摘要
闽东南沿海晚中生代变质带内出露的I型花岗岩、细晶岩和伟晶岩中常包含岩浆成因的石榴子石和原生白云母。其中石榴子石以富Mn ,Fe和贫Mg ,Ca为特征 ,锰铝榴石分子可达 4 0 %～5 0 % ;花岗岩中的黑云母具有明显高的MnO和Al2 O3含量 (分别是 0 .84 %～ 1.2 5 % ,16 .0 4 %～18.0 3% ) ;原生白云母以高Fe和低Al,Na为特征。温压计算表明富铝矿物形成于 75 0～ 6 0 0℃和0 .3～ 0 .2GPa的条件下。岩相学特征和地球化学模拟也都表明这些富铝矿物结晶较晚。长英质矿物早于黑云母和石榴子石结晶与岩浆侵位浅 (结晶压力低 )相关。相图分析指出弱过铝质和高的Mn/ (Mg +Fe)比值 (>0 .0 6 0 )是本区花岗质岩石形成石榴子石的关键化学因素。Mn/ (Mg +Fe)>0 .0 6 0的岩浆可以形成bt+grt或bt+grt+ms组合 ;而Mn/ (Mg +Fe) <0 .0 5 5的岩浆只可能形成bt或bt+ms组合 ;grt+ms组合是岩浆强烈演化的最终产物。除了黑云母成分存在差异 ,本区I型花岗岩的石榴子石和原生白云母成分都与S型花岗岩的相似 ,所以 。
I-type granites, aplites and pegmatites outcropping in Mesozoic metamorphic belt of the southeastern coast of Fujian Province contain commonly magmatic garnets and primary muscovites. The garnets are characterized by high Mn, Fe and low Mg, Ca, up to 40～50% spessartite component. The btotites in the granites also have high MnO and Al_2O_3 contents, up to 0.84～1.25% and 16.04～18.03% respectively. Primary muscovites exhibit high Fe and low Al and Na. T-P calculations indicate that these Al-rich minerals crystallized at 750～600℃ and 0.3～0.2 GPa. Both petrographic features and the geochemical modeling also show that they are the late-stage crystallization phases. Earlier crystallization of felsic minerals than biotite and garnet is related with much lowar crystallization pressure. Phase diagram analyses demonstrate that week peraluminity and high Mn/(Mg+Fe) ratio (> 0.060) are two key factors for the formation of garnet in the granitoids. Granitic magma with Mn/(Mg+Fe) >0.060 may produce bt+grt or bt+grt+ms, and that with Mn/(Mg+Fe) <0.055 only forms bt or bt+ms. Grt+ms assemblage is the ultimate products of strongly evolved magma. Garnet and primary muscovite from these I-type granites have similar composition to those from S-type granites, therefore they cannot be simply used for classifying granite types.
出处
《高校地质学报》
CAS
CSCD
2004年第3期364-377,共14页
Geological Journal of China Universities
基金
国家自然科学基金项目 (批准号 :4 0 132 0 10
4 0 372 0 87)资助
关键词
石榴子石
Ⅰ型花岗岩
矿物化学
岩浆演化
闽东南
garnet
I-type granite
mineral chemistry
magma evolution
southeastern Fujian
