The Study On Volcanic Rocks Of Permian In Santanghu Basin,Xinjiang

Santanghu basin,which is located in the east of Xinjiang, is the important part of Paleozoic orogenic belt in northern Xinjiang. It is lined-to-lined with Aermantai, Wukungu-Kupu depression and Kelamaili tectonic zone,all of that are making up the north-western basin and mountain tectonic zone as a whole in eastern area of Xinjiang.The eruption of Permian volcanics in basin was not only forming a significant substance-construction during the developing of the basin, but their rock association,isotope dating and geochemical characteristics provided the objective basis for the forming era,dynamic background and pale-tectonic settings of the basin. At the same time,the study of the volcanic rocks would have offered an important type of rock association for reservoir of Permian oil source rock related and oil-forming mechanism.By summarizing analysis of Permian volcanic rocks in Santanghu basin,including its isotope geochronology, areal stratigraphic correlation, reflection of seism and logging, petrofacies and distribution in time-space, petrology and its geochemistry,volcanism related oil gas reservoir and so on, some primary conclusions were obtained as follows:1. By using several isotope methods such as 40Ar-39Ar,zircon U-Pb SHRIMP,K-Ar and the study of biostratigraphy, it was concluded that Kalagang formation of Santanghu basin is a lithostratic unit with characteristic of diachroneity.The age of this formation is from late-Carboniferous to early-Permian(Permo-Carboniferous), so it has an effect on the distribution of volcanic rocks in different time of Permian. It's indicate that there is no volcanic eruption of middle-Permian within Tiaohu depression, only exist in its south-edge; but there is a massive eruption of Kalagang formation. Contrastingly,Malang depression show volcanic rocks in any time of Permian and each time own have different extent eruption.2. According to the data of seism and logging,there have established the lithofacies modal of volcanic rocks and the distributions of volcanic rocks in each time of Permian within basin combining with the information of isotope dating,seism,logging,some related biologic-fossils.To sum up,the volcanic rocks of Kalagang formation is volcanic series which mainly made up by outbreak facies and overflowing facies such as andesite, dacite,rhyolite and a small amount basalt.They possess of wide distribution,great thickness and continuously in cross direction. But the volcanic rocks of Lucaogou formation andTiaohu formation is just erupted in Malang depression and south-western edge of Tiaohu depression,and that more thicker especially in napping zone of southern edge which is composed of medium-basic eruptive with overflowing facies like basalt and basaltic andesite.3. Based on the analyzing results of major elements, REE and trace elements of Permian volcanic rocks in basin, its palaeo-tectonic settings would be judged more objectively. The gross of REE is changed greatly( 92ppm - 207.93ppm ). LREE/HREE ratio show the characteristics ranging from 3.8 to 10.40. Different vocanic rocks are all riched in LREE, no obviously Eu anomaly( 5 Eu=0.92 ~ 1.13) or positive anomaly lightly and LREE enrichment.Nb and Ta relativing to Th and Ce depleted strongly and showing "TNT'negative anomaly,which is similituded with characteristics of "the lagged arc volcanic rocks".This type of Vocanicle not only show the continental setting in post-collision,but also take the geochemical information of subduction zone. Combining with areal geological data,it was from late-Devonian to early- Carboniferous when there have finished subduction of oceanic crust,and middle-late Carboniferous when collided to orogeny,and the early-Permian became the key time of tectonic conversion in Santanghu basin and the whole northern Xinjiang too. Consequently,the volcanic rocks of Permian of basin would be formed in extention setting of post-orogenic and Santanghu basin would be the extentioning and depressing basin overriding to the orogenic belt of fore-Permian.4. The...