摘要
目前对新元古代中期江南造山带构造演化及钦杭结合带南西段构造性质存在不同认识。本文对湘西南城步地区新元古代火山岩和花岗岩进行了锆石SHRIMPU-Pb年龄测定并厘定其构造环境,从而为区域构造演化提供了约束。城步新元古代花岗岩侵入于云场里组变质火山-沉积地层中。云场里组变质火山岩与花岗岩的锆石SHRIMPU-Pb年龄分别为828±10Ma和805.7±9.2Ma。构造环境的地球化学判别图解表明花岗岩形成于岛弧环境;区域地质背景指示云场里组可能形成于活动陆缘弧前盆地。以城步火山岩和花岗岩研究为基础,结合区域地质资料,提出新元古代中期江南造山带西段构造演化过程:872～835Ma期间为陆缘盆地;835～820Ma期间俯冲造山,江南造山带形成基性—超基性岩和早阶段岛弧花岗闪长岩,东侧的城步地区为弧前盆地;820～810Ma期间江南造山带发生弧-陆碰撞;810～800Ma期间江南造山带进入后碰撞环境并形成晚阶段强过铝(黑云母)花岗岩,东侧城步地区因华南洋洋壳俯冲而形成新的岛弧;800Ma后华南进入伸展裂陷盆地演化阶段。上述认识揭示出扬子陆块东南缘的连续岛弧增生过程,同时为钦杭结合带南西段雪峰期"残留洋盆"属性提供了新证据。
There exist different recognitions about tectonic evolution of the Jian gnan orogenic belt （JOB） and the tectonic affinity of the southwestern Qinzhou-Hangzhou suture zone in middle Neoproterozoic. Zircon SHRIMP U-Pb dating was pe rformed for the Neoproterozoic volcanic rocks and granites of the Chengbu area,Hunan,and their tectonic settings were discussed,which gives some constraints on regional tectonic evolution. The Chengbu Neoproterozoic granites intruded the metamorphic volcanic-sedimentary sequences of the Yunchangli Formation,and th e zircon SHRIMP U-Pb dating yield （828±10）Ma and （805.7±9.2）Ma for the volcan ic rock and granites,respectively. Study of the major and trace elements sugges ts an island arc setting for the granites and a fore-arc basin of active contin ental margin for the Yunchangli Formation. Based on the study of the Chengbu vol canic rocks and granites as well as the regional geologic analysis,the authors put forward a new model for the Neoproterozoic tectonic evolution of the western section of JOB. During 872~835 Ma a continental margin basin developed in the a rea; during 835~820 Ma subduction-related orogenesis took place in JOB which re sulted in the formations of mafic-ultramafic rocks and the early phasic island arc granodiorites,while the Chengbu area to the east of JOB was forearc basin; during 820~810 Ma there arc-continental collision happened; during 810~800 Ma J OB turned to be in a post-collisional setting and the strong peraluminous grani tes were formed,while a new island arc was formed in Chengbu area for the ocean crust subduction of Huanan ocean; South China entered the stage of rifting basi n in 800 Ma. Above achievement revealed a series of island arc accretion process es in the southeastern margin of Yangtze block,and provided important evidence for the Xuefeng Period ＂remnant ocean basin＂ attribute of the southwestern secti on of Qinzhou-Hangzhou juncture.
出处
《地质学报》
EI
CAS
CSCD
北大核心
2010年第12期1715-1726,共12页
Acta Geologica Sinica
基金
中国地质调查局"湖南1:25万武冈市和永州市幅区调修测"项目
"中国地质构造区划综合研究与区域地质志修编"项目(编号1212010811032)
地质大调查项目(编号1212010610711)联合资助的成果
