地质学报2026，Vol.100Issue(8)：2680-2701,22.DOI:10.19762/j.cnki.dizhixuebao.2026242
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
Petrogenesis and tectonic implications of the late Triassic Lianghekou complex massif in the south Songpan-Ganze terrane
摘要
Abstract
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.关键词
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Key words
Songpan-Ganze terrane/late Triassic igneous rock/Danba complex/petrogenesis/tectonic evolution引用本文复制引用
彭弘韬,许志琴,郑碧海,黄煜,赵宇涵,马靖,高建国..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[J].地质学报,2026,100(8):2680-2701,22.基金项目
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. （编号2024ZB757）
