We report the oxide,element geochemistry and Nd isotopic geochemical data of apatite in the middle Pleistocene medium-and fine-grained trachyte in the Tianchi volcanic area(TVA)of Changbai Mountain,discussing the rela...We report the oxide,element geochemistry and Nd isotopic geochemical data of apatite in the middle Pleistocene medium-and fine-grained trachyte in the Tianchi volcanic area(TVA)of Changbai Mountain,discussing the relationship between apatite and the composition of the whole rock.The purpose is to use the apatite geochemical data to constrain the evolutionary process of trachytic magma and the petrogenesis of trachyte in the cone-forming period of the Tianchi volcano.Apatite(Ca_(5)(PO_(4))_(3)(OH,F,Cl))is a common accessory mineral that occurs widely in volcanic rocks in the TVA.The apatites in the trachyte are mainly subhedral-anhedral,having the characteristics of magmatic apatite.In terms of oxide and element geochemistry,they have homogeneous Al_(2)O_(3),SiO_(2),MgO,P_(2)O_(5),K_(2)O,CaO and heterogeneous TiO2,with high F content.They are generally enriched in Th,U and LREEs,depleted in Nb,Ta,Zr,Hf and HFSEs,showing negative Ba,Sr and Ti anomalies,similar to those of the whole-rock host trachytes.The ratios of high(La/Yb)_(N),low δEu(Eu/Eu*),Sr/Y value and ΣREE content in apatite,and the F,Sr,Y,Th/U,La/Sm,and Nd/Tb with ΣREE andδEu anomalies showed a linear correlation,all of those indicating that the host magma has the characteristic of high differentiation.The apatite grains generally having ^(147)Sm/^(144)Nd,^(143)Nd/^(144)Nd ratios and ε_(Nd)(t)values of 0.1072-0.1195,0.5123-0.5126 and -3.49 to -0.10,respectively,are similiar to those of the host rock.The Nd model ages TDM1 are 949-803 Ma in apatite.Combined with theεNd(t)value of the apatite core(-7.06 to-3.49),we conclude that the initial magma of the host trachyte was derived from the partial melting of Proterozoic crustal material and there was an assimilation of wall rocks during its evolution.展开更多
Changbaishan,an intraplate volcano,is characterized by an approximately 6 km wide summit caldera and last erupted in 1903.Changbaishan experienced a period of unrest between 2002 and 2006.The activity developed in thr...Changbaishan,an intraplate volcano,is characterized by an approximately 6 km wide summit caldera and last erupted in 1903.Changbaishan experienced a period of unrest between 2002 and 2006.The activity developed in three main stages,including shield volcano(basalts),cone-construction(trachyandesites to trachytes with minor basalts),and caldera-forming stages(trachytes to comendites).This last stage is associated with one of the more energetic eruptions of the last millennium on Earth,the 946 CE,VEI 7 Millennium Eruption(ME),which emitted over 100 km^(3) of pyroclastics.Compared to other active calderas,the plumbing system of Changbaishan and its evolution mechanisms remain poorly constrained.Here,we merge new whole-rock,glass,mineral,isotopic,and geobarometry data with geophysical data and present a model of the plumbing system.The results show that the volcano is characterized by at least three main magma reservoirs at different depths:a basaltic reservoir at the Moho/lower crust depth,an intermediate reservoir at 10-15 km depth,and a shallower reservoir at 0.5-3 km depth.The shallower reservoir was involved in the ME eruption,which was triggered by a fresh trachytic melt entering a shallower reservoir where a comenditic magma was stored.The trachytes and comendites originate from fractional crystallization processes and minor assimilation of upper crust material,while the less evolved melts assimilate lower crust material.Syn-eruptive magma mingling occurred during the ME eruption phase.The magma reservoirs of the caldera-forming stage partly reactivate those of the cone-construction stage.The depth of the magma storage zones is controlled by the layering of the crust.The plumbing system of Changbaishan is vertically extensive,with crystal mush reservoirs renewed by the replenishment of new trachytic to trachyandesitic magma from depth.Unlike other volcanoes,evidence of a basaltic recharge is lacking.The interpretation of the signals preceding possible future eruptions should consider the multi-level nature of the Changbaishan plumbing system.A new arrival of magma may destabilize a part of or the entire system,thus triggering eruptions of different sizes and styles.The reference model proposed here for Changbaishan represents a prerequisite to properly understand periods of unrest to potentially anticipate future volcanic eruptions and to identify the mechanisms controlling the evolution of the crust below volcanoes.展开更多
基金funded by research on the strategy of Improving the All-for-one Tourism Transportation Capacity of Changbai Mountain and the China Scholarship Council(Grant Nos.JL2021-03 and 202104190014)。
文摘We report the oxide,element geochemistry and Nd isotopic geochemical data of apatite in the middle Pleistocene medium-and fine-grained trachyte in the Tianchi volcanic area(TVA)of Changbai Mountain,discussing the relationship between apatite and the composition of the whole rock.The purpose is to use the apatite geochemical data to constrain the evolutionary process of trachytic magma and the petrogenesis of trachyte in the cone-forming period of the Tianchi volcano.Apatite(Ca_(5)(PO_(4))_(3)(OH,F,Cl))is a common accessory mineral that occurs widely in volcanic rocks in the TVA.The apatites in the trachyte are mainly subhedral-anhedral,having the characteristics of magmatic apatite.In terms of oxide and element geochemistry,they have homogeneous Al_(2)O_(3),SiO_(2),MgO,P_(2)O_(5),K_(2)O,CaO and heterogeneous TiO2,with high F content.They are generally enriched in Th,U and LREEs,depleted in Nb,Ta,Zr,Hf and HFSEs,showing negative Ba,Sr and Ti anomalies,similar to those of the whole-rock host trachytes.The ratios of high(La/Yb)_(N),low δEu(Eu/Eu*),Sr/Y value and ΣREE content in apatite,and the F,Sr,Y,Th/U,La/Sm,and Nd/Tb with ΣREE andδEu anomalies showed a linear correlation,all of those indicating that the host magma has the characteristic of high differentiation.The apatite grains generally having ^(147)Sm/^(144)Nd,^(143)Nd/^(144)Nd ratios and ε_(Nd)(t)values of 0.1072-0.1195,0.5123-0.5126 and -3.49 to -0.10,respectively,are similiar to those of the host rock.The Nd model ages TDM1 are 949-803 Ma in apatite.Combined with theεNd(t)value of the apatite core(-7.06 to-3.49),we conclude that the initial magma of the host trachyte was derived from the partial melting of Proterozoic crustal material and there was an assimilation of wall rocks during its evolution.
基金funded by the National Natural Science Foundation of China under Grant Nos.41972313 and 41790453by the Engineering Research Center of Geothermal Resources Development Technology and Equipment,Ministry of Education,Jilin University,China.
文摘Changbaishan,an intraplate volcano,is characterized by an approximately 6 km wide summit caldera and last erupted in 1903.Changbaishan experienced a period of unrest between 2002 and 2006.The activity developed in three main stages,including shield volcano(basalts),cone-construction(trachyandesites to trachytes with minor basalts),and caldera-forming stages(trachytes to comendites).This last stage is associated with one of the more energetic eruptions of the last millennium on Earth,the 946 CE,VEI 7 Millennium Eruption(ME),which emitted over 100 km^(3) of pyroclastics.Compared to other active calderas,the plumbing system of Changbaishan and its evolution mechanisms remain poorly constrained.Here,we merge new whole-rock,glass,mineral,isotopic,and geobarometry data with geophysical data and present a model of the plumbing system.The results show that the volcano is characterized by at least three main magma reservoirs at different depths:a basaltic reservoir at the Moho/lower crust depth,an intermediate reservoir at 10-15 km depth,and a shallower reservoir at 0.5-3 km depth.The shallower reservoir was involved in the ME eruption,which was triggered by a fresh trachytic melt entering a shallower reservoir where a comenditic magma was stored.The trachytes and comendites originate from fractional crystallization processes and minor assimilation of upper crust material,while the less evolved melts assimilate lower crust material.Syn-eruptive magma mingling occurred during the ME eruption phase.The magma reservoirs of the caldera-forming stage partly reactivate those of the cone-construction stage.The depth of the magma storage zones is controlled by the layering of the crust.The plumbing system of Changbaishan is vertically extensive,with crystal mush reservoirs renewed by the replenishment of new trachytic to trachyandesitic magma from depth.Unlike other volcanoes,evidence of a basaltic recharge is lacking.The interpretation of the signals preceding possible future eruptions should consider the multi-level nature of the Changbaishan plumbing system.A new arrival of magma may destabilize a part of or the entire system,thus triggering eruptions of different sizes and styles.The reference model proposed here for Changbaishan represents a prerequisite to properly understand periods of unrest to potentially anticipate future volcanic eruptions and to identify the mechanisms controlling the evolution of the crust below volcanoes.
