IMPLICATIONS OF THE DEEP-SEATED XENOLITHS IN CENOZOIC BASALT IN KANGXIWA, WEST KUNLUN,CHINA

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.

The Sytykanskaya kimberlite pipe:Evidence from deep-seated xenoliths and xenocrysts for the evolution of the mantle beneath Alakit,Yakutia,Russia

Mantle xenoliths(>150) and concentrates from late autolithic breccia and porphyritic kimberlite from the Sytykanskaya pipe of the Alakit field(Yakutia) were analyzed by EPMA and LAM ICP methods.In P-TX-f(O_2) diagrams minerals from xenoliths show widest variations,the trends P-Fe~#-CaO,f(O_2)for minerals from porphyric kimberlites are more stepped than for xenocrysts from breccia.Ilmenite PTX points mark moving for protokimberlites from the lithosphere base(7.5 GPa) to pyroxenite lens(5-3.5 GPa) accompanied by Cr increase by AFC and creation of two trends P-Fe#OI ~ 10-12%and13-15%.The Opx-Gar-based mantle geotherm in Alakit field is close to 35 mW/m2 at 65 GPa and 600 C near Moho was determined.The oxidation state for the megacrystalline ilmenites is lower for the metasomatic associations due to reduction of protokimberlites on peridotites than for uncontaminated varieties at the lithosphere base.Highly inclined linear REE patterns with deep HFSE troughs for the parental melts of clinopyroxene and garnet xenocrysts from breccia were influenced by differentiated protokimberlite.Melts for metasomatic xenoliths reveal less inclined slopes without deep troughs in spider diagrams.Garnets reveal S-shaped REE patterns.The clinopyroxenes from graphite bearing Cr-websterites show inclined and inflected in Gd spectrums with LREE variations due to AFC differentiation.Melts for garnets display less inclined patterns and Ba-Sr troughs but enrichment in Nb-Ta-U.The^(40)Ar/^(39)Ar ages for micas from the Alakit mantle xenoliths for disseminated phlogopites reveal Proterozoic(1154 Ma) age of metasomatism in early Rodinia mantle.Veined glimmerites with richterite- like amphiboles mark ~1015 Ma plume event in Rodinia mantle.The ~600-550 Ma stage manifests final Rodinia break-up.The last 385 Ma metasomatism is protokimberlite-related.

Lithospheric composition and structure beneath the northern margin of the Qinling orogenic belt——On deep-seated xenoliths in Minggang region of Henan Province

Swarms of mafic-intermediate volcaniclastic bodies occur in the Minggang region of Henan Province, a tectonic boundary between the North Qinling and the North China Block, and emplaced at (178.31±3.77) Ma. These volcanic rocks are subalkaline basaltic andesites and contain abundance of lower crust and mantle xenoliths. Thus this area is an ideal place to reveal the lithospheric composition and structure beneath the northern margin of the Qinling orogenic belt. Geochemical data indicate that these mafic granulites, eclogites and metagabbros have trace elemental and Pb isotopic characteristics very similar to those rocks from the South Qinling Block, representing the lower part of lower crust of the South Qinling which subducted beneath the North China Block. Talcic peridotites represent the overlying mantle wedge materials of the North China Block, which underwent the metasomatism of the acidic melt/fluid released from the underlying lower crust of the South Qinling Block. Deep tectonic model proposed in this paper is that after the Late Paleozoic South Qinling lithosphere subducted northward and decoupled, the upper part of the lithosphere emplaced under the North Qinling and the lower part continuously subducted northward under the North China Block. In Early Mesozoic, the North Qinling Block obducted northward and the North China Block inserted into the Qinling orogenic belt in a crocodile-mouth shape.

Decoupling of Lu-Hf and Sm-Nd Isotopic System in Deep-Seated Xenoliths from the Xuzhou-Suzhou Area,China: Differences in Element Mobility during Metamorphism

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.

Deep-seated rock fracture of valley slopes in China:A review

Deep-seated rock fractures(referred to as DSRF hereafter)in valley slopes are uncommon geological phenomena that challenge our previous understanding of slope unloading processes.These fractures weaken the strength and integrity of the rock mass,potentially forming unstable block boundaries with significant volume,thereby affecting the stability of slopes,chambers,and dam abutments.DSRF has emerged as a critical environmental and engineering geological issue that hinders large-scale projects in deep canyon areas.Despite the attention and practical treatment given to DSRF in engineering practice,theoretical research on this topic still lags behind the demands of engineering applications.To garner widespread attention and promote the resolution of DSRF-related problems,this review aims to redefine DSRF through comprehensive data collection and analysis,engineering geological analogies,and field investigations,and provide a summary and analysis of the research progress on DSRF,along with future research directions.The study defines DSRF as the intermittent tension cracks or relaxation zones within a slightly weathered or fresh,and intact or relatively intact rock mass distributed below the surface unloading zones of a deep canyon slope,and should be distinguished from"loose rock mass"and"deep-seated gravitational slope deformations".The article provides an overview of the development and distribution,rupture characteristics,and genesis mechanism of DSRF.It proposes that DSRF is formed based on the fluvial deviation-undercutting evolution mode,wherein the energy accumulated in the rock mass is violently released when the river further down cuts the slope after the rock mass has undergone cyclical loadingunloading.However,further research is necessary to establish a comprehensive database for DSRF,refine exploration techniques,understand evolutionary processes,develop engineering evaluation methods,and predict the distribution of DSRF.

Petrology of lherzolite xenoliths of HosséréSédévolcano(Adamawa plateau,Ngaoundéréarea,Cameroon)

Numerous mantle xenoliths 6–12 cm in size and sub-angular to rounded in shape occur within Mio-Pliocene basanite lavas of the monogenic volcano of HosséréSédé in the Adamawa plateau.Xenoliths of spinel lherzolite exhibit protogranular,equigranular or porphyroclastic texture.Microprobe chemical analyses show that olivine is highly magnesian(Fo_(88-90)),clinopyroxene crystals are diopside and augite(Wo_(41.6–49.6)En_(45.3–53.7)Fs_(4.2–6.2)),orthopyroxene crystals are enstatite(Wo 1.4–1.5 En_(88.6–89.0)Fs_(9.6–9.9))and spinel crystals are mainly Al-spinel associ-ated to minor Cr-spinel.Estimated temperatures and pressures through empirical formulas show that HosséréSédé noliths have equilibrated between 1085 and 1204℃and 1.08 to 1.57 GPa,corresponding to sampling depths of 36 and 52 km.Detailed petrographical and mineral chemistry of HosséréSédénoliths evidences the com-plex nature and composition of the subcontinental lithosphere under the Adamawa plateau.This may involve a probable uplift of the whole area after a limited exten-sional event,possible metasomatism through melt infiltration during shearing of the lithospheric mantle along the Pan African strike-slip fault system.

Garnet-bearing Granulite Facies Rock Xenoliths from Late Mesozoic Volcaniclastic Breccia, Xinyang, Henan Province

This paper presents the primary results of petrologic,mineralogical and petrochemical studies of garnet beating 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.

ULTRAMAFIC XENOLITHS FROM A KAMAFUGITE LAVA IN CENOZOIC VOLCANIC FIELD OF WEST QINLING, CHINA AND ITS GEOLOGICAL IMPLICATION

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.

Phlogopite in mantle xenoliths and kimberlite from the Grib pipe,Arkhangelsk province,Russia:Evidence for multi-stage mantle metasomatism and origin of phlogopite in kimberlite

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.

Granulite-facies Middle-Lower Crustal Xenoliths from Nushan Alkali Basalt in Northeastern Anhui Province,China

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.

Numerical modeling of deep-seated landslides interacting with man-made structures

This paper describes the interaction between deep-seated landslides and man-made structures such as dams, penstocks, viaducts, and tunnels. Selected case studies are reported first with the intent to gain insights into the complexities associated with the interaction of these structures with deep-seated landslides(generally referred to as deep-seated gravity slope deformations, DSGSDs). The main features, which characterize these landslides, are mentioned together with the interaction problems encountered in each case. Given the main objective of this paper, the numerical modeling methods adopted are outlined as means for increase in the understanding of the interaction problems being investigated. With the above in mind, the attention moves to an important and unique case history dealing with the interaction of a large-size twin-tunnel excavated with an earth pressure balance(EPB)tunnel boring machine(TBM) and a deep-seated landslide, which was reactivated due to the stress changes induced by tunnel excavation in landslide shear zone. The geological and geotechnical conditions are described together with the available monitoring data on the landslide movements, based on the advanced and conventional monitoring tools used. Numerical modeling is illustrated as an aid to back-analyze the monitored surface and subsurface deformations and to assist in finding the appropriate engineering solution for putting the tunnel into service and as a follow-up means for future understanding and control of the interaction problems. The simulation is based on a novel time-dependent model representing the landslide behavior.

Underplating of Mesozoic Mantle-derived Magmas in Tongling, Anhui Province: Evidence from Megacrysts and Xenoliths

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 underplafing 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.

Amphibole-Bearing Peridotite Xenoliths from Nushan,Anhui Province:Evidence for Melt Percolation Process in the Upper Mantle and Lithospheric Uplift

The spinel peridotite xenoliths of Group I in Quaternary basanites from Nushan, Anhui Province, can be classified as two suites: 8 hydrous suite characterized by the ubiquitous oc-currence of (Ti-) pargasite and an anhydrous suite. The mineral chemistry reveals that the an-hydrous suite and one associated phlogopite-bearing lherzolite are equilibrated under temperatureconditi0ns of 1000 - 1110℃, whereas amphibole-bearing peridotites display distinct disequilibrium features, indicating partial reequilibration from 1050 to 850℃ and locally down to 750℃.This amphibole-bearing peridotites were probably the uppermost part of the high temperatureanhydrous suite which was modally modified by fractionating H2O-rich metasomatic agent during regional upwelling. This relatively recent lithospheric uplift event foll0wed an older upliftevent recognized from pyroxene unmixing of domains in local equilibrium, as well as the dominant deformation texture in the anhydrous suite. The first thermal disturbance can be linkedwith the regional extension and widespread basaltic volcanism in Jiangsu-Anhui provinces sinceEarly Tertiary and the formation of the nearby Subei (North Jiangsu) fault-depression basinduring the Eocene, while the second event in association with the formation of amphibolesprobably indicates the continuation but diminution of upward mantle flux since Neogene in response to the change in tectonic regime for eastern China.

Chemical and Isotopic Characteristics of Gabbroic Xenoliths from Hannuoba,China

Nine pieces of gabbroic xenoliths from Hannuoba were examined for their major and trace elements and Nd,Sr and Pb isotopes.The results show that the gab-broic xenoliths are of more mafic basaltic composition .Their abundances show narrow variations in major elements.The trace element contents are highly variable in contrast with those of host basalts and lherzolite xenoliths.The gabbroic xenoliths are rich in Nd(0.51159-0.51249),Sr(0.70491-0.70768) and low in radiogenic Pb(16.283-17.046, 15.191-15.381 and 36.999-37.476),significantly different from basalts and lherzolites in isotopic space.The calculated Nd and Pb model ages are about 3.0-3.5 Ga.The rocks have relatively low equilibrium T(-850℃) and P(0.8-0.9 Gpa).They could be inter-preted to be the product of upper mantle melting at the boundary between the lower crust and the upper mantle.Their chemical and isotopic variations can be ascribed to different degrees of melting,segregation and long-term evolution.

Sulfide-melt inclusions in mantle xenoliths from the Changbaishan district,Jilin province,China

Mantle xenoliths are common in the Cenozoic basalts of the Changbaishan District,Jilin Province,China.Sulfide assemblages in mantle minerals can be divided into three types:isolated sulfide grains,sulfide-meh inclusions and filling sulfides in fractures.Sulfide-meh inclusions occur as single-phase sulfides,sulfide-silicate melt,and CO_2-sulfide-silicate melt inclusions. Isolated sulfide grains are mainly composed of pyrrhotite,but cubanite was found occasionally.Sulfide-meh inclusions are mainly composed of pontlandite and MSS,with small amounts of chalcopyrite and talnakhite.The calculated distribution coefficient K_(D3)for lherzolite are similar to that of mean experimental value.The bulk sulfides in lherzolite were in equilibrium with the enclosing minerals, indicating immiscible sulfide melts captured in partial melting of upper mantle.Sulfide in fractures has higher Ni/Fe and(Fe+Ni)/S than those of sulfide melt inclusions.They might represent later metasomatizing fluids in the mantle.Ni/Fe and(Fe+Ni)/S increase from isolated grains,sulfide inclusions to sulfides in fractures.These changes were not only affected by temperature and pressure,hut by geochemistry of Ni,Fe and Cu,and sulfur fugacity as well.

Geochemical Records of Mantle Processes in Mantle Xenoliths from Three Cenozoic Basaltic Volcanoes in Eastern China

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 volatilerich 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/44Nd 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.

Characteristics of Lower Crustal Granulite Xenoliths from the East Qinling Orogenic Belt and Their Tectonic Significance

The Tongbai granulites are present mainly as xenoliths in granodioritic gneisses. The xenoliths with a zircon age of 470Ma are older than the host rocks of granodioritic gneisses which yield a zircon age of 435Ma. It is suggested that the granulites were transported from the lower crust to the upper level along with granodioritic magma. Geothermometrical and geobarometrical studies based on the coexisting minerals (Opx-Cpx and Opx-Gar) show that the granulites were crystallized at 818-840℃ and 9.5-9.8 ×108 Pa corresponding to the lower crust. Tectonically, the Shangdan suture zone conshtutes the boundary between the North China and Yangtze plates. The zone is characterized by the occurrence of ophiolites in the western part and by that of granulites in the eastern part. So the western part marks the upper crustal level of the Qinling belt, while the eastern part represents the exposure of a deeper level. The results of isotopic dating and the geochemical characteristics of the xenoliths are consistent with those of meta-tholeiltes of the ophiolites in the western part.Therefore, it is assumed that both ophiolites found in the west and granulites found in the east all represent the renmants of the ancient Qinling ocean plate. The difference is that the ophiolites are pieces of obductal fragments from the ocean floor during the subduction in the Early Palaeozoic.However, in the Tongbai area, when the ocean floor was subducting towards the lower crust, it underwent a granulite facies metamorphism. Subsequently, granodioritic magma formed by partial melting trapped some fragments of granulite upwards.

Special Xenoliths in an Aegirine-Augite Syenite Porphyry in Liuhe,Yunnan,China:Discovery and Implications

捕虏体的三种特殊类型最近在 Liuhe 在 aegirine 辉石正长岩斑岩被发现了，云南，中国。 Petrographical ，石油化学，电子微探查，和扫描电子显微镜学研究显示那纯方解石 xenocrysts ，忍受石英的黄玉伟晶岩捕虏体源于在他们的迁居期间披风液体排除，并且黑微晶质的充满铁的硅酸盐融化捕虏体是伴随排除的披风液体的抽取的产品并且是，这石英主导地创作了，绿泥石，并且充满铁圆柱并且有典型矿物质的表硅酸盐矿物质例如本国的铁，磷灰石，和锆石。根据体积岩石化学药品和矿物质作文和结晶化国家，微晶质融化捕虏体不进一步是常规 magmatism，和特别本国的铁的存在的产品证明捕虏体是在减小或缺氧的条件下面的披风液体材料。特殊捕虏体的学习在学习区域在不同岩石和阶层中供应 polymetallic 矿化作用的一个重要深过程的 geochemical 背景。

Helium and Argon Isotopic Composition of Cenozoic Alkali Basalts and Mantle-Derived Xenoliths from Kuandian, Liaoning Province, China

The noble gas isotopic composition and content data of 2 alkali basalts, 3 lherzolite xenoliths and one clinopyroxene megacryst from the Kuandian region have confirmed the occurrence of a fractionation of noble gases during magmatism. Light noble gases such as He and Ne are high in mobility and appear to be incompatible as compared with heavy ones (such as Kr and Xe). Therefore, light noble gases are abundant in volcanics, especially in the volcanics with bubbles; lherzolite xenoliths have relatively high heavy noble gases. The clinopyroxene megacryst has the lowest abundance of noble gases, probably due to its high P-T origin. Noble gas isotopic composition of the clinopyroxene megacryst reveals that the mantle source beneath the Kuandian area has an MORB-like reservoir with 3He/4He ratio of ～10 Ra (Ra: atmospheric 3He/4He ratio) and 40Ar/36Ar ratio of 345.6. The lherzolite xenoliths possess moderate 3He/4He ratios of 2.59-4.53 Ra, reflecting the loss of primary helium during rock deformation or metasomatism caused by enriched mantle fluids during the up-lifting. The alkali volcanics have very low 3He/4He ratios (0.47-0.61 Ra), indicating a contribution of radiogenic 4He, probably having resulted from crust contamination. Most of the samples have excess 21Ne and 22Ne as compared with atmospheric neon, but Kr and Xe isotopic compositions are indistinguishable from atmospheric values within uncertainties with only individual samples having excess 129Xe, 134Xe and 136Xe.

Petrography and Geochemistry of Peridotite Xenoliths from Hannuoba and Significance for Lithospheric Mantle Evolution

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 , 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 clinopyroxenes from the Hannuoba lithospheric mantle.