论文部分内容阅读
地幔捕虏体中的流体组分记录了地幔演化的信息,可用来认识地幔中再循环地壳组分的性质和来源。采用分步加热质谱法测定中国东部二辉橄榄岩捕虏体组成矿物中流体挥发分的碳、氢和氧同位素组成,结合化学组成(Zhangetal.,2004)综合分析表明,早期流体包裹体、矿物晶格缺陷和空隙中的流体挥发分主要在高温段(800～1200℃)释出,CO2和CO显示较轻的δ13C值,与世界其它地区地幔捕虏体明显不同;晚期流体包裹体中的流体挥发分主要在低温段(300～600℃)释出。根据中国东部地幔演化事件和地幔矿物性质认为陆下岩石圈地幔中保存的三种的流体挥发分中均存在来源不同的再循环地壳组分:①地幔初始流体:主要为耐熔矿物橄榄石在800～1200℃释出的流体组分。华北克拉通地幔初始流体的化学组成(主要为CO)与华南克拉通(主要为CO2)明显不同,反映二者拼合前各自演化时期捕获的流体组分。地幔特征的δD、δ13CCH4和δ18OCO2反映初始流体组分可能为元古代克拉通大陆型岩石圈地幔成分,CO2和CO较轻的δ13C值揭示初始流体中存在部分再循环地壳流体,可能在1.9Ga的大陆碰撞过程中混入。②地幔交代流体:指斜方辉石和单斜辉石800～1200℃释气峰的流体组分,以H2为主。华北克拉通交代流体主要组分H2的含量(80.73mm3/g)明显低于华南克拉通(138.91mm3/g),地幔特征的δDH2和δ13CCH4表明交代流体主体为地幔来源,较轻的δ13CCO2,CO和较重的δ18OCO2揭示其中存在再循环陆壳流体,其可能来源于华北与华南中生代拼合过程中的壳幔相互作用。③岩石圈减薄流体:指二辉橄榄岩捕虏体组成矿物在400～600℃释放出的流体,华北与华南克拉通在流体组成方面相似,壳源特征的CO2、CO和CH4的δ13C值,以及较轻的δ18OCO2和δDH2O值指示该流体可能为岩石圈地幔减薄过程中引起的再循环洋壳流体,可能与中国东部转换带中水平俯冲的太平洋岩石圈(或其前身)脱气有关。
The fluid components in the mantle xenolith record information on the evolution of the mantle and can be used to recognize the nature and origin of recirculated crust components in the mantle. Determination of carbon, hydrogen and oxygen isotope composition of fluid volatiles in the marbles of the marxes in eastern China using fractional heat-up mass spectrometry. The chemical composition (Zhangetal., 2004) shows that the fluid inclusions, minerals Lattice defects and voids in the fluid volatile mainly in the high temperature (800 ~ 1200 ℃) release, CO2 and CO showed a lighter δ13C value, and the rest of the world mantle xenoliths significantly different; late fluid inclusions Fluid volatile mainly in the low temperature (300 ~ 600 ℃) release. According to the evolutionary events of the mantle and the mantle mineral in the eastern China, it is considered that there are different types of recirculated crust components in the three types of fluid volatiles stored in the mantle under the lithosphere: (1) the initial mantle fluid, mainly refractory mineral olivine 800 ~ 1200 ℃ fluid components released. The chemical composition (mainly CO) of the mantle fluid in the North China craton is significantly different from that of the southern China craton (mainly CO2), reflecting the fluid components captured during the evolution of the mantle before the combination. The δD, δ13CCH4 and δ18OCO2 of the mantle features indicate that the initial fluid component may be a component of the Proterozoic cratonic continental lithospheric mantle, and the δ13C values of the lighter CO2 and CO reveal that there are some recirculated crustal fluids in the initial fluid, probably at 1.9Ga Contaminated during the collision in the mainland. (2) Mantle replacement fluid: It refers to the fluid component of orthopyroxene and clinopyroxene 800 ~ 1200 ℃ gas release peak, mainly H2. The content of H2 (80.73mm3 / g), which is the main component of the intercalary fluid in North China craton, was significantly lower than that of southern China craton (138.91mm3 / g). The δDH2 and δ13CCH4 of the mantle showed that the main body of the metasomatism was mantle source, lighter δ13CCO2, CO And heavier δ18OCO2 revealed the presence of recirculated continental crust fluid, which may be derived from the crust-mantle interaction during Mesozoic splicing in North China and South China. ③ lithosphere thinning fluid refers to the fluid released by the lherzolite xenoliths at 400 ~ 600 ℃. The North China and South China Craton are similar in fluid composition, and the δ13C values of the CO2, CO and CH4 of the crust source are , And the lighter δ18OCO2 and δDH2O values indicate that this fluid may be a recirculation of oceanic crust fluids induced by lithospheric mantle reduction and may be associated with degassing of the horizontally subducted Pacific lithosphere (or its predecessor) in the transitional zone of eastern China .