Paleoproterozoic granulite-facies metamorphism and anatexis in the Oulongbuluke Block, NW China: Respond to assembly of the Columbia supercontinent
Paleoproterozoic granulite-facies metamorphism and anatexis in the Oulongbuluke Block, NW China: Respond to assembly of the Columbia supercontinent
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DOI：
10.1016/j.precamres.2017.01.016
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发表时间：
2017-04
影响因子：
3.8
通讯作者：
Sheng‐yao Yu;Jianxin Zhang;San-zhong Li;Deyou Sun;Yunshuai Li;Xin Liu;Ling‐li Guo;Y. Suo
中科院分区：
文献类型：
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作者：
Sheng‐yao Yu;Jianxin Zhang;San-zhong Li;Deyou Sun;Yunshuai Li;Xin Liu;Ling‐li Guo;Y. Suo
位于青藏高原东北缘的欧龙布鲁克地块，传统上被认为是塔里木盆地的一部分。本文对欧龙布鲁克地块镁铁质麻粒岩和混合岩进行了系统的岩石学、地球化学和锆石U-Pb、Hf同位素研究。镁铁质麻粒岩主要由单斜辉石、斜方辉石、斜长石、角闪石和石英组成，峰期变质温度为6.5- 8.8kbar，温度为745-770 °C。宏观和微观观察为欧龙布鲁克地块内长英质片麻岩的就地部分熔融提供了强有力的证据。具有Eu正异常、Sr含量高的富Pl的浅色体是早期形成的长石堆晶岩，而具有Eu负异常、Sr含量低的富Kfs的伟晶岩可能是冷却过程中捕获的分馏熔体。对欧龙布鲁克地块的镁铁质麻粒岩和混合岩进行锆石U-Pb定年和Hf同位素分析，揭示了两个不同的时代群体：早古元古代（1.93- 1.92Ga）和晚古元古代（1.37 ~ 1.92Ga）。混合岩中的岩浆锆石的εHf（t）值介于−4.3 ~ 0.4之间，两阶段Hf模式年龄（TDMC）主要介于2.82 ~ 3.05 Ga之间。基性麻粒岩和混合岩的1.93- 1.92Ga年龄被解释为晚古元古代变质作用和深熔作用的年龄。1.93- 1.92Ga变质和深熔锆石的176 Lu/177 Hf（t）值明显低于继承岩浆锆石核，而176 Hf/177 Hf（t）值明显高于继承岩浆锆石核，表明变质和深熔作用期间锆石U-Pb和Lu-Hf同位素组成发生了明显的重置。晚古元古代变质和深熔事件与许多大陆碎片中记录的全球造山事件相吻合，这表明它们与哥伦比亚超大陆有关。
The Oulongbuluke Block, which is located in the northeastern margin of the Tibet Plateau, has traditionally been considered to be a fragment of the Tarim Craton. Here we present a systematic petrologic, geochemical, and zircon U-Pb and Hf isotopic investigation on mafic granulite and migmatite in the Oulongbuluke Block. The mafic granulite is mainly composed of clinopyroxene, orthopyroxene, plagioclase, amphibole and quartz, with peak metamorphic P-T contions of 6.5–8.8 kbar, 745–770 °C. Macroscopic and microscopic observations provide strong evidence forin situpartial melting of the felsic gneiss involving breakdown of biotite within the Oulongbuluke Block. The Pl-rich leucosomes with positive Eu anomalies and higher Sr contents were generated as the early-formed feldspar cumulate, and the Kfs-rich pegmatite with negative Eu anomalies and lower Sr contents may represent percolating fractionated melt that was trapped during cooling. Zircon U–Pb dating and Hf isotopic analyses on the mafic granulite and migmatite of the Oulongbuluke Block reveal two distinct age populations: the early Paleoproterozoic (∼2.37 Ga) and late Paleoproterozoic (1.93–1.92 Ga). The ∼2.37 Ga magmatic zircon cores of the migmatite have εHf(t) values between −4.3 and 0.4, with two-stage Hf model ages (TDMC) mainly between 2.82 Ga and 3.05 Ga. The age of 1.93–1.92 Ga obtained from the mafic granulite and migmatite is interpreted as the age of Late Paleoproterozoic metamorphism and anatexis. Most of the 1.93–1.92 Ga metamorphic and anatectic zircons have significantly lower176Lu/177Hf ratios but higher176Hf/177Hf (t) values than the inherited magmatic zircon cores, which demonstrates that both the zircon U–Pb and Lu–Hf isotope compositions were significantly reset during metamorphism and anatexis. The late Paleoproterozoic metamorphic and anatectic event coincided with global orogenic events that are recorded in many continental fragments, which suggests their link to the Columbia supercontinent.