CAJ | 학술논문

在拉萨地块林芝杂岩体中新发现的石榴角闪岩矿物组合为石榴子石、角闪石、十字石、绿泥石、斜长石、钠云母以及少量的钛铁矿和磷灰石。石榴角闪岩中石榴石核部富锰（Xsps=0.12~0.15）贫铁（Xalm=0.45~0.50）而石榴子石边部相对贫锰（Xsps=0.01~0.03）富铁（Xalm=0.60~0.65），表明石榴子石的核部和边部分别形成于变质作用两个不同阶段。从核部到边部，镁铝榴石升高而钙铝榴石降低，表现为进变质环带特征，这表明石榴子石核部形成于进变质过程。生长在不同的变质阶段的角闪石具有不同的成分特征，作为变质基性岩中罕见的富铝矿物，十字石的结构特征记录了不同变质阶段的信息，结合石榴石的成分和结构特征，为相平衡模拟研究其P?T演化过程提供了可能。我们利用Perplex相图模拟软件在Mn?NCKMASHO体系中模拟出该石榴角闪岩的视剖面图，利用石榴子石边部镁铝榴石和钙铝榴石含量等值线确定出石榴角闪岩峰期温压为：610~630oC，12×105~13×105 kPa，对应峰期矿物组合为石榴子石，角闪石，十字石和白云母。同时结合十字石保存的退变信息得到该石榴角闪岩经历了一个顺时针的变质演化轨迹。
재랍살지괴림지잡암체중신발현적석류각섬암광물조합위석류자석、각섬석、십자석、록니석、사장석、납운모이급소량적태철광화린회석。석류각섬암중석류석핵부부맹（Xsps=0.12~0.15）빈철（Xalm=0.45~0.50）이석류자석변부상대빈맹（Xsps=0.01~0.03）부철（Xalm=0.60~0.65），표명석류자석적핵부화변부분별형성우변질작용량개불동계단。종핵부도변부，미려류석승고이개려류석강저，표현위진변질배대특정，저표명석류자석핵부형성우진변질과정。생장재불동적변질계단적각섬석구유불동적성분특정，작위변질기성암중한견적부려광물，십자석적결구특정기록료불동변질계단적신식，결합석류석적성분화결구특정，위상평형모의연구기P?T연화과정제공료가능。아문이용Perplex상도모의연건재Mn?NCKMASHO체계중모의출해석류각섬암적시부면도，이용석류자석변부미려류석화개려류석함량등치선학정출석류각섬암봉기온압위：610~630oC，12×105~13×105 kPa，대응봉기광물조합위석류자석，각섬석，십자석화백운모。동시결합십자석보존적퇴변신식득도해석류각섬암경력료일개순시침적변질연화궤적。
The newly found staurolite-bearing garnet amphibolites in Nyingchi complex of the Lhasa Block have the mineral <br> assemblage of garnet, amphibole, staurolite, chlorite, plagioclase, mica and minor ilmenite and apatite. The cores of the garnet in the garnet amphibolite are extremely rich in Mn (XSps=0.12-0.15) and poor in Fe (XAlm=0.45-0.50), whereas their rims are relatively Mn poor (XSps=0.01-0.03) and Fe rich (XAlm=0.60-0.65), implying that the core and the rim of the garnets belong to two metamorphic generations. Xpy increases and Xgr decreases from the garnet core to the rim, indicating characteristics of prograde metamorphic zonation. The amphibole growing at different metamorphic stages have obvious composition differences. Staurolite, as an uncommen aluminium-rich mineral in the metabasite, has also recorded different metamorphic processes in their microstructures. In combination with the garnet compositional profile, it is possible to calculate the P-T evolution by phase diagram. The authors modeled the pseudosection of the staurolite-bearing garnet amphibolite under the model system of Mn-NCKMASHO, using Perple-X program with the help of Xpy and Xgr isopleths of the garnet, and obtained the peak metamorphic condition of 620oC and 12kbar. The peak mineral assemblages are garnet, amphibole, staurolite and mica. In the meanwhile, the clockwise P-T path has also been demonstrated by the microstructures in the staurolites, suggesting that the staurolite-bearing garnet amphibolites have experienced three stages of metamorphism.