Petrology,geochemistry, and tectonic significance of Mesozoic shoshonitic volcanic rocks,Luzong volcanic basin,eastern China

We studied the geochemical characteristics of three types of Mesozoic igneous rocks from the Luzong volcanic basin: basaltic trachyandesite at Shuangmiao, pyroxene monzonite at Bajiatan, and quartz-syenite (A-type granite) at Huangmeijian. Based on analyses of whole-rock major elements, all investigated rocks are enriched in K, Na, Ti, Al, but depleted in Ca, representing a shoshonitic series. Trace element analyses show that these rocks are characterized by enrichments of large-ion lithophile elements and high field strength elements. Positive Nb and Ta anomalies in the chondrite-normalized spider diagram indicate that the shoshonitic volcanic rocks share similar features with Nb-enriched basalts, which are different from normal island-arc volcanical rocks (they are typically strongly depleted in Nb and Ta). Bulk-rock chemical compositions and Sr–Nd isotopes indicate that the three types of igneous rocks are geochemically comagmatic, suggesting that the melts were derived from an enriched mantle reservoir. We postulate an extensional tectonic setting for the formation of Luzong volcanic basin, possibly related to subduction of a palaeo-Pacific plate beneath the east Chinese continent during the Yanshanian period (Cretaceous). Therefore, the petrogenetic features of those volcanic rocks as well as A-type granites in the Luzong basin indicate that the regional large-scale Fe–Cu–Au mineralization was associated with oceanic slab melting, but not delamination or recycling of the ancient lower continental crust, as previously proposed.     

40Ar/39Ar ages of flood basalt provinces in Russia and China and their possible link to global faunal extinction events: A cautionary tale regarding alteration and loss of 40Ar1

The hypothesis that the Permo–Triassic boundary (PTB) mass extinctions were caused by flood basalt volcanism in Russia (Siberian Traps) and/or China (the Emeishan Traps) is investigated from the point of view of time of occurrence (⁴⁰Ar/³⁹Ar ages). Numerous published ages in the literature are rejected as good estimates of the time of crystallization. The filters applied in this respect are (a) statistical reliability of plateau/isochron sections of stepheating data and (b) the alteration state of the material that was dated. Alteration appears to be ubiquitous, unsurprising since most of the material dated was used without acid leaching – a procedure that is effective in yielding fresh(er) samples. Of ∼70 ages in the literature for the main pulse of Siberian Trap volcanism, less than ten prove to be reliable ages. Similar techniques applied to ⁴⁰Ar/³⁹Ar for the Emeishan Traps, leaves only a single reliable age for the magmatic episode. These ages are compared to both published and new ⁴⁰Ar/³⁹Ar ages for the PTB as based on analysis of minerals from critical ash beds in China. There is good overlap in the ages (PTB – 250.0 ± 0.1 Ma, Siberian Trap lavas – 250.1 ± 0.4 Ma), lending credence to a genetic link between the formation of the Siberian Traps and the faunal extinction event at the PTB. A similar link for the formation of the Viluy Traps (Russia) and the Late Devonian extinction event is investigated; only a single reliable ⁴⁰Ar/³⁹Ar age is available for the Viluy Traps, and falls close to the interpolated age for the Frasnian–Fammenian boundary. The use of the unspiked K–Ar technique to yield accurate ages for such (altered) samples is questioned.A review of U–Pb data pertinent to these problems suggests a close temporal link between the formation of the Siberian Traps and the PTB. Comparison of U–Pb and ⁴⁰Ar/³⁹Ar ages for the PTB, raises questions about the accuracy of high precision sanidine ages, possibly resulting from very slow leakage of ⁴⁰Ar¹ from this mineral.     

Genesis of anhydrite in hydrothermally altered basalt from the East Pacific Rise near 13°N

This study reports the occurrence of anhydrite in hydrothermally altered pillow basalt (12°50.55′N, 103°57.62′W, water depth 2 480 m), which may have been produced in the basalt during seawater-basalt interaction in the laboratory. The existence of anhydrite in the altered basalt indicates extensive hightemperature hydrothermal alteration at the surface of seafloor pillow basalt. Microprobe analysis shows significant chemical zoning in the hydrothermally altered pillow basalt, in which Ca, Si and Al contents decrease and P, Fe, Mn, Cr and S contents increase from fresh basalt to altered basalt. The negative correlation between Rb-Sr and Li-Sr, and negative correlation between Li-Ca and Rb-Ca in the high-temperature vent fluids show that these fluids underwent anhydrite precipitation before fluid jetting due to mixing with seawater in the sub-seafloor. Based on these observations, we show that not all Ca in the anhydrite comes from basalt in the reaction zone, and that the basalts on the seafloor or in the upflow zone may also provide Ca for anhydrite.     

峨眉山玄武岩大规模灾难性崩滑事件的地质构造约束

滇东台褶带内上二叠统峨眉山玄武岩(P3β)滑坡的规模、失稳方向及其灾难性并不是随机的而是受到了区内地质构造的严格约束。喜马拉雅运动使得包括P3β在内的地台盖层褶皱回返;赋存于单斜断块或褶皱翼部的P3β的倾斜状态为其顺层滑移奠定了基础。滇东台褶带构造线相对稀疏,P3β整体性较好,这对于其发生大规模失稳是重要的;控制P3β岩层产状的断裂和褶皱主要为北东向,这决定了其大规模失稳的主体方向只能为南东向或北西向。北东向构造线控制的不同级别河流下切所形成的同向线状空间为P3β顺层失稳提供了不同序次基准面。北东向干流的支流一般与其垂直或大角度斜交,它们的溯源侵蚀是P3β盖层剥离、P3β斜坡塑造、滑坡物质运移通道与堆积场所形成的直接贡献者。P3β滑坡的灾难性一方面与不同级别北东向干流及其北西向支流构成的网状负地形空间网络有关,同时还与P3β盖层建造特征有关。北东向干流河谷,尤其是其与支流汇合处多具较高的人口密度。北西向支流穿越的P3β盖层为一套易于风化成壤的陆相沉积岩系,不同支流之间的山地具有较高的土地开发程度或植被盖度。土(林)地及水资源的丰富程度及地形条件等因素共同导致北西向支流沟谷也具较高的人口密度。这样,P3β潜在滑坡运移路径及主堆积区内均有密集的人口分布,而滑坡一旦发生,结果很可能就是灾难性的。     

月球形成和演化的关键科学问题

我国正开展月球探测和科学研究,其成果将加深认识月球的组成、结构以及形成和演化,同时揭示地球的早期历史。通过对月球研究成果的总结,就月球形成和演化关键科学问题的现状作了较为详细的说明,从而为我国月球探测和科学研究提供有益的启示。主要的关键科学问题包括：地球一月球体系的大撞击成因、月球岩浆洋与月壳形成、39亿年大撞击事件、玄武岩浆喷发与月球内部结构和月球南极艾特肯（Aitken）撞击盆地的形成等。     

鄂北地区推覆构造重磁异常特征

利用区域重磁资料,对鄂北推覆构造的空间分布特征进行了定性、半定量的分析与研究,解决了鄂北复杂地质问题,拓宽了区域重力调查的研究领域.     

大同万泉河河谷区玄武岩含水系统供水前景分析

大同万泉河河谷区玄武岩孔隙裂隙水含水系统含水层厚度大,孔隙裂隙发肓,具有良好的储水空间,除了接受上覆松散层的越流补给外,西部口泉断裂破碎带的远源地下水的侧向补给也是其重要的组成部分,此含水系统属中等富水含水层,且水质良好,允许开采量可达3.4753×104m3/d,具有开采前景。     

福建漳州牛头山火山地质公园火山喷发层序及岩相

牛头山火山地质公园位于风景壮观秀丽的闽南漳州市海滨，构造位置处于平潭一东山北东向断裂带中段，火山口坐落在龙海市隆教乡白塘村附近，涨潮时古火山口部分被海水淹没成为孤立于海中的小岛，退潮时，火山口全貌再露海面，火山口附近有一深槽（凹地），直径约8m，低于周围岩石3m，火山岩地层为新第三纪佛昙组上段玄武岩，根据岩性分布特征及岩石结构构造和岩层的产状等。可划分为喷溢相和火山颈相，是省内保存较完好的新生代古火山机构。     

Experimental Constraints on the Role of Garnet Pyroxenite in the Genesis of High-Fe Mantle Plume Derived Melts

The anhydrous phase relations of an uncontaminated (primitive),ferropicrite lava from the base of the Early Cretaceous Paraná–Etendekacontinental flood basalt province have been determined between1 atm and 7 GPa. The sample has high contents of MgO (14·9wt %), FeO^* (14·9 wt %) and Ni (660 ppm). Olivine phenocrystshave maximum Fo contents of 85 and are in equilibrium with thebulk rock, assuming a of 0·32. A comparison of our results with previous experimental studiesof high-Mg rocks shows that the high FeO content of the ferropicritecauses an expansion of the liquidus crystallization field ofgarnet and clinopyroxene relative to olivine; orthopyroxenewas not observed in any of our experiments. The high FeO contentalso decreases solidus temperatures. Phase relations indicatethat the ferropicrite melt last equilibrated either at 2·2GPa with an olivine–clinopyroxene residue, or at 5 GPawith a garnet–clinopyroxene residue. The low bulk-rockAl₂O₃ content (9 wt %) and high [Gd/Yb]_n ratio (3·1)are consistent with the presence of residual garnet in the ferropicritemelt source and favour high-pressure melting of a garnet pyroxenitesource. The garnet pyroxenite may represent subducted oceaniclithosphere entrained by the upwelling Tristan starting mantleplume head. During adiabatic decompression, intersection ofthe garnet pyroxenite solidus at 5 GPa would occur at a mantlepotential temperature of 1550°C and yield a ferropicriteprimary magma. Subsequent melting of the surrounding peridotiteat 4·5 GPa may be restricted by the thickness of theoverlying sub-continental lithosphere, such that dilution ofthe garnet pyroxenite melt component would be significantlyless than in intra-oceanic plate settings (where the lithosphereis thinner). This model may explain the limited occurrence offerropicrites at the base of continental flood basalt sequencesand their apparent absence in ocean-island basalt successions. KEY WORDS: continental flood basalt; ferropicrite; mantle heterogeneity; mantle melting; phase relations; pyroxenite     

玄武岩微生物分解过程中的矿物表面效应

通过玄武岩微生物风化的模拟实验,探讨了造岩矿物表面特征对微生物风化的影响,发现在细菌Paeni-bacillus polymyoca(多粘芽孢杆菌)及其代谢产物的作用下,玄武岩的分解作用显著增强,其中橄榄石最易分解,辉石次之,长石则相对最稳定.根据实验溶液的成分变化,认为橄榄石在初始阶段的分解主要受控于表面化学特征,随着比表面积的增大,表面控制作用进一步增强,分解更为快速.