Abstract:The Altay orogen, which stretches across the boundary areas among China, Russia, Kazakhstan and Mongolia, is a major unit of the Central Asia OrogenicBelt. Numerous granitoid plutons occur in the orogen. This paper has summarized the spatial and temporal evolution of the plutons and discussed their tectonic setting and implications for crustal growth. According to zircon ages available, these plutons can be divided into three periods, namely early-middle Paleozoic, late Paleozoic and Mesozoic. The early-middle Paleozoic plutons can be subdivided into 470～440 Ma (middle-late Ordovician) and 425～360 Ma (late Ordovician-Late Devonian), the late Paleozoic into 355～318 Ma (early Carboniferous) and 290～270 Ma (early Permian), and the Mesozoic mainly into 245～190 Ma (middle-late Triassic-early Jurassic). The early-middle Paleozoic (470～360 Ma) plutons that occur widely are mainly of calc-alkaline I type subjected to various degrees of deformation, in which 470～440 Ma plutons occur as gneissic bodies. They were formed during syn-accretion orogenic processes, from the early active continental subduction (470～440 Ma) through continuous subduction/back-arc extension (420～380 Ma) to collision (380～360 Ma). The early Carboniferous plutons occur in the southern part of the orogen, and some of them are alkaline and show circular or irregular shape with insignificant deformation. They were emplaced in a late (or post) orogenic setting. The early Permian plutons mainly occur in the southern part of the orogen, with a few seen in the central part. They are mostly of circular shape and show very weak or no deformation except for a few deformed ones in the Ertix slip zone. The rock types are characterized by I and A types in association with mafic intrusions including dykes, displaying a post-orogenic extensional setting. The early Mesozoic plutons, showing circular or irregular shape without deformation, are characterized by high differentiation I-type and S-type, associated with rare metal deposits. They were emplaced in an intercontinental setting.Nd isotopic mapping of the plutons indicates that εNd(t) values are lower ( -4 to +2) in central Altay and higher (+1.4 to +6) in southern Altay; correspondingly, tDM values decrease from 1.6～1.1 Ga in central Altay to 1.0～0.5 Ga in southern Altay. These results demonstrate that central Altay contains widespread old continental basement, whereas southern Altay comprises a significant proportion of juvenile crust, suggesting that the crust grew southward. The horizontal (lateral) and vertical crustal growth contributed ca. 18%～28% and 7%～8%, respectively, to the area of Chinese Altay. The authors' studies also suggest that the Altay orogen preserved original accretional crustal structures during Mesozoic, without large-scale vertical tectonic superposition. The Altay orogen experienced formation of an active continental margin, splitting of the margin to form a back-arc ocean and the final closing of the back-arc ocean. It is also held that the CAOB underwent not only accretional processes but also back-arc opening and closure of microcontinent margins, which might have been a common process in the central Asian accretionary orogen.

Abstract:Numerous granitoids occur in northern Xinjiang and its adjacent areas, with Carboniferous-Permian granitoids being most typical. This paper summarizes the spatial and temporal distribution characteristics of these granitoids. Carboniferous-Permian granitoids show different features in different units, and the peak values of their formation epochs are also different. Formation epochs of the Carboniferous-Permian granitoids in Altay are mainly concentrated in early Permian (289～266 Ma), and late Carboniferous seemed to be a distinct magmatic calm period. Western Junggar Carboniferous-Permian granitoids formation periods can be subdivided into early Carboniferous (340～320 Ma) and late Carboniferous-early Permian (310～290 Ma), with the latter being more stronger. Aluminum A-type granites, concentratedly formed at about 300 Ma, are widely spread, constituting an important feature of western Junggar. Carboniferous-Permian granitoids in eastern Junggar occur along the fault zones and were formed mainly from late Carboniferous to early Permian (320～270 Ma), characterized by the continuous emplacement of quite a number of alkaline (A-type) granites in this region in this period. Carboniferous-Permian granitoids in western Tianshan can be divided into three stages: early Carboniferous (355～345 Ma), late early Carboniferous-late Carboniferous (335～305 Ma) and early Permian (300～255 Ma). The early Permian granitic magma activity is the strongest, and Carboniferous granitoids mainly intruded into northern Tianshan, and the early Permian alkaline (A-type) granitoids are not only distributed in a large zonal area of southern Tianshan but also spread in northern Tianshan. Eastern Tianshan-Beishan is an area with most developed Carboniferous-Permian granitoids, characterized by both large quantities and wide distribution. Zircon ages show two obvious peaks, being respectively at 335～310 Ma and 300～270 Ma. Granitoids in eastern Tianshan are mostly Carboniferous ones, whereas granitoids in Beishan are mostly Carboniferous ones. In general, Carboniferous-Permian granitoids of northern Xinjiang and its adjacent areas were mainly formed in the late Carboniferous-early Permian period, especially during the early Permian, showing synchronization in the whole region. This period is also characterized by most developed alkaline (A-type) granitoids, which is regarded as the reflection of the extensional setting, maybe revealing extension characteristics in different tectonics. This is a microcosm of lots of acid and mafic-ultramafic magmatism in the Central Asian Orogenic Belt and the implication of its extensional setting.

Abstract:The Central Asian Orogenic System (CAOS) is one of the largest accretionary orogenic belts characterized by the highest rate of Phanerozoic continental growth in the world. In recent years, extensive studies of the orogenic belts have been conducted, focused mainly on Paleozoic accretionary processes and granitic magmatism. By contrast, Mesozoic magmatism and tectonism are poorly understood. This paper tries to analyze and discuss temporal-spatial distribution and tectonic setting of the early Mesozoic granite magmatism. According to zircon U-Pb ages, the Early Mesozoic granitoids in the middle-south segment of the Central Asian Orogenic System can be roughly divided into two stages, i.e., early-middle Triassic (251～227 Ma) and late Triassic-early Jurassic (226～195 Ma). The early-middle Triassic rocks consist mainly of the monzogranite-granodiorite_syenite assemblage. These granitoids are distributed in such areas as the east-middle part of the East Tianshan orogenic belt, the north-middle part of the Beishan orogenic belt, the central Mongolian block, the western part of the Altay orogenic belt and the middle-western region of the Inner Mongolia-Jilin orogenic belt. They are spread along or near the suture zones. The granitoids have metaluminous-weakly peraluminous, calc-alkaline-high-K calc-alkaline or weak alkaline features. I-, S- and A-type or I-A type granites are all exposed. Some ultramafic-mafic rocks are associated with these granitoids. The late stage rocks widely occurring in every orogenic belt are composed of the alkali feldspar granite-K-feldspar granite-monzogranite-alkali feldspar quartz syenite assemblage. They are characterized by metaluminous-wealy peraluminum, high-K calc-alkaline or alkaline granites. Most of them are of A-type and I-A type. Some of them have the characteristics of highly fractionated I-type granites. There exist voluminous coeval ultramafic-mafic rocks. The early-middle Triassic granitoids have a higher ΣREE content, while the late ones have a significant negative Eu anomaly and are more depleted in Ba, Nb, Sr, P and Ti. The Sr-Nd isotopic characteristics reveal that the granitoids in the northern margin of the North China Craton show very low εNd（t） values (-19.6～-5.4) and the old tDM values (1.23～2.09 Ga), suggesting derivation from an ancient continental crust: those in the north Mongolia-west Transbaikalia orogenic belt and Inner Mongolia-Jilin orogenic belt were derived from a young source, whereas those in central Mongolian block, Altay orogenic belt, East Tianshan orogenic belt and Beishan orogenic belt were derived from an ancient micro-continental crust with some contributions of young mantle-derived components. In general, the early-middle Triassic granitoids were derived from dual-sources, while the late Triassic-early Jurassic granitoids mainly from the mantle source. Mantle-derived components have an increasing trend from early to late ones. Juvenile compositions of major sources for the granitoids were distributed in the Okhotsk belt and its adjacent areas, and also contributed by the ancient continental crust through underplating of young mantle-derived magma, leading to vertical continental growth in the post-orogenic or post-collision stage. According to recent researches, the early-middle Triassic granitoids in the eastern and western regions show some differences in tectonic settings. The north Mongolia-west Transbaikalia orogenic belt seems to show an intraplate tectonic setting of the continental rift. The central Mongolian block may represent the late stage of the syn-orogenic setting. The Altay orogen and the East Tianshan orogen are described as a post-orogenic extensional setting. The Beishan orogen reflects the late orogenic collision or post-orogenic tectonic setting. The Inner Mongolia-Jilin orogenic belt has the syn-orogenic characteristics. The late Triassic granitoids mainly reflect a post-orogenic, non-orogenic or intraplate extensional tectonic setting.

Abstract:Plenty of granitic rocks are exposed in the western Junggar region which has been regarded as one of the most typical areas in the world where the post-collisional vertical continental growth has been recorded. Previous studies were concentrated on the representative intrusions exposed in the eastern part of this region, such as Miaoergou granite pluton, Akebasitao granite pluton, Kelamayi granite pluton, Hongshan granite pluton, Hatu granite pluton and Baogutu adakitic pluton. However, rather insufficient studies were devoted to the granite pluton exposed in Tangbale-Mayile area in the western part of this region. In this paper, the study was concentrated on the geology, geochemistry and U-Pb chronology of the Laba intrusion in the Mayileshan Mountain in order to provide some new data for the discussion on the post-collisional magmatism along the southwestern margin of the western Junggar accretionary orogenic belt. The Laba pluton intruded into the Lower Carboniferous Baogutu Formation. This intrusion occupies about 23.95 km2 in the plan view, with the long axis extending about 8 km in NS direction and an EW width of about 5 km. The pluton is composed of granodiorites, quartz-diorites, tonalites and granites, predominantly of granites. Among them, the granodiorite and the granite belong to calc-alkaline to high-K calc-alkaline series and metaluminous to peraluminous rocks. The σ value of granitic rocks varies from 1.09 to 1.91, averagely 1.48；and the A/CNK value varies from 0.87 to 1.34，averagely 1.07, indicating that these rocks are metaluminous to peraluminous. The A/CNK values of two samples are 1.25 and 1.34 respectively, suggesting that they are peraluminous. The chondrite-normalized patterns of the samples assume LREE-enriched and HREE flat with a (La/Yb)N value varying from 1.04 to 1.39, 1.19 on average. Relative to the primitive mantle, the trace element spider diagram of the samples indicates that these rocks are enriched in large ion lithophile elements (K, Rb and Ba) and depleted in high strength field elements (Nb, Ta, Ti and P). The Laser-ICP-MS mean 206Pb/238U ages of 287 ± 5 Ma and 295.1 ± 2.3 Ma were obtained for two representative samples from this pluton, indicating that the age of this pluton is Early Permian. This age is similar to the age of post-collisional granites in the western Junggar region with a peak of 310～295 Ma. On the basis of an integration of geological and geochemical characteristics of this pluton and regional geology, the Laba pluton is held to be a magmatic product of the post-collisional extension in the western Junggar region. The pluton has similar trace element geochemical characteristics to island-arc granites, implying that its magma source had been metasomatized by previous subduction fluids. The closure of paleo-oceans in western Junggar and the adjacent northern Tianshan region happened earlier than 316 Ma. In other words, these regions were under a post-collisional extension episode during the period of Late Carboniferous to Early Permian. Both the oceanic ridge subduction and the subducted oceanic crust melting models cannot be employed to interpret the formation of the Laba granitic pluton.

Abstract:The Haladala pluton in northeast Tekes County is the largest basic-ultrabasic layered pluton in West Tianshan area; nevertheless, little work has been done on its petrogenesis. In this paper, the authors conducted a detailed study of its geochemistry and geochronology. With the data obtained in combination of regional tectonic evolution, this paper discusses its petrogenesis, tectonic setting and geological significance. This pluton consists of a series of gabbroic rocks such as troctolite, olivine gabbro, hornblende gabbro and gabbro. Secondary ion microprobe (SIMS) zircon U-Pb dating indicates that the gabbroic rocks crystallized at the age of 306.2 ± 2.7 Ma, belonging to the Late Carboniferous. These gabbroic rocks have SiO2 values ranging from 44.49% to 48.46% with low content of K2O and Na2O and high average Mg# value of 71.4. Chemical compositions of these rocks are tholeiitic, but show a variation trend with the magmatic evolution from low-K tholeiite series to calc-alkaline series and even high-K calc-alkaline series. Some samples show abnormally high MgO, Al2O3 and CaO content, which may be due to the accumulation of olivine and plagioclase. They are also significantly enriched in LILE such as Rb, Ba, K, Pb and Sr, but depleted in HFSE such as Nb, Ta and Ti, with La/Nb>1.4. All these data indicate characteristics of arcmagmas derived from fluid metasomatized mantle wedge. Their Th negative anomaly suggests that the magmas may have been contaminated by the lower crust. These rocks have low content of total REE with weak differentiation of LREE from HREE. Due to the role of plagioclase accumulation, some samples have significant positive Eu anomalies. Compared with the mafic plutons of different ages exposed in adjacent areas in North Xinjiang, the Haladala pluton has unique petrological and geochemical characteristics, which may imply that they contain both arc-like magma components and components from extensional environment magmatism. The compositional characteristics suggest that the rocks might have been formed during the change of the tectonic framework from compression to extension. Regional tectonic history indicates that there was a shift (from compression to extension) in the tectonic framework of West Tianshan region during Late Carboniferous to Early Permian. The authors made an overall analysis of various rocks concerning their petrologic and geochronologic features at the northern and southern edge of the Yili-Central Tianshan plate, and found out that the Yili plate underwent a transition from the subduction and collision to post-collision circumstances in 293～313 Ma. Based on geochronological and geochemical characteristics of the Haladata pluton, the authors believe that the Tekesi area was at the stage of this transition of tectonic settings. It is suggested that the late Paleozoic gabbroic rocks (the Haladala pluton) in Tekes County might also have been formed in this transition stage. Hence, these rocks may indicate a change of tectonic framework in the West Tianshan area and provide evidence for the presence of magmatism in this region during the tectonic frame change.

Abstract:Paleozoic granitic magmatism is well developed in Nalati area of West Tianshan Mountains. Based on field work, petrographic studies and LA-ICPMS zircon dating, the authors divided granitic magmatism in Nalati area into two stages. The first stage is from Late-Ordovician to Late_Devonian, and the granitoids formed in this stage have experienced a strong deformation and developed gneissic schistosity and large exposed areas of diorite, quartz diorite, granodiorite and monzogranite intrusions. From west to east, they include Senmutasi intrusion, Haerwenke intrusion, Kekesuhe intrusion and Nalati intrusion. Granitoids of this kind in the study area were mainly formed between 485 Ma and 366 Ma and constitute the main body of the granitoids in Nalati. The second stage is Carboniferous and the granitoids formed in this stage are located in the north of the first stage granitoids or intruded into the first stage granitoids, and their exposed area is usually small. They have only undergone a weak or no deformation. Along the NEE-trending Nalati tectonic belt, there exists the feature that the formation ages of the granitoids gradually become younger from west to east, and become younger from south to north across the Nalati tectonic belt. Zircon Hf isotope studies reveal that the granitoids formed between Late-Ordovician and Late-Devonian in this area have three kinds of sources. The first (t2DM=1200～1600 Ma) is Mesoproterozoic crust, the second (t2DM =700～1600 Ma) is Meso- and Neo-Proterozoic crust, and the third (the values of t2DM are similar to or a little older than the formation ages of the granitoids) is a juvenile crust. Carboniferous granitoids also have three kinds of sources. The first (t2DM =1000～1700 Ma) is a Meso and Neo-Proterozoic mixed source, the second (t2DM≈400 Ma) is an Early Paleozoic juvenile crust, and the third is a mixed region of Early-Carboniferous depleted mantle and ancient crust. Zircon Hf isotope researches on granitoids suggest that there exits a Meso- and Neo-Proterozoic crustal growth event in Nalati area. The Paleoproterozoic basement considered by present researchers may include Neoproterozoic, Mesoproterozoic, Paleoproterozoic and Archean materials, and its internal structure is so complex that we should do much future work on it. Chronological framework and deformation characteristics of granitoids suggest that the Late Devonian period may represent the end of the Paleozoic ocean-continent transition in the Tianshan Mountains. Zircon Hf isotope studies suggest that there were two events of mantle material addition that took place in Early Silurian and Early Carboniferous respectively. The former was a period of the Tianshan Paleozoic ocean subduction, and during this time the granitoids were formed by partial melting of a juvenile crust with the addition of some mantle materials. The latter represented a crustal growth event in Early Carboniferous, which suggests an influx of some mantle materials in a strong continental extension stage after a collisional orogeny.

Abstract:Located in the south margin of the Chinese Southwest Tianshan area, the Huoshibulake alkali feldspar granite pluton is composed mainly of alkali feldspar granite with a small amount of alkali feldspar granite porphyry. All samples from the pluton are characterized by high values of SiO2 and Al2O3 and low values of Fe2O3T, MgO, TiO2, P2O5. All samples are of alkaline affinities based on AR versus SiO2 diagram, and chiefly fall into the metaluminous area in the A/CNK versus A/NK diagram. The primitive mantle normalized trace element diagrams are characterized by the enrichment of the HFSE relative to the LILE, and negative anomalies of Sr, Ba, P, Ti. The samples exhibit a relative enrichment of LREE as well as strong negative anomalies of Eu, contain fluorite and have high ratios of FeOT/MgO and low values of CaO. The alkali feldspar granite pluton is also characterized by high 10000 Ga/Al ratios and Zr+Ni+Sr+Y values. Petrology and geochemistry of the pluton show that it belongs to typical A1-type granite, and is a product of the partial melting of the mafic lower crust in an intraplate environment. The low content of Ti results from a large quantity of residual magnetite minerals in the source area, and the high Nb-Ta value is caused by the enrichment of F in magmas. The tectonic setting is affected by the rift system within the Tarim Block. The pluton is rather insignificant in the study of the genesis of the Huoshibulake Pb-Zn deposit but displays Sn mineralization potential.

Abstract:Beishan area is located in the west of Inner Mongolia and Gansu Province, which is the conjunction zone of Tarim plate, Sino-Korea plate and Kazakhstan plate and plays an important role in the study of the Central Asia Orogenic Belt (CAOB). The relationship of the three plates is so complicated that there exists much controversy concerning Paleozoic tectonic evolution in this area. Granitoids, especially Late Paleozoic granitoids, are widely distributed in Beishan area, which are of great importance in the study of Paleozoic magmatic evolution. Through analyzing the spatial and temporal distribution of the Late Paleozoic granitoids, we can find the relationships between these granitoids and explore the crust-mantle interaction in Beishan area during Late Paleozoic, which is important for determining the geotectonic evolution of this area. In the southern belt of Beishan, the most important tectonic event in Permian is the formation of Yin'aoxia rift zone, which makes the study of Late Paleozoic evolution more complex. The results of studying Xijianquanzi granite lying in the southern belt of Beishan in such aspects as major elements, trace elements, REE and LA-ICP-MS zircon U-Pb geochronology have provided new evidence for regional tectonics. The LA-ICP-MS zircon U-Pb age of Xijianquanzi granite is 266.1±2.2 Ma, and the Hf modal ages are 746～871 Ma. εHf(t) values are +1.3～+4.7 with an averageof +2.7, which implies the mixture of crustal and mantle.derived magmas. This feature coincides with that of other areas in the Central Asia Orogenic Belt (CAOB). Therefore, the granites in the belt may have similar magma sources. The granitic body mainly consists of monzonitic granites which belong to alkaline series with high content of SiO2 (74.33%～76.67%), Na2O+K2O (9.26%～9.57%, NK/A=0.9～1.08) and K2O (Na2O/K2O<1) . In addition, chondrite-normalized REE patterns and primitive mantle normalized geochemical patterns of all samples are approximately parallel to each other, which shows that they evolved from the same magma source. Chondrite-normalized REE patterns of the intrusive body are of “V" types and show enrichment of light rare earth elements (LREE) with low ratio of (La/Yb) N (3.18～5.29) and negative Eu anomalies (δEu =0.10～0.16). Except for Eu, the abundance of rare earth elements are demonstrably over 10 times that of chondrite. Depletion of Nb, Ba, Sr, Ti, P and enrichment of Rb, Th, K can be seen in the spidergram. Based on regional geological and geochemical characteristics, the authors have reached the conclusion that the Xijianquanzi intrusive body is an alkali-rich potassium-high granite which is a mixed product of crustal and mantle-derived magmas and was formed at the stage of rifting in the post-collisional extensional period, affected greatly by Yin'aoxia rift zone. This implies that the area entered into the stage of rifting in Middle Permian.

Abstract:The northern Darhan Muminggan Joint Banner of Inner Mongolia, geotectonically crossing two geological-structural units, is divided into two parts by Bayan Obo-Chifeng deep fault (plate boundary fault). To the south of the deep fault is the North China block, and to the north is the accretion zone at the northern edge of North China plate. An important magmatic arc belt mainly composed of diorite, quartz diorite, tonalite and granodiorite is developed near Bart-Obao on the north side of Bayan Obo-Chifeng deep fault. In this paper, precise SHRIMP zircon U-Pb dating and hornblende 40Ar/39Ar dating defining the emplacement age of the intrusion and its thermal evolution history were conducted for inclusions of diorite and hornblendite hosted in granodiorite, and the constraints on Early Paleozoic subduction-collision event of the Paleo-Asian Ocean in central Inner Mongolia were provided from isotope geochronology. SHRIMP U-Pb zircon ages of the two diorite samples are 453±3 Ma and 446.8±5.3 Ma, and hornblende 40Ar/39Ar plateau ages are 459.2±2.4 Ma and 442.9±4.2 Ma. SHRIMP zircon U-Pb dating results indicate that the island arc intrusive rocks were formed around 450 Ma, resulting from the Middle-Late Ordovician (or earlier) oceanic subduction event. The results of SHRIMP zircon U-Pb dating are basically in accordance with those of hornblende conventional 40Ar/39Ar dating method, which suggests the crystallization and rapid cooling after the emplacement of the magma and may reveal collision between the Baoerhantu-Bainaimiao island arc zone and the North China plate. The dating results of the diorite imply that tectonic heat events after the emplacement and the cooling of the intrusive body did not affect the hornblende Ar-Ar closed system, and hence strong tectonic heat events did not occur later.

Abstract:In the Huluntaolegai area of western Inner Mongolia, close to China-Mongolia border, several granitoid plutons occur in the Mesoproterozoic and Carboniferous country rocks, of which the Yinggete-Bagemaode pluton is the largest one. This pluton has greatly varied lithologies, composed of quartz diorite, granodiorite and granite, which contain abundant relicts of country rocks and have experienced intrusion of younger granites and pegmatites. According to previous data, the Yinggete-Bagemaode pluton may be Late Paleozoic in age, whereas other small plutons dominated by red granite and potassium feldspar granite such as the Kuchuwula and Yilian plutons, which occur within or to the west of the largest pluton, were possibly emplaced in the Mesozoic. Unfortunately, neither reliable chronological constraints nor geochemical data for these plutons are available. In view of this situation, the authors conducted a preliminary study of these plutons in order to determine their emplacement ages and geochemical characteristics. SHRIMP zircon U-Pb dating reveals that the Yinggete-Bagemaode pluton was emplaced at 313 ± 5 Ma (Late Carboniferous), and this pluton was cut by the quartz monzonite at 130 ± 2 Ma (Early Cretaceous), whereas the Kuchuwula and Yilian red granite plutons were emplaced at 277±2 and 278±4 Ma, respectively, suggesting products of Early Permian instead of Mesozoic magmatism. Geochemically, Yinggete-Bagemaode pluton shares characteristics of I-and A- type granites, with 10000 Ga/Al of 2.15～3.04 and negative Ba, Nb, Ta, P, and Ti anomalies, while the Kuchuwula and Yilian plutons are aluminous A-type granites, showing significantly negative Ba, Nb, Ta, P and Ti anomalies and high 10000 Ga/Al ratios (4.02～4.89). All the Late Paleozoic plutons are characterized by positive εNd(t) values (0.90～3.43), like the coeval granitoids in North Xinjiang, Mongolia, and Northeast China in this respect, and thus are indicative of crustal growth in the study area. In contrast, the Early Cretaceous quartz monzonite has significantly negative εNd(t) value (-8.71), implying a dominantly crustal origin, possibly derived from the Mesoproterozoic metamorphic rocks in the study area, with some involvement of depleted-mantle derived materials.

Abstract:A suite of Late Paleozoic Hadamiao quartz diorites were discovered in the northern part of the North China Platform within eastern Central Asia Orogen, which were previously considered to be products of Yanshanian intrusion and fractionation. U-Pb age dating with the LA-ICP-MS method yielded 272.9±2.4 Ma (MSWD=2.0), which represents the crystallization age of the quartz diorites. The Hadamiao quartz diorites and the associated Hadamiao auriferous granitic porphyries all show features of high-potassium and calc_alkaline I-type. The quartz diorites can be distinguished from the auriferous granitic porphyries in high content of Al2O3, FeOT, CaO, MgO, TiO2, Sr, high mantle components（Co, Ni, Cr, Mn）, and low content of SiO2, K, Ta, Th, U. The total REE content is quite low, lower than the REE content of intermediate rocks in the crust (∑REE=196×10-6) and that of acid rocks in the crust（∑REE=290×10-6）. LREE is evidently enriched, and medium to weak negative anomalies of Eu can be seen. The granitic porphyries are stronger than the quartz diorites in the fractionation between LREE and HREE and the manifestation of negative anomalies of Eu. Compared with the primitive mantle, they are obviously enriched in LILE (K, Rb, Th, Zr, Hf ) and depleted in HFSE (Nb,Ta, Ti, P) , indicating features of SZC and continental arc. Both the quartz diorites and the auriferous granitic porphyries show features of fore-collision and syn-collision between plates. An isotopic analysis of Sr, Nd and Pb reveals that the original rocks of the Hadamiao complex were derived from the mixture of the crust and the mantle, assuming characteristics of newly-formed lower crust (paleoisland arc). The model ages of Nd (tDM=1054～1260 Ma) in Hadamiao area are comparable with those of the Bainaimiao arc greenschists (1130±16 Ma), suggesting the existence of some genetic relations. The relation graph of La/Sm versus La and the changing degree of the magma concentrations indicate that the quartz diorites were formed by crystallization separation whereas the auriferous granitic porphyries were produced through partial melting. The early separation of the biotite quartz diorites provided preferential conditions for Au concentration in the bodies of granitic porphyry within the sulfide-poor porphyry gold deposit. The abnormal enrichment of hydrophile elements (Rb, Ba, Th, U, K) in the Hadamiao auriferous granitic porphyries can be used to distinguish auriferous granites from barren granites. Therefore, this paper supplies prospecting clues to the gold deposits related to the Paleo-Asia Ocean subduction and accretion leading to collision in the Late Paleozoic.

Abstract:Located in the northern margin of the North China Craton, the Louzidian metamorphic core complex is one of the important areas with widely distributed Palaeozoic-Mesozoic granitoid rocks. The deformed plutonic intrusions in the Louzidian core complex area have not yet been precisely constrained by reliable isotopic ages. The plutons have long been considered to be Precambrian rocks. Recent studies have revealed that the deformed and metamorphosed rocks with protolithes of plutonic intrusions were genetically related to late ductile shear events. This paper presents newly obtained zircon U-Pb ages of the deformed granitoids from Zhalanyingzi (253.6±1.2 Ma), Chaoyanggou (150.42±0.98 Ma), Molihaigou (127.6±3.1 Ma) of the Liuzidian metamorphic core complex area in Chifeng, on the northern margin of the North China Plate. Hafnium analyses show that the three deformed granitoids have negative and variable εHf(t) values (-5.1 to -14.9) and Meso-Palaeoproterozoic (1.5 to 2.2 Ga) depleted-mantle model ages, suggesting the probable derivation from an isotopically heterogeneous old crust source. The source region for these magmas might have been related to Meso-Palaeoproterozoic material of the North China Craton underlying Chifeng. Based on zircon U-Pb data, the authors identified four stages of granitic magmatism, i.e., Late Carboniferous (327 Ma), Permian (285～252 Ma), Early Jurassic-Middle Triassic (241～184 Ma) and Early Cretaceous-Middle Jurassic (163～125 Ma). The new ages indicate that these plutons were emplaced in the late Palaeozoic-Mesozoic period. Early Carboniferous granite implies the existence of an Andean-style continental arc along the northern margin of the North China Block. The Permian granitic magmatism was probably related to the extension due to the final closure of the Paleo-Asian Ocean and the amalgamation of the Mongolian arc terrain with the northern North China Block. These events were followed by post-collisional/post-orogenic extension and large-scale magmatism during Triassic. Early Cretaceous-Middle Jurassic (163～125 Ma) magmatism in the Louzidian core complex area was developed in an extensional setting, possibly induced by lithospheric thinning in the North China Block. The geochronological framework provides important information for the constraint of the Paleozoic-Mesozoic tectonic evolution in the northern margin of the North China Block.

Abstract:The Alax metamorphic block (basement) distributed in the western margin of the North China Craton is mainly composed of Archean Diebusige Rock Group, Paleoproterozoic Bayan-Wulashan Rock Group, Paleo-Middle Proterozoic Alax Rock Group and some orthogneisses. There are some augen and banded gneisses in the Alax Rock Group, which were commonly referred to in the past as the metamorphic strata of Alax Rock Group. However, the authors' study indicates that these augen and banded gneisses are actually deformed granites (orthogneisses). Four samples of augen and banded gneisses were dated by zircon LA-ICPMS U-Pb technique. The zircons from the four samples show clear oscillatory growth zoning in CL images, suggesting that they are of magmatic origin. The augen gneiss (AL0820-2) from the Dabusushan area was formed at 913±7 Ma. The banded porphyritic gneiss (AL0815-3) and the banded amphibolite-bearing biotite-muscovite gneiss (AL0815-2) from Habuqigai area yielded magmatic crystallization ages of 921±7 Ma and 926±15 Ma, respectively. The magmatic age of banded gneiss (AL0817-1) from Keketuolegai area is 904±7 Ma. Geochemical characteristics of the deformed granites in Alax area indicate that they were formed at the syn-collision stage. The discovery of the Early Neoproterozoic granites in this area suggests that the Alax metamorphic basement was reformed by magmatic events of the Early Neoproterozoic orogenesis (Grenville orogenesis). The Alax metamorphic basement is different from the North China Craton, but is similar to the Qilianshan massif and northern Qinling massif in the evolutional history of Grenville. Therefore, the Alax metamorphic basement is an independent metamorphic massif.

Abstract:Granitoids are developed in Mordaoga area of Eerguna block, northern-central Da Hinggan Mountains. On the basis of granite batholith, the Taipingchuan porphyry Mo-Cu deposit was discovered. Metallogenic host rocks are granite porphyry, granodiorite porphyry and granodiorite, which are characterized by high-K calc-alkalic series, adakite magmatic affinity and slightly negative anomalies of Eu. In order to study the ages and sources of the mineralized porphyry and the relationship between the intrusive body and the Taipingchuan porphyry Mo-Cu deposit, zircon this paper reports U-Pb ages and Hf isotope characteristics of granite porphyry and granodiorite porphyry related to the porphyry molybdenite deposit. LA-ICP-MS zircon U-Pb dating results reveal that the Taipingchuan mineralized porphyries have ages of 183.6 Ma, 193.7 Ma and 199.1 Ma, suggesting that ganitoids were formed in early Jurassic and might stand for magmatic intrusion activities related to the closure of Mongolia-Okhotsk Ocean. Zircon Hf isotope characteristics indicate that three mineralized porphyry samples have zircon εHf（t）values ranging from -3.2 to 0.4, -3.1 to 1.8 and -3.7 to -1.1, with model ages of 1322 Ma, 1276 Ma and 1394 Ma respectively, implying that magma originated from the crustal growth and accretion of Meso-Neoproterozoic. Combined with previous zircon Hf isotope data obtained from Eerguna block, the authors hold that crustal growth and accretion took place in Meso-Neoproterozoic, and partial melting occurred in early Jurassic and resulted in the formation of granitic magma and mineralization in Eerguna block. The Taipingchuan mineralized porphyries are comparable with Wunugetushan porphyry in that they have similar tectonic setting, geochemical characteristics and ages of the host porphyry. It is thus inferred that the ore-forming age of the Taipingchuan porphyry molybdenite deposit should be 195 to 180 Ma.

Abstract:Located in the compound part of the EW-trending Paleozoic Central Asia-Mongolia orogenic belt and the eastern margin of the NNE-trending Asian continent orogenic belt of littoral West Pacific, the southwestern slope of the Da Hinggan Mountains in Inner Mongolia is a newly discovered nonferrous metallogenic belt with ideal mineralization potential. The unmetamorphosed magmatic rocks emplaced at the middle-late stage of Neopaleozoic are widely distributed in this area, and the lithologic association includes not only intermediate-acidic to alkaline rocks but also bimodal volcanic rocks. Although there exists great difference in their emplacement ages, they were all formed later than the metamorphic time of the Xilin Gol complex and the peak orogenic stage of the eastern segment of the Central Asia-Mongolia orogenic belt. Spatially, most of these magmatic rocks, with A-type or bimodal properties in geochemistry, are related to the extensional tectonic setting after the closure of the main suture. In this study, the authors acquired zircon SHRIMP U-Pb data of late Variscan magmatic rocks outcropped in southeastern Inner Mongolia, tectonically situated at the area between Erlian-Hegen suture and Solon-Xarmoron suture, with the purpose of making constraint on the closure time of the main suture between the Siberian plate and the Sino-Korean plate. Zircon SHRIMP U-Pb analyses yield emplacement ages of 310±2 and 311±2 Ma for quartz-diorite and diorite from the Weilasituo silver-polymetallic deposit, 319±3 Ma for granodiorite from the Bairendaba deposit, and 300±5 Ma for dacitic tuff from the Daolundaba deposit, indicating that they all belong to late Carboniferous. The emplacement ages of these magmatic rocks are about 20～40 Ma later than the metamorphic age (337±6 Ma) of the Xilin Gol complex formed at the peak stage of orogeny. These magmatic rocks were not affected by deformation and metamorphism, implying that they belong to late-/post-orogenic magmatic rocks. The authors hold that, although the Central Asia-Mongolia orogenic belt is characterized by poly-island arc accretions and poly-sutures, the orogenic process must have undergone many times of collision and convergence between palaeo-ocean crust and palaeocontinent, island arc and island arc, island arc and continent, palaeo-ocean crust and micro-continental block, micro-continental block and micro-continental block, and micro-continental block and palaeocontinent, and the main suture between the Siberian plate and the Sino-Korean plate is situated near the Erenhot-Hegenshan belt.

Abstract:Tectonic evolution of northern North China Block (NCB) and its relation with the Central Asia Orogenic Belt (CAOB) during the Late Paleozoic to Early Mesozoic period have aroused considerable interest among earth scientists in recently years. A summary of the recently obtained zircon U-Pb or 39Ar-40Ar ages of the Late Paleozoic-Early Mesozoic magmatic rocks in the northern margin of NCB indicates that at least three stages of magmatism including Devonian (400～360 Ma), late Early Carboniferous to Middle Permian (330～265 Ma) and latest Permian to Triassic (250～200 Ma) occurred during the Late Paleozoic to Early Mesozoic period. The main components of the Devonian magmatism are syenite and monzonite, together with some other rocks such as monzodiorite, alkaline granite, rhyolite and mafic-ultramafic rocks. These rocks exhibit high alkali content (K2O+Na2O) and have alkaline to high K calc-alkaline, metaluminous or weak peraluminous geochemical features. Rocks from the late Early Carboniferous-Middle Permian intrusive suite are composed mainly of diorite, quartz diorite, granodiorite and granite, with some gabbro and tonalite. The late Early Carboniferous-Middle Permian magmatic rocks have variable SiO2 content and calc-alkaline to high K calc-alkaline, metaluminous or weak peraluminous geochemical features. Some of the late emplaced magmatic rocks (latest Early Permian-Middle Permian) display shoshonitic or alkaline geochemical compositions, indicating a trend of transition from calc-alkaline to shoshonitic or alkaline series during magmatic evolution. The latest Permian magmatic rocks consist mainly of monzogranite, K-feldspar granite, syenite, monzonite, mafic-ultramafic rocks and some intermediate-felsic volcanic rocks. They are characterized by high content of SiO2, K2O and alkali (K2O+Na2O) and display geochemical signatures ranging from highly fractionated I-type to A-type. Magmatic evolution exhibits a transition trend from high K calc-alkaline series in the early stage to the coexistence of alkaline and high K calc-alkaline series during the late stage. Compared with the Devonian and late Early Carboniferous to Middle Permian rocks, the latest Permian to Triassic magmatic rocks show much more extensive distribution. The wide distribution of the Late Paleozoic to Early Mesozoic magmatic rocks indicates a very complex tectonomagmatic history of the northern margin of the NCB during the Late Paleozoic to Early Mesozoic period. The Devonian rocks are probably related to post-collisional extension after the arc-continental collision between the Early Paleozoic Bainaimiao arc belt and the northern margin of the North China Craton during the latest Silurian to earliest Devonian period. The late Early Carboniferous to Middle Permian intrusive rocks are interpreted as subduction-related magmatic rocks emplaced in an Andean-style continental margin arc during the southward subduction of the Paleo-Asian oceanic plate beneath the NCB. The formation of large quantities of latest Permian to Triassic magmatic rocks might have resulted from post-collisional/post-orogenic lithospheric extension after final collision and suturing of the Mongolian arc terranes with the NCB.