The Geological Environment of the Xenolith-Bearing Miocene Basalt from Siziwang County, Inner Mongolia

内蒙古四子王旗东八号地区出露一套含深源包体的中新世玄武岩,寄主岩石具有高钾(1.16%< K_2O含量< 3.36%),高钛(2.25%< TiO_2含量<2.51%)的特征;其母岩浆富集LREE和HFSE,强烈富集Nb,Ta和La,相对亏损K,Rb和Ba.其母岩浆来源于经历低度部分熔融,残留石榴石和金云母的软流圈地幔,运移过程中在高压环境下发生了分离结晶作用,分异相主要为单斜辉石和斜长石.玄武岩中出现橄榄岩和麻粒岩包体: 橄榄岩包体为尖晶石二辉橄榄岩,富集LREE,平衡温压范围为: 1050～1100℃,1.64～2.37 GPa,代表富集的或发生过富集事件的上地幔;麻粒岩包体为中基性麻粒岩,平衡温压范围为: 960～1000℃,0.82～1.13 GPa,其原岩包括原生的下地壳物质和与玄武质岩浆有关的产物.说明华北克拉通北缘的岩石圈受到地幔柱作用的影响,中新世时处在减薄状态.The xenolith-bearing Miocene basalts in Siziwang County, Inner Mongolia, are characterized with high-K (1.16 % < wt(K_2O)< 3.36%), high-Ti (2.25% < wt(TiO_2)< 2.51%). They are enriched in light rare earth elements (LREE), high field strength elements (HFSE), highly enriched in Nb, Ta and La, and depleted in K, Rb and Ba. The parental magma was derived from a small degree melting of an asthenosphere mantle with garnet and phlogopite being the restite, and experienced a fractional crystallization of clinopyroxene and plagioclase during the magma uplifting to surface. The basalts contain xenoliths of peridotite and granulite. The peridotite xenoliths are spinel-lherzolite, which is enriched in light rare elements (LREE), with P-T conditions of 1050-1100℃ and 1.64-2.3 7GPa, representing enriched upper mantle. The granulite xenoliths are intermediate to basic composition with P-T conditions of 960-1000℃ and 0.82-1.13 GPa, representing materials from lower crust or from the basic magma evolution. These indicate that the north margin of North China craton is subjected to thinning in the Miocene due to a mantle plume activity.国家自然科学基金中文核心期刊要目总览(PKU)中国科技核心期刊(ISTIC)中国科学引文数据库(CSCD)02215-2234