Origin and evolution of Pliocene–Pleistocene granites from the Larderello geothermal field (Tuscan Magmatic Province, Italy)

Extensive, mainly acidic peraluminous magmatism affected the Tuscan Archipelago and the Tuscan mainland since late Miocene, building up the Tuscan Magmatic Province (TMP) as the Northern Apennine fold belt was progressively thinned, heated and intruded by mafic magmas. Between 3.8 and 1.3 Ma an intrusive complex was built on Larderello area (Tuscan mainland) by emplacement of multiple intrusions of isotopically and geochemically distinct granite magmas. Geochemical and isotopic investigations were carried out on granites cored during drilling exploration activity on the Larderello geothermal field. With respect to the other TMP granites the Larderello intrusives can be classified as two-mica granites due to the ubiquitous presence of small to moderate amounts of F-rich magmatic muscovite. They closely resemble the almost pure crustal TMP acidic rocks and do not show any of the typical petrographic features commonly observed in the TMP hybrid granites (enclaves, patchy zoning of plagioclase, amphibole clots). On the basis of major and trace elements, as well as REE patterns, two groups of granites were proposed: LAR-1 granites (3.8–2.3 Ma) originated by biotite-muscovite breakdown, and LAR-2 granites (2.3–1.3 Ma) generated by muscovite breakdown. At least three main crustal sources (at 14–23 km depth), characterized by distinct ε_Nd(t) and ⁸⁷Sr/⁸⁶Sr values, were involved at different times, and the magmas produced were randomly emplaced at shallow levels (3–6 km depth) throughout the entire field. The partial melting of a biotite-muscovite-rich source with low ε_Nd(t) value (about −10.5) produced the oldest intrusions (about 3.8–2.5 Ma). Afterwards (2.5–2.3 Ma), new magmas were generated by another biotite-rich source having a distinctly higher ε_Nd(t) value (−7.9). Finally, a muscovite-rich source with high ε_Nd(t) (about −8.9) gave origin to the younger group of granites (2.3–1.0 Ma). The significant Sr isotope disequilibrium recorded by granites belonging to the same intrusion is interpreted, as due to the short residence time of magmas in the source region followed by their rapid transfer to the emplacement level. Partial melting was probably triggered by multiple, small-sized mafic intrusions, distributed over the last 3.8 Ma that allowed temporary overstepping of biotite- and muscovite-dehydration melting reactions into an already pre-heated crust. Dilution in time of the magmatic activity probably prevented melt mingling and homogenization at depth, as well as the formation of a single, homogeneous, hybrid pluton at the emplacement level. Moreover the high concentrations of fluxing elements (B, F, Li) estimated for the LAR granites modified melt properties by reducing solidus temperatures, decreasing viscosity and increasing H₂O solubility in granite melts. The consequences were a more efficient, fast, magma extraction and transfer from the source, and a prolonged time of crystallization at the emplacement level. These key factors explain the long-lived hydrothermal activity recorded in this area by both fossil (Plio-Quaternary ore deposits) and active (Larderello geothermal field) systems.     

Land degradation in the source region of the Yellow River, northeast Qinghai-Xizang Plateau: classification and evaluation

Land degradation imposes a great threat to the world. It is not merely an environmental issue, but also a social and economic problem. Land desertification is among the main aspects of environment changes in the source region of the Yellow River. Previous studies focused on water resource utilization and soil erosion, but land degradation in the source region of the Yellow River even the whole Qinghai-Xizang Plateau received little attention. Based on the data obtained by field investigation and TM satellite images of 2000, this study provides the classification and evaluation information of the land degradation in the source region of the Yellow River. There are six types of land degradation in this region: water erosion in the northern mountains around the Gonghe Basin, sandy desertification in the Gonghe Basin and Upland Plain Area, aridization in the lower reaches, salinization in the Gonghe Basin, vegetation degradation in the intramontance basin and freezing and thawing erosion in the high mountains. The total degraded area is 34,429.6 km², making up 37.5% of the land in the study area. Finally, land degradation in the source region of the Yellow River was evaluated according to changes in the physical structure and chemical component of soils, land productivity, secondary soil salt and water conditions.     

Environmental pollution impact on water and sediments of Kumaun lakes, Lesser Himalaya, India: a comparative study

A study of the water and sediment chemistry of the Nainital, Bhimtal, Naukuchiyatal and Sattal Lakes of Kumaun, has shown that the water of these lakes are alkaline and that electrical conductivity, total dissolved solid and bicarbonate HCO ₃ ⁻ are much higher in Nainital than in the other three lakes. The weathering of limestone lithology and anthropogenic pollution, the latter due to the very high density of population in the Nainital valley, are the primary sources of enhanced parameters. The low pH of Nainital Lake water is due to low photosynthesis and enhanced respiration, increasing CO₂ in the water and the consequent enhancement of Ca²⁺ and HCO ₃ ⁻ . The dissolved oxygen in Nainital Lake is less compared to other lakes, indicating anoxic conditions developing at the mud–water interface at depth. The PO ₄ ³⁻ content in Nainital is higher (124 μg/l), showing an increasing trend over time leading to eutrophic conditions. The trace metals (Cu, Co, Zn, Ni, Mn, and Sr) are present in greater amounts in the water of Nainital Lake than in the other three lakes, though Fe and Cr are high in Bhimtal and Fe in Naukuchiyatal. The higher abundance is derived from the leaching of Fe–Mg from metavolcanic and metabasic rocks. Most of the heavy metals (Cr, Ni, Cu, Mn, Fe, Sr, and Zn) significantly enrich the suspended sediments of the lakes compared to the bed sediments which due to their adsorption on finer particles and owing to multiple hydroxide coating and organic content, except for Fe, which is enriched in the bed sediments. The high rate of sedimentation, 11.5 mm/year in Nainital, compared to Bhimtal with 4.70 mm/year, Naukuchiyatal with 3.72 mm/year, and Sattal with 2.99 mm/year, has resulted in shorter residence time, poor sorting of grains, and lesser adsorption of heavy metals, leading consequently, their depletion in the bed sediments of Nainital Lake.     

程裕淇主编《中国地层典》记失

文章列数了《中国地层典》5个方面的重要失误:不是中国地层名称全览性的工具书,急于采用处于争议中的术语,大量地层单位名称的出处因考证不到位而形成张冠李戴,采用的历史优先律不是国际共识,在编撰过程中建立新名称。文章用选出的泰山杂岩、滹沱系、秦岭片岩和仑山石灰岩4个名称为例说明《中国地层典》对其出处的考证不到位,进而论证《中国地层典》的诸多解释可信度低。文章严肃地指出“历史优先律”给中国地层学造成的不良后果:它破坏了地层命名法的标准性,颠倒了中国地层命名史,干扰了中国地层名称的管理。     

华北地块东部晚中生代至新生代岩石圈不均一减薄与改造模式

本文综合运用不同时代幔源包体平衡温压对比、玄武岩地球化学性质对岩石圈厚度的反演以及不同时代岩石圈地幔地球化学性质的对比的方法，把华北地块东部岩石圈的减薄时间限定在晚中生代至新生代之间。减薄的机制可能是华北东部地区晚白垩世以来大陆岩石圈的拉张作用。由于机械性拉薄和热、机械和化学侵蚀作用，岩石圈厚度最终减薄到70km以下。但古老的岩石圈地幔并没有完全因减薄而消失，残留部分受到了来自软流圈物质的强烈改造，使其Sr、Nd同位素组成类似于软流圈，但Os同位素没有受到明显的改变。改造后的岩石圈地幔成为华北地块东部新生代岩石圈地幔的主体。在时空上，岩石圈的减薄具有不均一的性质。     

江西修水西部金矿成矿地质条件分析

通过对地层、岩浆岩、构造及化探异常与成矿关系的分析，认为江西修水西部地区具有寻找中一大型金矿床的潜力。     

地质遗迹旅游的可持续发展

从介绍地质遗迹及地质遗迹旅游的概念入手，着重就新时期地质遗迹旅游可持续发展的问题，提出了两种思路和相应的策略。     

“青藏高原南部空白区基础地质调查与研究”计划项目新成果、新进展

通过2 0 0 4年度各相关图幅的大力工作,在基础地质、矿产和资源等方面取得了大量实际材料,综合研究区域构造地层格架、青藏高原地质图和青藏高原南部火山岩及其地球动力学意义等,取得重要进展和新认识,在矿产资源、旅游和人文景观等方面也取得重要阶段性成果。     

西藏自治区乃东县劣布铜矿综合地质特征

文章介绍区域地质背景、矿区地物化特征，对成矿时代、流体包裹体特征进行初步研究，并指出找矿远景，希望对矿区的矿产勘查具有借鉴和指导意义。     

液体高膨胀材料充填堵漏试验应用

介绍了钻探施工中，利用膨胀材料充填、堵漏的新工艺，其具有经济、高效、安全的特点。