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首页> 外文期刊>Journal of Asian earth sciences >Petrogenesis of Early Cretaceous high-Mg# granodiorites in the northeastern Lhasa terrane, SE Tibet: Evidence for mantle-deep crustal interaction
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Petrogenesis of Early Cretaceous high-Mg# granodiorites in the northeastern Lhasa terrane, SE Tibet: Evidence for mantle-deep crustal interaction

机译：Lhasa Terrane东北地区早期白垩纪高MG＃Granodiorites的培养物：披着地壳互动的证据

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摘要

High-Mg# (molar Mg/[Mg + Fe]) intermediate to felsic rocks, such as high-Mg andesitic rocks (HMA) and Mg andesites (MA), are usually produced by melting of mantle-derived peridotites and/or interaction with mantle-derived peridotites. Both are crucial in tracking mantle-crust interaction processes in the deep crust. We present LA-ICP-MS in-situ zircon U-Pb isotopic data, whole-rock geochemistry and whole-rock Sr-Nd-Pb-Hf isotopic data for the Basu granodiorites which are exposed between the Jiali fault and the Bangong-Nujiang suture, SE Tibet. The LA-ICP-MS zircon U-Pb data show that the granodiorites were formed at ca. 122.1 +/- 1.0 Ma, coeval with other granitoids in this region. The granodiorites belong to the high-K talc-alkaline and high-Mg# (49.7-53.7) series, similar to typical MA. The decreasing A/CNK from 0.97 to 0.87 and increasing FM (molar Fe + Mg) from 0.08 to 0.16 indicate a clinopyroxene entrainment and I-type trend. The rocks also display enriched Rb, Th, U and Pb, but depleted P, Ti and obvious negative Eu anomalies. Evolved whole-rock isotopic compositions of Basu granodiorites include high initial Sr-87/Sr-86 (0.7097-0.7114), negative epsilon Nd(t) (-12.0 to -7.2) and epsilon Hf(t) values (-9.6 to -7.9), and lower to upper crustal affinity of Pb isotopes which imply that they were derived from an ancient and evolved lower crust source. Therefore, we suggest that these granodiorites were products of interaction between partial melting of ancient basaltic lower crust and mantle-derived peridotites. Together with a geochronology dataset from the literature, we suggest that there was intensive granitic magmatism occurred in the Early Cretaceous range from 133 to 113 Ma in the northeastern Lhasa tenrane, similar to those in the central and northern Lhasa terrane. Furthermore, we have compared with the dataset of in-situ zircon Lu-Hf isotopes, whole-rock Sr-Nd from the literatures and the relationship with zircon U-Pb ages in the northeastern Lhasa terrane, all of which indicate the importance of evolved and ancient continental crust source in the Early Cretaceous magmatism in the northeastern Lhasa terrane, but also that the mantle-derived materials play a necessary role in the generation. In addition, the amount of enriched and evolved isotopic component gradually decreased from ca.140 to 100 Ma.
机译：高麦克斯岩石中的高Mg＃（摩尔Mg / [Mg + Fe]）中间体，如高镁岩岩石（HMA）和Mg岩体（MA），通常通过熔化披露的恒星和/或相互作用来产生用披露的橄榄石。两者都在跟踪深层地壳中的地幔互动过程中至关重要。我们展示了La-ICP-MS原位锆石U-PB同位素数据，全岩地球化学和全岩SR-ND-PB-HF InsoTopicates，适用于Jiali断层和邦戈 - 怒江之间暴露的Basu Granodiorites缝合，西藏。 La-ICP-MS锆石U-PB数据显示Granodiorites在CA处形成。 122.1 +/- 1.0 mA，与该地区其他花岗岩的颈部。 Granodiorites属于高k滑石碱和高Mg＃（49.7-53.7）系列，类似于典型的MA。将0.97〜0.87的减少率下降，增加Fm（摩尔Fe + Mg）从0.08〜0.16表示临床夹带和I型趋势。岩石还展示富集的RB，TH，U和PB，但耗尽P，TI和明显的负欧盟异常。 Sholved全岩石同位素组合物的Basu Granodiorites包括高初始SR-87 / SR-86（0.7097-0.7114），阴性εnd（t）（-12.0至-7.2）和epsilon hf（t）值（-9.6至 - 7.9），低于Pb同位素的上层地壳亲和力，这意味着它们源自古老和演进的下地壳源。因此，我们建议这些Granodiorites是古代玄武岩下地壳和披露的恒星的部分熔化之间的相互作用的产品。与文献中的地球节数据集一起，我们建议在东北拉萨·斯坦兰的初期白垩纪中发生密集的花岗岩岩浆，从133到113 ma，类似于拉萨特拉拉特北部的中央和北部地区。此外，我们已经与原位锆石Lu-HF同位素的数据集相比，来自文献的全岩SR-ND以及与东北拉萨特兰地区的锆石U-PB年龄的关系，所有这些都表明了进化的重要性和古老的大陆地壳源在东北拉萨特兰省的早期白垩纪岩浆广场，也是披风衍生材料在一代中发挥了必要的作用。此外，富集和进化同位素成分的量逐渐从Ca.140逐渐降至100 mA。

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