Dismembered Guadalupian (Middle Permian) seamounts within the Yarlung-Tsangpo Suture Zone: Implications for the opening time of the Neo-Tethys Ocean

Abstract

The opening time of the Neo-Tethys Ocean has been the subject of intense debates. In this paper, we document several exotic limestone blocks within the ophiolite mélange in the southern branch of the Yarlung-Tsangpo Suture Zone (Daba-Xiugugabu ophiolite subzone), which provide insights into the early evolution of the Neo-Tethys Ocean. The limestone blocks contain diverse fusulines such as Neoschwagerina and Kahlerina in the limestones in the Gyanyima area (Burang County) as well as Codonofusiella, Lantschichites, Neoschwagerina, Chusenella, Yangchienia and Kahlerina in the Zhalairi area (Zhongba County). These fusuline assemblages totally suggest a Middle Permian (late Guadalupian) age. The faunal characteristics of the fusulines indicate marine conditions that were warmer than the Gondwanan-type fauna in the Tethys Himalaya Terrane and the Zhongba-Zhada microcontinent, indicating that the limestone blocks were originated from a lower latitude to the north of the Gondwana continent. They further suggest that the limestone blocks are not in situ but derived from the obducted mélange from the ophiolites in the north of the Zhongba-Zhada microcontinent (Dajiweng-Saga ophiolite subzone), further suggesting a homology between the two ophiolite belts on both sides of the Zhongba-Zhada microcontinent. Considering the paleobiogeographic affinities and the data from paleomagnetic and geochemical studies of the associated basalt, it is proposed here that a seamount chain was developed in the Neo-Tethys Ocean during the late Guadalupian time, and that the Neo-Tethys Ocean had opened during the Early Permian (Cisuralian) times.