This article presents an overview on recent developments in studies of chemical and physical processes of lithospheric delamination with respect to destruction of the North China Craton. It is emphasized that the pyro...This article presents an overview on recent developments in studies of chemical and physical processes of lithospheric delamination with respect to destruction of the North China Craton. It is emphasized that the pyroxenite source resulting from interaction between eclogite-derived melt and peridotite is a direct consequence of delamination. The pyroxenite source thus formed has unique mineralogical and geochemical features, which characterize Mesozoic basalts of the North China Craton. Melt-peridotite interaction played an important role in refertilization of cratonic lithospheric mantle, leading to density increase, weakening and final destabilization of the North China Craton. The nature of the melt is the key to distinguish mechanisms of destructing this craton.展开更多
Abundant deeply-derived xenoliths are discovered in a Mesozoic diorite at Jinling, Zibo, western Shandong, which mainly consist of dunite and pyroxenite. The dunite can be further subdivided into two subtypes. The fir...Abundant deeply-derived xenoliths are discovered in a Mesozoic diorite at Jinling, Zibo, western Shandong, which mainly consist of dunite and pyroxenite. The dunite can be further subdivided into two subtypes. The first type shows tabular texture and high Mg# values (93—94) in olivines. The second type is characterized by the metamorphic-deformation texture superimposed by later metasomatism and relatively low olivine Mg# values (86—87). The mineral chemical data indicate that the former could be derived from ancient lithospheric mantle and the latter could have resulted from silica-rich melt metasomatism. The exsolution texture and the high Mg# value in clinopyroxenes, together with the rather high equilibrium temperature, imply that the pyroxenite xenoliths could be the cumulates of mantle-derived magma in the uppermost mantle or near the crust-mantle boundary in the Mesozoic.展开更多
The total magmatic output in modern arcs,where continental crust is now being formed, is believed to derive from melting of the mantle wedge and is largely basaltic. Globally averaged continental crust, however, has a...The total magmatic output in modern arcs,where continental crust is now being formed, is believed to derive from melting of the mantle wedge and is largely basaltic. Globally averaged continental crust, however, has an andesitic bulk composition and is hence too silicic to have been derived directly from the mantle. It is well known that one way this imbalance can be reconciled is if the parental basalt differentiates into a mafic garnet pyroxenitic residue/cumulate(‘‘arclogite'') and a complementary silicic melt, the former foundering or delaminating into the mantle due to its high densities and the latter remaining as the crust.Using the Sierra Nevada batholith in California as a case study, the composition of mature continental arc crust is shown in part to be the product of a cyclic process beginning with the growth of an arclogite layer followed by delamination of this layer and post-delamination basaltic underplating/recharge into what remains of the continental crust.A model is presented, wherein continuous arc magmatism and production of arclogites in continental arcs are periodically punctuated by a delamination event and an associated magmatic pulse every *10–30 My. The recycling flux of arclogites is estimated to be *5 %–20 % that of oceanic crust recycling by subduction. Delaminated arclogites have the necessary trace-element compositions to yield time-integrated isotopic compositions similar to those inferred toexist as reservoirs in the mantle. Because of their low melting temperatures, such pyroxenites may be preferentially melted, possibly forming a component of some hotspot magmas.展开更多
Application of reliable thermobarometer on garnet-bearing mantle xenoliths and granulite xenoliths entrained by Cenozoic basalts in eastern China reveals two main types of geotherm. The first type, as exampled by Hann...Application of reliable thermobarometer on garnet-bearing mantle xenoliths and granulite xenoliths entrained by Cenozoic basalts in eastern China reveals two main types of geotherm. The first type, as exampled by Hannuoba （汉若坝）, Mingxi （明溪） and probably Northeast China, is characterized by constant slope of data in the P-T space. The second type, as exampled by the high geotherms of Niishan （女山） and probably Xinchang （新昌）, is characterized by variable slopes, with the samples with pressure 〈2 MPa defining a slow slope, whereas the samples with pressure 〉2 MPa define a virtually vertical slope. The different slopes in the second type of geotherm may correspond to different heat transfer mechanisms, with conductive transfer for the shallow upper mantle and advective transfer for the deep mantle. This observed transition in thermal transfer mechanism is consistent with theoretical modeling. The two types of geotherm are not mutually exclusive, because the second type may characterize the thermal state of whole lithospheric section including both mechanical boundary layer （MBL） and thermal boundary layer （TBL）, while the first type may only depict the MBL. The variable geotherms for different regions are indicative of a heterogeneous lithospheric structure in eastern China. （a） Eastern North China craton （NCC） is characterized by a second-type geotherm, corresponding to a thin lithosphere （-70 km）. Comparison of the equilibrium temperatures of spinel peridotites with this geotherm constrains the depth to Moho in eastern North China craton to be 30 kin. In contrast, western NCC （Hannuoba： the first-type geotherm） possesses a relatively low thermal gradient, indicative of a thick lithosphere （〉90-100 km） and a thick crust-mantle transition zone. The dramatic change in crustal and mantle structure across the DTGL （Daxing＇anling （大兴安岭）- Talhangshan （太行山） gravity lineament） is consistent with recent seismic studies. （b） T展开更多
In-situ excimer laser ICP-MS analysis of minerals of eclogites and garnet pyrox- enites from type localities (Shuanghe, Maowu, Bixiling, and Yangkou) in the Dabie-Sulu ultra- high-pressure metamorphic belt reveals hig...In-situ excimer laser ICP-MS analysis of minerals of eclogites and garnet pyrox- enites from type localities (Shuanghe, Maowu, Bixiling, and Yangkou) in the Dabie-Sulu ultra- high-pressure metamorphic belt reveals highly variable Ce anomalies from negative to positive in garnet. Similar Ce anomalies are also present in omphacite or clinopyroxene but to a much lesser extent. Such mixed negative and positive Ce anomalies mimic those found in severe weathering profiles developed under oxidizing conditions. They suggest the presence of sub- ducted sediment components in the eclogites and garnet pyroxenites, which in turn points to the potential importance of the recycled sediments in modification of the mantle composition during the deep subduction of the continental crust.展开更多
Recently, garnet pyroxenite enclaves within peridotites occurring near Raobazhai, Huoshan County, have been discovered. The garnet pyroxenite is small pods, decimeters in size, enclosed within intensively serpentinize...Recently, garnet pyroxenite enclaves within peridotites occurring near Raobazhai, Huoshan County, have been discovered. The garnet pyroxenite is small pods, decimeters in size, enclosed within intensively serpentinized peridotites. Major mineral components comprise: garnet (Prpas-as), sodium augite (Jd 10-25) with a small amount of ilmenite. There are two stages of retro-metamorphism: the retrogressive granulite facies mineral assemblage is superimposed by that of amphibolite facies. The host rocks of the garnet pyroxenite are spinel peridotites, including spinel harzburgite and Iherzolite. Due to intensive serpentinitization, only 5%-40% of the relic olivine (Fo92-93) are preserved. The orthopyroxenes are Mg-rich (En87-93) with bending of cleavages and granulation at their margins showing intracrystalline plasticity. On the basis of garnet-clinopyroxene Fe-Mg exchange equilibrium geothermometry proposed by Ellis & Green (1979) and Krogh (1988) KD= 4.06 - 5.28; T= 793-919℃, P= 1.5 GPa are estimated for the garnet pyroxenite. It is inferred that the peridotites are mantle rocks about 60 km in depth. During the exhumation of the orogenic belt, it was tectonically emplaced into the lower crust in the solid state and then uplifted to the shallow depth. Obviously, this kind of garnet pyroxenite must be petrogenetically related to its host rock. The REE distribution pattern and the Ni-Co-Sc diagram reveal that they are chemically equivalent to the basaltic melt and ultramafic residua respectively derived from partial melting of mantle rocks.展开更多
We present the results of a detailed micro-scale investigation of zircons from pyroxenites, Daoshicong Northern Dabie using a combination of SIMS and ICPMS. The SIMS measurements gave ages of 134-159 Ma. Its average o...We present the results of a detailed micro-scale investigation of zircons from pyroxenites, Daoshicong Northern Dabie using a combination of SIMS and ICPMS. The SIMS measurements gave ages of 134-159 Ma. Its average of (144.516.2) Ma is interpreted as the best estimate of the pyroxenite intrusion. The crystallization of zircons continued for quite a long time and underwent slow cooling. The pyroxenites are products of post-collision magmatism. The REE pattern is HREE-enriched, and its HREE concentrations fall between the magmatic and metamorphic range of gneissic zircons from the Dabie area, which indicate the involvement of crust material in its mantle source.展开更多
Pelletization of hematite ore requires high fineness and very high induration temperature（~1325 ℃） owing to its poor diffusion bonding unlike magnetite ore. Further, high-alumina hematite pellets show very high red...Pelletization of hematite ore requires high fineness and very high induration temperature（~1325 ℃） owing to its poor diffusion bonding unlike magnetite ore. Further, high-alumina hematite pellets show very high reduction degradation index（RDI） during low temperature（500-650 ℃） reduction due to their volume expansion and lattice distortion. Noamundi（India） hematite ore contains very high Al2O3（2.3%） with adverse ratio of alumina to silica（~2） for which, it shows very high RDI. In this work, the acid pellets prepared from Noamundi ore fines of optimum Blaine fineness show good cold crushing strength（CCS）. However, it shows very high RDI（77%）. In order to reduce RDI, Mg O in form of two different gangue-containing fluxes, such as pyroxenite and olivine in varying quantities has been added. The optimum requirement and performance of these fluxes has been examined and compared. Both pyroxenite and olivine fluxed pellets show significant lowering of RDI（26% and 23%, respectively） and improvement of other properties, viz CCS, swelling indices etc with good reducibility（70%-77%）. Finally, a good quality acidic hematite pellet was developed from high-alumina ore without using any lime which is very important charge material in combination of basic sinter in blast furnace.展开更多
The trace element compositions of melts and minerals from high-pressure experiments on hydrous pyroxenites containing K-richterite are presented. The experiments used mixtures of a third each of the natural minerals c...The trace element compositions of melts and minerals from high-pressure experiments on hydrous pyroxenites containing K-richterite are presented. The experiments used mixtures of a third each of the natural minerals clinopyroxene, phlogopite and K-richterite, some with the addition of 5% of an accessory phase ilmenite, rutile or apatite. Although the major element compositions of melts resemble natural lamproites, the trace element contents of most trace elements from the three-mineral mixture are much lower than in lamproites. Apatite is required in the source to provide high abundances of the rare earth elements, and either rutile and/or ilmenite is required to provide the high field strength elements Ti, Nb, Ta, Zr and Hf. Phlogopite controls the high levels of Rb, Cs and Ba.Since abundances of trace elements in the various starting mixtures vary strongly because of the use of natural minerals, we calculated mineral/melt partition coefficients (DMin/melt) using mineral modes and melting reactions and present trace element patterns for different degrees of partial melting of hydrous pyroxenites. Rb, Cs and Ba are compatible in phlogopite and the partition coefficient ratio phlogopite/K-richterite is high for Ba (136) and Rb (12). All melts have low contents of most of the first row transition elements, particularly Ni and Cu ((0.1-0.01)×primitive mantle). Nickel has high DMin/melt for all the major minerals (12 for K-richterite, 9.2 for phlogopite and 5.6 for Cpx) and so behaves at least as compatibly as in melting of peridotites. Fluorine/chlorine ratios in melts are high and DMin/melt for fluorine decreases in the order apatite (2.2) > phlogopite (1.5) > K-richterite (0.87). The requirement for apatite and at least one Ti-oxide in the source of natural lamproites holds for mica pyroxenites that lack K-richterite. The results are used to model isotopic ageing in hydrous pyroxenite source rocks: phlogopite controls Sr isotopes, so that lamproites with relatively low 87Sr/86Sr must come from phlogopite-poor sou展开更多
基金Supported jointly by the National Natural Science Foundation of China (Grant Nos. 90714010, 90714005, 90814003 and 40673019)Ministry of Education and State Administration of Foreign Experts of China (Grant No. B07039)the MOST special funds from State Key Laboratory of Continental Dynamics and State Key Laboratory of Geological Processes and Mineral Resources
文摘This article presents an overview on recent developments in studies of chemical and physical processes of lithospheric delamination with respect to destruction of the North China Craton. It is emphasized that the pyroxenite source resulting from interaction between eclogite-derived melt and peridotite is a direct consequence of delamination. The pyroxenite source thus formed has unique mineralogical and geochemical features, which characterize Mesozoic basalts of the North China Craton. Melt-peridotite interaction played an important role in refertilization of cratonic lithospheric mantle, leading to density increase, weakening and final destabilization of the North China Craton. The nature of the melt is the key to distinguish mechanisms of destructing this craton.
基金supported by the Foundation for Doctorate Subjects of the Ministry of Education of China(Grant No.20010183007)the National Natural Science Foundation of China(Grant No.40133020).
文摘Abundant deeply-derived xenoliths are discovered in a Mesozoic diorite at Jinling, Zibo, western Shandong, which mainly consist of dunite and pyroxenite. The dunite can be further subdivided into two subtypes. The first type shows tabular texture and high Mg# values (93—94) in olivines. The second type is characterized by the metamorphic-deformation texture superimposed by later metasomatism and relatively low olivine Mg# values (86—87). The mineral chemical data indicate that the former could be derived from ancient lithospheric mantle and the latter could have resulted from silica-rich melt metasomatism. The exsolution texture and the high Mg# value in clinopyroxenes, together with the rather high equilibrium temperature, imply that the pyroxenite xenoliths could be the cumulates of mantle-derived magma in the uppermost mantle or near the crust-mantle boundary in the Mesozoic.
文摘The total magmatic output in modern arcs,where continental crust is now being formed, is believed to derive from melting of the mantle wedge and is largely basaltic. Globally averaged continental crust, however, has an andesitic bulk composition and is hence too silicic to have been derived directly from the mantle. It is well known that one way this imbalance can be reconciled is if the parental basalt differentiates into a mafic garnet pyroxenitic residue/cumulate(‘‘arclogite'') and a complementary silicic melt, the former foundering or delaminating into the mantle due to its high densities and the latter remaining as the crust.Using the Sierra Nevada batholith in California as a case study, the composition of mature continental arc crust is shown in part to be the product of a cyclic process beginning with the growth of an arclogite layer followed by delamination of this layer and post-delamination basaltic underplating/recharge into what remains of the continental crust.A model is presented, wherein continuous arc magmatism and production of arclogites in continental arcs are periodically punctuated by a delamination event and an associated magmatic pulse every *10–30 My. The recycling flux of arclogites is estimated to be *5 %–20 % that of oceanic crust recycling by subduction. Delaminated arclogites have the necessary trace-element compositions to yield time-integrated isotopic compositions similar to those inferred toexist as reservoirs in the mantle. Because of their low melting temperatures, such pyroxenites may be preferentially melted, possibly forming a component of some hotspot magmas.
基金supported by the Knowledge Inno-vation Project of the Chinese Academy of Sciences (No. KZCX2-YW-Q08-3-6)the National Natural Science Founda-tion of China (Nos. 90714001, 40773015)the CAS/SAFEA International Partnership Program for Creative Research Teams (No. KZCX2-YW-Q04-06)
文摘Application of reliable thermobarometer on garnet-bearing mantle xenoliths and granulite xenoliths entrained by Cenozoic basalts in eastern China reveals two main types of geotherm. The first type, as exampled by Hannuoba （汉若坝）, Mingxi （明溪） and probably Northeast China, is characterized by constant slope of data in the P-T space. The second type, as exampled by the high geotherms of Niishan （女山） and probably Xinchang （新昌）, is characterized by variable slopes, with the samples with pressure 〈2 MPa defining a slow slope, whereas the samples with pressure 〉2 MPa define a virtually vertical slope. The different slopes in the second type of geotherm may correspond to different heat transfer mechanisms, with conductive transfer for the shallow upper mantle and advective transfer for the deep mantle. This observed transition in thermal transfer mechanism is consistent with theoretical modeling. The two types of geotherm are not mutually exclusive, because the second type may characterize the thermal state of whole lithospheric section including both mechanical boundary layer （MBL） and thermal boundary layer （TBL）, while the first type may only depict the MBL. The variable geotherms for different regions are indicative of a heterogeneous lithospheric structure in eastern China. （a） Eastern North China craton （NCC） is characterized by a second-type geotherm, corresponding to a thin lithosphere （-70 km）. Comparison of the equilibrium temperatures of spinel peridotites with this geotherm constrains the depth to Moho in eastern North China craton to be 30 kin. In contrast, western NCC （Hannuoba： the first-type geotherm） possesses a relatively low thermal gradient, indicative of a thick lithosphere （〉90-100 km） and a thick crust-mantle transition zone. The dramatic change in crustal and mantle structure across the DTGL （Daxing＇anling （大兴安岭）- Talhangshan （太行山） gravity lineament） is consistent with recent seismic studies. （b） T
基金co-supported by the National Natural Science Foundation of China(Grant No.40133020)the Chinese Ministry of Science and Technology(Grant No.G1999043202).
文摘In-situ excimer laser ICP-MS analysis of minerals of eclogites and garnet pyrox- enites from type localities (Shuanghe, Maowu, Bixiling, and Yangkou) in the Dabie-Sulu ultra- high-pressure metamorphic belt reveals highly variable Ce anomalies from negative to positive in garnet. Similar Ce anomalies are also present in omphacite or clinopyroxene but to a much lesser extent. Such mixed negative and positive Ce anomalies mimic those found in severe weathering profiles developed under oxidizing conditions. They suggest the presence of sub- ducted sediment components in the eclogites and garnet pyroxenites, which in turn points to the potential importance of the recycled sediments in modification of the mantle composition during the deep subduction of the continental crust.
文摘Recently, garnet pyroxenite enclaves within peridotites occurring near Raobazhai, Huoshan County, have been discovered. The garnet pyroxenite is small pods, decimeters in size, enclosed within intensively serpentinized peridotites. Major mineral components comprise: garnet (Prpas-as), sodium augite (Jd 10-25) with a small amount of ilmenite. There are two stages of retro-metamorphism: the retrogressive granulite facies mineral assemblage is superimposed by that of amphibolite facies. The host rocks of the garnet pyroxenite are spinel peridotites, including spinel harzburgite and Iherzolite. Due to intensive serpentinitization, only 5%-40% of the relic olivine (Fo92-93) are preserved. The orthopyroxenes are Mg-rich (En87-93) with bending of cleavages and granulation at their margins showing intracrystalline plasticity. On the basis of garnet-clinopyroxene Fe-Mg exchange equilibrium geothermometry proposed by Ellis & Green (1979) and Krogh (1988) KD= 4.06 - 5.28; T= 793-919℃, P= 1.5 GPa are estimated for the garnet pyroxenite. It is inferred that the peridotites are mantle rocks about 60 km in depth. During the exhumation of the orogenic belt, it was tectonically emplaced into the lower crust in the solid state and then uplifted to the shallow depth. Obviously, this kind of garnet pyroxenite must be petrogenetically related to its host rock. The REE distribution pattern and the Ni-Co-Sc diagram reveal that they are chemically equivalent to the basaltic melt and ultramafic residua respectively derived from partial melting of mantle rocks.
基金This work was supported by the Major State Basic Research Development Project (Grant No. 1999075503) and the National Natural Science Foundation of China (Grant Nos. 49973019 and 49794042).
文摘We present the results of a detailed micro-scale investigation of zircons from pyroxenites, Daoshicong Northern Dabie using a combination of SIMS and ICPMS. The SIMS measurements gave ages of 134-159 Ma. Its average of (144.516.2) Ma is interpreted as the best estimate of the pyroxenite intrusion. The crystallization of zircons continued for quite a long time and underwent slow cooling. The pyroxenites are products of post-collision magmatism. The REE pattern is HREE-enriched, and its HREE concentrations fall between the magmatic and metamorphic range of gneissic zircons from the Dabie area, which indicate the involvement of crust material in its mantle source.
文摘Pelletization of hematite ore requires high fineness and very high induration temperature（~1325 ℃） owing to its poor diffusion bonding unlike magnetite ore. Further, high-alumina hematite pellets show very high reduction degradation index（RDI） during low temperature（500-650 ℃） reduction due to their volume expansion and lattice distortion. Noamundi（India） hematite ore contains very high Al2O3（2.3%） with adverse ratio of alumina to silica（~2） for which, it shows very high RDI. In this work, the acid pellets prepared from Noamundi ore fines of optimum Blaine fineness show good cold crushing strength（CCS）. However, it shows very high RDI（77%）. In order to reduce RDI, Mg O in form of two different gangue-containing fluxes, such as pyroxenite and olivine in varying quantities has been added. The optimum requirement and performance of these fluxes has been examined and compared. Both pyroxenite and olivine fluxed pellets show significant lowering of RDI（26% and 23%, respectively） and improvement of other properties, viz CCS, swelling indices etc with good reducibility（70%-77%）. Finally, a good quality acidic hematite pellet was developed from high-alumina ore without using any lime which is very important charge material in combination of basic sinter in blast furnace.
基金funded by grants from the Deutsche Forschungsgemeinschaft,Germany (Fo 181/3)and the Australian Research Council,Australia (FL180100134).
文摘The trace element compositions of melts and minerals from high-pressure experiments on hydrous pyroxenites containing K-richterite are presented. The experiments used mixtures of a third each of the natural minerals clinopyroxene, phlogopite and K-richterite, some with the addition of 5% of an accessory phase ilmenite, rutile or apatite. Although the major element compositions of melts resemble natural lamproites, the trace element contents of most trace elements from the three-mineral mixture are much lower than in lamproites. Apatite is required in the source to provide high abundances of the rare earth elements, and either rutile and/or ilmenite is required to provide the high field strength elements Ti, Nb, Ta, Zr and Hf. Phlogopite controls the high levels of Rb, Cs and Ba.Since abundances of trace elements in the various starting mixtures vary strongly because of the use of natural minerals, we calculated mineral/melt partition coefficients (DMin/melt) using mineral modes and melting reactions and present trace element patterns for different degrees of partial melting of hydrous pyroxenites. Rb, Cs and Ba are compatible in phlogopite and the partition coefficient ratio phlogopite/K-richterite is high for Ba (136) and Rb (12). All melts have low contents of most of the first row transition elements, particularly Ni and Cu ((0.1-0.01)×primitive mantle). Nickel has high DMin/melt for all the major minerals (12 for K-richterite, 9.2 for phlogopite and 5.6 for Cpx) and so behaves at least as compatibly as in melting of peridotites. Fluorine/chlorine ratios in melts are high and DMin/melt for fluorine decreases in the order apatite (2.2) > phlogopite (1.5) > K-richterite (0.87). The requirement for apatite and at least one Ti-oxide in the source of natural lamproites holds for mica pyroxenites that lack K-richterite. The results are used to model isotopic ageing in hydrous pyroxenite source rocks: phlogopite controls Sr isotopes, so that lamproites with relatively low 87Sr/86Sr must come from phlogopite-poor sou
