THE STRUCTURES AND MECHANISM OF DEFORMATION OF PODIFORM CHROMITES, AND ITS IMPLICATION FOR SPREADING OF OCEANIC UPPER MANTLE: EVIDENCE FROM PODIFORM CHROMITITE IN ZUNHUA, NORTH CHINA
CHEN Zheng, LI Jianghai, CHENG Suhua and HUANG Xiongnan (Key Laboratory of Orogenic Belt and Crustal Evolution, School of Earth and Space Sciences, Peking University, Beijing 100871, China)
Podiform chromitite is a characteristic mineral deposit in ophiolitic complex. Its various textures indicate important implication for the spreading of oceanic upper mantle and mineralization. Thousands of ore samples from the Neoarchean podiform chromitite in Zunhua have been checked in detail, to identify high-temperature deformation structures, including banded, flattened antinodular textures, mylonitic foliation and so on. Through integrated geological correlation, the structural deformation of podiform chromitites is ascribed to being related to the lateral spreading process of oceanic lithosphere. As podiform chromitite shows stable physical and chemical properties at high temperature, it is very useful to investigate the early tectonic evolution of oceanic lithosphere, and can provide important clues to the dynamic mechanism of oceanic upper mantle.