摘要
辽东黑沟地区出露大面积辽河群变质表壳岩系,本文通过对辽河群中浅粒岩、黑云变粒岩、斜长角闪岩以及辽吉花岗岩等岩石系统的岩石学、锆石U-Pb年代学,并结合斜长角闪岩的地球化学特征来制约其原岩形成、变质时代和沉积环境,进而探讨辽吉造山带的大地构造属性。研究区辽河群变质火山岩和侵入其中的辽吉花岗岩锆石U-Pb定年结果显示区内辽河群形成时代早于~2.16Ga,辽吉花岗岩及辽河群变质岩中的变质锆石定年结果显示区内峰期变质年龄为~1.85Ga左右。锆石阴极发光(CL)图像显示区内辽河群变质沉积岩中的锆石具有清晰震荡环带,说明其具有岩浆成因的碎屑锆石特征,锆石U-Pb年龄分布直方图上显示1987Ma、2182Ma、2505Ma的主峰和2080Ma、2658Ma、2732Ma、3000Ma的次峰,峰值年龄与区域上古元古代弧岩浆岩及太古宙基底年龄相吻合,暗示它们为辽河群沉积岩提供了重要物源。区内辽河群斜长角闪岩属于拉斑玄武岩系列,以低TiO2和低MgO为特征,轻稀土轻微富集,并具有明显P以及轻微的Nb、Ta、Zr亏损,地球化学特征总体类似于MORB,同时兼具IAB的地球化学特征,不同于弧玄武岩和板内玄武岩,显示出有限的俯冲相关流体的交代作用,指示其形成于弧后盆地环境。结合前人对辽吉造山带内古元古代花岗岩和辽河群的研究成果,认为区内辽河群的沉积环境为活动大陆边缘弧后盆地,辽吉造山带的形成演化与弧-陆碰撞有关。
The Paleoproterozoic meta-supracrustal rocks,known as the Liaohe Group,are widely exposed in the Heigou area of the Liaoning province.In this paper,we study the petrology of the leptite,mica-quartz schist,tremolite granulite,biotite plagioclase,amphibolite,and hornblende adamellite,and undertake UPb dating of the zircons in these rocks.The aim is to constrain the petrogenesis of the Liao-Ji belt by investigating their composition,chronology,and metamorphism of the protolith,and petrogenesis.The zircon U-Pb dating results of the metamorphic volcanic rocks and the intrusive granites of the Liaohe Group in the study area show that the formation age of the Liaohe Group is older than^2.16 Ga.The metamorphic zircon dating results of the Liaoji granitoids and the Liaohe Group metamorphic rocks show that the metamorphic age in the peak period is about 1.85 Ga.Most detrital zircons from the metasedimentary rocks in the formation show oscillatory zones under Cathodoluminescence(CL)image indicating a magmatic origin.The U-Pb age distribution histogram of zircon shows the main peaks at 1987 Ma,2182 Ma and 2505 Ma,and secondary peaks at 2080 Ma,2658 Ma,2732 Ma and 3000 Ma.The main peaks are consistent with the ages of regional upper Paleoproterozoic granitoids,volcanic rocks of the Liaohe Group,and the Archean basement,suggesting that they provide important provenance for the sedimentary rocks of the Nanliaohe Group.The deposition time of the meta-sedimentary rocks is later than2.0 Ga as constrained by the youngest detrital zircons.The amphibolite of the Liaohe Group in this area is characterized by low TiO2 and MgO values,slightly enriched in light rare earths,shows obvious loss of P,and a slight loss of Nb,Ta,Zr,indicating that it belongs to the tholeiite series.The geochemical characteristics are generally similar to MORB and IAB,which are different from arc basalts and intraplate basalts,showing limited subduction-related fluid metasomatism,indicating that it was formed in the backarc basin environment.By comparing the previous research results on Paleoproterozoic granites and volcanic rocks of Liaohe Group in the Liaoji orogenic belt,we conclude that the sedimentary environment of this group in the study area was an active continental back-arc basin,and the formation and evolution of the Liaoji orogenic belt is related to arc-land collision.
作者
杨玉伟
余超
苏特
董洋
王广伟
田毅
鲍东明
YANG Yuwei;YU Chao;SU Te;DONG Yang;WANG Guangwei;TIAN Yi;BAO Dongming(Geophysical Measuring Exploration Institute of Liaoning Province,Shenyang 110031;Liaoning Survey Academy of Geology and Mineral Resources Investigation Shenyang,110031)
出处
《地质学报》
EI
CAS
CSCD
北大核心
2020年第5期1397-1412,共16页
Acta Geologica Sinica
基金
中国地质调查局地质调查项目(编号DD20160049-9)资助的成果。
