The Paleoproterozoic tectono-magmatic history of the Indian plate has been modelled mostly based on investigations of the Indian parts with limited studies considering the Pakistani domains of the mountain range. In this study we investigate basement rocks and younger intrusions of the Indian crust from within the core of the Indus Syntaxis and the Nanga Parbat Syntaxis in northern Pakistan, with the goal of establishing a chronology for the entire tectono-magmatic progression of northwestern Indian plate margin, including the source rocks that were ultimately involved in the formation of younger magmatic pulses. We present in-situ zircon U-Pb geochronology and O-isotopes complemented by whole rock geochemistry of granitoids and paragneisses that yielded evidence for two distinct, large-scale Paleoproterozoic magmatic events that took place in ∼ 1860 Ma and ∼ 2200 Ma in the Indian crust. Later, leucogranites (6.4 ± 0.1 Ma) intruded into the Nanga Parbat basement that were the result of melting of the basement induced by rapid uplift. The δ18OSMOW compositions of zircons from our basement samples range between 7.5 to 9.1 ‰, indicating the derivation of parental magma from the crustal source while the younger leucogranite is somewhat lighter with δ18O ranging between 7.06 to 8.23 ‰. Geochemical data show extensional tectonic settings for the basement rocks that have an A-type affinity, again pointing to a crustal precursor. We propose little to no δ18O exchange took place between the young anatectic melt and basement rocks during crustal evolution. Moreover, geochemical signatures record the crystallization of basement rocks dominated the northwestern margin of Indian plate in a post-orogenic setting in an overall extensional tectonic realm. Based on these observations, we infer that the northwestern Indian margin has experienced a large-scale magmatism during Paleoproterozoic associated with the amalgamation of the Columbia supercontinent.

中文翻译：

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古元古代喜马拉雅山西部印度地壳的构造岩浆演化：来自巴基斯坦北部 Nanga Parbat 和 Indus syntaxis 的见解


印度板块的古元古代构造岩浆历史主要基于对印度部分的调查进行建模，考虑到山脉的巴基斯坦领域，研究有限。在这项研究中，我们调查了巴基斯坦北部印度河 Indus Syntaxis 和 Nanga Parbat Syntaxis 核心内的基岩和印度地壳的年轻侵入体，目的是为印度西北部板块边缘的整个构造岩浆演变建立一个年表，包括最终参与年轻岩浆脉冲形成的烃源岩。我们提出了原位锆石 U-Pb 地质年代学和 O 同位素，并辅以花岗岩和副片麻岩的全岩石地球化学，为印度地壳中发生在 ∼ 1860 马 和 ∼ 2200 马的两个不同的大规模古元古代岩浆事件提供了证据。后来，白花岗岩（6.4 ± 0.1 马）侵入了 Nanga Parbat 基底，这是基底快速隆起诱导融化的结果。来自我们基底样品的锆石的 δ18OSMOW 成分在 7.5 至 9.1 ‰ 之间，表明母体岩浆来自地壳源，而较年轻的白花岗岩稍轻，δ18O 在 7.06 至 8.23 ‰ 之间。地球化学数据显示，基岩的伸展构造环境具有 A 型亲和力，再次指向地壳前体。我们认为，在地壳演化过程中，年轻的反晶熔体和基岩之间几乎没有发生 δ18O 交换。此外，地球化学特征记录了基底岩石的结晶在整个伸展构造领域的后造山环境中主导了印度板块的西北边缘。 基于这些观察，我们推断印度西北部边缘在古元古代经历了与哥伦比亚超大陆合并相关的大规模岩浆作用。