Search

This paper presents the distribution of total phosphorus (P), inorganic P (IP) and organic P in sediment cores from Sishili Bay, China. Their concentrations (μmol g − 1 ) ranged from 15.04 to 21.59, 12.43 to 18.27 and 0.15 to 5.11, respectively, showing 87.6–96.9% of TP is IP. The distribution of the fractionation of IP , obtained by a sequential extraction technique, was 1.9–3.2% for soluble and loosely bound P (Ex-P), 8.5–13.1% for Al-bound from (Al-P), 7.4–9.5% for Fe-bound P (Fe-P), 5.0–12.4% for reductant-soluble P (Oc-P), 9.7–15.6% for CaCO 3 -bound P (ACa-P) and 45.9–54.6% for detritus P (Det-P). The P distribution and concentration was consistent with other Chinese coastal seas. No significant difference was found for the sedimentary P forms between scallop cultivation area and background area, indicating that shellfish aquaculture did not have significant effect on the depositional environment in the studied area, at least in case of P. [ABSTRACT FROM AUTHOR]

The volcanic rock system of the Miaoling Formation contains the main ore-bearing rocks of two volcanogenic massive sulfide (VMS)-type deposits in the Yanbian area of NE China. Investigation of the VRSMF is needed to better understand the formation of these VMS-type deposits and the tectonic evolution of the Yanbian area. To determine the petrogenesis, material sources, and formation age of the VRSMF, and elucidate its late Paleozoic tectonic evolution and metallogenic significance, this paper presents new petrological, geochronological, geochemical, whole-rock Sr–Nd and in situ zircon Hf isotopic data for the VRSMF. The VRSMF is composed of marine carbonate, intermediate–felsic volcanic rocks (andesite–trachyandesite–dacite) and pyroclastic rocks. Laser-ablation–inductively coupled plasma–mass spectrometry zircon U–Pb dating gives an eruption age of ca. 265 Ma for the pyroclastic rocks in the VRSMF. These rocks are classified as low- to medium-K calc-alkaline series. They are characterized by enrichments in large-ion lithophile elements (e.g., K, Rb, and Ba) and light rare earth elements, and depletions in high field-strength elements (e.g., Nb, Ta, and Ti) and heavy rare earth elements, showing affinity to igneous rocks formed in arc-related tectonic settings. These features, together with homogeneous zircon ε Hf (t) values of 10.9–15.7 and depleted Sr–Nd isotopic compositions [ε Nd (t) values of 2.4–5.0], suggest that the parental magma was derived from the partial melting of depleted mantle that had been metasomatized by subduction-related fluids. These results, along with findings of regional geological investigations, suggest that the formation of the VRSMF was related to subduction of the Paleo-Asian oceanic plate during the middle Permian. The VMS-type mineralization in the Hongtaiping and Dongfengnanshan deposits is interpreted to have formed in a bimodal–felsic setting in a back-arc extensional tectonic environment. [ABSTRACT FROM AUTHOR]

Abstract: A variety of deep-seated xenoliths occur within the Mesozoic Jiagou dioritic porphyry in the southeastern margin of the North China Craton (NCC). In this study we present a combined petrologic, geochronological, Hf isotope and geochemical study on the different types of xenoliths and use these data to better constrain the composition and age of the deep crust beneath the area. Most of the xenoliths are mafic meta-igneous rocks, among which garnet-bearing lithologies are common. The xenoliths can be classified into three broad petrographic groups: spinel-bearing garnet clinopyroxenite/phlogopite clinopyroxenite/spinel pyroxenite (Group 1), garnet amphibolite or hornblendite/garnet granulite/mafic gneiss lacking pyroxene (Group 2), and garnet-bearing felsic (intermediate-acid) gneiss (Group 3). Among these, the mafic–ultramafic rocks constitute the dominant category. The protoliths of the studied xenoliths range from basalt through andesite to dacite. Geochemical and Hf-isotope data indicate that most xenoliths belonging to Groups 2 and 3 resemble magmatic rocks formed at convergent continental margin arc setting. A few of them (mostly belonging to Group 1) represent mantle-derived products. Multiple metasomatic imprints, with contribution from subduction-related or mantle-derived fluids or melts have been recognized from the multistage mineral assemblages and ages. SHRIMP zircon U–Pb dating, Hf isotope and geochemical data offer evidence for subduction-related adakite-like and arc-related rocks in the southeastern margin of the NCC at ca. 2.5Ga and 2.1Ga, and confirm the occurrence of high-pressure granulite-facies metamorphism at ca. 1.8Ga. These data suggest an episodic growth of Precambrian lower crust beneath this region in response to two stages of subduction–accretion and one vertical accretion of mantle-derived basaltic magma at the base of the lower crust. Additionally, a previously unknown late mantle-derived basaltic magmatism at 393±7Ma has also been recognized. The data presented in this paper demonstrate that the deep crust beneath the southeastern margin of the NCC is composed of hybrid protoliths derived from Paleozoic, Paleoproterozoic and late Neoarchean sources. [Copyright &y& Elsevier]

Abstract: Eocene is a critical time for the elevation of Tibetan Plateau and global climate change, and previous studies suggested that the Eocene elevation was caused by intra-continental subduction of the Songpan–Garze block beneath the Qiangtang block. This paper reports zircon U–Pb age and geochemistry of the Eocene volcanic rocks from the Zuerkenwula mountain area in the northern part of Qiangtang block, and proposes that both slab break-off of the Neo-Tethys oceanic slab along the Bangong–Nujiang suture and intra-continental subduction of the Songpan–Garze block beneath the Qiangtang block caused the extensive partial melting of lithospheric mantle and subducted Songpan–Garze continental crust, which resulted in the significant elevation of the Tibetan Plateau. The volcanic rocks have LA-ICP MS U–Pb zircon age of 40.25±0.15Ma (MSWD=2.1, 2σ), which is contemporaneous with the Eocene eclogites in the Great Himalayan and K-rich lavas in the southeastern Tibet. They display some adakitic characteristics with SiO2 =57.44 to 68.72%, TiO2 =0.38 to 0.81%, Na2O=2.89 to 4.35%, K2O=2.77 to 4.48%, Al2O3 =13.92 to 18.22%, A/CNK=0.69 to 1.03, MgO=0.27 to 5.86% with Mg# ranging from 13.2 to 72.0, strongly depleted in heavy rare earth elements (HREEs) (Yb=0.92 to 1.51ppm and Y=10.1 to 24.1ppm), in combination with their positive Sr anomalies, high Sr/Y ratios and no significant Eu anomalies, which suggest a garnet-in and plagioclase-free source residue. These volcanic rocks can be divided into high-Mg# (>45) and low-Mg# (<45) groups. Both of the two groups share evolved Sr–Nd–Pb isotopic compositions with 87Sr/86Sr=0.707412–0.708284; εNd(t)=−4.0 to −5.7; 206Pb/204Pb=18.7499–18.8189, 207Pb/204Pb=15.7189–15.7384; 208Pb/204Pb=39.166–39.262. The geophysical data and regional geological setting suggest that the low-Mg# adakitic rocks were derived from the decompression melting of a subducted lower continental crust, when low-Mg# adakitic melts in the overlying peridotite mantle wedge captured some olivine crystals, resulting in their elevated Mg# and MgO values. [Copyright &y& Elsevier]

Abstract: This paper reports whole-rock Sr–Nd and zircon U–Pb and Hf isotopic compositions, as well as major and trace element data, for the granodiorites and their mafic microgranular enclaves (MMEs) in the Tuokesalei area, northwestern Chinese Altai. The granodiorites are characterized by peraluminous compositions (A/CNK=1.01–1.45), with relatively high SiO2 (64.4 to 70.9wt.%) and low MgO (0.75 to 1.97wt.%) contents. These rocks possess low total rare earth element (REE) contents (67–187ppm) with weakly negative Eu anomalies and mantle-like whole-rock Nd–Sr isotopic compositions (εNd(t)=+2.5 to +4.5; (87Sr/86Sr)i =0.7038 to 0.7048) and zircon εHf(t) values (+5.93 to +12.9). The MMEs contain abundant magmatic amphiboles and needle-like apatites, have low SiO2 (51.7 to 54.3wt.%) and high MgO (2.86 to 3.75wt.%) and REE contents (162–298ppm), and are characterized by moderately negative Eu anomalies (Eu/Eu*=0.40–0.60) and slightly depleted to enriched LREE ((La/Nd)N =0.74–1.41) and flat HREE ((Gd/Yb)N =1.16–1.39) patterns. The MMEs have whole-rock Nd–Sr isotopic compositions (εNd(t)=+2.6 to +2.7, (87Sr/86Sr)i =0.7034–0.7050) similar to those of the host granodiorites. Their similarities in crystallization age, mineral assemblage and isotopic composition document that the MMEs may represent an early crystallized phase, which was broken into pieces and brought to the shallow level during the host magma ascent and emplacement. Their precursor magmas were probably derived from an oceanic lithospheric mantle, which was characterized by pronounced Nd–Ta depletions. Mineral compositions of MMEs suggest that amphibole was a major early fractional mineral, which effectively differentiated the mantle-derived basaltic liquids to silica-rich melts. Zircon U–Pb dating yielded an age of 313±5Ma for the host granodiorites and 313±13Ma for their MMEs. The geochemical data of this study records an important episode of magmatism in an environment transitional from a subduction-related regime to a post-tectonic extension. Results of this study suggest that the accretionary orogenic process did not completely terminate until the Late Carboniferous to Permian in this region. [Copyright &y& Elsevier]

Abstract: The extension of the suture zone between the Siberian and Kazakhstan continents in China has been a matter of debate because few outcrops of ophiolitic mélange have been found so far. The recently found Tuerkubantao ophiolitic mélange, which is located east of the Kekesentao Mt. in the Buerjin County of the Chinese Altay, provides an important clue for this problem. This paper presents the results of field investigation, petrology, U-Pb isotope dating of zircons and bulk-rock geochemistry of the Tuerkubantao mélange rocks. The mélange consists of fault-contacted ultramafic rocks, gabbro, diabase, basalt, flysch and granitoids. The ultramafic-mafic rocks are Mg-rich (#Mg = 4.25–6.35) and w(SiO2) spans 38.8%–46.8%. Basalt and gabbro are geochemically similar and are characterized by low w(FeOt) (10.9%), total alkali w(Na2O + K2O) = 2.58%) and w(TiO2) (1.17%) and affinity to the Mg-rich tholeiite series. The flat REE and trace-element patterns of the ultramafic-mafic rocks are indicative of their ophiolite origin, i.e., formation in a mid-oceanic ridge setting. The fragments of low-K gneissic granite formed in suprasubduction or syn-collisional setting. Zircons from gabbro and gneissic granite yielded U-Pb ages of 363 and 355 Ma, respectively, suggesting Late Devonian mid-oceanic spreading and oceanic subduction accompanied by suprasubduction magmatism. The Tuerkubantao ophiolite together with the Qiaoxiahala and Buergen ophiolites of the Kekesentao belt define an ophiolitic mélange belt extending along the Erqis fault. This belt probably belongs to the Ural-Zaisan-South Mongolian suture-shear zone formed during the subduction of the Paleo-Asian Ocean and subsequent collision of the Siberian and Kazakhstan continents. [Copyright &y& Elsevier]

Abstract: This paper reports some new results from U–Pb geochronological, Hf isotopic and REE geochemical studies of detrital zircons in the Ordovician sandstones from South Jiangxi within Cathaysia. 426 groups of U–Pb age determinations define five major age populations: 2560–2380Ma (a peak of 2460Ma), 1930–1520Ma (a peak of 1700Ma), 1300–900Ma (a major peak at 970Ma and two subordinate peaks at 1250Ma and 1130Ma), 850–730Ma (a prominent peak of 780Ma) and 670–530Ma (a major peak at 540Ma and a subordinate peak at 650Ma). We also report zircon U–Pb concordia age of 3.96Ga, which is the oldest age so far obtained from Cathaysia. The age peak at 2460Ma correlates with similar ages reported for Neoarchean global continental growth. The 1930–1520Ma population broadly overlaps with the time of amalgamation and disruption of the Columbia supercontinent. The major age peak at 970Ma and two secondary peaks at 1250Ma and 1130Ma reflect multiple tectonothermal events associated with the assembly of Rodinia. Similar ages are widely reported from the South China Craton (SCC). Our study reveals that the 850–730Ma population is consistent with the breakup period of Rodinia, suggesting that the SCC within Rodinia began to break up since 850Ma. Geologically, the evidence for this breakup event is widespread and presented by Neoproterozoic granites, bimodal igneous rocks, basic dyke swarms and formation of continental rift type basins. Our study also reveals a 670–530Ma population that correlates well with the assembly of Gondwana during end Neoproterozoic. However, direct geological evidence for this event has not yet been found within the studied area. Furthermore, the Hf isotopic model age data suggest two major stages of crustal evolution within Cathaysia. The first is the event dated at 1.6–2.8Ga and the second one at 3.5–3.9Ga. The zircons show a large range of εHf(t) values from +8.64 to −30.54, suggesting that they have different origins with a similar age of crystallization. The fact that most detrital zircons show negative εHf(t) values suggests the ancient provenances of Cathaysia were dominated by reworked crustal materials. [Copyright &y& Elsevier]

Abstract: In this paper we report zircon U–Pb age, chemical compositions of rock-forming minerals, and whole-rock elemental and Sr–Nd isotopic data for the No. II mafic-ultramafic intrusive complex (N2MC) in the Quruqtagh area at the northeastern margin of the Tarim Block, northwestern China to evaluate its petrogenesis and tectonic significance. The N2MC with an exposure area of ca. 12km2 has a funnel-shaped cross-section and intruded the Paleoproterozoic basement. U–Pb zircon dating gives a crystallization age of 760±6Ma. Rock types of the N2MC include lherzolite, pyroxenite, gabbro and minor diorite. Major elements geochemistry of these rocks exhibits a tholeiitic trend with a wide range of SiO2 contents (38.8–60wt.%). On the other hand, they are systematically enriched in LILE, LREE and depleted in HFSE and HREE, thus leading to low HFSE/LREE ratios (e.g., Nb/La≈0.3). Isotopically, the studied rocks are characterized by negative whole-rock εNd(t) values (−7.6 to −2.8) and variable high (87Sr/86Sr) i (0.7095–0.7059). These features, together with chemical compositions of the rock-forming minerals and the presence of the primary phlogopite and hornblende, suggest that N2MC was likely formed via crystal fractionation/cumulation (with negligible crustal contamination) of a tholeiitic magma derived from a metasomatized subcontinental lithosphere mantle (SCLM) in an extensional environment. The enrichment of the mantle source could be ascribed to the metasomatism by subducted-slab-released fluids before partial melting. Overall, reported Neoproterozoic igneous rocks throughout the Tarim Block constitute two major phases of Neoproterozoic igneous activities, i.e., ca. 825–800Ma and ca. 780–745Ma, respectively. Similar to that of many other Rodinian continents, this feature is interpreted to be related to the two phases of Neoproterozoic mantle plume activity under the Rodinia. Furthermore, there exist two types of mafic-ultramafic complex at Quruqtagh, i.e., the ca. 820Ma carbonatite-bearing and the ca. 760Ma tholeiitic, which could reflect the presence of two different mantle sources. [Copyright &y& Elsevier]

Abstract: The self-similar is a common phenomena arising in the field of geology. It has been shown that geochemical element data, mineral deposits, and spacial distribution conform to a fractal structure. A fractal distribution requires that the number of objects larger than a specified size have a power-law dependence on size. This paper shows that a number of distributions, including power-function, Pareto, lognormal, and Zipf, display fractal properties under certain conditions and that this may be used as the mathematical basis for developing fractal models for data exhibiting such distributions. The summation method is developed on the basis of fractal models to determine thresholds for Au data in Shandong Province, China. The anomalous area is enclosed by contours which have contour values greater than or equal to threshold (200×10−9) and contains known large-sized and super large-sized gold mineral deposits. [ABSTRACT FROM AUTHOR]