Geochemistry And Implications Of Basalts From Ophiolite In Northern Xinjiang

Paleo-Asian Ocean tectonic domain and Tethyan tectonic domain are the main two tectonic belts in northern and south-western China, respectively. They have different tectonic evolution history and distributions. This thesis present systematic study of elements and Sr-Nd-Pb isotopic geochemistry of the basaltic and related rocks in western Junggar and Tienshan in northern Xinjiang, in an effort to reveal the features of the Paleo-Asian Ocean mantle domain, to test if they belong to the Tethyan tectonic domain, or whether a significant boundary between the above two mantle domains.Three parts were included in this thesis. Firstly, the characteristics of major elements, trace elements and REE for all samples indicate that Dalabute ophiolite in western Junggar show N-MORB and E-MORB affinities. which formed in the the middle ocean ridge. Pillow basalts from Tangbale ophiolite show characteristics of E-MORB, and possibly originated from the strench environment in the beginning of Island arc. Secondly, by compareing with Tethyan oceanic ophiolite, the Sr-Nd-Pb isotopic composition of Dalabute basalts show that the mantle sources are similar to the MORB-type basalts in Indian Ocean, and so conformity to the MORB-type basalts in the Tethys. In the third part, a systematic comparison of trace element ratio among all basalt samples with the data of Tethys and West Qinling-Songpan tectonic node. Generally, trace element ratio characteristics of ophiolite in the western Junggar and northern Tien-shan are consistent to Tethyan ophiolites.To sum up of the mention above, although the Paleo-Asian Ocean and Tethys are tectonically belong to different tectonic domains, they show similar trace element and isotope geochemical characteristics. Two possible expanations could be applied for this. One is that the two diffferent domains have the same gechcemical features, another one is that the study area in northern Xinjiang is a part of the Tethyan domain, the real boundary between the two domains should site in further north position comparing to our area.