Geologic Features,Provenance Nature And Tectonic Significance Of Hongshuichuan Formation Located In The Southern Slope Of The East Kunlun Orogenic Belt(Eastern Part)

The depositional sequences in the orogenic belt play an indispensable role in orogenic belt tectonic evolution research. The source nature of clastic rocks can provide successive evidences for orogenic belt tectonic evolution. In this paper,We conducted a comprehensive study on the provenance nature of Hongshuichuan formation which belongs to lower triassic and is exposed in the southern slope of the East Kunlun orogenic belt(Eastern part).In the study,We used lots of research measures such as sedimentary petrology, conglomerate gravel statistics, debris component statistics in the clastic rock,geochemistry and detrital zircon geochronology.We can build a Subduction orogenic model of the south margin of East Kunlun(part of Paleo Tethys ocean)in the Early Triassic through the study.Also, This study can provide Sedimentology evidence for the tectonic evolution of the south margin of East Kunlun(part of Paleo Tethys ocean).In the study,We obtained the following recognition and progress:1、Hongshuichuan formation can be divided into six scctions according to lithology.It is belonged to lower triassic and exposed in southern slope of the East Kunlun orogenic belt(Eastern part).The first section is green and red detrital rock;The the second section is light gray to grey-green clastic rock;The third section is gray black to dark gray thin limestone;The fourth section is grey to black grey limestone and clastic rock;The fifth section is deep phase muddy rock;The sisth section is microclastic rock.From the aspects of sedimentary facies,the first and second section belong to a fan delta depositional system;The third and fourth section belong to mixed shallow shelf depositional system;The fifth section belongs to semi-deep to deep sea muddy fan depositional system;The sixth section belongs to mixed littoral-neritic to shallow shelf depositional system.2、The results of conglomerate gravel statistics shows that The depositional depth of northern zone of Hongshuichuan formation(a section) is more shallow than southern zone’s.This phenomenon indicates that northern sedimentary basin’s water is more shallow than the southern’s.So the source of Hongshuichuan formation maybe located in the north of the sedimentary basin.The source rocks include metamorphic rock,granite and vein quartz,which shows the characteristics of uplift base.This conclusion suggests that the tectonic background of Hongshuichuan formation’s source aera is active continental margin initially.3、The results of debris component statistics in the clastic rock shows that the tectonic background of the low Hongshuichuan formation(the first and second section)’s source aera is active continental margin,and the up formation(fourth、fifth and sisth section)’s is continental island arc.The source area of low Hongshuichuan formation(the first and secondsection)is uplift base, the up formation(fourth、fifth and sisth section)’s is continental island arc.4、The clastic rock Geochemical characteristics show that the tectonic background of the low Hongshuichuan formation(the first and second section)’s source aera is active continental margin,and the up formation(fourth、fifth and sisth section)’s is continental island arc. The source rocks of the low Hongshuichuan formation(the first and second section) include quartzite, granite, granodiorite and felsic volcanic rocks etc.These of the up formation(fourth、fifth and sisth section)include granodiorite, andesite, felsic volcanic rocks and so on5、The LA-ICP-MS detrital zircon U-Pb age spectrum of the first section reveals that the main source is the Caledonian magmatic arc.But the first section’s Geochemical characteristics suggest its source maybe the uplift base.Therefore,its source include both Caledonian magmatic arc and Pre Cambrian metamorphic rocks.6 、 After comprehensive analysis on the information about the provenance of Hongshuichuan formation,We think that the tectonic background of the low Hongshuichuan formation(the first and second section)’s source aera is active continental margin,and the up formation(fourth、fifth and sisth section)’s is continental island arc.The source of low Hongshuichuan formation(the first and second section)is mixed Caledonian magmatic arc with Pre Cambrian metamorphic rocks;And that of the up formation(fourth、fifth and sisth section)is mixed Caledonian magmatic arc and early Indosinian continental margin arc.The source rocks of the low Hongshuichuan formation(the first and second section)include quartzite, granite, granodiorite and felsic volcanic rocks etc;And these of the up formation(fourth、fifth and sisth section)include felsic volcanic rocks, granodiorite, andesite,quartzite and granitic gneiss...