北秦岭宽坪岩群的解体及新元古代N-MORB

The disintegration of Kuanping Group in North Qinling orogenic belts and Neo-proterozoic N-MORB

本文通过LA-ICPMS单颗粒锆石微区U-Pb测年方法研究,确定宽坪岩群中的变基性火山岩形成年龄为943Ma,宽坪岩群中的变质沉积岩原岩形成于小于600Ma。因此,本文提出宽坪岩群从地层学意义上应予废除或解体。即宽坪岩群中变沉积岩与变基性火山岩不属于一个延续的沉积层序,是晚期构造运动将这些形成于不同时代、不同构造环境的岩石单元混杂叠置在一起。宽坪岩群中绿片岩类具有典型N-MORB的特征,属于新元古代一套蛇绿岩残片,代表格林威尔造山期的地质记录。

Kuangping Group located in North Qinling orogenic belt which consists chiefly of metabasalts and meta-sedimentary.A new LA-ICPMS zircon U-Pb age of metabasalt of Kuanping Group is presented and gives a weighted mean 207Pb/206Pb age of 943Ma which in the Neo-proterozoic time.However,the meta-sedimentary of Kuanping Group is limited to that in Early Phanerozoic time,but the Proterozoic,as previously considered.Therefore,this indicate that the two types of rock is not a continuous stratigraphic unit,protoliths of metabasalts were tholeiitic basalts with N-MORB geochemical characteristics,which represents a dismembered ophiolite and indicate a remnants of Greenville orogeny in the North Qinling orogenic belts.