Provenance of Devonian Wenquan Formation from Changning-Menglian Suture Zone and Its Implication for Early Evolution of Paleo-Tethys
The Changning-Menglian suture zone is the main ocean of the Paleo-Tethys which is considered to be opened in the Devonian according to previous studies.Recently,some scholars put forward that it was formed in the Early Paleozoic.It is a controversial topic that when and how it opened.In this paper,samples were collected from the oldest strata Wenquan Formation within the suture zone,detrital zircon chronology of them obtain similar characteristics,showing two distinctive age peaks at～440 Ma and～980 Ma with other age population around 600 Ma,780 Ma,1 100 Ma,2 500 Ma,respectively.Zircons with～440 Ma have better crystalline morphology and more prominent magmatic oscillation zones,as well as a wide range of Lu-Hf isotopic compositions with in-situ εHf(t)values from-11.9 to+7.2.Zircons comprising the major age peak at～440 Ma are from the andesite dominant volcanic arc in the Lincang block and western Simao block,while is supported by the andesitic fragment in thin sections.Zircons forming the secondary age peak at～960 Ma come from the Gondwana.Zircons whose age larger than 500 Ma have rounded shape come from long distance transportation or resediments from Pre-Devonian sandstone.To sum up,the Lincang and Simao blocks located to the east of the suture zone are the main provenance of Wenquan Formation,while the Gondwana and Baoshan block contributes a small number of debris,based on sedimentology,petrology and detrital zircon chronology.The Wenquan Formation deposited on the west side of the Paleo-Tethyan ophiolites,but it received detrital materials from the opposite continental margin.Thus,the main Paleo-Tethyan Ocean basin was not broad enough to cut off the transport of detrital materials.It was a narrow basin in the Devonian during the rifting stage,rather than a mature,broad pelagic oceanic basin.
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