Experimental investigation of the effect of metasomatism by carbonatic melt on the composition and structure of the deep mantle

The compositions of various transition-zone and lower-mantle phases and coexisting carbonatic melts were determined by exploratory melting experiments in chemically complex CO₂-bearing systems at 20–24.5 GPa and 1600–2000 °C. The melts are highly ultramafic, enriched in K, Na, Ca, Fe, and Mg, and depleted in Al and Si. Melting experiments were also carried out with the compositions on the join Mg₂SiO₄–Na₂CO₃ at 3.7 GPa and 1200–1600 °C. The solidus assemblage of MgCO₃ and Na₂MgSiO₄ melts incongruently to produce forsterite and Na-rich melt. The new results and other recent studies in CO₂-bearing systems suggest that carbonatic melt could be present, either transiently or permanently, in the whole Earth's upper mantle and at least the uppermost lower mantle. Carbonate-melt metasomatism is recognized as a process that could have a major effect on the composition and structure of the deep mantle, and thus play an important role in its evolution. Due to the unique properties of the carbonatic melt, its circulation in an otherwise static mantle could be a more efficient process than the solid-state convection for maintaining equilibrium in most of the mantle not involved directly in plate tectonics.     

Subsolidus and melting phase relations of basaltic composition in the uppermostlower mantle

The phase relations and the element partitioning in a mid-oceanic ridge basalt composition were determined for both above-solidus and subsolidus conditions at 22 to 27.5 GPa by means of a multianvil apparatus. The mineral assemblage at the solidus changes remarkably with pressure; majorite and stishovite at 22 GPa, joined by Ca-perovskite at 23 GPa, further joined by CaAl₄Si₂O₁₁-rich CAS phase at 25.5 GPa, and Mg-perovskite, stishovite, Ca-perovskite, CF phase (approximately on the join NaAlSiO₄-MgAl₂O₄), and NAL phase ([Na,K,Ca]₁[Mg,Fe²⁺]₂[Al,Fe³⁺,Si]_5.5-6.0O₁₂) above 27 GPa. The liquidus phase is Ca-perovskite, and stishovite, a CAS phase, a NAL phase, Mg-perovskite, and a CF phase appear with decreasing temperature at 27.5 GPa. Partial melt at 27 to 27.5 GPa is significantly depleted in SiO₂ and CaO and enriched in FeO and MgO compared with those formed at lower pressures, reflecting the narrow stability of (Fe,Mg)-rich phases (majorite or Mg-perovskite) above solidus temperature. The basaltic composition has a lower melting temperature than the peridotitic composition at high pressures except at 13 to 18 GPa (Yasuda et al., 1994) and therefore can preferentially melt in the Earth’s interior. Recycled basaltic crusts were possibly included in hot Archean plumes, and they might have melted in the uppermost lower mantle. In this case, Ca-perovskite plays a dominant role in the trace element partitioning between melt and solid. This contrasts remarkably with the case of partial melting of a peridotitic composition in which magnesiowüstite is the liquidus phase at this depth.     

重庆高燕地区菱锰矿热水沉积成因地球化学证据

重庆高燕锰矿床位于晚震旦世秦巴成锰沉积盆地,主要赋存于陡山沱组顶部,以鲕粒或球粒状产出.为了查明其成因,在收集该区锰矿相关成果的基础上,对ZK129-3^#、ZK115-7^#、ZK127-7^#、ZK133-7^#、ZK115-11^#五个钻孔的陡山沱组鲕状菱锰矿进行系统采样,并测试了包括Mn、Fe、P、SiO₂、CaO、MgO、Al₂O₃和LOI在内的8个地球化学指标,进而运用指相元素地球化学分析了Mn/Al、（MgO/Al₂O₃）×10²、Al/（Al+Fe+Mn）和SiO₂/Al₂O₃比值.结果表明：重庆高燕菱锰矿受陆源物质的影响很小,与海洋沉积有关,主要是海洋自生产物;Al/（Al+Fe+Mn）和SiO₂/Al₂O₃值则指示其沉积过程中有热水参与,是热水沉积的产物.     

抚顺油页岩开发利用条件分析

对抚顺油页岩样品的容重测定、工业分析、低温干馏、元素分析、发热量测定、灰分成分分析及灰熔点测定,可知油页岩容重为1.4～2.7 t/m³、含油率为1.17%～20.70%、发热量为0.45～11.18 MJ/kg。油页岩的颜色多为浅褐-深褐色,条痕为褐色,颜色越深含油率越高。低温干馏时,温度控制在510℃,焦油率最高。油页岩有机质主要由C、H、O、N元素组成,无机物主要由Si、Al、Fe、Ca、Mg等元素组成,其伴生元素主要为Ti、Zr、Ge和Ga;油页岩灰分主要由SiO₂、Al₂O₃、Fe₂O₃、CaO、MgO和SO₃组成,其中SiO₂的含量最高,Al₂O₃、Fe₂O₃次之。     

The nature of the sub-continental mantle: constraints from the major-element composition of continental flood basalts

Many continental flood basalts (CFB) have isotope and trace-element signatures that differ from those of oceanic basalts and much interest concerns the extent to which these reflect differences in their upper mantle source regions. A review of selected data sets from the Mesozoic and Tertiary CFB confirms significant differences in their major- and trace-element compositions compared with those of basalts erupted through oceanic lithosphere. In general, those CFB suites characterised by low Nb/La, high (⁸⁷Sr/⁸⁶Sr)_i and low εNd_i tend to exhibit relatively low TiO₂, CaO/Al₂O₃, Na₂O and/or Fe₂O₃, and relatively high SiO₂. In contrast, those which have high Nb/La, low (⁸⁷Sr/⁸⁶Sr)_i and high εNd_i ratios, like the upper units in the Deccan Traps, have major- and trace-element compositions similar to oceanic basalts. It would appear that those CFB that have distinctive isotope and trace-element ratios also exhibit distinctive major-element contents, suggesting that major and trace elements have not been decoupled significantly during magma generation and differentiation.

When compared (at 8% MgO) with oceanic basalt trends, the displacement of many CFB to lower Na₂O, Fe₂O₃^*, TiO₂ and CaO/Al₂O₃, but higher SiO₂, at similar Mg#, is not readily explicable by crustal contamination. Rather, it reflects source composition and/or the effects of the melting processes. The model compositions of melts produced by decompression of mantle plumes beneath continental lithosphere have relatively low SiO₂ and high Fe₂O₃^*. In contrast, the available experimental data indicate that partial melts of peridotite have low TiO₂, Na₂O and Fe₂O₃^*CaO/Al₂O₃, if the peridotite has been previously depleted by melt extraction. Moreover, melting of hydrated, depleted peridotite yields SiO₂-rich, Fe₂O₃- and CaO-poor melts. Since anhydrous, depleted peridotite has a high-temperature solidus, it is argued that the source of these CFB was variably melt depleted and hydrated mantle, inferred to be within the lithosphere. Isotope data suggest these source regions were often old and relatively enriched in incompatible trace elements, and it is envisaged that H₂O±CO₂ were added at the same time as the incompatible elements. An implication is that a significant proportion of the new continental crust generated since the Permian reflected multistage processes involving mobilization of continental mantle lithosphere that was enriched in minor and trace elements during the Proterozoic.     

重庆石柱二叠纪栖霞组地球化学特征及其环境意义

在对重庆市石柱县二叠纪栖霞组地层野外露头沉积特征研究的基础上,结合室内薄片观察,根据碳酸盐岩样品的元素含量、比值及相关性,探讨了栖霞组沉积地球化学特征与古环境意义.用于古环境分析的10件栖霞组样品SiO₂、MgO含量低,且两者具有较好的正相关性,Sr含量高,平均为1 751×10-6,Mn/Sr<0.1,Fe/Sr<1,δ18O_PDB>-10‰,表明成岩过程中样品几乎不受硅化及白云岩化作用的影响,未发生化学性质上的改变,可作为古环境分析的可靠对象.栖霞组碳酸盐岩CaO含量高,平均为53.81%,接近纯灰岩的理论化学组成,陆源元素Al₂O₃、TiO₂含量很低,平均值分别为0.17%与0.012%,表明其形成于陆源碎屑影响微弱的稳定古海洋环境.古气候指标MgO/CaO比值极低,平均为0.026,古盐度指标100×(MgO/Al₂O₃)比值高,平均为1 241,古水深判别指标Sr/Ba、1000×(Sr/Ca)比值高,平均值分别为286和4.54,指示了栖霞组碳酸盐岩为潮湿气候下的陆表海(远岸)沉积.古氧相地球化学指标U/Al、V/Al、Mo/Al、Cr/Al、Co/Al、V/(V+Ni)和U/Th特征一致表明栖霞组碳酸盐岩沉积于贫氧—缺氧环境.垂向上,陆源元素∑(Al₂O₃+TiO₂)含量逐渐降低,古水深指标Sr/Ba、1000×(Sr/Ca)比值逐渐增大,表明栖霞组沉积过程中离岸渐远、陆源供给逐步减少、水体持续加深.     

甘肃天水全新世黄土-古土壤序列化学风化特征及其古气候意义

对甘肃天水地区师家崖典型黄土-古土壤剖面化学元素的测定和分析结果表明:该剖面中氧化物SiO₂、Fe₂O₃、K₂O和Al₂O₃含量变化趋势基本一致,均在古土壤层（S_0上和S_0下）中较高,黄土层（L₀、L₁和L_t）中较低;而氧化物CaO和Na₂O变化呈相反趋势;根据钙镁比（Ca/Mg）、钾钠比（K/Na）、淋溶系数、退碱系数、残积系数和化学蚀变系数（CIA）等化学参数的统计分析结果,揭示了古土壤层形成时期风化成壤作用强烈,黄土层堆积时期风化成壤作用微弱的规律;以Ti为参比,Si、Fe、K和Al相对富集,而Na和Ca发生不同程度的淋溶,总体处于脱Ca、Na的低等化学风化阶段;SJY剖面全新世以来的沉积环境分为化学风化较弱期、波动增强期和减弱期,记录了该区域气候经历了早全新世温凉、中全新世温暖湿润但不稳定,晚全新世凉干的演变过程,对天水地区的古气候变化具有重要意义。     

Compositional effects on element partitioning between Mg-silicate perovskite and silicate melts

High-pressure melting experiments were performed at ~26 GPa and ~2,200–2,400°C on synthetic peridotite compositions with varying FeO and Al₂O₃ contents and on a synthetic CI chondrite analogue composition. Peridotite liquids show a crystallisation sequence of ferropericlase (Fp) followed down temperature by Mg-silicate perovskite (MgPv) + Fp, which contrasts a sequence of MgPv followed by MgPv + Fp observed in the chondritic composition. The difference in crystallisation sequence is a consequence of the different bulk Mg/Si ratios. MgPv/melt partition coefficients for major, minor and trace elements were determined by electron microprobe and secondary ion mass spectrometry. Partition coefficients of tri- and tetravalent elements increase with increasing Al concentration in MgPv. A lattice strain model indicates that Al³⁺ substitutes predominantly onto the Si-site in MgPv, whereas most elements substitute onto the Mg-site, which is consistent with a charge-compensating coupled substitution mechanism. MgPv/melt partition coefficients for Mg (D_Mg) and Si (D_Si) are related to the melt Mg/Si ratio such that D_Si becomes lower than D_Mg at low Mg/Si melt ratios. We use a crystal fractionation model, based on upper mantle refractory lithophile element ratios, to constrain the amount of MgPv and Ca-silicate perovskite (CaPv) that could have fractionated during a Hadean magma ocean event and could still be present as a chemically distinct heterogeneity in the lower mantle today. We show that a fractionated crystal pile composed of 96% MgPv and 4% CaPv could comprise up to 13 wt% of the entire mantle.     

Diffusion in silicate melts: II. Multicomponent diffusion in CaOAl2O3SiO2 at 1500°C and 1 GPa

Chemical diffusion profiles in molten CaO---Al₂O₃---SiO₂ have been measured over a large range of compositions at 1500°C and l GPa. The diffusion profiles have been inverted for effective binary diffusion coefficients (EBDCs) and for the chemical diffusion matrix. The EBDCs are shown to depend strongly on both composition and direction of diffusion in composition space. The dependence of EBDCs on direction in composition space, which for the system studied here can be as large as a factor of seven, severely limits the applicability of EBDCs to interdiffusion in any direction other than the one used to derive the EBDCs.

The chemical diffusion matrix for molten CaO---Al₂O₃---SiO₂ was determined using diffusion profiles from two or three mutually orthogonal diffusion couples in the ternary composition space. All features of the diffusion profiles shown in this work can be reproduced by representing the chemical fluxes in the three-component system as a linear combination of concentration gradients via a 2 × 2 diffusion matrix. Chemical diffusion in molten CaO---Al₂O₃---SiO₂ shows clear evidence of strong diffusive coupling among the components. This can be seen in the uphill diffusion profiles of components that were initially uniform, in the fact that the apparent rate of diffusion of some components is a strong function of direction in composition space, and most quantitatively in the magnitude of off-diagonal elements of the diffusion matrix relative to the magnitude of the diagonal elements. SiO₂ for example, is found to be strongly coupled with CaO in relatively silicic melts, whereas Al₂O₃ is strongly coupled with CaO in less silicic melts. Furthermore, the coupling of CaO with either Al₂O₃ or Si02 reverses sign between more and less polymerized compositions. Interdiffusion profiles in natural melts have numerous features that suggest similar coupling between Al₂O₃ and CaO and between SiO₂ and CaO.     

Petrology and geochemistry of potassic and ultrapotassic volcanism in central Italy: petrogenesis and inferences on the evolution of the mantle sources

Major, trace element, Sr isotopic and mineral chemical data are reported for mafic volcanic rocks (Mg-value 65) from the northern-central sector of the potassic volcanic belt of Central Italy. The rocks investigated range from potassic series (KS) and high-K series (HKS) to lamproitic (LMP) and kamafugitic (KAM) through a transitional series (TRANS), thus covering the entire compositional spectrum of potassic and ultrapotassic magmas. KAM rocks are strongly silica undersaturated and, compared with the other rock series, have low SiO₂, Al₂O₃, Na₂O, Sc and V and high CaO, K/Na, (Na + K)/Al. KS and HKS have high Al₂O₃, CaO and variable enrichment in K₂O and incompatible elements. LMP rocks are saturated in silica and have high SiO₂, K₂O, K₂O/Na₂, MgO, Ni and Cr and low Al₂O₃, CaO, Na₂O, Sc and V. TRANS rocks display intermediate compositional characteristics between LMP and KS.

All the rocks under study have fractionated hygromagmaphile element patterns with high LIL/HFS element values and negative anomalies of Ti, Ta, Nb and Ba. Negative Sr anomalies are observed in the LMP and TRANS rocks. LIL elements show overall positive correlations with K₂O, whereas different trends of Sr and HFSE vs. K₂O are defined by LMP-TRANS and KS-HKS-KAM. ⁸⁷Sr/⁸⁶Sr range from about 0.710 to 0.716. KS, HKS and KAM rocks have similar ⁸⁷Sr/⁸⁶Sr values clustering around 0.710. LMP and TRANS rocks have the highest ⁸⁷Sr/⁸⁶Sr values.

Geochemical and isotopic data reported for the most primitive Italian potassic and ultrapotassic rocks support the hypothesis that the interaction between crustal and mantle reservoirs was a main process in the genesis of Italian potassic magmatism. Simple mass balance calculations exclude, however, an important role of crustal assimilation during ascent of subcrustal magmas to the surface and indicate that the sources of Central Italy volcanics underwent contamination with fluids and/or melts released by upper crustal material previously brought into the mantle by subduction processes.

Different trends of incompatible elements vs. K₂O observed in the studied rocks suggest distinct metasomatic processes for the sources of the investigated magmas. Liquids derived by bulk melting of pelitic sediments are believed to be the most likely contaminants of the source of LMP rocks. Fluids or melts rich in Ca, Sr and with high LILE/HFSE value and Sr isotopic composition around 0.710 are the most likely contaminant of the source region of KS, HKS and KAM volcanics. Variations in CaO, Na₂O and ferromagnesian element abundances and ratios suggest that, in some zones, the mantle source of potassic magmas experienced partial melting with extraction of basaltic liquids prior to metasomatism.     

Titanian clinohumite–garnet–pyroxene rock from the Su-Lu UHP metamorphic terrane, China: chemical evolution and tectonic implications

A garnet–pyroxene rock containing abundant Ti-clinohumite (ca. 40 vol.%) occurs along with eclogites as small blocks in quartzo-feldsparthic gneiss in the southern end of the Chinese Su-Lu ultrahigh-pressure (UHP) metamorphic terrane. It consists of three aggregates: (1) Ti-clinohumite-dominated aggregate with interstitial garnet and pyroxene, (2) garnet+pyroxene aggregate with Ti-clinohumite inclusions, and (3) Ti-clinohumite-free aggregate dominated by garnet. Apatite, phlogopite, zircon, hematite, pentlandite, and an unknown Ni-Fe-volatile-Si (NFVS) mineral, which is replaced by Ni-greenalite, occur as accessories. Serpentine is the major secondary mineral. Garnet (Prp_63.9–64.6Alm_25.8–26.9Grs_1.4–7.9Uva_0.5–7.6Sps_1.0) in all three aggregates is pyrope-rich with very low grossular component, with that in the aggregate (2) most enriched in Cr (Cr₂O₃=2.55 wt.%). Orthopyroxene is depleted in Al (Al₂O₃=0.16 wt.% in the cores) and Ca (CaO=0.06–0.09 wt.% in the cores), with X_Mg (Mg/(Mg+Fe)) values at ca. 0.900. Clinopyroxene is chromian diopside with Fe³⁺≥Fe²⁺. Matrix clinopyroxene has a lower X_Mg (0.862) than that (0.887) included in Ti-clinohumite. The rock contains modest amount of heavy rare earth elements (HREE) (10 to 12×C1 chondrite), with significant enrichment in Cr, Co, Ni, V, Sr, and light rare earth elements (LREE) (22 to 33×C1 chondrite). The clinopyroxene is very enriched in Cr (Cr₂O₃ is up to 2.09 wt.% in the cores) and Sr (ca. 350 ppm) and LREE (Ce_N/Yb_N=157.7). Ti-clinohumite is enriched in Ni (1981 ppm), Co (123 ppm), and Nb (85 ppm).

While it is possible to enrich ultramafites in incompatible elements in a subducted slab, the high Al, Fe, Ti, and low Si, Ca, and Na contents in the Ti-clinohumite rock are difficult to account for by crustal metasomatism of an ultramafite. On the other hand, the similarity in major and trace element compositions and their systematic variations between the Ti-clinohumite-garnet-pyroxene rock of this study and those of Mg-metasomatised Fe–Ti gabbros reported in the literature suggest that crustal metasomatism occurred in a gabbroic protolith, which resulted in addition of Cr, Co, Ni, and Mg and removal of Si, Ca, Na, Al, and Fe. This implies that the rock was in contact with an ultramafite at low pressure. During subsequent subduction, the metagabbro was thrust into the country gneiss, where gneiss-derived hydrous fluids caused enrichment of Sr and LREE in recrystallised clinopyroxene. P–T estimates for the high-pressure assemblage are ca. 4.2 GPa and ca. 760 °C, compatible with those for the eclogites and gneisses in this terrane. It is possible that the Ti-clinohumite-garnet-pyroxene rock and associated eclogites represent remnants of former oceanic crust that was subducted to a great depth.     

The origin of medium-K ankaramitic arc magmas from Lombok (Sunda arc, Indonesia): Mineral and melt inclusion evidence

High-calcium, nepheline-normative ankaramitic basalts (MgO > 10 wt.%, CaO/Al₂O₃ > 1) from Rinjani volcano, Lombok (Sunda arc, Indonesia) contain phenocrysts of clinopyroxene and olivine (Fo_85–92) with inclusions of spinel (Cr# 58–77) and crystallised melt. Olivine crystals have variable but on average low NiO (0.10–0.23 wt.%) and high CaO (0.22–0.35 wt.%) contents for their forsterite number. The CaO content of Fo_89–91 olivine is negatively correlated with the Al₂O₃ content of enclosed spinel (9–15 wt.%) and positively correlated with the CaO/Al₂O₃ ratios of melt inclusions (0.9–1.5). Major and trace element patterns of melt inclusions are similar to that of the host rock, indicating that the magma could have formed by accumulation of small batches of melt, with compositions similar to the melt inclusions. The liquidus temperature of the magma was  1275 °C, and its oxygen fugacity ≤ FMQ + 2.5. Correlations between K₂O, Zr, Th and LREE in the melt inclusions are interpreted to reflect variable degrees of melting of the source; correlations between Al₂O₃, Na₂O, Y and HREE are influenced by variations in the mineralogy of the source. The melts probably formed from a water-poor, clinopyroxene-rich mantle source.     

http://www.sciencedirect.com/science/article/pii/S1674987111000909

We have performed measurements of minerals based on the synchrotron source for single crystal and powder X-ray diffraction,inelastic scattering,spectroscopy and radiography by using diamond anvil cells.We investigated the properties of iron（Fe）,iron-magnesium oxides（Fe,Mg）O, silica（SiO₂）,iron-magnesium silicates（Fe,Mg）SiO₃ under simulated high pressure-high temperature extreme conditions of the Earth’s crust,upper mantle,low mantle,core-mantle boundary,outer core, and inner core.The results provide a new window on the investigation of the mineral properties at Earth’s conditions.     

吉林省白山市板石沟铁矿断裂构造地球化学特征

断裂构造中元素的迁移变化规律是构造地球化学研究的主要内容.白山市板石沟铁矿断裂构造发育,是开展断裂构造地球化学研究的有利地区.通过对板石沟铁矿17矿组和赵家沟矿组典型逆断层剖面测量,采集构造岩和周围岩石,分析常量元素和微量元素,利用构造地球化学剖面法、质量等比线法和特征元素比值来反映元素在逆断层中分布特征和迁移变化规律.通过分析认为在逆断层中常量元素SiO₂、Fe₂O₃、CaO、Na₂O亏损,Al₂O₃、K₂O富集,微量元素中Rb、Sr等离子半径较大元素富集,离子半径较小元素Co、Cr、Ni亏损,K₂O/Na₂O、V/Cr、Rb/（Ni+Co）在逆断层中呈现出高值,SiO₂/Al₂O₃、（Fe₂O₃+CaO+MgO）/Al₂O₃呈现出低值.依据这些构造地球化学特征可以用来判断断裂构造的存在,为断裂构造地球化学研究和板石沟铁矿勘查提供构造地球化学依据.     

Pressure dependence on partition coefficients for trace elements between olivine and the coexisting melts

Partition coefficients between olivine and melt at upper mantle conditions, 3 to 14 GPa, have been determined for 27 trace elements (Li, Be, B, Na, Mg, Al, Si, P, K, Ca, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Rb, Sr, Y, Zr, Cs, Ba, La and Ce) using secondary-ion mass-spectrometry (SIMS) and electron-probe microanalysis (EPMA). The general pattern of olivine/melt partitioning on Onuma diagrams resembles those reported previously for natural systems. This agreement strongly supports the argument that partitioning is under structural control of olivine even at high pressure. The partition coefficients for mono- and tri-valent cations show significant pressure dependence, both becoming larger with pressure, and are strongly correlated with coupled substitution into cation sites in the olivine structure. The dominant type of trace element substitution for mono- and tri-valent cations into olivine changes gradually from (Si, Mg)↔(Al, Cr) at low pressure to (Si, Mg)↔(Al, Al) and (Mg, Mg)↔(Na, Al) at high pressure. The change in substitution type results in an increase in partition coefficients of Al and Na with pressure. An inverse correlation between the partition coefficients for divalent cations and pressure has been observed, especially for Ni, Co and Fe. The order of decreasing rate of partition coefficient with pressure correlates to strength of crystal field effect of the cation. The pressure dependence of olivine/melt partitioning can be attributed to the compression of cation polyhedra induced by pressure and the compensation of electrostatic valence by cation substitution. Received: March 6, 1997 / Revised, accepted: March 12, 1998     

福建李坊重晶石矿床形成环境及矿床成因

为了解福建李坊重晶石矿床成因和成矿物质来源,对重晶石单矿物的主量元素、稀土元素、微量元素和硫同位素进行了研究,研究结果显示:重晶石单矿物表现出富Al、Si、Fe的特征;ΣREE总量较低,富集轻稀土元素;δEu呈正异常,δCe呈负异常;微量元素富集Ba、Rb、Nb、Th、P等元素,亏损K、Zr等元素;各个中段δ34S均值大于32.6‰,且直方图中只显示一个主峰。重晶石单矿物成因判别图解、ΣREE-La/Yb图解,分别指示了重晶石单矿物形成于热水沉积区,成矿物质来源于沉积岩区;Si O2/Al2O3、MnO/TFe2O3、U/Th等比值指示了弱碱性—碱性的氧化环境;(La/Ce)N、Al/(Al+Fe)等比值指示大陆边缘环境。研究表明,李坊重晶石矿床形成于大陆边缘构造环境的热水沉积成矿作用,其Ba主要来源于沉积岩区,S主要来源于寒武纪海水,并且有较多陆源物质的输入。     

上天、入地、下海:极端条件下矿物学研究

上天、入地、下海,进行极端条件下的矿物学研究,研究微矿物,发现新矿物。主要利用金刚石压机,结合使用国内外同步辐射X-光源、中子源,以及其他多种物理的、化学的、光学的测试手段(如岩石矿物化学分析,光薄片测定,电子探针,离子探针,扫描电镜,透射电镜,红外、紫外、拉曼光谱,激光加热等),对来自天外的陨石、陨石坑样品、地球深处地幔源矿物以及海底甲烷水合物进行了一些研究。模拟不同温度和压力下各种不同成分的矿物材料的晶体结构、物理和化学性质。文章着重研究从地球内核到地壳海底的各种不同组分在不同温度、压力极端环境下形成的各种各样的典型矿物:从金属固体内核和金属液体外核中的ε-Fe到核幔边界(CMB)地球D″层的后钙钛矿(Post-Perovskite)结构(ppv)镁铁硅酸盐(Mg,Fe)SiO₃,从下地幔中的铁磁性钙钛矿(Perovskite)结构(pv)镁铁硅酸盐布里奇曼石(Bridgmanite)(Mg,Fe)SiO₃、镁铁氧化物(Fe,Mg)O和后尖晶石(Post-Spinel)结构的含Fe³⁺毛河光矿(Maohokite)(HP-Mg$Fe^{3+}_{2}O_{4}$)到过渡带、上地幔和地壳中的镁铁硅酸盐、硅氧化物、铬铁氧化物和金刚石及其内含物以及甲烷水合物(CH₄·H₂O)等。进行高温高压极端条件下的矿物学研究,为探索地球结构性质、形成动力和发展历史提供了新的窗口。     

Melting experiment of a Wannienta basalt in the Kuanyinshan area,northern Taiwan,at pressures up to 2.0 GPa

Melting experiments involving fifteen runs were performed at pressures between 1.0 and 2.0 GPa in order to locate the liquidus temperatures, the solidus temperatures, and the melting intervals of the Wannienta basaltic magma, northern Taiwan. The experimental results showed that the liquidus and solidus temperatures were raised by 60 GPa and 40 GPa respectively. The liquidus mineral at 1.0 GPa is orthopyroxene, whereas the liquidus mineral is clinopyroxene at 1.5 and 2.0 GPa. The crystallized phases are clinopyroxene and plagioclase at temperatures between 1220 and 1270°C and pressures between 1.0 and 2.0 GPa. Garnet appears at 2.0 GPa near the solidus. The geochemical evolution of the residual magma with decreasing temperature show the following trends: At 1.0 GPa, Al, Na, and K are progressively enriched while depletions occur in Mg. At 2.0 GPa, Si, Fe and K are progressively enriched with decreasing temperature while depletions occur in Mg, Ca, and Na. The fractionation trend of the Kuanyinshan volcanic series is similar to the trend observed in residual magmas at pressures between one atmosphere and 1.0 GPa. These results indicate that the depth for fractional crystallization of the Wannienta basaltic magma to produce andesites could be modeled at low pressure. The fractionates involved included iron-titanium oxides, olivine, plagioclase, and clinopyroxene.     

Melting relations of peridotite and the density crossover in planetary mantles

Melting relations of primitive peridotite were studied up to 25 GPa. The change of the liquidus phase from olivine to majorite occurs at 16 GPa. We confirmed the density crossover of the FeO-rich peridotite melt and the equilibrium olivine (Fo₉₀) at 7 GPa. Sinking of equilibrium olivine (Fo₉₅) in the primitive peridotite melt was observed up to 10 GPa. The compression curves of FeO-rich peridotitic and komatiite melts reported in this and earlier work suggest that the density crossover in the Earth's mantle will be located at 11–12 GPa at 2000°C, consistent with an previous estimation by C.B. Agee and D. Walker.

The density crossover can play a key role in the Moon and the terrestrial planets, such as the Earth, Venus and Mars. Majorite and some fraction of melt could have separated from the ascending diapir and sunk downwards at the depths below the density crossover. This process could have produced a garnet-rich transition zone in the Earth's mantle. The density crossover may exist in the FeO-rich lunar mantle at around the center of the Moon. The density crossover which exists at the depth of 600 km in the Martian mantle plays a key role in producing a fractionated mantle, which is the source the parent magmas of the SNC meteorites.     

青藏高原东部黄土沉积元素地球化学示踪

青藏高原东部广泛分布着典型黄土沉积,对气候变化有着敏感的响应。对青藏高原东部地区典型表土、黄土、古土壤以及砂样,进行系统的常量、微量元素组成分析,结果显示,高原东部黄土常量元素氧化物主要为SiO₂、Al₂O₃、Fe₂O₃和CaO,黄土中SiO₂和CaO含量差别较大;Rb、Sr、Ba、Zr、V含量占了微量元素含量的大部分,表土、黄土、古土壤微量元素含量差别不一。与高原东部的风沙沉积、黄土高原黄土、河西走廊黄土的对比结果表明,青藏高原东部黄土组分的常量元素之间的比值（SiO₂/Al₂O₃、TiO₂/Al₂O₃）、常量与微量元素之间的比值（Zr/Al、Zr/Ti）、常量元素三角图（Ca-Mg-K、Ca-Mg-Na）等与其他地区黄土有明显差异,而青藏高原东部黄土与高原表土沉积物及河流砂、风成砂样品比较接近。这些异同点指示青藏高原东部黄土与黄土高原黄土的物源不同;其物源可能主要来自于青藏高原内部,高原内部的河流沉积物、冰碛物等粉尘物质可能为青藏高原东部黄土的主要物源。