Microstructures and Melt Characteristics of Deformed Quartz Diorite Under High Temperature and High Pressure
详细信息
- 责任者：Liu Gui(State Key Laboratory of Earthquake Dynamics ; Institute of Geology ; China Earthquake Administration ; Beijing 100029 ; China) ; Zhou YongSheng
- 刊名：Acta Petrologica Sinica
- 出版年：2012
- 卷期：28(3)
- 页码：p.1005-1016
- issnNo：ISSN1000-0569
- isbnNo：CN11-1922/P
摘要
This paper focus on microstructures and deformation mechanism as well as partial melt of dehydrated hornblende in experimental deformed quartz diorite samples. The effect of plagioclase fabric to the rheological strength was studied under optical microscope, and melt distribution and chemical composition were analyzed using microprobe. Microstructure observation reveals that the deformation mechanisms of deformed samples changed from brittle-plastic transition to dislocation climb and dynamic recrystallization with temperature increasing. Under high temperature, partial molten happened accompanied with dehydration of hornblende and the melt is nonequilibrium and heterogeneity both in distribution and chemical composition. Melt appeared around grain rims of dehydrated hornblende and biotite, or in grain boundaries of hornblende and plagioclase. The chemical composition of melts is strongly dependent to minerals which participated in melting. The contents of SiO2 and Al2O3 in melts at the rims of hornblende and biotite are lower and contents of FeO and MgO are higher, but contents of SiO2 and Al2O3 in melts at the rims of plagioclase are higher and contents of FeO and MgO are lower, the chemical composition of melts at grain boundaries of plagioclase and hornblende are between that of two minerals. The phenomenon of nonequilibrium and heterogenous melting could explain forming mechanism of leucosome and mesosome in migmatite, the melt with richer SiO2 and Al2O3 could crystallize to leucogranite, and the melt with poor SiO2 and Al2O3 could crystallize to mafic rocks. Dehydration of hornblende was effected by sealed environments of samples. It is found that hornblende did not dehydrated when samples were packed closely using thin nickel film, but most of hornblende grains dehydrated when samples were not packed, and water from dehydraion sealed to open environments, which implicated that open system in crust, such as detachment faults, could promote dehydration and partial melting of hornblende. The mechanical data and microstructures reveal that rheological strength is obviously higher when orientation of coarse grain plagioclase is nearly perpendicular with max principal stress, which suggest that rocks are hard to deformation when foliation is perpendicular to the orientation of the maximum principal stress, while parallel to foliation, it promotes rock deformation, and favorable for developing detachment fault.