Evolution Characteristics and Rheological Significance of Dehydration Melting and Water-Fluxed Melting in Deep Continental Crust
Anatexis is significant for the evolution and rheological properties of the continental crust,linking metamorphism,tec-tonic deformation,and magmatic activities in deep crust.According to the presence or absence of free water,anatexis can be divid-ed into water-fluxed melting and dehydration melting.Dehydration melting involves the breakdown of hydrous phases,such as muscovite,biotite or amphibole.Generally,dehydration melting reactions begin at～650℃and produce melt,peritectic garnet and K-feldspar.Melt resulting from dehydration melting is water unsaturated,characterized by high Rb,high Rb/Sr ratio,high 87Sr/86Sr ratio,and low Sr,Ba,Ca.Melt productivity of dehydration melting reaction is controlled by P-T condition and water con-tent in rock,and it is only possible to produce a large amount of melt at granulite facies.Water-fluxed melting reactions involve the presence of free water.Its most significant feature is that the temperature required is relatively low,and can produce voluminous melting at amphibolite facies.The resulting melt is water-saturated or water unsaturated that can extract from the source.Melt de-rived from water-fluxed melting reactions has high Sr,Ba,Ca,low Rb/Sr ratio and low Rb.Anatexis has a profound impact on the thermodynamic and rheological properties of the rocks.At the same time,the movement of melt out of the lower continental crust promotes the chemical differentiation of the crust and forms a wide range of leucogranite,playing a crucial role in the origin,reworking,and stability of the continental crust.
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