摘要
华南花岗岩中存在两类矿物组合:（1）铁透闪石+钛铁矿+榍石+磁铁矿+石英;（2）钛铁矿+方解石+石英+磁铁矿+榍石。可通过以下关系分别计算上述两组矿物组合的岩浆氧逸度。组合（1）为: logfo2=-24940.31/T+9.25+243.43（P-105Pa）/T+0.86logfH2O-0.86logα铁透闪石组合（2）为: logfo2=-3673.68/T-37.73+590.53（P-105Pa）/T+6logfco2岩浆作用过程的氧逸度（fo2）是控制磁铁矿、钛铁矿、榍石等铁、钛副矿物形成和稳定的重要因素。
Magnetite,titanite and ilmenite are common Fe-Ti accessary mineral in granitoid,and have important genetic signifficance. Based on the study of main rock-forming minerals and accessary minerals, it has been proved that there are two kinds of mineral assemblages in the granitoid of South China; (1) ferrotremolite+ilmenite+titanite+magnetite+quartz; (2) ilmenite+calcite+quartz+ magnetite+titanite. The relation among oxyen fugacity (f_(o2)), temperature (T) and pressure (P) can be shown as follows:
For the mineral assemblage ( 1 ):
logf_(o2) = -24940.30/T + 9.25+ 243.43(P-10~5Pa)T+0.86logf_(H2O)-0.86logα_(ferrotremolite)
For the mineral assemblage (2):
logf_(o2) = -3673.68/T-37.73+590.53(P- 10~5Pa)/T +6 log f_(co2)
By the use of the two formulas, oxygen fugacity of magma can be calculated.
It has also been proved that oxygen fugacity in granitic magma is an important factor in controlling the formation and stability of magnetite, titanite and ilmenite. Magnetite and titanite are formed with relatively high f_(o2), while ilmenite with low f_(o2). The higher the diagenetic temperature and the lower the diagenetie pressure, the higher diagenetic f_(o2) is for the formation and stabilization of the Fe-Ti accessary minerals. The diagenctic oxygen fugacity is higher in the hornblend-bearing granites than that in the granites with no hornblend.
出处
《岩石学报》
SCIE
EI
CAS
CSCD
北大核心
1991年第2期89-94,共6页
Acta Petrologica Sinica
关键词
花岗岩
磁铁矿
钛铁矿
榍石
氧逸度
Granite
Magnetite
Ilmenite
Titanite
Oxygen fugacity
