囊谦盆地新生代钾质火山岩成因岩石学研究

囊谦新生代钾质火山岩形成于碰撞后的板内构造环境,基性、中性和中酸性熔岩之间不存在分异和演化的关系,它们地球化学性质上的差异是源区部分熔融程度不同所致;钾质岩浆形成于50～80 km深处的富集交代地幔.横断山地区一些拉分盆地中火山岩源区的部分熔融可能与来自软流圈小而分散的上涌体的底侵有关.大型走滑断裂带的强烈活动为熔体的快速上升提供了通道.

PETROGENESIS OF CENOZOIC POTASSIC VOLCANIC ROCKS IN NANGQEN BASIN

The Nangqen Basin is one of the Tertiary pull-apart basins situated at the east of the Qiangtang block. Similar to the adjacent Dingqing and Bashu Basins, there occurred a series of potassic volcanic and sub-volcanic rocks ranging from basic, intermediate to intermediate-acid. Based on a study of petrology, mineralogy and geochemistry including REE, trace elements, isotopic elements and chronology, we suggested that the Cenozoic potassic volcanic rocks in the Nangqen basin were formed in a post-collisional intra-plate tectonic setting. The geochemical variability of the basic, intermediate and intermediate acid rocks may be mainly attributable to the different partial melting degrees of the mantle sources formed at about 50～80 km depth, instead of a relation of magmatic differentiation or evolution. The sources of the potassic rocks are enriched metasomatic mantle that has experienced multiple mixture of components mainly derived from the crust. The partial melting of the sources of the volcanic rocks in some pull-apart basins in the Hengduan Mts. area may be related to the underplating of the small-scattered magma upwelling derived from the asthenosphere. The tectonic movements of the large-scale strike-slip faults provided the channel-ways for the melts ascending.