摘要
产于大陆板内环境的女山中更新世碧玄质火山岩及其所含幔源二辉橄榄岩捕虏体的研究结果揭示，在裂谷作用初始阶段，由于软流圈地幔柱上隆减压，造成深部溶解于地幔橄榄岩高压固体矿物相中的挥发组分出溶，这些出溶的初始地幔流体相在一定部位聚集，于３０Ｍａ前，大约３７ｋｍ之下，在地幔橄榄岩中诱发同步的部分熔融和交代作用，并相应产生原生碧玄质岩浆。后者上升速度较快，既未经历壳内高位岩浆房贮集，也没有遭受大陆地壳混染，只是在输送往地表的途中伴随结晶分离作用，发生一定程度演化。
The results of study on the middle-pleistocene basanites and the mantle-derived lherzolite xenoliths entrained by the formers from Nushan indicate that the volatils dissolved in high-pressure solid mineral phases of mantle peridotite at mantle depth might be exsolved under the decompressive conditions at welling of asthenospheric mantle plume during preliminary continental rifting. These exsolvedly initial free fluid phases, which mainly consist of CO2, CO, H2O and small amounts of N2, SO2, H2S, CH4, H2, Cl2 and F, accumulate in some regions of mantle, and they resulted in lowring of mantle solidus (and liquidus ) and might initiate partial melting in the upper mantle. The mantle fluids and the melts produced by partial melting of mantle peridotites under inducement of the formers would be highly enriched in incompatible elements. Interaction between them and depleted mantle could bring the latter about substantial local enrichments of LREE and incompatible elements. namely resulted in mantle metasomatic effect. The authors' studies reveal that the mantle metasomatism and partial melting had been synchronized under the Inducement of initial mantle fluids before 30 Ma and below the 37km depth within the mantle peridotites beneath Nushan. and the primary basanitic magmas, which would have the eutectic composition for mantle lherzolite system, would be simultaneously generated. The latters, segregated from their source region, ascended more rapidly and they might not undergo storage in high-level magma chamber within the crust and neither undergo contamination processes of the continental crust. The primary mantle-derived basanitic magmas might only undergo a modification to some extent during transport to the surface. being accompanied by a slight crystal fractionation
出处
《岩石学报》
SCIE
EI
CAS
CSCD
北大核心
1994年第3期223-235,共13页
Acta Petrologica Sinica
基金
国家自然科学基金
关键词
碧玄岩
岩浆起源
岩浆发育
火山岩
Basanite
Magmatic origin
Magmatic evolution
Nushan of Anhui province
