Fractional crystallization models and B–Be–Li systematics at Mt Somma-Vesuvius volcano (Southern Italy)

A compilation of B–Be–Li data on rocks that cover the entire eruptive history of Somma-Vesuvius is presented and interpreted in the light of evolution models for the Somma-Vesuvius rocks. Using major and trace element data, fractional crystalllization models are presented for different geochemical units. These data were used to constrain the source mineralogy of the Somma-Vesuvius rocks (ol-opx-cpx-gar-amp of 0.4-0.3-0.1-0.1-0.1), the amount of sediment added (5–10%) and the melt fraction from batch partial melting computations (0.05–0.1). From the B–Li data it is inferred that the main process responsible for the B isotopic signature is sediment recycling. However, the B–Li data show a major variation in Li abundances respect to B which is explained with Li dehydration before the fluid enriched the mantle wedge that produced the arc magmas. The Somma-Vesuvius B isotope composition is intermediate between that of the Campi Flegrei and the broad field of the Eolian Island arc. A low Be isotopes in the recent volcanic rocks can be explained as: (a) the top 1–22 m of the incoming sediment is accreted, (b) large amounts of sediment erosion, (c) a slow rate of subduction which have provoked a long magmatic history for the Vesuvius magma, (d) the sediment component takes several Myr longer than the subducting plate to reach the magma source region beneath Italy.     

Pelagic records from the Equatorial Ninetyeast Ridge and significant environmental events during the past 3.5 Ma

This paper presents pelagic records of planktic foraminifera, as well as data of stable isotope stratigraphy and carbonate stratigraphy since 3.5 Ma B.P. from site ODP758 in the Ninetyeast Ridge of the Indian Ocean. Based on these data, manifestations and related mechanisms of major tectonic and environmental events such as the rapid uplift of the Himalaya Mountains, “middle Pleistocene climatic transition” and “mid-Brunhes dissolution event” in the region are discussed. According to the analysis and comparison of various indices and changes in terms of foraminifera assemblage, paleotemperature, paleosalinity and themocline from site ODP758, the authors deduce that the paleoclimatic changes might correlate with the mid-Pleistocene transition at 1.4–1.7 Ma B.P. The changes of CaCO₃, mass accumulation rates (MAR) of CaCO₃ and non- CaCO₃ MAR indicate that the loaded terrigenous sediments increased at 1.7 Ma, which is in agreement with the uplift history of the Qinghai-Tibet plateau as shown by the available data. The last two changes coincide with the uplift of the Qinghai-Tibet plateau, hence they are called “Qinghai-Tibet movement” (1.7 Ma), and the “Kunlun-Yellow River movement” (1.2–0.6 Ma). The changes of the CaCO₃ content, coarse fraction (> 150 μm) content and planktonic foraminifera biostratigraphy show that strong dissolution of abyssal CaCO₃ occurred in the study region during 0.5–0.4 Ma. The event was consistent with the “mid-Brunhes dissolution event” in the sedimentary records of the Atlantic Ocean, Pacific Ocean, Indian Ocean and Nansha sea area of the South China Sea. __________ Translated from Geological Bulletin of China, 2007, 26(12): 1627–1632 [译自: 地质通报]     

Dynamics of the mid-ocean ridge plate boundary: Recent observations and theory

The global mid-ocean ridge system is one of the most active plate boundaries on the earth and understanding the dynamic processes at this plate boundary is one of the most important problems in geodynamics. In this paper I present recent results of several aspects of mid-ocean ridge studies concerning the dynamics of oceanic lithosphere at these diverging plate boundaries. I show that the observed rift valley to no-rift valley transition (globally due to the increase of spreading rate or locally due to the crustal thickness variations and/or thermal anomalies) can be explained by the strong temperature dependence of the power law rheology of the oceanic lithosphere, and most importantly, by the difference in the rheological behavior of the oceanic crust from the underlying mantle. The effect of this weaker lower crust on ridge dynamics is mainly influenced by spreading rate and crustal thickness variations. The accumulated strain pattern from a recently developed lens model, based on recent seismic observations, was proposed as an appealing mechanism for the observed gabbro layering sequence in the Oman Ophiolite. It is now known that the mid-ocean ridges at all spreading rates are offset into individual spreading segments by both transform and nontransform discontinuities. The tectonics of ridge segmentation are also spreading-rate dependent: the slow-spreading Mid-Atlantic Ridge is characterized by distinct bulls-eye shaped gravity lows, suggesting large along-axis variations in melt production and crustal thickness, whereas the fast-spreading East-Pacific Rise is associated with much smaller along-axis variations. These spreading-rate dependent changes have been attributed to a fundamental differences in ridge segmentation mechanisms and mantle upwelling at mid-ocean ridges: the mantle upwelling may be intrinsically plume-like (3-D) beneath a slow-spreading ridge but more sheet-like (2-D) beneath a fast-spreading ridge.     

Platinum-group element distribution in chromite ores from ophiolite complexes: implications for their exploration

Compilation of some new data on ophiolites for Greece and Yugoslavia, and published data from previous studies, indicate that platinum-group element (PGE) and gold concentrations in chromite ores are generally low, ranging from less than 100 ppb to a few hundred ppb. However, samples from several ophiolite complexes exhibit an enrichment (of a few ppm) (a) only in Os, Ir and Ru,(b) only in Pt and/or Pd or (c) in all PGE. This enrichment (up to 10s ppm) is mainly related with chromitites hosted in supra-Moho dunites and dunites of the uppermost stratigraphic levels of the mantle sequence and it seems to be local, independent of the chromitite major element composition and the chromite potential of the ophiolite complexes. The contents of PGE combined with less chalcophile elements (Ni, Co, Cu), the ratios of incompatible/compatible elements, and PGE-patterns provide evidence for discrimination between chromitites derived from primitive magmas and those derived from partially fractionated magmas, although they have a similar major element composition. Thus, they can be used for a stratigraphic orientation in the mantle sequence, and therefore for exploration targets. Moreover, PGE data offer valuable information for the evaluation of the chromite potential in ophiolite complexes. The most promising ophiolites seem to be those which apart from the petrological and geochemical characteristics indicating extensive degree of partial melting in the mantle source contain only one chromite ore type (the other type being only in small proportion) of limited compositional variation, in both major elements and PGE, low ratios of , while PGE-enriched chromitites in the mantle sequence are only occasionally present. In contrast, ophiolites which contain both high-Cr and -Al chromitites, and where their chalcophile element data implies relatively extensive fractionation trend are not good exploration targets for chromite ores, although they are related with a SSZ environment.     

A dynamic box model of bioactive elements in the southern Taiwan Strait

A dynamic box model was applied to study the characteristics of biogeochemical cycling of PO_4-P,NO_3-N,AOU,POC and PON in the southern Taiwan Strait region based on field data of the"Minnan Taiwan Bank Fishing Ground Upwelling Ecosystem Study" during the period of Dec.1987-Nov.1988.According to the unique hydrological and topographical features of the region,six boxesand three layers were considered in the model.The variation rates and fluxes of elements induced by hor-izontal current,upwelling,by diffusion,sinking of particles and biogeochemical processes were estimatedrespectively.Results further confirmed that upwellings had important effects in this region.Thenearshore upwelling areas had net input fluxes of nutrients brought by upwelling water,also had high de-pletion rates of nutrients and production rates of particulate organic matter and dissolved oxygen.Theabnormal net production of nutrients in the middle layer(10-30m) indicated the important role of bacte-ria in this high production region.Th     

极性转换期间地球磁场形态学研究

本文对采自中国黄土高原西峰（35.7°N,107.6°E）和段家坡（34.2°N,109.2°E）两个剖面中黄土层L8和古土壤层S8的1281块定向古地磁样品做了详细的岩石磁学和古地磁学研究.证实了Matuyama-Brunhes（M-B）极性转换带位于L8的中下部.提出了下列观点:1.M-B极性转换过程与地球磁场方向变化相联系的持续时间为3600-4500a,而与地球磁场强度变化相联系的持续时间则为8000-9000a,即强度变化存在“超前和滞后” 效应;2.M-B转换场的形态是由三次快速倒转和一次不成功的倒转构成,或者说,转换场具有快速变换极性的振荡特征;3.M-B转换过程中地球磁场并不是以轴对称的非偶极子场为主,而是偶极子场至少与非偶极子场相当;4.中国黄土-古土壤沉积物所含磁性矿物的主要成分是磁铁矿,它是研究极性转换期间地球磁场详细结构的良好物质.     

全球不同构造环境蛇纹岩全岩和矿物微量元素组成及非传统稳定同位素(Fe- Zn- Cu同位素)特征

蛇纹岩对地球深部和浅部的元素循环以及氧化还原状态调节具有非常重要的作用。蛇纹岩中的流体活动性元素(fluid- mobile element, FME)是揭示地幔岩石水化、脱水以及元素循环的关键。本文系统收集和分析了前人报道的不同构造环境的蛇纹岩矿物化学、全岩微量元素和非传统稳定同位素(Fe、Zn、Cu)的组成特征，试图从多个角度总结蛇纹岩脱水过程的元素迁移规律及流体性质。蛇纹岩主要矿物蛇纹石微量元素含量具有以下主要特征：① 不同变质程度的蛇纹岩中的蛇纹石既包含轻稀土元素(light rare earth element, LREE)富集，又包含LREE亏损的特征；② 纤蛇纹石的REE和微量元素分布在利蛇纹石和叶蛇纹石的范围内，利蛇纹石重稀土元素(heavy rare earth element, HREE)整体上略高于叶蛇纹石且更加富集FME；③ 通过中度不相容元素与REE含量相结合，能够较好地区分橄榄石和辉石蛇纹石化所形成的蛇纹石，即辉石形成的蛇纹石富集相容元素(如Sc、Zn、Cr、Y和Ti等)并具有较高的HREE，而橄榄石形成的蛇纹石则表现为平坦且整体较低的REE分布型式。在蛇纹岩全岩微量元素和稀土元素(rare earth element, REE)含量方面，不同构造环境的蛇纹岩具有较大范围的重叠，但也有一定的差异：① 慢速扩张的印度洋中脊蛇纹岩REE和微量元素含量要整体高于快速扩张的大西洋中脊和太平洋中脊的蛇纹岩；② 马里亚纳蛇纹岩泥相比于蛇纹岩和蛇纹石化纯橄岩具有更高的REE和微量元素，而蛇纹石化纯橄岩相比于蛇纹岩则具有相对低的REE及流体不活动性元素含量。因此，利用微量元素的含量在区分不同环境的蛇纹岩方面存在一定的困难。但是，碱金属元素与U元素含量及其相应的比值，则可以较明显区分出大洋蛇纹岩和弧前蛇纹岩。目前已发表的蛇纹岩Fe、Zn、Cu同位素数据表明：① 蛇绿岩中的蛇纹岩Fe和Zn同位素的分馏与其变质程度密切相关。蛇纹岩在进变质过程中δ 56Fe值与Fe 3+/∑Fe值呈负相关，而Zn含量和δ 66Zn值则呈现正相关，表明蛇纹岩变质脱水能够释放氧化性流体；② 与橄榄岩相比，蛇纹岩具有明显低的δ 65Cu值，表明橄榄岩蛇纹石化过程中存在氧化性流体的加入。蛇纹岩Fe、Zn、Cu同位素在示踪流体性质和氧化还原状态方面有很大潜力，对壳幔系统的化学循环具有重要意义。     

胶东海阳所超镁铁岩中强亲铁元素的地球化学特征及其构造环境探讨

强亲铁元素与亲石元素具有不同的地球化学行为，因此能够从不同的角度为造山带中超镁铁岩的成因及演化提供重要信息。位于苏鲁造山带东北端的胶东海阳所超镁铁岩主要由橄榄岩和辉石岩组成，它们常以团块状赋存于花岗质片麻岩中。虽然前人对这些超镁铁岩已经开展大量岩石学研究，但关于其成因及构造属性仍存在较大争议。本文开展了海阳所超镁铁岩的全岩主微量元素、强亲铁元素及Re-Os同位素的分析工作，结果显示蛇纹石化橄榄岩具有较高的MgO和Fe₂O₃^T含量，较低的Al₂O₃、TiO₂和CaO含量，明显富集流体迁移元素（U、Pb），亏损高场强元素（Zr、Hf），强亲铁元素没有发生明显分异，但Ru显示正异常，表明海阳所蛇纹石化橄榄岩是经历了低-中等程度部分熔融及熔/流体交代作用影响的残余地幔橄榄岩。海阳所辉石岩的主量元素表现出明显的结晶分异特征，稀土元素较原始地幔富集，铂族元素（PGEs）含量较低且发生了明显的分异，表明辉石岩的地幔源区经历过高程度的部分熔融和硫化物的分离。海阳所蛇纹石化橄榄岩的Os同位素地球化学特征表现出大洋亲和性，与辉石岩不具有熔体-残留体的关系。由于该地区发育较深层次的韧性剪切带，蛇纹石化橄榄岩中的橄榄石与辉石表现出韧性变形的特征，同时有辉石岩侵入到橄榄岩的现象，表明该地区的蛇纹石化地幔橄榄岩与辉石岩既不同时，也不同源，因此，暗示了该套岩石组合可能形成于大洋核杂岩（OCC）与洋脊型蛇绿岩（MOR）堆晶岩交互发育环境。     

碳中和目标下关键矿产在清洁能源转型中的作用、供需分析及其建议

在"碳中和"目标的驱动下，全球能源系统向清洁化、低碳化甚至无碳化发展已是大势所趋。针对向清洁能源转型的需求，采用了统计对比、分类汇总、综合分析等方法，分析研究了关键矿产在电池、电网、低碳发电和氢能等行业中的作用和需求。结合当前关键矿产产量的地理集中度高、项目开发周期长、资源质量下降等矿产供应和投资计划不能满足清洁能源转型的需求等问题，提出确保关键矿产多样性供应，推动价值链各环节的技术创新，扩大回收利用，增强供应链弹性和市场透明度，将更高的环境、社会和治理标准纳入主流程及加强生产者和消费者之间的国际合作等建议。     

GGR Critical Review of Analytical Developments in 2004–2005

In 2005 Geostandards and Geoanalytical Research embarked upon a new initiative for its readers. Key researchers in various fields of geoanalytical technique development and their application were identified and invited to provide reviews pertinent to their expertise. As noted in the first of these publications "…instead of revisiting the historical context or decades of development in each analytical technique, the goal here has been to capture a snapshot of "hot topics" across a range of fields as represented in the… literature" (Hergt et al . 2005). Rather than prepare an annual review, a decision was taken earlier this year to provide a biennial summary of progress and accomplishments, in this case for the years 2004–2005. The principal techniques employed in Earth and environmental sciences are covered here, and include laser ablation and multicollector ICP-MS, ICP-AES, thermal ionisation and secondary ion mass spectrometry, as well as neutron activation analysis, X-ray fluorescence and atomic absorption spectrometry. A comprehensive review of the development of reference materials, often essential to these techniques, is also provided. The contributions assembled serve both to keep readers informed of advances they may be unfamiliar with, but also as a means of showcasing examples of the breadth and depth of work being conducted in these fields.