不同构造环境基性岩浆作用碳组成及其环境意义

The Chemical Compositions and Environmental Implications of Carbonaceous Volatile Species of the Mafic Magmatism in Different Tectonic Settings

地球内部的碳储量远高于地球表层系统,基性岩浆作用使地球深部的含碳挥发分排放到地球表层系统中,导致大气圈中CO_2和CH_4等组分含量及地表温度升高。本文总结了不同构造环境基性岩浆作用形成岩石中含碳挥发分的含量及其意义,认为大洋和大陆环境的玄武岩及基性岩浆侵入体中含碳挥发分均以CO_2为主,CH_4等烃类气体的含量较低。大洋玄武岩CO_2含量从洋岛玄武岩(210mm^3·STP/g,STP-标准温度压力条件,下同)、洋中脊玄武岩(263)、弧后盆地玄武岩(1060)到岛弧玄武岩(1246)逐步升高。大陆玄武岩的CO_2含量变化较大,西伯利亚二叠纪大火成岩省苦橄岩中CO_2(276.98)低于准噶尔盆地二叠纪玄武岩(643.99)。西秦岭造山带玄武岩CO_2含量为237.27mm^3·STP/g,而腾冲新生代玄武岩CO_2含量只有11.97mm^3·STP/g;华北-华南克拉通新生代玄武岩CO_2含量较低(140~202.8mm^3·STP/g)。镁铁质-超镁铁质侵入体CO_2含量为105~384mm^3·STP/g,含碳挥发分的组成与氧化还原条件有关,大规模基性岩浆作用排放大量的CO_2到地球表层环境系统,诱发了环境变化。

The interior of earth has higher carbon contents than surface system of Earth. Carbon in the Earth interior occurs in various forms, such as carbonatite melt, carbonous minerals（ diamonds and graphite etc. ） , carbonaceous volatiles（ CO2 and CH4 etc. ）. Carbonous species in the solid state are difficult to emit into earth surface environmental system. The earbonous volatile species（ CO2 and CH4 etc. greenhouse gases）are volumetrically significant, are dispersed as free elemental or inorganic and hydrocarbon molecular species along grain boundaries, charged species in fluid inclusions or in mineral structures, structural defects or vacancies. The carbonous volatile species have been emitted or leaked constantly into earth surface system by extensive marie magmatism or associated fracture, and resulted in the rising of CO2 concentration and temperature in global surface system nowadays and in geological time. Carbonous volatile species in mafic magmatism vary in concentration with tectonic settings. The extensive oceanic basahic magmatism is the strongest emitting channel of carbonous volatiles from the earth interior（especially mantle） , and shows dominant CO2 with minor CH4. Mid-Ocean-Ridge- Basalts（MORB） are dominated by CO2（ av. 263 mm^3·STP/g）with minor CO and CH4 components. Atlantic MORB has higher CO2（av. 598 mm^3·STP/g）than Pacific and Indian MORB （av. 292 and 157 mm^3·STP/g, respectively）. Ocean-is- land basahs（OIB） are characterized by the lowest CO2 content（ 210 mm^3·STP/g）. CO2 contents increase from OIB （210） , MORB（263）, BAB（1060） to IAB（ 1246 mm^3·STP/g）.The CO2 contents of basalts vary largely in continental environ ments. The average contents of CO2 in the gabbroic and picrite rocks in Permian Siberian large igneous province（LIP） are measured to be 102 and 276.98 mm^3·STP/g, respectively. Permian basalts in Northwest Junger basin, Xinjiang, China show high CO2 content（av., 643.99 mm^3·STP/g）. The av. CO2 contents of Cenozoic basalts in the orogenic belts western China vary from 237.27 in western Qinling to 11.97 mm^3·STP/g in Tengchong. The CO2 contents in Ni-Cu sulfide bearing magmatic mafic ultramafic intrusions are av. 153.9 mm^3·STP/g for Xiarihamu in the East Kunlun orogenic belt and av. 257.4 mm^3·STP/g for Karatonke in the Central Asian Orogenic Belt of Xingjiang, China, and 110.6 for the Siberian LIP and 227.5 for Emeishan LIP. The speciation of carbonous volatiles is related to the oxidation state and associated tectonic setting of mafic magma. The large scale of mafic magmatism in marine and continental environments had emitted crucially large amounts of CO2 into the atmosphere. The mantle plume magmatic system emitted huge amounts of COs into the atmos- phere due to large volume, and could be a trigger for the mass extinction.