AN EARLY CRETACEOUS TRENCH-PLUME INTERACTION IN SOUTHERN TIBET: UNDERSTANDING COMPLICATED OROGENIC PROCESS IN GLOBAL TECTONICS

Plates and plume generally move in lateral/horizontal and vertical, respectively. However, there has little consideration on their interaction in an orogenic belt. Our study shows that southern Tibet has experienced such an interaction during Early Cretaceous. Southern Tibet locates to south of Gangdese arc, which develops since Jurassic, and 130 Ma Yarlung-Tsangpo ophiolitic belt, and it was regarded as northern margin of Indian Craton or a component of NW Australian plate. Other researchers noticed that some fragments of oceanic crusts outcropping in southern Tibet and Triassic sediments can compare with those in the Indo-Burma Range in Myanmar, component of an accretionary complex, and alternatively hypothesized that southern Tibet located at forearc setting. However, when it formed is unknown.

We took surveys on structural characteristics in the Triassic, Jurassic and Early Cretaceous strata from Zedang to Cuomei, southern Tibet. Overturned folds, most of whose vergence towards south, are widespread, indicating generation near trench or in accretionary complex in subduction zone, not in a rifting setting. Plenty of outcrops show that the folds are truncated by ~130 Ma dikes. These dikes include OIB-type mafic dikes, diorite and dacite dikes. The mafic dikes have about 20% MgO content for parental magmas of the picritic porphyrites through olivine-liquid equilibrium calculation, corresponding to mantle potential temperature at about 1560ºC, which is regarded as products of Cuomei large igneous province (LIP). Therefore, a tectonic model of subduction zone interacting with the Cuomei LIP can be established.

This model not only implies complicated geodynamics of interaction of horizontal plate’s movement with vertical plume upwelling, but also intrudes high temperature magmatic rocks into forearc setting, where generally develops low to medium temperature ones.

This abstract is dedicated to Prof. Eldridge Moores for his encouragement to JEZ.