆斯林巴格蛇绿岩的基底二辉橄榄岩，并根据其单斜辉石的微量元素特征讨论了其成因。基底二辉橄榄岩具有碎斑-糜棱岩结构。碎斑单斜辉石的原始地幔标准化微量元素模式的特征是轻稀土元素（LREE）与重稀土元素（HREE）的比值低，HREE丰度低，Sr正异常。这些地球化学特征与二辉橄榄岩及其单斜辉石不一致，后者是由洋中脊环境中橄榄岩的低程度部分熔融和熔融提取后的残留物形成的。相反，单斜辉石的成分与开放系统熔融相一致，该熔融是由板片衍生流体渗透到已耗尽稀土元素的残留橄榄岩中引起的。基底橄榄岩序列的铬铁矿中铬尖晶石的成分也与其形成于弧形环境相一致。我们的结论是，穆斯林巴格蛇绿岩的基底二辉橄榄岩代表了相对高度的部分熔融后的残留物，单斜辉石是作为交代结晶从板片衍生的弧相关的熔体添加到这个残留的亏损橄榄岩在俯冲设置。
The origin of basal lherzolites in the mantle section of harzburgite‐dominated ophiolites is enigmatic. The basal part of the mantle section is well exposed in the Muslim Bagh Ophiolite, Pakistan, which is one of the harzburgite‐dominated ophiolites of the Tethys Ophiolite Belt. In this contribution, we describe the basal lherzolite of the Muslim Bagh Ophiolite, Pakistan, and discuss its origin based on the trace‐element characteristics of its clinopyroxenes. The basal lherzolite exhibits porphyroclastic to mylonitic textures. Primitive mantle‐normalized trace‐element patterns of the porphyroclastic clinopyroxenes were characterized by low ratios of light rare‐earth elements (LREEs) to heavy rare‐earth elements (HREEs), low abundances of HREEs, and positive Sr anomalies. These geochemical characteristics are not consistent with a lherzolite and its clinopyroxenes, which is formed by a residue after a low degree of partial melting and melt extraction from peridotites in a mid‐ocean ridge setting. Instead, the compositions of the clinopyroxenes are consistent with open‐system melting induced by the infiltration of slab‐derived fluids into residual peridotites that had been depleted in REEs. The compositions of chromian spinels in the chromitites of the basal peridotite sequence are also consistent with their formation in an arc setting. We conclude that the basal lherzolites of the Muslim Bagh Ophiolite represent a residue after a relatively high degree of partial melting, and that the clinopyroxenes were added as metasomatic crystallization from slab‐derived arc‐related melts to this residual depleted peridotite in a subduction setting.