| The Tianshan orogenic belt,located in the hinterland of the Asian continent,is an important part of the Central Asian Orogenic Belt(CAOB).It mainly experienced paleozoic collision and proliferation and Meso-Cenozoic reconstituted orogenic activities.Tianshan is divided into East and West Tianshan by the east longitude of about 88°.The East Tianshan can be divided into South,Middle and North Tianshan and Bogda Mountains from south to north,the Turpan-Hami basin sandwiched between the North Tianshan Mountains and the Bogda Mountains,reveals complete strata from the late Paleozoic to the Cenozoic,and where rich in uranium,coal,oil and gas and other resources.At present,some scholars have carried out some research on the uranium mineralization of the southwestern margin of the Tuha basin.However,there are still few studies on the uranium deposits,the uranium source,the formation of uranium deposits and the changes or preservation after mineralization..Therefore,the study of the Mesozoic and Cenozoic tectonic uplift and sedimentary evolution processes in the southwestern margin of the Tuha basin can not only deepen the understanding of the basin-mountain coupling relationship in the eastern Tianshan area,but also help to identify the source and mineralization of uranium resources in the Tuha Basin.The post-mineralization changes provide a scientific basis for the exploration and development of uranium resources in the Tuha basin.Based on the study of tectonic deformation and sedimentary evolution in the southwestern margin of Tuha basin,the relationships among tectonic deformation,sedimentary evolution,thermal evolution and uranium mineralization in the study area are analyzed and discussed by means of the thermal chronology of apatite fission track,zircon U-Pb chronology,trace and rare earth elements of fine clastic rocks,and Pb isotopes,electron microprobe and ? etching track.The study shows that the tectonic deformation pattern of the Shihongtan-Baxiankou area in the southwestern margin of the Tuha basin is relatively simple.The piedmonttectonic belt is a monoclinic structure,and new strata are gradually exposed to the interior of the basin.Some faults,thrust faults and In the folds,the faults are mostly reverse faults or translational faults;the Bourges area is relatively complex,except for the development of a large number of thrust faults,which also have folds and inverted folds.The fault structure has many thrust properties,and the folds are mainly Keerjian sycline.The alkali is inclined,and the oblique axis is nearly east-west,and is irregularly curved.In contact with the thrust fault,see the inverted back-tilt structure.The target layer detrital zircon is dominated by magmatic zircon,a few are metamorphic zircon,and the detrital zircon age is 270-684 Ma,indicating the Mesozoic,Paleozoic magmatism and Neoproterozoic metamorphic basement of the eastern Tianshan Mountains;The range of 206Pb/204 Pb,207Pb/204 Pb and 208Pb/204 Pb of the granite and the ore-bearing clastic rocks in the area are 16.364-19.216,15.482-15.820 and 37.184-39.082,respectively.The variation range is large,including radioactive anomaly Pb characteristics,and the sample Pb total.The shell source Pb is mainly composed of some mantle Pb;the debris composition statistics and fine debris trace element analysis show that the parent rock has experienced strong weathering,its composition is similar to that of the upper crust,LREE enrichment,HREE The flattening,Eu loss is more obvious;combined with the surface of the petrological features,the ore-bearing debris in the study area is mainly from the southern margin of the basin,and the parent rock sedimentary tectonic setting is the sedimentary basin related to the active continental margin island arc;the source area is acidic volcanic rock,The development of uranium-rich rocks such as granite provides an important source of uranium for later uranium mineralization.The second section of the Xishanyao Formation in the Shihongtan-Baxiankou area contains mainly the braided delta sedimentary front facies.The uranium mineralization develops in the braided delta underwater distributary channel microfacies and the estuary dam microfacies environment,or the underwater distributary channel The micro-phase and the shunt are near the micro-phase interface of the bay.The second section of the Xishanyao Formation in the Bulga area also mainly develops the braided delta front subfacies;the comprehensive analysis of the well profile,sand body thickness map and sedimentary facies plan shows that the uranium mineralization is mainly distributed in the braided delta front Contact interface between micro-phases such as flow channels,diversion bays,and estuaries.The mean length of the apatite limit track is 11.7-12.9 ?m,the age of the central age pool is 25-82 Ma;the track distribution type is mainly bimodal and unimodal,indicating that the sample in the study area has experienced relatively Complex tectonic thermal activity;thermal history simulation results show that there have been two relatively rapid tectonic uplift events in the southwestern margin of the Tuha Basin since the Mesozoic,namely the Late Cretaceous-early Paleogene(90-60 Ma)and Paleogene Mid-late(40-25Ma).Combined with the analysis of predecessor low-temperature chronology data and regional tectonic deformation characteristics,there are obvious spatial and temporal differences in the Tuha Basin and its surrounding tectonic uplift.Since the Mesozoic and Cenozoic,multi-period rapid uplift events occurred in the southwestern margin of the Tuha Basin.Tectonic activity became relatively stable during the late Cenozoic,and the northern margin of the basin experienced a strong rapid uplift and denudation event since the Late Cenozoic.The thermal evolution process experienced since the Mesozoic in the southwestern margin of the Tuha Basin is a thermodynamic response to basin tectonic and sedimentary activities.Since the Mesozoic,the study area has experienced multi-period and multi-stage rapid uplift events,which caused the rapid uplift of the source strata and the emergence of a large number of deep uranium-rich rock masses.Since the Cenozoic,the tectonic activities in the southwestern margin of the basin have been relatively stable.The stable tectonic uplift event promoted the activation and migration of uranium in the source and strata,fully enriched,and finally formed into ore.However,the uranium-rich uranium in the northern margin of the Tuha Basin has relatively little exposure,and since the Late Cenozoic,the strong rapid uplifting tectonic activity in the northern margin has prevented uranium from accumulating enough time.Therefore,the uranium in the target layer in the northern margin of the basin The degree of enrichment is relatively limited. |
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