New field observations and petrological data from Early Cretaceous metamorphic rocks in the Central Cordillera of the Colombian Andes allowed the recognition of thermally overprinted high-pressure rocks derived from o...New field observations and petrological data from Early Cretaceous metamorphic rocks in the Central Cordillera of the Colombian Andes allowed the recognition of thermally overprinted high-pressure rocks derived from oceanic crust protoliths.The obtained metamorphic path suggests that the rocks evolved from blueschist to eclogite facies towards upper amphibolite to high-pressure granulite facies transitional conditions.Eclogite facies conditions,better recorded in mafic protoliths,are revealed by relic lawsonite and phengite,bleb-to worm-like diopside-albite symplectites,as well as garnet core composition.Upper amphibolite to high pressure granulite facies overprinting is supported by coarse-grained brown-colored Ti-rich amphibole,augite,and oligoclase recrystallization,as well as the record of partial melting leucosomes.Phase equilibria and pressure-temperature(P-T)path modeling suggest initial high-pressure metamorphic conditions M1 yielding 18.2-24.5 kbar and 465-580℃,followed by upper amphibolite to high pressure granulite facies overprinting stage M2 yielding 6.5-14.2 kbar and 580-720℃.Retrograde conditions M3 obtained through chlorite thermometry yield temperatures ranging around 286-400℃at pressures below 6.5-11 kbar.The obtained clockwise P-T path,the garnet zonation pattern revealing a decrease in X_(grs)/X_(prp)related to Mg#increment from core to rim,the presence of partial melting veins,as well as regional constraints,document the modification of the thermal structure of the active subduction zone in Northern Andes during the Early Cretaceous.Such increment of the metamorphic gradient within the subduction interface is associated with slab roll-back geodynamics where hot mantle inflow was triggered.This scenario is also argued by the reported trench-ward magmatic arc migration and multiple extensional basin formation during this period.The presented example constitutes the first report of Cretaceous roll-back-related metamorphism in the Caribbean and Andean realms,representing an additional piece of evidence for a margin-scale extensional event that modified the northwestern border of South America during the Early Cretaceous.展开更多
Overprinting of an earlier formed deposit may obscure the nature of the deposit and hinder our understanding of regional metallogeny.The Qiaoxiahala Fe(-Cu/Au)deposit in eastern Junggar,NW China,is characterized by ma...Overprinting of an earlier formed deposit may obscure the nature of the deposit and hinder our understanding of regional metallogeny.The Qiaoxiahala Fe(-Cu/Au)deposit in eastern Junggar,NW China,is characterized by magnetite mineralization later replaced by sulfide minerals such as chalcopyrite.To reveal the genesis of Qiaoxiahala,we conducted Re-Os dating on post-magnetite molybdenite separated from chalcopyrite and rare earth elements(REEs)for basal-tic volcanic rock,magnetite,chalcopyrite and diorite.An isochron age of 377±7 Ma was obtained together with a weighted mean age of 375±3 Ma,which is indistinguishable from mineralization ages determined in previous studies.Rare earth element(REE)data for basaltic volcanic rocks hosting the ore are comparable to that of the magnetite,while the REE signatures of chalcopyrite from the Cu ore and local intrusive diorite share a similar pattern.These suggest that two distinct fluid sources are responsible for the deposition of Fe and Cu in the Qiaoxiahala deposit.According to these experimental results,we consider that the iron mineralization in Qiaoxiahala is the result of fluid exsolution from basaltic volcanism which was further overprinted by fluids that deposited copper and gold,which may have been sourced from nearby dioritic intrusions.展开更多
The Precambrian Homrit-Waggat granite is a post-orogenic batholithic intrusion located in the northern region of the Nubian Shield,characterized by a typical annular morphology and significant secondary alteration.Thi...The Precambrian Homrit-Waggat granite is a post-orogenic batholithic intrusion located in the northern region of the Nubian Shield,characterized by a typical annular morphology and significant secondary alteration.This study aims to elucidate the processes that have shaped the intrusion in both macroscopic and microscopic perspectives,employing a combination of field observation and petrographic analysis alongside major and trace element compositions of minerals.Within the central region of the pluton,biotite and amphibole are observed sporadically,while the predominant crystallization of anhydrous oligoclase in the outer regions has led to a progressive increase in volatile components within the residual melt,ultimately resulting in a volatile-saturated aluminosilicate melt.The exsolved fluids subsequently interacted with the previously crystallized mineral assemblage,producing metasomatic overprinting.As the cooling and crystallization continued,the water pressure within the magma chamber gradually escalated until it equaled or surpassed the confining pressure,leading to the formation of fractures and veins filled with minerals that crystallized from the residual aqueous fluids.The ongoing degassing and expulsion of aqueous fluids from the magma chamber’s interior ultimately contributed to the collapse of the chamber’s roof,resulting in the annular ring-dike morphology observed in the Homrit Waggat pluton.展开更多
The Zhaxikang Pb-Zn-Ag-Sb deposit, the largest polymetallic deposit known in the Himalayan Orogen of southern Tibet, is characterized by vein-type mineralization that hosts multiple mineral assemblages and complicated...The Zhaxikang Pb-Zn-Ag-Sb deposit, the largest polymetallic deposit known in the Himalayan Orogen of southern Tibet, is characterized by vein-type mineralization that hosts multiple mineral assemblages and complicated metal associations. The deposit consists of at least six steeply dipping vein- type orebodies that are hosted by Early Jurassic black carbonaceous slates and are controlled by a Cenozoic N-S-striking normal fault system. This deposit records multiple stages of mineralization that include an early period （A） of massive coarse-grained galena-sphalerite deposition and a later period （B） of Sb-bearing vein-type mineralization. Period A is only associated with galena-sphalerite mineralization, whereas period B can be subdivided into ferrous rhodochrosite-sphalerite-pyrite, quartz -sulfosalt-sphalerite, calcite-pyrite, quartz-stibnite, and quartz-only stages of mineralization. The formation of brecciated galena and sphalerite ores during period A implies reworking of pre-existing Pb -Zn sulfides by Cenozoic tectonic deformation, whereas period B mineralization records extensive open- space filling during ore formation. Fluid inclusion microthermometric data indicate that both periods A and B were associated with low-medium temperature （187-267℃） and low salinity （4.00-10.18% wt. NaCl equivalent） ore-forming fluids, although variations in the physical-chemical nature of the period B fluids suggest that this phase of mineralization was characterized by variable water/rock ratios. Microprobe analyses indicate that Fe concentrations in sphalerite decrease from period A to period B, and can be divided into three groups with FeS concentrations of 8.999-9.577, 7.125-9.109, 5.438-1.460 mol.%. The concentrations of Zn, Sb, Pb, and Ag within orebodies in the study area are normally distributed in both lateral and vertical directions, and Pb, Sb, and/or Ag concentrations are positive correlation within the central part of these orebodies, but negatively correlate in the margins. Sulfide S isotope compositions are highly variable （4‰-13‰）, varying from 4‰ to 11‰ in period A and 10‰ to 1‰ in period B. The Pb isotope within these samples is highly radiogenic and defines linear trends in 206pb/204pb vs. 207pb/204pb and 206pb/204pb vs. 208pb/204pb diagrams, respectively. The S and Pb isotopic characteristics indicate that the period B orebodies formed by mixing of Pb-Zn sulfides and regional Sb- bearing fluids. These features are indicative of overprinting and remobilization of pre-existing Pb-Zn sulfides by Sb-bearing ore-forming fluids during a post-collisional period of the Himalayan Orogeny. The presence of similar ore types in the north Rhenish Massif that formed after the Variscan Orogeny suggests that Zhaxikang-style mineralization may be present in other orogenic belts, suggesting that this deposit may guide Pb-Zn exploration in these areas.展开更多
A novel method for source effect correction based on integral equation method is proposed.By taking the electrical horizontal field Ex of current source as an example,the correction method is validated using both simu...A novel method for source effect correction based on integral equation method is proposed.By taking the electrical horizontal field Ex of current source as an example,the correction method is validated using both simulated data and field data.The results show that the correction method is feasible and effective for isotropic media.When the field data are processed,the correction method normalizes the sources with different geological structures,which eliminates the geological difference among sources,and retains the geological difference among receivers.The correction results are in line with the expectation in whole.展开更多
The dating of the uplift onset of the Huangshan pluton in the southern part of Anhui Province associated with the collision between paleo-Pacific Block and the Eurasian Block is a fundamental issue to better understan...The dating of the uplift onset of the Huangshan pluton in the southern part of Anhui Province associated with the collision between paleo-Pacific Block and the Eurasian Block is a fundamental issue to better understand the uplift mechanisms and the regional tectonic evolution. Х^2 values of seven zircon fission track （ZFF） samples collected from the south part of the Huangshan pluton were all 〈5%. Based on the grain ages of four typical ZFr samples, three thermal overprints ranging in 113-123, 72-95 and 49-66 Ma were distinguished respectively using the binomial peak-fitting method in accordance with the tectonic thermal events after south China shifted into circum-Pacific tectonic region. Apatite fission track （AFT） study of the Huangshan pluton shows ages lie between 15±3 and 56±6 Ma with all Х^2 values 〉5%, and all are significantly younger than their host rock formation ages, indicating that the samples have experienced post-formation thermal history. Based on the AFT resuits and topography characteristics in the Huangshan pluton, three zones with different denudation intensities caused by the differential uplift of the fault blocks were recognized in this paper, indicating that denudation was driven by the increase in elevation significantly. Modeling of the AFT data shows that the earlier cooling phase took place in the early Cenozoic and involved 3.3, 3.8 and 6.0℃/Ma of cooling rates equivalent to the exhumation rates of 90, 104 and 167 m/Ma in different fault blocks. The last phase of cooling took place from -10 Ma with average cooling rate of -5.6℃/Ma, equivalent to average denudation rates of -156 m/Ma. The fission track results imply that the regional compression field plays an important role for the differential exhumation between individual fault blocks of the Huangshan pluton.展开更多
基金The National University of Colombia is acknowledged for its financial support。
文摘New field observations and petrological data from Early Cretaceous metamorphic rocks in the Central Cordillera of the Colombian Andes allowed the recognition of thermally overprinted high-pressure rocks derived from oceanic crust protoliths.The obtained metamorphic path suggests that the rocks evolved from blueschist to eclogite facies towards upper amphibolite to high-pressure granulite facies transitional conditions.Eclogite facies conditions,better recorded in mafic protoliths,are revealed by relic lawsonite and phengite,bleb-to worm-like diopside-albite symplectites,as well as garnet core composition.Upper amphibolite to high pressure granulite facies overprinting is supported by coarse-grained brown-colored Ti-rich amphibole,augite,and oligoclase recrystallization,as well as the record of partial melting leucosomes.Phase equilibria and pressure-temperature(P-T)path modeling suggest initial high-pressure metamorphic conditions M1 yielding 18.2-24.5 kbar and 465-580℃,followed by upper amphibolite to high pressure granulite facies overprinting stage M2 yielding 6.5-14.2 kbar and 580-720℃.Retrograde conditions M3 obtained through chlorite thermometry yield temperatures ranging around 286-400℃at pressures below 6.5-11 kbar.The obtained clockwise P-T path,the garnet zonation pattern revealing a decrease in X_(grs)/X_(prp)related to Mg#increment from core to rim,the presence of partial melting veins,as well as regional constraints,document the modification of the thermal structure of the active subduction zone in Northern Andes during the Early Cretaceous.Such increment of the metamorphic gradient within the subduction interface is associated with slab roll-back geodynamics where hot mantle inflow was triggered.This scenario is also argued by the reported trench-ward magmatic arc migration and multiple extensional basin formation during this period.The presented example constitutes the first report of Cretaceous roll-back-related metamorphism in the Caribbean and Andean realms,representing an additional piece of evidence for a margin-scale extensional event that modified the northwestern border of South America during the Early Cretaceous.
基金This study was supported by the the International Partnership Program of Chinese Academy of Science(No.132744KYSB20190039)National Key R&D Program of China(No.2017YFC0601206).
文摘Overprinting of an earlier formed deposit may obscure the nature of the deposit and hinder our understanding of regional metallogeny.The Qiaoxiahala Fe(-Cu/Au)deposit in eastern Junggar,NW China,is characterized by magnetite mineralization later replaced by sulfide minerals such as chalcopyrite.To reveal the genesis of Qiaoxiahala,we conducted Re-Os dating on post-magnetite molybdenite separated from chalcopyrite and rare earth elements(REEs)for basal-tic volcanic rock,magnetite,chalcopyrite and diorite.An isochron age of 377±7 Ma was obtained together with a weighted mean age of 375±3 Ma,which is indistinguishable from mineralization ages determined in previous studies.Rare earth element(REE)data for basaltic volcanic rocks hosting the ore are comparable to that of the magnetite,while the REE signatures of chalcopyrite from the Cu ore and local intrusive diorite share a similar pattern.These suggest that two distinct fluid sources are responsible for the deposition of Fe and Cu in the Qiaoxiahala deposit.According to these experimental results,we consider that the iron mineralization in Qiaoxiahala is the result of fluid exsolution from basaltic volcanism which was further overprinted by fluids that deposited copper and gold,which may have been sourced from nearby dioritic intrusions.
基金supported by Science and Technology Development Fund(STDF)of the Arab Republic of Egypt(No.23080)entitled―Rare Metal Ore Deposits in Egypt:A comparative survey in altered granites from selected areas in the Central Eastern Desert‖(to M.A.ABU EL-RUS)National Key Research and Development Program of China(No.2023YFF0804200).
文摘The Precambrian Homrit-Waggat granite is a post-orogenic batholithic intrusion located in the northern region of the Nubian Shield,characterized by a typical annular morphology and significant secondary alteration.This study aims to elucidate the processes that have shaped the intrusion in both macroscopic and microscopic perspectives,employing a combination of field observation and petrographic analysis alongside major and trace element compositions of minerals.Within the central region of the pluton,biotite and amphibole are observed sporadically,while the predominant crystallization of anhydrous oligoclase in the outer regions has led to a progressive increase in volatile components within the residual melt,ultimately resulting in a volatile-saturated aluminosilicate melt.The exsolved fluids subsequently interacted with the previously crystallized mineral assemblage,producing metasomatic overprinting.As the cooling and crystallization continued,the water pressure within the magma chamber gradually escalated until it equaled or surpassed the confining pressure,leading to the formation of fractures and veins filled with minerals that crystallized from the residual aqueous fluids.The ongoing degassing and expulsion of aqueous fluids from the magma chamber’s interior ultimately contributed to the collapse of the chamber’s roof,resulting in the annular ring-dike morphology observed in the Homrit Waggat pluton.
基金supported by grants from the Ministry of Science and Technology of China(National Key Research and Development Project of China:2016YFC0600308)a Program of the China Geological Survey(DD20160015)NSFC(41702086&41503040)
文摘The Zhaxikang Pb-Zn-Ag-Sb deposit, the largest polymetallic deposit known in the Himalayan Orogen of southern Tibet, is characterized by vein-type mineralization that hosts multiple mineral assemblages and complicated metal associations. The deposit consists of at least six steeply dipping vein- type orebodies that are hosted by Early Jurassic black carbonaceous slates and are controlled by a Cenozoic N-S-striking normal fault system. This deposit records multiple stages of mineralization that include an early period （A） of massive coarse-grained galena-sphalerite deposition and a later period （B） of Sb-bearing vein-type mineralization. Period A is only associated with galena-sphalerite mineralization, whereas period B can be subdivided into ferrous rhodochrosite-sphalerite-pyrite, quartz -sulfosalt-sphalerite, calcite-pyrite, quartz-stibnite, and quartz-only stages of mineralization. The formation of brecciated galena and sphalerite ores during period A implies reworking of pre-existing Pb -Zn sulfides by Cenozoic tectonic deformation, whereas period B mineralization records extensive open- space filling during ore formation. Fluid inclusion microthermometric data indicate that both periods A and B were associated with low-medium temperature （187-267℃） and low salinity （4.00-10.18% wt. NaCl equivalent） ore-forming fluids, although variations in the physical-chemical nature of the period B fluids suggest that this phase of mineralization was characterized by variable water/rock ratios. Microprobe analyses indicate that Fe concentrations in sphalerite decrease from period A to period B, and can be divided into three groups with FeS concentrations of 8.999-9.577, 7.125-9.109, 5.438-1.460 mol.%. The concentrations of Zn, Sb, Pb, and Ag within orebodies in the study area are normally distributed in both lateral and vertical directions, and Pb, Sb, and/or Ag concentrations are positive correlation within the central part of these orebodies, but negatively correlate in the margins. Sulfide S isotope compositions are highly variable （4‰-13‰）, varying from 4‰ to 11‰ in period A and 10‰ to 1‰ in period B. The Pb isotope within these samples is highly radiogenic and defines linear trends in 206pb/204pb vs. 207pb/204pb and 206pb/204pb vs. 208pb/204pb diagrams, respectively. The S and Pb isotopic characteristics indicate that the period B orebodies formed by mixing of Pb-Zn sulfides and regional Sb- bearing fluids. These features are indicative of overprinting and remobilization of pre-existing Pb-Zn sulfides by Sb-bearing ore-forming fluids during a post-collisional period of the Himalayan Orogeny. The presence of similar ore types in the north Rhenish Massif that formed after the Variscan Orogeny suggests that Zhaxikang-style mineralization may be present in other orogenic belts, suggesting that this deposit may guide Pb-Zn exploration in these areas.
基金Project(2018YFC0807802)supported by the National Key R&D Program of ChinaProject(41874081)supported by the National Natural Science Foundation of China。
文摘A novel method for source effect correction based on integral equation method is proposed.By taking the electrical horizontal field Ex of current source as an example,the correction method is validated using both simulated data and field data.The results show that the correction method is feasible and effective for isotropic media.When the field data are processed,the correction method normalizes the sources with different geological structures,which eliminates the geological difference among sources,and retains the geological difference among receivers.The correction results are in line with the expectation in whole.
基金supported by National Natural Science Foundation of China(Grant Nos.40772134)Open Research Program of the State Key Laboratory of Geological Processes and Mineral Resources,China University of Geosciences(Grant No.200643)
文摘The dating of the uplift onset of the Huangshan pluton in the southern part of Anhui Province associated with the collision between paleo-Pacific Block and the Eurasian Block is a fundamental issue to better understand the uplift mechanisms and the regional tectonic evolution. Х^2 values of seven zircon fission track （ZFF） samples collected from the south part of the Huangshan pluton were all 〈5%. Based on the grain ages of four typical ZFr samples, three thermal overprints ranging in 113-123, 72-95 and 49-66 Ma were distinguished respectively using the binomial peak-fitting method in accordance with the tectonic thermal events after south China shifted into circum-Pacific tectonic region. Apatite fission track （AFT） study of the Huangshan pluton shows ages lie between 15±3 and 56±6 Ma with all Х^2 values 〉5%, and all are significantly younger than their host rock formation ages, indicating that the samples have experienced post-formation thermal history. Based on the AFT resuits and topography characteristics in the Huangshan pluton, three zones with different denudation intensities caused by the differential uplift of the fault blocks were recognized in this paper, indicating that denudation was driven by the increase in elevation significantly. Modeling of the AFT data shows that the earlier cooling phase took place in the early Cenozoic and involved 3.3, 3.8 and 6.0℃/Ma of cooling rates equivalent to the exhumation rates of 90, 104 and 167 m/Ma in different fault blocks. The last phase of cooling took place from -10 Ma with average cooling rate of -5.6℃/Ma, equivalent to average denudation rates of -156 m/Ma. The fission track results imply that the regional compression field plays an important role for the differential exhumation between individual fault blocks of the Huangshan pluton.
