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

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/CNK1),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εHf(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。

Chronology,Geochemistry,Hafnium Isotope Characteristics and Tectonic Implications of Muztag Kongur Indosinian Intrusive Rocks

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 (K2 O + Na2 O > 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 εHf (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 .