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Abstract:Well-preserved graptolites of the genus Kiaerograptus are first reported from the upper Tremadocian Yinchupu Formation in the Nanba section, Yiyang, Hunan Province, South China, including four species, i.e., Kiaerograptus lauzonensis (Erdtmann, 1966), Kiaerograptus stoermeri (Erdtmann, 1965), Kiaerograptus cf. supremus? Lindholm, 1991, and Kiaerograptus sp., which are robust in form. Based on these new specimens, the Kiaerograptus biozone is established for the first time in South China, increasing the late Tremadoc graptolite biozones in South China from four to five, in ascending order as follows: the Adelograptus tenellus biozone, the Aorograptus victoriae biozone, the Kiaerograptus biozone, the Sagenograptus murrayi biozone, and the Hunnegraptus copiosus biozone. A review of the occurrence records for robust Kiaerograptus species worldwide reveals that the distribution is restricted to the Aorograptus victoriae biozone and Kiaerograptus biozone in the late Tremadocian. This limited stratigraphical distribution makes Kiaerograptus a valuable taxon for precise biostratigraphical correlation at both the regional and global scales.

Abstract:The thrust nappe played an important role in the Mesozoic tectonic evolution of the middle part of the Central Asian Orogenic Belt (CAOB). However, the timing, structural style and kinematic processes of the thrust nappe remain controversial, particularly the detail of the thrust nappe in the Guaizihu region (110 km east of Ejinaq). In this study, we investigate new field mapping, seismic sections, geochronology and low-temperature thermochronometric dating to provide constraints on the history of this thrust nappe in the Chaheilingashun area (northwestern Guaizihu region). The field mapping, seismic sections and structural analysis reveal that the autochthonous system had developed a series of strong fold structures in the upper Permian strata. The allochthonous system mainly contains Devonian monzogranite (U-Pb age, ranges from 386.7 to 389.0 Ma) and Meso–Neoproterozoic schists (the maximum depositional age, ~880 Ma), which were thrust upon the upper Permian strata during Middle to Late Triassic. Based on similar rocks, geochronological dating and the Yagan thrust, we suggest that the postulated root zone of this allochthon might have originated from the Huhetaoergai area (40–60 km northwest of the study area). The geochronological results reveal that the lower age limit of this thrust nappe is constrained by the Lower–Middle Triassic syntectonic sediments (tuffaceous sandstone, ~247 Ma), which is the sedimentary response of the fold structure.,The timing of the termination of this thrust nappe is defined by the cooling age (40Ar/39Ar data, 217–211 Ma) of the Devonian monzogranite and Meso–Neoproterozoic schists. Thus, we consider this thrust event in the study area to potentially have occurred in the period from 247 Ma to 211 Ma, which may represent the tectonic response to the closure of the Paleo-Asian Ocean.

Abstract:The Neoproterozoic evolution of the Jiangnan Orogen is important for understanding the tectonic history of South China. As a volcanic-sedimentary sequence developed in the Nanhua rift, the Banxi Group preserves the records of important magmatic and tectonic events linked to the assembly and breakup of the Rodinia supercontinent. In this study, we report the results from whole-rock major- and trace-element concentrations, with zircon LA-(MC)-ICP-MS U-Pb ages, trace elements and Lu-Hf isotopic compositions of sandstones from the Banxi Group. The rocks are characterized by high SiO2 (65.88%–82.76%, with an average of 75.50%) contents, moderate (Fe2O3T + MgO) (1.81%–7.78%, mean: 3.79%) and TiO2 (0.39%–0.54%, mean: 0.48%), low K2O/Na2O (0.03–0.40, mean: 0.10) ratios and low Al2O3/SiO2 (0.11–0.24, mean: 0.15) ratios. The sandstones have high ΣREE contents (mean: 179.1 ppm), with chondrite-normalized REE patterns similar to the upper crust and PAAS, showing enriched LREE ((La/Yb)N mean: 14.85), sub-horizontal HREE curves and mild Eu (Eu/Eu*: 0.75–0.89, mean: 0.81) negative anomalies. Their geochemical characteristics resemble those of passive continental margin sandstones. Most of the zircons are magmatic in origin and yield a U-Pb age distribution with three peaks: a major age peak at 805 Ma and two subordinate age peaks at 1990 Ma and 2470 Ma, implying three major magmatic sources. The Neoproterozoic zircons have εHf(t) values ranging from ?47.4 to 12.4 (mostly ?20 to 0), suggesting a mixture of some juvenile arc-derived material and middle Paleoproterozoic heterogeneous crustal sources. The Hf model ages of middle Paleoproterozoic zircons (~1990 Ma) with negative εHf(t) values (?12.65 to ?6.21, Ave. = ?9.8) concentrated around the Meso-Paleoarchean (mean TDMC = 3.3–3.1 Ga). For late Neoarchean detrital zircons (~2470 Ma), εHf(t) values are divided into two groups, one with negative values (?9.16 to ?0.6) with model ages of 3.5–2.9 Ga, the other featuring positive values (1.0 to 3.9) with model ages of 2.9–2.7 Ga, recording a crustal growth event at ~2.5 Ga. Neoproterozoic zircons show volcanic arc affinities with partly intraplate magmatic features. We propose that the Banxi Group formed in a rift basin within a passive continental margin setting, which derived detritus from felsic to intermediate rocks from the Yangtze Block and a small amount of arc volcanic rocks. The middle Paleoproterozoic detrital zircon data suggest Columbia-aged basement lies beneath the western Jiangnan orogen.

Abstract:Despite extensive efforts to understand the tectonic evolution of the Jiangnan Orogen in South China, the orogenic process and its mechanism remain a matter of dispute. Previous geodynamic studies have mostly focused on collisional orogeny, which is commonly invoked to explain the Jiangnan Orogen. However, it is difficult for such hypotheses to reconcile all the geological and geophysical data, especially the absence of ultrahigh-pressure metamorphic rocks. Based on the magnetotelluric data, we present a group of resistivity models produced through the combination of two-dimensional and three-dimensional inversions, revealing the geo-electrical structures of Jiangnan and a typical collisional orogen. In our models, the resistive crust is separated into three parts by a prominent conductive layer with opposite dipping directions on both sides. A special thrust-nappe system, which is different from that developed in a typical collisional process, is revealed in the Jiangnan Orogen. This structure suggests a process different from the simple collisional orogeny. To interpret our observations, an ‘intra-continental orogeny’ is proposed to address the development of the Jiangnan Orogen in the Mesozoic. Furthermore, this ‘reactivated’ process may contain at least two stages caused by the decoupling of the lithosphere, which is revealed by an extra conductive layer beneath Jiangnan.

Abstract:Reports of shoshonitic rocks in Precambrian terrains are relatively rare. Pl-Grt amphibolites and Hbl-Bt mafic granulites occurring in the migmatitic gneisses of the Chhotanagpur Gneissic Complex (CGC) show calc-alkaline and shoshonitic characteristics. Relict porphyritic, sub-ophitic and poikilitic textures are noted in these rocks. Their parent magma was emplaced during the waning phase of the regional metamorphism. Geochemically, these?metamafics are similar to the Group III potassic and ultrapotassic rocks of Foley et al. (1987). The magma was derived from the metasomatized subcontinental lithospheric mantle (SCLM). Subduction-related sediment melts metasomatized the SCLM. Compositionally, The emplacement of shoshonitic magma and subsequent decompression happened at the slab break-off stage of continental collision (~990 Ma).

Abstract:The Xiaobaishitou gabbro-diorite pluton comprises a medium-grained gabbro-diorite suite and a fine-grained diorite suite, which intrude the Kawabulag Group in the East Tianshan Orogen of the Central Asian Orogenic Belt (CAOB). A combination of mineral chemistry, zircon U-Pb age, whole-rock geochemistry, Sr-Nd isotopes, and in situ zircon Hf isotopes for newly found gabbro-diorite from the Xiaobaishitou district in the Central Tianshan Terrane (CTT) is presented to investigate the petrogenesis and tectonic or even crustal evolution of the East Tianshan Orogen. Laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) zircon U-Pb analyses indicate that the gabbro-diorite was formed at 324.7 ± 2.4 Ma. The isolated clinopyroxene formed under higher P-T-fO2 melt conditions (10.7–14.6 kbar; 1199–1269°C; high fO2) than those for the hornblende, plagioclase, and zircon (557–687°C; moderate fO2) in the gabbro-diorite, which reveals a multilevel, magmatic storage system. The gabbro-diorite is characterized by fractioned REE patterns, enriched LILEs (e.g., Ba and Pb), negative anomalies of HFSEs (e.g., Nb and Ta), and low La/Yb and Sr/Y ratios, which are typically indicative of crustal contamination and accounted for by subduction-related fluids. The rock also characterized by typical features of high compatible elements (MgO = 3.14–11.65 wt%, Cr = 1–157 ppm, Ni = 6–830 ppm), high Mg# (47–74), positive εHf(t) values (+5.1 to +10.3) and εNd(t) values (+2.3 to +4.4). These features suggest that the Xiaobaishitou gabbro-diorite was most likely derived from metasomatic mantle and contaminated minor crustal components. Taking into account the spatial and temporal distribution of the Carboniferous magmatic rocks in the CTT, we suggest the formation of the Xiaobaishitou gabbro-diorite was attributed to southward subduction of the Kangguer Ocean.

Abstract:The Xiejiaba and Fuqiangbei plutons form part of the newly identified Neoproterozoic Niushan complex, which is located in the southern South Qinling belt (SQB). The plutons are compositionally similar, were emplaced at 750–711 Ma, and provide insights into Neoproterozoic tectonism within the South Qinling belt. The Xiejiaba pluton contains diorite, quartz diorite, granodiorite, and granite phases, all of which are sub-alkaline and have variable major element compositions with negative correlations between SiO2 and MgO, TFe2O3, Al2O3, CaO, TiO2 and P2O5. These rocks are enriched in light rare earth elements (LREEs) and large ion lithophile elements (LILEs) and have negative Nb, Ta, P and Ti anomalies, all of which are indicative of arc-type magmatism. The Fuqiangbei pluton contains granitoids that are compositionally similar to the rocks in the Xiejiaba pluton. Samples from these plutons have similar εNd(t) values (1.24–5.99) but very variable (87Sr/86Sr)i values (0.7010–0.7054). Combining these data with the geochemical data for these rocks suggests that the magmas that formed the Niushan complex were derived from the crust–mantle boundary. This, combined with the results of previous research, suggests that the transition from low pressure-low temperature to low pressure-high temperature conditions within a subduction zone caused melting during a period of late subduction and backarc extension. This constrain the timing of subduction within the South Qinling belt and the northern Yangtze Block (YB) to 750–711 Ma, with this Neoproterozoic subduction associated with an ocean to the north overprinting an existing continental rift-type tectonic setting within the northern margin of the Yangtze Block and the South Qinling belt.

Abstract:The formation of titanite coronae after rutile is common in retrograde high- to ultrahigh-pressure meta-mafic rocks, which provides a good opportunity to address the geochemical behavior of HFSE in crustal environments. In the Sumdo eclogite, titanite occurs either as a corona around rutile grains or as semi-continuous veins cross-cutting the major foliation, whereas rutile grains occur either as inclusions in garnet or omphacite or as a relict core surrounded by titanite. Textural relationships and trace elements characteristics of rutile and titanite with different occurrences indicate that both minerals preferentially incorporate Nb and Hf over Ta and Zr in aqueous fluid. Moreover, the breakdown of omphacite and epidote could release substantial amounts of aqueous fluids enriched in Ca, Si, Fe and REE, which would react with rutile to form titanite coronae and veins. During this process, water-insoluble elements, like HFSE and HREE, behave like mobile elements, but they do not migrate substantially out of the system, instead, tending to react in situ. This suggests that the aqueous fluids released during the retrograde metamorphic reactions in mafic rocks could not substantially transfer fluid-immobile elements into the overlying mantle wedge in subduction environments.

Abstract:The Fuchuan ophiolite is located in the northeasternmost segment of the Neoproterozoic Jiangnan orogen and consists mainly of harzburgites, with minor dunites, pyroxenite and gabbro veins and dykes. In order to investigate the genesis and tectonic setting of the Fuchuan ophiolite and chromitites, in situ analyses of unaltered chromites and silicates were carried out. Trace element analyses of unaltered chromites from the Fuchuan chromitites indicate the parental magma is of mid-ocean ridge basalt (MORB)-like origin, with the Ti/Fe3+#–Ga/Fe3+# diagram of chromites showing that the chromitites are a result of melt/rock interaction of MORB melts with mantle peridotites, and that the Fuchuan harzburgites present the dual features of MORB and supra-subduction zone peridotites (SSZP). Trace and rare earth element (REE) analyses of olivines and orthopyroxenes from the Fuchuan harzburgites hint at the possibility of mantle metasomatism influenced by SSZ-subducted fluids. Finally, integrating with previous study, the Fuchuan ophiolite and chromitites might have been formed in a back-arc spreading ridge between the Yangtze and Cathaysia blocks during the Neoproterozoic.

Abstract:The identification of anomalies within stream sediment geochemical data is one of the fastest developing areas in mineral exploration. The various means used to achieve this objective make use of either continuous or discrete field models of stream sediment geochemical data. To map anomalies in a discrete field model of such data, two corrections are required: background correction and downstream dilution correction. Topography and geomorphology are important factors in variations of element content in stream sediments. However, few studies have considered, through the use of digital terrain analysis, the influence of geomorphic features in downstream dilution correction of stream sediment geochemical data. This study proposes and demonstrates an improvement to the traditional downstream dilution correction equation, based on the use of digital terrain analysis to map single-element anomalies in stream sediment geochemical landscapes. Moreover, this study compares the results of analyses using discrete and continuous field models of stream sediment geochemical data from the Xincang area, Tibet. The efficiency of the proposed methodology was validated against known mineral occurrences. The results indicate that catchment-based analysis outperforms interpolation-based analysis of stream sediment geochemical data for anomaly mapping. Meanwhile, the proposed modified downstream dilution correction equation proved more effective than the original equation. However, further testing of this modified downstream dilution correction is needed in other areas, in order to investigate its efficiency further.

Abstract:The Tortonian–Calabrian strata of Offshore Makran (Pakistan) is investigated for the purpose of reservoir assessment. The stratigraphy and petrophysics indicate that the Neogene sediments have tight reservoir potential with porosities in the range of 3%–9% and 40%–50% water saturation. The mineralogical cross plots indicate a mixed lithology with an abundance of dolomite and calcite, together with minor quartz content and shale. The seismic interpretation demonstrates medium–high amplitude reflection patterns, mud diapirs coupled with onlapping strata and the occurrence of bottom simulating reflectors (BSRs). The BSRs are characterized by diminished amplitude, low continuity and exhibiting acoustic blanking zones. The high formation pressure results indicate overpressure zones, suggesting the occurrence of overpressured shales in the Jal Pari-1A. The presence of mud diapirs and gas chimneys are the result of tectonic forces acting at the junction of the Arabian, Indian and Eurasian plates, whereas, BSRs prove the existence of gas charged sediments supporting the formation of mud diapirism in the region. It is concluded that the high rates of sedimentation during the Neogene are likely to have contributed to the development of the high formation pressure. Revised mud weights, casing policies, pore pressure transients and geophysical inversion studies will help alleviate drilling risks in future exploration strategies.

Abstract:Reservoir classification is a key link in reservoir evaluation. However, traditional manual means are inefficient, subjective, and classification standards are not uniform. Therefore, taking the Mishrif Formation of the Western Iraq as an example, a new reservoir classification and discrimination method is established by using the K-means clustering method and the Bayesian discrimination method. These methods are applied to non-cored wells to calculate the discrimination accuracy of the reservoir type, and thus the main reasons for low accuracy of reservoir discrimination are clarified. The results show that the discrimination accuracy of reservoir type based on K-means clustering and Bayesian stepwise discrimination is strongly related to the accuracy of the core data. The discrimination accuracy rate of Type I, Type II, and Type V reservoirs is found to be significantly higher than that of Type III and Type IV reservoirs using the method of combining K-means clustering and Bayesian theory based on logging data. Although the recognition accuracy of the new methodology for the Type IV reservoir is low, with average accuracy the new method has reached more than 82% in the entire study area, which lays a good foundation for rapid and accurate discrimination of reservoir types and the fine evaluation of a reservoir.

Abstract:An integrated geological-petrophysical analysis of the rudist-bearing sequence of the Cretaceous Sarvak Formation is given one giant oilfield, and provides an improved understanding of this main reservoir in the Abadan Plain, in the Zagros Basin, SW Iran. The main objective of this study is to evaluate reservoir potential of the Sarvak Formation, and then to utilize the calibrated well log signature to correlate reservoir potential in un-cored wells. Eight main facies are recognized and categorized in five facies groups: lagoon, shoal, rudist-biostrome, slope, and shallow open marine, deposited on a shelf carbonate platform. Given the distribution of diagenetic products and their effects on pore systems, three diagenetic facies namely, (DF-1) low dissolution and cementation; (DF-2); high dissolution; and (DF-3) high cementation are differentiated. The initial sedimentary characteristics in combination with distribution of diagenetic products play an important role in reservoir quality heterogeneity. The effect of diagenetic processes related to disconformities mainly depends on the facies nature below these surfaces. Grain-dominated facies of shoal and rudist debris, observed below the Cenomanian–Turonian disconformity, are mostly characterized by high dissolution and interconnected pore systems. Finally, depositional and diagenetic facies in the studied wells are correlated by petrophysical well log data, leading to distribution of the reservoir zones. Data obtained can be utilized for efficient reservoir characterization of the Sarvak Formation and its equivalent units in the Arabian Plate.

Abstract:A thrust-fold belt consisting of a series of thrusts and buckling folds developed in the Mesozoic and Cenozoic strata within the Kuqa Depression, Tarim Basin. In this study, a structural interpretation model of the Kuqa Depression is established and the Mesozoic proto-basin is reconstructed on the basis of outcrop geology along the basin margin, seismic, well-log and CEMP data. The model is called ‘delaminate contractional deformation’, which emphasizes the decoupling between the Cenozoic, Mesozoic, pre-Mesozoic and the basin-basement within the Kuqa Depression, but there is no unified detachment. The model has a shortening amount ranging from 12 km to 16 km and the depth involved in contractional deformation ranges from 21 km to 28 km. A prototype of the Mesozoic basin reconstructed by interpretation model is a sub-basin superposed on the transitional zone between the uplift at the northern edge of the Tarim Craton and the southern Tianshan orogenic wedge formed in the Hercynian orogeny. Lithospheric thermal and crustal isostatic activity after the Hercynian orogeny maybe the controlling dynamic factors of basin subsidence during the Mesozoic and early Cenozoic, the difference in rock mechanical properties between different levels, craton and orogenic wedge being the major cause of the ‘delaminate contractional deformation’ during the Himalayan orogeny.

Abstract:In situ stress measurement data was analyzed to estimate the temporal and spatial stress variations at shallow depths in the Longmenshan fault zone (LMSF), prior to and following the 2008 Wenchuan earthquake (WCEQ). Analysis of the stress field related to fault strength and behavior is useful for understanding geodynamic processes and conducting hazard assessments. The shallow stress changes after the WCEQ show clear along-strike variations. Degrees of stress orientation rotations have a negative correlation with the horizontal principal stress ratios and the WCEQ apparently reduced the magnitude difference between horizontal principal stresses. Taking stress magnitudes and orientation distribution relative to the fault strike into account, we propose an intermediate-strength of LMSF, with a friction coefficient generally constrained between 0.35 and 0.6. In addition, high-pressure fluids in the fault zone reduce the effective normal stress and to a certain degree weaken the fault strength. The accumulated stress over a certain period following release of the WCEQ indicates the start of another earthquake cycle. The changing crustal stress field makes the LMSF stable or slipping optimally during geodynamic processes. The segmentation feature of the shallow crustal stress field in the LMSF may imply a different tectonic loading and seismic release processes along the fault. The southwestern section to the epicenter of the WCEQ favors the occurrence of future earthquakes, as high μm in a state of critical failure was present in this area, which indicates that the Wenchuan and Lushan earthquakes did not release the accumulated stress to a sufficient extent there.

Abstract:An analysis of Thalassinoides ichnofabrics in the Cambrian Stage 4 Longwangmiao Formation from six sections near Chonqing in the Middle and Upper Yangtze Block of South China was conducted to promote the understanding of the paleoenvironment of this period. Thalassinoides ichnofabrics are divided into three types according to their morphology, bioturbation index, abundance and related parameters: banded, mottled and grid. The completeness of the ichnofabrics gradually increases from banded to grid, the scale of the burrows expands, and the structure transitions from two-dimensional to three-dimensional. Malacostracans, phyllocarids and enteropneusts are the most likely burrowers. The findings reveal that frequent changes in paleoenvironmental conditions are the dominant factors for generating the various Thalassinoides ichnofabrics. The changes in depositional rate, substrate properties and nutrient levels affect the behavior and building patterns of the burrowers, thus leading to the diversity of Thalassinoides ichnofabrics. In the lower Longwangmiao Formation beds, many incomplete Thalassinoides burrow systems were built in the substrates with terrigenous detrital minerals, revealing significant environmental pressure on the burrowers. Later, the Thalassinoides burrows went into complete three-dimensional boxworks. At the end of the stage, bioturbation almost disappeared, which indicates that burrowers were finding it difficult to survive in the harsh environment.

Abstract:This research is focused on the analysis of the sequence stratigraphic units of F3 Block, within a wave-dominated delta of Plio–Pleistocene age. Three wells of F3 block and a 3D seismic data, are utilized in this research. The conventional techniques of 3D seismic interpretation were utilized to mark the 11 surfaces on the seismic section. Integration of seismic sequence stratigraphic interpretation, using well logs, and subsequent 3D geostatistical modeling, using seismic data, aided to evaluate the shallow hydrocarbon traps. The resulting models were obtained using System Tract and Facies models, which were generated by using sequential stimulation method and their variograms made by spherical method, moreover, these models are validated via histograms. The CDF curve generated from upscaling of well logs using geometric method, shows a good relation with less percentage of errors (1 to 2 for Facies and 3 to 4 for System Tract models) between upscaled and raw data that complements the resulted models. These approaches help us to delineate the best possible reservoir, lateral extent of system tracts (LST and/or HST) in the respective surface, and distribution of sand and shale in the delta. The clinoform break points alteration observed on seismic sections, also validates the sequence stratigraphic interpretation. The GR log-based Facies model and sequence stratigraphy-based System Tract model of SU-04-2 showed the reservoir characteristics, presence of sand bodies and majorly LST, respectively, mainly adjacent to the main fault of the studied area. Moreover, on the seismic section, SU-04-2 exhibits the presence of gas pockets at the same location that also complements the generated Facies and System Tract models. The generated models can be utilized for any similar kind of study and for the further research in the F3 block reservoir characterization.

Abstract:Three-dimensional unmanned aerial vehicle (UAV) oblique photogrammetric data were used to infer mountainous gravel braided river lithofacies, lithofacies associations and architectural elements. Hierarchical architecture and lithofacies associations with detailed lithofacies characterizations were comprehensively described to document the architectural model, architectural element scale and gravel particle scale. (1) Nine lithofacies (i.e., Gmm, Gcm, Gcc, Gci, Gcl, Ss, Sm, Fsm and Fl) were identified and classified as gravel, sand and fine matrix deposits. These are typical depositional features of a mountainous dryland gravel-braided river. (2) Three architectural elements were identified, including channel (CH), gravel bar (GB) and overbank (OB). CH can be further divided into flow channel and abandoned channel, while GB consists of Central Gravel bar (CGB) and Margin Gravel bar (MGB). (3) The gravel bar is the key architectural element of the gravel braided river, with its geological attributes. The dimensions of GBs and their particles are various, but exhibit good relationships with each other. The grain size of GB decreases downstream, but the dimensions of GB do not. The bank erosion affects the GB dimensions, whereas channel incision and water flow velocity influence the grain size of GB. The conclusions can be applied to the dryland gravel braided river studies in tectonically active areas.

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Abstract:The geologic production of abiotic organic compounds has been the subject of increasing scientific attention due to their use in the global carbon flux balance, by chemosynthetic biological communities, and for energy resources. Extensive analysis of methane (CH4) and other organics in diverse geologic settings, combined with thermodynamic modelings and laboratory simulations, have yielded insights into the distribution of specific abiotic organic molecules on Earth and the favorable conditions and pathways under which they form. This updated and comprehensive review summarizes published results of petrological, thermodynamic, and experimental investigations of possible pathways for the formation of particular species of abiotic simple hydrocarbon molecules such as CH4, and of complex hydrocarbon systems, e.g., long-chain hydrocarbons and even solid carbonaceous matters, in various geologic processes, distinguished into three classes: (1) pre- to early planetary processes; (2) mantle and magmatic processes; and (3) the gas/water-rock reaction processes in low-pressure ultramafic rock and high-pressure subduction zone systems. We not only emphasize how organics are abiotically synthesized but also explore the role or changes of organics in evolutionary geological environments after synthesis, such as phase transitions or organic-mineral interactions. Correspondingly, there is an urgent need to explore the diversity of abiotic organic compounds prevailing on Earth.

Abstract:CaCO3 is an important component of marine sediments and one of the major deep-carbon carriers at subduction zones. Some subducted CaCO3 can be dissolved in subduction fluids and recycled back to the surface via arc volcanoes degassing. At the same time, there still remain large amounts of CaCO3 and its reaction products, which could be further transported into Earth’s deep interior. These internal processes link atmosphere, hydrosphere and biosphere with the deep solid Earth, modifying the environments of our planet. In this review, we summarize current understanding from high pressure-temperature experiments and field petrological observations on the physical and chemical properties of CaCO3. In particular, the phase stability and reactions of CaCO3 largely control the migration and reservation of oxidized carbon in subducting slabs. Finally, we present several critical but unsolved questions on CaCO3 subducting in the deep mantle.

Abstract:The carbon cycle is an important process that regulates Earth’s evolution. We compare two typical periods, in the Paleoproterozoic and Neoproterozoic, in which many geological events occurred. It remains an open question when modern plate tectonics started on Earth and how it has influenced the carbon cycle through time. In the Paleoproterozoic, intense weathering in a highly CO2 and CH4 rich atmosphere caused more nutritional?elements to be carried into the ocean. Terrestrial input boosted high biological productivity, deposition of sediments and the formation of an altered oceanic crust, which may have promoted an increase in the oxygen content. Sediment lubrication and a decrease in mantle potential temperature made cold and deep subduction possible, which carried more carbon into the deep mantle. Carbon can be stored in the mantle as diamond and carbonated mantle rocks, being released by arc and mid-ocean ridge outgassing at widely different times. From the Paleoproterozoic through the Neoproterozoic to the Phanerozoic, the carbon cycle has promoted the evolution of a habitable Earth.

Abstract:Continental epithermal ore deposits are commonly associated with sedimentary organic matter, oils or solid bitumen. These organics embedded in mineral deposits can convey valuable information of the ore genesis. However, the extent to which the formation of ore minerals was recorded by organic compounds remains largely unknown, as also is how metal-rich ores interfere with the molecular proxies in the temperature regime envisaged for hydrothermal activity. The molecular compositional changes of various polycyclic aromatic steranes and polycyclic aromatic hydrocarbons and compounds derived from the Jinding Pb/Zn deposit, SW China provide new data. Aliphatic regular steranes are present as traces. The transformation from polycyclic aromatic steranes to unsubstituted polycyclic aromatic hydrocarbons is observed to show an increased trend with increasing hydrothermal alteration levels; this is consistent with the transformation from unsubstituted polycyclic aromatic hydrocarbons to heterocyclic compounds. Dehydrocyclization (aromatization) of polycyclic biological compounds and hydrodecyclization (dearomatization) of polycyclic aromatic compounds are two important reaction pathways in hydrothermal systems with moderate temperature. This detailed investigation of organic-inorganic interactions of two groups of polycyclic compounds with metal-rich ores provides insights into the questions on how and to what extent the formation of Pb/Zn deposits can be recorded by organics. This work will improve our understanding of carbon reduction, oxidation or condensation in the deep Earth and the carbon exchange between the Earth’s crust and mantle, and may shed light on the processes for ultra-deep hydrocarbon exploration.

Abstract:Natural gas, consisting primarily of methane (CH4), has become a major source of clean energy in modern society in many parts of the globe. Recent experimental observations and discoveries of deep-sourced abiotic CH4 in cold subduction zones indicate the important ability of cold subducted slabs to generate natural gas reservoirs. However, most CH4 flux and reservoirs remain unknown and their potential is overlooked in global carbon flux estimations. Massive abiotic CH4-rich fluid inclusions (FIs) in garnet and omphacite from ultrahigh-pressure (UHP) eclogites have been found in the Western Tianshan (WT) UHP metamorphic belt, which provides one ideal case for quantification of abiotic CH4 stored in the cold subducted crust. By two methods, we assess the abiotic CH4 content stored in the Chinese WT HP– UHP metamorphic belt. Our calculations show that at least 113 Mt CH4 isstored in the WT eclogites. We also discuss the implications for CH4 reservoirs in subduction zones worldwide and speculate that the cold subduction zones may represent one of the largest, yet overlooked, sources of abiotic CH4 on Earth, which should not be ignored in the global natural resource and carbon flux estimations.

Abstract:The high-pressure behavior of deep carbonate dictates the state and dynamics of oxidized carbon in the Earth's mantle, playing a vital role in the global carbon cycle and potentially influencing long-term climate change. Optical absorption and Raman spectroscopic measurements were carried out on two natural carbonate samples in diamond-anvil cells up to 60 GPa. Mg-substitution in high-spin siderite FeCO3 increases the crystal field absorption band position by approximately 1000 cm?1, but such an effect is marginal at >40 GPa when entering the low-spin state. The crystal field absorption band of dolomite cannot be recognized upon compression to 45.8 GPa at room temperature but, in contrast, the high-pressure polymorph of dolomite exhibits a strong absorption band at frequencies higher than (Mg,Fe)CO3 in the low-spin state by 2000–2500 cm?1. Additionally, these carbonate minerals show more complicated features for the absorption edge, decreasing with pressure and undergoing a dramatic change through the spin crossover. The optical and vibrational properties of carbonate minerals are highly correlated with iron content and spin transition, indicating that iron is preferentially partitioned into low-spin carbonates. These results shed new light on how carbonate minerals evolve in the mantle, which is crucial to decode the deep carbon cycle.

Abstract:It is generally believed that the lithospheric mantle and the mantle transition zone are important carbon reservoirs. However, the location of carbon storage in Earth's interior and the reasons for carbon enrichment remain unclear. In this study, we report CO2-rich olivine-hosted melt inclusions in the mantle xenoliths of late Cenozoic basalts from the Penglai area, Hainan Province, which may shed some light on the carbon enrichment process in the lithospheric mantle. We also present a detailed petrological and geochemical investigation of the late Cenozoic basalts and mantle xenoliths from northern Hainan Island. The collected samples of late Cenozoic Hainan Island basalts belong to both alkaline and subalkaline series, showing fractionated REE patterns with high (La/Yb)N values of 3.52–11.77, which are typical for OIB. Based on Al-in-olivine thermometry, the temperatures estimated for the mantle xenoliths can be divided into two groups. One group has temperatures of less than 1050°C, and the other group has temperature ranging from 1050°C to 1282°C. Clinopyroxene (La/Yb)N–Ti/Eu and clinopyroxene Ca/Al–Mg# diagrams indicate that the mantle peridotite experienced metasomatism from both silicate and carbonate melts. Melt inclusions in the olivine of mantle xenoliths include (1) CO2 bubble–rich melt inclusions; (2) multiphase melt inclusions (glass + CO2 bubble + daughter minerals); (3) pure glass melt inclusions. Magnesite is a daughter mineral in the olivine-hosted melt inclusions, which could be interpreted as a secondary mineral formed by the interactions of CO2-rich fluids with an olivine host, due to post-entrapment effects. The glasses in olivine-hosted melt inclusions have high SiO2 contents (60.21–77.72 wt%). Our results suggest that a considerable amount of CO2-rich melt inclusions are captured in the lithospheric mantle during metasomatism. The lithospheric mantle can therefore act as is a ‘carbon trap’, with much CO2 being absorbed by the lithospheric mantle in this way.

Abstract:The transportation of magma in sedimentary basins often occurs through extensive dyke-sill networks. The role of sills on the plumbing system in rifted margins and the impact of sills on hydrocarbon reservoirs of prospective sedimentary basins has long been an area of great industrial interest and scientific debate. Based on 2D seismic reflection, we present data on how the sills emplaced to form a magmatic plumbing system of the volcanic system for the Zhongjiannan Basin (ZJNB). The results show that sixty-nine sills and fourteen forced folds have been identified. The distribution and geometry of the sills suggest that magma flowed from west to east and then ascended to near the surface. The onlap relationship of the forced folds indicates that the timing of magmatic activities can be constrained at ca. 0.2 Ma. The spatial and temporal occurrences of intrusions imply that the strong post-rift magmatism in ZJNB was associated with the Hainan mantle plume arising from the core-mantle boundary. Furthermore, these forced folds could produce several types of hydrocarbon traps, due to accommodation through bending and uplift of the overlying rock and free surface, but it is critical to evaluate the effect of such emplacement when setting exploration targets.