Yunnan South Lancang Tectonic-magmatic With The Early Jurassic Post-collisional Volcanic Rocks

The early Jurassic post-collision of the South Lancangjiang tectonomagmatic belt of Yunnan,means the early Jurassic volcanic rocks is situated from Yunxian County to Jinghong County,Southwester Yunnan Province,along the South Lancangjiang River,It is more than 400km length,and range from 15 to 80km in width.Petrographic category are complicated,including busic rock, intermediate rock, acid rock and ultramafic rock..Volcanic rocks compose with clastic rocks together,form sedimentary-eruption rhythm or cycle.According to producing place and rock association,the South Lancangjiang tectonomagmatic belt can be divided into four zone:Mingle-Nanxianhe, Chahe-Weili, Bangdongjie-Pingchun and Kanjiehe-tuantian.The volcanic rocks in Mingle-Nanxianhe Zone and Bangdongjie-Pingchun Zone,are characterized by high alk,low Fe and Mg,belong to Shoshonite series;The volcanic rocks in Mingle-Nanxianhe Zone tend from under-saturated, metaluminous, alkalic to over-saturated, peraluminous , subalkalic; The volcanic rocks in Bangdongjie-Pingchun Zone,tend from over-saturated, peraluminous to saturated, metaluminous.The both are HREE-flat and shrink,LREE-tip-to-right and spread,The major feature of the evolution of magma is LREE-divided. The volcanic rocks in Chahe-Weili Zone belong to calc-alkalic series, over-saturated, peraluminous. E REE increased with SiO₂. ∑REE alteration is the major feature of magma evolution.Trace elements model show Th-rich,Zr, Ti, P-depleted.Be correlated with representative volcanic rocks in the wold,they have typical characteristics of arc volcanic rocks,at the same time,have some characteristics of continental intraplata volcanic rocks.The origination of the magma is related with the dehydration of the subducting plate of the Palezoic Tethy Sea and the early tension of the form of the Lancangjiang belt red layer basin.It is special magma generated in basin - orogen transformation stage.It has the following feature:(1) Petrographic category are complicated,occurred during busic rock to acid rock.Eruption rhythm transformated frequently from busic to intermediate,or, busic to intermediate-busic,intermediate-busic to acid.(2)It commonly fall into the field of B-S₁-S₂-S₃-T-R in diagrams of TAS,between alkali olivine basaltic and subalkali in SiO₂—alk,no F-rich tendency in FAM,It belongs to calc-alkalic series and tends to Shoshonite series.(3)REE content is partial to low or middle,LREE-rich or flat,HREE-flat, Trace elements model show Th-rich,Zr, Ti, P-depleted.(4)The determination of tectonic setting show typical characteristics of arc volcanic rocks,and some characteristics of continental intraplata volcanic rocks.The magma has strong inheritance in the early character of the source region,be different to the tectonic setting of eruption period. It belongs to post-collision volcanism.