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- Title
High-Ti phengite in the eclogitic rocks at Yangkou from the Sulu.
- Authors
Zhang, Lingmin; Liu, jingbo
- Abstract
The Yangkou eclogitic rocks from the Sulu ultrahigh-pressure metamorphic belt can be classified into four typesbased on the rock textural features: coronal metagabbro, coronal eclogite, fine-grained and coarse-grained eclogite,which formed in a prograde metamorphism during the subduction-collision between the north China and Yangtzecratons. Phengites in the four rock types range from 0.20 to 3.90 wt% TiO2, with 1.02 to 3.90 wt% in coronalmetagabbro, 0.59 to 1.31 wt% in coronal eclogite, 0.65 to 1.41 wt% in fine-grained eclogite and 0.29 to 0.75 wt%in coarse-grained eclogite, respectively. Ti change of phengites may be described as the substation of AlVI + Si =AlIV + Ti in association with the substitution of Ba + AlIV = K + SiIV and dissolution of biotite component. HighTi contents in phengites can be attributed to the result of high-temperature metamorphism, which is evidencedby (1) high-pressure granulite facies mineral assemblages in local reactive sites in coronal metagabbro, e.g.,albite + kyanite + K-feldspar + zoisite garnet omphacite quartz in plagioclase pseudomorphs and garnet+ K-feldspar + melt at the reactive sites between biotite and plagioclase pseudomorph; and (2) Ti-in-zirconthermometer yields the metamorphic temperature estimates from 680 to 955 C. Zr-in-rutile thermometer is alsoused to estimate the metamorphic temperatures of the rocks, which gives the temperatures from 609 to 685 C at2.0 GPa and 639 to 717 C at 3.5 GPa, respectively. The lack of T> 750 C in rutiles is interpreted as a result ofcompletely resetting of Zr in rutile during the late UHP to retrograde metamorphism. The systematical change ofTi content in phengite and mineral assemblages in the four rock types suggest that the Yangkou eclogitic rockshave suffered an anti-clockwise P–T path. Such P–T path is interpreted that the Yangkou protolith of eclogiticrocks came from the arc setting of hanging wall, and was juxtaposed with subducted continental slab during thesubduction-collision process between the Yangtze and North China cratons.
- Subjects
CHINA; GARNET; ROCKS; METAMORPHIC rocks; PLAGIOCLASE; ECLOGITE; ORTHOCLASE
- Publication
Geophysical Research Abstracts, 2019, Vol 21, p1
- ISSN
1029-7006
- Publication type
Article