The Study Of Geochemistry Characteristics Of The Hala’alate Formation Volcanic Rocks In Western Junggar,XinJiang

This article through to hala’alate formation volcanics petrology，chronology，mainelements and trace element geochemical system research，the following main achievementsand cognition：1. The predecessors’ in hala’alate formation of limestone mezzanine found abundantfossils，including brachiopods，mosses，insect and so on，all of late carboniferous epoch atthat time，and the author in the formation rhyolite zircon U-Pb age was304±3.1Ma（MSWD=0.63，95%confidence level），307±5.5Ma（MSWD=1.8，95%confidence level）consistent with previous conclusion， therefore， will hala’alate formation set to latecarboniferous epoch.2. Hala’alate formation rocks in the study area is a zonal distribution，rock assemblageis： the conglomerate，sandstone，volcanic breccia and volcanic lava，a small amount ofvolcanic agglomerate，formation as a whole in the volcanic rocks，pyroclastic rocks andcharacteristics of coarse clastic rocks.Basalt，andesite，basalt，andesite，dacite，rhyolitecombination is complete，may is bi-model volcanic rocks. Formation s will be divided intoseven segments and paragraphs is conformable contact more，local fault reconstruction，theoverall equivalent of hala’alate is a formation of lower layer type volcanic strata.3. Hala’alate formation，according to the geochemical characteristics of SiO2contentwas57.09%on average，show it as the acid，the alkali content is higher，relatively rich Napoor K，belong to calc-alkalic series，have lower TiO2，CaO，higher Al2O3，largerdifferentiation index （DI），felsic index （FL） and magnesium iron （MF） reflects thegroup volcanic rocks in the process of magma evolution has higher separation andcrystallization.Spider diagram of trace element show that hala’alate formation volcanic rocksshow strong loss of Nb，Ta，high field strength elements （HFSE） and relative enrichmentof Ba，Rb，K and other large ion lithophile elements （LILE） geochemical properties，hinted that it may be associated with subduction， enrichment mantle shows certaincharacteristics.Rare earth element distribution curve， according to the sample withenrichment of light rare earth elements and heavy rare earth relative loss of the right type ofcharacter，（La/Yb）Nbetween1.52~15.88，shows obvious differentiation and heavy rareearth elements，with a mean of6.27，and is similar to the value of island arc calc-alkaline volcanic rocks （La/Yb）N.4. Nature of the volcanic rocks in the provenance is related to the subduction，theprimitive magma is rising by the subduction zone fluid metasomatism of overlying mantleformed by partial melting, reduce sediment melt to join, and in the process of magma risinghas experienced a certain degree of crustal contamination and high separation andcrystallization.