| The Eastern and Western Junggar orogenic belts are located between the Altai orogenic belt and the Tianshan orogenic belt.They are in the Siberian plate and the Junggar-Kazakhstan plate.They are an important part of the Central Asian Orogenic Belt.They experienced complex oceanic basin expansion and plate subduction,collision and post collision and other complex ocean continent conversion process.In this paper,the Late Paleozoic magmatic rocks and some ophiolites in the eastern and western Junggar regions were selected for petrology,geochemistry and LA-ICP-MS zircon U-Pb chronology to study the genesis of magmatic rocks,for the inversion tectonic evolution of East and West Junggar area to provide evidence.Seven granites in the western Junggar region were studied.We divided them into two types according to the formed tectonic environment.The first group was Akeqiaoke granodiorite(granodiorite-porphyry)with a age of 410.4 ± 1.5 Ma(Early Devonian).The samples are strongly depleted of Nb,Ti,Ta,enrich of Pb,high Sr high Yb,high Al,low K,LREE enrichment,no Eu anomalies,low compatible elements Cr,Ni,Co,V,and low MgO and Mg#(<48)are lower,and the adakitic rocks in the subduction environment are characterized by the subduction of the Kujibai – Hebukesaier – Hongguleleng ophiolite belt,while the sample with a change of Th and lower MgO and Mg#,indicating that in the process of melting and emplacement may have ocean sediments to join or by the crust of different degrees of mixing.The second type is granite formed by the Carboniferous-Permian formation in the post-collision environment.There are mainly Kulumusu K-feldspar granite ages of 326.3 ± 3.4Ma(early Carboniferous and A2-type granites)320.2 ± 1.6Ma(Late Paleocene Early,A2-type granite);Seerdeng monzonitic granite age of 309.0 ± 1.1Ma(late Carboniferous medium,high Sr high Y,I granite);the north of Kezilekeya K-feldspar granite age is 305.4 ± 0.78 Ma(late late Carboniferous);Kezilekeya K-feldspar granite age is 301.8 ± 1.7 Ma(late Late Carboniferous,A2-A1 transitional granite);The age of the north of seerdeng monzonitic granite is 291.4 ± 1.1 Ma(in the middle of the Early Permian,which is a crust-mantle mixed granite with volcanic arc granite).A2 type granite samples deplete of Ba?Nb?Ta?Sr?P?Eu?Ti,enrichment of Rb?Th?K?Pb,which are close to the geochemical characteristics of the lower crust,Which may be in the post-collision environment,the thinning of the lower crust material under the action of the mantle undergone partial melting products.At the same time,the formation of A2-A1 type transitional granite in this period and the high Sr and high Y formed with the same period,the type I granite with volcanic arc magma is the first discovery in the area,and its formation means that in the late Carboniferous,mantle activity is strong,from the deep enrichment mantle upwill brought a lot of heat,resulting in a high degree of partial melting of the source area,the original low-pressure environment in the existence of plagioclase is also hot melt,the formation of such high Sr high Y The granite has the characteristics of volcanic arc magmatic rock.The feature inherits from the source area,indicating that the source area has the characteristics of volcanic arc,suggesting that the source area may be a new volcanic arc material,enrichment mantle strong upwelling,The partial enrichment of mantle material into the magma,resulting in magma with high Nb,Ta content and low Y / Nb,Ce / Nb,but with A2-type granite similar to the 10000 Ga / Al and R1,and ultimately the formation of such Collisional environment with A2-A1 transitional Kezilekeya K-feldspar granite.Seven magmatic rocks in the eastern Junggar are studied.The volcanic rocks are formed in the early Carboniferous,and the integrated cover is covered with the thick molasse.It shows that it is formed in the post-collision environment,and both has island arc and the intraplate features;plagioclase granite and gabbro belong to the composition of kalamaili ophiolite,the age of which are 365.6 ± 2.4Ma and 366.0 ± 0.8Ma(late Late Devonian);the biotite quartz monzonite age is 345.1 ± 0.97Ma(early Carboniferous mid-period),with I-type granite characteristics;quartz diorite age of 339.5 ± 1.9Ma(early Carboniferous mid-term),with volcanic granite characteristics;biotite granite age of 315.8 ± 0.88 Ma(Carboniferous mid-period),A2-type granite;Laoyaquan porphyritic granite,coarse grain granite,fine grained granite ages were 318.6 ± 1.1Ma(the early stage of Late Carboniferous),312.4 ± 1.6Ma(Late Carbon Medium),308.5 ± 2.1Ma(Late Carboniferous Medium),which is granulated granite A2 type granite.Biotite quartz monzonite,biotite granite and the Laoyaquan granites Rb,Th,U,K,Pb are enriched,and Ba,Nb,Sr,P and Ti are depleted,and Zr/Nb,Ba/Nb,Th/Nb and Zr,Hf are slightly higher,indicate that the rock mass may be contaminated by the upper crust during the process of emplacement.Quartz diorite enrichment of large ion lithophile elements Cs,Rb,Ba,Pb,Th,U,Sr,etc.,deplete of high field strength elements Nb,Ta,Ti,P,etc.,no Eu negative anomaly,volcanic arc properties are shown,and the samples are plotted in the mantle region in R1-R2,and it is considered that the source area of the quartz diorite is subjected to subduction fluid(the oceanic basin represented by Kalamaili phiolite is dehydrated to the north subduction plate)of the hydrothermal mantle,in the post-collision environment,the mantle ascending decompression occurs partially melted,the melt inherits the geochemical characteristics of the previous magma,and the lower La/Sm and potassium contents,indicating that the magma rises during the process by the weaker crust contamination.In the study,we believe that the oceanic basin represented by the Kalamaili ophiolite in the late Late Devonian is still expanding,and the presence middle of the Early Carboniferous biotite quartz monzonite marks the closure of the Kalamaili basin,The closing time of the Karamari basin is limited to between 365.6 and 345.1 Ma.The occurrence of type A granite shows that the post collision tension effect is strong in the region,and the mantle is strongly upwelling,leading to large-scale partial melting of the lower crust.On the basis of this study,we have compared the strata,ophiolite zone and magmatic events in the Eastern and Western Junggar regions,and found that:1)The West Junggar area is from the north to the south,the Sawuer stratigraphic area,the Shaerbuertishan stratigraphic area,the Miyilishan area and the Karamay stratigraphic area,respectively.The east Junggar region is from north to the south,Ertai stratigraphic area,the Kalamaili stratigraphic area and the Jiangjunmiao stratigraphic area,the depositional age,lithological assemblage and depositional environment can be one to one correspondence.2)The formation ages of the Kujibai-Hebukesaier-Hongguleleng ophiolite belt in the north of the west Junggar and the Zaheba-Aermantai ophiolite belt in the northern part of the eastern Junggar are mainly concentrated in the late Cambrian-Early Ordovician and Early Devonian Late-Middle Devonian),belonged to SSZ type ophiolite,geophysical anomaly zoning map with similar properties,and in space spread close,that its second can be compared to connect,to construct a transcendent ophiolite zone.Daerbute ophiolite(SSZ type)and Karamay ophiolite(N-MORB type)in the southern Junggar are considered to be associated with the Kalamaili ophiolite(SSZ)and Dishuiquan ophiolite(N-MORB type)in the southern Junggar can one-to-one contrast connection.3)The age of the intermediate acid intrusive rock in the West Junggar is mainly distributed in the range of 400 ~ 430 Ma(volcanic arc environment)and 260 ~ 350 Ma(post collision environment).The ages of the intermediate acid intrusive rock in the East Junggar are mainly distributed from 410 to 450 Ma(volcanic arc environment)390Ma(350 ~ 390Ma)is associated with the subduction environment,and the transitional environment is from 350 Ma.After the magmatic rock age and genesis,the Late Paleozoic tectonic evolution process is very close.In this paper,we think that the east and west Junggar have similar tectonic evolution processes in the Late Paleozoic,mainly in the soft-collision orogeny,which entered the large-scale,long-term collision process in the early Carboniferous,The Late Paleozoic A2-A1 transitional granites of the Junggar and the simultaneous formation of I-type granites and the large-scale A-type granites and bimodal volcanic rocks in the East Junggar indicate that the Late Paleozoic mantle in the region is very strong and may be related to the mantle Column related.In the Junggar region,the basement of the mantle-derived magmatic bottom and the strong crust of the lower crust are formed to form large-scale collision magmatic rocks under the strong undercurrent of the mantle plume. |
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