地质学报2026，Vol.100Issue(3)：859-878,20.DOI:10.19762/j.cnki.dizhixuebao.2024590
新疆南天山老虎台地区混合岩地质特征、年代学与锆石Hf-O同位素组成
Geological characteristics,geochronology and zircon Hf-O isotopes of migmatite in the Laohutai area,South Tianshan,Xinjiang
摘要
Abstract
Migmatization,recording the crustal anatexis,plays a vital role in continental crustal evolution;it can occur at various stages of orogenesis and is considered direct petrological evidence for crustal growth and reworking.The South Tianshan Orogenic Belt(STOB),located in the southwestern segment of the giant Central Asian Orogenic Belt,formed through the long-term subduction of the South Tianshan Ocean and subsequent continental collision.This study presents systematic geochronological,whole-rock geochemical,and zircon Hf-O isotope analyses of migmatite from the Laohutai area in the South Tianshan.Our results show that these migmatites originated from the partial melting of supracrustal rocks dominated by volcanic components.Based on their geochemical characteristics,the migmatite samples can be divided into two groups:Leucosome-dominated samples consistently exhibit negative Nb,Ta,and Sr anomalies,with insignificant Eu anomalies;melanosome-rich samples demonstrate not only negative Nb and Ta anomalies but also pronounced positive Sr and Eu anomalies.All samples present a relatively gentle right-inclined rare earth element(REE)pattern,with enrichment in light rare earth elements(LREE)and depletion in heavy rare earth elements(HREE).The U-Pb ages of anatectic zircons from both leucosomes and melanosomes range predominantly from 436 to 376 Ma,indicating regional anatectic events that occurred mainly during the Middle Silurian to Late Devonian periods.The isotopic compositions of anatectic zircons from the melanosomes include εHf(t)values ranging from-15.98 to-2.06(TDM2:3.0～1.6 Ga)and δ18O values ranging between 4.14‰ and 9.93‰.Anatectic zircons from the leucosomes yield comparable values,with εHf(t)ranging from-15.7 to-1.69(T DM2:2.4～1.6 Ga)and δ18 O ranging from 4.30‰ to 10.02‰.In combination with previous studies,this study establishes the genetic link between the southward subduction of the South Tianshan Ocean and the anatectic events.A regional tectonic transition occurred at ca.420 Ma.From～460 to 420 Ma,low-angle,advancing subduction created a compressional regime in the STOB and the northern Tarim margin.Under these conditions,supracrustal rocks were underthrusted into deep crustal levels,generating limited anatexis.Following the tectonic transition,retreating subduction(or slab rollback)dominated from～420 to～390 Ma.This phase was accompanied by extensive mantle underplating and a significant rise in the geothermal gradient,placing the upper plate in an extensional setting.Intense anatexis occurred in response to this tectonic transition.关键词
西南天山/深熔作用/混合岩/南天山洋/锆石Hf-O同位素Key words
SW Tianshan/anatexis/migmatite/south Tianshan Ocean/zircon Hf-O isotopes引用本文复制引用
李海舟,黄河,吴欢欢,潘蓓蓓,姚雪娇,薛怀民..新疆南天山老虎台地区混合岩地质特征、年代学与锆石Hf-O同位素组成[J].地质学报,2026,100(3):859-878,20.基金项目
本文为国家重点研发计划课题(编号2019YFA0708601)和国家自然科学基金面上项目(编号42173052)资助的成果. （编号2019YFA0708601）
