The Qarhan Salt Lake area is the Quaternary depocenter of the Qaidam Basin, and carries thick lacustrine sediments, as well as rich potassium and magnesium salt deposits. The abundant resources and thick sediments in ...The Qarhan Salt Lake area is the Quaternary depocenter of the Qaidam Basin, and carries thick lacustrine sediments, as well as rich potassium and magnesium salt deposits. The abundant resources and thick sediments in this lake provide an ideal place for the study of biogas formation and preservation, salt lake evolution, and the uplift of the Tibetan Plateau. In this study, we attempt to construct a paleomagnetic and ^(230)Th age model and to obtain information on tectonic activity and salt lake evolution through detailed studies on a 1300-m-long drill core(15DZK01) from the northwestern margin of the Qarhan Salt Lake area(Dongling Lake). Based on gypsum ^(230)Th dating, the age of the uppermost clastic deposit was calculated to be around 0.052 Ma. The polarity sequence consist of 13 pairs of normal and reversed zones,which can be correlated with subchrons C2r.1r-C1n of the geomagnetic polarity timescale(GPTS 2012)(from ~2.070 Ma to ~0.052 Ma). Sedimentary characteristics indicate that Dongling Lake witnessed freshwater environment between ~ 2.070 Ma and 1.546 Ma. During this period, the sedimentary record reflects primarily lakeshore, shallow-water and swamp environments, representing favourable conditions for the formation of hydrocarbon source rocks. Between 1.546 Ma and ~ 0.052 Ma, the Dongling Lake was in sulphate deposition stage, which contrasts with the central Qarhan Salt Lake area, where this stage did not occur in the meantime. During this stage, Dongling Lake was in a shallow saltwater lake environment, but several periods of reduced salinity occurred during this stage. During the late Pleistocene at ~0.052 Ma, the Dongling Lake experienced uplift due to tectonic activity, and saltwater migrated through the Sanhu Fault to the central Qarhan Salt Lake area, resulting in the absence of halite deposition stage. The residual saline water was concentrated into magnesium-rich brine due to the lack of freshwater, and few potassium salt deposits occur in the Dongling Lake area.展开更多
This paper carried out a study on U—Th—Pb behavior of zircons in a'dry'rock system during high-grade metamorphism in the Archean basement of eastern Shandong.The studied sample has a mineral assemblage of pl...This paper carried out a study on U—Th—Pb behavior of zircons in a'dry'rock system during high-grade metamorphism in the Archean basement of eastern Shandong.The studied sample has a mineral assemblage of plagioclase + K-feldspar + clinopyroxene + biotite + quartz and its protolith is considered to be diorite.The zircons are stubby,equant or irregular in shape and show fir-leaf, sectorial,banded or oscillatory zoning.They contain inclusions,including mineral assemblages of clinopyroxene + orthopyroxene + hornblende + quartz and plagioclase + K-feldspar + biotite + quartz. Fifty SHRIMP analyses were performed on 34 zircon grains,which commonly yielded high Th/U ratios (mostly>0.5).Most analyses are distributed along concordia from 2.54 to 2.25 Ga,with the youngest age being～1.95 Ga.Compositions and ages show large variations even in a same zircon grain.Combined with early studies,conclusions can be drawn as follows:1) the diorite underwent two episodes of high-grade metamorphism.at the end of the Neoarchean and the Paleoproterozoic(～2.50 Ga and～1.95 Ga or slightly later):2) high-grade metamorphism in a'dry'rock system may partially reset the U—Th—Pb system of zircons and.in this case,the ages between the oldest and youngest展开更多
Kimberlite and lamproite,the major source of diamonds,are volatile-rich potassic ultramafic rocks that originate from the deep lithospheric mantle.These rocks are important for deciphering the composition
Recently the (U\|Th)/He method on apatite has been applied to studies of cooling and exhumation in mountain belts in order to place constraints on the low temperature cooling history (Wolf et al., 1997; House et al., ...Recently the (U\|Th)/He method on apatite has been applied to studies of cooling and exhumation in mountain belts in order to place constraints on the low temperature cooling history (Wolf et al., 1997; House et al., 1998). Because the closure temperature of the method is 65～75℃, it provides useful information regarding the exhumation of rocks through the upper few kilometers of the earth’s crust. When the (U\|Th)/He method is coupled with methods such as 40 Ar/ 39 Ar with higher closure temperatures (210～500℃), a cooling history can be reconstructed over a wide range of temperatures. In eastern Nepal, in the Dudh Kosi valley a suite of samples from the Main Central Thrust (MCT) to the middle of the Higher Himalayan section was previously dated using 40 Ar/ 39 Ar on K\|feldspar, biotite, muscovite, and hornblende (Hubbard and Harrison,1989). We have applied the (U\|Th)/He method to apatite from these same samples. The structurally highest site, Ngozumba, is in the middle to upper part of the Higher Himalaya in the Gokyo valley. At Ngozumba previous 40 Ar/ 39 Ar ages include: muscovite at (16 6±0 4)Ma (closure temperature (CT)350℃), biotite at (16 8±1 4)Ma (CT 300℃), and K\|feldspar at (15 5±1 8)Ma (CT 250℃).The apatite age for an augen gneiss from this location was (6 3±3 8)Ma suggesting slower cooling for that part of the range during the last 15Ma. Structurally below Ngozumba, in the MCT zone, 40 Ar/ 39 Ar ages include:(20 9±0 2)Ma for hornblende (CT 500℃), (12 0±0 2)Ma for muscovite, and (8 0±0 2)Ma for K\|feldspar (CT 220℃). The apatite age obtained for a biotite schist at this location was (4 6±0 2)Ma and is consistent with relatively constant cooling since 12Ma. In between the MCT and the Ngozumba site samples were collected near the settlement of Ghat that yielded anomalously young 40 Ar/ 39 Ar ages:(7 7±0 4)Ma for muscovite, (7 5±0 6)Ma for biotite, and (3 6±0 2)Ma for K\|feldspar (CT 210℃). The apatite age is consistent with these young ages at (0 8±0 1)Ma. Plausible explanations for the young ages at this site include: post\|MCT age movement on a small\|scale shear zone or late\|stage movement of hydro\|thermal fluids through this localized zone. The MCT zone 40 Ar/ 39 Ar ages were used to constrain a one\|dimensional thermal model aimed at understanding rates of exhumation (Hubbard et al., 1991). The model yielded exhumation rates of 0 7～1 9km/Ma for the MCT zone region. The (U\|Th)/He age for apatite from this region is consistent with the model results. By coupling the (U\|Th)/He ages with the 40 Ar/ 39 Ar ages in this region we can determine that exhumation processes have acted at a relatively constant rate during the last 15～20 million years (with the possible exception of the Ghat location). Major fault activity likely pre\|dates this time period, or has had little affect on the cooling history.展开更多
For magmatic rocks,it is often found that zircon 206 Pb/238 U and 207 Pb/235 U ratios continuously plot on the concordia line with a relatively large age span for the same sample,which gives rise to large dating error...For magmatic rocks,it is often found that zircon 206 Pb/238 U and 207 Pb/235 U ratios continuously plot on the concordia line with a relatively large age span for the same sample,which gives rise to large dating errors or even unrealistic dating results.As the trace element concentrations of zircon can reflect its equilibrated magma characteristics,they can be used to determine whether all the analytical spots on the zircons selected to calculate the weighted mean age are cogenetic and formed in a single magma chamber.This work utilizes the results of zircon trace element concentrations and U-Pb isotopic analyses to explore the screening of reasonable U-Pb ages,which can be used to determine a more accurate intrusion crystallization age.The late Mesozoic Huayuangong granitic pluton complex,which is located in the Lower Yangtze region,eastern China,was selected for a case study.The Huayuangong pluton comprises the central intrusion and the marginal intrusion.Two samples from the marginal intrusion yielded consistent zircon weighted mean 206 Pb/238 U ages of 124.6±2.0 Ma and 125.9±1.6 Ma.These analytical spots also exhibit Zr/Hf and Th/U ratios concordant with the evolution of a single magma,from which the dated zircons crystallized.However,for the central intrusion,the analytical spots on zircons from two samples all show a continuous distribution on the concordia line with a relatively large age span.For each sample from the central intrusion,the zircon Zr/Hf ratios do not conform to a single magma evolutionary trend,but rather can be divided into two groups.We propose that zircon Zr/Hf ratios can provide a new constraint on U-Pb zircon dating and zircon Th/U ratios can also be used as a supplementary indicator to constrain zircon dating and determine the origins of the zircons and whether magma mixing has occurred.By screening zircon analytical spots using these two indicators,the two samples from the central intrusion of the Huayuangong pluton produce results of 122.8±4.3 Ma and 122.9±2.2 Ma,which are consistent with the field observations that the central intrusion is slightly younger than the marginal intrusion.展开更多
The Grove Mountains, 400 km south of the Chinese Antarctic Zhongshan Station, are an inland continuation of the Pan-African-aged (i.e., Late Neoproterozoic/Cambrian) Prydz Belt, East Antarctica. In this paper we carri...The Grove Mountains, 400 km south of the Chinese Antarctic Zhongshan Station, are an inland continuation of the Pan-African-aged (i.e., Late Neoproterozoic/Cambrian) Prydz Belt, East Antarctica. In this paper we carried out a combined U-Th-Pb monazite and Sm-Nd mineral-whole-rock dating on para-and orthogneisses from bedrock in the Grove Mountains. U-Th-Pb monazite dating of a cordierite-bearing pelitic paragneiss yields ages of 523 ± 4 Ma for the cores and 508 ± 6 Ma for the rims. Sm-Nd mineral-whole-rock isotopic analyses yield isochron ages of 536 ± 3 Ma for a coarse-grained felsic orthogneiss and 507 ± 30 Ma for a fine-grained quartzofeldspathic paragneiss. Combined with previously published age data in the Grove Mountains and adjacent areas, the older age of ～530 Ma is interpreted as the time of regional medium-to low-pressure granulite-facies metamorphism, and the younger age of ～510 Ma as the cooling age of the granulite terrane. The absence of evidence for a Grenville-aged (i.e., Late Mesoproterozoic/Early Neoproterozoic) metamorphic event indicates that the Grove Mountains have experienced only a single metamorphic cycle, i.e., Pan-African-aged, which distinguishes them from other polymetamorphic terranes in the Prydz Belt. This will provide important constraints on the controversial nature of the Prydz Belt.展开更多
Pitchblende mineralization was studied in the younger granite samples collected from Gabal Gattar, north Eastern Desert, Egypt using electron scanning microscope (ESM) and electron probe microanalyses (EPMA). This stu...Pitchblende mineralization was studied in the younger granite samples collected from Gabal Gattar, north Eastern Desert, Egypt using electron scanning microscope (ESM) and electron probe microanalyses (EPMA). This study revealed that this pitchblende contains significant Zr content reaching up to (66.80% ZrO2), which suggests that volcanic rocks were probably the source of such a deposit. High level emplaced high-K Calc-alkaline plutons as Qattar granite may have been associated with their volcanic equivalent emplaced in the surrounding area or now eroded. Lead content of the pitchblende mineralization is high and with moderate volcanics (up to 7.71% PbO). In contrast, it is low in ThO2, Y2O3 and REE2O3. High Zr and Pb content associated with pitchblende mineralization from Gattar granite indicates that the source of this mineralization derived from volcanic magma not from granitic magma. According to the calculation of U-Pb chemical ages using U, Th and Pb content measured with an electron microprobe for this pitchblende yielded ages within 543 - 657 Ma indicating a Pan-African age for this mineralization. This is the first time that a Pan-African age (543 to 657 Ma) is recorded for a U-mineralization in Gabal Gattar younger granite in the north Eastern Desert, Egypt.展开更多
On July 7th,the press conference of the 9th China (Dalang) International Woolen Knitwear Fair(WKF)was held at the Great Hall of the People in Beijing.Chen Shujin,Vice President of China National Textile and Apparel Co...On July 7th,the press conference of the 9th China (Dalang) International Woolen Knitwear Fair(WKF)was held at the Great Hall of the People in Beijing.Chen Shujin,Vice President of China National Textile and Apparel Council。展开更多
The Yuhuang hydrothermal field(YHF)is located between the Indomed and Gallieni fracture zones near the top of the off-axis slope on the south rift wall of Segment 29 on the ultraslow Southwest Indian Ridge(SWIR).Previ...The Yuhuang hydrothermal field(YHF)is located between the Indomed and Gallieni fracture zones near the top of the off-axis slope on the south rift wall of Segment 29 on the ultraslow Southwest Indian Ridge(SWIR).Previous studies have shown that sulfides in the YHF formed during different mineralization episodes and the YHF has the greatest potential for the formation of large-scale seafloor massive sulfide deposits.However,the sulfide chronology and hydrothermal activity of the YHF remain poorly constrained.In this study,mineralogical analyses and 230Th/U dating were performed.Hydrothermal activity may start about(35.9±2.3)ka from the southwest part of the YHF and may cease about(708±81)a ago from the northeast part of the YHF.The 74 nonzero chronological data from hydrothermal sulfide samples provide the first quantitative characterization of the spatial and temporal history along the SWIR.Hydrothermal activity in the SWIR has been relatively active over the past20 ka.In contrast,between 40 ka and 100 ka,hydrothermal activity was relatively infrequently and short in duration.The maximum activity occurred at 15–11 ka,9–7 ka,6–0.2 ka.There was a slight positive correlation between the maximal age and estimated surface area or estimated tonnage.The minimum mass accumulation rate of YHF is about 278 t/a,which is higher than most HFs related to ultramafic systems.The ultraslow spreading SWIR has the greatest potential to form large-scale seafloor massive sulfides(SMS)deposits.The results of this study provide new insights into the metallogenic mechanism of hydrothermal sulfides along ultraslow-spreading ridges.展开更多
基金co-supported by the Geological Survey Project of China(Grant No. 1212331413023)the National Natural Science Foundation of China(Grant No. U1407207)
文摘The Qarhan Salt Lake area is the Quaternary depocenter of the Qaidam Basin, and carries thick lacustrine sediments, as well as rich potassium and magnesium salt deposits. The abundant resources and thick sediments in this lake provide an ideal place for the study of biogas formation and preservation, salt lake evolution, and the uplift of the Tibetan Plateau. In this study, we attempt to construct a paleomagnetic and ^(230)Th age model and to obtain information on tectonic activity and salt lake evolution through detailed studies on a 1300-m-long drill core(15DZK01) from the northwestern margin of the Qarhan Salt Lake area(Dongling Lake). Based on gypsum ^(230)Th dating, the age of the uppermost clastic deposit was calculated to be around 0.052 Ma. The polarity sequence consist of 13 pairs of normal and reversed zones,which can be correlated with subchrons C2r.1r-C1n of the geomagnetic polarity timescale(GPTS 2012)(from ~2.070 Ma to ~0.052 Ma). Sedimentary characteristics indicate that Dongling Lake witnessed freshwater environment between ~ 2.070 Ma and 1.546 Ma. During this period, the sedimentary record reflects primarily lakeshore, shallow-water and swamp environments, representing favourable conditions for the formation of hydrocarbon source rocks. Between 1.546 Ma and ~ 0.052 Ma, the Dongling Lake was in sulphate deposition stage, which contrasts with the central Qarhan Salt Lake area, where this stage did not occur in the meantime. During this stage, Dongling Lake was in a shallow saltwater lake environment, but several periods of reduced salinity occurred during this stage. During the late Pleistocene at ~0.052 Ma, the Dongling Lake experienced uplift due to tectonic activity, and saltwater migrated through the Sanhu Fault to the central Qarhan Salt Lake area, resulting in the absence of halite deposition stage. The residual saline water was concentrated into magnesium-rich brine due to the lack of freshwater, and few potassium salt deposits occur in the Dongling Lake area.
基金supported by the Key Program of the Ministry of Land and Resources of China(Grant Nos.1212010811033, 1212010711815)
文摘This paper carried out a study on U—Th—Pb behavior of zircons in a'dry'rock system during high-grade metamorphism in the Archean basement of eastern Shandong.The studied sample has a mineral assemblage of plagioclase + K-feldspar + clinopyroxene + biotite + quartz and its protolith is considered to be diorite.The zircons are stubby,equant or irregular in shape and show fir-leaf, sectorial,banded or oscillatory zoning.They contain inclusions,including mineral assemblages of clinopyroxene + orthopyroxene + hornblende + quartz and plagioclase + K-feldspar + biotite + quartz. Fifty SHRIMP analyses were performed on 34 zircon grains,which commonly yielded high Th/U ratios (mostly>0.5).Most analyses are distributed along concordia from 2.54 to 2.25 Ga,with the youngest age being～1.95 Ga.Compositions and ages show large variations even in a same zircon grain.Combined with early studies,conclusions can be drawn as follows:1) the diorite underwent two episodes of high-grade metamorphism.at the end of the Neoarchean and the Paleoproterozoic(～2.50 Ga and～1.95 Ga or slightly later):2) high-grade metamorphism in a'dry'rock system may partially reset the U—Th—Pb system of zircons and.in this case,the ages between the oldest and youngest
文摘Kimberlite and lamproite,the major source of diamonds,are volatile-rich potassic ultramafic rocks that originate from the deep lithospheric mantle.These rocks are important for deciphering the composition
文摘Recently the (U\|Th)/He method on apatite has been applied to studies of cooling and exhumation in mountain belts in order to place constraints on the low temperature cooling history (Wolf et al., 1997; House et al., 1998). Because the closure temperature of the method is 65～75℃, it provides useful information regarding the exhumation of rocks through the upper few kilometers of the earth’s crust. When the (U\|Th)/He method is coupled with methods such as 40 Ar/ 39 Ar with higher closure temperatures (210～500℃), a cooling history can be reconstructed over a wide range of temperatures. In eastern Nepal, in the Dudh Kosi valley a suite of samples from the Main Central Thrust (MCT) to the middle of the Higher Himalayan section was previously dated using 40 Ar/ 39 Ar on K\|feldspar, biotite, muscovite, and hornblende (Hubbard and Harrison,1989). We have applied the (U\|Th)/He method to apatite from these same samples. The structurally highest site, Ngozumba, is in the middle to upper part of the Higher Himalaya in the Gokyo valley. At Ngozumba previous 40 Ar/ 39 Ar ages include: muscovite at (16 6±0 4)Ma (closure temperature (CT)350℃), biotite at (16 8±1 4)Ma (CT 300℃), and K\|feldspar at (15 5±1 8)Ma (CT 250℃).The apatite age for an augen gneiss from this location was (6 3±3 8)Ma suggesting slower cooling for that part of the range during the last 15Ma. Structurally below Ngozumba, in the MCT zone, 40 Ar/ 39 Ar ages include:(20 9±0 2)Ma for hornblende (CT 500℃), (12 0±0 2)Ma for muscovite, and (8 0±0 2)Ma for K\|feldspar (CT 220℃). The apatite age obtained for a biotite schist at this location was (4 6±0 2)Ma and is consistent with relatively constant cooling since 12Ma. In between the MCT and the Ngozumba site samples were collected near the settlement of Ghat that yielded anomalously young 40 Ar/ 39 Ar ages:(7 7±0 4)Ma for muscovite, (7 5±0 6)Ma for biotite, and (3 6±0 2)Ma for K\|feldspar (CT 210℃). The apatite age is consistent with these young ages at (0 8±0 1)Ma. Plausible explanations for the young ages at this site include: post\|MCT age movement on a small\|scale shear zone or late\|stage movement of hydro\|thermal fluids through this localized zone. The MCT zone 40 Ar/ 39 Ar ages were used to constrain a one\|dimensional thermal model aimed at understanding rates of exhumation (Hubbard et al., 1991). The model yielded exhumation rates of 0 7～1 9km/Ma for the MCT zone region. The (U\|Th)/He age for apatite from this region is consistent with the model results. By coupling the (U\|Th)/He ages with the 40 Ar/ 39 Ar ages in this region we can determine that exhumation processes have acted at a relatively constant rate during the last 15～20 million years (with the possible exception of the Ghat location). Major fault activity likely pre\|dates this time period, or has had little affect on the cooling history.
基金financially supported by the National Natural Science Foundation of China(Grant No.41672052)the National Key R&D Program of China(Grant No.2016YFC0600203)。
文摘For magmatic rocks,it is often found that zircon 206 Pb/238 U and 207 Pb/235 U ratios continuously plot on the concordia line with a relatively large age span for the same sample,which gives rise to large dating errors or even unrealistic dating results.As the trace element concentrations of zircon can reflect its equilibrated magma characteristics,they can be used to determine whether all the analytical spots on the zircons selected to calculate the weighted mean age are cogenetic and formed in a single magma chamber.This work utilizes the results of zircon trace element concentrations and U-Pb isotopic analyses to explore the screening of reasonable U-Pb ages,which can be used to determine a more accurate intrusion crystallization age.The late Mesozoic Huayuangong granitic pluton complex,which is located in the Lower Yangtze region,eastern China,was selected for a case study.The Huayuangong pluton comprises the central intrusion and the marginal intrusion.Two samples from the marginal intrusion yielded consistent zircon weighted mean 206 Pb/238 U ages of 124.6±2.0 Ma and 125.9±1.6 Ma.These analytical spots also exhibit Zr/Hf and Th/U ratios concordant with the evolution of a single magma,from which the dated zircons crystallized.However,for the central intrusion,the analytical spots on zircons from two samples all show a continuous distribution on the concordia line with a relatively large age span.For each sample from the central intrusion,the zircon Zr/Hf ratios do not conform to a single magma evolutionary trend,but rather can be divided into two groups.We propose that zircon Zr/Hf ratios can provide a new constraint on U-Pb zircon dating and zircon Th/U ratios can also be used as a supplementary indicator to constrain zircon dating and determine the origins of the zircons and whether magma mixing has occurred.By screening zircon analytical spots using these two indicators,the two samples from the central intrusion of the Huayuangong pluton produce results of 122.8±4.3 Ma and 122.9±2.2 Ma,which are consistent with the field observations that the central intrusion is slightly younger than the marginal intrusion.
基金financial support from the National Natural Science Foundation of China (Grant no.41530209)the Central Public-Interest Scientific Institution Basal Research Fund (Grant no.JYYWF201819)
文摘The Grove Mountains, 400 km south of the Chinese Antarctic Zhongshan Station, are an inland continuation of the Pan-African-aged (i.e., Late Neoproterozoic/Cambrian) Prydz Belt, East Antarctica. In this paper we carried out a combined U-Th-Pb monazite and Sm-Nd mineral-whole-rock dating on para-and orthogneisses from bedrock in the Grove Mountains. U-Th-Pb monazite dating of a cordierite-bearing pelitic paragneiss yields ages of 523 ± 4 Ma for the cores and 508 ± 6 Ma for the rims. Sm-Nd mineral-whole-rock isotopic analyses yield isochron ages of 536 ± 3 Ma for a coarse-grained felsic orthogneiss and 507 ± 30 Ma for a fine-grained quartzofeldspathic paragneiss. Combined with previously published age data in the Grove Mountains and adjacent areas, the older age of ～530 Ma is interpreted as the time of regional medium-to low-pressure granulite-facies metamorphism, and the younger age of ～510 Ma as the cooling age of the granulite terrane. The absence of evidence for a Grenville-aged (i.e., Late Mesoproterozoic/Early Neoproterozoic) metamorphic event indicates that the Grove Mountains have experienced only a single metamorphic cycle, i.e., Pan-African-aged, which distinguishes them from other polymetamorphic terranes in the Prydz Belt. This will provide important constraints on the controversial nature of the Prydz Belt.
文摘Pitchblende mineralization was studied in the younger granite samples collected from Gabal Gattar, north Eastern Desert, Egypt using electron scanning microscope (ESM) and electron probe microanalyses (EPMA). This study revealed that this pitchblende contains significant Zr content reaching up to (66.80% ZrO2), which suggests that volcanic rocks were probably the source of such a deposit. High level emplaced high-K Calc-alkaline plutons as Qattar granite may have been associated with their volcanic equivalent emplaced in the surrounding area or now eroded. Lead content of the pitchblende mineralization is high and with moderate volcanics (up to 7.71% PbO). In contrast, it is low in ThO2, Y2O3 and REE2O3. High Zr and Pb content associated with pitchblende mineralization from Gattar granite indicates that the source of this mineralization derived from volcanic magma not from granitic magma. According to the calculation of U-Pb chemical ages using U, Th and Pb content measured with an electron microprobe for this pitchblende yielded ages within 543 - 657 Ma indicating a Pan-African age for this mineralization. This is the first time that a Pan-African age (543 to 657 Ma) is recorded for a U-mineralization in Gabal Gattar younger granite in the north Eastern Desert, Egypt.
文摘On July 7th,the press conference of the 9th China (Dalang) International Woolen Knitwear Fair(WKF)was held at the Great Hall of the People in Beijing.Chen Shujin,Vice President of China National Textile and Apparel Council。
基金The National Key R&D Program of China under contract No.2022YFE0140200the National Natural Science Foundation of China under contract Nos 42127807 and 42006074+1 种基金the China Ocean Mineral Resources R&D Association Project under contract Nos DY135-S1-1-02 and DY135-S1-1-01the Macao Science and Technology Development Fund under contract No.FDCT-002/2018/A1。
文摘The Yuhuang hydrothermal field(YHF)is located between the Indomed and Gallieni fracture zones near the top of the off-axis slope on the south rift wall of Segment 29 on the ultraslow Southwest Indian Ridge(SWIR).Previous studies have shown that sulfides in the YHF formed during different mineralization episodes and the YHF has the greatest potential for the formation of large-scale seafloor massive sulfide deposits.However,the sulfide chronology and hydrothermal activity of the YHF remain poorly constrained.In this study,mineralogical analyses and 230Th/U dating were performed.Hydrothermal activity may start about(35.9±2.3)ka from the southwest part of the YHF and may cease about(708±81)a ago from the northeast part of the YHF.The 74 nonzero chronological data from hydrothermal sulfide samples provide the first quantitative characterization of the spatial and temporal history along the SWIR.Hydrothermal activity in the SWIR has been relatively active over the past20 ka.In contrast,between 40 ka and 100 ka,hydrothermal activity was relatively infrequently and short in duration.The maximum activity occurred at 15–11 ka,9–7 ka,6–0.2 ka.There was a slight positive correlation between the maximal age and estimated surface area or estimated tonnage.The minimum mass accumulation rate of YHF is about 278 t/a,which is higher than most HFs related to ultramafic systems.The ultraslow spreading SWIR has the greatest potential to form large-scale seafloor massive sulfides(SMS)deposits.The results of this study provide new insights into the metallogenic mechanism of hydrothermal sulfides along ultraslow-spreading ridges.
