新疆北部晚古生代的底侵作用——来自橄榄玄粗岩与埃达克岩的证据

Underplating During Late Paleozoic in North Xinjiang——Evidence from Shoshonitic Series Volcanic Rocks and Adakite

新疆北部广泛分布晚古生代橄榄玄粗岩系火山岩和埃达克岩,它们均明显富碱,与区内同时代碱性花岗岩共同构成新疆北部富碱火成岩省。橄榄玄粗岩系火山岩和埃达克岩同位素年龄为250-280Ma,143Nd/144Nd比值高,εNd(t)值为正值,Nd模式年龄低(tDM<1.0Ga),较低而变化范围较大的(87Sr/86Sr)i(0.7040-0.710),这些特点均表明它们的源区物质为底侵幔源玄武质岩浆,并可能受到下地壳混染。结合区内地球物理资料,如加厚的地壳、复杂的莫霍面结构、高热流值及广泛分布的基性岩墙群和碱性花岗岩,均一致表明在晚古生代(晚石炭-二叠纪)新疆北部发生过较广泛的幔源玄武质岩浆底侵作用,陆壳发生了明显垂向增生。

Late Paleozoic shoshonitic series volcanic rocks and adakite are wide spread in north Xinjiang. They are rich in alkali together with the widely distributed alkali-rich granites to constitute alkali-rich igneous rock province of north Xinjiang. Different isotopic dating methods gave the age of 250-280 Ma for the shoshonitic series volcanic rocks and adakite. High 143Nd/144 Nd ratios, positive εNd（t） （〉0）, lower Nd model ages（tDM〈1.0Ga） and lower with wide variation of （^87Sr/^86Sr）i（0. 7040-0. 710） have shown their source rocks are mantle-derived and/or contaminated by crust. Thickened crust, complex Moho, high geothermal heat flow and widely distributed basic dike swarms and alkali-rich granites have systematicly proved evidences for the underplating during late Paleozoic （later Carboniferous--Permian） in north Xinjiang.