地质通报2017，Vol.36Issue(10)：1760-1771,12.
昌宁-孟连结合带奥陶纪洋岛玄武岩的识别及其构造意义——来自地球化学和锆石U-Pb年龄的证据
Identification of Ordovician oceanic island basalt in the Changning-Menglian suture zone and its tectonic implications:Evidence from geochemical and geochronological data
摘要
Abstract
The Changning-Menglian tectonic belt has been traditionally known as one of the Paleo-Tethys suture zones in the Sanji-ang orogenic domain, Southwest China. This study focused on the newly found volcano-sedimentary rocks consisting of vesicular and amygdaloidal basalts, andesitic basalt, siliceous rock, and meta-mud siltstone in the Mengyong-Manghong area located to the east of the Tongchangjie ophiolitic rocks in the central Changning-Menglian suture zone. LA-ICP-MS zircon U-Pb dating reveals that the 206Pb/238U weighted mean age of the amygdaloidal basalt is 449.3 ± 8.4Ma(MSWD=3.5), suggesting that this suite of volcanic rocks was emplaced in Ordovician. The basaltic rocks are rich in Al2O3 (12.11%~15.04%), show high K2O/N2O ratios of 0.03~0.44 and high MgO (6.78%~12.34%, 9.43% on average) with high Mg# of 45.9~61.7, and Cr, Ni, Nb values of 58.6 × 10-6~636 × 10-6, 57.4×10-6~410×10-6 and 18.9×10-6~32.8×10-6 ( 310.3×10-6, 202.1×10-6 and 25.06×10-6 on average) respectively. They have flat chondrite-normalized REE patterns with low (La/Yb)N (averagely 5.25), (Ce/Yb)N (4.42 on average ) and (Ce/Sm)N (1.68 on aver-age ). TheΣREE value of the basaltic rocks increases with the increasing of the total alkaline, which suggests that the rocks are simi-lar to the Azores-type oceanic island basalts (OIB). Generally, this suite of volcanic rocks is alkaline with OIB affinity, which might have resulted from the melting of the head of the hotspot in the Intra-oceanic plate. The new discovery of the Azores-type OIB in the Changing-Menglian records the product of OIB activity in the Early Paleozoic evolution of Tethys Ocean, which provides im-portant basic information for further understanding of the composite arc-basin system in the Tethyan domain of Southwest China.关键词
亚速尔型洋岛/碱性玄武岩/地球化学/LA-ICP-MS锆石U-Pb定年/奥陶纪/昌宁-孟连结合带Key words
Azores-type oceanic island/alkaline basalt/geochemistry/LA-ICP-MS zircon U-Pb dating/Ordovician/Changning-Menglian suture zone分类
天文与地球科学引用本文复制引用
孙载波,曾文涛,周坤,吴嘉琳,李龚健,黄亮,赵江泰..昌宁-孟连结合带奥陶纪洋岛玄武岩的识别及其构造意义——来自地球化学和锆石U-Pb年龄的证据[J].地质通报,2017,36(10):1760-1771,12.基金项目
云南省科技领军人才培养计划项目《西南"三江"叠合成矿作用与成矿预测》(编号:2013HA001)和中国地质调查局项目《西南三江有色金属资源基地调查》(编号:121201010000150007) （编号:2013HA001）
