蚌埠淮光“混合花岗闪长岩”的形成时代及源区:锆石SHRIMP U-Pb地质年代学证据

Formation Time and Sources of the Huaiguang "Migmatitic Granodiorite" in Bengbu,Anhui Province:Evidence from SHRIMP Zircon U-Pb Geochronology

对蚌埠淮光花岗闪长岩的岩相学和锆石阴极发光图象研究表明,淮光“混合花岗闪长岩”为岩浆结晶作用的产物,岩石形成后受到了应力作用的改造。锆石SHRIMP U—Pb定年结果和岩浆锆石的SHRIMP U-Pb年龄显示淮光花岗闪长岩形成于130.0±2.0 Ma;大多数继承锆石的年龄集中在1 800～1 900 Ma、2 300～2 517 Ma和3 443 Ma,这意味着淮光花岗闪长岩的母岩浆起源于华北地块基底的部分熔融。早白垩世(130 Ma左右)的岩浆作用是引起继承锆石和碎屑锆石Pb丢失的重要原因,同时也是华北地块东部岩石圈减薄的最重要时期。130 Ma左右的岩浆作用和岩石圈减薄应与太平洋板块的俯冲相联系。

Petrography of the Huaiguang 'migmatitic granodiorite' and existence of magmatic zircons indicate that the granodiorite was formed by the crystallization of magma and was subjected to late stress. The granodiorite was formed at 130 ± 2.0 Ma based on the ages of magmatic zircons. Most inherited zircons were formed at 1 800-1900 Ma,2 300 - 2 517 Ma and 3 443 Ma,suggesting that the Huaiguang granodioritic magma might have been derived from the partial melting of the basement of the North China Block. The early Cretaceous (130 Ma ± ) magmatism probably resulted in a major Pb loss in some inherited and detrital zircons and might have been an important period of the lithospheric thinning in the eastern part of the North China Block. The 130 Ma magmatism and lithospheric thinning could be attributed to the subduction of the Pacific plate.