Early Permian–Late Triassic granitic magmatism in the Jiamusi–Khanka Massif, eastern segment of the Central Asian Orogenic Belt and its implications
Early Permian–Late Triassic granitic magmatism in the Jiamusi–Khanka Massif, eastern segment of the Central Asian Orogenic Belt and its implications
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中亚造山带东段佳木斯—兴凯地块早二叠世—晚三叠世花岗质岩浆作用及其意义
DOI：
10.1016/j.gr.2014.01.011
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发表时间：
2015-06
影响因子：
6.1
通讯作者：
Zhang Yanlong
中科院分区：
文献类型：
--
作者：
Yang Hao;Ge Wenchun;Zhao Guochun;Yu Jiejiang;Zhang Yanlong
本文报道了中亚造山带东段佳木斯-汉卡地块中部花岗质侵入体的全岩常量、微量元素和锆石U-Pb、Hf同位素资料，以探讨其精确的年代学格架、岩石成因、物质来源及构造意义。LA-ICP-MS锆石U-Pb数据结合前人的年龄资料表明，佳木斯-兴卡地块主要经历了三期花岗质岩浆活动，即：寒武纪（530-493 Ma）、二叠纪（299-254 Ma）和晚三叠世（223-212 Ma），志留纪（434-416 Ma）和石炭纪（331-317 Ma）可能有两次岩浆事件。二叠系闪长岩和花岗闪长岩中Al_2 O_3含量高（15.81- 19.07wt.%），Na_2 O（K_2 O/Na_2 O = 0.25-0.44）和Sr（748-949 ppm）含量，Y（4-18 ppm）和Yb（0.37-1.94 ppm）含量较低，Sr/Y比值较高（54-207），表明它们可能来自高压条件下镁铁质下地壳的部分熔融。而同时代的二长花岗岩和花岗斑岩具有较高的SiO2、Y、Yb和HREE含量，较低的Al 2 O3、Na 2 O/K2 O比和Sr含量，并具有富集LILE、亏损HFSE和Nb-Ta-Ti槽的特征，反映它们可能是在地壳较浅层次上由弧型地壳物质部分熔融产生的。同时，晚三叠世花岗岩中SiO2含量较高（75.90-77.40 wt.%）。和K2 O（4.17-4.87重量%），低Sr、高Y、高HREE，表明它们可能是由地壳物质在低压条件下与板片流体共同形成的。花岗岩类均具有较高的176 Hf/177 Hf比值（0.282518-0.282842），Hf两阶段模式年龄为2005-809 Ma，且大部分岩浆锆石εHf（t）值为正值，表明这些岩石的原始岩浆来源于以“老”源为主的部分熔融，并可能有大量的新生源物质加入。根据地球化学资料和区域地质调查结果，我们认为佳木寺-汉卡地块在早二叠世-晚三叠世时期可能是一个来自冈瓦纳大陆的外来地块，其位置可能比现今偏南，面向古太平洋。二叠纪花岗岩类形成于活动大陆边缘环境，晚三叠世花岗岩类形成于局部拉张环境，二者均与古太平洋Farallon板块向西俯冲至佳木斯-汉卡地块之下密切相关。
Whole-rock major and trace elements, together with zircon U–Pb and Hf-isotope data, are reported for the granitic intrusions in the central part of the Jiamusi–Khanka Massif in the eastern segment of the Central Asian Orogenic Belt (CAOB), in order to investigate their precise geochronological framework, petrogenesis, sources and tectonic implications. LA-ICP-MS zircon U–Pb data, combined with previous ages, indicate that the Jiamusi–Khanka Massif is dominated by three stages of granitic magmatism, i.e., Cambrian (530–493 Ma), Permian (299–254 Ma) and Late Triassic (223–212 Ma), with two possible subordinate magmatic events that occurred in the Silurian (434–416 Ma) and Carboniferous (331–317 Ma). The Permian diorite and granodiorite contain high Al2O3(15.81–19.07 wt.%), Na2O (K2O/Na2O = 0.25–0.44) and Sr (748–949 ppm) contents and low Y (4–18 ppm) and Yb (0.37–1.94 ppm) contents, with high Sr/Y ratios of 54–207, indicating that they probably originated from partial melting of a mafic lower crust at high-pressure conditions. However, the coeval monzogranite and granite porphyry have higher SiO2, Y, Yb and HREE contents and lower Al2O3, Na2O/K2O ratio and Sr contents, together with the features of LILE-enriched, HFSE-depleted and Nb–Ta–Ti troughs, reflecting that they were likely produced by partial melting of arc-type crustal materials at a relatively shallow crustal level. Meanwhile, the Late Triassic granites contain high SiO2(75.90–77.40 wt.%) and K2O (4.17–4.87 wt.%), combined with low Sr and high Y and HREE, suggesting that they were possibly generated from crustal materials with involvement of slab-derived fluids at low pressure. All the granitoids have high176Hf/177Hf ratios (0.282518–0.282842) with Hf two-stage model ages of 2005–809 Ma, and most of the magmatic zircons have positiveεHf(t) values, indicating that the primary magmas of these rocks were derived from partial melting of a dominantly “old” source with a possible significant addition of juvenile materials. Based on the geochemical data and the regional geological investigations, we propose that the Jiamusi–Khanka Massif was an exotic block probably derived from Gondwana, which might be located in a relatively southerly place compared with the current position and faced the Paleo-Pacific Ocean during the Early Permian–Late Triassic time. The Permian granitoids would form in an active continental margin setting, whereas the Late Triassic granites were most likely generated within a local extensional environment, both of which were closely related to the westward subduction of the Farallon plate of the Paleo-Pacific Ocean beneath the Jiamusi–Khanka Massif.
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