Genesis of oxidized- and reduced-type granites
Genesis of oxidized- and reduced-type granites
复制标题
DOI：
10.2113/gsecongeo.92.1.81
复制
发表时间：
1997-02
期刊：
影响因子：
5.8
通讯作者：
T. Takagi;K. Tsukimura
中科院分区：
文献类型：
--
作者：
T. Takagi;K. Tsukimura
本文从热力学角度讨论了氧化型（磁铁矿系列）和还原型（钛铁矿系列）花岗岩的成因。在1/T-f（sub O2）图上，SO2-H2S缓冲线与普通辉石-磁铁矿-石英缓冲线相交，说明岩浆中的SO2可随温度降低氧化普通辉石形成磁铁矿。当岩浆中SO2含量大于250 ppm，f（sub O2）受SO2-H2S缓冲层的限制时，岩浆形成氧化型花岗岩（> 0.2%的磁铁矿）。当SO2含量小于250 ppm时，岩浆凝固为还原型花岗岩（磁铁矿含量小于0.2%）。如果岩浆的f（sub O2）被H2 O-H2、CO2-CO或CH 4 -CO2缓冲，则磁铁矿不能结晶，形成还原型花岗岩。因此，氧化型和还原型花岗岩的成因可归因于岩浆中挥发分的差异。
The genesis of oxidized-type (magnetite series) and reduced-type (ilmenite series) granites is discussed on the basis of thermodynamic considerations. We show that SO 2 in the magma can oxidize augite to form magnetite with decreasing temperature because the SO 2 -H 2 S buffer line intersects with the augite-magnetite-quartz buffer line on a 1/T - f (sub O 2 ) diagram. When the magma contains SO 2 above 250 ppm and the f (sub O 2 ) is constrained by the SO 2 -H 2 S buffer, the magma forms oxidized-type granites (>0.2 modal % magnetite). On the other hand, when the SO 2 content is less than 250 ppm, the magma solidifies as a reduced-type granite (<0.2 modal % magnetite). If the f (sub O 2 ) of the magmas is buffered by H 2 O-H 2 , CO 2 -CO, or CH 4 -CO 2 no magnetite will crystallize and reduced-type granites will be formed. As a result, the genesis of oxidized-type and reduced-type granites can be attributed to the difference in volatile components in magmas.