Proterozoic orogens commonly host a range of hydrothermal ores that form in diverse tectonic settings at different times. However, the link between mineralization and the regional-scale tectonothermal evolution of oro...Proterozoic orogens commonly host a range of hydrothermal ores that form in diverse tectonic settings at different times. However, the link between mineralization and the regional-scale tectonothermal evolution of orogens is usually not well understood, especially in areas subject to multiple hydrothermal events.Regional-scale drivers for mineral systems vary between the different classes of hydrothermal ore, but all involve an energy source and a fluid pathway to focus mineralizing fluids into the upper crust. The Mount Olympus gold deposit in the Proterozoic Capricorn Orogen of Western Australia, was regarded as an orogenic gold deposit that formed at ca. 1738 Ma during the assembly of Proterozoic Australia. However,the trace element chemistry of the pyrite crystals closely resembles those of the Carlin deposits of Nevada,with rims that display solid solution gold accompanied by elevated As, Cu, Sb, Hg, and Tl, surrounding gold-poor cores. New SHRIMP UeP b dating of xenotime intergrown with auriferous pyrite and ore-stage alteration minerals provided a weighted mean^(207) Pb*/^(206) Pb* date of 1769 ± 5 Ma, interpreted as the age of gold mineralization. This was followed by two discrete episodes of hydrothermal alteration at 1727 ± 7 Ma and 1673 ± 8 Ma. The three ages are linked to multiple reactivation of the crustal-scale Nanjilgardy Fault during repeated episodes of intracratonic reworking. The regional-scale drivers for Carlin-like gold mineralization at Mount Olympus are related to a change in tectonic regime during the final stages of the intracratonic 1820 -1770 Ma Capricorn Orogeny. Our results suggest that substantial sized Carlin-like gold deposits can form in an intracratonic setting during regional-scale crustal reworking.展开更多
This paper provides a synthetic review of researches on Meishan Section D, the Global Stratotype Section and Point of the Permian-Triassic Boundary （PTB）. The history of research, geographic and geological setting o...This paper provides a synthetic review of researches on Meishan Section D, the Global Stratotype Section and Point of the Permian-Triassic Boundary （PTB）. The history of research, geographic and geological setting of the section are briefly introduced. Changhsingian to ＂Griesbachian＂ conodont and ammonoid zonations, the most perfect Permo-Triassic zonations over the world, are presented, with a short discussion on the age of Otoceras, The Changhsingian to ＂Griesbachian＂ strata are subdivided into three 3rd order sequences, and the sedimentary structure of each sequence is indicated. The paper presents a correlation of the Changhsingian to ＂Griesbachian＂ magneetostratigraphy of the Meishan section with the general scale, and informed the negation of a short magnetic reversal at the PTB suggested by Zhu and Liu （1999）. Recent developments of chemostratigraphy of δ^13C and δ^34S are introduced, especially the discovery of more than one negative δ^13C excursions across the PTB. Two important molecular researches reveal the profound changes at the base of eco-system, the microbial catastrophy, and the euxinic conditions in the photic zone during the Permian-Triassic superanoxic event. The paper reports the changes in dating the age of PTB since 2001. According to recent achievements, the age of volcanogenic claybed 25, 14 cm below the PTB, is now set at 252.4±0.3 Ma. A discussion on the eventostratigraphy concludes that, although there is a major event episode at beds 25-26, the events across the PTB at Meishan are multi-episodic and commenced prior to the Event Beds 25-26, thus the possibility that the mass extinction was mainly induced by an exterrestrial impact is largely excluded.展开更多
An early Paleozoic Proto-Tethys ocean in western Yunnan has long been postulated although no robust geological evidence has been identified.Here we investigated the recently-identified Mayidui and Wanhe ophiolitic m&#...An early Paleozoic Proto-Tethys ocean in western Yunnan has long been postulated although no robust geological evidence has been identified.Here we investigated the recently-identified Mayidui and Wanhe ophiolitic mélanges in SW Yunnan,which occurs in a N-S trending belt east of the late Paleozoic Changning-Menglian suture zone.The ophiolites consist mainly of meta-basalts(amphibole schists),meta-(cumulate)gabbros and gabbroic diorites,and meta-chert-shale,representing ancient oceanic crust and pelagic and hemipelagic sediments,respectively.Six samples of gabbros and gabbroic diorites from 3 profiles(Mayidui,Kongjiao and Yinchanghe)yielded zircon U-Pb ages between 462±6 Ma and 447±9 Ma,constraining the formation of the Mayidui and Wanhe ophiolites to Middle Ordovician.Gabbros from the Mayidui and Kongjiao profiles share similar geochemical characteristics with affinities to tholeiitic series,and are characterized by depleted to slightly enriched LREEs relative to HREEs with(La/Sm)N=0.69-1.87,(La/Yb)N=0.66-4.72.These,along with their predominantly positive wholerock eNd(t)and zircon eHf(t)values,indicate a MORB-like magma source.By contrast,the meta-mafic rocks from the Yinchanghe profile show significantly enriched LREEs((La/Sm)N=0.97-3.33,(La/Yb)N=1.19-14.93),as well as positive whole-rock eNd(t)and positive to negative zircon eHf(t)values,indicating an E-MORB-type mantle source.These geochemical features are consistent with an intra-oceanic setting for the formation of the Mayidui-Wanhe ophiolites.Our data,integrated with available geological evidence,provide robust constraints on the timing and nature of the Mayidui-Wanhe ophiolitic mélange,and suggest that the ophiolites represent remnants of the Proto-Tethys Ocean,which opened through separation of the Indochina and Simao blocks from the northern margin of Gondwana before the Early Cambrian,and evolved through to the Silurian.展开更多
Frequency-size relation of earthquakes in a region can be approximated by the Gutenberg-Richter law(GR). This power-law model involves two parameters: a-value measuring seismic activity or earthquake productivity, and...Frequency-size relation of earthquakes in a region can be approximated by the Gutenberg-Richter law(GR). This power-law model involves two parameters: a-value measuring seismic activity or earthquake productivity, and b-value describing the relation between frequencies of small and large earthquakes.The spatial and temporal variations of these two parameters, especially the b-value, have been substantially investigated. For example, it has been shown that b-value depends inversely on differential stress. The b-value has also been utilized as earthquake precursor in large earthquake prediction.However, the physical meaning and properties of b-value including its value range still remain as an open fundamental question. We explore the property of b-value from frequency-size GR model in a new form which relates average energy release and probability of large earthquakes. Based on this new form of GR relation the b-value can be related to the singularity index(1-2/3 b) of fractal energy-probability power-law model. This model as applied to the global database of earthquakes with size M ≥ 5 from 1964 to 2015 indicates a systematic increase of singularity from earthquakes occurring on mid-ocean ridges, to those in subduction zones and in collision zones.展开更多
Diverse models have been proposed for the role of the Tarim Craton within the Paleoproterozoic Columbia supercontinent assembly. Here we report a suite of-1.71 Ga Nb-enriched meta-gabbro lenses in the eastern Quanji M...Diverse models have been proposed for the role of the Tarim Craton within the Paleoproterozoic Columbia supercontinent assembly. Here we report a suite of-1.71 Ga Nb-enriched meta-gabbro lenses in the eastern Quanji Massif, within the Tarim Craton in NW China. The meta-gabbroic rocks have Nb contents of 11.5-16.4 ppm with Nb/La ratios varying from 0.84 to 1.02((Nb/La)_N = 0.81-0.98) and Nb/U ratios from 38.0 to 47.2. They show low SiO_2(45.1-48.5 wt.%) and MgO(5.96-6.81 wt.%) and Mg#(Mg# = Mg/(Mg + Fe) = 43.5-47.7), high FeO^t(13.0-15.7 wt.%) and moderate Ti02(1.70-2.51 wt.%).with tholeiitic affinities. These rocks possess low fractionated REE patterns without obvious Eu anomalies(Eu/Eu~* = 0.87-1.02). Their primitive mantle-normalized elements patterns display significant Zr-Hf troughs, positive Nb anomalies, weak negative Ti and P anomalies, and high contents of Rb and Ba,resembling Nb-enriched basalts generated in arc-related tectonic settings. Their arc-like geochemical signatures together with whole rock εNd(t) values of 0.4-2.1 and corresponding old T_(DM)(2.22-2.37 Ga)as well as(^(143)Nd/^(144)Nd)_t and(^(87)Sr/^(86)Sr)t(t = 1712 Ma) values of 0.5104-0.5105 and 0.7030-0.7058,respectively, suggest that their precursor magma originated from mantle wedge peridotite metasomatised by subduction-derived melts. The results from our study reveal subduction along the eastern periphery of the Tarim Craton and marginal outgrowth continuing to ~1.7 Ga within the Columbia supercontinent.展开更多
To determine the lateral and vertical variations in crustal structure and their influence on the seismicity of the Western North China Craton,the Trans-North China Orogen,and the surrounding regions,the wavelet multi-...To determine the lateral and vertical variations in crustal structure and their influence on the seismicity of the Western North China Craton,the Trans-North China Orogen,and the surrounding regions,the wavelet multi-scale structures,Moho depth,crustal density structures,and isostatic state are modelled using Bouguer gravity anomaly data,topography,and earthquake focal mechanisms.We obtained homogeneous crustal densities and deviations of<1 km between the crustal thicknesses estimated from the isostatic model and those inverted from the Bouguer gravity anomalies in the Ordos Block,the Inner Mongolia Suture Zone,the Sichuan Basin,and the Jizhong Depression.These results provide new evidence for relatively simple and stable continental crustal structures,and indicate that these regions will remain stable in both the vertical and lateral directions.The Hetao Graben,Yinchuan Graben,Weihe Basin,and Shanxi graben system have heterogeneous crustal densities and are isostatically over-compensated.In contrast,the crust beneath the Yinshan Uplift,Lvliang Uplift,and northern and central Taihang Uplift is thin and under-compensated.The heterogeneous crustal densities and non-isostatic state beneath the Tibetan Plateau and Qinling Central China Orogen indicate that these two blocks are unstable in the vertical and lateral directions.Although Cenozoic deformation of the North China Craton is thought to be driven by lithospheric stresses related to the India-Eurasia collision and Pacific slab retreat in South East Asia,we suggest that gravitational potential energy created by the heterogeneous crustal structure modulates these first-order forces.The results of this study could constrain the causes of seismicity in systems surrounding the Ordos Block.展开更多
In this study,we investigated Early Paleozoic magmatic rocks of the Manlai Formation exposed along the eastern margin of the Lancang terrane to better understand the tectonic history of the Proto-Tethys.We present pet...In this study,we investigated Early Paleozoic magmatic rocks of the Manlai Formation exposed along the eastern margin of the Lancang terrane to better understand the tectonic history of the Proto-Tethys.We present petrological,geochemical and whole-rock Sr-Nd and zircon Hf isotopic data for basalts and gabbros sampled from the Qianmai mélange.Zircon grains from six basaltic and gabbroic samples yielded U-Pb ages of 495-482 Ma.These rocks are characterized by tholeiitic and Nbenriched compositions,with Nb/La ratios in the range of 0.38-1.38,similar to the typical Nb-enriched basalts.All the mafic rocks show slightly negative to positiveε_(Nd)(t)(-1.67 to+4.32)and zirconε_(Hf)(t)values(-7.3 to+3.8).Elemental and isotopic data suggest that the Qianmai Nb-enriched mafic rocks were mainly derived from the mixing of an OIB-like source with a subduction-modified mantle wedge source.Together with magmatic and sedimentary records of similar ages in the Lancang terrane and the Baoshan Block,our results reveal Early Paleozoic magmatic and sedimentary sequences along an active margin of the Proto-Tethys.Taking into account the recently identified Early Paleozoic ophiolitic mélange in the Yunxian-Menghai belt,we consider the Qianmai magmatic rocks to represent the products of early-stage subduction-related magmatism within a primitive island arc or fore-arc setting associated with the southward subduction of the Proto-Tethys.We infer that prolonged south-dipping subduction on the northern margin of Gondwana persisted from the Cambrian to the Late Ordovician.展开更多
The systematic study of extreme geological events(such as plate collision and subduction, extreme cold and extreme hot events, biological extinction and revival, earthquakes, volcanoes, mineralization, and oil accumul...The systematic study of extreme geological events(such as plate collision and subduction, extreme cold and extreme hot events, biological extinction and revival, earthquakes, volcanoes, mineralization, and oil accumulation) that occurred during the evolution of the earth is essential not only for understanding the “abrupt changes in the evolution of the earth”, but also for an in-depth understanding of the co-evolution of material-life-environment of the livable earth. However, due to the temporal and spatial anomalies and complexity of extreme geological events, classical mathematical models cannot be effectively applied to quantitively describe such events. After comparative studies of many types of geological events, the author found that such extreme geological events often depict “singular” characteristics(abnormal accumulation or depletion of matter or massive release or absorption of energy in a small space or time interval). On this basis, the author proposes a unified definition of extreme geological events, a new concept of “fractal density” and a “local singularity analysis” method for quantitative description and modeling of extreme geological events. Applications of these methods to several types of extreme geological events have demonstrated that the singularity theory and methods developed in the current research can be used as general approaches for the characterization, simulation, and prediction of geological events.展开更多
The relation of heat flow and floor depth across the mid-ocean ridges versus lithosphere age can be described by linear functions of square root of age according to plate thermal conductive Half Space Models(HSM).Howe...The relation of heat flow and floor depth across the mid-ocean ridges versus lithosphere age can be described by linear functions of square root of age according to plate thermal conductive Half Space Models(HSM).However,one of the long-standing problems of these classical models is the discrepancies between predicted and observed heat flow and floor depth for very young and very old lithosphere.There have been several recent attempts to overcome this problem:one model incorporates temperature-and pressure-dependent parameters and the second model includes an additional low-conductivity crustal layer or magma rich mantle layer(MRM).Alternatively,in the current paper,the ordinary density of lithosphere in the plate conductive models is substituted with a reduction of lithosphere density towards axis that features the irregularity and nonlinearity of plates across the mid-ocean ridges.A new model is formulated incorporating the new form of density for predicting both peak heat flow and floor depth.Simple solutions of power-law forms derived from the model can significantly improve the predicting results of heat flow and floor depth over the mid-ocean ridges.Several datasets in the literature were reutilized for model validation and comparison.These datasets include both earlier datasets used for original model calibration and the more recently compiled high-quality datasets with both sedimentary and crustal loading corrections.The results indicate that both the heat flow and the slope(first orderderivative)of sea floor approach infinity(undifferentiability or singularities)around the mid-ocean ridges.These singularities are partially due to the boundary condition as it has been already known in the literature and partially to the reduction of density of lithosphere as discovered for the first time in the current research.展开更多
Understanding the tectono-magmatic evolution history of the Tengchong block is crucial for elucidating the formation of the Eastern Tethys tectonic domain.However,the correlation and evolution of the Tengchong block w...Understanding the tectono-magmatic evolution history of the Tengchong block is crucial for elucidating the formation of the Eastern Tethys tectonic domain.However,the correlation and evolution of the Tengchong block with the Sibumasu and Lhasa blocks is controversial during the Permian and Cretaceous.This study explores the information contained within magmatic rocks using big data and spatio-temporal analysis,providing quantitative constraints for the discussion of the tectonomagmatic evolution of the Tengchong block.To more accurately assess true magma activities and reduce errors caused by preservation and sampling processes,we utilized local singularity analysis to obtain the singularity index time-series.Correlation analysis of zircon ages and eHf(t)(correlation coefficient0.5)values indicates that the Tengchong block is more similar to the Sibumasu block.Results from timelagged cross-correlation analysis indicate that the Tengchong block and Sibumasu block exhibit a shorter lag in magmatic activities(3 Myr).Wavelet analysis reveals similar periods of collision-related magmatic activities(57 Myr and 43 Myr).Integrating evidence from paleontology and ophiolite belts,we propose that the Tengchong block co-evolved more closely with the Sibumasu block than with the Lhasa block,suggesting similar tectonic processes during the Early Permian to Early Cretaceous.Approximately 250–236 Ma,in the western Tengchong block,partial melting of the lower crust occurs due to crustal thickening.Around 219–213 Ma and 198–180 Ma,after the Tengchong block collided with the Eurasian continent,the subduction of the Meso-Tethys Ocean commenced.Around 130–111 Ma,the overall tectonic feature was a scissor-like closure of the Meso-Tethys Ocean from north to south.展开更多
Podiform chromitites are generally lenticular bodies of massive to disseminated chromite typically hosted in mantle peridotites in ophiolites. Most such chromitites are surrounded by envelopes of dunite, a few centime...Podiform chromitites are generally lenticular bodies of massive to disseminated chromite typically hosted in mantle peridotites in ophiolites. Most such chromitites are surrounded by envelopes of dunite, a few centimeters to a few meters wide. Based on their textures and compositions, podiform chromitites have been interpreted as magmatic rocks formed as partial melting of mantle peridotite under low-pressure conditions in the upper mantle or by magma mingling and melt-rock reaction.展开更多
基金funded through an ARC linkage grant (LP130100922) and industry scholarship by Northern Star Resources as a part of a PhD by I. O.Fielding. S. P. the financial support of the Australian Research Council and Auscope NCRIS
文摘Proterozoic orogens commonly host a range of hydrothermal ores that form in diverse tectonic settings at different times. However, the link between mineralization and the regional-scale tectonothermal evolution of orogens is usually not well understood, especially in areas subject to multiple hydrothermal events.Regional-scale drivers for mineral systems vary between the different classes of hydrothermal ore, but all involve an energy source and a fluid pathway to focus mineralizing fluids into the upper crust. The Mount Olympus gold deposit in the Proterozoic Capricorn Orogen of Western Australia, was regarded as an orogenic gold deposit that formed at ca. 1738 Ma during the assembly of Proterozoic Australia. However,the trace element chemistry of the pyrite crystals closely resembles those of the Carlin deposits of Nevada,with rims that display solid solution gold accompanied by elevated As, Cu, Sb, Hg, and Tl, surrounding gold-poor cores. New SHRIMP UeP b dating of xenotime intergrown with auriferous pyrite and ore-stage alteration minerals provided a weighted mean^(207) Pb*/^(206) Pb* date of 1769 ± 5 Ma, interpreted as the age of gold mineralization. This was followed by two discrete episodes of hydrothermal alteration at 1727 ± 7 Ma and 1673 ± 8 Ma. The three ages are linked to multiple reactivation of the crustal-scale Nanjilgardy Fault during repeated episodes of intracratonic reworking. The regional-scale drivers for Carlin-like gold mineralization at Mount Olympus are related to a change in tectonic regime during the final stages of the intracratonic 1820 -1770 Ma Capricorn Orogeny. Our results suggest that substantial sized Carlin-like gold deposits can form in an intracratonic setting during regional-scale crustal reworking.
基金The work was supported by the National Natural Science Foundation of China(project no.40232025).
文摘This paper provides a synthetic review of researches on Meishan Section D, the Global Stratotype Section and Point of the Permian-Triassic Boundary （PTB）. The history of research, geographic and geological setting of the section are briefly introduced. Changhsingian to ＂Griesbachian＂ conodont and ammonoid zonations, the most perfect Permo-Triassic zonations over the world, are presented, with a short discussion on the age of Otoceras, The Changhsingian to ＂Griesbachian＂ strata are subdivided into three 3rd order sequences, and the sedimentary structure of each sequence is indicated. The paper presents a correlation of the Changhsingian to ＂Griesbachian＂ magneetostratigraphy of the Meishan section with the general scale, and informed the negation of a short magnetic reversal at the PTB suggested by Zhu and Liu （1999）. Recent developments of chemostratigraphy of δ^13C and δ^34S are introduced, especially the discovery of more than one negative δ^13C excursions across the PTB. Two important molecular researches reveal the profound changes at the base of eco-system, the microbial catastrophy, and the euxinic conditions in the photic zone during the Permian-Triassic superanoxic event. The paper reports the changes in dating the age of PTB since 2001. According to recent achievements, the age of volcanogenic claybed 25, 14 cm below the PTB, is now set at 252.4±0.3 Ma. A discussion on the eventostratigraphy concludes that, although there is a major event episode at beds 25-26, the events across the PTB at Meishan are multi-episodic and commenced prior to the Event Beds 25-26, thus the possibility that the mass extinction was mainly induced by an exterrestrial impact is largely excluded.
文摘An early Paleozoic Proto-Tethys ocean in western Yunnan has long been postulated although no robust geological evidence has been identified.Here we investigated the recently-identified Mayidui and Wanhe ophiolitic mélanges in SW Yunnan,which occurs in a N-S trending belt east of the late Paleozoic Changning-Menglian suture zone.The ophiolites consist mainly of meta-basalts(amphibole schists),meta-(cumulate)gabbros and gabbroic diorites,and meta-chert-shale,representing ancient oceanic crust and pelagic and hemipelagic sediments,respectively.Six samples of gabbros and gabbroic diorites from 3 profiles(Mayidui,Kongjiao and Yinchanghe)yielded zircon U-Pb ages between 462±6 Ma and 447±9 Ma,constraining the formation of the Mayidui and Wanhe ophiolites to Middle Ordovician.Gabbros from the Mayidui and Kongjiao profiles share similar geochemical characteristics with affinities to tholeiitic series,and are characterized by depleted to slightly enriched LREEs relative to HREEs with(La/Sm)N=0.69-1.87,(La/Yb)N=0.66-4.72.These,along with their predominantly positive wholerock eNd(t)and zircon eHf(t)values,indicate a MORB-like magma source.By contrast,the meta-mafic rocks from the Yinchanghe profile show significantly enriched LREEs((La/Sm)N=0.97-3.33,(La/Yb)N=1.19-14.93),as well as positive whole-rock eNd(t)and positive to negative zircon eHf(t)values,indicating an E-MORB-type mantle source.These geochemical features are consistent with an intra-oceanic setting for the formation of the Mayidui-Wanhe ophiolites.Our data,integrated with available geological evidence,provide robust constraints on the timing and nature of the Mayidui-Wanhe ophiolitic mélange,and suggest that the ophiolites represent remnants of the Proto-Tethys Ocean,which opened through separation of the Indochina and Simao blocks from the northern margin of Gondwana before the Early Cambrian,and evolved through to the Silurian.
基金financially supported by China Natural Science Foundation(NSF)(No.41430320)
文摘Frequency-size relation of earthquakes in a region can be approximated by the Gutenberg-Richter law(GR). This power-law model involves two parameters: a-value measuring seismic activity or earthquake productivity, and b-value describing the relation between frequencies of small and large earthquakes.The spatial and temporal variations of these two parameters, especially the b-value, have been substantially investigated. For example, it has been shown that b-value depends inversely on differential stress. The b-value has also been utilized as earthquake precursor in large earthquake prediction.However, the physical meaning and properties of b-value including its value range still remain as an open fundamental question. We explore the property of b-value from frequency-size GR model in a new form which relates average energy release and probability of large earthquakes. Based on this new form of GR relation the b-value can be related to the singularity index(1-2/3 b) of fractal energy-probability power-law model. This model as applied to the global database of earthquakes with size M ≥ 5 from 1964 to 2015 indicates a systematic increase of singularity from earthquakes occurring on mid-ocean ridges, to those in subduction zones and in collision zones.
基金supported by the National Science Foundation of ChinaNSFC grants(Grant Nos.41602056,41372075,41172069)+1 种基金the China Postdoctoral Science Foundation(Grant No.2016M590729)the Fundamental Research Funds for National Universities,China University of Geosciences(Wuhan)(Grant No.CUG160846)
文摘Diverse models have been proposed for the role of the Tarim Craton within the Paleoproterozoic Columbia supercontinent assembly. Here we report a suite of-1.71 Ga Nb-enriched meta-gabbro lenses in the eastern Quanji Massif, within the Tarim Craton in NW China. The meta-gabbroic rocks have Nb contents of 11.5-16.4 ppm with Nb/La ratios varying from 0.84 to 1.02((Nb/La)_N = 0.81-0.98) and Nb/U ratios from 38.0 to 47.2. They show low SiO_2(45.1-48.5 wt.%) and MgO(5.96-6.81 wt.%) and Mg#(Mg# = Mg/(Mg + Fe) = 43.5-47.7), high FeO^t(13.0-15.7 wt.%) and moderate Ti02(1.70-2.51 wt.%).with tholeiitic affinities. These rocks possess low fractionated REE patterns without obvious Eu anomalies(Eu/Eu~* = 0.87-1.02). Their primitive mantle-normalized elements patterns display significant Zr-Hf troughs, positive Nb anomalies, weak negative Ti and P anomalies, and high contents of Rb and Ba,resembling Nb-enriched basalts generated in arc-related tectonic settings. Their arc-like geochemical signatures together with whole rock εNd(t) values of 0.4-2.1 and corresponding old T_(DM)(2.22-2.37 Ga)as well as(^(143)Nd/^(144)Nd)_t and(^(87)Sr/^(86)Sr)t(t = 1712 Ma) values of 0.5104-0.5105 and 0.7030-0.7058,respectively, suggest that their precursor magma originated from mantle wedge peridotite metasomatised by subduction-derived melts. The results from our study reveal subduction along the eastern periphery of the Tarim Craton and marginal outgrowth continuing to ~1.7 Ga within the Columbia supercontinent.
基金supported by National Key Research and Development Program of China (Grant No. 2016YFC0600501)National Basic Research Program of China (Grant No. 2015CB452605)+2 种基金National Natural Science Foundation of China (Grant Nos. 41702075 and 41572315)Geological Survey Project of China (Grant No. DD20160045)the State Key Program of National Natural Science of China (Grant No. 41430320)
文摘To determine the lateral and vertical variations in crustal structure and their influence on the seismicity of the Western North China Craton,the Trans-North China Orogen,and the surrounding regions,the wavelet multi-scale structures,Moho depth,crustal density structures,and isostatic state are modelled using Bouguer gravity anomaly data,topography,and earthquake focal mechanisms.We obtained homogeneous crustal densities and deviations of<1 km between the crustal thicknesses estimated from the isostatic model and those inverted from the Bouguer gravity anomalies in the Ordos Block,the Inner Mongolia Suture Zone,the Sichuan Basin,and the Jizhong Depression.These results provide new evidence for relatively simple and stable continental crustal structures,and indicate that these regions will remain stable in both the vertical and lateral directions.The Hetao Graben,Yinchuan Graben,Weihe Basin,and Shanxi graben system have heterogeneous crustal densities and are isostatically over-compensated.In contrast,the crust beneath the Yinshan Uplift,Lvliang Uplift,and northern and central Taihang Uplift is thin and under-compensated.The heterogeneous crustal densities and non-isostatic state beneath the Tibetan Plateau and Qinling Central China Orogen indicate that these two blocks are unstable in the vertical and lateral directions.Although Cenozoic deformation of the North China Craton is thought to be driven by lithospheric stresses related to the India-Eurasia collision and Pacific slab retreat in South East Asia,we suggest that gravitational potential energy created by the heterogeneous crustal structure modulates these first-order forces.The results of this study could constrain the causes of seismicity in systems surrounding the Ordos Block.
基金supported by projects from the“Xingdian Talent”Youth Talent Program in Yunnan Province(No.XDYCQNRC-2022-0041)the National Natural Science Foundation of China(Nos.42162020,41873062,92055314)。
文摘In this study,we investigated Early Paleozoic magmatic rocks of the Manlai Formation exposed along the eastern margin of the Lancang terrane to better understand the tectonic history of the Proto-Tethys.We present petrological,geochemical and whole-rock Sr-Nd and zircon Hf isotopic data for basalts and gabbros sampled from the Qianmai mélange.Zircon grains from six basaltic and gabbroic samples yielded U-Pb ages of 495-482 Ma.These rocks are characterized by tholeiitic and Nbenriched compositions,with Nb/La ratios in the range of 0.38-1.38,similar to the typical Nb-enriched basalts.All the mafic rocks show slightly negative to positiveε_(Nd)(t)(-1.67 to+4.32)and zirconε_(Hf)(t)values(-7.3 to+3.8).Elemental and isotopic data suggest that the Qianmai Nb-enriched mafic rocks were mainly derived from the mixing of an OIB-like source with a subduction-modified mantle wedge source.Together with magmatic and sedimentary records of similar ages in the Lancang terrane and the Baoshan Block,our results reveal Early Paleozoic magmatic and sedimentary sequences along an active margin of the Proto-Tethys.Taking into account the recently identified Early Paleozoic ophiolitic mélange in the Yunxian-Menghai belt,we consider the Qianmai magmatic rocks to represent the products of early-stage subduction-related magmatism within a primitive island arc or fore-arc setting associated with the southward subduction of the Proto-Tethys.We infer that prolonged south-dipping subduction on the northern margin of Gondwana persisted from the Cambrian to the Late Ordovician.
基金supported by the National Natural Science Foundation of China (Grant No. 42050103)the Ministry of Science and Technology (Grant No. 2016YFC0600500)the Ministry of Natural Resources and the China Geological Survey (Grant No. DD20160045)。
文摘The systematic study of extreme geological events(such as plate collision and subduction, extreme cold and extreme hot events, biological extinction and revival, earthquakes, volcanoes, mineralization, and oil accumulation) that occurred during the evolution of the earth is essential not only for understanding the “abrupt changes in the evolution of the earth”, but also for an in-depth understanding of the co-evolution of material-life-environment of the livable earth. However, due to the temporal and spatial anomalies and complexity of extreme geological events, classical mathematical models cannot be effectively applied to quantitively describe such events. After comparative studies of many types of geological events, the author found that such extreme geological events often depict “singular” characteristics(abnormal accumulation or depletion of matter or massive release or absorption of energy in a small space or time interval). On this basis, the author proposes a unified definition of extreme geological events, a new concept of “fractal density” and a “local singularity analysis” method for quantitative description and modeling of extreme geological events. Applications of these methods to several types of extreme geological events have demonstrated that the singularity theory and methods developed in the current research can be used as general approaches for the characterization, simulation, and prediction of geological events.
基金supported by National Natural Science Foundation of China(grant number 42050103)Guangdong Research Team Development Grant(grant number 2021ZT09H399)。
文摘The relation of heat flow and floor depth across the mid-ocean ridges versus lithosphere age can be described by linear functions of square root of age according to plate thermal conductive Half Space Models(HSM).However,one of the long-standing problems of these classical models is the discrepancies between predicted and observed heat flow and floor depth for very young and very old lithosphere.There have been several recent attempts to overcome this problem:one model incorporates temperature-and pressure-dependent parameters and the second model includes an additional low-conductivity crustal layer or magma rich mantle layer(MRM).Alternatively,in the current paper,the ordinary density of lithosphere in the plate conductive models is substituted with a reduction of lithosphere density towards axis that features the irregularity and nonlinearity of plates across the mid-ocean ridges.A new model is formulated incorporating the new form of density for predicting both peak heat flow and floor depth.Simple solutions of power-law forms derived from the model can significantly improve the predicting results of heat flow and floor depth over the mid-ocean ridges.Several datasets in the literature were reutilized for model validation and comparison.These datasets include both earlier datasets used for original model calibration and the more recently compiled high-quality datasets with both sedimentary and crustal loading corrections.The results indicate that both the heat flow and the slope(first orderderivative)of sea floor approach infinity(undifferentiability or singularities)around the mid-ocean ridges.These singularities are partially due to the boundary condition as it has been already known in the literature and partially to the reduction of density of lithosphere as discovered for the first time in the current research.
文摘Understanding the tectono-magmatic evolution history of the Tengchong block is crucial for elucidating the formation of the Eastern Tethys tectonic domain.However,the correlation and evolution of the Tengchong block with the Sibumasu and Lhasa blocks is controversial during the Permian and Cretaceous.This study explores the information contained within magmatic rocks using big data and spatio-temporal analysis,providing quantitative constraints for the discussion of the tectonomagmatic evolution of the Tengchong block.To more accurately assess true magma activities and reduce errors caused by preservation and sampling processes,we utilized local singularity analysis to obtain the singularity index time-series.Correlation analysis of zircon ages and eHf(t)(correlation coefficient0.5)values indicates that the Tengchong block is more similar to the Sibumasu block.Results from timelagged cross-correlation analysis indicate that the Tengchong block and Sibumasu block exhibit a shorter lag in magmatic activities(3 Myr).Wavelet analysis reveals similar periods of collision-related magmatic activities(57 Myr and 43 Myr).Integrating evidence from paleontology and ophiolite belts,we propose that the Tengchong block co-evolved more closely with the Sibumasu block than with the Lhasa block,suggesting similar tectonic processes during the Early Permian to Early Cretaceous.Approximately 250–236 Ma,in the western Tengchong block,partial melting of the lower crust occurs due to crustal thickening.Around 219–213 Ma and 198–180 Ma,after the Tengchong block collided with the Eurasian continent,the subduction of the Meso-Tethys Ocean commenced.Around 130–111 Ma,the overall tectonic feature was a scissor-like closure of the Meso-Tethys Ocean from north to south.
文摘Podiform chromitites are generally lenticular bodies of massive to disseminated chromite typically hosted in mantle peridotites in ophiolites. Most such chromitites are surrounded by envelopes of dunite, a few centimeters to a few meters wide. Based on their textures and compositions, podiform chromitites have been interpreted as magmatic rocks formed as partial melting of mantle peridotite under low-pressure conditions in the upper mantle or by magma mingling and melt-rock reaction.
