滇西腾冲地块新生代火山岩中高温麻粒岩包体的发现及成因

腾冲地块芒棒乡新生代新近纪芒棒组火山岩的研究，发现粗面安山岩中含有较多麻粒岩包体，主要类型为长英质麻粒岩和二辉麻粒岩，直径一般为3~5 cm，略具定向排列构造，粒状变晶结构特征.长英质麻粒岩包体平衡温度和压力为:869~969 ℃，0.94~1.00 GPa，二辉麻粒岩包体平衡温度为:841~972 ℃，均显示为高温麻粒岩相变质；寄主岩粗面安山岩中斑晶结晶估算的温度和压力为:1 008~1 059 ℃，1.26~1.33 GPa，表明它们形成和起源于下地壳到上地幔顶部之间.二辉麻粒岩包体电子背散射衍射(EBSD)显微组构分析表明，斜方辉石(紫苏辉石)和单斜辉石(普通辉石)均具有明显晶格优选方位(LPO)，斜方辉石和单斜辉石主滑移系分别为:(010)001]和(100)001]、(010)001]，变形机制为位错蠕变，说明麻粒岩包体经历了高温塑性变形变质作用.新生代新近纪火山岩中高温麻粒岩的发现和研究表明，腾冲新生代岩浆活动可能与印度板块和腾冲地块俯冲-碰撞造山后的伸展垮塌-拆沉和板片断离，以及随后的上地幔物质上涌减压熔融产生玄武质岩浆底侵，导致的下地壳发生高温变质及火山岩浆作用有密切关系. 

Characteristics and Genetic Significance of High Temperature Granulite Xenoliths in Cenozoic Volcanic Rocks,Tengchong, Western Yunnan Province,China

Researches on the Cenozoic volcanic rocks of the Mangbang Formation in the Mangbang area of the Tengchong block, South China, reveals many granulite xenoliths of felsic granulite and two-pyroxene granulite in trachyandesite. The granulite xenoliths range 3-5 cm in diameters, featured with aligned formation and blastic texture. Equilibrium temperature and pressure estimates for the felsic granulite xenoliths and two-pyroxene granulite xenoliths are 869-969 ℃, 0.94-1.00 GPa and 841-972 ℃ respectively, indicating that they are high temperature granulites. The crystallization temperature and pressure of trachyandesite phenocryst is 1 008-1 059 ℃, 1.26-1.33 GPa, indicating that they were formed in and originated from the lower crust to the top of the upper mantle. Electron backscatter diffraction(EBSD) analyses of two-pyroxene granulite xenoliths show that orthopyroxene and clinopyroxene have obvious lattice preferred orientation (LPO), and the main slip systems are: (010) 001] and (100) 001], (010) 001] respectively. The deformation mechanism is dislocation creep, which indicates that granulite xenoliths experienced a strong plastic deformation and metamorphism. The discovery of high temperature granulite in Cenozoic volcanic rocks suggests that Tengchong Cenozoic magmatic activity may be related with volcanic magamatism and high temperature metamorphism in the lower crustal caused by post-collisional extensional collapse, delamination and slab break-off after subduction and collision of the Indian Plate and the Tengchong block.