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1.
西藏高原南部花岗岩类同位素地质年代学   总被引：19，自引：0，他引：19  
In the study of isotopic geochronology of grauitoids in the southern part of Xizang plateau, 103 mica and zircon ages were determined by K-At method and U-Pb method. Based upon the above mica and zircon ages of various types of granitoid, together with their geological setting, three intrusive stages have been distinquished for granitoids in Southern Xizang : the first stage, 120--70 m. y. (late Yenshanian) ; the second stage,50---30 m.y. (early Himalayan) ; the third stage, 20--10 m.y. (late Himalayan). It is evident from the characteristic zonal distribution patterns of granitoids and the spacial-temporal consistency in their isotopic geochronology that there exists a close inter-connection between the subduetion stage and the collision stage.  相似文献   

2.
The coefficient (K) and distribution frequency of alkali feldspars in Xizang granitoids arc higher in later stages as compared with those in earlier stages The An value of plagioclase gradually decreases from earlier to later Stages. The Ab value of alkali feldspars of earlier stages is lower than that of later stages. Alkali feldspars from ordered to disordered have been all discovered. For most plutons, the extent of orer-disorder between alkali feldspar phenocrysts and groundmass is basically similar. On the other hand, however, the majority of plagioclase is of ordered type. Feldspars of late Yenshanian are of higher order state than that of Himalayan. In the light of composition and structure state as mentioned above it can be said that granitoids in Southern Xizang have a magmatie origin and they tend to be more acidic during their evolution from earlier to later stages.  相似文献   

3.
High-temperature geothermal water has abundant lithium (Li) resources, and research on the development and utilization of geothermal-type lithium resources around the world are increasing. The Qinghai–Tibetan Plateau contains huge geothermal resources; especially, Li-rich geothermal resources in southern Xizang, southwestern China, are widely developed. The Li-rich geothermal spots in Xizang are mainly distributed on both sides and to the south of the Yarlung Zangbo suture zone. Such resources are often found in the intensely active high-temperature Li-rich geothermal fields and, compared with other Li-rich geothermal fields around the world, the Li-rich geothermal fluid in the Xizang Plateau, southern Xizang is characterized by good quality: the highest reported Li concentration is up to 239 mg/L; the Mg/Li ratio is extremely low and ranges from 0.03 to 1.48 for most of the Li-rich geothermal fluid; the Li/TDS value is relatively high and ranges from 0.25–1.14% compared to Zhabuye Li-rich salt lake (0.19%) and Salar de Uyuni (Bolivia) (0.08–0.31%). Continuous discharge has been stable for at least several decades, and some of them reach industrial grades of salt lake brine (32.74 mg/L). In addition, elements such as boron (B), caesium (Cs), and rubidium (Rb) are rich and can be comprehensively utilized. Based on still-incomplete statistics, there are at least 16 large-scale Li-rich hot springs with lithium concentration of 20 mg/L or more. The total discharge of lithium metal is about 4300 tons per year, equivalent to 25,686 tons of lithium carbonate. Drilling data has shown that the depth is promising and there is a lack of volcanism (non-volcanic geothermal system). With a background of the partial-melting lower crust caused by the collision of the Indo-Asia continent and based on a comprehensive analysis of the tectonic background of southern Xizang and previous geological, geophysical, and geothermal research, deep molten magma seems to provide a stable heat source for the high-temperature Li-rich geothermal field. The Li-rich parent geothermal fluid rushes to the surface to form hot springs along the extensively developed tectonic fault zones in southern Xizang; some of the Li-rich fluid flows in to form Li-rich salt lakes. However, most of the Li-rich geothermal fluid is remitted to seasonal rivers and has not been effectively exploited, resulting in great waste. With the continuous advance of lithium extraction technologies in Li-rich geothermal fluid, the lithium resource in geothermal water is promising as a new geothermal type of mineral deposit, which can be effectively exploited. This is the first study to undertake a longitudinal analysis on the characteristics, distribution and scale, origin and utilization prospects of Li-rich geothermal resources in southern Xizang, research that will contribute to a deeper understanding of Li-rich geothermal resources in the area and attract attention to these resources in China.  相似文献   

4.
The Nanling region is an important nonferrous and rare metal metallogenic province in South China, in which most of the deposits are related to granitoids in genesis. It covers southern Hunan, southern Jiangxi, Guangxi, Guangdong and Fujian provinces, with a total area of about 550,000 km2. This metallogenic province is well known in the world for its rich tungsten and tin resources. In the past 40-odd years, a vast amount of mineral exploration activities and studies of the geology of mineral deposits have been carried out and great achievements obtained in the province. This paper is focused on a discussion about the deep tectonic processes in the orogenic belt during the Mesozoic and their contribution to the superaccumulation of metals. Tectonically, this metallogenic province is composed of three units: (1) the marginal continental orogenic belt in the Southeastern Coast fold system in the Yanshanian; (2) the intercontinental orogenic belt in the collision suture belt between the Yangtze and Cathay  相似文献   

5.
The tectonic setting of Cretaceous granitoids in the southeastern Tibet Plateau, east of the Eastern Himalaya Syntax, is debated. Exploration and mining of the Laba Mo–Cu porphyry-type deposit in the area has revealed Late Cretaceous granites. New and previously published zircon U–Pb dating indicate that the Laba granite crystallized at 89–85 Ma. Bulk-rock geochemistry, Sr–Nd isotopic data and in situ zircon Hf isotopic data indicate that the granite is adakitic and was formed by partial melting of thickened lower crust. The Ca, Fe, and Al contents decrease with increasing SiO2 content.These and other geochemical characteristics indicate that fractional crystallization of garnet under high-pressure conditions resulted in the adakitic nature of the Laba granite. Cretaceous granitoids are widespread throughout the Tibetan Plateau including its southeastern area, forming an intact curved belt along the southern margin of Eurasia. This belt is curved due to indenting by the Indian continent during Cenozoic, but strikes parallel to both the Indus–Yarlung suture zone and the Main Frontal Thrust belt. It is therefore likely that Cretaceous granitoids in both the Gangdese and southeastern Tibetan Plateau areas resulted from subduction of Neo-Tethyan lithosphere.  相似文献   

6.
LA-ICPMS U-Pb zircon dating of the Sanpinggou, Gangou and Fengzishan granitoids in the Douling Group of the Eastern Qinling yields ages of 760-685 Ma, which represents a strong tectono-magmatic event in the southern Qinling during the late Neoproterozoic. Geochemical data show that these intrusions have wide compositions ranging from minor gabbros through diorites to granodiorites. They are relatively enriched in LILE, poor in HFSE and strongly depleted in Nb and Ta, displaying affinities of Ⅰ-type granites formed in an active continental margin with oceanic subduction. In contrast to granitoids, gabbros and enclaves in the granitoids have higher REE abundances, relatively flat REE patterns, lower LILE, slightly higher HFSE and more depletion in Nb and Ta. All these suggest that the gabbros were formed by partial melting of the upper mantle above the subduction zone and the granitoids by the partial melting of the lower crust. Combined with regional geological data, the subduction-related granitoids in  相似文献   

7.
This paper reports sensitive high resolution ion micro-probe U-Pb zircon ages for the "Huoqiu Group" and granitoids of the Early Precambrian basement in the Huoqiu area, southeastern margin of the North China Craton. The "Huoqiu Group" is similar in rock association and metamorphism to the khondalite series, apart from it containing considerable amounts of banded iron formation. All detrital zircons from the "Huoqiu Group" meta-sedimentary rocks are 3.0 Ga and 2.75 Ga, without any 2.5 Ga and younger ones, as is commonly found in Paleoproterozoic khondalite series in other areas of the North China Craton. In the Huoqiu area, 2.75 Ga and 2.56 Ga granitoids have also been identified. This basement assemblage underwent strong metamorphism during the late Paleoproterozoic (~1.84 Ga) tectonothermal event that is widely developed in the North China Craton. Thus the formation time of the "Huoqiu Group" can be constrained between 2.75 and 1.84 Ga in terms of detrital and metamorphic zircon ages. It is considered, combined with regional data, that there may be a Paleoproterozoic collision orogen extending in a NWW–SEE direction to the southern margin of the North China Craton.  相似文献   

8.
Carboniferous magmatism is one of the most important tectonothermal events in the Central Asian Orogenic Belt(CAOB). However, the final closure time of the Kalamaili Ocean between East Junggar and Harlik Mountain is still debated. Early Carboniferous(332 Ma) and late Carboniferous(307–298 Ma) granitic magmatism from Kalamaili fault zone have been recognized by LA-ICP-MS zircon U-Pb dating. They are both metaluminous highly fractionated I-type and belong to the high-K calc-alkaline. The granitoids for early Carboniferous have zircon ε_(Hf)(t) values of-5.1 to +8.5 with Hf model ages(T_(DM2)) of 1.78–0.83 Ga, suggesting a mixed magma source of juvenile material with old continental crust. Furthermore, those for late Carboniferous have much younger heterogeneous zircon ε_(Hf)(t) values(+5.1 to +13.6) with Hf model ages(T_(DM2)=1.03–0.45 Ga) that are also indicative of juvenile components with a small involvement of old continental crust. Based on whole-rock geochemical and zircon isotopic features, these high-K granitoids were derived from melting of heterogeneous crustal sources or through mixing of old continental crust with juvenile components and minor AFC(assimilation and fractional crystallization). The juvenile components probably originated from underplated basaltic magmas in response to asthenospheric upwelling. These Carboniferous highly fractionated granites in the Kalamaili fault zone were probably emplaced in a post-collisional extensional setting and suggested vertical continental crustal growth in the southern CAOB, which is the same or like most granitoids in CAOB. This study provides new evidence for determining the post-accretionary evolution of the southern CAOB. In combination with data from other granitoids in these two terranes, the Early Carboniferous Heiguniangshan pluton represents the initial record of post-collisional environment, suggesting that the final collision between the East Junggar and Harlik Mountain might have occurred before 332 Ma.  相似文献   

9.
The three I-type plutons of Guantian(GT),Guidong(GD),Shangbao(SB)and the two S-type plutons of Xucun(XC)and Xiuning(XN) as well as their microgranitoid enclaves in southern China have been studied,Restite in the Motianling(MT) metasomatic granite in this area is described in this paper as well,Microgranitoid enclaves in the I-type granitoids may be divied into autoliths and schlierens which have marked differences both in petrography and geochemistry.In the S-type granitoids,schlierens are the major microgranitoid enclaves,but autoliths are rare.The metasomatic granite contains only restite without other enclaves.The microgranitoid enclaves and their host rocks have close ∈Nd(T)values and the same minerals within them are similar in composition.The microgranitoid enclaves,in general,don‘t represent the products of mixing of the syn-plutonic foreign mafic magma and the host acidic magma.They are the records of the evolution of intermediate-acidic magma itself.The formation of autoliths is related to the interdiffusion of different constituents in magma.Schlierens are the products of immiscible fractionation of the magma.  相似文献   

10.
The eastern margin of the Qaidam Basin lies in the key tectonic location connecting the Qinling, Qilian and East Kunlun orogens. The paper presents an investigation and analysis of the geologic structures of the area and LA-ICP MS zircon U-Pb dating of Paleozoic and Mesozoic magmatisms of granitoids in the basement of the eastern Qaidam Basin on the basis of 16 granitoid samples collected from the South Qilian Mountains, the Qaidam Basin basement and the East Kunlun Mountains. According to the results in this paper, the basement of the basin, from the northern margin of the Qaidam Basin to the East Kunlun Mountains, has experienced at least three periods of intrusive activities of granitoids since the Early Paleozoic, i.e. the magmatisms occurring in the Late Cambrian (493.1±4.9 Ma), the Silurian (422.9±8.0 Ma-420.4±4.6 Ma) and the Late Permian-Middle Triassic (257.8±4.0 Ma-228.8±1.5 Ma), respectively. Among them, the Late Permian - Middle Triassic granitoids form the main components of the basement of the basin. The statistics of dated zircons in this paper shows the intrusive magmatic activities in the basement of the basin have three peak ages of 244 Ma (main), 418 Ma, and 493 Ma respectively. The dating results reveal that the Early Paleozoic magmatism of granitoids mainly occurred on the northern margin of the Qaidam Basin and the southern margin of the Qilian Mountains, with only weak indications in the East Kunlun Mountains. However, the distribution of Permo-Triassic (P-T) granitoids occupied across the whole basement of the eastern Qaidam Basin from the southern margin of the Qilian Mountains to the East Kunlun Mountains. An integrated analysis of the age distribution of P-T granitoids in the Qaidam Basin and its surrounding mountains shows that the earliest P-T magmatism (293.6-270 Ma) occurred in the northwestern part of the basin and expanded eastwards and southwards, resulting in the P-T intrusive magmatism that ran through the whole basin basement. As the Cenozoic basement thrust system developed in the eastern Qaidam Basin, the nearly N-S-trending shortening and deformation in the basement of the basin tended to intensify from west to east, which went contrary to the distribution trend of N-S-trending shortening and deformation in the Cenozoic cover of the basin, reflecting that there was a transformation of shortening and thickening of Cenozoic crust between the eastern and western parts of the Qaidam Basin, i.e., the crustal shortening of eastern Qaidam was dominated by the basement deformation (triggered at the middle and lower crust), whereas that of western Qaidam was mainly by folding and thrusting of the sedimentary cover (the upper crust).  相似文献   

11.
The Jiangda–Deqen–Weixi continental margin arc(DWCA) developed along the base of the Changdu–Simao Block and was formed as a result of the subduction of the Jinsha River Ocean Slab and the subsequent collision. The Ludian batholith is located in the southern part of the DWCA and is the largest batholith in northwest Yunnan. Granite samples from the Ludian batholith yield an early Middle Permian age of 271.0 ± 2.8 Ma. The geochemical data of the early Middle Permian granitoids show high Si2 O, low P2 O5 and MgO contents that belong to calc-alkaline series and peraluminous I-type rocks. Their εHf(t) values range from-5.01 to +0.58, indicating that they were formed by hybrid magmas related to the subduction of the Jinsha River Tethys Ocean. The monzonite and monzogranite samples yield Late Permian ages of 250.6 ± 1.8 Ma and 252.1 ± 1.3 Ma, respectively. The Late Permian granitoids are high-K calc alkaline and shoshonite series metaluminous I-type rocks. Their εHf(t) values range from-4.12 to-1.68 and from-7.88 to-6.64, respectively. The mixing of crustal and mantle melts formed the parental magma of the Late Permian granitoids. This study, combined with previous work, demonstrates the process from subduction to collision of the Jinsha River Paleo-Tethys Ocean.  相似文献   

12.
The granitoids of the continental crust transformation series in South China may be divided into threetypes: (1) synorogenic migmatic and magmatic type. (2) anorogenic continental crust anatexis type, and (3)syncollision type. Based on the results of Sr and Nd isotopic determinations, the source material compositionof the three types of granitoids is calculated with crust-mantle binary mixing simulation. The calculations indi-cate that the granitoids of the first type consist of 78.6-89.7% upper crust endmember materials and15.0-10.3% depleted mantle endmember materials, the granitoids of the second type are composed of 63.7%upper crust endmember materials and 36.3% depleted mantle endmember materials, and those of the third type100% upper crust endmember materials. Hence. the source material composition of the granitoids of all thethree types is dominated by upper crust endmembers.  相似文献   

13.
西藏南部花岗岩类中重结晶的黑云母与板块碰撞的关系   总被引：2，自引：0，他引：2  
Recrystallized biotite occurs in granitoid rocks from some plutens in the Lhagoi Kangri and Kangdese belts in southern Xizang. These plutons are characterized by well-developed micro-fractures, orientational arrangement of dark minerals showing gneissose structures to varing extents. This is consistent with the fact that K-Ar ages of crystallized biotite (30--17 my) are much younger as compared with the host rooks. Recrystallized biotites are mostly recognized along the tectonic suture line between the Indian plate and the Eurasian continental plate, i.e., in the neighborhood of the Yarlung Zangbo River and its north bank as well as in the Lhagoi Kangri Ranges.The authors postulate that when drifting north-northeastward, the Indian sub-continental plate was conteracted by the Kangdese belt as a result of the subduction of the Indian plate underneath the Eurasian Continental plate, causing a dramatic increase instress on the southern side, i.e., near the tectanic suture line, of the rock belt followed by the rising of temperature which resulted in the recrystallization of biotite in some plutons.  相似文献   

14.
Obvious differences in mineralization characteristics exist between the southern and northern parts of the eastern part of the Jiangnan Uplift in northern Jiangxi Province and southern Anhui Province. The regional metallogeny is discussed, and the ore-forming fluid systems are classified in this article. It is proposed that the fluid ore-forming activities in the Jiangnan Uplift both in northern Jiangxi and southern Anhui have close relationships with the crust-mantle interaction and magmatic-tectonic activities. The types and scales of the mineralization on the both sides of the eastern Jiangnan Uplift were determined by fluid ore-forming systems and geological backgrounds.  相似文献   

15.
Granitoids are widely spread in the Nanling Region of China.Four rockbodies in the region the been studied for their REE,Rb,Sr,Ba and Sc distributions.The four rockbodies occurred in different locations and are characterized as being different in age and type.The rock types are presented as follows:Qinghu monzonite,Guangxi;Fuxi granodiorite,Guangdong;Jiufeng monzonitic granite,Hunan;Zudong K-feldspar granite,Jiangxi.From the major and trace element distributions in these granitoids it is clearly shown that Rb/Sr ratios in the rocks tend to increase with increasing SiO2 content and differentiation index(DI),but LREE/HREE,La/Yb and K/Rb ratios tend to decrease,suggesting a correlation between trace element distribution and major element composition for the granitoids.The distribution characteristics of trace elements in each of the rockbodies are described in detail.From the comparative analysis of the Qinghu monzonite and Fuxi granodiorite it is evidenced that the REE distribution is closely related to the sequence of crystallization for the minerals,and also to the petrochemical types of these granitoids in addition to their crystal chemistry.  相似文献   

16.
The Tafresh granitoids are located at the central part of the Urumieh-Dokhtar Magmatic Arc(UDMA) in Iran. These rocks, mainly consisting of diorite and granodiorite, were emplaced during the Early Miocene. They are composed of varying proportions of plagioclase + K-feldspar + hornblende ± quartz ± biotite. Discrimination diagrams and chemical indices of amphibole phases reveal a calc-alkaline affinity and fall clearly in the crust-mantle mixed source field. The estimated pressure, derived from Al in amphibole barometry, is approximately 3 Kb. The granitoids are I-type, metaluminous and belong to the calc-alkaline series. They are all enriched in light rare earth elements and large ion lithophile elements, depleted in high field strength elements and display geochemical features typical of subduction-related calc-alkaline arc magmas. Most crystal size distribution(CSD) line patterns from the granitoids show a non-straight trend which points to the effect of physical processes during petrogenesis.The presence of numerous mafic enclaves, sieve texture and oscillatory zoning along with the CSD results show that magma mixing in the magma chamber had an important role in the petrogenesis of Tafresh granitoids. Moreover, the CSD analysis suggests that the plagioclase crystals were crystallized in a time span of less than 1000 years, which is indicative of shallow depth magma crystallization.  相似文献   

17.
A systematic geological and geochemical study was conducted for the granitoids of different periods in the western Kunlun erogenic belt. The study indicates that the granitoids belong to tholeiitic, calc-alkaline, high-K calc-alkaline, alkaline and shoshonitic series, and that there are 5 genetic types, i.e., I-, S-, M-, A- and SH-type, of which SH-type is first put forward in this paper, which corresponds to shoshonitic granitoids.  相似文献   

18.
By analyzing the characteristics of development, structural evolution and reservoir beds of the residual carbonate strata, this study shows that the residual carbonate strata in the Yingmaili low uplift are favorable oil and gas accumulation series in the Tabei （northern Tarim uplift） uplift. There are different patterns of hydrocarbon accumulation on the northern and southern slopes of the Yingmaili low uplift. The north-south differentiation of oil reservoirs were caused by different lithologies of the residual carbonate strata and the key constraints on the development of the reservoir beds. The Mesozoic terrestrial organic matter in the Kuqa depression and the Palaeozoic marine organic matter in the Manjiaer sag of the Northern depression are the major hydrocarbon source rocks for the northern slope and southern slope respectively. The hydrocarbon accumulation on the northern and southern slopes is controlled by differences in maturity and thermal evolution history of these two kinds of organic matter. On the southern slope, the oil accumulation formed in the early stage was destroyed completely, and the period from the late Hercynian to the Himalayian is the most important time for hydrocarbon accumulation. However, the time of hydrocarbon accumulation on the northern slope began 5 Ma B.P. Carbonate inner buried anticlines reservoirs are present on the southern slope, while weathered crust and paleo-buried hill karst carbonate reservoirs are present on the northern slope. The northern and southern slopes had different controlling factors of hydrocarbon accumulation respectively. Fracture growth in the reservoir beds is the most important controlling factor on the southern slope; while hydrocarbon accumulation on the northern slope is controlled by weathered crust and cap rock.  相似文献   

19.
Paleoproterozoic granitoids are an important constituent of the Jiao–Liao–Ji Belt(JLJB). The spatial-temporal distribution and types of Paleoproterozoic granitoids are closely related to the evolution of the JLJB. In this paper, we review the field occurrence, petrography, geochronology, and geochemistry of Paleoproterozoic granitoids on Liaodong Peninsula, northeast China. The Paleoproterozoic granitoids can be divided into pre-tectonic(～2.15 Ga; peak age=2.18 Ga) and post-tectonic(～1.85 Ga) granitoids. The pre-tectonic granitoids are magnetite and hornblende–biotite monzogranites and granodiorites. Pre-tectonic monzogranites are widespread in the JLJB and have A_2-type affinities. In contrast, pretectonic granodiorites are only present in the Simenzi area and have adakitic affinities. The post-tectonic granitoids consist of porphyritic monzogranite, syenite, diorite, granodiorite, quartz monzonite, monzogranite, and granitic pegmatite, which are adakitic rocks and I-, S-, and A_2-type granitoids. The assemblage of pre-tectonic A_2-type granitoids and adakitic rocks indicates the initial tectonic setting of the JLJB was a continental back-arc basin. The assemblage of post-tectonic adakitic rocks and I-, S-, and A_2-type granitoids indicates a post-collisional setting. The 2.20–2.15 Ga A_2-type granitoids and adakitic rocks were associated with the initial stage of back-arc extension, and the peak of back-arc extension is inferred from the subsequent(2.15–2.10 Ga) mafic intrusive activity. The ～1.90 Ga adakitic rocks mark the beginning of the postcollisional stage, which was followed by the intrusion of low-temperature S-and I-type granitoids. High-to low-pressure granitoids(S-type) were generated during the peak of post-collisional lithospheric delamination and asthenospheric upwelling. The emplacement of later granitic pegmatites occurred during the waning of the orogeny.  相似文献   

20.
This study is concerned mainly with the concentrations of uranium and thorium in sedimentary strata which comprise the High Himalaya Belt and the Tertise Himalaya Belt in Southern Xizang,as well as with the relationship between th/L^ and the major composition of the same rock.The law governing the evolution of U and Th,and the Th/U ratio with time is discussed,too.  相似文献   

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