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Geological Journal
Liverpool Geological Society and Manchester Geological Association
Geological Journal

Liverpool Geological Society and Manchester Geological Association

0072-1050

Geological Journal/Journal Geological JournalSCIISTPAHCI
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    Prelude to Late Triassic Ni-Cu sulphide mineralization in the eastern Central Asian Orogenic Belt: Geochronological and geochemical constraints from Middle Triassic mafic-ultramafic magmatism in central and eastern Jilin Province, NE China

    Xue, Hao-RiSun, Feng-YueLi, Bi-LeZhang, Ya-Jing...
    18页
    查看更多>>摘要：The Hongqiling-Piaohechuan region in the east Central Asian Orogenic Belt (CAOB) is an economically important Ni-Cu sulphide mineralization region in China. It is widely accepted that these Ni-Cu sulphide deposits mainly formed during the Late Triassic period. The early Middle Triassic mafic-ultramafic plutons are therefore key in understanding the mineralization process. Here, we report the laser ablation inductively coupled plasma mass spectrometer (LA-ICP-MS) U-Pb dating of zircon and geochemical data for two Middle Triassic mafic-ultramafic plutons and one felsic pluton in central and eastern Jilin Province, NE China. The mafic-ultramafic plutons are composed of gabbronorite and olivine websterite. Zircon dating results indicate that these mafic-ultramafic plutons crystallized at 243 +/- 1 to 245 +/- 1 Ma in the Middle Triassic. The coeval felsic pluton is mainly quartz diorite. Zircon dating results indicate that the felsic pluton crystallized at 239.7 +/- 0.63 Ma in the later period of Middle Triassic. The mafic-ultramafic plutons are low in SiO2 (43.49-49.66 wt%), depleted in K2O (0.28-2.74 wt%) and Na2O (0.70-1.18 wt%). They have low rare earth element (REE) abundances without Eu anomalies, exhibit depletion in high-field-strength elements (HFSEs), and hold various epsilon(Hf)(t) values (-15.3 to +2.9). These findings suggest that the primary magma of mafic-ultramafic plutons was derived from the partial melting of the depleted lithospheric mantle, metasomatized by subducted-slab-derived fluids/melts. Remarkably, these mafic-ultramafic plutons have extremely high Cu-Ni contents (23.6-669.4 and 419-1,956 ppm, respectively). The coeval quartz diorites have 59.55-64.86 wt% of SiO2, 3.02-4.21 wt% of K2O and 3.97-4.49 wt% of Na2O. They are enriched in light REEs (LREEs) and large-ion lithophile elements (LILEs); depleted in heavy REEs (HREEs) and HFSEs, and they have epsilon(Hf)(t) values in the range -6.4 to +2.9. Additionally, the felsic rocks exhibit adakitic-features with high Sr/Y (28.5-58.7) and (La/Yb)(N) (4.9-12.2) ratios, implying the thickening crustal sources of the North China Craton (NCC) and CAOB, respectively. The above findings, combined with the regional geological data, suggest that the Middle Triassic mafic-ultramafic plutons are the prelude to the large-scale Late Triassic mineralization. This was induced by the thickening event of the later period of Middle Triassic felsic rocks, accompanying the final closure of the Palaeo-Asian Ocean (PAO) in the eastern CAOB.
      原文链接:
    • NSTL
    • Wiley

    Distinguishing the Miocene Kiel and Antwerpen Members (Berchem Formation) and their characteristic horizons using cone penetration tests in Antwerp (northern Belgium)

    Deckers, JefEveraert, Stijn
    15页
    查看更多>>摘要：The glauconitic sands in the upper part of the lower-middle Miocene Berchem Formation are subdivided into the Kiel and Antwerpen Members. Although lithological differences between both members are well known from temporary outcrops in the Antwerp city area, they are difficult to distinguish in boreholes, which hinders regional mapping of these units. In this study, we investigate whether both members can be distinguished on cone penetration tests (CPTs). For this purpose, we correlated multiple outcrops-in which the Kiel and/or Antwerpen Members have been identified-with nearby CPTs. On the CPTs, the boundary between the Kiel and Antwerpen Members is clearly identifiable as it coincides with an abrupt upwards decrease in cone resistance (q(c)). The lower q(c) of the basal part of the Antwerpen Member is probably related to the finer grain size with more clayey admixture compared to the underlying Kiel Member. This change to a finer grain size is caused by a decrease in depositional energy and sedimentation rates as the region was transgressed during the eustatic sea-level rise at the start of the Mid-Miocene Climatic Optimum. On the CPTs, several spikes in q(c) values were observed within the Antwerpen and Kiel Members. These spikes could be correlated to shell beds, three horizons with sandstones and possibly a hardground. The sandstones appear to be discontinuous, whereas some of the shell beds could be traced across the entire study area. Most shell beds probably represent storm deposits within an otherwise relatively low energetic sedimentary environment. A phosphatic shell bed above the base of the Antwerpen Member is interpreted as the maximum flooding surface, lying in a zone with the lowest q(c) values for the Antwerpen Member, which might reflect maximum fining. The shell beds and interlayered sands of the Antwerpen Member thin in a southern direction, indicating reduced accommodation space in this direction.
      原文链接:
    • NSTL
    • Wiley

    Formation and evolution of Th-REE mineralizing fluids at the Kiruna-type Choghart iron oxide-apatite deposit, Central Iran: Insights from fluid inclusions and H-C-O isotopes

    Khoshnoodi, KhaleghYazdi, MohammadGhannadi-Maragheh, MohammadZiapour, Samaneh...
    16页
    查看更多>>摘要：The Choghart iron oxide-apatite (IOA) deposit is one of the largest iron mines of the Bafq district in Central Iran. This deposit is hosted by the Early Cambrian rhyolites, and diabase dikes crosscut both host rocks and the ore bodies. The Choghart rhyolites erupted in a continental arc setting, while the Choghart diabase dikes formed in a back-arc basin environment. Thorite, minor titanite, and REE-oxide are the main hosts of Th and REEs. The mineralogy and geochemistry support that the Th-REE mineralization formed at relatively reduced conditions. The presence of calcite accompanied by thorite and titanite suggests that Th and REE probably migrated as carbonate complexes in the mineralizing hydrothermal fluids. Microthermometric data of calcite associated with thorite indicate that the salinity of the ore-forming fluids varies from 20 to 30 wt% NaCl equivalent with temperature estimates between 300 and 370 degrees C. The narrow range of homogenization temperature and low salinities of the fluid inclusions imply the presence of only one fluid phase in the Th-REE mineralization. The calcite delta C-13(PDB) (-3.9 to -4.1 parts per thousand) and delta O-18(SMOW) (6.6-7.0 parts per thousand) support a magmatic source for the ore-forming fluids. Actinolite delta D (5.55-6.72 parts per thousand) and delta O-18 (-100.8 to -82.4 parts per thousand) also suggest a magmatic source of the ore-forming fluids. Microthermometric data imply that fluid-rock interaction and cooling were critical factors triggering the thorite precipitation at Choghart IOA deposit. Stable isotopic data indicate that post-magmatic fluids derived from rhyolitic magmas played a significant role in the Th-REE mineralization.
      原文链接:
    • NSTL
    • Wiley

    First record of late Carboniferous palynoassemblage from Ganmachidam Formation, Spiti Valley: Implications for age assessment and extent of Glossopterid elements in the Tethyan realm

    Gupta, SuyashSaxena, AnjuShabbar, HusainMurthy, Srikanta...
    19页
    查看更多>>摘要：The present work elucidates miofloral records from the Ganmachidam Formation (late Carboniferous-earliest Permian) of Spiti Valley, Tethyan Himalaya. The Ganmachidam Formation was hitherto considered as unfossiliferous, both for the faunal as well as floral records, and has been subjected to contentious age assessment. The present study has been carried out to find out the microfloral remains, assess the palynostratigraphic status, and the age of the Ganmachidam Formation. From the splintery shale sequence, a rich assemblage of palynomorphs has been recovered, having a dominance of monosaccate pollen grains, namely Parasaccites (Cannanoropollis), Crucisaccites, Divarisaccus, Densipollenites, Maculatasporites, followed by diverse bisaccate pollen grains, namely Scheuringipollenites, Crescentipollenites, Faunipollenites (Protohaploxypinus), Lunatisporites, Striatopodocarpites, Striatites, Rhizomaspora, Primuspollenites, and the spores Callumispora (Punctatisporites) and Calamospora in addition to woody fragments and fungal spores. Three palynoassemblages are identified. The recovered palynocomposition is corroborated with known records of palynomorphs from the Tethyan realm of India and from the late Carboniferous-Early Permian records of contemporaneous sequences across the globe. The composition of these palynoassemblages shows close correlation with the Crucisaccites monoletus Zone and Vittatina costabilis Interval Zone in the northeastern area of the Parana Basin, Brazil, and lower Barakar palynozone (Scheuringipollenites barakarensis Assemblage Zone) of Peninsular India which indicates the studied section of the Ganmachidam Formation is late Pennsylvanian to early Permian in age. Moreover, occurrences of palynomorphs from the Carboniferous sequences having a glossopterid affinity further strengthen the idea that glossopterids might have originated in Carboniferous time.
      原文链接:
    • NSTL
    • Wiley

    Palaeoenvironment, palaeogeography, and palaeoclimatology of the Mississippian carbonate ramp in the Alborz tectonostratigraphic zone: Implications for deciphering the controlling factors on ramp evolution

    Zandkarimi, KeyvanBayet-Goll, AramFalahatgar, MostafaSharafi, Mahmoud...
    30页
    查看更多>>摘要：The Mississippian successions of the Alborz tectonostratigraphic zone have been studied in several sections (Dozdehban, Naserabad, Shahmirzad, and Mighan) extending from north to southeast. The sedimentological data indicate three main facies associations (FA): (FA1) a basin to distal outer ramp of low-energy, low-oxygen environment with low bioturbation and less developed in situ fossils; (FA2) a middle ramp facies accompanied by storm-induced sediments (tempestites), echinoderm-dominated mud mounds, and high fragmentation of skeletal components; and (FA3) an inner ramp facies, represented by sand shoal, and lagoonal/back-barrier, mainly characterized by the dominance of oolitic, bioclast, and intraclast grainstones. The sedimentary features imply the formation of the succession on a broad flat-topped, high-to-moderate-energy shelfal carbonate ramp which had been open to the N/NE, the downslope direction, as revealed by local palaeoenvironmental reconstructions. Analysis of several proxies indicates a subtropical palaeoclimate evidenced by (a) widespread tempestite facies and occurrence of storm-depositional processes, (b) diverse and abundant pellet-forming thalassinoideans and burrowing echinoids trace fossil assemblages, (c) geochemical proxy indicating a palaeotemperature of 23 degrees-25 degrees, and (d) a rich subtropical heterozoan fossil association. The data provided here imply the palaeolatitudinal position of the Alborz Mississippian ramp is 30-40 degrees S along the southern margin of the Palaeotethys.
      原文链接:
    • NSTL
    • Wiley

    Early Palaeogene mafic-intermediate dykes, Robert Island, West Antarctica: Petrogenesis, zircon U-Pb geochronology, and tectonic significance

    Zheng, Guang-GaoLiu, XiaochunPei, JunlingZhao, Yue...
    12页
    查看更多>>摘要：Geochemical, geochronological, and Lu-Hf isotopic data for mafic-intermediate dykes on Robert Island, West Antarctica, are systematically investigated in order to decipher their petrogenesis and the genetic relationship between the South Shetland Islands and the north-western Antarctic Peninsula. These dykes are enriched in large-ion lithophile elements with significantly negative Nb and Ta anomalies, and low (Hf/Sm)(N) and (Nb/La)(N) and high Ba/La and Ba/Th ratios, with high epsilon(Hf)(t) values of +8.2 to +14.2. They were derived from partial melting of depleted mantle metasomatized by slab-derived fluids. Precise ages of 55-54 Ma for the dykes confirm the occurrence of Early Eocene magmatism on Robert Island, corresponding to the final peak of subduction-related magmatism. The available data suggest that Early Palaeogene (62-54 Ma) igneous rocks on the South Shetland Islands and the north-western Antarctic Peninsula are products of contemporaneous and different lithofacies magmatism with precursors originating from depleted mantle in a magmatic arc setting. Furthermore, the Early Palaeogene igneous activities were most likely associated with slab rollback and extension in fore-arc regions resulting from the decreasing convergence rate for the subduction of the Phoenix Plate beneath the Antarctic Plate at similar to 60 Ma.
      原文链接:
    • NSTL
    • Wiley

    The sedimentary characteristics and depositional evolution in the Middle Jurassic Xishanyao Formation, Southeastern Xiayan Rise, Junggar Basin, NW China

    Chen, JingHe, NaixiangWang, YiFu, Lei...
    14页
    查看更多>>摘要：The significant hydrocarbon discoveries have been found during the past few years in Middle Jurassic Xishanyao Formation in Southeastern Xiayan Rise, Junggar Basin. The braided delta front deposits and shore-shallow lacustrine deposits are well preserved in Xishanyao Formation, their history being documented by integrated analysis of seismic volumes and borehole datasets (wireline logs, cores, grain size etc). The results reveal that five sedimentary microfacies are identified. Among them, the braided delta front deposits include subaqueous distributary channel, inter-distributary channel and mouth bar, while shore-shallow lacustrine deposits consist of lacustrine mud and swamp. In addition, depositional evolution of braided delta front deposits and shore-shallow lacustrine deposits from bottom to top in Xishanyao Formation is characterized by retrogradation and progradation during depositional period. The depositional evolution during depositional period of Xishanyao Formation is controlled by interactions of the source and distribution of provenance, the catchments, the lacustrine fluctuations and the climates.
      原文链接:
    • NSTL
    • Wiley

    Metallogenesis of the giant Maoping carbonate-hosted lead-zinc deposit, southwestern Yangtze Craton: New insights from structural geology and whole-rock geochemistry

    Guan, Yu-ChunZhao, De-ShunMao, Rong-WeiZhao, Wei-Ce...
    20页
    查看更多>>摘要：The southwestern Yangtze Craton hosts more than 400 carbonate-hosted Pb-Zn deposits, and is well endowed with enormous base metals. The giant Maoping deposit is one of the most representative deposits, and the mineralization mainly occurs in the Devonian to Carboniferous dolomitic rocks. Its metallogenesis has been thoroughly discussed from many perspectives by previous studies, but it remains controversial, especially about the relationship between the structural process and the Pb-Zn mineralization. In this paper, we conducted large-scale structural mapping and whole-rock geochemical analysis to investigate the structural process and its control on the mineralization at Maoping. Three stages of deformation have been recognized, including the NE-SW-striking folds and thrusts (D-1), the N-S-striking transtensional faults (D-2), and the NW-SE-striking transpressional structures (D-3). The geochemical analysis shows relatively higher contents of the ore-related trace elements in the tectonites from the N-S-striking faults, indicating a close relationship between the N-S-striking faults and the mineralization. Combined with field evidence and geochemical analysis, we propose that the N-S-striking transtensional faults are likely the major ore-conducting structures, and the NE-SW-striking interlayer fractures serve as the assistant structures at the deposit scale. The regional NE-SW-striking fold-and-thrust belts are suggested to dominate the spatial distribution and location of the Pb-Zn deposits in northeastern Yunnan at the regional scale. Our study enhances the understanding of the metallogenesis at Maoping and provides new insights into the Pb-Zn prospecting at both the regional scale and the deposit scale.
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    • NSTL
    • Wiley

    Sequence stratigraphy of the Miocene siliciclastic-carbonate sediments in Sadat Area, north-west of Gulf of Suez: Implications for Miocene eustasy

    Hewaidy, Abdel Galil A.Al-Labaidy, Naser A.Ayyad, Haitham M.
    16页
    查看更多>>摘要：The Miocene sequences in the north-west of the Gulf of Suez represent transition zones between carbonate-dominated and siliciclastic-dominated strata. These rocks were greatly influenced by the Gulf of Suez rifting, which resulted in lateral variations of facies and hence presented a complicated stratigraphic setting. Here, we interpret the sequence stratigraphy of the Sadat Area to the north-west of the Gulf of Suez by integrating biostratigraphic data and microfacies analysis to contribute primarily to the geology of the studied successions and incorporate the existing knowledge of syn-rift deposition. We determined the ages of the studied formations by biostratigraphic examination of the integrated calcareous nannoplankton, planktic, and benthic foraminifera. Our results distinguish four genetic Miocene sequences. These sequences are defined by four major sequence boundaries that outline sedimentation cycles and were chiefly deposited in a lagoon to outer-shelf settings. The proposed Miocene eustacy is well-correlated with global curves, implying a rise in sea level in the lower parts of Zones M4, M5, and M8. In contrast, the reduction of sea-level rise resulted in the decrease of accommodation space in the upper part of Zone M5. The studied Miocene deposits mainly formed in a shallower marine environment, as shown by a comparison between data from the eastern side of the Gulf of Suez and the data presented in this paper. Furthermore, we demonstrate that the local tectonic activity linked with the Gulf of Suez rifting and the eustatic sea-level changes were significant factors in the deposition of the Miocene in the studied successions.
      原文链接:
    • NSTL
    • Wiley

    Spatio-temporal distribution and genetic mechanism of Paleogene extension amounts in the Liaodong Bay, Bohai Bay Basin

    Xia, ShiqiangLin, ChangsongLi, XinDu, Xiaofeng...
    13页
    查看更多>>摘要：Based on seismic interpretation of 18 regional 3D high-resolution seismic sections across Liaodong Bay, extension amounts, extension rates and extension coefficients of different seismic sections from the south to the north are calculated by employing balanced section technique. Then, spatio-temporal distribution of extension amounts is characterized and interpreted. Finally, the analysis of genetic mechanism is conducted and analysed. The results indicate that tectonic evolution in the Paleogene of Liaodong Bay is characterized by episodic extension. Furthermore, spatio-temporal distribution of extension amounts is relatively uneven. In terms of space, extension amounts are mainly caused by extensional displacement of main depression-controlled boundary faults and syn-depositional faults in the depression. In addition, extensional amounts along main depression-controlled boundary faults are characterized by larger displacement. In terms of time, the periods for horizontal extensional movement can be divided into three stages: The Palaeocene-Early Eocene (Kongdian Formation-third member of Shahejie Formation), Middle-Late Eocene-Early Oligocene (first and second member of Shahejie Formation) and Middle-Late Oligocene (Dongying Formation). Among them, extension during the Palaeocene-Early Eocene occurs both in the north and south of Liaodong Bay. However, extension intensity in the north is stronger than that in the south. Extension intensity in the middle and north during Middle-Late Eocene-Early Oligocene obviously increases. In contrast, it is dominated by strike-slip movement during depositional period of Dongying Formation. Therefore, extension intensity is characterized by significant inheritance. Spatial-temporal distribution of extension amounts is predominantly controlled by tectonic evolution and associated tectonic deformation.
      原文链接:
    • NSTL
    • Wiley