Chronology,geochemistry and tectonic significance of the Taotugaen-wusu diabase porphyrite in the northern margin of the Qaidam Basin
The early Paleozoic Taotugaenwusu diabase-prophyrite,outcroped in the Huaitoutala area in the northern margin of the Qaidam Basin,intruded into the Cambrian-Ordovician Tanjianshan Group.It contains important information about the evolution of the northern Qaidam oceanic basin and is of great significance for studying the early Paleozoic accretionary orogeny.In this paper,the petrology,geochemistry and isotopic chronology of the diabase-prophyrite have been studied.Its magma source,petrogenesis and tectonic environment have been discussed by analyzing characteristics of major,trace and rare earth elements of the rock samples The results show that the diabase-prophyrite has zircon 206Pb/238U age of 447 Ma.The rock is relatively alkaline,with average value of the Ritman index of 1.785 which is＜3.3.It belongs to the calc-alkaline rock.The rock samples are relatively enriched in LILE,depleted in HFSE,with generally right-declined REE distribution patterns and not obvious Eu anormalies,indicating that its magma was not very highly differentiated.The(Th/Nb)N mean of 2.485(＞1),Nb/La mean of 0.555(＜1),La/Ta mean of 31.06(＞25),Sm/Ndmean of 0.215(＜0.3),and Rb/Sr mean of 0.145(which is between the upper mantle(0.034)and the earth's crust(0.35))indicate that the magma was originated from the lithospheric mantle and has characteristics of the mixture of crust and mantle materials.Combined with the regional geological background,it is believed that the diabase-prophyrite was formed in the accretionary orogenic tectonic environment of the Late Ordovician oceanic crust subduction.
Diabase prophyriteGeochemistryU-Pb zircon datingIsland arc basaltQaidam margin tectonic belt
万方数据
维普
