Granites play a crucial role in the Earth's thermal regime and its evolution.Radiogenic heat production(RHP)by the decay of radioactive elements(U,Th,K)in granites is a significant parameter in estimating the ther...Granites play a crucial role in the Earth's thermal regime and its evolution.Radiogenic heat production(RHP)by the decay of radioactive elements(U,Th,K)in granites is a significant parameter in estimating the thermal structure of the lithosphere.RHP variability of granites with their emplacement ages could provide insights for thermal modeling in different geological epochs.An aggregated RHP from 2877 globally-distributed granitic samples of continental crust are analyzed for this study;these sample cover the entire geological history.The average bulk RHP in all types of granitic rocks of all ages is 2.92±1.86μW/m^(3).The RHP tends to increase gradually with progressively younger geologic emplacement age,based on a statistical analysis of the data.However,the youngest granites do not necessarily have the highest RHP.The mean RHP in 181 representative Cenozoic Himalayan leucogranitesdwhich are the youngest granites found on Earth,is as low as 1.84μW/m^(3).This is probably related to the initial conditions of magma formation,magmatic source material,and differentiation processes in the HimalayaneTibetan plateau.By correcting the decay factor,variations of the RHP in the emplaced granitic rocks are obtained,indicating the changing levels of heat production and different thermal regimes on Earth in various geological epochs.The highest RHP in granitic rocks emplaced in the Archean and Early Proterozoic corresponds to two global-scale collisional events during supercontinent cycles,at 2.7 and 1.9 Ga respectively.RHPs of granites can be an important indicator in the study of Earth's thermal regime and its evolution.展开更多
The presence of geothermal manifestation in Bangka Island(Southeast Sumatra,Indonesia)with the absence of Quaternary volcanic activity and also relatively low seismicity events has raised intriguing questions on the c...The presence of geothermal manifestation in Bangka Island(Southeast Sumatra,Indonesia)with the absence of Quaternary volcanic activity and also relatively low seismicity events has raised intriguing questions on the control of the geothermal system in this area.As the regional tectonic setting of Indonesia volcanic geothermal systems has been known,that of non-volcanic geothermal systems such as radiogenic system become an issue to be investigated.This study reports the geochemistry and petrography analysis of Triassic granite related to radiogenic production at the vicinity of hot springs in Bangka Island.Surface temperatures of the Bangka hot springs range from 37 to 70.7 and pH values vary between 5.6 and 7.5.These hot springs are discharging either in close to massive granite bodies or occur in between two major NE-SW striking faults zones,i.e.,Pemali fault and Payung fault.Our results indicate the average radiogenic heat production of Late Triassic Klabat granite in the northern area ranges from 28.5 to 38.34μWm^(-3)and the southern area ranges from 28.3 to 49.5μWm^(-3).In comparison to similar granite belt located in Malaysia,heat production of granitoid in Bangka hot springs is four times higher,possibly due to their different granite origins.展开更多
The Mianhuakeng uranium deposit,characterized by uranium-rich granite,serves as a key site for research into crustal radioactive heating.Based on 45 rock samples,this study reviews that the host granite in the Mianhua...The Mianhuakeng uranium deposit,characterized by uranium-rich granite,serves as a key site for research into crustal radioactive heating.Based on 45 rock samples,this study reviews that the host granite in the Mianhuakeng uranium deposit has a high radioactive heat production rate(avg.5.50μW/m³)and a low Th/U ratio(avg.2.62).Uranium-rich granite and its alteration zone within the upper crust(0-5 km depth)contribute about 45%of the total radioactive heat production,wich is crucial for controlling geothermal resource distribution.For uranium-thermal at tectonic plate margins,a symbiotic geological model was proposed:Firstly,subduction of the Pacific Plate caused upwelling of the asthenosphere,generating a high heat-flow background.Secondly,heat transfer is enhanced by major faults such as the Youdong and Mianhuakeng faults.Subsequently,uranium was mobilized,transported,and enriched within the granite through deep siliceous hydrothermal activity and associated alteration.Ultimately,the uranium enrichment in granite leads to increased radioactive heat production,resulting in local thermal anomalies.This model provides a theoretical support for exploring and developing uranium-thermal symbiotic resources in South China.展开更多
Hot dry rock(HDR)is an important geothermal resource and clean energy source that may play an increasingly important role in future energy management.High-temperature HDR resources were recently detected in deep regio...Hot dry rock(HDR)is an important geothermal resource and clean energy source that may play an increasingly important role in future energy management.High-temperature HDR resources were recently detected in deep regions of the Gonghe Basin on the northeastern edge of the Tibetan Plateau,which led to a significant breakthrough in HDR resource exploration in China.This research analyzes the deep temperature distribution,radiogenic heat production,heat flow,and crustal thermal structure in the Qiaboqia Valley,Guide Plain,and Zhacanggou area of the Gonghe Basin based on geothermal exploration borehole logging data,rock thermophysical properties,and regional geophysical exploration data.The results are applied to discuss the heat accumulation mechanism of the HDR resources in the Gonghe Basin.The findings suggest that a low-velocity layer in the thickened crust of the Tibetan Plateau provides the most important source of constant intracrustal heat for the formation of HDR resources in the Gonghe Basin,whereas crustal thickening redistributes the concentrated layer of radioactive elements,which compensates for the relatively low heat production of the basal granite and serves as an important supplement to the heat of the HDR resources.The negative effect is that the downward curvature of the lithospheric upper mantle caused by crustal thickening leads to a small mantle heat flow component.As a result,the heat flows in the Qiaboqia Valley and Guide Plain of the Gonghe Basin are 106.2 and 77.6 m W/m2,respectively,in which the crust-mantle heat flow ratio of the former is 3.12:1,indicating a notably anomalous intracrustal thermal structure.In contrast,the crust-mantle heat flow ratio in the Guide Plain is 1.84:1,which reflects a typical hot crust-cold mantle thermal structure.The Guide Plain and Zhacanggou area show the same increasing temperature trend with depth,which reflects that their geothermal backgrounds and deep high-temperature environments are similar.These results provide important insight on the heat source mechanism of HDR resource formation in the Tibetan Plateau and useful guidance for future HDR resource exploration projects and target sites selection in similar areas.展开更多
The Qinghai Gonghe-Guide Basin together with the alternatively distributed mountainous region shows characteristics that the conductive geothermal resource of the basin has high geothermal gradient, the granite occurs...The Qinghai Gonghe-Guide Basin together with the alternatively distributed mountainous region shows characteristics that the conductive geothermal resource of the basin has high geothermal gradient, the granite occurs in the bottom of borehole for geothermal exploration, and the convective hot springs in the basin-edge uplift fracture are in zonal distribution and with high-temperature geothermal water. There are still some divergences about the heat source mechanism of the basin. In this paper, queries to the view of mantle-derived heat source have been put forward, coming up with geochemical evidences to prove that the radiogenic heat of granite is the heat source within the mantle. Additionally, temperature curve is drawn based on the geothermal boring and geochemical geothermometer has been adopted for an estimation of the temperature and depth of the geothermal reservoir, it has been found that the surrounding mountains belong to the medium-temperature geothermal system while the area within the basin belongs to the high-temperature geothermal system with the temperature of borehole bottom reaching up to 175-180 ℃. In this paper, discussions on the problems existing in the calculation of geothermal gradient and the differences generated by the geothermal system have been carried out.展开更多
With the progress of science and technology, human beings explore the energy underground with thousands of meters. As a thermophysical parameter, initial formation temperature （IFT） plays an essential role in deep w...With the progress of science and technology, human beings explore the energy underground with thousands of meters. As a thermophysical parameter, initial formation temperature （IFT） plays an essential role in deep well engineering. However, it is not easy to predict the IFT accurately before drilling. This work uses a new method to analyze the effect factors of the underground temperature field, and assumes an artificial surface to eliminate the disturbance of the human errors and equipment errors on the surface temperature and thermal conductivity. Considering different distributions of the formation thermal conductivity and the rock radiogenic heat production, an optimized model was established. With this model, the paper predicted the bottom temperature of the main hole of the Chinese Continental Scientific Drilling （CCSD） as 132.80 ℃ at 4 725 m depth with 0.5% error. When the thermal conduction is dominant in the formation, this simple method can predict the IFT distribution effectively for deep well in the exploration stage. However, it is almost impossible to avoid aquifers in the formation of drilling deep well, an existing drillhole including groundwater is needed to predict for testing the model＇s accuracy.展开更多
The Rb-Sr whole-rock isochron,age 1636±66 Ma of Mirgarani granite,is the one of the oldest granite dated in the northwestern part of the Chhotanagpur Granite Gneiss Complex(CGGC).The initial Sr ratio is 0.715...The Rb-Sr whole-rock isochron,age 1636±66 Ma of Mirgarani granite,is the one of the oldest granite dated in the northwestern part of the Chhotanagpur Granite Gneiss Complex(CGGC).The initial Sr ratio is 0.715±0.012(MSWD=0.11),showing an S-type affinity.The Mirgarani granite has intruded the migmatite complex of the Dudhi Group and forms the Mirgarani formation comparable to the granites of the Bihar Mica Belt around Hazaribagh(1590±30 Ma).The present studies have established the chronostratigraphy of the Dudhi Group and adjoining areas in CGGC.Petro-graphic and geochemical studies revealed that the granite is enriched in Rb(271 ppm),Pb(77 ppm),Th(25 ppm),and U(33 ppm)and depleted in Sr(95 ppm),Nb(16 ppm),Ba(399 ppm)and Zr(143 ppm)contents as compared to the normal granite.The Mirgarani granite is a peraluminous(A/CNK=1.23),high potassic(K_(2)O 6.42%),Calc-Alkalic to Alkali-Calcic{(Na_(2)O+K_(2)O)-CaO=6.29}S-Type granite,a feature supported by the presence of modal garnet and normative corundum(2.68%).The Mirgarani granite is considered to have been formed by the anatexis of a crustal sedimentary protolith at a depth of approximately 30 km with temperatures ranging from 685-700℃ during the Co-lumbian-Nuna Supercontinent.展开更多
Early Palaeozoic Cambrian A-type Kathalguri Granites in the Mikir Hills of northeastern (NE) India were studied to better understand the geodynamic settings in this region. This research presents new whole-rock geoche...Early Palaeozoic Cambrian A-type Kathalguri Granites in the Mikir Hills of northeastern (NE) India were studied to better understand the geodynamic settings in this region. This research presents new whole-rock geochemical and Sr, Nd, Pb isotopic data for the Cambrian granites in the Kathalguri Granite in Mikir Hills. The Kathalguri Granite shows geochemical characteristics of high SiO2, K2O and low FeOT, MgO, CaO, and P2O5 compositions. They belong to a high K Shoshonite to ultra-potassic series and display a weak metaluminous to peraluminous feature with A/CNK values of 0.83 to 1.02 with corundum and anorthite normative. FeOT/MgO varies from 2.93 - 7.49, is moderately oxidized and belongs to magnetite series. The rocks have a high ΣREE composition of 370.80 - 1353.23 ppm (average 568.55) and are enriched in LREE with flat HREE and (La/Yb)N values of 8.10 - 18.99, and display obvious strong negative Eu anomalies. Trace elements of the studied granites are characterized by enrichment in Rb, Th, U, Pb, Hf, and Sm, and depletion of Ba, Nb, Ta, and Sr. They display geochemical features of high Zr + Y + Nb + Ce values (241 - 934 ppm) and Ga/Al ratios 2.49 - 3.01 consistent with A-Type granites. Based on particular geochemical features, such as high Rb/Nb (3.10 - 19.53) and Low Y/Nb (0.09 - 2.28), Kathalguri Granite can be further classified as an A1-type subgroup. Granites display relatively low Sr (N ratio varying between 0.53 - 0.89 suggesting that the melts generated at greater depths (18 - 40 km), and fractionation at low pressures (−3 and total HGU 98.96 to 214.20. Kathalguri Granite dated by Rb-Sr isotopic isochrone as 489 ± 19 Ma with an initial 87Sr/86Sr 0.7199 ± 0.0017 and MSWD of 4.1, εSr(I) varied between 161.62 - 332.08 suggests that the Kathalguri Granite have originated from partial melting of ancient, evolved continental crustal material. The Sm-Nd Systematics has given a depleted mantle model (TDM) age ranging from 1733 - 2063 Ma with high negative εNd(t) values (−10.39 to −15.18) also hint at some heterogeneity or multiple source contributions in the melting process of the protolith. Xenoliths of older mafic rocks and Barapani arenites are seen within the Kathalguri Granite and are also supported by geochemical signatures of recycled crustal materials both mafic and sedimentary. It formed during the Cambrian reorganization of lithospheric plate motion related to the Pan-African-Braziliano event.展开更多
The U-Th-40K concentrations of granite are on 1–2 orders of magnitude greater than those of basaltic-ultrabasic rocks. Radiogenic heat of a granitic melt has significant influence on the cooling-crystallization perio...The U-Th-40K concentrations of granite are on 1–2 orders of magnitude greater than those of basaltic-ultrabasic rocks. Radiogenic heat of a granitic melt has significant influence on the cooling-crystallization period of the melt. In this paper we derived a formula to calculate prolongation period (t A) of cooling-crystallization of a granitic melt caused by radiogenic heat. Calculation using this formula and radioactive element concentrations (U=5.31×10?6; Th=23.1×10?6; K=4.55%) for the biotite adamellite of the Jinjiling batholith shows that the t A of the adamellite is 1.4 times of the cooling period of the granitic melt without considering radiogenic heat from the initial temperature (T m=960°C) to crystallization temperature (T c=600°C) of the melt. It has been demonstrated that the radiogenic heat produced in a granitic melt is a key factor influencing the cooling-crystallization process of the granitic melt, and is likely one of the reasons for inconsistence between emplacement ages and crystallization ages of many Meso-Cenozoic granitoids.展开更多
基金supported by National Key Research and Development projects(No.2019YFC0604903,No.2021YFA0716004)by Joint Funds of the National Natural Science Foundation of China(Grant No.U20B6001).
文摘Granites play a crucial role in the Earth's thermal regime and its evolution.Radiogenic heat production(RHP)by the decay of radioactive elements(U,Th,K)in granites is a significant parameter in estimating the thermal structure of the lithosphere.RHP variability of granites with their emplacement ages could provide insights for thermal modeling in different geological epochs.An aggregated RHP from 2877 globally-distributed granitic samples of continental crust are analyzed for this study;these sample cover the entire geological history.The average bulk RHP in all types of granitic rocks of all ages is 2.92±1.86μW/m^(3).The RHP tends to increase gradually with progressively younger geologic emplacement age,based on a statistical analysis of the data.However,the youngest granites do not necessarily have the highest RHP.The mean RHP in 181 representative Cenozoic Himalayan leucogranitesdwhich are the youngest granites found on Earth,is as low as 1.84μW/m^(3).This is probably related to the initial conditions of magma formation,magmatic source material,and differentiation processes in the HimalayaneTibetan plateau.By correcting the decay factor,variations of the RHP in the emplaced granitic rocks are obtained,indicating the changing levels of heat production and different thermal regimes on Earth in various geological epochs.The highest RHP in granitic rocks emplaced in the Archean and Early Proterozoic corresponds to two global-scale collisional events during supercontinent cycles,at 2.7 and 1.9 Ga respectively.RHPs of granites can be an important indicator in the study of Earth's thermal regime and its evolution.
基金upported by Penelitian Disertasi Doktor grant of Ministry of Education,Culture,Research and Technology of Indonesia(0267/E5/AK.04/2022)scholarship from Institut Teknologi Sumatera.
文摘The presence of geothermal manifestation in Bangka Island(Southeast Sumatra,Indonesia)with the absence of Quaternary volcanic activity and also relatively low seismicity events has raised intriguing questions on the control of the geothermal system in this area.As the regional tectonic setting of Indonesia volcanic geothermal systems has been known,that of non-volcanic geothermal systems such as radiogenic system become an issue to be investigated.This study reports the geochemistry and petrography analysis of Triassic granite related to radiogenic production at the vicinity of hot springs in Bangka Island.Surface temperatures of the Bangka hot springs range from 37 to 70.7 and pH values vary between 5.6 and 7.5.These hot springs are discharging either in close to massive granite bodies or occur in between two major NE-SW striking faults zones,i.e.,Pemali fault and Payung fault.Our results indicate the average radiogenic heat production of Late Triassic Klabat granite in the northern area ranges from 28.5 to 38.34μWm^(-3)and the southern area ranges from 28.3 to 49.5μWm^(-3).In comparison to similar granite belt located in Malaysia,heat production of granitoid in Bangka hot springs is four times higher,possibly due to their different granite origins.
基金supported by the National Natural Science Foundation of China(41902310,42372348,42372286)Deep Earth Probe and Mineral Resources Exploration-National Science and Technology Major Project(2024ZD1003607)+2 种基金China Geological Survey Projects(DD20230700802,DD20221819)the Basic Research Fund of the Chinese Academy of Geological Sciences(JKYQN202306)Key Research and Development Program of Shanxi Province,China(202102090301009).
文摘The Mianhuakeng uranium deposit,characterized by uranium-rich granite,serves as a key site for research into crustal radioactive heating.Based on 45 rock samples,this study reviews that the host granite in the Mianhuakeng uranium deposit has a high radioactive heat production rate(avg.5.50μW/m³)and a low Th/U ratio(avg.2.62).Uranium-rich granite and its alteration zone within the upper crust(0-5 km depth)contribute about 45%of the total radioactive heat production,wich is crucial for controlling geothermal resource distribution.For uranium-thermal at tectonic plate margins,a symbiotic geological model was proposed:Firstly,subduction of the Pacific Plate caused upwelling of the asthenosphere,generating a high heat-flow background.Secondly,heat transfer is enhanced by major faults such as the Youdong and Mianhuakeng faults.Subsequently,uranium was mobilized,transported,and enriched within the granite through deep siliceous hydrothermal activity and associated alteration.Ultimately,the uranium enrichment in granite leads to increased radioactive heat production,resulting in local thermal anomalies.This model provides a theoretical support for exploring and developing uranium-thermal symbiotic resources in South China.
基金supported by National Key R&D Program of China(Grant No.2018YFB1501803)。
文摘Hot dry rock(HDR)is an important geothermal resource and clean energy source that may play an increasingly important role in future energy management.High-temperature HDR resources were recently detected in deep regions of the Gonghe Basin on the northeastern edge of the Tibetan Plateau,which led to a significant breakthrough in HDR resource exploration in China.This research analyzes the deep temperature distribution,radiogenic heat production,heat flow,and crustal thermal structure in the Qiaboqia Valley,Guide Plain,and Zhacanggou area of the Gonghe Basin based on geothermal exploration borehole logging data,rock thermophysical properties,and regional geophysical exploration data.The results are applied to discuss the heat accumulation mechanism of the HDR resources in the Gonghe Basin.The findings suggest that a low-velocity layer in the thickened crust of the Tibetan Plateau provides the most important source of constant intracrustal heat for the formation of HDR resources in the Gonghe Basin,whereas crustal thickening redistributes the concentrated layer of radioactive elements,which compensates for the relatively low heat production of the basal granite and serves as an important supplement to the heat of the HDR resources.The negative effect is that the downward curvature of the lithospheric upper mantle caused by crustal thickening leads to a small mantle heat flow component.As a result,the heat flows in the Qiaboqia Valley and Guide Plain of the Gonghe Basin are 106.2 and 77.6 m W/m2,respectively,in which the crust-mantle heat flow ratio of the former is 3.12:1,indicating a notably anomalous intracrustal thermal structure.In contrast,the crust-mantle heat flow ratio in the Guide Plain is 1.84:1,which reflects a typical hot crust-cold mantle thermal structure.The Guide Plain and Zhacanggou area show the same increasing temperature trend with depth,which reflects that their geothermal backgrounds and deep high-temperature environments are similar.These results provide important insight on the heat source mechanism of HDR resource formation in the Tibetan Plateau and useful guidance for future HDR resource exploration projects and target sites selection in similar areas.
文摘The Qinghai Gonghe-Guide Basin together with the alternatively distributed mountainous region shows characteristics that the conductive geothermal resource of the basin has high geothermal gradient, the granite occurs in the bottom of borehole for geothermal exploration, and the convective hot springs in the basin-edge uplift fracture are in zonal distribution and with high-temperature geothermal water. There are still some divergences about the heat source mechanism of the basin. In this paper, queries to the view of mantle-derived heat source have been put forward, coming up with geochemical evidences to prove that the radiogenic heat of granite is the heat source within the mantle. Additionally, temperature curve is drawn based on the geothermal boring and geochemical geothermometer has been adopted for an estimation of the temperature and depth of the geothermal reservoir, it has been found that the surrounding mountains belong to the medium-temperature geothermal system while the area within the basin belongs to the high-temperature geothermal system with the temperature of borehole bottom reaching up to 175-180 ℃. In this paper, discussions on the problems existing in the calculation of geothermal gradient and the differences generated by the geothermal system have been carried out.
文摘With the progress of science and technology, human beings explore the energy underground with thousands of meters. As a thermophysical parameter, initial formation temperature （IFT） plays an essential role in deep well engineering. However, it is not easy to predict the IFT accurately before drilling. This work uses a new method to analyze the effect factors of the underground temperature field, and assumes an artificial surface to eliminate the disturbance of the human errors and equipment errors on the surface temperature and thermal conductivity. Considering different distributions of the formation thermal conductivity and the rock radiogenic heat production, an optimized model was established. With this model, the paper predicted the bottom temperature of the main hole of the Chinese Continental Scientific Drilling （CCSD） as 132.80 ℃ at 4 725 m depth with 0.5% error. When the thermal conduction is dominant in the formation, this simple method can predict the IFT distribution effectively for deep well in the exploration stage. However, it is almost impossible to avoid aquifers in the formation of drilling deep well, an existing drillhole including groundwater is needed to predict for testing the model＇s accuracy.
文摘The Rb-Sr whole-rock isochron,age 1636±66 Ma of Mirgarani granite,is the one of the oldest granite dated in the northwestern part of the Chhotanagpur Granite Gneiss Complex(CGGC).The initial Sr ratio is 0.715±0.012(MSWD=0.11),showing an S-type affinity.The Mirgarani granite has intruded the migmatite complex of the Dudhi Group and forms the Mirgarani formation comparable to the granites of the Bihar Mica Belt around Hazaribagh(1590±30 Ma).The present studies have established the chronostratigraphy of the Dudhi Group and adjoining areas in CGGC.Petro-graphic and geochemical studies revealed that the granite is enriched in Rb(271 ppm),Pb(77 ppm),Th(25 ppm),and U(33 ppm)and depleted in Sr(95 ppm),Nb(16 ppm),Ba(399 ppm)and Zr(143 ppm)contents as compared to the normal granite.The Mirgarani granite is a peraluminous(A/CNK=1.23),high potassic(K_(2)O 6.42%),Calc-Alkalic to Alkali-Calcic{(Na_(2)O+K_(2)O)-CaO=6.29}S-Type granite,a feature supported by the presence of modal garnet and normative corundum(2.68%).The Mirgarani granite is considered to have been formed by the anatexis of a crustal sedimentary protolith at a depth of approximately 30 km with temperatures ranging from 685-700℃ during the Co-lumbian-Nuna Supercontinent.
文摘Early Palaeozoic Cambrian A-type Kathalguri Granites in the Mikir Hills of northeastern (NE) India were studied to better understand the geodynamic settings in this region. This research presents new whole-rock geochemical and Sr, Nd, Pb isotopic data for the Cambrian granites in the Kathalguri Granite in Mikir Hills. The Kathalguri Granite shows geochemical characteristics of high SiO2, K2O and low FeOT, MgO, CaO, and P2O5 compositions. They belong to a high K Shoshonite to ultra-potassic series and display a weak metaluminous to peraluminous feature with A/CNK values of 0.83 to 1.02 with corundum and anorthite normative. FeOT/MgO varies from 2.93 - 7.49, is moderately oxidized and belongs to magnetite series. The rocks have a high ΣREE composition of 370.80 - 1353.23 ppm (average 568.55) and are enriched in LREE with flat HREE and (La/Yb)N values of 8.10 - 18.99, and display obvious strong negative Eu anomalies. Trace elements of the studied granites are characterized by enrichment in Rb, Th, U, Pb, Hf, and Sm, and depletion of Ba, Nb, Ta, and Sr. They display geochemical features of high Zr + Y + Nb + Ce values (241 - 934 ppm) and Ga/Al ratios 2.49 - 3.01 consistent with A-Type granites. Based on particular geochemical features, such as high Rb/Nb (3.10 - 19.53) and Low Y/Nb (0.09 - 2.28), Kathalguri Granite can be further classified as an A1-type subgroup. Granites display relatively low Sr (N ratio varying between 0.53 - 0.89 suggesting that the melts generated at greater depths (18 - 40 km), and fractionation at low pressures (−3 and total HGU 98.96 to 214.20. Kathalguri Granite dated by Rb-Sr isotopic isochrone as 489 ± 19 Ma with an initial 87Sr/86Sr 0.7199 ± 0.0017 and MSWD of 4.1, εSr(I) varied between 161.62 - 332.08 suggests that the Kathalguri Granite have originated from partial melting of ancient, evolved continental crustal material. The Sm-Nd Systematics has given a depleted mantle model (TDM) age ranging from 1733 - 2063 Ma with high negative εNd(t) values (−10.39 to −15.18) also hint at some heterogeneity or multiple source contributions in the melting process of the protolith. Xenoliths of older mafic rocks and Barapani arenites are seen within the Kathalguri Granite and are also supported by geochemical signatures of recycled crustal materials both mafic and sedimentary. It formed during the Cambrian reorganization of lithospheric plate motion related to the Pan-African-Braziliano event.
基金Supported by the National Natural Science Foundation of China (Grant Nos. 40372036 and 40221301)
文摘The U-Th-40K concentrations of granite are on 1–2 orders of magnitude greater than those of basaltic-ultrabasic rocks. Radiogenic heat of a granitic melt has significant influence on the cooling-crystallization period of the melt. In this paper we derived a formula to calculate prolongation period (t A) of cooling-crystallization of a granitic melt caused by radiogenic heat. Calculation using this formula and radioactive element concentrations (U=5.31×10?6; Th=23.1×10?6; K=4.55%) for the biotite adamellite of the Jinjiling batholith shows that the t A of the adamellite is 1.4 times of the cooling period of the granitic melt without considering radiogenic heat from the initial temperature (T m=960°C) to crystallization temperature (T c=600°C) of the melt. It has been demonstrated that the radiogenic heat produced in a granitic melt is a key factor influencing the cooling-crystallization process of the granitic melt, and is likely one of the reasons for inconsistence between emplacement ages and crystallization ages of many Meso-Cenozoic granitoids.
