西昆仑慕士塔格—公格尔印支期侵入岩岩石与锆石地球化学特征及研究意义

doi:10.13278/j.cnki.jjuese.201505114

摘要/Abstract

摘要：

西昆仑造山带南侧的麻扎康西瓦缝合带,是古特提斯洋闭合的位置。慕士塔格—公格尔作为昆仑山的主峰,紧邻该缝合带的东北侧分布,主要岩性为花岗闪长岩和黑云母二长花岗岩。作者系统研究了两种岩性的地球化学及年代学特征,探讨了岩石成因,反演了古特提斯洋的构造演化历史。岩体岩浆锆石LA-ICP-MS U-Pb测年结果显示,花岗闪长岩和黑云母二长花岗岩的成岩年龄分别为(213.0±0.5)~(215.4±0.9)Ma和(220.6±0.5)~(222.1±0.4)Ma,是晚三叠世岩浆活动的产物。两种岩性均为高硅(w(SiO₂)>65%)、富碱(w(K₂O+Na₂O) >6%)、钙碱性-高钾钙碱性、准铝质(A/CNK< 1),富集大离子亲石元素(LILE)和轻稀土元素(LREE),亏损高场强元素(HFSE)和重稀土(HREE)。微量元素组成特征、低锆石饱和温度及高分异指数显示慕士塔格—公格尔花岗岩体为高分异I型花岗岩。岩体锆石的ε_Hf(t)值变化范围较小,为-4.46~-0.17,指示岩浆以壳源为主。综合研究表明,慕士塔格—公格尔花岗岩体可能是同碰撞造山环境下,老的下地壳受地幔热源影响部分熔融,形成的长英质壳源岩浆侵入地壳内部而冷却结晶形成。

关键词: 花岗岩, 地球化学, 锆石LA-ICP-MS年龄, Hf同位素, 古特提斯洋, 慕士塔格&mdash, 公格尔

Abstract:

Mazha-Kangxiwa suture zone (MKSZ), located to the south of the western Kunlun orogenic belt, is the location where Paleo-Tethys ocean finally closed. As the main peaks of Kunlun Mountain ranges, Muztag-Kongur granitoids closely distributed to the northeast of MKSZ and composed mainly of granodiorite and monzonitic granites. Based on the geochemical characteristics and U-Pb dating of Muztag-Kongur granitoids, we discussed the petrogenesis of granitoids and the evolution history of Paleo-Tethys ocean. The zircon LA-ICP-MS U-Pb dating results show that the forming ages of granodiorite and monzonitic granite are at (213.0±0.5)-(215.4±0.9) Ma and (220.6±0.5)-(222.1±0.4) Ma respectively, which is the result of Late Triassic magmatism activities. Muztag-Kongur granitoids contain high silicon (SiO₂>65%) and total alkali (K₂O+Na₂O>6%), and are characterized by high K calc-alkaline and metaluminous (A/CNK< 1). They are enriched in LILE and LREE and depleted of HFSE and HREE. The contents of minor elements, low zircon saturation temperature, and high differentiation index suggest that Muztag-Kongur granitoids are highly fractionated I-type granites. The zircon Hf isotopic results show a narrow range of ε_Hf(t)=-4.46--0.17, suggesting that the magmas originated mainly from lower crust. The comprehensive studies indicate that Muztag-Kongur granitoids formed likely in a syn-collisional orogenic setting where old lower crust melted partially under the heating of uprising mantle magmas. These felsic magmas intruded into crust level and formed Muztag-Kongur granitoids.

Key words: granite, geochemistry, zircon LA-ICP-MS age, Hf isotope, Paleo-Tethys ocean, Muztag-Kongur

中图分类号:

P588.12

宋樾, 王建, 刘金霖, 包真艳. 西昆仑慕士塔格—公格尔印支期侵入岩岩石与锆石地球化学特征及研究意义[J]. 吉林大学学报(地球科学版), 2015, 45(5): 1418-1435.

Song Yue, Wang Jian, Liu Jinlin, Bao Zhenyan. Chronology, Geochemistry, Hafnium Isotope Characteristics and Tectonic Implications of Muztag-Kongur Indosinian Intrusive Rocks[J]. Journal of Jilin University(Earth Science Edition), 2015, 45(5): 1418-1435.

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