内蒙古白云鄂博地区元古宙构造-岩浆演化史与超大型REE-Nb-Fe矿床成因

Bayan Obo giant REE-Nb-Fe deposit in the northen margin of the North China Craton (NCC) is well known in the world for its abundant rare earth element resources. There is nearly one hundred year of studying history in substance component, chronology and geochemistry of the ore deposit, since the main ore body was found in 1927. However, there still exist remarkable divergences in genesis, mineralized age and material origin. Especially the REE enrichment mechanism leaves us a secret. Recent research shows that the Bayan Obo ore deposit likely resulted from the carbonatite magma activity, which is a favorable factor for REE accumulation. Based on the analysis of tectonic evolution history of north margin of NCC this thesis mainly discussed the formation background of cratonic margined rifts in Bayan Obo, and presented the analytical results of formation environment, intrusion age and deep origin of Proterozoic carbonatite magma. These research results can provide evidence for ore genesis. LA ICP-MS U-Pb dating on zircon shows that the Neoarchean basement was mainly composed of calc-alkaline TTG gneisses (2588±16Ma). The collision orogeny movement of the northen margin of the NCC between 2.0 Ga to 1.9 Ga brought the swarm of diorite-granodiotite magma (2023±16Ma) and intense regional metamorphism event (1906.3±7.7 Ma to 1892.7±6.7 Ma). In the sequent super continent break up background, intense metamorphic and deformed basement complex was uplifted to the surface suffered denudation, forming Mesoproterozoic Bayan Obo group in the contemporary continental margin rifts. The uplift of basement complex and formation of continental rifts were likely related with mantle plume activity. Evidence from petrological and geochemical data suggests that abundant alkaline-basic magma resulted from enhancement of continental breakup activity, that separated into carbonatite veins and mafic dykes by melt immiscibility mechanism, intruded in Bayan Obo margin rifts at the late stage of extension movement. Carbonatite veins can be divided into three main types by mineral composition: dolomite carbonatite, dolomite-calcite coexistent carbonatite and calcite carbonatite. Intrusion relationship between different types of carbonatite veins show that the calcite carbonatite veins were formed latter than the dolomite type as well as the coexistent type. Moreover, geochemical data also reveals successive and evolutive character between them. The content of REE increases together with the calcite minerals component. That is to say that REE gradually accumulated as the evolution of carbonatite magma. High precision Sm-Nd isochron data shows that the intrusion age of carbonatite veins was at 1319±48Ma. Moreover, the REE mineralization age in calcite carbonatite veins was around 1275±87Ma that is consistent with the intrusion age in error range. According to these data the abundant REE already existed in the carbonatite magma before intrusion and result in the earlier ore mineralization. The average age of mineralized dolomite was at 1353±100Ma, and the mineralization age of apatite in coarse grain dolomite was around 1329±150Ma. These data is consistent with carbonatite. Considering the coincident rare, trace element and isochron composition between them, it is presumed that mineralized dolomite was also the carbonatite intrusion and was the mainly factor for huge REE enrichment.

大别山高压-超高压带片麻岩锆石的研究

The zircons from gneisses in high and ultrahigh pressure (HP-UHP) metamorphic zones of the Dabie Mountains have been studied on three aspects in this paper, including (1) radiation damage of zircon using Laser Raman spectrum; (2) genesis determination of zircons based on geochemistry; (3) temperature estimate of the HP-UHP metamorphism using Ti-in-zircon thermometer. The zircons have the full widths at half-maximum less than 15 cm-1 at the 1008 cm-1 peak, suggesting that they are well crystallized to moderately damaged. The early inherited zircons from gneisses had undergone significant annealing and recrystallization during the HP-UHP metamorphic event. The α-doses that zircons suffered were accumulated from about 200Ma, indicating that HP-UHP metamorphic rocks have been exhumed to the surface of the earth at this time. The studies from the CL images, mineral inclusions, U-Pb ages and trace elements reveal that metamorphic zircons were formed as two kinds of mechanisms: metamorphic growth and recrystallization. The zircons of metamorphic growth and recrystallization zircons that were completely equilibrated during the HP-UHP metamorphic event have been chosen to carry out for temperature estimate using the Ti-in-zircon thermometer. The result shows that the HP-UHP terrain of the Dabie Mountains can be divided into five zones with temperature gaps, suggesting that the terrain consists of tectonic slices with different metamorphic history.

山东莒南地区韧性剪切带的变形特征与形成演化

Ju Nan of Shandong province is located at southwest of Sulu UHP (ultrahigh-pressure) metamorphic terrane. It is composed of gneiss, paragneiss, eclogites, ultramafic rocks, marble and quartzite. A large ductile shear zone extends east-west has been found at the Zhubian, The south of Junan county. The Zhubian ductile shear zone is composed of high srain rock and mylonites. The mylonites fall into 3 types: Initial gneiss mylonite, mylonite and altramylonit.obvious lineation of penetration,foliation,S-Cfabrics,porphyroclasts,folds,irregularundulatory,extinction,subgrain boundary, dynamic recrystallization microstructure, core-mantle structure and are common in the ductile shear zone. Based on field work and microstructural analyse, a conclution is arrived: The ductile shear zone is an approximately SE trending faults. The Zhubian ductile shear zone formed at Ep ―Hb facies conditions which could be proved by deformaed and metamorphosed mineral aggregates, Deformation behavior, Ternary-feldspar geothermometry and so on. Zircon MC―ICP―MS U-Pb analysis is performed on the mylonite and have an average age ―835.9±13.9Ma, it’s the primary rocks formed age. The Zhubian ductile shear zone maybe formed at 224-242Ma.

内蒙古克什克腾旗小东沟斑岩型钼矿床的成矿作用

In this paper, the Xiaodonggou porphyry molybdenum deposit located in the Xarmoron molybdenum metallogenic belt is chose as the research area. We have analyzed the petrology of the Xiaodonggou pluton in detail and made chemical analysis of the major and trace elements, Rb-Sr and Sm-Nd isotope, common lead isotope and SHRIMP zircon U-Pb dating et al; in the other hand, we use the molybdenite to make common lead analysis and Re-Os isotopic dating. The Xiaodonggou pluton is rich in silicon, potass, zirconium, and low in REE. In addition, it has no minus Eu abnormity and show a isotopic composition high in εNd(t) and low in Sri, indicating its magma origining from the melting of juvenile thicken lower crust. In the meanwhile, it contained the features of high temperature, quick melting, quick segregation and quick emplacement. The common lead analysis of the pluton orthoclase and molybdenite show that the former transfer from orogen to mantle and the latter come from mantle, which is consistent to the molybdenite sulfur isotopic and quartz oxygen isotopic composition, demonstrating that the rock and ore-forming materials of deposit having different sources, magma from the lower crust mixing with mantle fluid. In plus, we use the physical experiments results of the water-magma reaction to explain the interaction of magma and mantle fluid. In the deep crust, these two systems uplifted in a immiscible state; when they reached low depth, the stream film between fluid-magma collapsed, and the magma was broken into small agglomerates by the fluid, then they mixed thoroughly. The SHRIMP zircon U-Pb dating gave a result of 142±2Ma and the molybdenite Re-Os dating result is 138.1±2.8Ma, corresponding to the big tectonic transition period of 140Ma, when the major stress field changing from south and north to west and east. At this time, the Da Hinggan ling ranges area was under an extensive background, underplating proceeded and mantle materials could add into the magmas forming in the lower crust. So, from the above analysis, we propose the following model for the Xiaodonggou porphyry molybdenum deposit: in the early Cretaceous period, the Da Hinggan ling ranges area was under a extensive background, the adding of mantle fluid containing ore materials into heated lower crust made it melting to produce magmas. Following more mantle fluid got into the magma room and urged the magma to segregate from the source quickly. The fluid and magma uplifted together, when they arrived at shallow depth, the fluid-magma became unstable and the latter was broken into many small agglomerates with fluid connecting them in the interspaces. Because of the H+, K+ and various elements existing in the fluid, it would reacted with the magma and the rock through alteration and ore minerals crystallized out, forming the Xiaodonggou porphyry deposit with disseminated mineralization phenomenon.

班公湖带多不杂超大型富金斑岩铜矿床的成岩成矿年代学、岩石学及高氧化岩浆¬流体-成矿作用

Duobuza copper deposit, newly discovered typical gold-rich porphyry copper deposit with superlarge potential, is located in the Tiegelong Mesozoic tectonic -magmatic arc of the southern edge of Qiangtang block and the northern margin of Bangonghu-Nujiang suture. Quartz diorite porphyrite and grandiorite porphyry, occurred in stock, are the main ore-bearing porphyries. As the emplacement of porphyry stock, a wide range of hydrothermal alteration has developed. Within the framework of the ore district, abundant hydrothermal magnetite developed, and the relationship between precipitation of copper and gold and hydrothermal magnetite seems much close. Correspondingly, a series of veinlets and network veinlets occurred in all alteration zones. Therefore, systematic research on such a superlarge high-grade Duobuza gold-rich porphyry copper deposit can fully revealed the metallogenic characteristics of gold-rich porphyry copper deposits in this region, establish metallogenetic model and prospecting criteria, and has important practical significance on the promotion of regional exploration. In addition, this research on it can enrich metallogenic theory of strong oxidation magma-fluid to gold-rich porphyry copper deposit, and will be helpful to understand the metallogenic characteristics in early of subduction of Gangdese arc stages and its entire evolution history of the Qinghai-Tibet Plateau, the temporal and spatial distribution of ore deposits and their geodynamics settings. Northern ore body of Duobuza copper deposit have been controlled with width (north-south) about 100 ~ 400 m, length (east-west) about 1400 m, dip of 200 °, angle of dip 65 °~ 80 °. And controlled resource amount is of 2.7 million tons Cu with grade 0.94% and 13 tons Au with 0.21g/tAu. Overall features of ore body are large scale, higher grade copper, gold-rich. Ore occurred in the body of granodiotite porphyry and quartz diorite porphyrite and its contact zone with wall rock. Through the detailed mapping and field work studies, some typies of alteration are identificated as follows: albitization, biotititation, sericitization, silication, epidotization, chloritization, carbonatization, illitization, kaolinization and so on. The range of alteration is more than 10km2. Wall alteration zone can be divided into potassic alteration, moderate argillization alteration, argillization, illite-hydromuscovite or propylitization from ore-bearing porphyry center outwards, but phyllic alteration has not well developed and only sericite-quartz veins occurred in local area. Moreover, micro-fracture is development in ore district , and correspondingly a series of veinlets are development as follows: biotite vein (EB type), K-feldspar-biotite-chalcopyrite-quartz vein, magnetite-antinolite-K-feldspar vein, quartz-chalcopyrite-magnetite veins (A-type), quartz-magnetite-biotite-K-feldspar vein, chalcopyrite veinlets in potassic alteration zone; (2) chalcopyrite occurring in the center vein–quartz vein (B type), chalcopyrite veinlets, chalcopyrite-gypsum vein in intermediate argillization alteration; (3) chalcopyrite- pyrite-quartz vein, pyrite-quartz vein, chalcopyrite-gypsum veins, quartz-gypsum- molybdenite-chalcopyrite vein in argillization alteration; (4) gypsum veins, quartz-(molybdenite)-chalcopyrite vein, quartz-pyrite vein, gypsum- chalcopyrite vein, potassium feldspar veinlets, Carbonate veins, quartz-magnetite veins in the wall rock. In short, various veins are very abundant within the framework of the ore district. The results of electronic probe microscopy analysis (EMPA) indicate that Albite (Ab 91.5~99.7%) occurred along the rim of plagioclase phenocryst and fracture, and respresents the earliest stages of alteration. K-feldspar (Or 75.1~96.9%) altered plagioclase phenocryst and matrix or formed secondary potassium feldspar veinlets. Secondary biotite occurred mainly in phenocryst, matrix and veinlets, belong to magnesium-rich biotite formed under the conditions of high-oxidation magma- hydrothermal. Chloritization developed in all alteration zones and alterd iron- magnesium minerals such as biotite and hornblende and then formed chlorite veinlets. As the temperature rises, Si in the tetrahedral site of chlorite decreased, and chlorite component evolved from diabantite to ripiolite. The consistent 280℃~360℃ of formation temperature hinted that chlorite formed on the same temperature range in all alteration zones. However, formation temperature range of chlorite from the gypsum-carbonate-chlorite vein was 190℃~220℃, and it may be the product of the latest stage of hydrothermal activity. The closely relationship between biotite and rutile indicate that most of rutiles are precipitated in the process of biotite alteration and recrystallization. In addition, the V2O3 concentration of rutile from ore body in Duobuza gold-rich porphyry copper deposit is >0.4％, indicate that V concentration in rutile has important significance on marking main ore body of porphyry copper deposit. Apatites from Duobuza deposit all are F-rich. And apatite in the wall rock contained low MnO content and relatively high FeO content, which may due to the basaltic composition of the wall rocks. The MnO in apatite from altered porphyry show a strong positive correlation with FeO. In addition, Cl/F ratio of apatite from wall rock was highest, followed by the potassic alteration zone and potassic alteration zone overprinted by moderate argillization alteration was the lowest. SO2 in Apatite are in the scope of 0 to 0.66%, biotite in the apatite has the highest SO2, followed by the potassic alteration zone, potassic alteration zone overprinted by moderate argillization alteration, and the lowest in the surrounding rocks, which may be caused by the decrease of oxygen fugacity of hydrothermal fluid and S exhaust by sulfide precipitation in potassic alteration. Magnetite in the wall rock have higher Cr2O3 and lower Al2O3 features compared with altered porphyry, this may be due to basalt wall rock generally has high Cr content. And magnetites have higher TiO2 content in potassic alteration than moderate argillization alteration overprinted by potassic alteration, argillization and wall rock, suggested that its formation temperature in potassic alteration was the highest among them. The ore minerals mainly are chalcopyrite and bornite, and Au contents of chalcopyrite, bornite, and pyrite are similar with chalcopyrite slightly higher. The Eu* negative anomaly of disseminated chalcopyrite was relatively lower than chalcopyrite in veinlets. Within a drill hole, the Eu* negative anomaly of disseminated chalcopyrite was gradually larger from bottom to top. Magnetite has the same distribution model, with obvious negative Eu* abnormal, and ΣREE in great changes. The gypsum has the highest ΣREE content and the obvious negative anomaly, and biotite obviously has the Eu* abnormal. Based on the petrographic and geochemical characteristics, five series of magmatic rocks can be broadly classified; they are volcanic rocks of the normal island arc, high-Nb basaltic rocks, adakites, altered porphyry and diorite. The Sr, Nd, Hf isotopes and geochemistry of various series of magmatic rock show that they may be the result of mixing between basic magma and various degrees of acid magma coming from lower crust melted by high temperature basic underplating from partial melting of the subduction sediment melt metasomatic mantle wedge. Furthermore S isotope and Pb isotope of the sulfide, ore-bearing porphyries and volcanic rocks indicated ore-forming source is the mantle wedge metasomatied by subduction sediment melt. Oxygen fugacity of magma estimated by Fe2O3/FeO of whole rock and zircon Ce4+/Ce3+ indicated that the oxidation of basalt-andesitic rocks is higher than ore-forming porphyry, and might imply high-oxidation characteristics of underplated basic magma. Its high oxidative mechanism is likely mantle sources metasomatied by subduction sediment magma, including water and Fe3+. And such high oxidation of basaltic magma is conducive to the mantle of sulfides in the effective access to melt. And the An component of dark part within plagioclase phenocryst zoning belong to bytownite (An 74%), and its may be a result of magma composition changes refreshment by basaltic magma injection. SHRIMP zircon U-Pb and LA-ICP-MS zircon U-Pb geochronology study showed that the intrusions and volcanic rocks from Duobuza porphyry copper deposit belong to early Cretaceous magma series (126~105Ma). The magma evolution series are as follows: the earliest diorite and diorite porphyrite → ore-bearing porphyry and barren grandiorite porphyry →basaltic andesite → diorite porphyrite → andesite → basaltic andesite, and magma component shows a evolution trend from intermediate to intermediate-acid to basic. Based on the field evidences, the formation age of high-Nb basalt may be the latest. The Ar-Ar geochronology of altered secondary biotite, K-feldspar and sericite shows that the main mineralization lasting a interval of about 4 Ma, the duration limit of whole magma-hydrothermal evolution of about 6 Ma, and possibly such a long duration limit may result in the formation of Duobuza super-large copper deposit. Moreover, tectonic diagram and trace element geochemistry of volcanic rocks and diorite from Duobuza porphyry copper deposit confirm that it formed in a continental margin arc environment. Zircon U-Pb age of volcanic rocks and porphyry fall in the range of 105~121Ma, and Duobuza porphyry copper deposit locating in the north of the Bangonghu- Nujiang suture zone, suggested that Neo-Tethys ocean still subducted northward at least early Cretaceous, and its closure time should be later than 105 Ma. Three major inclusion types and ten subtypes are distinguished from quartz phenocrysts and various quartz veins. Vapor generally coexisting with brine inclusions, suggest that fluid boiling may be the main ore-forming mechanism. Raman spectrums of fluid inclusions display that the content of vapor and liquid inclusion mainly contain water, and vapor occasionally contain a little CO2. In addition, the component of liquid inclusions mainly include Cl-, SO42-, Na+, K+, a small amount of Ca2+, F-; and Cl- and Na+ show good correlation. Vapor mainly contains water, a small amount of CO2, CH4 and C2H6 and so on. The daughter minerals identified by Laman spectroscopy and SEM include gypsum, chalcopyrite, halite, sylvite, rutile, potassium feldspar, Fe-Mn-chloride and other minerals, and ore-forming fluid belong to a complex hydrothermal system containing H2O-NaCl-KClFeCl2CaCl2. H and O isotopic analysis of quartz phenocryst, vein quartz, magnetite, chlorite and gypsum from all alteration zones show that the ore-forming fluid of Duobuza gold-rich porphyry copper deposit consisted mainly of magmatic water, without addition of meteric water. Duobuza gold-rich porphyry copper deposit formed by the primary magmatic fluid (600-950C), which has high oxidation, ultra-high salinity and metallogenic element-rich, exsolution direct from the magma, and it is representative of the typical orthomagmatic end member of the porphyry continuum. Moreover, the fluid evolution model of Duobuza gold-rich porphyry copper deposit has been established. Furthermore, two key factors for formation of large Au-rich porphyry copper deposit have been summed up, which are ore-forming fluids earlier separated from magma and high oxidation magma-mineralization fluid system.

东天山后碰撞镁铁-超镁铁岩镍铜硫化物矿床PGE地球化学示踪与富集规律研究

Eastern Tianshan area, a Paleozoic complex trench-arc-basin system, experienced multi-period sudbuction and collision in geological history. A large number of Early Permian mafic-ultramafic intrusions emplaced along deep faults in post-collision extension tectonic stage and hosted a series of magmatic Cu-Ni sulfide deposits. This paper sets newly-discovered Tianyu magmatic Cu-Ni sulfide deposit related to small intrusion as an example. On basis of the study of ore-forming mechanism of Cu-Ni deposit, we compared PGE content and discussed enrichment mechanism and regularity of mafic-ultramafic rocks and ores in Jueluotage tectonic belt and Central Tianshan Massif. PGE and Cu, Ni, S contents correlate with each other. PGE is mainly controlled by S content.Samilar PGE distribution patterns of mafic-ultramafic show that complex originated from the same parental magma; Pd/Ir and Ni/Cu ratios indicate that high-Mg basaltic magma and deep sulfide segregation happened during magma evolution process. PGE and Cu-Ni ores are enriched in liquid sulfide and only individual samples completely control by monosulfide solid solution. Comparison of all control factors, early segregation of sulfide and quality of supply of magma may be the key factors leading to the Eastern Tianshan magmatic copper-nickel sulfide deposits don’t reach PGE grade, but we do not rule out the possibility of occurrence continuous mafic-ultramafic rocks and PGE-rich layer in deep.

东准噶尔和尔赛斑岩铜矿特征及其形成的构造背景

Hersai porphyry copper deposit(PCD) of eastern junggar, newly discovered copper deposit, is located at the eastern segment of the Xiemisitai-Kulankazigan-Zhifang-Qiongheba Paleozoic island arc, Eastern Junggar. The Hersai PCD is developed in a intrusive complex, characterized by intensive and multiform hydrothermal alteration, including potassic alteration, silification, chloritization，sericitization，kaolinitization and carbonatization. Granodiorite, grandiorite porphyry, granite and concealed explosion breccia are hosts of the ore bodies containing veinlet and disseminated ore. Ore-bearing granite (ZK107-1-9), granodiorite (ZK107-1-9) and Ore-barren granodiorite (HES2-1) are selected to date zircon U-Pb age by SHRIMP method, and have an age of 429.4±6.4Ma ,413.0±3.4Ma and 411.1±4.8Ma, respectively, showing that they were emplaced from Late Silurian to Early Devonian. In addition, sample ZK107-1-9 has some hydrothermal zircons with a weighted mean 206Pb/238U age of 404.9±3.7Ma which is interpreted to be related to the granodiorite porphyry. Re-Os dating of five molybdenite samples yielded a weighted average model age of 408.0±2.9Ma, indicating the metallogenic epoch of the Hersai PCD. The ore-forming age is close to the petrogenic time of garnodiorite (411-413Ma), this suggests the ore-forming porphyry is most possiblely granodiorite porphyry. Systematic major - trace elements and Rb-Sr-Sm-Nd-Pb-Hf isotopic characteristics were studied. Analysis results show that these intrusives have some interesting and special characteristics, as following:1) containing both calc-alkaline rocks and high potassium calc-alkaline rocks ; 2) have some characteristics of adakite, but not totally, such as much lower La/Yb ratios and no Eu anomaly or just faint Eu anomaly; 3) have an initial 87Sr/86Sr ratios(0.703852-0.704565) similar to that of BSE, positive εNd(t) values between 6.1 and 7.4, the initial 206Pb/204Pb values (17.576-17.912), 207Pb/204Pb values (15.400-15.453) , 208Pb/204Pb values (37.252-37.466) , and high εHf(t) values (10.2-15.4) close to the value of depleted mantle. These geochemical features suggest that these igneous rocks in the Hersai area not only have some characteristics of island arc, but also some characteristics that only appear in the continental margin arc. It is suggested that Hersai PCD is formed in the subduction setting by the partial melting of young crust. These works and advancements mentioned in the paper are helpful to understand the deposit geology, geochemistry and metallogenesis of Hersai PCD. It is also significant to understand mineralization and tectonic setting in the Qiongheba area.

内蒙古中部道郎和都格铜多金属矿的地质特征矿床类型及找矿模式研究

Daolangheduge copper polymetallic deposit is located on east edge of Ondor Sum-Bainaimiao metallogenic belt, which is a prospective area of porphyry copper deposit, in Xianghuangqi of central Inner Mongolia. Geotectonically, it occurred in the continental margin accretion belt along the north margin of North China Plate, south of the suture zone between North China Plate and Siberian Plate. The intrusive rocks in this area mainly consist of intermediate-acid magmatic rocks, and the quartz veins, tourmaline veins and the transitional phase are comparatively developed. According to our research, the ore-bearing rock body is mainly quartz diorite while the surrounding rock is mainly biotite granite. Besides, the wall rock alteration are mainly propylitization, pyritization and silicification, which consist of epidotization, actinolitization, chloritzation and so on. The metallic minerals are mainly chalcopyrite and pyrite. In addition, the primary ore is mainly of quartz-chalcopyrite-pyrite type. Above all, Daolangheduge copper polymetallic deposit is suggested to be categorized in the porphyry copper type. With isotopic dating and geochemical research on quartz diorite of ore-bearing rock body, the zircon LA-ICP-MS U-Pb dating of two samples yields an age of 266±2 Ma, falling into the range of late Permian Epoch. It is the first accurate age data in Xianghuangqi area, so it should play a key role in the research of deposit and magmatic rocks in this area. With the major elements and trace elements analysis of 14 samples, the quartz diorite should be among the calc-alkaline series, the geochemical characteristics show higher large-ion lithophile elements of Rb, Sr and LREE, low high-field strength elements of Nb, Ta and high transition elements of Cu, Cr . Also, the REE patterns have negative Eu anomalies. With the same analysis of 4 sample for the biotite granite, the geochemical characteristics show higher Rb, Th,, Zr, Hf and LREE, low Nb, Sm and HREE and Eu has no anomaly. It should be among the calc-alkaline series, over aluminum quality and has characteristics of Adakites. According to isotopic dating and geochemical characteristics of ore-bearing rock body, it is suggested that its materials mainly derived from upper mantle that had fractional crystallization and its magma source region may be affected by fluid metasomatism of paleo-asian ocean. It should be an extensional process of post-orogeny according to regional tectonic evolution. Consequently, because of the decrease of temperature and pressure, the ore forming fluid was raised to surface and mineralized accompanied by magmatic activity which might occur in south of the suture zone. By geological survey, further geophysical and geochemical work is needed. In this area, we have accomplished high precision magnetic prospecting, high density electrical survey, gravity prospecting, soil geochemical prospecting, X-ray fluorescence analyzer prospecting and so on. According to geophysical and geochemical abnormal and surface occurrence, 11 drills are arranged to verification. The type of ores are mainly quartz-chalcopyrite-pyrite ores within 3 drills by drill core logging. Although the grade as well as the scale of already-found Cu deposits are insufficient for industrial exploitation, the mineralization prospect in this region is supposed to be great and the potential in mineral exploration at depth is excellent.

碎屑锆石年龄和Nd-Hf同位素组成对扬子基底演化的制约

The South China craton was formed by the collision of the Yangtze and Cathaysia blocks during the Neoproterozoic Jiangnan orogeny (also termed as the Jingnin or Sibao orogeny in Chinese literature). Basement rocks within the Yangtze block consist mainly of Proterozoic sediments of the Lengjiaxi and Banxi Groups. U-Pb ages of detrital zircons obtained by the LA-ICP-MS dating technique imply that the deposition of the Lengjiaxi Group continued until the Neoproterozoic. The youngest detrital zircons suggest a maximum deposition age of ~830 Ma for the Lengjiaxi Group, consistent with the initiation time of the deposition of the overlying Banxi Group, likely indicating continuous deposition of these two groups and a short temporal hiatus (~10 Ma) between the Neoproterozoic sedimentary rocks distributed in the South China craton. Detrital zircons from both the Lengjiaxi and Banxi Groups have a wide range of εHf(t) values from -12 to 14.2 and a continuous Nd and Hf model age spectrum from ~820 Ma to 2200 Ma. Some grains have model ages ranging up to ca. 2.9-3.5 Ga, indicating that both juvenile mantle material and ancient crust provided sedimentary detritus. This is also consistent with the Nd isotopic signature of sedimentary rocks recorded in the Lengjiaxi Group, suggesting a back-arc tectonic setting. The Banxi Group has slightly enriched Nd isotopic signatures relative to the Lengjiaxi Group, implying a higher percentage of old continental material in the sedimentary source. Combined with previously published data, new results can help us to reconstruct the Neoproterozoic tectonic evolution of the South China craton. The age spectrum of detrital zircons and Nd-Hf isotopic composition suggests a two-stage collision: Between 1000 Ma to 870 Ma, a continental magmatic arc was build up along the eastern margin of the Yangtze block. Convergence led to continent-based back-arc extension, subsidence and formation of a back-arc basin. Detritus originating from arc-related magmatic and old basement rocks was transported into this back-arc basin resulting in formation of the Lengjiaxi Group and its equivalents. At around 870 Ma, a second (oceanic) arc was formed by extension of an inter-arc basin, subduction subsequently led to the first collision and the emplacement of the blueschist mélange. Accretion of the magmatic arc lasted until the closure of an oceanic basin between the Yangtze and Cathaysia blocks at about 830 Ma. Shortly after the collision, subsequent uplift, further extension of the former back-arc basin and post-collisional granitoid magmatism caused a tilting of the Lengjiaxi sediments. Between 830 Ma and 820 Ma, subsequent closure of the oceanic back-arc basin and formation of the Jiangnan orogen took place, leaving a regional unconformity above the Lengjiaxi Group. Above this unconformity the Banxi Group was immediately deposited during the post-tectonic stage.

湘西地区上震旦统上部－下寒武统底部黑色岩系沉积学及地球化学

Widespread black chert-shales occur in the Ediacaran-Cambrian(E-C) boundary successions along the flank of Yangtze Platform, South China, remarkable changes in sedimentology, geochemistry and biology were recorded. Although extensive studies were carried out upon this boundary succession, the origin of black chert-shales still remain controversial. This paper focuses on the E-C black chert-shales in western Hunan, South China, upon which detailed depositional and geochemical changes are documented, accordingly a depositional model for black chert-shales is proposed. Stratigraphic anatomy across the depositional strike demonstrates that the shallow-water Dengying dolostone along the platform margin sharply pass basinward into the Liuchapo chert successions, which indicate syndepositional extensional faulting at depth could have occurred along the platform margin. The deep-water Niutitang phosphorite-rich black shales are either underlain by the Dengying dolostones on the platform margin toward platform interior or directly by the Liuchaopo chert successions farther basinwards. By detailed investigation, silica chimneys are firsly identified approximately in the chert along platform margin; two types of silica chimneys, including mounded and splayed/funnelized chert(generally brecciated) bodies are further sorted out. The mounded chert are exitbited by domed or hummocky surfaces on the top and irregular spongy to digitiform internal fabrics; within the silica mounds, abundant original vesicles/voids and/or channels were mostly plugged by initial chalcedony, quartze crystals with minor dolomite and bladed barite crystals. Splayed/funnelized brecciated chert “intrusion” cross-cut the uppermost dolostones capping to the horizon underneath, and are directly overlain by the Niutitang phosphorite-rich black shales. Their similarities to the silica chimneys reported from the oceanic spreading centres suggest a similar origin responsible for these unique silica bodies which is also supported by the microthermonmetric data and element geochemistry. High P, Ba, Fe contents and positive correlation between Fe and TOC concentrations in the Niutitang black shales indicate a high palaeo-productivity in the Early Cambrian ocean. The low Th/U and the high V/Cr, V/Sc, V/(V+Ni) ratios in the black shales suggest an anoxic water condition during this interval. Furthermore, Positive Eu anomalies and high Ba contents in the sediments also imply a hydrothermal influence on the formation of Niutitang black shales. To better constrain the placement of deep-water successions straddling the E-C boundary and the timing of hydrothermal silica chimneys, sensitive high-resoluton ion microprobe(SHRIMP) U-Pb dating of zircon grains from tuffs within the chert succession of Liuchapo Formation at Ganziping was conducted and yields a weighted-mean 206Pb/238Pb age at 536.6±5.5Ma, younger than E-C boundary age(542.0±0.3Ma). This age combined with carbon isotopic data is then proposed to correspond to the U-Pb age of zircons(538.2±1.5Ma) from the Zhongyicun member of Meishucun Formation at Meishucun in eastern Yunna, thus, the E-C boundary in Gazngziping was placed between the Dengying formations and Liuchapo formatioms. therefore, the silica chimneys took place at the beginning of the Cambrian period. The temporal coincidence of silica chimneys and negative excursions of δ13C and δ34Spy pairs suggest hydrothermal activities were likely responsible for the isotopic changes. Under such a circumstance, vast amounts of greenhouse gases(CO2, CH4, H2S), with highly 13C-depleted carbon and 34S-depleted sulfur would be released into the ocean and atmosphere. A positive shift in δ34Scas and Δ34S values from the late Ediacaran to the Early Cambrian could be a reflection of enhanced bacterial sulfate reduction(BSR), strengthened by the intensified oceanic anoxia stimulated by hydrothermal activities. Based on the analyses of sedimentology and geochemistry, a model- “oceanic anoxia induced by hydrothermal–volcanic activies” was proposed to responsible for the formation of black chert-shales during this E-C transition. Under this case, hydrothermal-volcanic activies could release large large amount of greenhouse into atmosphere and metal micronutrients into the ocean, which may lead to global warming, stratified ocean, thereby a high palaeoproductivity; on the other hand, the massive releasing of reduced hydrothermal fluids with abundant H2S, could have in turn enhanced the ocean anoxia. All of these were favourable the for preservation of organic matter, and subsequent extensive deposition of black silica-shales.

特提斯喜马拉雅带晚白垩世-始新世沉积源区分析及其构造意义

Tethyan Himalayan Sequence (THS) is located at the frontier of the India-Asia collision zone, which can preserve critical information about collision. This paper reports detailed petrology, geochemistry, spinels electron microprobe data, and in situ U-Pb ages and Lu-Hf isotopic data on detrital zircons from the late Cretaceous to early Eocene strata in Gyantze and Gamba area, south Tibet that provide important constraints on the early tectonic evolution of the India-Asia collision. In Gyantze, the lithic arkose in Zongzhuo mélange is characterized by, SiO2 =80.4%, Al2O3=8.6%, Na2O=1.6%, K2O=1.1%, LaN/YbN=8.90, and εNd (0) =-10.27. Spinels compositions are characterized by low TiO2 (generally <0.1%) and a Cr number mainly between 70 and 80. The largest population of detrital zircons is within the 73-169Ma range with high εHf (t) and > 500 Ma with complex εHf (t) values. The lithic arkose in Rilang conglomerate is characterized by, SiO2 =56.5%, Al2O3=15.6%, Na2O=4.7%, K2O=0.6%, LaN/YbN=5.00-5.29, and εNd (0) =1.92. Spinels of 2006T98 display high TiO2 (generally >0.2%) and a Cr number mainly between 70 and 85, other spinels are characterized by low TiO2 (generally <0.2%) and a Cr number mainly between 60 and 90. The largest population of detrital zircons is within 90-146 Ma range with high εHf (t). The lithic arkose in Jiachala formation is characterized by, SiO2 =64.6%, Al2O3=12.1%, Na2O=1.9%, K2O=1.8%, LaN/YbN=7.73-9.13, and εNd (0) =-5.52~-8.43. Spinels in the Jiachala formation have low TiO2 (generally <0.2%) and a Cr number between 39 and 88. Detrital zircons have a wide range of age distribution of 82-3165Ma with complex εHf (t). In Gamba, The quartze sandstone in Jidula formation is characterized by, SiO2=97.4%, Al2O3=0.9%, Na2O=0.03%, K2O=0.18%, LaN/YbN=18.70-21.684, and εNd (0) between -13.1~-7.4. While the lithic arkose in Zhepure formation is characterized by, SiO2=68.4%, Al2O3=7.3%, Na2O=1.15%, K2O=0.52%, LaN/YbN=6.09-8.99, and εNd(0)=-5.8~-6.3. Based on our geochemical analysis, spinles electron microprobe data, U–Pb ages and Hf isotope data for detrital zircons of the late Cretaceous-Eocene strata in Gyantze and Gamba, southern Tibet, the following major conclusions can be drawn: 1. In Gyantze, the Zongzhuo mélange was mainly derived from accretionary prism/THS of continental slop and Gangdese arc. Rilang conglomerate was totally from Gangdese arc. The Jiachala formation was derived from THS, suture zone and Gangdese arc. 2. In Gamba, the Jidula formation was from India craton, while the Zhepure formation was derived from THS, suture zone and Gangdese arc. 3. The deposite of Zongzhuo mélange and Rilang conglomerate (73-55Ma) marks the collision between India and Asia. 4. Late Paleocene-Eocene tectonic evolution is consistent with foreland basin system.

东喜马拉雅构造结新生代碰撞变形与岩石圈演化

The Eastern Himalayan Syntaxis (EHS) is one of the strongest deformation area along the Himalayan belt resulted from the collision between Indian plate and the Eurasian Plate since the 50～60Ma, and has sensitivity tracked and preserved the whole collisional processes. It should depend on the detail geological investigations to establish the deformational accommodate mode, and the uplift history, to elucidate the deep structure and the crust-mantle interaction of the Tibet Plateau of the EHS. The deep-seated (Main Mantle Thrusts) structures were exhumed in the EHS. The MMT juxtapose the Gangdese metamorphic basement and some relic of Gangdese mantle on the high Himalayan crystalline series. The Namjagbawa group which is 1200～1500Ma dated by U/Pb age of zircon and the Namla group which is 550Ma dated by U/Pb age of zircon is belong to High Himalayan crystalline series and Gangdese basement respectively. There is some ophiolitic relic along the MMT, such as metamorphic ocean mantle peridotite and metamorphic tholeiite of the upper part of ocean-crust. The metamorphic ocean mantle peridotites (spinel-orthopyroxene peridotite) show U type REE patterns. The ~(87)Sr/~(86)Sr ratios were, 0.709314～0.720788, and the ~(143)Nd/~(144)Nd ratios were 0.512073～0.512395, plotting in the forth quadrant on the ~(87)Sr/~(86)Sr-~(143)Nd/~(144)Nd isotope diagram. Some metamorphic basalt (garnet amphibolite) enclosures have been found in the HP garnet-kynite granulite. The garnet amphibolites can be divided two groups, the first group is deplete of LREE, and the second group is flat or rich LREE, and their ~(87)Sr/~(86)Sr, ~(143)Nd/~(144)Nd ratios were 0.70563～0.705381 and 0.512468～0.51263 respectively. Trace element and isotopic characteristics of the garnet amphibolites display that they formed in the E-MORB environment. Some phlogolite amphibole harzburgites, which exhibit extensive replacement by Phl, Amp, Tc and Dol etc, were exhumed along the MMT. The Phl-Amp harzburgites are rich in LREE and LILE, such as Rb, K etc, and depletes Eu (Eu~* = 0.36 ～ 0.68) and HFSE, such as Nb, Ta, Zr, Hf, P, Ti etc. The trace element indicate that the Phl-Amp harzburgites have island arc signature. Their ~(87)Sr/~(86)Sr are varied from 0.708912 to 0.879839, ~(143)Nd/~(144)Nd from 0.511993 to 0.512164, ε Nd from- 9.2 to - 12.6. Rb/Sr isochrone age of the phlogolite amphibole harzburgite shows the metasomatism took place at 41Ma, and the Amp ~(40)Ar/~(39)Ar cooling age indcate the Phl-Amp harzburgite raising at 16Ma. There is an intense crust shortening resulted from the thrust faults and folds in the Cayu block which is shortened more 120km than that of the Lasha block in 35～90Ma. With the NE corner of the India plate squash into the Gangdese arc, the sinistral Pai shear fault and the dextral Aniqiao shear fault on the both sides of the Great bent of Yalun Zangbu river come into active in 21～26Ma. On the other hand, the right-lateral Gongrigabu strike-slip faults come into activity at the same period, a lower age bound for the Gongrigabu strike-slip fault is estimated to be 23～24Ma from zircon of ion-probe U/Pb thermochronology. The Gongrigabu strike-slip faults connect with the Lhari strike-slip fault in the northwestern direction and with the Saganing strike-slip at the southeastern direction. Another important structure in the EHS is the Gangdese detachment fault system (GDS) which occurs between the sedimental cover and the metamorphic basement. The lower age of the GDS is to be 16Ma from the preliminary 40Ar/39Ar thermochronology of white mica. The GDS is thought to be related to the reverse of the subducted Indian crust and the fast uplift of the EHS. Structural and thermochronology investigation of the EHS suggest that the eastern Tibet and the western Yunnan rotated clockwise around the EHS in the period of 35～60Ma. Later, the large-scale strike-slip faults (RRD, Gaoligong and Saganing fault) prolongate into the EHS, and connect with the Guyu fault and Gongrigabu fault, which suggest that the Indianchia block escape along these faults. Two kind of magmatic rocks in the EHS have been investigated, one is the mantle-derived amphibole gabbro, dioposide diorite and amphibole diorite, another is crust origin biotit-garnet adamellite, biotit-garnet granodiorite and garnet-amphibole-biotite granite. The amphibole gabbro dioposite diorite and amphibole diorite are rich in LREE, and LILE, such as Ba, Rb, Th, K, Sr etc, depleted in HFSE, such as Nb, Ta, Zr, Hf, Ti etc. The ratio of ~(87)Sr/~(86)Sr are from 0.7044 to 0.7048, ~(143)Nd/~(144)Nd are from 0.5126 to 0.5127. The age of the mantle origin magamatic rocks, which result from the partial melt of the raising and decompression anthenosphere, is 8Ma by ~(40)Ar/~(39)Ar dating of amphibole from the diorite. The later crust origin biotite-garnet adamellite, biotite-garnet granodiorite and garnet-amphibole-biotite granite are characterized by aboudance in LREE, and strong depletion of Eu. The ratios of ~(87)Sr-~(86)Sr are from 0.795035 to 0.812028, ~(143)Nd/~(144)Nd from 0.51187 to 0.511901. The ~(40)Ar/~(39)Ar plateau age of the amphibole from the garnet-amphibole-biotite granite is 17.5±0.3Ma, and the isochrone age is 16.8±0.6Ma. Their geochemical characteristics show that the crust-derived magmatic rocks formed from partial melting of the lower curst in the post-collisional environment. A group of high-pressure kaynite-garnet granulites and enclave of high-pressure garnet-clinopyroxene grnulites and calc-silicate grnulites are outcroped along the MMT. The peak metamorphic condition of the high-pressure granulites yields T=800～960 ℃, P=1.4～1.8Gpa, corresponding the condition of 60km depth. The retrograde assemblages of the high-pressure grnulites occur at the condition of T=772.3～803.3 ℃, P=0.63～0.64Gpa. The age of the peak metamorphic assemblages are 45 ～ 69Ma indicated by the zircon U/Pb ion-plobe thermochronology, and the retrograde assemblage ages are 13～26Ma by U/Pb, ~(40)Ar/~(39)Ar thermochronology. The ITD paths of the high-pressure granulites show that they were generated during the tectonic thickening and more rapid tectonic exhumation caused by the subducting of the Indian plate and subsequent break-off of the subducted slab. A great deal of apatite, zircon and sphene fission-track ages, isotopic thermochronology of the rocks in the EHS show that its rapid raising processes of the EHS can be divided into three main periods. There are 35～60Ma, 13～25Ma, 0～3Ma. 3Ma is a turn in the course of raising in the EHS which is characterized by abruptly acceleration of uplifting. The uplift ratios are lower than 1mm .a~(-1) before 3Ma, and higher than 1mm .a~(-1) with a maximum ratio of 30mm .a~(-1) since 3Ma. The bottom (knick point) of the partial anneal belt is 3.8km above sea level in the EHS, and correspond to age of 3Ma determined by fission-track age of apatite. The average uplift ratio is about 1.4 mm .a~(-1) below the knick point. The EHS has raised 4.3km from the surface of 2.36km above sea level since 3Ma estimated by the fossil partial anneal belt of the EHS. We propose a two-stage subduction model (B+A model) basing on Structural, thermochronological, magmatical, metamorphic and geophysical investigations of the EHS. The first stage is the subduction of the Indian continental margin following after the subduction of the Tethys Ocean crust and subsequent collision with the Gangdese arc, and the second stage is the Indian crust injecting into the lower crust and upper mantle of the Tibet plateau. Slab break-off seems to be occurred between these two stages.

胶东地区金矿床成矿时代及其成矿地球动力学背景-兼论壳幔相互作用与成岩成矿

Jiaodong Peninsula is the largest repository of gold in China. Varieties of studies have been involved in the mechanism of metallogenesis. This thesis is a part of the project "Study of basic geology related to the prespecting of the supra-large deposits" which supported by National Climbing Program of China to Prof. Zhou. One of the key scientific problems is to study the age and metallogenic dynamics of ore deposit and to understand how interaction between mantle and crust constrains on metallogenesis and lithogenesis. As Jiaodong Peninsula to be study area, the Rb-Sr, Sm-Nd and Pb isotopic systematics of pyrite and altered rocks are measured to define the age and origin of gold. The elemental and Sr-Nd-Pb isotopic compositions of dikes and granites was studied to implicate the source and lithogenesis of the dike and granite and removal of lithosphere and the interaction between mantle and crust in the Jiaodong Peninsula. Considering the tectonic of Jiaodong Peninsula, basic on the time and space, this thesis gives a metallogenic dynamics of gold mineralization and discusses the constraints of the interaction between mantle and crust on the metallogenesis and lithogenesis. This thesis reports the first direct Rb-Sr dating of pyrites and ores using sub-sampling from lode gold deposit in Linglong, Jiaodong Peninsula and the results demonstrate this as a useful geochronological technique for gold mineralization with poor age constraint. The Rb-Sr data of pyrites yields an isochron age of (121.6-122.7) Ma, whereas, those of ore and ore-pyrite spread in two ranges from 120.0 to 121.8 Ma and 110.0-111.7 Ma. Studies of characteristic of gold deposit, microscopy of pyrite and quartz indicate that the apparent ages of ore and ore-pyrite are not isochron ages, it was only mixed by two end members, i.e., the primitive hydrothermal fluids and wall rocks. However, the isochron age of pyrite samples constrains the age of gold mineralization, i.e., early Cretaceous, which is in good consistence with the published U-Pb ages of zircon by using the SHRIMP technique. The whole rock Rb-Sr isochron age of altered rocks indicates that the age of gold mineralizing in the Xincheng gold deposit is 116.6 ± 5.3 Ma. The Sr, Nd and Pb isotopic compositions of pyrite and altered rocks indicate that the gold and relevant elements were derived from multi-sources, i.e. dikes derived from enriched lithospheric mantle and granites, granodiorites and metamorphic rocks outcropped on the crust. It also shows that the hydrothermal fluids derived from mantle magma degassing had play an important role in the gold mineralizing. The major and trace elements, Sr-Nd-Pb isotopic data of granites and granodiorites suggest that the Linglong Granite and Kunyushan Granite were derived from partial melting of basement rocks in the Jiaodong Peninsula at post-collision of North China Craton with South China Craton. Guojialing Granodiorite was considered to be derived from a mixture source, that is, mixed by magmas derived from an enriched lithospheric mantle and crust during the delamination of lithosphere induced by the subduction of Izanagi Plate and the movement of Tancheng-Lujiang Fault. There are kinds of dikes occurred in the Jiaodong Peninsula, which are accompanying with gold mineralization in time and space. The dikes include gabrro, diabase, pyroxene diorite, gabrrophyre, granite-porphyry, and aplite. The whole rock K-Ar ages give two age intervals: 120-124 Ma for the dikes that erupted at the gold mineralizing stage, and <120 Ma of the dikes that intruded after gold mineralizing. According to the age and the relationship between the dikes and gold mineralizing, the dikes could be divided into two groups: Group I (t = 120-124 Ma) and Group II (t < 120Ma). Group I dikes show the high Mg and K, low Ti contents, negative Nb anomalies and positive Eu anomalies, high ~(87)Sr/~(86)Sr and negative εNd(t) values and an enrichment in light rare earth elements, large ion lithosphile elements and a depletion in high field strength elements. Thus the elemental and isotopic characteristics of the Group I dikes indicate that they were derived from an enriched lithospheric mantle perhaps formed by metasomatism of the melt derived from the recycled crustal materials during the deep subduction of continent. In contrast, the Group II dikes have high Ti, Mg and K contents, no negative Nb anomalies, high ~(87)Sr/~(86)Sr and positive or little negative εNd(t) values, which indicate the derivation from a source like OIB-source. The geochemical features also give the tectonic constraints of dikes, which show that Group I dikes were formed at continental arc setting, whereas Group II dikes were formed within plate background. Considering the tectonic setting of Jiaodong Peninsula during the period of gold mineralizing, the metallogenic dynamics was related to the subduction of Izanagi Plate, movement of Tancheng-Lujiang Fault and removal of lithopheric mantle during Late Mesozoic Era.

青海德尔尼铜钴锌矿床地质构造背景与成因

The Derni large Cu-Co-Zn sulfide deposit is occurred in the Derni melange belt, which is located in the eastern section of the A'nyemaqen ophiolite melange belt. The Derni deposit is hosted in the mantle peridotites and is very special in the world. Because the studying area is of very bad natural environment and very low geological research, the geotectonic setting and genesis of the deposit have long been debated. This paper studied these two questions and answered them. The research is of great significance to reveal impotant information of deep geology, crust-mantle interaction and geotectonic evolution, to enrich theories in the study of mineral deposit and provide scientific basic data for exploration and exploit of this kind of deposit. Based on the series of new achievements and new cognitions, to start with the geologic setting of the Derni deposit, through detailed field, tectonics, petrology, geochemistry, isotopic geochronology, microfossil, and study of mineral deposit, belongs to a melange belt, including mantle peridotites slice with ore, Late Precambrian sandstone and slate slice, metamorphic rock slice. 2. Petrological and geochemical characteristics indicate that the Derni mantle peridotite is not ophiolite mantle peridotite, but is occurred under the continental crust. 3. The U-Pb isotopic age of single-grain zircon form the accumulative rock suggests that the Derni mantle peridotite were formed in 747±10Ma, and underwent a great period of metamorphic process in 441.5±2.5Ma. 4. Microfossil assemblage from the carbonaceous slate belongs to Late Precambrian. Through petrography and petrochemistry, sandstone and slate were formed in the continental margin. 5. Sideronitic texture, which is first discovered in this study, reveals the characteristics of magmatic liquation. 6. Fluid inclusion explosion temperature of pyrite is in the range of -6.15～+6.64‰, and Pb isotope is consistent with mantle peridotite, which suggest ore-forming materials are from the mantle. To sum up, the upper mantle was melting partially, when it was metasomated by the mantle fluids with abundant Cu, Co, Zn, S, Au and LREE etc. The pockets of magma became enlarged by mantle tenacity shearing, and the pockets of magma occurred magmatic differentiation in the stable field, then the magma and ore pulp together with mantle refractory remnant dirpired and crystallized in the shallow part of the crust.

内蒙古东部喀喇沁地区早中生代底侵作用

Mafic granulite xenoliths have been extensively concerned over the recent years because they are critical not only to studies of composition and evolution of the deep parts of continental crust but to understanding of the crust-mantle interaction. Detailed petrology, geochemistry and isotope geochronology of the Early Mesozoic mafic-ultramafic cumulate xenoliths and mafic granulite xenoliths and their host diorites from Harqin area, eastern Inner-Mongolia have been studied here. Systematic Rb-Sr isochron, ~(40)Ar-~(39)Ar and K-Ar datings for mafic-ultramafic cumulate xenoliths give ages ranging from 237Ma to 221Ma. Geochemical research and forming temperature and pressure estimates suggest that cumulates are products of the Early Mesozoic mantle-derived magmatic underplating and they formed in the magmatic ponds at the lowermost of the continental crust and are later enclaved by the dioritic magma. Detailed study on the first-discovered mafic granulite xenoliths reveals that their modal composition, mineral chemistry and metamorphic P-T conditions are all different from those of the Precambrian granulite exposed on the earth surface of the North China craton. High-resolution zircon U-Pb dating suggests that the granulite facies metamorphism may take place in 253 ～ 236Ma. Hypersthene single mineral K-Ar dating gives an age of 229Ma, which is believed to represent a cooling age of the granulite. As the host rock of the cumulate and granulite xenoliths, diorites intruded into Archean metamorphic rocks and Permian granite. They are mainly composed of grandodiorite, tonalite and monzogranite and show metaluminous and calc-alkaline features. Whole rock and single mineral K-Ar dating yields age of 221 ～ 223Ma, suggesting a rapid uplift in the forming process of the diorites. Detailed field investigation and geochemical characteristics indicate that these diorites with different rock types are comagmatic rocks, and they have no genetic correlation with cumulate and granulite xenoliths. Geochemical model simulating demonstrates that these diorites in different lithologies are products of highly partial melting of Archean amphibolite. It is considered that the Early Mesozoic underplating induced the intrusion of diorites, and it reflects an extensional geotectonic setting. Compression wave velocity V_P have been measured on 10 representative rock samples from the Early Mesozoic granulite and mafic-ultramafic cumulate xenoliths population as an aid to interpret in-situ seismic velocity data and investigating velocity variation with depth in a mafic lower crust. The experiments have been carried out at constant confining pressures up to 1000MPa and temperatures ranging from 20 ℃ to around 1300 ℃, using the ultrasonic transmission technique. After corrections for estimated in situ crustal pressures and temperatures, elastic wave velocities range from 6.5 ～ 7.4 km s~(-1). On the basis of these experimental data, the Early-Mesozoic continental compression velocity profile has also been reestablished and compared with those of the present and of the different tectonic environments in the world. The result shows that it is similar to the velocity structure of the extensional tectonic area, providing new constraints on the Early Mesozoic continental structure and tectonic evolution of the North-China craton. Combining with some newly advancements about the regional geology, the thesis further proposes some constraints on the Mesozoic geotectonic evolution history, especially the features of deep geology of the North China craton.