Showing papers in "Acta Petrologica Sinica in 2005"

Mesozoie large-scale metallogenic pulses in North China and corresponding geodynamic settings

Abstract: We describe the temporal-spatial distribution of the main Mesozoic metallogenic belts and regions in North China, comprising the Middle Lower Yangtze River valley, the Xiaoqinling-Xiong'ershan (eastern Qinling) and western Qinling, North margin of the North China craton, and southern part of the Daxing'anling as well as the eastern Shandong peninsular and Wulugetu-Jiawula ( Manzhuli) After collecting and documenting the precise radiometric age data of the ore deposits there appear three metallogenic pulses, i e 190 - 160 Ma, ca 140 Ma, and ca 120 Ma Almost all the gold only depoists in eastern Shandong peninsular formed at time of ca 120 Ma It is obvious there are two pulses of mineralization at ca 140 Ma and ca 120 Ma in the Middle Lower Yangtze River valley, and Xiaoqinling-Xiong'ershan region, where the porphyry-skarn-manto Cu-Au-Mo-Fe and Mo-(W) deposits occurred at the age of ca 140 Ma whereas the gold deposits and terrestrial volcanic rock related iron deposits appeared at age of ca 120 Ma The Mesozoic mineralization in the northern margin of the North China craton developed in three pulses and their ages are getting older from the eastern margin of the Euroasian continent inward The gold deposits in the western Qinling are dated to be an age range of 190 -160 Ma In southern part of the Daxing'anling the granite-related Cu-Ag and Pb-Zn-Cu deposits are ca 160 - 177 Ma, granite-related Sn-Cu-Pb-Zn and Sn deposits are ca 140 Ma, and Nb-Y-Zr deposit is 127 Ma Based on the study of Mesozoic tectonic evolution, we propose these three pulses of large-scale mineralization are the consequences of the postcollisional process of the Triassic convergence between the northern China craton and the Yangtze craton, late stage of the tectonic regime changing its main stress from NS-trending to EW-trending, and lithosphere thinning process, repectively The gold deposits associated with S-type granite of 200 - 160Ma develop in the extension setting of postcollisional stage At ca 140 Ma a great amount of I-type granite porphyry derived from the upper mantle and lower crust emplcaced at the shllow crust and are accompanied by porphyry-skarn-( manto ) Cu-Mo-Fe-Au and Mo-W mineralization Due to lithosphere rapid thinning at ca 120 Ma the asthenosphere got into the curst, which gave up to the mixed fluids from the mantle, metamorphic process, and crust to leach the metallic elements so as to form the gold ore-forming system as well as the iron deposit association related to terrestrial volcanic activity

Evolution of syn-to post-collisional magmatism from north Sulu UHP belt,eastern China:zircon U-Pb geochronology.

Abstract: Numerous Mesozoic plutons are exposed within the ultrahigh-pressure (UHP) metamorphic terranes in the Weihai area of the northern SuLu UHP belt.They occur as multi-pulse intrusive complexes or small size stocks of diversity rock types including shoshonitic gabbros and syenites,S-type granites,and I-type granites of high K alkaline series.A temporal evolution has be established on the basis of precise zircon U-Pb ages by single grain isotope dilution method and SHRIMP technique and petrochemical investigations.(1) Shoshonitic magmatism commenced 20Ma after UHP metamorphism in the late Triassic.Typical plutons of shoshonitic series represented by Xingjia alkali gabbros (211±5Ma and 213±5Ma),Jiazishan pyroxene syenite (211.9±1.5 Ma and 209.0±6.5Ma) and Chashan syenogranite (205.7±1.4Ma).They derived from enriched mantle contaminated by subducted continental crust,and were likely the response to mantle upwelling induced by slab breakoff after continental subduction.(2) Jurassic calc-alkaline intrusions postdated the UHP metamorphism by 60～80Ma.The Duogushan granodiorite (161±1Ma),the Wendeng monzogranite (160±3Ma) and the Kunyushan monzogranite and garnet-bearing leueogranite (142±3Ma) are representative plutons. These granites contain most inherited zircons of 700～800Ma suggesting that they were melting products of the South China Block.They were likely to be originated from crustal melting induced by lower crustal delamination after the Triassic UHP collision.(3) The final magma pulse appeared in early Cretaceous at ～110Ma,represented by the Liudusi pyroxene diorite (114.5±0.8Ma),Taiboding Kf-porphyritic granite (114±1Ma),Sanfoshan Kf-porphyritic granite (113±1Ma) and Weideshan granite (108±2Ma) and numerous small intrusions.They show characteristics of the high-K calc-alkaline and shoshonitie series.These granites are ascribed to strongly crust-mantle interaction during Cretaceous mantle upwelling and lithospheric thinning commonly observed in eastern China.

Zircon U-Pb ages and its significance of the Mesozoic granites in the Wulanhaote region, central Da Hinggan Mountain.

Abstract: The timing and stages of the Mesozoic granites in the Da Hinggan Mountain is the key to the tectonic and magmatic evolution of Northeast China. In this paper, we present new zircon U-Pb age data of granites using laser ablation ICP-MS technique. The result shows three stages of granites in the Wulanhaote-Suolun region, central Da Hinggan Mountain, i. e. , Middle to Late Triassic granites (235 -225 Ma) , Early to Middle Jurassic granites (182 - 175 Ma) and Early Cretaceous granites (140 - 125 Ma) , which are consistent with the stages of volcanic rocks. This geochronological framework is also comparable to that in the Zhangguangcai-Lessor Hinggan Mountain in the east to the Songliao Basin. The identification of - 800 Ma inherited zircons, consistent with Neoproterozoic granites in Eguna block, suggests that there existed Precambrian basement in this region. Considering their petrography and geological data of adjacent regions, we propose that the formation of Triassic granites is related to post-orogenic lithospheric extension after closure of the Paleo-Asian Ocean, Jurassic granites are results of subduction of oceanic plate in the western Jiamusi block and assembly of Jiamusi and Songnen blocks, while, Early Cretaceous granites are product of intra-plate extension.

SHRIMP dating of adakites in western Qinling and their implications.

Abstract: There are a lot of granite from Xiahe to Lixian along the west Qinling which is of the adakite geochemical feature. The paper reports the SHRIMP dating of Yeliguan and Xiahe granite plutons. The SHRIMP ages are 245±6 Ma and 238±4 Ma respectively, belong to early Indosinian period. The adakite is rich of potassium, is classified by high potassium calc-alkalic series. Geology and geochemical data show that the adakite in the western Qinling was formed in the active plate margin, and was associated with the melting of thicken lower crust in the active crust margin. The dating implicated that the convergent and consuming of palaeotethys was processing at early Indosinian.

Application of polymer flooding technology in Daqing Oilfield

Abstract: According to the results of the research in the laboratory and field tests, the experiences of polymer flooding in Daqing Oilfield in seven years are analyzed The actual recovery in the field and the major factors influencing recovery efficiency are investigated The methods for enhancing recovery efficiency, the measures to obtain a uniform polymer flooding front and ways to lower the costs for producing crude oil by polymer flooding are discussed The effectiveness of polymer flooding technology applied in Daqing Oilfield can provide some references for further application of polymer flooding in China

Zircon U-Pb ages and Hf isotopes and their geological significance of the Miyun rapakivi granites from Beijing,China.Acta Petrologica

Abstract: The Miyun pluton,a typical A-type rapakivi pluton,is located in the eastern North China Craton and is mainly composed of rapakivi granite and porphyric biotite granitesZircon LA-ICPMS U-Pb dating gives that the emplacement ages of Miyun rapakivi granites are 1681±10Ma and 1679±10Ma,whereas,their host gneiss formed at 2521±14MaThe mean e_ (t) value of zircons from Archean gneiss is about +45,indicating the protolith of gneiss was derived from a depleted mantle sourceIt suggests that the 25 Ga is an important period of crustal growth of the North China CratonThe zircons in the rapakivi granites have e_ (t) value of-50, indicating that the rapakivi granites were derived from a crustal sourceThe two-stage model ages (T_(DM2)) of rapakivi granites are about 26 to 28 Ga,similar to those of host Archean gneisses,indicating that the rapakivi granites were derived from partial melting of the crust formed during Late ArcheanThe Miyun rapakivi granites were emplaced in an intra-plate extensional setting,which may be related to breakup of Paleoproterozoic Columbia supercontinent

Zircon U-Pb geochronology and geochemistry of the Mesozoic magmatism in the Taihang Mountains and other places of the North China craton, with implications for petrogenesis and geodynamic setting

Abstract: The Mesozoic rocks from eastern North China Craton(NCC) range in composition from gabbroic to monzogranitic, showing high-K calc-alkaline to shoshonitic affinity, high Sr-Ba and high Sr/Y, La/Yb, and highly enriched Sr-Nd isotopic compositions. SHRIMP zircon dating for four pinions from the Taihang Mountains, westernmost NCC, yields ages of 138-127 Ma, which, along with published ages for magmatic rocks from other parts of eastern Kast Asia, reveal a northwestward younging trend of calc-alkaline magmatism from Japan island chain (and Korean peninsula; 210 Ma) , through Jiaodong and Liaodong Peninsula ( 180 Ma) , and to the Taihang orogen ( 138 Ma). This suggests the genesis of the Mesozoic rocks in the NCC was linked to the subduction of the paleo-Pacific plate, rather than to the Triassic collision between the Yangtze block and NCC. The lack of a regular variation in compositions from the coastal areas to interiors of eastern China as is shown by the magmatic rocks in the Basin and Range is probably related to the "flat subduction" of the paleo-Pacific slab beneath the NCC. Moreover, they probably originated from mixing between mafic magmas from enriched mantle sources and crust-derived granitic melts, followed by fractionation, rather than from melting of mafic lower crust as previously suggested by many others.

Geochronology of Cretaceous A-type granitoids or alkaline intrusive rocks in the hinterland, South China: constraints for late-Mesozoic tectonic evolution.

Abstract: In the hinterland of South China, there are some Cretaceous A-type granitiods or alkaline intrusive rocks, e. g. , Huashan aegiriteaugite riebeckite granite in Anhui, Dayuancun aegiriteaugite arfvedsonite granite in Fujian, Ejinao nepheline sodalite syenite in Guangdong and Daheshan pyroxene quartz syenite porphyry and Sucun geode-like Kf-granite in Zhejiang. The geochronology of zircon SHRIMP and some minerals (amphibole and K-feldspar) 40Ar -39Ar dating indicates that they were mainly formed in 137 - 86 Ma. Combining with previous published isotopic ages of Late Mesozoic A-type granitiods or alkaline intrusive rocks in South China, our study also suggests that these A-type granitoids alkaline intrusive rocks may be classified as three periods. (1) Jurassic (184 - 152Ma) rocks: they distribute along the southern segment of the ' Shi-Hang rift zone' and in the south of Jiangxi, and their petrogenesis was possibly related to the strike-slip and extension due to low-speed and oblique subducting or transcurrent moving of paleo-Pacific plate or lithospheric extension which was independent of the movement of paleo-Pacific plate. (2) Early Cretaceous (139 - 123Ma) rocks: they distribute to the west of Zhenghe-Dapu fault zone and the lithospheric thinning or back-arc extension in relation to fast-speed and oblique subducting of paleo-Pacific plate is a likely responsible mechanism for their formation. (3) Late Cretaceous (101 - 86Ma) rocks: they mainly occur along the coastal of Fujian-Zhejiang area but distribute sporadically in the hinterland of South China, and they possibly resulted from the lithospheric extension owing to the collapse of the continental marginal arc or the roll-back of subducting oceanic crust.

SHRIMP dating and geological significance of Late Achaean high-Mg diorite (sanukite) and hornblende-granite at Guyang of Inner Mongolia

Abstract: High-Mg diorite - hornblende-granite occurs at Guyang, Inner Mongolia Geochemically, the high-Mg diorite is similar to late Archean sanukite that was formed in mantle wedge above subduction zones Sanukite, which finds common in Archean terrains worldwide, is characterized by high MgO content and high Mg-# associated with enrichments of Cr and Ni This paper reports SHRIMP U-Pb ages of a high-Mg diorite (2556 +/- 14 Ma) and a hornblende-granite (2520 +/- 9 Ma) in the Guyang area Accordingly, the subduction of the North China plate possibly initiated during the late times of the late Achaean The Archean Sanukites outside of China have been well documented in the range of 30 similar to 25 Ga with the youngest (251 similar to 255 Ga) occurring in the Dharwar Craton of India It is suggested that the North China and synchronous India could be the latest areas developing plate tectonics on Earth

Late Paleoproterozoic granitic magmatism and crustal evolution in the Tonghua region, northeast China.

Abstract: The Paleoproterozoic metamorphic complex, widespread in the Liaoning-Jilin Region of northeastern North China Craton, was thought to be the result of intra-plate rifting. However, our filed observations show that the magmatites are not metamorphic rocks but granitic plutons with different degree deformation and metamorphism, consisting of gneissic hornblende syenogranite (termed by " striated granite" or " Liaoji granite") , gneissic quartz diorites, porphyric biotite monzogranite, porphyric-rapakivi garnet granite and hornblende pyroxene syenite. This paper presents the new zircon SHRIMP U-Pb data of gneissic quartz diorite and porphyric-rapakivi garnet granite. The results show that they were emplaced during 1872 - 1850 Ma, similar to those of porphyric biotite monzogranite and hornblende pyroxene syenitic complex. Petrography and geochemical features indicate that the gneissic quartz diorite belong to I-type granites with geochemistry of Arc-type granitoids, whereas, porphyric-rapakivi garnet-bearing granites with rapakivi texture have geochemistry of S-type granites. With consideration of the P-T path of the regional metamorphism coeval with the emplacement of these granites, the concurrence of I-, S- and A-type granites indicates that these granites formed in the post-orogenic setting. The difference of the basement rocks between Langlin (Korea)-Liaonan (China) block and Longgang block indicates that the North China Craton is composed of Langlin-Liaonan-Jiaodong and Longgang-Luxi-Wuhuai blocks in the east and west block, not of West and East blocks. These two blocks in the east North China Craton assembled at about 1.9 Ga, and then collided with the West Block at about 1.85 Ga.

The post-collision intracontinental rifting and olistostrome on the southern slope of Bogda Mountains, Xinjiang.

Abstract: A regional-scale tectonic event of closure of ocean and collision-orogeny took place in the interval from Late Devonian to Late Carboniferous in the Xinjiang area. At the late stage of collision, some tectonic changes occurred in the piedmont area. The preliminary framework of mountains-basins of northern Xinijiang was composed of both Late Carboniferous-Early Permian orogenic belt and piedmont basins. In the direction toward continent, post-collision intracontinental rifting and olistostrome developed well. The bedded diabase and bimodal volcanic rocks were distributed in the Early Permian strata in the piedmont area. The most typical area is located on the southern slope of Bogda Mountains, namely the Qijiaojing-Cheguluquan segment of Harm city and the Baiyanggou section of Urumgi. This paper studied the geometrical, petrological and geochemical features of intracontinent bimodal volcanic rocks and olistostrome. Of them, post-collision olistostrome is the first time discovery by us. In the Qijiaojing-Cheguluquan segment, basalt and rhyolite are ranged alternately that overlie the Early Permian red molasses. This post-collision bimodal volcanic series with a big thickness is distributed in parallel with the sub-E-W mountain extension. In the Baiyanggou section, post-collision underwater olistostrome co-exists with underwater eruption and is composed of olistostrome zone, pillow lava and pore basalt zone, and siliceous shale and siltstone zone; the bottom plane is contacted with Late Carboniferous limestone and sandstone series by a NEE-trending detachment fault.

Tectono - thermal event of post-HP/UHP metamorphism in the Xitieshan area of the North Qaidam Mountains, western China: isotopic and geochemical evidence of granite and gneiss

Abstract: Conventional zircon U-Pb dates (TIMS) from the Xitieshan granite of the North Qaidam Mountains gave Concordia age of 428±1 Ma, reflecting the magmatic crystallization age. Based on petrographic studes, separated zircons from the host gneiss were measured on SHRIMP Ⅱ icon microprobe. Th/U ratios of 10 point range from 0. 01- 0. 08, which indicates that the zircons were crystallized during metamorphic event. 10 data points gave a mean 206 Pb/238U age of 435±7Ma (weighted mean age) , which is interpret to represent the age of ampibolite-facies metamorphism. U-Pb age of zircons from both granite and host gneiss is identical within error. Geochemical data suggest that the Xitieshan granite indicates as I-type granite. Similar compositions (major, REE and trace elements) between granite and host gneiss imply that the granite probable originated from rocks, which composition similar to host gneiss, However, Nd model age of granites ( TDM = 1.4-1.5Ga) is younger than that host gneiss (TDM =1.9 -2.2 Ga). This difference in Nd model age suggests the input of mantle material in the generation of the granite. Thus, we explained that the Xitieshan granite is formed in post-collisional extend setting at early-Paleozoic.

Pan-African and Early Paleozoic orogenic events in the Himalaya terrane: Inference from SHRIMP U-Pb zircon ages

Abstract: The Himalayan terrane is an accretional terrane formed during the collision between the India Plate and the Eurasian Plate since 55 10 Ma. SHRIMP U-Pb dating has been performed on zircons from the amphibolite facies aluminum-rich metasediments and granitic gneisses from the Greater Himalaya and the Tethyan-Himalayan units of the Himalayan terrane. The dating results indicate an widespread 529 - 457Ma deformation and metamorphism event, and greater than 835 Ma metamorphic basement formation age, except for the latest tectonic event at 12 -20 Ma. Field observations on the Himalayan slice which has been exhumed since 20 Ma have documented earlier than Cenozoic tectonic events represented by the early intense folding, oblique southward thrusting and concurrent amphibolite facies metamorphism and the Ordovician basal conglomerate. Recent studies also yielded a number of Pan-African and Early Paleozoic ages for the metasedimentary and metamorphic basement rocks by Ion Probe U-Pb zircon dating. These lines of evidence together with our new dating results lead us to propose that the Early middle Proterozoic metamorphic basement of the India block once located in the southern hemisphere has undergone the Pan-African - Early Paleozoic orogenic events. The geochronological data suggest that: (1) the Proto-Himalaya formed as a result of the Pan-African and the Early Paleozoic orogenic events; (2 ) reactivation of the Early-middle Proterozoic metamorphic basement of the India block has played a key role in the formation of the Proto-Himalayan Mountains; ( 3) the building of the present-day Himalaya Mountains may have been initiated as early as the Pan-African and the Early Paleozoic.

Origin and dynamic significance of Guangtoushan granitic plutons to the north of Mianlue zone in southern Qinling.

Abstract: The granitoid plutons to the north of Mianlue zone in southern Qinling have a calc-alkaline association with a range from diorites through granodiorites to granites, composed mainly of feldspars, quarts, biotites and minor hornblendes with accessory minerals of zircons, apatites, magnetites and sphenes. They have high K, Sr and Zr/Y ratios, as well as LEE and LILE enrichment and poor HFSE, similar to those of post-collisional high-K calc-alkaline I-type granitoids. Moreover, they are characterized by low Y and Yb abundances, high LaN/YbN and Sr/Y ratios and depleted in Nb and Ta. The mafic microgranular enclaves, displaying an evidently different rear earth and trace elements than those of host rocks, are quite developed in plutons. All of those give evidence that they were resulted from mixture of two-end magmas derived from mantle and lower crust, which were possibly trigged by lower crustal delamination. High differentiation pluton is high in Fetot/Mg and depleted in Sr、Ba、Ti、P, showing characteristics of post-collisional high-K peraluminous subalkalic granitoids transformed to strong differentiation A-type granites in the final stage. Thus, based on the older ages of granitoid plutons outcropped in the west area and younger ages in the east, the west plutons with large amounts of enclaves represented the start of lower crustal delamination, and the higher differentiation calc-alkaline I-type granitoid plutons in the east area indicate a transition from collisional convergence to extension between south and north continental blocks. Where the formation of strong differentiation Jiangjiaping high-K granitic pluton demonstrate that Qinling Orogenic Belt evolved into extension period after main collision and promise a coming of new intraplate period.

Zircon U-Pb SHRIMP age and origin of post-orogenic Lamazhao granitic pluton from Altai orogen: its implications for vertical continental growth.

Abstract: The Lamazhao pluton is a typical post-tectonic pluton in the Altai orogen, but its emplacement time is still conclusively undetermined. This paper presents a zircon SHRIMP 206Pb/238 U age of 276±9Ma (MSWD = 1.1), which is interpreted as his emplacement age. This provides an evidence for post-orogenic granitic magmatism and post orogeny. Major and trace elements show that the pluton has transition features from high-K calc-alkaline or high- fractionated I-type granites to A-type granites. Integration analysis of structural pattern, geochronology, geochemistry, and geological setting suggest that this pluton is post orogenic. Its Sr(T)i values are between 0.704 and 0.71659,eNd(T) values between +1.3 and +2.8, and TDM-2 from 0.93 to 0.81 Ga, which are similar to those of high (positive)-eNd(T) value granites from the Central Asian Orogenic Belt. Importantly, its eNd(T) values are slightly higher than these of syn-orogenic granites in the same area. This suggests that new juvenile mantle-derived materials, beside subducted juvenile ocean crust or arc rocks, probably contributed to the generation of the granites during post orogen in Altai orogen with Precambrian basement. This study provides an evidence for vertical continental crustal growth in the Central Asian Orogenic Belt.

Alkane carbon isotopic composition and gas source in giant gas fields of Ordos Basin

Abstract: The Ordos Basin is secondary big sedimentary basin of China. Four giant gas fields had been proven in the basin,including Sulige,Yulin,Wushenqi and Jingbian gas fields with proven reserves over 100 billion cubic meters for each gas field to the end of 2002.The hydrocarbon source rocks of the Sulige,Yulin and Wushenqi gas fields are coal measures of the Upper Paleozoic.The Jingbian gas field was found in the carbonates of Majiagou Formation in the Ordovician of the Lower Paleozoic. There are still existing arguments about the gas sources of Jingbian gas field.The alkane carbon isotopes analyses of 125 gas samples collected from the above-mentioned four gas fields show that the carbon isotopes of giant gas fields in the Upper Paleozoic are heavy,and the range of values is narrow. The gases are characterized by coal-formed gas. The δ 13C iC4 value is bigger than the δ 13C nC4 value. Reversal of carbon isotope values in single type appears in the Upper Paleozoic gas fields. In the Lower Paleozoic Jingbian gas field,the δ 13C 1 dominant peak values, the δ 13C B values and the δ 13C T values are similar to those in the Upper Paleozoic.However,there are still some different characteristics in Jingbian gas field from other three gas fields.The reversals of carbon isotope values are of multiple types. The values of δ 13C 1,δ 13C 2 and δ 13C 3 are ranged widely,and the δ 13C 2 value is smaller.These characteristics show that the gases are mixed from mainly humic and some sapropelic sources.It is suggested that the humic and sapropelic sources are all from C-P coal measures and the Taiyuan Formation carbonates with a high abundance of organic matter in the Upper Paleozoic rather than the conventional idea suggested that sapropelic gases are mainly from the Majiagou Formation carbonates with the total organic content of 0.20%.

Metamorphic evolution of the Yuka eclogite in the North Qaidam,NW China:evidences from the compositional zonation of garnet and reaction texture in the rock.

Abstract: The typical mineral assemblage of the Yuka eclogite in North Qaidam is composed of garnet (Grt),omphacite (Omp), phengite(Phe) and rutile(Ru).Coarse-grained garnet porphyroblast with obvious zoning in both composition and mineral inclusions, can be divided,from core to rim,into four rings,i.e.,core (GrtⅠ),mantle (GrtⅡA),rim (GrtⅡB) and outermost rim (GrtⅡC). Petrographic and mineral chemistry studies indicate that the Yuka eclogite has undergone three successive stages of pre-eclogite, eclogite and post-eclogite,recording a process evolved from subduction to exhumation of the rock.The pre-eclogite stage (Ⅰ) is represented by the assemblage in the core part of garnet porphyblast (GrtⅠ+AmpⅠ+Zoi+PⅡ+Q),P-T metamorphic conditions are estimated to be 450 to 500℃ and 0.6 to 0.7 GPa.Eclogite facies stage can be further divided into three sub-stages of early-,peak-and retrograde-eclogites.Early-eclogite stage (ⅡA) is characterized by the assemblage of GrtⅡA+OmpⅡA+PheⅡA+Ru preserved in the mantle part of garnet porphyblast,which recorded the metamorphic conditions of 580 to 640℃ and 2.4 to 2.5 GPa.Peak-eclogite stage (ⅡB) is represented by the rim part of garnet porphyblast,and the core part of omphacites and phengites in the matrix (GrtⅡB+ OmpⅡB+PheⅡB+Ru),P-T estimates give peak metamorphic conditions of 620 to 680℃ and 3.0 to 3.4 GPa.Retrograde-eclogite stage (ⅡC) is characterized by the outermost rim part of garnet porphyblast,Mg - kataphaprite,the rim of omphaeite and phengite in the matrix (GrtⅡC+OmpⅡC+PheⅡC+AmⅡ),P-T estimates give the first retrograde conditions of 700 to 720℃ and 2.3 to 2.4GPa. Post-eclogite stage is mainly of granulite-amphibolite facies,which is inferred from the breakdown of omphaeite to produce diopside+ plagioelase amphibole symplectites.This was overprinted by abundant amphibole and plagioclase of amphibolite facies formed from garnet,clinopyroxene and Mg-kataphaprite.P-T estimates give the metamorphic conditions of 550～600℃ and 0.6～1GPa.The metamorphic conditions of different stages of the Yuka eclogite construct a clockwise metamorphic evolution path from prograde to retrograde,and the peak stage was formed at 630～680℃ and 3.0～3.4GPa,indicate that the Yuka eclogite underwent an ultrahigh pressure metamorphism.The preservation of prograde mineral assemblages and compositional zoning in garnet porphyblast suggest that the Yuka eclogite underwent an evolution history of rapid burial and uplift.

Rising of Da Hinggan Mts in Mesozoic: A possible mechanism of intracontinental orogeny.

Abstract: The Mesozoic ground geology of Da Hinggan Mts. is studied in this work in combination with the structural features of the crust, upper mantal, and asthenosphere at various depths to reconstruct the geologic evolution of this area. The results reveal a two-stage orogenesis of the Da Hinggan Mts. : the first stage of contenantal-crust accretion starts from the Early Mesozoic underplating and goes through an extenssive crust-mantle magma intrusion and eruption until the Late Mesozoic, and the the second stage of upwellung is marked by formation of the basin-and-range structure in the Early Cretaceous. Upon such a special orogeny duscovered in Da Hinggan Mts. , a possible mechanism - extentional orogenesis - is proposed to explain some of the intracontenantal orogenes, and a preliminary understanding is obtained about their complucated features that are those of the plate-marginal orogenes.

Geochronological and geochemical study on the wallrock of Tuwu-Yandong porphyry copper deposits,eastern Tianshan mountains.

Abstract: This paper reports the isotopic age of Qi'eshan Group,the wallrock of Tuwu-Yandong porphyry copper deposits in eastern Tianshan moontainsThe analyses by SHRIMP shows that the zircon crystals separated from the andesite within Qi'eshan Group have the concordant U-Pb age of 3365±66 Ma,and the Sm-Nd isochronic age of the basalt and its constituent minerals,diopside and plagioclase,collected from the same group is 334±36 MaThese results conformably demonstrate that Qi'eshan Group was formed in early Carboniferous epochThe basalts of Qi'eshan Group are of island are tholeiite series,and are characterized by moderate enrichment of the LREE relative to the HREEThey all show significant enrichment of large ion lithophile elements and relative depletion in high strength field elements relative to N-MORB,indicating that Qi'eshan Group was formed at a subduction zone setting, in accordance with the tectonic discrimination diagramThe geochronological determination of Qi'eshan Group provides important constraints for the petrogenetic and metallogenic age of the deposits and its tectonic setting,which were much controversial issues before

Zircon LA-ICPMS U-Pb dating and geochemical characteristics of Huangshaping granite in southeast Hunan province, China.

Abstract: There are two types granitoid in the middle of Nanling granitoid zone, including Qianlishan and Qitianling granites and Shuikoushan, Tongshanling and Baoshan granodiorite intrusions. The Huangshaping granite, which is close to the former granites, is characterized by higher values of SiO2 and K2O, higher ratio of K2O/Na2O, high abundances of Rb, Th, U, Ta and Nb, but lower contents of Ba, Sr, P, Eu and Ti. Chondrite-normalized REE patterns show strong negative Eu anomalies. The Huangshaping granite is dated 161. 6 1. 1 Ma by zircon LA-ICPMS U-Pb method, which is in accordance with ages of the Qianlishan(162. 55±3. 25Ma) and Qitianling (161±2Ma) granites. These ages imply a major emplacement period of the Yanshanian granites in southeast Hunan province as well as the whole Nanling Range area. In this study, the geochemical and geochronological characteristics are similar between Huangshaping granite and the Qianlishan and Qitianling granites. They are the same type granitoid. Their lithogenesis was related to the lithospheric extension after the Indosinian Orogenesis, and formed from partial melting of the crust material. All this are different from granodiorite intrusions in Shuikoushan, Tongshanling and Baoshan.

The formation and tectonic evolution of UHP metamorphic belt in southwestern Tianshan,Xinjiang.

Abstract: The recent study in geological occurrence,petrology,geochemistry and geochronology of the UHP metamorphic belt in Southwestern Tianshan has been summarized in this paperAccording to their geological occurrences,the eclogites in Southwestern Tianshan can be grouped into three types,ie,the lenticular body around by blueschist,pillow structure eclogite and banded eclogite within marbleThe petrological study shows that all these three kinds' eclogites have undergone ultrahigh pressure metamorphism Their UHP metamorphic evolution can be divided into three stages:peak UHP eclogite stage with PT conditions of 560～600℃ and 495～507 GPa,main eclogite stage with PT conditions of 598～496℃ and 2572～2666±1kbar and retrograde stage of epidote blueschist facesThe geochemical study suggests that the protoliths of Southwestern Tianshan cclogites should be the affinity of OIB originated from the enriched mantle with e_(Nd)=-14～-04,NMORB from depleted mantle with e_(Nd)=+67～+74 and EMORB from the enriched mantle with e_(Nd)=-25～+32The above three protoliths of eelogites may be formed in sea mountain environmentThe SHRIMP dating of zircon from eclogites shows that the protoliths of eelogite were formed before Carboniferous (310 Ma),the oceanic subduetion Tarim plate northward beneath Yili-central Tianshan Craton began in the end of Permian (280～290 Ma) and the HP-UHP metamorphism happened in Triassic (220～230 Ma)Combined with the discovery of the low pressure granulites in the north side of the UHP belt,the tectonic model based on the paired metamorphic belt in Southwestern Tianshan has been proposed in this paper

Nature, composition, enrichment processes and its mechanism of the Mesozoic lithospheric mantle beneath the southeastern North China Craton

Abstract: This paper aims to constrain the nature and composition of the Mesozoic lithospheric mantle beneath the southeastern North China Craton on the basis of a systematic review on the temporal and spatial distribution and geochemical features of Mesozoic mantle-derived magmatism in the region,and to farther understand the temporal and spatial evolution,enrichment processes and its mechanism of the lithosphere through the comparison with the Mesozoic lithospheric mantle beneath the central,i.e.Luzhong region. Sr-Nd-Pb isotopic features of mantle-derived rocks imply that apparently temporal and spatial heterogeneity of the Mesozoic lithospheric mantle existed beneath the eastern North China Craton,the mantle under the central North China Craton,i.e the Luzhong region was dominantly slightly enriched and that under the southeastern North China Craton such as Luxi and Jiaodong region was EM2-like (~(87)Sr/~(86)Sr_i up to 0.7114).It is also apparent that the Mesozoic lithospheric mantle beneath the southeastern North China Craton evolved with time.These geochemical features of mantle-derived rocks and compositional and textural characteristics of the basalt-borne mantle xenoliths (peridotites and pyroxenites) and xenoerysts (olivine and pyroxene) demonstrate that the Mesozoic lithospherie mantle beneath the southeastern North China Craton was severely affected by the silica-rich melts.Reaction between lithospheric peridotite and infiltrated melt was considered to be an important type of lithospheric reconstruction and transformation,which led to the transformation of the Paleozoic high-Mg~# peridotite to late Mesozoic low-Mg~# peridotite and pyroxenite.Influx of melts into the lithospheric mantle, which had the geochemical characteristics of partial melting of the lower/middle crust,resulted in rapid enrichment of the late Mesozoic lithospheric mantle beneath the southeastern North China Craton.Relevant scientific issues such as the timing,processes and its mechanism of Mesozoic lithospheric thinning and reconstruction of the eastern North China Craton have also been discussed.

Origin of late Mesozoic intermediate- felsic volcanic rocks from the northern Da Hinggan Mountain, NE China.

Abstract: Major, trace element and Sr-Nd isotope data of two types late Mesozoic intermediate-felsic volcanic rocks from the southern Da Hinggan Mountain, NE China are reported in this paper. One type is represented by the andesite-dacites and rhyolites occurring in the Manketou'ebo Formation (Fm). These rocks span a SiO2 range of 60 - 74. 9% and MgO range of 0. 36 - 2. 04% , characterized by moderate LREE/HREE fractionation (Ce/YbCN = 2. 6 - 3. 0) , strong LILE enrichment and variable Nb-Ta and Ti-P-Sr depletion. They have more radiogenic Sr and less radiogenic Nd isotopic compositions (87Sr/86Sr(i) = 0.70522-0.70709; eNd(t) = -1.5- -0.4) than the contemporaneous basaltic lavas. In combination with the spatial coexistence between them and the basaltic lavas, we interpret these melts as differentiates of the primary basaltic magmas via variable degrees of fractional crystallization or assimilation and fractional crystallization (AFC). The other type of intermediate-felsic lavas occurs in the Manitu Fm. They are dacites rich in Al2O3 (15. 87 - 16. 36%) and Na2O (4. 63 - 4. 79% , K2O/Na2O 0. 4 ) , high Sr (709 - 832 μg/g) and low Y (6. 9 - 10.4 μg/g) and HREE (e. g. , Yb = 0. 37 - 0. 51 μg/g) , signatures of modern adakites from the subduction zones. Compared with the basaltic lavas, they have less radiogenic Sr but more radiogenic Nd isotopic compositions (87Sr/86Sr(i) = 0.70409 -0.70425; eNd(t) = +0.9 - +2. 1 ) , arguing against an origin of differentiates of the contemporaneous basalts. These rocks are considered as melts of mafic protoliths from the lower crust beneath the orogen under the heating of the underplating basaltic magmas. The adakitic trace element features suggest the presence of garnet and amphibole during melting with decomposition of plagioclase. The petrogenesis of these two types late Mesozoic intermediate-felsic rocks favors a lithospheric extension model in post-orogenic stage, during which mantle-derived basalts underwent extensive differentiation or AFC, or underplated into the lower crust to provide heat for anatexis of the mafic protoliths to produce the wide spectrum of intermediate-felsic melts in the NE China orogenic belt.

Studies on petrology and geochernistry of the Later Cretaceous basalts and mantle-derived xenoliths from eastern Shandong.

Abstract: The Wangshi group basalts cropped out in Daxizhuang, Jiaolai basin, eastern Shandong, belong to high-Ti alkaline basalt series. The basalt was emplaced at Late Cretaceous with Ar-40-Ar-39 plateau age of 73.2 +/- 0.3 Ma. The basalt is enriched in Na2O and has Mg# values of 63 similar to 66 and normative (Ne-Hy-Q) of 6.03 similar to 11.05, suggesting a depths of generation of 50 similar to 70 km for the basalt. The enrichment of light rare earth elements (LREE) with (La/Yb)(N) of 11.18 similar to 12.56 and large ion lithophile elements (LILE), such as Th and Zr, and reletively differentiated heavy rare earth element (HREE) patterns suggest a continental intraplate setting. High Positive epsilon(Nd) (T) value of 7.08 similar to 7.55 and low Sr-87/Sr-86(T) ratio of 0.7035 similar to 0.7038 for basalt in Daxizhuang suggest that the basalt was virtually not contaminated by crustal materials during their ascending and the initial basltic magma was generated by a depleted mantle source. The parantal basaltic magma was a mixture of melts derived from the asthenospheric mantle and young depleted lithospheric mantle. Mantle derived spinel-iherzolite xenoliths have been discovered in the basalt. The estimated equilibrium P-T condition of xenoliths was about 20 kb and 1010 similar to 1140degreesC. The estimated equilibrium P-T condition of xenoliths and depth of the generation of the basaltic magma suggested that the lithosphric thickness in Jiaozhou area was about 60 similar to 70 km in Late Cretaceous. This further inferred that the lithospheric thinning and asthenospheric upwelling in eastern China took place at 125 to 73 Ma B. C. Hereafter, there was a uniform dynamic setting in eastern China.

Age, geochemistry and petrogenesis of the cumulate gabbro in Tahe, northern Da Hinggan Mountain.

Abstract: In this paper, geochemical data of the major and trace elements, and Hf isotope are reported for the Tahe cumulate gabbro exposed in the northern Da Hinggan Mountain. Basen on these data, its petrogenesis, protolith and tectonic implications are discussed in detail. The Tahe cumulate gabbro, characterized by low SiO2 (42. 59-47. 4wt. %) , TiO2 (0. 5wt. %) , P2O5 (0. 1wt.%) and high Al2O3(15.9 -32.9 wt.%) , CaO (11.7-17.1 wt. %) , is enriched in large ion lithophile elements (LILE) and depleted in high field strength elements (HFSE) , showing the similar geochemical characteristics to the gabbros formed in the active continental margin or island arc. Zircon laser ablation (LA) -ICP-MS U-Pb analyses indicated that the Tahe gabbro was emplaced at 333±8 Ma with negative eHf(t) values of - 2 - -5. Therefore, it is concluded that the Tahe gabbroic magma was derived from partial melting of the mantle pyroxenite in the enriched lithospheric mantle or lower crust which was metasomatized by fluid released from the subducted slab. Hence, the occurrence of the Tahe cumulate gabbro indicates that a subduction process was conducted beneath this area at -330Ma, which was considered to be related to the assembly of the Songnen and Xing' an blocks.

Geochemical characteristics of the Yao'an and Machangqing alkaline-rich intrusions

Abstract: The Yao'an and Machangqing alkaline-rich intrusions, lying in east margin of the NW-WNW Ailaoshan-Jinshajiang fault zone, form parts of the Ailaoshan-Jinshajiang alkaline-rich intrusive belt. The Yao'an intrusion consists mainly of syenite porphyry, and the Machangqing intrusion consists mainly of granite porphyry. Chemically these two intrusions are characterized by enrichment in alkaline and potassium. They enrich in LREE and LILE (such as Rb, Sr, Ba, Th, La etc. ) , deplet HFSE (such as Nb、Ta and Ti etc. ) , have high Rb/Sr, La/Nb, Ba/Nb and LREE/HREE ratios, and don't show obvious Eu anomalies. The ISr values of these two intrusions are relatively high, and eNd values are relatively low. It is suggested that the intrusions were derived from partial melting of an enriched upper mantle ( EMII) , a mixture between normal mantle and subducted oceanic crust, in a continental arc of extension tectonic setting. Although these two intrusions share similar characteristics on tectonic setting in the Himalayan period, age and source region, they have some difference on lithology and chemical composition, which was probably related to the difference on physical-chemical condition (such as T, P and fO2 etc. ) during magmatic crystallization, and on different melted degress of source rocks. Au mineralization is considered to be associated with the intrusions of alkaline series while Cu mineralization with the intrusions of alkaline-subalkaline series in Ailaoshan- Jinshajiang alkaline intrusive belt.

Characteristics of the granitoid complex and its zircon SHRIMP dating at the south margin of the Bashikaogong Basin, North Altun, NW China.

Abstract: The 49 km long, E-W trending granitic belt with an area of - 90 km2 at the south margin of the Bashikaogong Basin intruded into the Precambrian sandstones, schists, mudstones and tuffs. Field observations show that it consists of four types of granites, e. g. , gigantic phenocryst granites (Ⅰ) , fine to intermediate grained red granites (Ⅱ) , intermediate to coarse grained porphyritic grey granites (Ⅲ) , and intermediate to coarse grained porphyritic pink granites (Ⅳ) . Petrochemically, these granites are peraluminous in that they have (1) contents of SiO2 and alkaline (Na2O+K2O) ranging from 65. 14% to 75. 66% , and from 7. 49% to 8. 96%,respectively; (2) K2O/Na2O ratios ranging from 1. 12 to 2. 68; (3) Rittmann index from 1. 83 to 2. 81, with an average of 2.34; and (4) corundum (AC) (0.77-3.93%, and average 1. 78) CIPW normative. These granites have total REE contents of 89. 44 -335. 28×10-6, and substantial negative Eu anomalies. From type Ⅰ through Ⅲ and Ⅳ to Ⅱ granites, Eu/Eu* ratios decrease from 0. 65 over 0. 51 and 0. 48 to 0. 30. Trace element compositional data show that (1) these granites have pronounced negative Ba, Nb, Sr, P and Ti anomalies; (2) their trace element abundances decrease, but the magnitude of Ba, Nb, Sr, P and Ti anomalies increase from type Ⅰ through Ⅲ and Ⅳ to Ⅱ granites. Major element and trace element data indicate that they have an S-type granite affinity. Zircons separated from these four types of granites were used to perform SHRIMP U-Pb zircon dating to constrain their formation ages. Dating results show that their formation ages are 474. 3±6. 8Ma for type Ⅰ granite, 446. 6±5. 2Ma for type Ⅱ granite, 434. 5±3. 8Ma for type Ⅲ, and 431. 1±3. 8Ma for type Ⅳ granite, respectively. Combined with field observational data, these data suggest that these granites were derived from partial melting of crustal materials during syn-collision and post collision events between Altun and Tarim continental blocks in Paleozoic time.

The Jurassic deformation in the Dabie Mountains and its tectonic significances.

Abstract: It was widely accepted that the Dabie orogen underwent an ultrahigh-pressure metamorphism as a result of the Triassic collision between the North China and Yangtze continents.However,there has been much debate on the deformation within the orogen and tectonic setting during the Jurassic.The study on the folding of the pre-Jurassic strata and deep reflection seismic exploration in the foreland belt,the SE deformation of amphibolite facies in the high- and ultrahigh~pressure rocks,and the igneous records of 160～120 Ma in the orogen suggest that a strong orogeny took place in the Dabie Mountains in the middle Jurassic.The orogeny was related to the Yanshanian movement.Because the North China and Yangtze blocks have collided and formed an uniform continent in Triassic,the Jurassic deformation was of intra-continental origin.A separation of Jurassic deformation from the Triassic collisional process of the Dabie Mountains could reasonably explain the second exhumation of ultrahigh-pressure metamorphic rocks from the mantle-crust boundary to the upper crust,the genesis of migmatization at 150 Ma and magmatic activity at 130～120 Ma,and the offset of MOHO in the Dabie foreland belt.

The petrogenesis and SHRIMP dating of the Baiyinbaolidao adakitic rocks in southern Suzuoqi, Inner Mongolia

Abstract: The geochemical characteristics of the Baiyinbaolidao tonalites, in Southern Suzuoqi, Inner Mongolia are similar to those of typical adakites For example, the tonalities have SiO2≥56 wt % (61 1 -616wt % ) , Al2O3 15 wt % ( 16 6- 17 1wt % ) , MgO 3 wt % (2 3wt % ) , Na2O 3 wt % , low Y and HREE ( Y = 14 5 - 16 2μg/g, 18μg/g; Yb = 161 - 1 64μg/g, 19μg/g) and high Sr (604-649μg/g, 400μg/g) The tonalities are proposed to may be products of young subducted oceanic crust High-precision SHRIMP U-Pb zircon analysis indicate that the tonalites were formed at 464±8Ma- 479±8Ma According to the previous SHRIMP data, the Baiyinbaolidao tonalites were possibly emplaced at 464Ma - 490Ma It is suggested that the subduction event of the Middle Inner Mongolia took place in the Early Ordovician

Elastic-plastic analysis of casing-concrete sheath-rock combination

Abstract: Based on the theory of multi-layer composed thick-wall cylinder,the elastic-plastic analysis of the casing-concrete sheath-rock combination was madeThe equations for expressing the distribution of stress in the combination under elastic and elastic-plastic conditions were deducedAlso the characteristics of the force on the composed cylinder in the different working status such as elastic and plastic conditions were analyzedThe research results show that the ideal property of concrete sheath should be of high strength and low stiffnessThe high strength of concrete sheath could resist higher loads of formation stressAt the same time,the low stiffness of that could reduce the transfer coefficient of stress greatlyFrom this point,the development of new type plastic concrete with high strongth and low stiffness should be enhanced