Doctoral thesis

Ophiolites du protérozoïque de Yanbian et de Shimian (Sichuan, Chine) : pétrographie, géochimie, pétrogenèse et l’environnement géotectonique

ContributorsSun, Chuan Min
DirectorsVuagnat, Marc
Number of pages157
Imprimatur date1992-07-20

The Middle Proterozoic ophiolite complexes of Yanbian and Shimian (Sichuan Province, Southeastern China) occur as allochthoneous fragments embedded within the Late Proterozoic orogenic belt on the western rim of the Yangtse Craton. They are two of the oldest ophiolitic terrains in China. These complexes, dismembered and metamorphosed to greenschist facies during the Late-proterozoic orogenic period, include the following three sequences: mantle-derived tectonite peridotites, plutonic cumulates and submarine volcanics. However, no sheeted-dike complex has been found. Mantle sequence, exposed only in Shimian area, is characterized by serpentinites, in which albitite veins and strongly rodingitized dolerite dikes are also found. These serpentinites were harzburgites, which can be considered as representing a impoverished residual material after a high degree of partial melting of supper mantle (>30%).

Plutonic sequence, which appears in the two areas but better in Yanbian, is composed of ultramafic cumulates (plagioclase dunites and plagioclase lherzolites), Mg-gabbros (troctolites, anorthosites, olivine gabbros), gabbronorites (including olivine-free gabbros), ferrgabbros and minor albitites. This sequence is cut by gabbroic pegmatite veins and doleritic dykes. The petrographical, mineralogical and geochemical studies indicate a tholeiitic differentiation with the following order of appearance of minerals throughout the sequence: olivine + spinel -> plagioclase -> clinopyroxene -> orthopyroxene -> apatite + titanomagnetite + ilmenite -> brown hornblende -> zircon -> quartz. The succession and the chemical composition of the sequence are similar to those of the plutonic rocks of typical Phanerozoic high Ti-ophiolites, even to those of the plutonic rocks dredged from the modern mid-ocean ridges. [...]

Citation (ISO format)
SUN, Chuan Min. Ophiolites du protérozoïque de Yanbian et de Shimian (Sichuan, Chine) : pétrographie, géochimie, pétrogenèse et l’environnement géotectonique. 1992. doi: 10.13097/archive-ouverte/unige:175062
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