松潘-甘孜地体南缘晚三叠世两河口复式岩体成因及构造意义OA
Petrogenesis and tectonic implications of the late Triassic Lianghekou complex massif in the south Songpan-Ganze terrane
松潘-甘孜地体南缘两河口地区出露的晚三叠世复式岩体由闪长岩、二长花岗岩和似斑状花岗闪长岩组成,记录了松潘-甘孜地体晚三叠世岩石圈不同层次的局部熔融作用,是理解松潘-甘孜地体的组成和晚三叠世构造演化过程的重要窗口.LA-ICP-MS锆石 U-Pb定年结果表明两河口闪长岩、二长花岗岩和似斑状花岗闪长岩分别形成于205.6±1.1～206.3±1.4 Ma,198.5±2.3 Ma和199.3±0.9 Ma.两河口闪长岩具有较高的 MgO(6.74％～8.24％)和 Mg#(64～66),属于高镁闪长岩,且具有富集轻稀土元素(La/Smcn=1.81～2.41),亏损高场强元素,低Sr/Y比值(4.1～7.2)的地球化学特征,以及富集的 Nd(εNd(t)=-9.0～-9.5)和 Hf(εHf(t)=-6.1～-12.2)同位素组成,表明其可能来源于俯冲沉积物交代的富集岩石圈地幔熔融.两河口二长花岗岩和似斑状花岗闪长岩都表现出I型花岗岩特征,其中二长花岗岩经历了较高的分异,具有高SiO2(74.2％～74.7％),低 Nb/Ta比值(3.53～4.15),Eu负异常(δEu=0.66～0.71),及相对亏损的 Nd(εNd(t)=-0.7～-1.0)和 Hf(εHf(t)=-0.8～+2.8)同位素组成,可能由新元古代基底熔融及之后的结晶分异所形成.似斑状花岗闪长岩属于准铝质-弱过铝质花岗岩(A/CNK=0.93～1.07),具有较高的 K2O/Na2O比值(0.90～1.17),富集轻稀土元素(La/Smcn=3.41～4.87),亏损重稀土元素(Gd/Ybcn=1.70～2.76),以及相对富集的 Nd(εNd(t)=-5.7～-6.3)和 Hf(εHf(t)=-1.3～-4.3)同位素组成,可能形成于高钾镁铁质下地壳的熔融.两河口复式岩体的源区性质揭示了晚三叠世松潘-甘孜地体具有富集的岩石圈地幔和基性下地壳.综合区域研究成果,提出金沙江洋和甘孜-理塘洋闭合后的同碰撞-后碰撞阶段,板片断离诱发的软流圈上涌为松潘-甘孜地体晚三叠世的岩浆活动提供了热源.
The late Triassic Lianghekou complex massif,comprising diorite,monzogranite,and porphyritic granodiorite,crops out in the southern Songpan-Ganze terrane.This complex records late Triassic partial melting of the lithosphere at various depths,serving as an important window into the lithospheric composition and tectonic evolution of the Sonpan-Ganze terrane.LA-ICP-MS zircon U-Pb dating indicates that the Lianghekou diorite,monzogranite,and porphyritic granodiorite formed at 205.6±1.1 to 206.3±1.4 Ma,198.5±2.3 Ma,and 199.3±0.9 Ma,respectively.The Lianghekou diorites exhibit high MgO(6.74%～8.24%)and Mg#(64～66),identifying them as high-magnesium diorites.Their enrichment in light rare earth elements(LREE),depletion in high-field-strength elements(HFSE),low Sr/Y ratios(4.1～7.2),and enriched Nd(εNd(t)=-9.0 to-9.5)and Hf(εHf(t)=-6.1 to-12.2)isotopic compositions suggest an origin from the partial melting of an enriched lithospheric mantle metasomatized by subducted metasediments.Both the Lianghekou monzogranites and porphyritic granodiorites show characteristics of I-type granites.The monzogranites experienced extensive fractional crystallization and exhibit relatively high SiO2(74.2%～74.7%)contents,low Nb/Ta ratios(3.53～4.15),negative Eu anomalies(δEu=0.66～0.71),and relatively depleted Nd(εNd(t)=-0.7 to-1.0)and Hf(εHf(t)=-0.8 to+2.8)isotopic compositions.These features indicate they formed through partial melting of Neoproterozoic basement followed by fractional crystallization.The porphyritic granodiorites are metaluminous to weakly peraluminous(A/CNK=0.93～1.07)and exhibit relatively high K2O/Na2O ratios(0.90～1.17).They are enriched in LREE(La/Smcn=3.41～4.87),depleted in HREE(Gd/Ybcn=1.70～2.76),and possess enriched Nd(εNd(t)=-5.7 to-6.3)and Hf(εHf(t)=-1.3 to-4.3)isotopic compositions,suggesting formation via partial melting of high-potassium mafic lower crust.The sources of the Lianghekou complex massif reveal that the Songpan-Ganze terrane in the late Triassic was underlain by enriched lithospheric mantle and mafic lower crust.Integrating regional data,we propose that during the syn-collision to post-collision transition following the closure of the Jinshajiang and Ganze-Litang oceans,asthenospheric upwelling triggered by slab break-off provided the heat source for late Triassic magmatism in the Songpan-Ganze terrane.
彭弘韬;许志琴;郑碧海;黄煜;赵宇涵;马靖;高建国
南京大学地球科学与工程学院,关键地球物质循环与成矿全国重点实验室,南京大学大陆动力学研究院,江苏 南京,210023南京大学地球科学与工程学院,关键地球物质循环与成矿全国重点实验室,南京大学大陆动力学研究院,江苏 南京,210023南京大学地球科学与工程学院,关键地球物质循环与成矿全国重点实验室,南京大学大陆动力学研究院,江苏 南京,210023南京大学地球科学与工程学院,关键地球物质循环与成矿全国重点实验室,南京大学大陆动力学研究院,江苏 南京,210023南京大学地球科学与工程学院,关键地球物质循环与成矿全国重点实验室,南京大学大陆动力学研究院,江苏 南京,210023南京大学地球科学与工程学院,关键地球物质循环与成矿全国重点实验室,南京大学大陆动力学研究院,江苏 南京,210023中国石油化工股份有限公司西南油气分公司勘探开发研究院,四川 成都,610041
松潘-甘孜地体晚三叠世岩浆岩丹巴杂岩岩浆成因构造演化
Songpan-Ganze terranelate Triassic igneous rockDanba complexpetrogenesistectonic evolution
《地质学报》 2026 (8)
2680-2701,22
本文为江苏省"卓越博士后计划"(编号2024ZB757)、国家自然科学基金项目(编号92162211,91955203)和南京大学卓越计划"川西伟晶岩型锂矿科学钻探"项目联合资助的成果.
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