Geochemistry and chronology of the Jiehekou Group metamorphic basic volcanic rocks in the Lüliang Mountain area,Shanxi, China

Samples were systematically collected from metamorphic basic volcanic rocks in the Jiehekou and Xiyupi areas on both sides of the Lüliang Mountains, Shanxi Province and analyzed for their major elements, trace elements and rare earth elements (REE). The geochemical characteristics of their major, trace and rare-earth elements indicated that the metamorphic basic volcanic rocks in this area were emplaced in the tectonic environment like a modern continental rift. Sm-Nd and Rb-Sr isotope chronological studies demonstrated that the Jiehekou Group metamorphic basic volcanic rocks were formed during the 2600-Ma crust/mantle differentiation event, and were transformed by granulite facies metamorphism during the late Neo-Archaean period (2500 Ma ±), making the Sm-Nd systematics of the rocks reset. During the late Paleoproterozoic period (1800 Ma ±) the Rb-Sr systematics of the rocks were disturbed again in response to the Lüliang movement. Since the extent of disturbance was so weak that the Sm-Nd systematics was not affected, the age of 1600 Ma ± obtained from this area seems to be related to local magmatic activities within the craton. Research results lend no support to the idea that the Lüliang Group was formed during the Archaean. Instead, it should be formed during the Proterozoic.     

Ar-Ar geochronology of Late Mesozoic volcanic rocks from the Yanji area, NE China and tectonic implications

Ar-Ar dating results of late Mesozoic-Cenozoic volcanic rocks from the Yanji area, NE China provide a new volcano-sedimentary stratigraphic framework. The previously defined “Triassic-Jurassic” volcanic rocks (including those from Sanxianling, Tuntianying, Tianqiaoling and Jingouling Fms.) were erupted during 118―106 Ma, corresponding to Early Cretaceous. The new eruption age span is slightly younger than the main stage (130―120 Ma) of the extensive magmatism in the eastern Central Asian Orogenic Belt and its adjacent regions. Subduction-related adakites occurring in the previously defined Quanshuicun Fm. were extruded at ca. 55 Ma. Based on these new Ar-Ar ages, the late Mesozoic to Palaeocene volcano-sedimentary sequences is rebuilt as: Tuopangou Fm., Sanxianling/Tuntianying Fm. (118―115 Ma), Malugou/Tianqiaoling Fm. (K1), Huoshanyan/Jingouling Fm. (108―106 Ma), Changcai Fm. (K2), Quanshuicun Fm. (~55 Ma) and Dalazi Fm. Our results suggest that subduction of the Pa- laeo-Pacific Ocean beneath the East Asian continental margin occurred during 106 to 55 Ma, consistent with the paleomagnetic observations and magmatic records which indicated that the Izanagi-Farallon ridge subduction beneath the southwestern Japan took place during 95―65 Ma.     

Geochemistry and Sr-Nd-Pb isotopic characteristics of the Mugouriwang Cenozoic volcanic rocks from Tibetan Plateau:Constraints on mantle source of the underplated basic magma

The Mugouriwang Cenozoic volcanic rocks exposed in the north Qiangtang Block of Tibetan Plateau are mainly composed of basalt and andesitic-basalt,both characterized by the lower SiO2 (51%―54%),high refractory elements (i.e. Mg,Cr,Ni) as well as the moderate enrichment in light rare earth elements (LREE) relative to a slight depleted in Eu and high strength field elements (HFSE,i.e. Nb,Ta,Ti). Be-sides,the fairly low Sm/Yb value (3.07―4.35) could signify that the rocks should be derived directly from partial melting of the spinel lherzolite at the upper part of the asthenosphere. These rocks have radiogenic Sr and Pb (87Sr/86Sr = 0.705339 to 0.705667; 208Pb/204Pb = 38.8192 to 38.8937; 207Pb/204Pb = 15.6093 to 15.6245; 206Pb/204Pb = 18.6246 to 18.6383),and non-radiogenic Nd (143Nd/144Nd = 0.512604 to 0.512639; εNd = 0.02 to -0.66) in agreement with those values of the BSE mantle reservoir. The DUPAL anomaly of the rocks can be evidently attested by the △8/4Pb = 66.82 to 74.53 ,△7/4Pb = 9.88 to 11.42,△Sr>50,implying that the Mugouriwang volcanic rock is likely to be generated by partial melting of a Gondwana-bearing asthenospheric mantle ever matasomatised by the fluid from subduction zone. Depending on the previous study on the high-K calc-alkaline intermediate-felsic volcanics in the study area,this paper proposed that the fluids derived from the subducted Lhasa Block metasomatised the asthenosphere beneath the Qiangtang Block,and induced its partial melting,and then the melt under-plated the thickened Qiangtang lithosphere and caused the generation of the Cenozoic adakite-like felsic magmas in the Qiangtang region.     

(40)~Ar/(39)~Ar chronology and geochemistry of high-K volcanic rocks in the Mangkang basin, Tibet

Our two newly obtained high-quality 40Ar/39Ar ages suggest that the high-K volcanic rocks of the Lawuxiang Formation in the Mangkang basin, Tibet were formed at 33.5±0.2 Ma. The tracing of elemental and Pb-Sr-Nd isotopic geochemistry indicates that they were derived from an EM2 enriched mantle in continental subduction caused by transpression. Their evidently negative anomalies in HFSEs such as Nb and Ta make clear that there is an input of continental material into the mantle source. The high-K rocks at 33.5±0.2 Ma in the Mangkang basin may temporally, spatially and compositionally compare with the early one of two-pulse high-K rocks in eastern Tibet distinguished by Wang J. H. et al., implying that they were formed in the same tectonic setting.     

Isotopic feature and uranium dating of the volcanic rocks in the Okinawa Trough

1 Introduction The Okinawa Trough(OT) extends for ~1200 km between Taiwan and Kyushu, and is an incipient back-arc basin bounded by the Ryukyu Arc to the south and east, and by Diaoyudao Uplift Belt[1,2] (Tai- wan-Sinzi Belt[3]) to the north and west. Drastic faults and volcanic activities are the typical features in the OT. Generally, the OT is divided into three segments (north, middle and south) by the Tokara Strait and Kerama Gap[4]. The geological features, such as tec- tonics, m…     

Geochemistry and zircon U–Pb ages of the Paleoproterozoic ultramafic rocks of the Mbi Valley,Boali area,Central African Republic

This paper investigates the geochemistry of bulk rock and infers the petrogenesis of ultramafic rocks in the Boali Precambrian terrane in Mbi Valley, in the North of the Central African Republic(CAR). The studied rocks comprise coarse primary olivine and orthopyroxene relics(dominant phase), magnesio-hornblende, magnetite, and antigorite. Whole-rock analysis indicates low SiO₂(average of 43.14 wt%) and high MgO(19.84–26.98 wt%)contents and their Mg number(Mg#) ranges from 74 to 82.The...     

Geochemistry of ore-forming fluids and geological significance of the Kuoerzhenkuola gold field in Xinjiang, China

The Kuoerzhenkuola gold field (including the Kuo- erzhenkuola and the Buerkesidai gold deposits), lo- cated 68 km east of Jimunai County in northern Xing- jiang, China, is an important component of the Sawuer gold belt which is the eastward extending part of the Zarma-Sawur gold-copper belt in Kazakhstan. Some studies are concerned with the geology of the gold ores[1―3], the associated volcanic rocks[4], radiogenic isotope[5―8], and the ore-forming environment[8]. Most researchers inferr…     

Geochronological and geochemical comparison of Precambrian meta-mafic volcanics in Zhongtiaoshan and Lüliangshan Regions in Shanxi,North China Craton

To unravel the geochemical heterogeneity and its origin in different terranes of North China, we conducted geochronological and geochemical analyses of the meta-mafic rocks from the Lüliang–Zhongtiao rift zone(Shanxi Province). LA-ICP-MS zircon U–Pb dating yielded mostly End-Neoarchean to Proterozoic ages for the basement rocks(Sushui Complex: 2516 ± 26 Ma; Metamafic rocks: 2494 ± 31 Ma), Jiangxian Group(～ 2213 Ma), Zhongtiao Group(2077 ± 29 Ma), Jiehekou Group(1998 ± 23 Ma), and Lü liang Group(2152 ± 52 Ma). Petrographic characteristics show that the meta-mafic rocks from the Neoarchean–Paleoproterozoic Zhongtiaoshan(Sushui Complex) have similar geochemical characteristics to the overlying Jiangxian and Zhongtiao Groups. The Paleoproterozoic Lüliang andYejishan Group meta-mafic rocks from Lü liangshan also have similar geochemical characteristics but are geochemically different from similar-age rocks from Zhongtiaoshan. This shows that the late-stage rocks have a geochemical inheritance from the early-stage rocks in the same region and that the geochemical heterogeneity of rocks from different areas was originated from the inherited heterogeneity of the magma source.     

Thermal Process in the Crust and Upper Mantle in Xingtai-Shulu area of Hebei Province,China

Study of geothermal field data,terrestrial heat flow values,and other geophysical data from the Xingtai-Shulu area of Hebei Province made us more understanding of the distribution of geothermal fields and deep structures and their interrelation.The study illustrates that the geothermal field has an apparent lateral inhomogeneity and is evidently correlated by the structure of the crust and upper mantle in the area.The relation of the geothermal field distribution to the structure indicates that in comparison with the depression zone,the uplift zone has a higher heat flow value and a larger geothermal gradient.The analysis of the relation between distribution of earthquake epicenters and geothermal field and mathematical simulation of thermal stress in the area suggests that thermal stress plays an important role in the process of earthquake generation.     

SHRIMP zircon U-Pb age and significance of Early Paleozoic volcanic rocks in East Kunlun orogenic belt, Qinghai Province, China

A great deal of practical data in recent years have proved that the East Kunlun orogenic belt and even the China central orogenic belt are complex orogenic belts that underwent polycycle orogenic evolvement[1―7]. Each orogenic cycle has left a compositional print, the multi-period ophiolites[4―6] and various types of tec-tono-magmatic production in the same orogenic belt. There is a suite of shallow metamorphic volcanic rocks in the Nuomuhong area in the east part of the East Kunlun orogen…     

Holocene Paleoseismic Activity Along the Northern Piedmont Fault of the Hengshan Mountain, South of Datong Basin in Shanxi Province

INTRODUCTIONTheDatongbasinislocatedinthenorthernpartofShanxiProvinceandisoneoftheimportantpartsoftheCenozoicfaultedbasinintheShanxifaulteddepressionsystem .IntheresearchofactivefaultsinChina ,theShanxifaulteddepressionsystemhasattractedgreatattentionwithitsspecifictectonicpatternandfrequencyofhistoricstrongearthquakes (DengQidongetal.,1 973;1 995;LiuGuangxunetal.,1 982 ;DingGuoyuetal.,1 983;XuXiwei,1 989) .AnearthquakewithM6 1occurredintheDatongbasinin 1 989.Sincethenseveraldiscus…     

Three-dimensional seismic velocity tomography of the upper crust in Tengchong volcanic area, Yunnan Province

Introduction Tengchong is one of youngest volcanic areas in Chinese mainland. Since Pliocene, the volcanoes have erupted several times. Nowadays, the thermal activity is very intensive there. The possibility of re-eruption and the reserve of geothermal energy in the area are the questions to which the publics pay much attention, and the volcanists and seismologists dedicated. HAN, et al (1996) reviewed all of the studies carried out in Tengchong area. In the late 1990s, an integrative volca…     

Evidence of microstructures and fluid inclusions for the origin of polycrystalline quartz ribbons in high-grade metamorphic rocks in Daqingshan region

Polycrystalline quartz ribbons in high-grade metamorphic rocks from the Daqingshan region, are typi- cal microfabrics of, and provide information for, deep crust deformation and metamorphism. The quartz ribbons have straight boundaries and extend stably along gneissosity. They truncate other mineral grains in the rocks and may contain inclusions of such minerals that are lens-shaped and oriented. They frequently end into branching termination. Analysis fluid inclusions in polycrystalline quartz rib- bons reveal that the complex types of fluid inclusions are inhomogeneously distributed. They are ob- viously different from inclusions captured at granulite facies, in both fluid compositions and T-P esti- mations. Based on microfabric and fluid inclusion analysis, the polycrystalline quartz ribbons are suggested to be formed by SO2-rich fluids filling micro-fractures that are parallel to early gneissosity. The SO2 composition is derived from the deformed host rocks. The fluid phase has significant effects on the rheological characteristics, fracturing of rocks, and formation of quartz ribbons.     

U–Pb ages of zircons from metamorphic rocks in the upper sequence of the Hidaka Metamorphic Belt,Hokkaido, Japan: Identification of two metamorphic events and implications for regional tectonics

The Hidaka Metamorphic Belt is a well-known example of island-arc crustal section, in which metamorphic grade increases westwards from unmetamorphosed sediment up to granulite facies. It is divided into lower (granulite to amphibolite facies) and upper (amphibolite to greenschist facies) metamorphic sequences. The metamorphic age of the belt was considered to be ~55 Ma, based on Rb – Sr whole-rock isochron ages for granulites and related S-type tonalities. However, zircons from the granulites in the lower sequence yield U – Pb ages of ~21 – 19 Ma, and a preliminary report on zircons from pelitic gneiss in the upper sequence gives a U – Pb age of ~40 Ma. In this paper we provide new zircon U – Pb ages from two pelitic gneisses in the upper sequence to assess the metamorphic age and also the maximum depositional age of the sedimentary protolith. The weighted mean ²⁰⁶Pb/²³⁸U ages from a biotite gneiss in the central area of the belt yield 39.6 ± 0.9 Ma for newly grown metamorphic rims and 53.1 ± 0.9 Ma for the youngest detrital cores. The ages of zircons from a cordierite–biotite gneiss in the southern area are 35.9 ± 0.7 Ma for metamorphic rims and 46.5 ± 2.8 Ma for the youngest detrital cores. These results indicate that metamorphism of the upper sequence took place at ~40 – 36 Ma, and that the sedimentary protolith was deposited after ~53 – 47 Ma. These metamorphic ages are consistent with the reported ages of ~37–36 Ma plutonic rocks in the upper sequence, but contrast with the ~21–19 Ma ages of metamorphic and plutonic rocks in the lower sequence. Therefore, we conclude that the upper and lower metamorphic sequences developed independently but coupled with each other before ~19 Ma as a result of dextral reverse tectonic movement.     

Geochemistry and mineralogy of the Late Permian coals from the Songzao Coalfield, Chongqing, southwestern China

Mineralogy and geochemistry of the four main workable coal seams (No.6, No.7, No.8, and No.11) of Late Permian age from the Songzao Coalfield, Chongqing, Southwest China, were examined using in- ductively coupled plasma-mass spectrometry (ICP-MS), X-ray fluorescence spectrometry (XRF), cold-vapor absorption spectrometry (CV-AAS), ion-selective electrode (ISE), scanning electron mi- croscopy equipped with an energy-dispersive X-ray spectrometer (SEM-EDX), and X-ray diffraction analysis (XRD). The results showed that the main workable No.8 Coal that accounts for about 60% of the total coal reserves in the Songzao Coalfield was not enriched in hazardous trace elements. The No.11 Coal has high concentrations of alkaline elements, Be (9.14 μg/g), Sc (12.9 μg/g), Ti (9508 μg/g), Mn (397 μg/g), Co (23.7 μg/g), Cu (108 μg/g), Zn (123 μg/g), Ga (32 μg/g), Zr (1304 μg/g), Nb (169 μg/g), Hf (32.7 μg/g), Ta (11.4 μg/g), W (24.8 μg/g), Hg (0.28 μg/g), Pb (28.1 μg/g), Th (24.1 μg/g), and rare earth elements (509.62 μg/g). The concentration of Nb and Ta in the No. 11 Coal is higher than the industrial grade, and their potential utilization should be further studied. Besides pyrite, quartz, calcite, and clay minerals, trace minerals including chalcopyrite, marcasite, siderite, albite, mixed-layer clay minerals of illite and smectite, monazite, apatite, anatase, chlorite, and gypsum were found in the No.11 Coal. It should be noted that alabandite of hydrothermal origin and anatase occurring as cement were identi- fied in coal. In addition, the clayey microbands derived from alkaline volcanic ashes were identified in the coal. The dominant compositions of these clayey microbands were mixed-layer clay minerals of illite and smectite, which were interlayered with organic bands. The modes of occurrence of alkaline volcanic ash bands indicate that the volcanic activities were characterized by the multiple eruptions, short time interval and small scale for each eruption during peat accumulation. The alkaline volcanic ashes were the dominant factors for the enrichment of alkaline elements, Nb, Ta, Zr, Hf, and rare earth elements, and the sulfide minerals are the main carriers of Ga, Cu, and Hg in the No. 11 Coal.     

Space–time relationships between volcanic associations of different alkalinities: The Belogolovskii Massif,Sredinnyi Range,Kamchatka. Part II. Geochemistry of volcanic rocks and magma sources

Data are presented relating to volcanic series in the Belogolovskii Massif, Sredinnyi Range, Kamchatka. We discuss new geochronologic data, the distributions of rare elements and platinum elements in the rocks, and list the isotope characteristics of volcanic series with normal and moderate alkalinities. We show that the Late Pliocene to Early Pleistocene rocks that belong to the moderate alkaline series of the Belogolovskii volcanic massif are different from rocks in the normally alkaline series of the Late Miocene to Middle Pliocene volcanogenic basement in having higher concentrations of the HFSE and LILE components. We propose a model for the generation of moderate alkaline magmas involving a heterogeneous depleted and a heterogeneous enriched source of material. According to the isotope data, one of these sources may be the subducted oceanic lithosphere of the Pacific and the Commander-Islands type, while the other source was recycled material of the Indian MORB type.     

Regional differences and determinants of built-up area expansion in China

Based on remote sensing data on land use provided by the Chinese Academy of Sciences and socio-economic data collected by the authors,this paper analyzes the trends and regional differences in built-up area(BUA) expansion in China from the late 1980s to 2000,and empirically estimates the major determinants of BUA expansion in different regions in 1996―2000.In 1989―2000,although China's overall BUA expansion accelerated,the trends differed significantly among regions.BUA expansion in the central and western regions accelerated significantly,but it slowed down considerably in the east-ern region.The estimation results from our econometric analysis reveal that BUA expansion in the eastern region reached a period when economic growth had no further significant impact on per capita BUA,the land utilization in this region has become more intensive with further expansion of the economy.In the central and western regions,the BUA has expanded remarkably due to the relatively more flexible land development policies and the relatively cheap land prices.Therefore,as the econ-omy continues to grow rapidly,policies relating to BUA expansion and cultivated land reductions may face more serious challenges in the central and western regions.     

Some geologic signatures of fault creep in the continental area of China

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Characteristics and origins of primary fluids and noble gases in mantle-derived minerals from the Yishu area, Shandong Province, China

springerlink.com Studies of mantle fluids are currently one of the hot topics in the earth science, greatly contributing to re-vealing origins and evolutions of fluids. In general, the concept of mantle fluids refers to their active compo-nents, such as CO2, H2O, N2, etc., while the noble gases inert in chemical properties belong to another research system. Due to their marked differences in various fluid sources of the Earth[1], the isotopic sig-natures of He and Ar have been widely used a…     

Characteristics of fault rocks and paleo-earthquake source along the Koktokay-Ertai fault zone,Xinjiang,China

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