The tectonic environment of granitoids has always been a concern of the academic community.The Nb vs.Y and Rb vs.Nb+Y diagrams have had a substantial impact.The present work uses more than 110,000 granitoid samples(Si...The tectonic environment of granitoids has always been a concern of the academic community.The Nb vs.Y and Rb vs.Nb+Y diagrams have had a substantial impact.The present work uses more than 110,000 granitoid samples(SiO_(2)≥56%)from the globally shared database to discuss the validity and also explain why these diagrams used for discrimination between the different tectonic settings of granitoid rocks.The amount of data from the spreading center is sparse and the data are highly scattered and so,the present study focuses mainly on granites from the ocean islands and convergent margins tectonic environments.On the TAS diagram most of the ocean island data are alkaline series and trachybasalt series,and some are bimodal.In contrast,the granitoids on the convergent margin are mainly sub-alkaline.This work shows that the tectonic discrimination diagrams of granitoids remain valid,and only the boundaries need to be slightly adjusted.展开更多
Geochemistry is a powerful tool to help characterize the tectonic setting of igneous rocks associations.However,when continental mafic dykes and flood basalts are the target most of the proposed geochemical discrimina...Geochemistry is a powerful tool to help characterize the tectonic setting of igneous rocks associations.However,when continental mafic dykes and flood basalts are the target most of the proposed geochemical discrimination diagrams fail to correctly classify them,i.e.many mafic展开更多
In this paper, a new discrimination diagram using absolute measures of Th and Nb is applied to postArchean ophiolites to best discriminate a large number of different ophiolitic basalts. This diagram was obtained usi...In this paper, a new discrimination diagram using absolute measures of Th and Nb is applied to postArchean ophiolites to best discriminate a large number of different ophiolitic basalts. This diagram was obtained using 〉2000 known ophiolitic basalts and was tested using -560 modern rocks from known tectonic settings. Ten different basaltic varieties from worldwide ophiolitic complexes have been examined. They include two basaltic types that have never been considered before, which are: (1) medium-Ti basalts (MTB) generated at nascent forearc settings; (2) a type of mid-ocean ridge basalts showing garnet signature (G-MORB) that characterizes Alpine-type (i,e., non volcanic) rifted margins and ocean-continent transition zones (OCTZ). In the Th-Nb diagram, basalts generated in oceanic subductionunrelated settings, rifted margins, and OCTZ can be distinguished from subduction-related basalts with a misclassification rate 〈 1%. This diagram highlights the chemical variation of oceanic, rifted margin, and OCTZ basalts from depleted compositions to progressively more enriched compositions reflecting, in turn, the variance of source composition and degree of melting within the MORB-OIB array. It also highlights the chemical contributions of enriched (OIB-type) components to mantle sources. Enrichment of Th relative to Nb is particularly effective for highlighting crustal input via subduction or crustal contamination. Basalts formed at continental margin arcs and island arc with a complex polygenetic crust can be distinguished from those generated in intra-oceanic arcs in supra-subducrion zones (SSZ) with a misclassification rate 〈1%. Within the SSZ group, two sub-settings can be recognized with a misclassification rate 〈0.5%. They are: (1) SSZ influenced by chemical contribution from subduction- derived components (forearc and intra-arc sub-settings) characterized by island arc tholeiitic (IAT) and boninitic basalts; (2) SSZ with no contribution from subduction-derived components (nascent forearc sub-settings) characterized by MTBs and depleted-MORBs. Two additional discrimination diagrams are proposed: (1) a Dy-Yb diagram is used for discriminating boninite and IAT basalts; (2) a Ce/Yb-Dy/Yb diagram is used for discriminating G-MORBs and normal MORBs. The proposed method may effectively assist in recovering the tectonic affinity of ancient ophiolites, which is fundamental for establishing the geodvnamic evolution of ancient oceanic and continental domains, as well as orogenic belts.展开更多
Systematical analyses of data from GEOROC and PetDB database show that large amount of Cenozoic andesites occurred in the various oceanic environments such as mid-oceanic ridge,plumerelated island and oceanic arc.In t...Systematical analyses of data from GEOROC and PetDB database show that large amount of Cenozoic andesites occurred in the various oceanic environments such as mid-oceanic ridge,plumerelated island and oceanic arc.In this study,we employed the geochemical data of 351 mid-ocean ridge andesites(MORA),2539 plume-related andesites(PRA)and 3488 oceanic arc andesites(OAA)from the database to discuss the relationship between andesite tectonic settings and their geochemical features,thereby making an attempt to construct tectonic discrimination diagrams.Based on the data-driven pattern,all available elements were employed to derive logratios for the possible coordinates,and the overlap-rate calculation was adopted to evaluate the discrimination effect of more than 330000 prospective diagrams.Finally,four tectonic discrimination diagrams have been successfully established to identify MORA,PRA and OAA,which can be utilized to identify the original settings of andesite with an age range from Cenozoic to Archean a certain extent.Of these diagrams,PRA is mainly distinguished by high LREE/HREE ratio due to enriched mantle source.Whereas,OAA is mainly characterized by high LILE/HFSE ratio,which reveals that fluids derived from subducted slab play an important role in forming oceanic arc andesites.Consequently,the petrogenesis of andesites is closely related to their tectonic settings.However,it should be noted that those andesites formed in both continental and oceanic environments cannot be effectively distinguished using these diagrams.We strongly recommend integrating the discrimination diagrams result with other geological information to reach a comprehensive interpretation of evolution history with those ancient andesites.This paper presents a case study which suggests that data-driven method is a powerful tool for solving geological problems in this’big data’era.展开更多
The Xingmeng orogenic belt is located in the eastern section of the Central Asian orogenic belt,which is one of the key areas to study the formation and evolution of the Central Asian orogenic belt.At present,there is...The Xingmeng orogenic belt is located in the eastern section of the Central Asian orogenic belt,which is one of the key areas to study the formation and evolution of the Central Asian orogenic belt.At present,there is a huge controversy over the closure time of the Paleo-Asian Ocean in the Xingmeng orogenic belt.One of the reasons is that the genetic tectonic setting of the Carboniferous volcanic rocks is not clear.Due to the diversity of volcanic rock geochemical characteristics and its related interpretations,there are two different views on the tectonic setting of Carboniferous volcanic rocks in the Xingmeng orogenic belt:island arc and continental rift.In recent years,it is one of the important development directions in the application of geological big data technology to analyze geochemical data based on machine learning methods and further infer the tectonic background of basalt.This paper systematically collects Carboniferous basic rock data from Dongwuqi area of Inner Mongolia,Keyouzhongqi area of Inner Mongolia and Beishan area in the southern section of the Central Asian Orogenic Belt.Random forest algorithm is used for training sets of major elements and trace elements in global island arc basalt and rift basalt,and then the trained model is used to predict the tectonic setting of the Carboniferous magmatic rock samples in the Xingmeng orogenic belt.The prediction results shows that the island arc probability of most of the research samples is between 0.65 and 1,which indicates that the island arc tectonic setting is more credible.In this paper,it is concluded that magmatism in the Beishan area of the southern part of the Central Asian Orogenic belt in the Early Carboniferous may have formed in the heyday of subduction,while the Xingmeng orogenic belt in the Late Carboniferous may have been in the late subduction stage to the collision or even the early rifting stage.This temporal and spatial evolution shows that the subduction of the Paleo-Asian Ocean is different from west to east.Therefore,the research results of this paper show that the subduction of the Xingmeng orogenic belt in the Carboniferous has not ended yet.展开更多
文摘The tectonic environment of granitoids has always been a concern of the academic community.The Nb vs.Y and Rb vs.Nb+Y diagrams have had a substantial impact.The present work uses more than 110,000 granitoid samples(SiO_(2)≥56%)from the globally shared database to discuss the validity and also explain why these diagrams used for discrimination between the different tectonic settings of granitoid rocks.The amount of data from the spreading center is sparse and the data are highly scattered and so,the present study focuses mainly on granites from the ocean islands and convergent margins tectonic environments.On the TAS diagram most of the ocean island data are alkaline series and trachybasalt series,and some are bimodal.In contrast,the granitoids on the convergent margin are mainly sub-alkaline.This work shows that the tectonic discrimination diagrams of granitoids remain valid,and only the boundaries need to be slightly adjusted.
基金The Brazilian Sao Paulo State Research Foundation(FAPESP)partially supported this research(grants 2012/15824-6 and 2012/07243-3)
文摘Geochemistry is a powerful tool to help characterize the tectonic setting of igneous rocks associations.However,when continental mafic dykes and flood basalts are the target most of the proposed geochemical discrimination diagrams fail to correctly classify them,i.e.many mafic
文摘In this paper, a new discrimination diagram using absolute measures of Th and Nb is applied to postArchean ophiolites to best discriminate a large number of different ophiolitic basalts. This diagram was obtained using 〉2000 known ophiolitic basalts and was tested using -560 modern rocks from known tectonic settings. Ten different basaltic varieties from worldwide ophiolitic complexes have been examined. They include two basaltic types that have never been considered before, which are: (1) medium-Ti basalts (MTB) generated at nascent forearc settings; (2) a type of mid-ocean ridge basalts showing garnet signature (G-MORB) that characterizes Alpine-type (i,e., non volcanic) rifted margins and ocean-continent transition zones (OCTZ). In the Th-Nb diagram, basalts generated in oceanic subductionunrelated settings, rifted margins, and OCTZ can be distinguished from subduction-related basalts with a misclassification rate 〈 1%. This diagram highlights the chemical variation of oceanic, rifted margin, and OCTZ basalts from depleted compositions to progressively more enriched compositions reflecting, in turn, the variance of source composition and degree of melting within the MORB-OIB array. It also highlights the chemical contributions of enriched (OIB-type) components to mantle sources. Enrichment of Th relative to Nb is particularly effective for highlighting crustal input via subduction or crustal contamination. Basalts formed at continental margin arcs and island arc with a complex polygenetic crust can be distinguished from those generated in intra-oceanic arcs in supra-subducrion zones (SSZ) with a misclassification rate 〈1%. Within the SSZ group, two sub-settings can be recognized with a misclassification rate 〈0.5%. They are: (1) SSZ influenced by chemical contribution from subduction- derived components (forearc and intra-arc sub-settings) characterized by island arc tholeiitic (IAT) and boninitic basalts; (2) SSZ with no contribution from subduction-derived components (nascent forearc sub-settings) characterized by MTBs and depleted-MORBs. Two additional discrimination diagrams are proposed: (1) a Dy-Yb diagram is used for discriminating boninite and IAT basalts; (2) a Ce/Yb-Dy/Yb diagram is used for discriminating G-MORBs and normal MORBs. The proposed method may effectively assist in recovering the tectonic affinity of ancient ophiolites, which is fundamental for establishing the geodvnamic evolution of ancient oceanic and continental domains, as well as orogenic belts.
基金jointly supported by the National Natural Science Foundations of China(Nos.41772189,41421002)the MOST Special Fund from the State Key Laboratory of Continental Dynamics,Northwest University,Xi’an,China(No.201210133)。
文摘Systematical analyses of data from GEOROC and PetDB database show that large amount of Cenozoic andesites occurred in the various oceanic environments such as mid-oceanic ridge,plumerelated island and oceanic arc.In this study,we employed the geochemical data of 351 mid-ocean ridge andesites(MORA),2539 plume-related andesites(PRA)and 3488 oceanic arc andesites(OAA)from the database to discuss the relationship between andesite tectonic settings and their geochemical features,thereby making an attempt to construct tectonic discrimination diagrams.Based on the data-driven pattern,all available elements were employed to derive logratios for the possible coordinates,and the overlap-rate calculation was adopted to evaluate the discrimination effect of more than 330000 prospective diagrams.Finally,four tectonic discrimination diagrams have been successfully established to identify MORA,PRA and OAA,which can be utilized to identify the original settings of andesite with an age range from Cenozoic to Archean a certain extent.Of these diagrams,PRA is mainly distinguished by high LREE/HREE ratio due to enriched mantle source.Whereas,OAA is mainly characterized by high LILE/HFSE ratio,which reveals that fluids derived from subducted slab play an important role in forming oceanic arc andesites.Consequently,the petrogenesis of andesites is closely related to their tectonic settings.However,it should be noted that those andesites formed in both continental and oceanic environments cannot be effectively distinguished using these diagrams.We strongly recommend integrating the discrimination diagrams result with other geological information to reach a comprehensive interpretation of evolution history with those ancient andesites.This paper presents a case study which suggests that data-driven method is a powerful tool for solving geological problems in this’big data’era.
文摘The Xingmeng orogenic belt is located in the eastern section of the Central Asian orogenic belt,which is one of the key areas to study the formation and evolution of the Central Asian orogenic belt.At present,there is a huge controversy over the closure time of the Paleo-Asian Ocean in the Xingmeng orogenic belt.One of the reasons is that the genetic tectonic setting of the Carboniferous volcanic rocks is not clear.Due to the diversity of volcanic rock geochemical characteristics and its related interpretations,there are two different views on the tectonic setting of Carboniferous volcanic rocks in the Xingmeng orogenic belt:island arc and continental rift.In recent years,it is one of the important development directions in the application of geological big data technology to analyze geochemical data based on machine learning methods and further infer the tectonic background of basalt.This paper systematically collects Carboniferous basic rock data from Dongwuqi area of Inner Mongolia,Keyouzhongqi area of Inner Mongolia and Beishan area in the southern section of the Central Asian Orogenic Belt.Random forest algorithm is used for training sets of major elements and trace elements in global island arc basalt and rift basalt,and then the trained model is used to predict the tectonic setting of the Carboniferous magmatic rock samples in the Xingmeng orogenic belt.The prediction results shows that the island arc probability of most of the research samples is between 0.65 and 1,which indicates that the island arc tectonic setting is more credible.In this paper,it is concluded that magmatism in the Beishan area of the southern part of the Central Asian Orogenic belt in the Early Carboniferous may have formed in the heyday of subduction,while the Xingmeng orogenic belt in the Late Carboniferous may have been in the late subduction stage to the collision or even the early rifting stage.This temporal and spatial evolution shows that the subduction of the Paleo-Asian Ocean is different from west to east.Therefore,the research results of this paper show that the subduction of the Xingmeng orogenic belt in the Carboniferous has not ended yet.