The simple mineral assemblage of serpentinite and the extensive thermobaric stability range of its primary mineral,serpentine,pose challenges in determining the thermobaric conditions of the serpentinite.This paper addresses this issue by utilizing high-pressure experiments,establishing that Ti-chondrodite serves as a diagnostic mineral for serpentinite undergoing ultra-high pressure metamorphism.Based on experimental observations,Ti-chondrodite is found to form within the temperature range of 600～700℃,reaching pressures of 3.0～3.5 GPa,signifying its stability at pressures exceeding 3.0～3.5 GPa.However,temperatures above 750℃ lead to a gradual reduction and eventual disappearance of Ti-chondrodite.The experimental conditions define the determination of the upper pressure limit for Ti-chondrodite.Ti-clinohumite typically forms earlier than Ti-chondrodite and persists lon-ger,exhibiting a broader range of stability.In this experiment,a noteworthy observation is the intergrowth of Ti-chondrodite,Ti-clinohumite,and olivine.The observed phenomena in this experiment align with natural occur-rences.Under the conditions of low temperature and high pressure,due to the similarity of the structure of these three types of minerals,Ti-clinohumite and olivine usually appear each other's nuclear edge.With the increase of temperature,Ti-clinohumite appears in olivine as patches or lamellae until it finally decomposes.The appearance of Ti-chondrodite depends on the temperature and pressure:under the conditions of low temperatures and low pres-sures,Ti-chondrodite is unstable and decomposes into Ti-clinohumite,then the phenomenon of Ti-chondrodite coa-ted with Ti-clinohumite appeares;under the conditions of low temperatures and high pressures,the Ti-chondrodite becomes stable,and the Ti-chondrodite develops on the edge of Ti-clinohumite;at high temperatures,Ti-chon-drodite is unstable and exists in the form of lamellae in olivine or Ti-clinohumite.This study establishes Ti-chon-drodite as an indicator of ultrahigh-pressure metamorphism for serpentinites in cold subduction zones.Detailed pet-rographic investigations elucidate the behavior of titanium-humite minerals during the metamorphic process,offering a theoretical foundation for the examination of ultramafic rock metamorphism.
关键词
高温高压实验/蛇纹岩/钛粒硅镁石/钛斜硅镁石/变质反应
Key words
high pressure experiment/serpentinite/Ti-chondrodite/Ti-clinohumite/metamorphism
维普
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