The lower crustal xenolith of mafic two_pyroxene granulite (the majority) and hypersthene granulite in the Cenozoic basalt at Hannuoba have the characteristics of igneous blastic structure and granulite facies metamor...The lower crustal xenolith of mafic two_pyroxene granulite (the majority) and hypersthene granulite in the Cenozoic basalt at Hannuoba have the characteristics of igneous blastic structure and granulite facies metamorphic recrystallization. Study on the zircon chronology and REE geochemistry of granulite xenolith shows that the underplating of basic magma into the lower crust during late Mesozoic led to the formation of mafic accumulate, which further through metamorphism of granulite facies formed the high_density and high_velocity crustal bottom layer at the lower crust. This suggests that the underplating of mantle magma is the important way for the vertical overgrowth of continental crust since the Phanerozoic and provides new evidence for crust_mantle interaction.展开更多
Backscattered electron images, in situ Hf isotopes, U-Pb ages and trace elements of zircons in a banded granulite xenolith from Hannuoba basalt have been studied.The results show that the banded granulite is a sample ...Backscattered electron images, in situ Hf isotopes, U-Pb ages and trace elements of zircons in a banded granulite xenolith from Hannuoba basalt have been studied.The results show that the banded granulite is a sample derived from the early lower crust of the North China craton.It is difficult to explain the petrogenesis of the xenolith with a single process. Abundant information on several processes,however, is contained in the granulite. These processes include the addition of mantle material, crustal remelting,metamorphic differentiation and the delamination of early lower crust. About 80% of zircons studied yield ages of 1842±40Ma, except few ages of 3097-2824 Ma and 2489-2447Ma. The zircons with ages older than 2447Ma have high εHr(up to+18.3) and high Hf model age (2.5-2.6Ga), indicating that the primitive materials of the granulite were derived mainly from a depleted mantle source in late Archean. Most εHr of the zircons with early Proterozoic U-Pb age vary around zero, but two have high εHr up to+9.2-+10.2, indicating mantle contribution during the collision and assembly between the Eastern and Western blocks in the early Proterozoic that resulted in the amalgamation of the North China craton.展开更多
Neutron activation analysis after preconcentration of nickel sulfide fire assay was used in measurement of Ru, Ph, Pd, Os, Ir, Pt (i.e. PGE elements) and Au concentrations for basalt, mantle and granulite xenoliths in...Neutron activation analysis after preconcentration of nickel sulfide fire assay was used in measurement of Ru, Ph, Pd, Os, Ir, Pt (i.e. PGE elements) and Au concentrations for basalt, mantle and granulite xenoliths in Hannuoba. The chondrite- and primitive mantle-normalized PGE patterns generally exhibit flat (for Iherzolite), negative slope (for harzburgite),展开更多
Garnet-rich granulite xenoliths collected from the Hannuoba basalts, the North China craton （NCC）, were studied to reveal the Mesozoic crnst-mantle interaction. These xenoliths are characterized by low SiO2 （37.7 w...Garnet-rich granulite xenoliths collected from the Hannuoba basalts, the North China craton （NCC）, were studied to reveal the Mesozoic crnst-mantle interaction. These xenoliths are characterized by low SiO2 （37.7 wt.%-46.0 wt.%） and high Al2O3 （10.8 wt.%-17.9 wt.%） contents. Their Mg# （60-75, Mg#=100×Mg/（Mg＋Fe）, atomic number） are relatively low for their low SiO2 contents. They have low rare-earth element （REE） contents and LREE-rich REE patterns, and show remarkable enrichments in Sr relative to the adjacent REE. Some of them exhibit convex RISE patterns with a maximum at Nd and remarkably positive Eu anomalies. Taking into account their high garnet mode （generally 〉30%）, these features suggest that they are high-pressure metamorphic products of lowpressure cumulates （e.g., gabbro） after it had been depressed into the garnet stability field. They have evolved Nd and Sr isotopic compositions （143Nd/144Nd=0.511 763-0.512 173, STSr/86Sr=0.705 34-0.706 99） and fall in the trend defined by the 〉110 Ma Mesozoic basalts and high-Mg# andesites from the NCC. Zircon U-Pb dating by LA-ICP-MS shows a wide age range from 83 to 2 581 Ma, most of which cluster in 83-134 Ma. CL images of some Mesozoic zircons from the granulites show typical features of igneous zircons, providing direct evidence for the Mesozoic underplating event in this area. Neither peridotite-derived basaltic underplating model nor residue model of ancient lower crust after lithospheric thinning alone can reasonably explain the above features of the garnet-Hch granulite xenoliths. Combined with the previous research, we propose that most of the granulite xenoliths from the Hannuoba basalts are products of the Mesozoic magmatie underplating and mixing with the pre-existing lower crust （i.e., AFC process）. However, the melts could be mostly derived from partial melting of basaltic layers that were previously subducted （a fossil oceanic slab） or underplated into the base of the lithospheric mantle, or from pa展开更多
The discovery of the Early Mesozoic basic granulite xenoliths in the Harqin area of the Inner Mongolia Autonomous Region (for short Inner Mongolia) is reported for the first time in this paper. According to the minera...The discovery of the Early Mesozoic basic granulite xenoliths in the Harqin area of the Inner Mongolia Autonomous Region (for short Inner Mongolia) is reported for the first time in this paper. According to the mineral assemblage the xenoliths include two-pyroxene granulite, clinopyroxene granulite, and hypersthene granulite. Their protolytes are mainly gabbroite rocks. The zircon U-Pb age of the granulite xenoliths is 251 Ma, and K-Ar age of the hypersthene is 229 Ma. They represent the times of metamorphism and cooling of the granulite facies respectively. The host rock of the xenoliths is Early Mesozoic biotite-quartz diorites, whose whole-rock K-Ar age is 219 Ma. This discovery confirms existence of an Early Mesozoic underplating in the North China Craton, which is of much importance in research on the Early Mesozoic mantle-crust interaction in the concerned area.展开更多
文摘The lower crustal xenolith of mafic two_pyroxene granulite (the majority) and hypersthene granulite in the Cenozoic basalt at Hannuoba have the characteristics of igneous blastic structure and granulite facies metamorphic recrystallization. Study on the zircon chronology and REE geochemistry of granulite xenolith shows that the underplating of basic magma into the lower crust during late Mesozoic led to the formation of mafic accumulate, which further through metamorphism of granulite facies formed the high_density and high_velocity crustal bottom layer at the lower crust. This suggests that the underplating of mantle magma is the important way for the vertical overgrowth of continental crust since the Phanerozoic and provides new evidence for crust_mantle interaction.
文摘Backscattered electron images, in situ Hf isotopes, U-Pb ages and trace elements of zircons in a banded granulite xenolith from Hannuoba basalt have been studied.The results show that the banded granulite is a sample derived from the early lower crust of the North China craton.It is difficult to explain the petrogenesis of the xenolith with a single process. Abundant information on several processes,however, is contained in the granulite. These processes include the addition of mantle material, crustal remelting,metamorphic differentiation and the delamination of early lower crust. About 80% of zircons studied yield ages of 1842±40Ma, except few ages of 3097-2824 Ma and 2489-2447Ma. The zircons with ages older than 2447Ma have high εHr(up to+18.3) and high Hf model age (2.5-2.6Ga), indicating that the primitive materials of the granulite were derived mainly from a depleted mantle source in late Archean. Most εHr of the zircons with early Proterozoic U-Pb age vary around zero, but two have high εHr up to+9.2-+10.2, indicating mantle contribution during the collision and assembly between the Eastern and Western blocks in the early Proterozoic that resulted in the amalgamation of the North China craton.
文摘Neutron activation analysis after preconcentration of nickel sulfide fire assay was used in measurement of Ru, Ph, Pd, Os, Ir, Pt (i.e. PGE elements) and Au concentrations for basalt, mantle and granulite xenoliths in Hannuoba. The chondrite- and primitive mantle-normalized PGE patterns generally exhibit flat (for Iherzolite), negative slope (for harzburgite),
基金study was co-supported by the National Natural Science Foundation of China (Nos. 90914007, 40821061, 90714010)the State Administration of Foreign Expert Affairs of China (No. B07039)+1 种基金the MOST Special Fund of State Key Laboratory of Geological Processes and Mineral Resources and State Key Laboratory of Continental Dynamicsthe Special Fund For Basic Scientific Research of Central Colleges, China University of Geosciences (Wuhan)
文摘Garnet-rich granulite xenoliths collected from the Hannuoba basalts, the North China craton （NCC）, were studied to reveal the Mesozoic crnst-mantle interaction. These xenoliths are characterized by low SiO2 （37.7 wt.%-46.0 wt.%） and high Al2O3 （10.8 wt.%-17.9 wt.%） contents. Their Mg# （60-75, Mg#=100×Mg/（Mg＋Fe）, atomic number） are relatively low for their low SiO2 contents. They have low rare-earth element （REE） contents and LREE-rich REE patterns, and show remarkable enrichments in Sr relative to the adjacent REE. Some of them exhibit convex RISE patterns with a maximum at Nd and remarkably positive Eu anomalies. Taking into account their high garnet mode （generally 〉30%）, these features suggest that they are high-pressure metamorphic products of lowpressure cumulates （e.g., gabbro） after it had been depressed into the garnet stability field. They have evolved Nd and Sr isotopic compositions （143Nd/144Nd=0.511 763-0.512 173, STSr/86Sr=0.705 34-0.706 99） and fall in the trend defined by the 〉110 Ma Mesozoic basalts and high-Mg# andesites from the NCC. Zircon U-Pb dating by LA-ICP-MS shows a wide age range from 83 to 2 581 Ma, most of which cluster in 83-134 Ma. CL images of some Mesozoic zircons from the granulites show typical features of igneous zircons, providing direct evidence for the Mesozoic underplating event in this area. Neither peridotite-derived basaltic underplating model nor residue model of ancient lower crust after lithospheric thinning alone can reasonably explain the above features of the garnet-Hch granulite xenoliths. Combined with the previous research, we propose that most of the granulite xenoliths from the Hannuoba basalts are products of the Mesozoic magmatie underplating and mixing with the pre-existing lower crust （i.e., AFC process）. However, the melts could be mostly derived from partial melting of basaltic layers that were previously subducted （a fossil oceanic slab） or underplated into the base of the lithospheric mantle, or from pa
文摘The discovery of the Early Mesozoic basic granulite xenoliths in the Harqin area of the Inner Mongolia Autonomous Region (for short Inner Mongolia) is reported for the first time in this paper. According to the mineral assemblage the xenoliths include two-pyroxene granulite, clinopyroxene granulite, and hypersthene granulite. Their protolytes are mainly gabbroite rocks. The zircon U-Pb age of the granulite xenoliths is 251 Ma, and K-Ar age of the hypersthene is 229 Ma. They represent the times of metamorphism and cooling of the granulite facies respectively. The host rock of the xenoliths is Early Mesozoic biotite-quartz diorites, whose whole-rock K-Ar age is 219 Ma. This discovery confirms existence of an Early Mesozoic underplating in the North China Craton, which is of much importance in research on the Early Mesozoic mantle-crust interaction in the concerned area.
