摘要
世界上绝大多数与碱性岩浆岩 (包括碳酸岩 )有关的稀土矿床产于裂谷化环境中 ,但四川牦牛坪稀土矿床却形成于新生代造山过程中。牦牛坪是一个与碱性杂岩体密切有关的稀土矿床 ,矿化与岩浆碳酸岩直接有关。碳酸岩的同位素地球化学组成变化很小 ,2 0 6Pb/2 0 4Pb=1 8.1 6 2～ 1 8.1 94 ,2 0 7Pb/2 0 4Pb=1 5 .5 36～ 1 5 .5 6 7,2 0 8Pb/2 0 4Pb=38.2 83～ 38.390 ,87Sr/86Sr=0 .70 6 0 5～ 0 .70 6 91 ,1 4 3 Nd/1 4 4 Nd=0 .5 1 2 32 7～ 0 .5 1 2 4 36 ,与 EMI型地幔源区的同位素组成基本一致 ,表明牦牛坪稀土元素的成矿作用与深部动力学过程有关。在强烈的挤压造山过程中能够有 EMI型地幔物质上侵 ,表明进入新生代以来 ,龙门山造山带乃至整个青藏高原及周边地区的地球动力学背景不仅限于板块的水平挤压与俯冲 ,还应考虑到地幔物质及其活动过程的显著贡献。
Most of the REE deposits related to alkalic magmatic rocks (including carbonatite) formed in a rift environment. The REE deposit in Maoniuping is an exception. It formed during the Cenozoic orogeny process. The Maoniuping deposit is a large LREE deposit hosted within alkalic complex rocks, with most of the REE minerals distributed in carbonatites. The carbonatite has a well-distributed isotopic composition, 206Pb/ 204Pb=18.162~18.194, 207Pb/ 204Pb=15.536~15.567, 208Pb/ 204Pb=38.283~38.390, 87Sr/ 86Sr=0.70605~0.70691, 143Nd/ 144Nd= 0.512327~0.512436. Such a EMI-type isotopic composition suggests an enriched mantle source for the rare earth elements mineralization and a dynamic process involving mantle materials and tectonics. However, the Maoniuping area was situated at the Longmenshan-Jinpingshan Orogen during its Cenozoic compression process, and the alikalic igneous rocks and carbonatites were intruded at the same time. The underplating and upwelling of mantle materials from a EMI-type source region indicate that the movement of mantle materials and the transport of heat and fluids do have contributed a lot to the building of Longmenshan-Jinpingshan mountains and the formation of REE deposits. So, the plate-collision is not the merely solution to the enigma of the world roof. In fact, the Himalayan movement is the coupling of the crustal compression with the mantle materials and heat injecting up into the thickening crust.
出处
《成都理工学院学报》
CSCD
北大核心
2002年第5期539-544,共6页
Journal of Chengdu University of Technology
基金
国家重点基础研究项目 ( G1 9990 4 32 0 3)
中国地质大调查项目 ( K1 .4 -3-4 )
关键词
岩浆碳酸岩
同位素地球化学
四川
稀土矿床
成矿动力学
magma carbonatite
geochemistry
REE deposit
mineralization dynamics
Maoniuping
Sichuan
