摘要
(一)岩体形态及产出地质环境岩体出露于云南省金平县长坡头、桥头至马鞍底一带,向南延伸出国境到越南境内。岩体呈岩墙、岩枝产出,厚度较大,数条平行伸展的岩墙、岩枝向南合并成东、西两支(即勐平岩体和大平岩体)。东长逾35公里;宽2250米;西长26公里,宽7公里。在国境内,岩体出露面积达160平方公里。岩体产于哀牢山群变质岩系中(图1)。哀牢山群由混合岩化片麻岩、变粒岩、斜长角闪岩等组成,原岩为类复理石建造碎屑岩系夹中性火山岩。原岩时代不清楚。
The Mengping-Daping rock body occurred in the metamorphic rock series of Ailaoshan Group was controlled by the deep-seated structure belt of the Jinshajiang-Ailaoshan strike-slip fracture system during the process of emplacement and diagenesis. It was intensely mylonized, with the S-C fabric developed and commonly situated in the ductile shear zones with its country rocks. This rock body is a complex one composed mainly of riebeckite-aegirine alkali granite with slightly low silicon, rich alkali, poor aluminium and very rare calc-magnesium contained. It is rich in rare-earth elements (the total amount reaching 693.11--865.11 ppm), especially the light rare-earths and element ytttrium of heavy rare-earths which has formed the fergusonite placer in weathering crust, with a Rb-Sr isotopic age of 108.3±17 Ma and particularly high initial ratio of ^(87)Sr/^(86)Sr (up to 0.763). The rocks were formed by low viscosity, high rheidity magma under a high pressure, closed and homothermal environment showing the features of type--A granite. From the petrochemistry of paragenetic rock type assemblages, the mantle--source characters of intrusive rock body can be observed.
出处
《云南地质》
1989年第3期239-248,共10页
Yunnan Geology
