Metamorphic evolution of relict lawsonite-bearing eclogites from the (U)   HP metamorphic belt in the Chinese southwestern Tianshan

doi:10.1111/jmg.12080

CORC > 北京大学 > 地球与空间科学学院

	Metamorphic evolution of relict lawsonite-bearing eclogites from the (U) HP metamorphic belt in the Chinese southwestern Tianshan
	Du, J. X. ; Zhang, L. F. ; Bader, T. ; Chen, Z. Y. ; Lu, Z.
刊名	journal of metamorphic geology
	2014
关键词	Chinese southwestern Tianshan fluid composition lawsonite lawsonite preservation phase equilibria P-T PATH HIGH-PRESSURE METAMORPHISM EFFECTIVE BULK-COMPOSITION CHLORITOID-GLAUCOPHANE SCHIST CALCULATED PHASE-EQUILIBRIA SUBDUCTED OCEANIC-CRUST NORTH QILIAN OROGEN WESTERN TIANSHAN NW CHINA TECTONIC IMPLICATIONS
DOI	10.1111/jmg.12080
英文摘要	In the Chinese southwestern Tianshan (U) HP belt, former lawsonite presence has been predicted for many (U) HP metamorphic eclogites, but only a very few lawsonite grains have been found so far. We discovered armoured lawsonite relicts included in quartz, which, on its part, is enclosed in porphyroblastic garnet in an epidote eclogite H711-14 and a paragonite eclogite H711-29. H711-14 is mainly composed of garnet, omphacite, epidote and titanite, with minor quartz, paragonite and secondary barroisite and glaucophane. Coarse-grained titanite occasionally occurs in millimetre-wide veins in equilibrium with epidote and omphacite, and relict rutile is only preserved as inclusions in matrix titanite and garnet. H711-29 shows the mineral assemblage of garnet, omphacite, glaucophane, paragonite, quartz, dolomite, rutile and minor epidote. Dolomite and rutile are commonly rimed by secondary calcite and titanite respectively. Porphyroblastic garnet in both eclogites is compositionally zoned and exhibits an inclusion-rich core overgrown by an inclusion-poor rim. Phase equilibria modelling predicts that garnet cores formed at the P-peak (490-505 degrees C and 23-25.5 kbar) and coexisted with the lawsonite eclogite facies assemblage of omphacite + glaucophane + lawsonite + quartz. Garnet rims (550-570 degrees C and similar to 20 kbar) grew subsequently during a post-peak epidote eclogite facies metamorphism and coexisted with omphacite + quartz +/- glaucophane +/- epidote +/- paragonite. The results confirm the former presence of a cold subduction zone environment in the Chinese southwestern Tianshan. The P-T evolution of the eclogites is characterized by a clockwise P-T path with a heating stage during early exhumation (thermal relaxation). The preservation of lawsonite in these eclogites is attributed to isolation from the matrix by quartz and rigid garnet, which should be considered as a new type of lawsonite preservation in eclogites. The complete rutile-titanite transition in H711-14 took place in the epidote eclogite facies stage in the presence of an extremely CO2-poor fluid with X(CO2) [CO2/(CO2 + H2O) in the fluid] <<0.008. In contrast, the incomplete rutile-titanite transition in H711-29 may have occurred after the epidote eclogite facies stage and the presence of dolomite reflects a higher X(CO2) (>0.01) in the coexisting fluid at the epidote eclogite facies stage.; Geology; SCI(E); 3; ARTICLE; lfzhang@pku.edu.cn; 6; 575-598; 32
语种	英语
内容类型	期刊论文
源URL	[http://ir.pku.edu.cn/handle/20.500.11897/155429]
专题	地球与空间科学学院
推荐引用方式 GB/T 7714	Du, J. X.,Zhang, L. F.,Bader, T.,et al. Metamorphic evolution of relict lawsonite-bearing eclogites from the (U) HP metamorphic belt in the Chinese southwestern Tianshan[J]. journal of metamorphic geology,2014.
APA	Du, J. X.,Zhang, L. F.,Bader, T.,Chen, Z. Y.,&Lu, Z..(2014).Metamorphic evolution of relict lawsonite-bearing eclogites from the (U) HP metamorphic belt in the Chinese southwestern Tianshan.journal of metamorphic geology.
MLA	Du, J. X.,et al."Metamorphic evolution of relict lawsonite-bearing eclogites from the (U) HP metamorphic belt in the Chinese southwestern Tianshan".journal of metamorphic geology (2014).