| 其他摘要 | A large number of case studies confirmed that the refractory peridotite evolved to fertile peridotite in the North China Craton lithospheric mantle, there is currently a heated debate on the mechanism of this evolution. Cratonic lithosphere between continental crust and mantle asthenosphere in the space, therefore lithospheric mantle evolution are closely related with these two layers. Continental crust can form silicon-fertile melt in the lithospheric mantle by subduction or delamination, while asthenosphere upwelling can form silicon-depleted melt in the lithospheric mantle. In order to investigate the effect of these melt-rock (mineral) reactions in the lithospheric mantle, we choose tonalitic melt to represent silicon-fertile melt and basaltic melt to represent silicon-depleted melt, carrying on silicate melt and mantle peridotite/olivine/orthopyroxene reacion on a six-anvil apparatus. These detail including: (1) 1250-1450°C, 2.0-5.0 GPa, tonalitic melts and olivine reactions; (2) 1250-1400°C, 2.0-4.0GPa, tonalitic melt and lherzolite reactions; (3) 1300-1450°C, 2.0-4.5GPa, basaltic melts and lherzolite reactions; (4) 1300-1450°C, 2.0-4.5GPa, basaltic melt and orthopyroxene reactions. The petrographic and chemical composition of minerals in these reaction products can offer directly evidence for the mechanism of the lithospheric mantle evolution of North China Craton. The followings are the main conclusions of the paper: （1）The orthopyroxene is the main product of the reaction between tonalitic melts and mantle peridotite (olivine), while the reaction rims were formed by minerals assemblage Opx+Grt in the case of low temperature and high pressure. The reaction rim formed by minerals assemblage Cpx+Grt+Opx is the most common case in basaltic melt and mantle rocks reactions, while Cpx+Opx formed at high temperature conditions. The reaction rim formed by minerals assemblage Cpx+Grt is the most common case in basaltic melt and orthopyroxene reaction, while Cpx becomes the main product in the case of high temperature （2）Reaction mechanisms of silicate melts and mantle rocks (minerals) reaction are diffusion and dissolution-crystallization, and dissolution-crystallization is the dominant mechanism of the reaction. Because the dissolution-crystallization progress controls the kinds of minerals in reaction rims and the chemical composition of the new formed minerals. （3）After tonalitic melts and mantle peridotie (olivine) reactions, the MgO content and Mg# of residual melts increase sharply, MgO-SiO2 evolution trends in residual melts and the in HMAs located in North China craton are very similar. Therefore, silicon-fertile melts and mantle peridotite reacion is a possible way to form HMA inner craton. Meanwhile, Garnets form in some run, which will lead to residual melts "Adakite-like". And therefore silicon-fertile melts and mantle peridotite reacion is a possible way to form adakite inner cratons. (4) Silicon-fertile melts (derived from continental crust) and peridotite reactions form the olivine-free pyroxenite or garnet pyroxenite in lithospheric mantle. While silicon-depleted melt (derived from asthenosphere) and peridotite reaction from the clinopyroxene-rich pyroxenite and lherzolite. So, the mantle rock reacts with silicate melts can lead the cratonic lithospheric mantle form refractory type to fertile type. In addition, sieve-texture garnets were found in some runs, so quartz-bearing sieve-texture garnets can form during silicate melts and mantle rocks (minerals) reaction. Therefore the quartz/coesite-bearing garnets in HP and UNP metamorphic rocks may be the products of melt-rock reactions in mantle. Quartz in Sieve-texture garnets has a different quartz-coesite phase transition boundary comparing with pure silica system. So when we use the quartz-coesite phase transition boundary to estimate the diagenetic conditions of metamorphic rock, we should carefully consider the effect of the system. |
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