Mineralogical data are presented for the peridotite xenoliths from Miocene(~19 Ma)Qingyuan basalts in the eastern North China Craton(NCC),with the aim of constraining on property of the sub-continental lithospheric ma...Mineralogical data are presented for the peridotite xenoliths from Miocene(~19 Ma)Qingyuan basalts in the eastern North China Craton(NCC),with the aim of constraining on property of the sub-continental lithospheric mantle(SCLM)beneath the northern Tan-Lu fault zone(TLFZ)during the Cenozoic.The Qingyuan peridotites are dominated by spinel lherzolites with moderate-Mg^(#)olivines(89.4 to 91.2),suggesting that the regional SCLM is mainly transitional and fertile.Light rare earth element(LREE)-depleted,slightly depleted and enriched clinopyroxenes(Cpx)are identified in different peridotites.Chemical compositions of the LREE-enriched Cpx and the presence of phlogopite suggest that the Qingyuan SCLM has experienced silicate-related metasomatism.The synthesis of available mineral chemical data of the mantle xenoliths across the NCC confirms the SCLM beneath the NCC is highly heterogeneous in time and space.The Mesozoic–Cenozoic SCLM beneath the TLFZ and neighboring regions are more fertile and thinner than that beneath the region away from the fault zone.The fertile and refractory peridotite xenoliths experienced varying degrees of silicate and carbonatite metasomatism,respectively.The spatial-temporal lithospheric mantle heterogeneity in composition,age and thickness suggest that the trans-lithosphere fault zone played an important role in heterogeneous replacement of refractory cratonic lithospheric mantle.展开更多
Fabrics of five spinel peridotites collected from Baker Rocks in northern Victoria Land,Antarctica,were investigated to elucidate the evolution of the lithospheric mantle surrounding the Transantarctic Mountains.Analy...Fabrics of five spinel peridotites collected from Baker Rocks in northern Victoria Land,Antarctica,were investigated to elucidate the evolution of the lithospheric mantle surrounding the Transantarctic Mountains.Analyses revealed the development of crystallographic preferred orientations(CPOs),a slight decrease in mean grain size and J-index across varying proportions of clinopyroxene,and interlobate to amoeboid textures.These findings indicate that dislocation creep is the dominant deformation mechanism for the analyzed samples.展开更多
The alkaline volcanism of the Cameroon Volcanic Line in its northern domain has raised many fresh enclaves of peridotites. The samples selected come from five (05) different localities (Liri, in the plateau of Kapsiki...The alkaline volcanism of the Cameroon Volcanic Line in its northern domain has raised many fresh enclaves of peridotites. The samples selected come from five (05) different localities (Liri, in the plateau of Kapsiki, Mazélé in the NE of Ngaoundéré, Tello and Ganguiré in the SE of Ngaoundéré and Likok, locality located in the west of Ngaoundé). The peridotite enclaves of the above localities show restricted mineralogical variation. Most are four-phase spinel-lherzolites, indicating that this is the main lithology that forms the lithospheric mantle below the shallow zone. No traces of garnet or primary plagioclase were detected, which strongly limits the depth range from which the rock fragments were sampled. The textures and the wide equilibrium temperatures (884˚C - 1115˚C) indicate also entrainment of lherzolite xenoliths from shallow depths within the lithosphere and the presence of mantle diapirism. The exchange reactions and equilibrium state established in this work make it possible to characterize the chemical composition of the upper mantle of each region and test the equilibrium state of the phases between them. Variations of major oxides and incompatible elemental concentrations in clinopyroxene indicate a primary control by partial melting. The absence of typical “metasomatic” minerals, low equilibration temperatures and enriched LREE patterns indicate that the upper mantle below septentrional crust of Cameroun underwent an event of cryptic metasomatic enrichment prior to partial melting. The distinctive chemical features, LREE enrichment, strong U, Ce and Pr, depletion relative to Ba, Nb, La, Pb, and T, fractionation of Zr and Hf and therefore ligh high Zr/Hf ratio, low La/Yb, Nb/La and Ti/Eu are all results of interaction of refractory peridotite residues with carbonatite melts.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） There is a decrease in thermal gradient and in lithospheric thickness from the coast （Xinchang： the second-type geotherm） to the inland （Mingxi： the first-type geotherm） in South China （from -80 km to 〉90 kin）, which is collaborated with westward variation in basalt geochemistry. （c） The weak convex-upward pattern of the geo- therm in Qilin （麒麟） and Leizhou （雷州） Peninsula is peculiar, probably reflecting a transitional feature between conductive and advective heat transfer. It may result from impregnation of mantle plume on the base of the lithosphere. These new results not only provide a basic framework for the ongoing 4-D lithosphere mapping project in eastern China, but also yield important implications for deep processes that operated over the past.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 partial melting of Archean lithospheric mantle that was variably hybridised by melts derived from foundered lower crustal edogite, although it cannot be excluded that some of the melts were derived from depleted man. tie peridotite. In other words, parent melts of most granulite xenoliths could share the same petrogenesis as the〉110 Ma Mesozoic basalts from the NCC.展开更多
Lithological observations and mineralogical analyses on pyroxene and hornblende megacrysts and pyroxene and hornblende cumulates in xenoliths in the Mesozoic plutons of the Tongling region, Anhui Province, provide evi...Lithological observations and mineralogical analyses on pyroxene and hornblende megacrysts and pyroxene and hornblende cumulates in xenoliths in the Mesozoic plutons of the Tongling region, Anhui Province, provide evidence for the magmatic underplating of mantle-derived alkali-olivine basalt at circa 140 Ma. The pyroxene and hornblende megacrysts and cumulates were formed through the AFC process at depths ranging from 27 to 35 km.展开更多
This paper presents the primary results of petrologic, mineralogical and petrochemical studies of garnet-bearing granulite facies rock xenoliths from Xinyang, Henan Province. These xenoliths, which are found in a pipe...This paper presents the primary results of petrologic, mineralogical and petrochemical studies of garnet-bearing granulite facies rock xenoliths from Xinyang, Henan Province. These xenoliths, which are found in a pipe of late Mesozoic volcaniclastic breccia, are of high density (3.13–3.30 g/cm3) and high seismic velocity (Vp = 7.04–7.31 km/s), being products of underplating of basaltic magmas and had experienced granulite facies metamorphism. The underplating and metamorphism took place before the eruption of the host rock. Petrographical studies and equilibrium T-P calculations show that these xenoliths were captured at a 49 km depth and experienced at least a 16 km uplift before they were captured. The dynamics of the uplift could be related to the continent-continent collision between the North China plate and the Yangtze plate during the Triassic.展开更多
Our understanding of solid earth is from the surface, but the depth we can reach is very limited. So, most of the interpretations of geological processes and mechanisms extrapolated from all kinds of the surface pheno...Our understanding of solid earth is from the surface, but the depth we can reach is very limited. So, most of the interpretations of geological processes and mechanisms extrapolated from all kinds of the surface phenomena is greatly uncertain. Recently many researchers concentrate their efforts to the geological and geophysical studying of the deep processes of the solid earth. The International Lithosphere Project (ILP) started in 1981 now is also a frontier field. One of the concentrations of this project is the 3\|D structure, tectonic evolution and the dynamic models of lithosphere\|asthenosphere system (Li Xiaobo etc., 1997). The studying of the igneous rocks and bearing deep\|seated xenoliths, as one of the effective methods probing the structure and evolution of the lithosphere, plays a very important role in these aspects (Deng Jinfu et al., 1996; Lu Fengxiang, 1997).Commonly, magmas come to the surface in great speed and the covering lithosphere should be relatively thinner. For example, the thickness of the lithosphere in East China is about 60～80km in the era when the volcanoes erupted (Deng Jinfu et al. 1994). Recently, many deep\|seated xenoliths were found in several localities of southwest Tianshan (Han Baofu et al., 1998). But in Qinghai—Xizang plateau, “So far no any xenoliths of mantle rocks as peridotites, lherzolites and harzburgites and high pressure granulites were found (Deng Wanming et al., 1997)”.. But in the fieldwork of 1998 we find some deep\|seated xenoliths in Cenozoic basaltic rocks in Kangxiwa region, West Kunlun, China. This work is a part of the project “XinJiang DuShanZi—QuanShuiGou transect” managed by academician Xiao Xuchang.展开更多
Rare earth element (REE) contents, and Sr and Nd isotopic compositions were measured for three suites of mantle xenoliths from the Kuandian, Hannuoba and Huinan volcanoes in the north of the Sino-Korean Platform. From...Rare earth element (REE) contents, and Sr and Nd isotopic compositions were measured for three suites of mantle xenoliths from the Kuandian, Hannuoba and Huinan volcanoes in the north of the Sino-Korean Platform. From the correlations of Yb contents with Al/Si and Ca/Si ratios, the peridotites are considered to be the residues of partial melting of the primitive mantle. The chondrite-normalized REE compositions are diverse, varying from strongly LREE-depleted to LREE-enriched, with various types of REE patterns. Metasomatic alteration by small-volume silicate melts, of mantle peridotites previously variably depleted due to fractional melting in the spinel peridotite field, can account for the diversity of REE patterns. The Sr/ Ba versus La/Ba correlation indicates that the metasomatic agent was enriched in Ba over Sr and La, suggestive of its volatile-rich signature and an origin by fluid-triggered melting in an ancient subduction zone. The Sr and Nd isotopic compositions of these xenoliths, even from a single locality, vary widely, covering those of Cenozoic basalts in eastern China. The depleted end of the Sr-Nd isotope correlation is characterized by clearly higher 143Nd/144Nd and a broader range of 87Sr/86Sr compared to MORB. The low-143Nd/144Nd and high-87Sr/86Sr data distribution at the other end of data array suggests the existence of two enriched mantle components, like EM1 and EM2. The correlations between 143Nd/l44Nd and 147Sm/N4Nd ratios in these xenoliths suggest at least two mantle metasomatic events, i.e. events at 0.6-1.0 Ga and 280-400 Ma ago.展开更多
Three special types of xenoliths have recently been found in an aegirine-augite syenite porphyry in Liuhe, Yunnan, China. Petrographical, petrochemical, electron microprobe, and scanning electron microscopy studies in...Three special types of xenoliths have recently been found in an aegirine-augite syenite porphyry in Liuhe, Yunnan, China. Petrographical, petrochemical, electron microprobe, and scanning electron microscopy studies indicate that pure calcite xenocrysts and quartz-bearing topaz pegmatite xenoliths result from the degassing of mantle fluids during their migration, and that black microcrystalline iron-rich silicate-melt xenoliths are the product of the extraction of mantle fluids accompanying degassing and are composed dominantly of quartz, chlorite, and iron-rich columnar and sheet silicate minerals with characteristic minerals, such as native iron, apatite, and zircon. According to the bulk-rock chemical and mineral compositions and crystallization states, the microcrystalline melt xenoliths are not the product of conventional magmatism, and especially the existence of native iron further proves that the xenoliths were mantle fluid materials under reduction or anoxic conditions. The study of the special xenoliths furnishes an important deep-process geochemical background of polymetallic mineralization in different rocks and strata in the study area.展开更多
Metamorphic xenoliths within the Nushan alkali basalt of northeastern Anhui (NEA),China ,are from the middle-lower crust.They could be divided into two end-members:basic and acid.Interme-diate xenoliths are scarcely f...Metamorphic xenoliths within the Nushan alkali basalt of northeastern Anhui (NEA),China ,are from the middle-lower crust.They could be divided into two end-members:basic and acid.Interme-diate xenoliths are scarcely found.Basic two-pyroxene granulites(pyriclasites) were formed at 720-810℃ and 7-8kb.Petrological and geochemical studies indicate that the primary magma of the protoliths of basic granulites was derived from the metasomatized upper mantle, while the pa-rental magma of the acid end-member was probably produced by partial melting of the basic rocks. The protoliths of charnockites and grey gneisses represent respectively the early and late crystallization products of the granitic magma.The Nushan granulites are much different in many aspects from the granulites exposed in the northern part of North China ,which implies the inhomogeneity regarding to the early evolution of the North China terranc.展开更多
Cenozoic potassic mafic volcanism (kamafugite magamtism) in West Qinling, Gansu province of China is a important section of Cenozoic volcanic belt of Qingzang (Tibet) plateau and adjacent area. The kamafugite magma sh...Cenozoic potassic mafic volcanism (kamafugite magamtism) in West Qinling, Gansu province of China is a important section of Cenozoic volcanic belt of Qingzang (Tibet) plateau and adjacent area. The kamafugite magma show near\|primary magma characteristics. Strong incompatible elements concentrations in the volcanic rocks infer the kamafugite magmas may be origined from a enrichment mantle sources earlier.Four groups of deep\|seated xenoliths were collected from a kamafugite lava in West Qinling, Gansu province, China: (1)spinel Iherzolite and garnet Iherzolite; (2) harzburgite; (3) dunite and (4) clinopyroxenite. All suite of peridotite xenoliths are Cr\|diopside series. The main textures of peridotite xenoliths are granoblastic, porphyroclastic and granular, but the textures of clinopyroxenite are mainly poikilitic. The textural characteristics, mineral chemical variations and mineral geothermometric data show that the mantle source region of the Cenozoic kamafugite magam are very complex and undertook partial melting and enrichment associated with alkaline metasomatism by fluid and carbonatite melts. Geothermometry indicates the equilibration p and T conditions of the spinel lherzolite and garnet lherzolite are 970℃, 18 9GPa and 1219℃,27 61GPa corresponding to depth of 62km and 92km representatively. We suggest, combining with geophysical data, the spinel lherzolite formed at the top of upper mantle, the garnet lherzolite represent the base of lithosphere or the top of asthenosphere, but the clinopyroxenite is formed by cumulation in shallower magma reservoir. Kamafugite magmas formed within the stability field of garnet lherzolite by partial melting, the partial melting degree is only about 1%～2%. There is a superheating condition in Cenozoic mantle of West Qinling, which may be related to strong uplift of Qingzang (Tibet) plateau since cenozoic and extrusion east forward of asthenosphere beneath the Qingzang (Tibet) plateau.展开更多
The Precambrian lower crust rocks at the southeastern margin of the North China Craton （NCC） are mainly exposed as granulite xenoliths hosted by Mesozoic dioritic porphyry and metamorphic terrains in the Xuzhou-Suzh...The Precambrian lower crust rocks at the southeastern margin of the North China Craton （NCC） are mainly exposed as granulite xenoliths hosted by Mesozoic dioritic porphyry and metamorphic terrains in the Xuzhou-Suzhou area. Garnet amphiholites and garnet granulites are two kinds of typical lower-crustal xenoliths and were selected to reconstruct different stages of the metamorphic process. In this study, in view of multistage metamorphic evolution and reworking, phase equilibria modeling was used for the first time to better constrain peak P-T conditions of the xenoliths. Some porphyroblastic garnets have a weak zonal structure in composition with homogeneous cores and were surrounded by thin rims with an increase in XMg and a decrease in X Ca （or X Mg）- Clinopyroxene contain varying amounts of Na2O and Al2O3 as well as amphibole of TiO2, while plagioclases are different in calcium contents. Peak metamorphic P-T conditions are calculated by the smallest garnet x（g） （Fe2＋/（Fe2＋＋Mg）） contours and the smallest plagioclase ca（pl） （Ca/（Ca＋Na）） contours in NCFMASHTO （Na2O-CaO-FeO-MgO-Al2O3-SiO2- H20-TiO2-Fe2O3） system, which are consistent with those estimated by conventional geothermobarometry. The new results show that the peak and decompressional P-T conditions for the rocks are 850-900 ℃/ 1.4-1.6 GPa and 820-850 ℃/0.9-1.3 GPa, respectively, suggestive of high and middle-low pressure granulite-facies metamorphism. Combined with previous zircon U-Pb dating and conventional geothermobarometry data, it is indicated that the xenoliths experienced a clockwise P-T-t evolution with nearisothermal deeompressional process, suggestive of the Paleoproterozoic subduction-collision setting. In this regard, the studied region together with Jiao-Liao-Ji belt is further documented to make up a Paleopro- terozoic collisional orogen in the eastern block of the NCC.展开更多
The xenoliths in host rocks of hydrothermal gold deposits can generally provide much geochemical information of the deep rocks, which may have an implication for the sources of ore-forming materials. Geochronology and...The xenoliths in host rocks of hydrothermal gold deposits can generally provide much geochemical information of the deep rocks, which may have an implication for the sources of ore-forming materials. Geochronology and geochemical characteristics are reported for a granite xenolith, which is enclosed by the lamprophyre in the Zhenyuan gold deposit(Yunnan Province, SW China). This granite xenolith mainly consists of K-feldspar, quartz, and plagioclase with trace amounts of magnetite, titanite, apatite, zircon, and sulfides. Zircons from the granite xenolith yield a weighted average U-Pb age of 281.1 ± 1.3 Ma(MSWD = 2.1), which could represent the crystallization age of this granite xenolith. The Ti-in-zircon geothermometer and the Mn concentration in apatite calculate that this granite xenolith formed at 685 ± 43℃ with the logf_(O2) values ranging from NNO + 3.7 to NNO + 6.4. The zircons in the granite xenolith have a restricted range of positive ε_(Hf)(t) values ranging from +9.4 to +10.8, and the corresponding Hf TDM2 model ages range from 588 to 678 Ma. The zircon U-Pb age and the Hf isotopic compositions indicate this granite xenolith within the lamprophyre is mainly derived from partial melting of juvenile crustal rocks before the completed closure of the Ailaoshan Ocean. The pyrites in the granite xenolith have higher Bi concentrations, and lower As, Sb, and Tl concentrations than the gold-bearing pyrites of the ores in the Zhenyuan gold deposit. The low Au concentrations of the pyrites together with the ore-forming age of the Zhenyuan gold deposit(Oligocene) indicate the granite xenolith may have limited contribution to the gold mineralization of the Zhenyuan gold deposit.展开更多
We present petrography and mineral chemistry for both phlogopite,from mantle-derived xenoliths (garnet peridotite,eclogite and clinopyroxene-phlogopite rocks) and for megacryst,macrocryst and groundmass flakes from th...We present petrography and mineral chemistry for both phlogopite,from mantle-derived xenoliths (garnet peridotite,eclogite and clinopyroxene-phlogopite rocks) and for megacryst,macrocryst and groundmass flakes from the Grib kimberlite in the Arkhangelsk diamond province of Russia to provide new insights into multi-stage metasomatism in the subcratonic lithospheric mantle (SCLM) and the origin of phlogopite in kimberlite.Based on the analysed xenoliths,phlogopite is characterized by several generations.The first generation (Phl1) occurs as coarse,discrete grains within garnet peridotite and eclogite xenoliths and as a rock-forming mineral within clinopyroxene-phlogopite xenoliths.The second phlogopite generation (Phl2) occurs as rims and outer zones that surround the Phl1 grains and as fine flakes within kimberlite-related veinlets filled with carbonate,serpentine,chlorite and spinel.In garnet peridotite xenoliths,phlogopite occurs as overgrowths surrounding garnet porphyroblasts,within which phlogopite is associated with Cr-spinel and minor carbonate.In eclogite xenoliths,phlogopite occasionally associates with carbonate bearing veinlet networks.Phlogopite,from the kimberlite,occurs as megacrysts,macrocrysts,microcrysts and fine flakes in the groundmass and matrix of kimberlitic pyroclasts.Most phlogopite grains within the kimberlite are characterised by signs of deformation and form partly fragmented grains,which indicates that they are the disintegrated fragments of previously larger grains.Phl1,within the garnet peridotite and clinopyroxeneephlogopitexenoliths,is characterised bylow Ti and Cr contents (TiO2<1 wt.%,Cr2O3<1 wt.% andMg#=100×Mg/(MgtFe)>92) typical of primary peridotite phlogopite in mantle peridotite xenoliths from global kimberlite occurrences.They formed during SCLM metasomatism that led to a transformation from garnet peridotite to clinopyroxene-phlogopite rocks and the crystallisation of phlogopite and high-Cr clinopyroxene megacrysts before the generation of host-kimberlite magmas.One of the possible processes to generate low-Ti-Cr phlogopite is via the replacement of garnet during its interaction with a metasomatic agent enriched in K and H2O.Rb-Sr isotopic data indicates that the metasomatic agent had a contribution of more radiogenic source than the host-kimberlite magma.Compared with peridotite xenoliths,eclogite xenoliths feature low-Ti phlogopites that are depleted in Cr2O3 despite a wider range of TiO2 concentrations.The presence of phlogopite in eclogite xenoliths indicates that metasomatic processes affected peridotite as well as eclogite within the SCLM beneath the Grib kimberlite.Phl2 has high Ti and Cr concentrations (TiO2 > 2 wt.%,Cr2O3 > 1 wt.% and Mg#=100 × Mg/(Mg + Fe)< 92) and compositionally overlaps with phlogopite from polymict breccia xenoliths that occur in global kimberlite formations.These phlogopites are the product of kimberlitic magma and mantle rock interaction at mantle depths where Phl2 overgrew Phl1 grains or crystallized directly from stalled batches of kimberlitic magmas.Megacrysts,most macrocrysts and microcrysts are disintegrated phlogopite fragments from metasomatised peridotite and eclogite xenoliths.Fine phlogopite flakes within kimberlite groundmass represent mixing of high-Ti-Cr phlogopite antecrysts and high-Ti and low-Cr kimberlitic phlogopite with high Al and Ba contents that may have formed individual grains or overgrown antecrysts.Based on the results of this study,we propose a schematic model of SCLM metasomatism involving phlogopite crystallization,megacryst formation,and genesis of kimberlite magmas as recorded by the Grib pipe.展开更多
The compositions of the whole rocks and trace elements of minerals in peridotites can reflect the characteristics of the lithospheric mantle. The nature and evolution of the Cenozoic lithospheric mantle beneath Hannuo...The compositions of the whole rocks and trace elements of minerals in peridotites can reflect the characteristics of the lithospheric mantle. The nature and evolution of the Cenozoic lithospheric mantle beneath Hannuoba （汉诺坝）, located on the north edge of the intra-North China orogenic belt, are discussed based on the in-situ LAM-ICPMS detected trace element compositions of clinopyroxenes in the Hannuoba peridotitic xenoliths combined with detailed petrography and geochemistry studies. The Hannuoba lithospheric mantle was formed by different partial meltings of the primitive mantle. Most of the samples reflect the partial melting degree of lower than 5% with a few samples of 15%-20%. Major element compositions of the whole rocks and geochemical compositions of clinopyroxenes reveal the coexistence of both fertile and depleted mantle underneath the Hannuoba region during the Cenozoic. This was probably caused by the asthenospheric mantle replacing the aged craton mantle through erosion, intermingling and modification. Our conclusion is further supported by the existence of both carbonatitic magmatic material and silicate melt/ fluid metasomatism as magnified by the trace elements of the clinopyroxencs from the Hannuoba lithospherJc mantle.展开更多
This paper presents whole-rock Hf isotopic data for a suite of eclogite and garnet clinopyroxenite xenoliths hosted in the Early Cretaceous dioritic intrusions from the Xuzhou-Suzhou area along the southeastern margin...This paper presents whole-rock Hf isotopic data for a suite of eclogite and garnet clinopyroxenite xenoliths hosted in the Early Cretaceous dioritic intrusions from the Xuzhou-Suzhou area along the southeastern margin of the Eastern Block of the North China Craton(NCC).Six of the eight studied xenolith samples plot significantly above the terrestrial Hf-Nd isotopic array and haveεHf(0)value up to+60.All the samples define a well correlated 147 Sm/144 Nd-143 Nd/144 Nd age of 2081 Ma,which is considered to record the granulite-facies metamorphism.In contrast,the Lu-Hf isotope system faithfully records the protolith information.The mineralogical assemblage,especially garnet and/or zircon(rutile to some extent)mainly controlled the decoupling of Hf-Nd isotope.The metamorphic modification on protolith characteristics and the differences in element mobility during metamorphism may also reinforce the observed decoupling between the Sm-Nd and Lu-Hf isotope systems;i.e.,the absence of the correlations inεNd-εHf and also 87 Sr/86 Sr-143 Nd/144 Nd diagram.The Lu/Hf isochron age of 2424 Ma is similar to the zircon age peak of the studied xenoliths and the dominant age of NCC basement,indicating that the igneous protolith has an affinity to the Archean basement of the NCC.Furthermore,the positiveεHf(t)values at 2500 Ma indicate a crustal growth event of 2500 Ma in the NCC.展开更多
It is known that large amounts of Cenozoic high potassium volcanic rocks occur on the Tibetan plateau. The question is where do those high potassium magmas come from? Since the plateau is being compressed by subductio...It is known that large amounts of Cenozoic high potassium volcanic rocks occur on the Tibetan plateau. The question is where do those high potassium magmas come from? Since the plateau is being compressed by subduction and collision from the surrounding continents,it is a puzzle for us what is the formational environment and tectonic setting of these volcanic rocks? In particular,what is the relationship between these special rocks and formation and uplift of the plateau? We recently carried out an investigation on these Cenozoic volcanic rocks in Hoh Xil,northern Tibetan plateau,including volcanic rocks in the Jingyuhu,Xiongyingtai and Shuangquanzi areas. In the region,some older lava flows occur as thick sheets with a flat surface and weathering crust; while some relatively younger lavas remain a relict volcanic cone or vent. Most of the relict cones are small (<100m in diameter) and some are over hundred meters,distributed along faults,particular strike\|slip fault,e.g.,East Kunlun strike slip fault. Relatively,intermediate\|acid volcanic rocks are prominent,and basic\|intermediate and acid are subordinate. Petrological and geochemical results show that these volcanic rocks have many common affinities,characterized by high contents of w (K 2O)+ w (Na 2O) (about 8%),and w (K\-2O)/ w (Na\-2O)>1 or close to 1,and mostly belonged to shoshonite\|trachyte association and some to ultra\|potassic rocks. The K\|Ar dating of whole rock and mica shows that the volcanism lasts from middle Miocene (15 47Ma) to Pleistocene (0 69Ma); they are 0 69Ma,13 77Ma and 15 47Ma in Jingyuhu; 11 05Ma,12 22Ma and 12 83Ma in Xiongyingai,; 1 58Ma,2 24Ma,5 23Ma,5 85Ma,8 20Ma,8 41Ma and 10 67Ma in Shuangquanzi.Two types of xenolith and xenocryst were found in Jingyuhu and Xiongyingtai,i.e..,crustal xenolith and mantle xenocryst.展开更多
Two types of melt pockets, closed melt pocket （CMP） and open melt pocket （OMP）, are recognized from the peridotite xenoliths entrained in the Cenozoic kamafugites in western Qinling （秦岭）, Central China. The Ha...Two types of melt pockets, closed melt pocket （CMP） and open melt pocket （OMP）, are recognized from the peridotite xenoliths entrained in the Cenozoic kamafugites in western Qinling （秦岭）, Central China. The Haoti （好梯） CMPs have a mineral assemblage of olivine＋ clinopyroxene＋amphibole＋K- feldspar, whereas the Baiguan （白关） CMPs are composed of olivine＋clinopyroxene＋Umenite＋carbonate. The components of the OMPs are more complicated. In the Haoti OMPs, there are olivine, ciinopyroxene, glass, low modal abundances of amphibole, K-feldspar （Kfs）, Umenite, sulfide, chlorite, perovskite, chromite and phlogopite. The Baiguan OMPs contain olivine, clinopyroxene, glass, chlorite and chromite. Compositionally, ofivines in the CMPs and OMPs are both apparently depleted in Ni, and those in the OMPs are also depleted in Fe and Mg, and enriched in Ca compared to the primary ones. Ciinopyroxenes display large and systematical compositional variations between the CMPs and OMPs, particularly in Al, Cr, Na, Ca and Ti. Glasses are generally depleted in Si compared to the worldwide glasses in melt pockets, although they still have large variations. Amphiboles and K-feldspars have relatively restricted compositional variations. The petrographical observations and mineral chemistry suggest that the Haoti and Baiguan CMPs were generated by the in-sitn decompression melting of orthopyroxenes, olivines and clinopyroxenes, and by the addition of minor external K-rich and Ca-rich melt/fluids. The OMPs formed during the latest metasomatic event in the lithospheric mantle beneath the western Qinling.展开更多
In order to distinguish the primary microstructures developed under mantle conditions from the secondary phenomena after xenolith entrainment in the host magma, this study intends to discuss the genesis of spongy, sie...In order to distinguish the primary microstructures developed under mantle conditions from the secondary phenomena after xenolith entrainment in the host magma, this study intends to discuss the genesis of spongy, sieve-textured, and reaction rims on mineral grains of mantle xenoliths in the Cenozoic basalts from the western North China craton. The spongy rims on primary clinopyroxene show neither obvious compositional zoning nor preferential development towards the host basalt and probably suggest an origin via partial melting within the lithospheric mantle or pressure release as the xenoliths were carried upwards. The sieve-textured rims on primary spinel show clear chemical zoning with increasing Cr# and decreasing AI towards the host basalt. They are interpreted as the result of partial melting due to heating of the host basaltic magma and decreasing pressure during ascent proc- ess. Post-entrainment reaction mainly generated secondary minerals at contacts between the host ba- saltic melt and xenoliths. The secondary clinopyroxene in reaction rims develops on primary clinopy- roxene and has higher Ti, Ca, and Fe contents and lower Mg# and Si contents than primary one, while the secondary spinel on primary Cr-AI spinel is titanomagnetite. The secondary olivine and clinopy- roxene in the reaction rims on primary orthopyroxene are enriched in Fe, Al, and Ti. The occurrence of reaction rims in mantle xenoliths reflects disequilibrium processes after xenolith entrainment in the basaltic melt. The spongy rims on primary clinopyroxene may not be related to the interaction with thehost basaltic melt, while the sieve-textured rims on primary spinel and reactions rims on primary clinopyroxene, spinel, and orthopyroxene may result from post-entrainment reaction between the host basaltic melt and xenolith minerals.展开更多
基金supported by funds from the Ministry of Science and Technology of the People's Republic of China(No.2019YFA0708603)NSFC(Nos.41973050,42288201,41930215)the Key Special Project for Introduced Talents Team of Southern Marine Science and Engineering Guangdong Laboratory(Guangzhou)(No.GML2019ZD0202)。
文摘Mineralogical data are presented for the peridotite xenoliths from Miocene(~19 Ma)Qingyuan basalts in the eastern North China Craton(NCC),with the aim of constraining on property of the sub-continental lithospheric mantle(SCLM)beneath the northern Tan-Lu fault zone(TLFZ)during the Cenozoic.The Qingyuan peridotites are dominated by spinel lherzolites with moderate-Mg^(#)olivines(89.4 to 91.2),suggesting that the regional SCLM is mainly transitional and fertile.Light rare earth element(LREE)-depleted,slightly depleted and enriched clinopyroxenes(Cpx)are identified in different peridotites.Chemical compositions of the LREE-enriched Cpx and the presence of phlogopite suggest that the Qingyuan SCLM has experienced silicate-related metasomatism.The synthesis of available mineral chemical data of the mantle xenoliths across the NCC confirms the SCLM beneath the NCC is highly heterogeneous in time and space.The Mesozoic–Cenozoic SCLM beneath the TLFZ and neighboring regions are more fertile and thinner than that beneath the region away from the fault zone.The fertile and refractory peridotite xenoliths experienced varying degrees of silicate and carbonatite metasomatism,respectively.The spatial-temporal lithospheric mantle heterogeneity in composition,age and thickness suggest that the trans-lithosphere fault zone played an important role in heterogeneous replacement of refractory cratonic lithospheric mantle.
基金supported by the Korea Polar Research Institute project PE24050.
文摘Fabrics of five spinel peridotites collected from Baker Rocks in northern Victoria Land,Antarctica,were investigated to elucidate the evolution of the lithospheric mantle surrounding the Transantarctic Mountains.Analyses revealed the development of crystallographic preferred orientations(CPOs),a slight decrease in mean grain size and J-index across varying proportions of clinopyroxene,and interlobate to amoeboid textures.These findings indicate that dislocation creep is the dominant deformation mechanism for the analyzed samples.
文摘The alkaline volcanism of the Cameroon Volcanic Line in its northern domain has raised many fresh enclaves of peridotites. The samples selected come from five (05) different localities (Liri, in the plateau of Kapsiki, Mazélé in the NE of Ngaoundéré, Tello and Ganguiré in the SE of Ngaoundéré and Likok, locality located in the west of Ngaoundé). The peridotite enclaves of the above localities show restricted mineralogical variation. Most are four-phase spinel-lherzolites, indicating that this is the main lithology that forms the lithospheric mantle below the shallow zone. No traces of garnet or primary plagioclase were detected, which strongly limits the depth range from which the rock fragments were sampled. The textures and the wide equilibrium temperatures (884˚C - 1115˚C) indicate also entrainment of lherzolite xenoliths from shallow depths within the lithosphere and the presence of mantle diapirism. The exchange reactions and equilibrium state established in this work make it possible to characterize the chemical composition of the upper mantle of each region and test the equilibrium state of the phases between them. Variations of major oxides and incompatible elemental concentrations in clinopyroxene indicate a primary control by partial melting. The absence of typical “metasomatic” minerals, low equilibration temperatures and enriched LREE patterns indicate that the upper mantle below septentrional crust of Cameroun underwent an event of cryptic metasomatic enrichment prior to partial melting. The distinctive chemical features, LREE enrichment, strong U, Ce and Pr, depletion relative to Ba, Nb, La, Pb, and T, fractionation of Zr and Hf and therefore ligh high Zr/Hf ratio, low La/Yb, Nb/La and Ti/Eu are all results of interaction of refractory peridotite residues with carbonatite melts.
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） There is a decrease in thermal gradient and in lithospheric thickness from the coast （Xinchang： the second-type geotherm） to the inland （Mingxi： the first-type geotherm） in South China （from -80 km to 〉90 kin）, which is collaborated with westward variation in basalt geochemistry. （c） The weak convex-upward pattern of the geo- therm in Qilin （麒麟） and Leizhou （雷州） Peninsula is peculiar, probably reflecting a transitional feature between conductive and advective heat transfer. It may result from impregnation of mantle plume on the base of the lithosphere. These new results not only provide a basic framework for the ongoing 4-D lithosphere mapping project in eastern China, but also yield important implications for deep processes that operated over the past.
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 partial melting of Archean lithospheric mantle that was variably hybridised by melts derived from foundered lower crustal edogite, although it cannot be excluded that some of the melts were derived from depleted man. tie peridotite. In other words, parent melts of most granulite xenoliths could share the same petrogenesis as the〉110 Ma Mesozoic basalts from the NCC.
基金the NationalNatural Science Foundation of China(Grants 40272034, 40133020)the Ministry of Science and Technology of China(Grant 1999043206) the Korea Science and Engineering Foundation(Grant KOSEF-20005-131-03-02).
文摘Lithological observations and mineralogical analyses on pyroxene and hornblende megacrysts and pyroxene and hornblende cumulates in xenoliths in the Mesozoic plutons of the Tongling region, Anhui Province, provide evidence for the magmatic underplating of mantle-derived alkali-olivine basalt at circa 140 Ma. The pyroxene and hornblende megacrysts and cumulates were formed through the AFC process at depths ranging from 27 to 35 km.
文摘This paper presents the primary results of petrologic, mineralogical and petrochemical studies of garnet-bearing granulite facies rock xenoliths from Xinyang, Henan Province. These xenoliths, which are found in a pipe of late Mesozoic volcaniclastic breccia, are of high density (3.13–3.30 g/cm3) and high seismic velocity (Vp = 7.04–7.31 km/s), being products of underplating of basaltic magmas and had experienced granulite facies metamorphism. The underplating and metamorphism took place before the eruption of the host rock. Petrographical studies and equilibrium T-P calculations show that these xenoliths were captured at a 49 km depth and experienced at least a 16 km uplift before they were captured. The dynamics of the uplift could be related to the continent-continent collision between the North China plate and the Yangtze plate during the Triassic.
文摘Our understanding of solid earth is from the surface, but the depth we can reach is very limited. So, most of the interpretations of geological processes and mechanisms extrapolated from all kinds of the surface phenomena is greatly uncertain. Recently many researchers concentrate their efforts to the geological and geophysical studying of the deep processes of the solid earth. The International Lithosphere Project (ILP) started in 1981 now is also a frontier field. One of the concentrations of this project is the 3\|D structure, tectonic evolution and the dynamic models of lithosphere\|asthenosphere system (Li Xiaobo etc., 1997). The studying of the igneous rocks and bearing deep\|seated xenoliths, as one of the effective methods probing the structure and evolution of the lithosphere, plays a very important role in these aspects (Deng Jinfu et al., 1996; Lu Fengxiang, 1997).Commonly, magmas come to the surface in great speed and the covering lithosphere should be relatively thinner. For example, the thickness of the lithosphere in East China is about 60～80km in the era when the volcanoes erupted (Deng Jinfu et al. 1994). Recently, many deep\|seated xenoliths were found in several localities of southwest Tianshan (Han Baofu et al., 1998). But in Qinghai—Xizang plateau, “So far no any xenoliths of mantle rocks as peridotites, lherzolites and harzburgites and high pressure granulites were found (Deng Wanming et al., 1997)”.. But in the fieldwork of 1998 we find some deep\|seated xenoliths in Cenozoic basaltic rocks in Kangxiwa region, West Kunlun, China. This work is a part of the project “XinJiang DuShanZi—QuanShuiGou transect” managed by academician Xiao Xuchang.
文摘Rare earth element (REE) contents, and Sr and Nd isotopic compositions were measured for three suites of mantle xenoliths from the Kuandian, Hannuoba and Huinan volcanoes in the north of the Sino-Korean Platform. From the correlations of Yb contents with Al/Si and Ca/Si ratios, the peridotites are considered to be the residues of partial melting of the primitive mantle. The chondrite-normalized REE compositions are diverse, varying from strongly LREE-depleted to LREE-enriched, with various types of REE patterns. Metasomatic alteration by small-volume silicate melts, of mantle peridotites previously variably depleted due to fractional melting in the spinel peridotite field, can account for the diversity of REE patterns. The Sr/ Ba versus La/Ba correlation indicates that the metasomatic agent was enriched in Ba over Sr and La, suggestive of its volatile-rich signature and an origin by fluid-triggered melting in an ancient subduction zone. The Sr and Nd isotopic compositions of these xenoliths, even from a single locality, vary widely, covering those of Cenozoic basalts in eastern China. The depleted end of the Sr-Nd isotope correlation is characterized by clearly higher 143Nd/144Nd and a broader range of 87Sr/86Sr compared to MORB. The low-143Nd/144Nd and high-87Sr/86Sr data distribution at the other end of data array suggests the existence of two enriched mantle components, like EM1 and EM2. The correlations between 143Nd/l44Nd and 147Sm/N4Nd ratios in these xenoliths suggest at least two mantle metasomatic events, i.e. events at 0.6-1.0 Ga and 280-400 Ma ago.
基金supported by National Natural Science Foundation of China grant 40473027 and 40773031Foundation of Open Subjects of the State Key Laboratory of Geological Processes and Mineral Resources of the China University of Geosciences grant GPMR0509 and GPMR200705the Project of the State Key(Preparation Support)Disciplines of Mineralogy,Petrology and Mineral Deposit Geology of Sichuan Province.
文摘Three special types of xenoliths have recently been found in an aegirine-augite syenite porphyry in Liuhe, Yunnan, China. Petrographical, petrochemical, electron microprobe, and scanning electron microscopy studies indicate that pure calcite xenocrysts and quartz-bearing topaz pegmatite xenoliths result from the degassing of mantle fluids during their migration, and that black microcrystalline iron-rich silicate-melt xenoliths are the product of the extraction of mantle fluids accompanying degassing and are composed dominantly of quartz, chlorite, and iron-rich columnar and sheet silicate minerals with characteristic minerals, such as native iron, apatite, and zircon. According to the bulk-rock chemical and mineral compositions and crystallization states, the microcrystalline melt xenoliths are not the product of conventional magmatism, and especially the existence of native iron further proves that the xenoliths were mantle fluid materials under reduction or anoxic conditions. The study of the special xenoliths furnishes an important deep-process geochemical background of polymetallic mineralization in different rocks and strata in the study area.
文摘Metamorphic xenoliths within the Nushan alkali basalt of northeastern Anhui (NEA),China ,are from the middle-lower crust.They could be divided into two end-members:basic and acid.Interme-diate xenoliths are scarcely found.Basic two-pyroxene granulites(pyriclasites) were formed at 720-810℃ and 7-8kb.Petrological and geochemical studies indicate that the primary magma of the protoliths of basic granulites was derived from the metasomatized upper mantle, while the pa-rental magma of the acid end-member was probably produced by partial melting of the basic rocks. The protoliths of charnockites and grey gneisses represent respectively the early and late crystallization products of the granitic magma.The Nushan granulites are much different in many aspects from the granulites exposed in the northern part of North China ,which implies the inhomogeneity regarding to the early evolution of the North China terranc.
文摘Cenozoic potassic mafic volcanism (kamafugite magamtism) in West Qinling, Gansu province of China is a important section of Cenozoic volcanic belt of Qingzang (Tibet) plateau and adjacent area. The kamafugite magma show near\|primary magma characteristics. Strong incompatible elements concentrations in the volcanic rocks infer the kamafugite magmas may be origined from a enrichment mantle sources earlier.Four groups of deep\|seated xenoliths were collected from a kamafugite lava in West Qinling, Gansu province, China: (1)spinel Iherzolite and garnet Iherzolite; (2) harzburgite; (3) dunite and (4) clinopyroxenite. All suite of peridotite xenoliths are Cr\|diopside series. The main textures of peridotite xenoliths are granoblastic, porphyroclastic and granular, but the textures of clinopyroxenite are mainly poikilitic. The textural characteristics, mineral chemical variations and mineral geothermometric data show that the mantle source region of the Cenozoic kamafugite magam are very complex and undertook partial melting and enrichment associated with alkaline metasomatism by fluid and carbonatite melts. Geothermometry indicates the equilibration p and T conditions of the spinel lherzolite and garnet lherzolite are 970℃, 18 9GPa and 1219℃,27 61GPa corresponding to depth of 62km and 92km representatively. We suggest, combining with geophysical data, the spinel lherzolite formed at the top of upper mantle, the garnet lherzolite represent the base of lithosphere or the top of asthenosphere, but the clinopyroxenite is formed by cumulation in shallower magma reservoir. Kamafugite magmas formed within the stability field of garnet lherzolite by partial melting, the partial melting degree is only about 1%～2%. There is a superheating condition in Cenozoic mantle of West Qinling, which may be related to strong uplift of Qingzang (Tibet) plateau since cenozoic and extrusion east forward of asthenosphere beneath the Qingzang (Tibet) plateau.
基金financially supported by the National Natural Science Foundation of China (No. 41773020)the National Basic Research Program of China (No. 2015CB856104)the PhD Foundation of the Ministry of Education of China (No. 20133402130008)
文摘The Precambrian lower crust rocks at the southeastern margin of the North China Craton （NCC） are mainly exposed as granulite xenoliths hosted by Mesozoic dioritic porphyry and metamorphic terrains in the Xuzhou-Suzhou area. Garnet amphiholites and garnet granulites are two kinds of typical lower-crustal xenoliths and were selected to reconstruct different stages of the metamorphic process. In this study, in view of multistage metamorphic evolution and reworking, phase equilibria modeling was used for the first time to better constrain peak P-T conditions of the xenoliths. Some porphyroblastic garnets have a weak zonal structure in composition with homogeneous cores and were surrounded by thin rims with an increase in XMg and a decrease in X Ca （or X Mg）- Clinopyroxene contain varying amounts of Na2O and Al2O3 as well as amphibole of TiO2, while plagioclases are different in calcium contents. Peak metamorphic P-T conditions are calculated by the smallest garnet x（g） （Fe2＋/（Fe2＋＋Mg）） contours and the smallest plagioclase ca（pl） （Ca/（Ca＋Na）） contours in NCFMASHTO （Na2O-CaO-FeO-MgO-Al2O3-SiO2- H20-TiO2-Fe2O3） system, which are consistent with those estimated by conventional geothermobarometry. The new results show that the peak and decompressional P-T conditions for the rocks are 850-900 ℃/ 1.4-1.6 GPa and 820-850 ℃/0.9-1.3 GPa, respectively, suggestive of high and middle-low pressure granulite-facies metamorphism. Combined with previous zircon U-Pb dating and conventional geothermobarometry data, it is indicated that the xenoliths experienced a clockwise P-T-t evolution with nearisothermal deeompressional process, suggestive of the Paleoproterozoic subduction-collision setting. In this regard, the studied region together with Jiao-Liao-Ji belt is further documented to make up a Paleopro- terozoic collisional orogen in the eastern block of the NCC.
基金supported by the National Natural Science Foundation of China (Grant Nos. 91962105, 41802113)the Fundamental Research Funds for the Central Universities (Grant No.2019B08214)a grant from Jiangsu Provincial “Double Innovation Doctors” Program (Grant No.(2020) 30462)。
文摘The xenoliths in host rocks of hydrothermal gold deposits can generally provide much geochemical information of the deep rocks, which may have an implication for the sources of ore-forming materials. Geochronology and geochemical characteristics are reported for a granite xenolith, which is enclosed by the lamprophyre in the Zhenyuan gold deposit(Yunnan Province, SW China). This granite xenolith mainly consists of K-feldspar, quartz, and plagioclase with trace amounts of magnetite, titanite, apatite, zircon, and sulfides. Zircons from the granite xenolith yield a weighted average U-Pb age of 281.1 ± 1.3 Ma(MSWD = 2.1), which could represent the crystallization age of this granite xenolith. The Ti-in-zircon geothermometer and the Mn concentration in apatite calculate that this granite xenolith formed at 685 ± 43℃ with the logf_(O2) values ranging from NNO + 3.7 to NNO + 6.4. The zircons in the granite xenolith have a restricted range of positive ε_(Hf)(t) values ranging from +9.4 to +10.8, and the corresponding Hf TDM2 model ages range from 588 to 678 Ma. The zircon U-Pb age and the Hf isotopic compositions indicate this granite xenolith within the lamprophyre is mainly derived from partial melting of juvenile crustal rocks before the completed closure of the Ailaoshan Ocean. The pyrites in the granite xenolith have higher Bi concentrations, and lower As, Sb, and Tl concentrations than the gold-bearing pyrites of the ores in the Zhenyuan gold deposit. The low Au concentrations of the pyrites together with the ore-forming age of the Zhenyuan gold deposit(Oligocene) indicate the granite xenolith may have limited contribution to the gold mineralization of the Zhenyuan gold deposit.
基金financially supported by the Program for Development MSU.N.Korotaeva (Lomonosov Moscow State University) assisted with mineral microprobe analysessupported by the Russian President Grant for State Support of Young Russian Scientists (Project No.MK575.2017.5)to A.K.and N.L.+1 种基金by the Russian Foundation for Basic Research (Project No.16-05-00298a)by the Program of Basic Research of the Institute of the Geology of Ore Deposits, Petrography, Mineralogy, and Geochemistry (IGEM), Russian Academy of Sciences
文摘We present petrography and mineral chemistry for both phlogopite,from mantle-derived xenoliths (garnet peridotite,eclogite and clinopyroxene-phlogopite rocks) and for megacryst,macrocryst and groundmass flakes from the Grib kimberlite in the Arkhangelsk diamond province of Russia to provide new insights into multi-stage metasomatism in the subcratonic lithospheric mantle (SCLM) and the origin of phlogopite in kimberlite.Based on the analysed xenoliths,phlogopite is characterized by several generations.The first generation (Phl1) occurs as coarse,discrete grains within garnet peridotite and eclogite xenoliths and as a rock-forming mineral within clinopyroxene-phlogopite xenoliths.The second phlogopite generation (Phl2) occurs as rims and outer zones that surround the Phl1 grains and as fine flakes within kimberlite-related veinlets filled with carbonate,serpentine,chlorite and spinel.In garnet peridotite xenoliths,phlogopite occurs as overgrowths surrounding garnet porphyroblasts,within which phlogopite is associated with Cr-spinel and minor carbonate.In eclogite xenoliths,phlogopite occasionally associates with carbonate bearing veinlet networks.Phlogopite,from the kimberlite,occurs as megacrysts,macrocrysts,microcrysts and fine flakes in the groundmass and matrix of kimberlitic pyroclasts.Most phlogopite grains within the kimberlite are characterised by signs of deformation and form partly fragmented grains,which indicates that they are the disintegrated fragments of previously larger grains.Phl1,within the garnet peridotite and clinopyroxeneephlogopitexenoliths,is characterised bylow Ti and Cr contents (TiO2<1 wt.%,Cr2O3<1 wt.% andMg#=100×Mg/(MgtFe)>92) typical of primary peridotite phlogopite in mantle peridotite xenoliths from global kimberlite occurrences.They formed during SCLM metasomatism that led to a transformation from garnet peridotite to clinopyroxene-phlogopite rocks and the crystallisation of phlogopite and high-Cr clinopyroxene megacrysts before the generation of host-kimberlite magmas.One of the possible processes to generate low-Ti-Cr phlogopite is via the replacement of garnet during its interaction with a metasomatic agent enriched in K and H2O.Rb-Sr isotopic data indicates that the metasomatic agent had a contribution of more radiogenic source than the host-kimberlite magma.Compared with peridotite xenoliths,eclogite xenoliths feature low-Ti phlogopites that are depleted in Cr2O3 despite a wider range of TiO2 concentrations.The presence of phlogopite in eclogite xenoliths indicates that metasomatic processes affected peridotite as well as eclogite within the SCLM beneath the Grib kimberlite.Phl2 has high Ti and Cr concentrations (TiO2 > 2 wt.%,Cr2O3 > 1 wt.% and Mg#=100 × Mg/(Mg + Fe)< 92) and compositionally overlaps with phlogopite from polymict breccia xenoliths that occur in global kimberlite formations.These phlogopites are the product of kimberlitic magma and mantle rock interaction at mantle depths where Phl2 overgrew Phl1 grains or crystallized directly from stalled batches of kimberlitic magmas.Megacrysts,most macrocrysts and microcrysts are disintegrated phlogopite fragments from metasomatised peridotite and eclogite xenoliths.Fine phlogopite flakes within kimberlite groundmass represent mixing of high-Ti-Cr phlogopite antecrysts and high-Ti and low-Cr kimberlitic phlogopite with high Al and Ba contents that may have formed individual grains or overgrown antecrysts.Based on the results of this study,we propose a schematic model of SCLM metasomatism involving phlogopite crystallization,megacryst formation,and genesis of kimberlite magmas as recorded by the Grib pipe.
基金This paper is supported by the Research Foundation for OutstandingYoung Teachers , China University of Geosciences ( Wuhan )(CUGQNL0510)the National Natural Science Foundation of China(No .40425002) .
文摘The compositions of the whole rocks and trace elements of minerals in peridotites can reflect the characteristics of the lithospheric mantle. The nature and evolution of the Cenozoic lithospheric mantle beneath Hannuoba （汉诺坝）, located on the north edge of the intra-North China orogenic belt, are discussed based on the in-situ LAM-ICPMS detected trace element compositions of clinopyroxenes in the Hannuoba peridotitic xenoliths combined with detailed petrography and geochemistry studies. The Hannuoba lithospheric mantle was formed by different partial meltings of the primitive mantle. Most of the samples reflect the partial melting degree of lower than 5% with a few samples of 15%-20%. Major element compositions of the whole rocks and geochemical compositions of clinopyroxenes reveal the coexistence of both fertile and depleted mantle underneath the Hannuoba region during the Cenozoic. This was probably caused by the asthenospheric mantle replacing the aged craton mantle through erosion, intermingling and modification. Our conclusion is further supported by the existence of both carbonatitic magmatic material and silicate melt/ fluid metasomatism as magnified by the trace elements of the clinopyroxencs from the Hannuoba lithospherJc mantle.
基金supported by the National Natural Science Foundation of China (Nos. 41876037,41273013)the SDUST Research Fund (No. 2015TDJH101)+1 种基金the Scientific Research Foundation of Shandong University of Science and Technology for Recruited Talents (Nos. 2016RCJJ008 and 2015RCJJ012)the Shandong Provincial Natural Science Foundation of China (No. ZR2019PD017)
文摘This paper presents whole-rock Hf isotopic data for a suite of eclogite and garnet clinopyroxenite xenoliths hosted in the Early Cretaceous dioritic intrusions from the Xuzhou-Suzhou area along the southeastern margin of the Eastern Block of the North China Craton(NCC).Six of the eight studied xenolith samples plot significantly above the terrestrial Hf-Nd isotopic array and haveεHf(0)value up to+60.All the samples define a well correlated 147 Sm/144 Nd-143 Nd/144 Nd age of 2081 Ma,which is considered to record the granulite-facies metamorphism.In contrast,the Lu-Hf isotope system faithfully records the protolith information.The mineralogical assemblage,especially garnet and/or zircon(rutile to some extent)mainly controlled the decoupling of Hf-Nd isotope.The metamorphic modification on protolith characteristics and the differences in element mobility during metamorphism may also reinforce the observed decoupling between the Sm-Nd and Lu-Hf isotope systems;i.e.,the absence of the correlations inεNd-εHf and also 87 Sr/86 Sr-143 Nd/144 Nd diagram.The Lu/Hf isochron age of 2424 Ma is similar to the zircon age peak of the studied xenoliths and the dominant age of NCC basement,indicating that the igneous protolith has an affinity to the Archean basement of the NCC.Furthermore,the positiveεHf(t)values at 2500 Ma indicate a crustal growth event of 2500 Ma in the NCC.
文摘It is known that large amounts of Cenozoic high potassium volcanic rocks occur on the Tibetan plateau. The question is where do those high potassium magmas come from? Since the plateau is being compressed by subduction and collision from the surrounding continents,it is a puzzle for us what is the formational environment and tectonic setting of these volcanic rocks? In particular,what is the relationship between these special rocks and formation and uplift of the plateau? We recently carried out an investigation on these Cenozoic volcanic rocks in Hoh Xil,northern Tibetan plateau,including volcanic rocks in the Jingyuhu,Xiongyingtai and Shuangquanzi areas. In the region,some older lava flows occur as thick sheets with a flat surface and weathering crust; while some relatively younger lavas remain a relict volcanic cone or vent. Most of the relict cones are small (<100m in diameter) and some are over hundred meters,distributed along faults,particular strike\|slip fault,e.g.,East Kunlun strike slip fault. Relatively,intermediate\|acid volcanic rocks are prominent,and basic\|intermediate and acid are subordinate. Petrological and geochemical results show that these volcanic rocks have many common affinities,characterized by high contents of w (K 2O)+ w (Na 2O) (about 8%),and w (K\-2O)/ w (Na\-2O)>1 or close to 1,and mostly belonged to shoshonite\|trachyte association and some to ultra\|potassic rocks. The K\|Ar dating of whole rock and mica shows that the volcanism lasts from middle Miocene (15 47Ma) to Pleistocene (0 69Ma); they are 0 69Ma,13 77Ma and 15 47Ma in Jingyuhu; 11 05Ma,12 22Ma and 12 83Ma in Xiongyingai,; 1 58Ma,2 24Ma,5 23Ma,5 85Ma,8 20Ma,8 41Ma and 10 67Ma in Shuangquanzi.Two types of xenolith and xenocryst were found in Jingyuhu and Xiongyingtai,i.e..,crustal xenolith and mantle xenocryst.
基金supported by the Special Research Project of the State Key Laboratory of Lithospheric Evolution, Institute of Geology and Geophysics, Chinese Academy of Sciences (No. 1008)the National Natural Science Foundation of China (No. 90714008)
文摘Two types of melt pockets, closed melt pocket （CMP） and open melt pocket （OMP）, are recognized from the peridotite xenoliths entrained in the Cenozoic kamafugites in western Qinling （秦岭）, Central China. The Haoti （好梯） CMPs have a mineral assemblage of olivine＋ clinopyroxene＋amphibole＋K- feldspar, whereas the Baiguan （白关） CMPs are composed of olivine＋clinopyroxene＋Umenite＋carbonate. The components of the OMPs are more complicated. In the Haoti OMPs, there are olivine, ciinopyroxene, glass, low modal abundances of amphibole, K-feldspar （Kfs）, Umenite, sulfide, chlorite, perovskite, chromite and phlogopite. The Baiguan OMPs contain olivine, clinopyroxene, glass, chlorite and chromite. Compositionally, ofivines in the CMPs and OMPs are both apparently depleted in Ni, and those in the OMPs are also depleted in Fe and Mg, and enriched in Ca compared to the primary ones. Ciinopyroxenes display large and systematical compositional variations between the CMPs and OMPs, particularly in Al, Cr, Na, Ca and Ti. Glasses are generally depleted in Si compared to the worldwide glasses in melt pockets, although they still have large variations. Amphiboles and K-feldspars have relatively restricted compositional variations. The petrographical observations and mineral chemistry suggest that the Haoti and Baiguan CMPs were generated by the in-sitn decompression melting of orthopyroxenes, olivines and clinopyroxenes, and by the addition of minor external K-rich and Ca-rich melt/fluids. The OMPs formed during the latest metasomatic event in the lithospheric mantle beneath the western Qinling.
基金supported by GEMOC and the Department of Earth and Planetary Sciences,Macquarie University,Australia
文摘In order to distinguish the primary microstructures developed under mantle conditions from the secondary phenomena after xenolith entrainment in the host magma, this study intends to discuss the genesis of spongy, sieve-textured, and reaction rims on mineral grains of mantle xenoliths in the Cenozoic basalts from the western North China craton. The spongy rims on primary clinopyroxene show neither obvious compositional zoning nor preferential development towards the host basalt and probably suggest an origin via partial melting within the lithospheric mantle or pressure release as the xenoliths were carried upwards. The sieve-textured rims on primary spinel show clear chemical zoning with increasing Cr# and decreasing AI towards the host basalt. They are interpreted as the result of partial melting due to heating of the host basaltic magma and decreasing pressure during ascent proc- ess. Post-entrainment reaction mainly generated secondary minerals at contacts between the host ba- saltic melt and xenoliths. The secondary clinopyroxene in reaction rims develops on primary clinopy- roxene and has higher Ti, Ca, and Fe contents and lower Mg# and Si contents than primary one, while the secondary spinel on primary Cr-AI spinel is titanomagnetite. The secondary olivine and clinopy- roxene in the reaction rims on primary orthopyroxene are enriched in Fe, Al, and Ti. The occurrence of reaction rims in mantle xenoliths reflects disequilibrium processes after xenolith entrainment in the basaltic melt. The spongy rims on primary clinopyroxene may not be related to the interaction with thehost basaltic melt, while the sieve-textured rims on primary spinel and reactions rims on primary clinopyroxene, spinel, and orthopyroxene may result from post-entrainment reaction between the host basaltic melt and xenolith minerals.
