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dunite Xenoliths and Olivine Xenocrysts in Gabbro from Taihang Mountains: Characteristics of Mesozoic Lithospheric Mantle in Central China

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Journal of Earth Science 2010年第5期21卷 692-710页

作者：许文良王春光杨德彬王枫裴福萍 College of Earth Sciences Jilin University State Key Laboratory of Geological Processes and Mineral Resources China University of Geosciences

This article reports the petrography and mineral chemistry of dunite xenoliths and olivine xenocrysts entrained by the Early Cretaceous Xi＇anli （西安里） hornblende （Hb）-gahbros from the southern Taihang （太行） Mountains, with the aim of constraining the nature of the Mesozoic lithospheric mantle in Central China. Rounded dunite xenoliths are 1-3 cm3 in size and display porphyroelastic, tabular, and protogranular textures. Chromite with Cr#=60-89 is common in the xenoliths. Oilvine xenocrysts of 4-6 mm in size are also found in the Hb-gabbros. Orthopyroxene reaction rims are commonly observed around olivine xenocrysts or between dunite xenoliths and host rocks. The porphyroclastic olivines within dunite xenoliths and olivine xenoerysts have kink bands and Mg#=83-94. The Mg# of olivine cores and rims are 89-94 （average, 90） and 83-86 （average, 84.4）, respectively. The CaO contents of all olivines from the xenoliths and xenocrysts are less than 0.1 wt.%, suggesting a Hthospheric mantle origin. The Ca content （214 ppm-818 ppm） and Ti content （15 ppm-137 ppm） in the xenoliths and xenocrysts are similar to those of olivines from the dunite xenoliths, but are much higher than those of olivines from harzburgite and lherzolite xenoliths in the Fushan （符山） intrusion. This finding implies that the xenoliths and xenocrysts may have originated from harzburgites or lherzolites that were intensively modified by silica-rich melts. This result, combined with high Mg# （92-94） of olivine cores from the dunite xenoliths and xenocrysts, indicates that these ofivine xenocrysts and dunite xenoliths could represent the residue of ancient （Archean or Paleopro. terozoic） lithospheric mantle and might have experienced the same intensive modification by silica-rich melts as the host magma, resulting in enrichment in MgO and SiO2.

关键词： North China craton Xi'anli Hb-gabbro dunite xenocryst lithospheric mantle.

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Thermal properties of harzburgite and dunite at 0.8–3 GPa and 300–823 K and implications for the thermal evolution of Tibet

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Geoscience Frontiers 2021年第2期12卷 947-956页

作者： Jianhua Ge Baohua Zhang Zili Xiong Lanfang He Heping Li Key Laboratory for High-Temperature and High-Pressure Study of the Earth’s Interior Institute of GeochemistryChinese Academy of SciencesGuiyang 550081China University of Chinese Academy of Sciences Beijing 100049China State Key Laboratory of Lithospheric Evolution Institute of Geology and GeophysicsChinese Academy of SciencesBeijing 100029China

Thermal diffusivity(D)and thermal conductivity(κ)of harzburgite and dunite from Luobusha ophiolite were simultaneously measured up to 3 GPa and 823 K using the transient plane-source method in a multi anvil *** results show that the values of D andκof both samples systematically decrease with increasing temperature and increase with increasing *** combination of the thermal physical data of rocks and minerals and geophysical constraints,we performed numerical simulation on the thermal evolution of Tibet vary over depth,distance and geologic *** present results provide new constraints on occurrence of partial melting and its geophysical significance beneath Tibetan crust.

关键词： Thermal diffusivity Thermal conductivity Harzburgite dunite Thermal evolution Tibet

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Exsolution Lamellae in Olivine Grains of dunite Units from Different Types of Mafic-Ultramafic Complexes

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Acta Geologica Sinica(English Edition) 2018年第2期92卷 586-599页

作者： LIANG Zi XIAO yan Joyashish THAKURTA SU Benxun CHEN Chen BAI Yang Patrick A. SAKYI State Key Laboratory of Lithospheric Evolution Institute of Geology and Geophysics Chinese Academy of Sciences Beijing 100029 China University of Chinese Academy of Sciences Beijing 100049 China Department of Geosciences Western Michigan University 1903 West Michigan Avenue Kalamazoo MI 49008 USA Key Laboratory of Mineral Resources Institute of Geology and Geophysics Chinese Academy of Sciences Beijing 100029 China Department of Earth Science School of Physical and Mathematical Sciences University of Ghana Legon-Accra Ghana

Exsolution microstructures in olivine grains from dunite units in a few selected tectonic environments are reported here. They include lamellae of clinopyroxene and clinopyroxene-magnetite intergrowth in the Gaositai and Yellow Hill Alaskan-type complexes, clinopyroxene-magnetite intergrowth in the Klzildag ophiolite, and chromite lamellae in the Hongshishan mafic-ultramafic intrusive complex. These lamellae commonly occur as needle- or rod-like features and are oriented in olivine grains. The host olivine grains have Fo contents of 92.5-92.6 in the Gaositai complex, 86.5-90.1 in the Yellow Hill complex, 93.2-93.4 in the Klzlldag ophiolite and 86.9-88.3 in the Hongshishan complex. Clinopyroxene in the rod-like intergrowth exsolved in olivine grains in the Gaositai and Yellow Hill is diopside with similar major element compositions of CaO （23.6-24.3wt%）, SiO2 （52.2-54.0wt%）, A1203 （0.67-2.15wt%）, Cr203 （0.10-0.42wt%） and Na20 （0.14-0.26wt%）. It falls into the compositional field of hydrothermal clinopyroxene and its origin is thus probably related to reaction between dunite and fluids. The enrichment of the fluids in Ca2＋, Fe3＋, Cr3＋ and Na＋, resulted in elevated concentrations of these cations in olivine solid solutions via the reaction. With decreasing temperature, the olivine solid solutions altered to an intergrowth of magnetite and clinopyroxene. The Fe3＋ and Cr3＋ preferentially partitioned into magnetite, while Ca2＋ and Na＋ entered clinopyroxene. Since the studied Alaskan-type complexes and ophiolite formed in a subduction environment, the fluids were probably released from the subducted slab. In contrast, the exsolved chromite in olivine grains from the Hongshishan complex that formed in post-orogenic extension setting can be related to olivine equilibrated with Cr-bearing liquid. Similarly, these lamellae have all been observed in serpentine surrounding olivine grains, indicating genetic relations with serpentinization.

关键词： olivine dunite clinopyroxcne lamella intergrowth of clinopyroxenc and magnetite maficultramafic complex

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Petrogenesis of Songshugou dunite body in the Qinling orogenic belt, Central China: Constraints from geochemistry and melt inclusions

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Science China Earth Sciences 2005年第8期48卷 1146-1157页

作者： SU Li1,2, SONG Shuguang3 & ZHOU Dingwu1 1. Key Laboratory of Continental Dynamics of the Ministry of Education, Department of Geology, Northwestern University, Xi’an 710069, China 2. The Geological Lab Center, China University of Geosciences (Beijing), Beijing 100083, China 3. Key Laboratory of Orogenic Belts of the Ministry of Education, Department of Geology, Peking University, Beijing 100871, China Key Laboratory of Continental Dynamics of the Ministry of Education Department of Geology Northwestern University Xi’an China The Geological Lab Center China University of Geosciences (Beijing)Beijing China Key Laboratory of Orogenic Belts of the Ministry of Education Department of Geology Peking University Beijing China

The Songshugou dunite body, which occupies an area of about 20 km2, is the largest ultramafic massif in the eastern Qinling orogenic belt, Central China. The major compo-nent of this body is dunitic rocks including mylonitic dunite and coarse-grained dunite; they oc-cupy about 95 vol% of the total body. Petrography, mineral composition, major and trace ele-ments and primitive melt inclusions have been investigated in this paper; all revealed that this dunite body is the product of melt-rock interaction by porous percolation flow. In comparison with dunite sills or veins in harzburgite from the basal part of Oman ophiolite, this dunite body is characterized by lower contents of Al2O3, CaO and HREE but higher content of highly incom-patible elements and Zr and Hf. The LREE enriched patterns and primitive mantle normalized spidergrams of trace elements are also different from the Oman dunite. Combining with melt in-clusions observed in olivines, we conclude that this dunite body is the product of large- scale porous percolation flow of high-MgO melts within depleted mantle peridotites. The high-MgO magma, in essence, was most probably produced at the hot head of an upwelling mantle plume. The occurrence of the Songshugou dunite body is closely associated with the activity of mantle super-plume in Neo-Proterozoic era in the Yangtze Craton.

关键词： Songshugou dunite body, geochemistry, melt inclusion, mantle plume, Qinling orogenic belt.

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Exsolutions of Diopside and Magnetite in Olivine from Mantle dunite,Luobusa Ophiolite,Tibet,China

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Acta Geologica Sinica(English Edition) 2008年第2期82卷 377-384页

作者： REN Yufeng CHEN Fangyuan YANG Jingsui GAO Yuanhong Key Laboratory of Continental Dynamics of the Ministry of Land and Resources Institute of Geology CAGS Beijing 100037

The exsolutious of diopside and magnetite occur as intergrowth and orient within olivine from the mantle dunite, Luobusa ophiolite, Tibet. The dunite is very fresh with a mineral assemblage of olivine （〉95%）＋ chromite （1%-4%）＋ diopside （〈1%）. Two types of olivine are found in thin sections： one （Fo = 94） is coarse-grained, elongated with development of kink bands, wavy extinction and irregular margins; and the other （Fo = 96） is fine-grained and poly-angied. Some of the olivine grains contain minor Ca, Cr and Ni. Besides the exsolutions in olivine, three micron-size inclusions are also discovered. Analyzed through energy dispersive system （EDS） with unitary analytical method, the average compositions of the inclusions are： Na20, 3.12%-3.84%; MgO, 19.51%-23.79%; Al2O3, 9.33%-11.31%; SiO2, 44.89%-46.29%; CaO, 11.46%-12.90%; Cr2O3, 0.74%-2.29%; FeO, 4.26%- 5.27%, which is quite similar to those of amphibole. Diopside is anhedral f＇dling between olivines, or as micro-inclusions oriented in olivines. Chromite appears euhedral distributed between olivines, sometimes with apparent compositional zone. From core to rim of the chromite, Fe content increases and Cr decreases; and A! and Mg drop greatly on the rim. There is always incomplete magnetite zone around the chromite. Compared with the nodular chromite in the same section, the euhedral chromite has higher Fe3O4 and lower MgCr2O4 and MgAI2O4 end member contents, which means it formed under higher oxygen fugacity environment. With a geothermometer estimation, the equilibrium crystalline temperature is 820℃-960℃ for olivine and nodular chromite, 630℃-770℃ for olivine and euhedral chromite, and 350℃-550℃ for olivine and exsoluted magnetite, showing that the exsolutions occurred late at low temperature. Thus we propose that previously depleted mantle harzburgite reacted with the melt containing Na, Al and Ca, and produced an olivine solid solution added with Na^＋, Al^3＋, Ca^2＋, Fe^3＋, Cr^3＋. With temperature decreasing, t

关键词： diopside magnetite exsolution olivine dunite ophiolite Luobusa Tibet

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Experimental study on electrical conductivity of dunite at high temperature and pressure——The evidence of electrical conductivity of cold mantle in the Gaize-Lugu area

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Chinese Science Bulletin 2001年第24期46卷 2089-2092页

作者： WANG Duojun LI Heping LIU Congqiang ZHAO Zhidan MO Xuanxue GUO Tieying SU Gengli DING Dongye Laboratory for Study on the Earth’s Interior and Geofluids Institute of GeochemistryChinese Academy of SciencesGuiyang 550002China Institute of Geochemistry Chinese Academy of SciencesGuiyang 550002China School of Earth Sciences and Land Resources China University of GeoscieneesBeijing 100083China

The electrical conductivities of the dunite from the Qinghai-Xizang (Tibetan) Plateau were measured with the impedance spectra method at 1.0-4.0 GPa and 643-1093 K. The experimental results indicated that activation enthalpies of the dunite are smaller than 0.9 eV, the conduction mechanism in dunite may be attributed to the mixed electrical conduction involving grain interiors and boundaries. On the basis of the results of this experiment, we can deduce that there exists cold mantle in the area of Gaize-Lugu in the Qinghai-Xizang (Tibetan) Plateau by reverse methods from the magnetotelluric sounding data (conductivity-depths profile) available for western Tibet. The result provides the present cold mantle viewpoint with strong proof on the basis of high temperature and pressure experiments.

关键词： high temperature and pressure dunite electrical con- ductivity conduction mechanism cold mantle.

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Methane-rich fluid inclusions from ophiolitic dunite and post-coilisional mafic-ultramafic intrusion:the mantle dynamics underneath the Palaeo-Asian Ocean through to the post-eollisional period

Methane-rich fluid inclusions from ophiolitic dunite and pos...

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中国科学院地质与地球物理研究所2006学术年会

作者： Wei Liu,Pan Xiao Fei State Key Laboratory of Lithospheric Evolution and Key Laboratory of Mineral Resources,Institute of Geology and Geophysics,Chinese Academy of Sciences,P.O.Box 9825,Beijing 100029,China

The protracted development history of the Palaeo-Asian Ocean starting from～1000 Ma to～320 Ma,and continuation of mantle-derived magmatism right through the post-collisional period as manifested by the widespread mafic-ultramafic intrusion and alkaline-peralkaline granite suggest a vigorous,long-running mantle *** the micro-laser Raman spectrometer,we analyzed olivine- and plagioclase-hosted fluid inclusions from ophiolitic dunite,Kudi of the western Kunlun Range,and post-collisional mafic-ultramafic intrusions of the Xiangshan and the Huangshandong,eastern Chinese Tienshan *** results show that fluids brought from the mantle by these rocks are rich in HO and CH with variable amounts of *** of the redox state,pressure and depth of formation for the melt-CH-HO+N fluid systems from the 3 rock suites of the Xinjiang,and comparison of these parameters with those of the peridotite-fluid parageneses for the sub-cratonic upper mantle give meaningful *** fluids were formed in the asthenosphere,were originally CH-N-rich,primordial mantle fluid,but have been progressively diluted with HO and become oxidized by repeated subduction of oceanic *** propose that repeated redox melting in the mantle due to dilution of CH with HO and oxidation caused formation of the long-lived Palaeo-Asian Ocean,brought about extensive intrusion of mafic-ultramafic complexes and alkaline-peralkaline granites right through the post-collisional period,and,consequently,resulted in significant Phanerozoic continental growth in the Central Asian Orogenic *** of atmospheric O and the Earth’s major oxidation occurred at about 2.4 to 2.2 *** of the Earth’s mantle promoted the mantle melting and magma input to the crust,resulting in major continental growth after 2.5 ***,much-postponed oxidation of the primordial mantle underneath the Central Asian Orogenic Belt led to significant continental growth in the Phanerozoic times.

关键词： CH4-H2O+N2 fluid inclusion dunite mafic-ultramafic intrusion redox melting Palaeo-Asian Ocean

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Thermophysical properties of dunite rocks as a function of temperature along with the prediction of effective thermal conductivity

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Natural Science 2010年第6期2卷 626-630页

作者： Aurang Zeb Tayyaba Firdous Asghari Maqsood 不详

The thermal conductivity, thermal diffusivity and heat capacity per unit volume of dunite rocks taken from Chillas near Gilgit, Pakistan have been measured simultaneously using transient plane source technique. The temperature dependence of thermal transport properties is studied in the temperature range 83-303 K. Different relations for the estimation of thermal conductivity are also tested. Thermal conductivity data obey the modified Eucken’s law in the temperature range of measurements.

关键词： dunite Density Porosity Thermal Conductivity Transient Plane Source (TPS) Technique

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Experimental studies of melt-peridotite reactions at 1–2 GPa and 1250–1400°C and their implications for transforming the nature of lithospheric mantle and for high-Mg signatures in adakitic rocks

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Science China Earth Sciences 2014年第3期57卷 415-427页

作者： YU Yang XU WenLiang WANG ChunGuang College of Earth Sciences Jilin University Research Center of Palaenotology and Stratigraphy Jilin University

Experiments of the melt-peridotite reaction at pressures of 1 and 2 GPa and temperatures of 1250–1400°C have been carried out to understand the nature of the peridotite xenoliths in the Mesozoic high-Mg diorites and basalts of the North China Craton,and further to elucidate the processes in which the Mesozoic lithospheric mantle in this region was *** used Fuxin alkali basalt,Feixian alkali basalt,and Xu-Huai hornblende-garnet pyroxenite as starting materials for the reacting melts,and lherzolite xenoliths and synthesized harzburgite as starting materials for the lithospheric *** experimental results indicate that:(1)the reactions between basaltic melts and lherzolite and harzburgite at 1–2 GPa and 1300–1400°C tended to dissolve pyroxene and precipitate low-Mg#olivine(Mg#=83.6–89.3),forming sequences of dunite-lherzolite(D-L)and duniteharzburgite(D-H),respectively;(2)reactions between hornblende-garnet pyroxenite and lherzolite at 1 GPa and 1250°C formed a D-H sequence,whereas reactions at 2 GPa and 1350°C formed orthopyroxenite layers and lherzolite;and(3)the reaction between a partial melt of hornblende-garnet pyroxenite and harzburgite resulted in a layer of orthopyroxenite at the boundary of the pyroxenite and *** reacted melts have higher MgO abundances than the starting melts,demonstrating that the melt-peridotite reactions are responsible for the high-Mg#signatures of andesites or adakitic *** experimental results support the proposition that the abundant peridotite and pyroxenite xenoliths in western Shandong and the southern Taihang Mountains might have experienced multiple modifications in reaction to a variety of *** suggest that melt-peridotite reactions played important roles in transforming the nature of the Mesozoic lithospheric mantle in the region of the North China Craton.

关键词： experimental study melt-peridotite reaction dunite lithospheric mantle North China Craton

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Highly refractory Archaean peridotite cumulates:Petrology and geochemistry of the Seqi Ultramafic Complex,SW Greenland

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Geoscience Frontiers 2018年第3期9卷 689-714页

作者： Kristoffer Szilas Vincent van Hinsberg Iain McDonald Tomas Naeraa Hugh Rollinson Jacob Adetunji Dennis Bird Department of Geological Sciences Stanford University450 Serra MallStanfordCA 94305USA Department of Earth&Planetary Sciences McGill UniversityQuebecCanada Department of Geology Lund UniversitySovegatan 12223 62 LundSweden School of Earth and Ocean Sciences Cardiff UniversityMain BuildingCardiff CF10 3ATUnited Kingdom College of Science University of DerbyDerbyDE22 1GBUK

This paper investigates the petrogenesis of the Seqi Ultramafic Complex, which covers a total area of approximately 0.5 km^2. The ultramafic rocks are hosted by tonalitic orthogneiss of the ca. 3000 Ma Akia terrane with crosscutting granitoid sheets providing an absolute minimum age of 2978 ± 8 Ma for the Seqi Ultramafic Complex. The Seqi rocks represent a broad range of olivine-dominated plutonic rocks with varying modal amounts of chromite, orthopyroxene and amphibole, i.e. various types of dunite(s.s.),peridotite(s.l.), as well as chromitite. The Seqi Ultramafic Complex is characterised primarily by refractory dunite, with highly forsteritic olivine with core compositions having Mg# ranging from about 91 to 93. The overall high modal contents, as well as the specific compositions, of chromite rule out that these rocks represent a fragment of Earth's mantle. The occurrence of stratiform chromitite bands in peridotite, thin chromite layers in dunite and poikilitic orthopyroxene in peridotite instead supports the interpretation that the Seqi Ultramafic Complex represents the remnant of a fragmented layered complex or a magma conduit, which was subsequently broken up and entrained during the formation of the regional continental *** all of the characteristics of the Seqi Ultramafic Complex points to formation of these highly refractory peridotites from an extremely magnesian(Mg# ~ 80), near-anhydrous magma, as olivinedominated cumulates with high modal contents of chromite. It is noted that the Seqi cumulates were derived from a mantle source by extreme degrees of partial melting(>40%). This mantle source could potentially represent the precursor for the sub-continental lithospheric mantle(SCLM) in this region,which has previously been shown to be ultra-depleted. The Seqi Ultramafic Complex, as well as similar peridotite bodies in the Fiskefjord region, may thus constitute the earliest cumulates that formed during the large-scale melting event(s), which

关键词： North Atlantic Craton Archaean dunite Platinum-group elements Ultra-depleted mantle Fiskefjord

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