Trace element geochemistry of the Mt Vulture carbonatites,southern Italy

The Mt Vulture carbonatites are the only carbonatite occurrence in the southern Apennines. We present new trace element data for these rocks in order to evaluate the factors influencing rare earth element (REE) and other trace element fractionations and their REE grade. This study focuses on massive hyalo-alvikites from two lava flows and one dike, which have different relative abundances of silicate and carbonate (i.e. Si/Ca). These differences are also evident from CaO/(CaO + MgO + FeO(T) + MnO) and Sr/Ba ratios. The REE grade of the Mt Vulture carbonatites is very similar to that of the global average for calcio-carbonatites. R-mode factor analysis shows that most of the trace element variance reflects the relative roles of carbonate and silicate minerals in influencing trace element distributions. Silicates largely control heavy rare earth element (HREE), transition metal, Zr, and Th abundances, whereas carbonate minerals control light rare earth element (LREE), Ba, and Pb abundances. In addition, apatite influences LREE concentrations. Increasing silica contents are accompanied by decreases in (La/Yb)N and (La/Sm)N ratios and less marked LREE enrichment. In contrast, higher carbonate contents are associated with increases in (La/Yb)N and (La/Sm)N. The Si/Ca ratio has little influence on Eu anomalies and middle rare earth element (MREE) to HREE fractionations. Apatite has a negligible effect on inter-REE fractionations amongst the carbonatites.     

页岩气藏缝网压裂裂缝间距优化研究

页岩气藏一般具有低孔隙、低渗透等特征,对其实施缝网压裂是高效开发页岩气的最佳途径。采用位移不连续法建立线弹性二维均质地层诱导应力场分布数学模型,通过水平应力差异系数对顺序压裂和交替压裂的裂缝间距进行优化研究。结果表明,水平应力差异系数受到裂缝净压力、裂缝缝长、原地应力场等因素的影响;裂缝净压力越大、缝长越长,水平应力差异系数越小;随着与裂缝距离的增加,水平应力差异系数呈现先减小后增加的趋势,因此,存在后续裂缝形成复杂网络的最佳裂缝间距;顺序压裂裂缝间距不宜过大,且后续压裂裂缝间距应适当减小;交替压裂裂缝间距最优时,缝间水平应力差异系数最小,对中间裂缝形成缝网最有利。     

Decline and recovery of the Aptian carbonate factory in the southern Apennine carbonate shelves (southern Italy): Climatic/oceanographic vs. local tectonic controls

In interpreting the inception and demise of different carbonate depositional systems, climatic-oceanographic variations together with sea-level oscillations are commonly considered key elements. However, local tectonic controls cannot be ruled out. In attempts to discriminate among the main factors controlling the evolution of the southern Apennine mid-Cretaceous carbonate system, detailed facies analyses have been performed on Aptian–Albian carbonate successions in the Matese Group (southern Apennines). Since the mid Aptian, the analysed successions testify to a tectonically-driven topography, replacing the previous large tropical shallow-water domain with subdomains characterised by diversified sedimentological trends. Nevertheless, around the middle part of the Aptian, the studied successions register palaeoecological signals that cannot be linked exclusively with tectonic disturbance because of the coeval appearance of analogous signals at a global scale, including a significant change in biological assemblages and an outbreak of organisms indicative of stressful conditions in the water mass.Upper Bedoulian strata clearly record open marine settings characterised by a significant richness of the benthic communities. The biota included rudists, gastropods and echinoids plus many different benthic foraminifers and green algae. Rudists considered to be typically “tropical” forms (the caprinid Offneria nicolinae (Mainelli) and Offneria murgensis Masse, the requieniid Lovetchenia Masse and the monopleurid Agriopleura Kühn) characterise thick subtidally deposited strata in which large coral colonies and mollusc shells contributed to occasional storm-related skeletal concentrations.The analysed Gargasian strata show impoverished biota: caprinids totally disappear, both as in situ and storm-related layer components, and hermatypic corals are drastically reduced. Muddy lithofacies prevail in intertidal metric cycles in which cyanobacterial consortia, both in the form of dense laminae and coalescent oncoids, orbitolinids and small gastropods (cerithiids) suggest restricted, nutrient-rich water. Large oncoids of Bacinella irregularis/Lithocodium aggregatum and mollusc (mostly chondrodontids and gastropods) shell fragments significantly contribute to storm-related coarse skeletal intercalations, in which oligotrophic condition-adapted forms (e.g., hermatypic corals) are reduced or absent. This pattern suggests generalised conditions of stress in the water mass and in more marginal open areas.During the mid-Aptian interval, characterised by the flourishing of assemblages adapted to mesotrophic–eutrophic conditions, the southern Apennines shallow-water domain shows a progressive reduction of the previous mainly aragonite-dominated chlorozoan assemblages and an increase of calcite-dominated skeletal components, including rudists with thickened calcitic outer shell layers. Cyanobacteria and polychaetes characteristically marked the first phases of recovery in the shallow-water domains, rapidly evolving into more complex and differentiated assemblages. The outbreak of nerineid and acteonid gastropods seems to be related to a flourishing of cyanobacterial mats and related microphytae and also to the presence of polychaetes tubes (Thartarella cocumeriformis (Wahlman)). Moreover, the grazing activity of the nerineids favoured the flourishing of oyster-like bivalves. Among the rudists, the persistence and radiation of species adapted to a wide range of temperatures, such as Requieniidae and Monopleuridae as well as the first elevator Radiolitidae suggests some kind of oceanographic change (e.g., seawater chemistry and/or temperature).On the basis of the features described above, we propose the existence of a complex environmental scenario in which cooler conditions, presumably coupled with meso/eutrophic and locally oligophotic conditions, related to climatic/oceanographic global changes, cooperated in modifying the carbonate factory characterisation in a tectonically controlled setting.     

Carbonatites in a subduction system: The Pleistocene alvikites from Mt. Vulture (southern Italy)

We report here, for the first time, on the new finding of extrusive calciocarbonatite (alvikite) rocks from the Pleistocene Mt. Vulture volcano (southern Italy). These volcanic rocks, which represent an outstanding occurrence in the wider scenario of the Italian potassic magmatism, form lavas, pyroclastic deposits, and feeder dikes exposed on the northern slope of the volcano. The petrography, mineralogy and whole-rock chemistry attest the genuine carbonatitic nature of these rocks, that are characterized by high to very high contents of Sr, Ba, U, LREE, Nb, P, F, Th, high Nb/Ta and LREE/HREE ratios, and low contents of Ti, Zr, K, Rb, Na and Cs. The O–C isotope compositions are close to the “primary igneous carbonatite” field and, thus, are compatible with an ultimate mantle origin for these rocks. The Sr–Nd–Pb–B isotope compositions, measured both in the alvikites and in the silicate volcanic rocks, indicate a close genetic relationship between the alvikites and the associated melilitite/nephelinite rocks. Furthermore, these latter products are geochemically distinct from the main foiditic-phonolitic association of Mt. Vulture. We propose a petrogenetic/geodynamic interpretation which has important implications for understanding the relationships between carbonatites and orogenic activity. In particular, we propose that the studied alvikites are generated through liquid unmixing at crustal levels, starting from nephelinitic or melilititic parent liquids. These latter were produced in a hybrid mantle resulting from the interaction through a vertical slab window, between a metasomatized mantle wedge, moving eastward from the Tyrrhenian/Campanian region, and the local Adriatic mantle. The occurrence of carbonatite rocks at Mt. Vulture, that lies on the leading edge of the Southern Apennines accretionary prism, is taken as an evidence for the carbonatation of the mantle sources of this volcano. We speculate that mantle carbonatation is related to the introduction of sedimentary carbon from the Adriatic lithosphere during Tertiary subduction.     

Identification and comparison of perennial yield estimation models using Mt. Amiata Aquifer (southern Tuscany,Italy) as an example

With the principal aim of identifying and comparing suitable evaluation and forecasting models of perennial yield, detailed hydrogeological research was conducted on the cold phreatic aquifer located in the volcanites of Mount Amiata, southern Tuscany's most important water reservoir. The study was based on spring discharge, precipitation, and temperature data. It permitted the identification of the following models: (1) ratios between discharge values measured at the springs, (2) depletion urve analysis of the springs, (3) multiple regression with climatic data, and (4) water balance, coefficients of potential infiltration and runoff coefficients derived on a physiographic basis. Analysis of the results obtained using these models shows their excellent ability to forecast in the medium and long term; for short-term (yearly) forecasts, highly satisfactory results have been obtained for most of the methods used. With regard to Mt. Amiata's average perennial yield, it is estimated at 55×10⁶ m³/yr (the maximum deviation among the various evaluations performed varies from 4 to 8 percent), and it presents a decreasing trend, which is proportional to the reduction of local precipitation.     

塔河岩溶型碳酸盐岩缝洞系统流体动态连通性研究

塔里木盆地塔河油田下奥陶统碳酸盐岩储集体属于表生岩溶作用形成的喀斯特缝洞系统。其储集体孔隙空间类型主要为与原始组构无关的连通孔洞,其孔隙系统由岩溶洞穴、溶蚀裂缝和溶蚀孔三大类型的储集空间复合而成。油田开发实践证实,油藏呈现出多压力系统、差异连通的特征。文中针对缝洞型碳酸盐岩连通缝洞孔隙系统的特征,分析了区别于分散型碳酸盐岩储集体的特征。基于油藏的孔洞系统复杂的特点,说明利用各类动态资料对油藏储层缝洞体研究十分重要。通过动态研究方法,推测喀斯特缝洞系统中的连通体--“缝洞单元”。笔者提出了利用动态信息分析油藏之间缝洞连通性的研究思路和方法:（1）同一缝洞单元内,单井地层压力趋势下降相似;（2）井间干扰系统测试是较直接的连通确定方法;（3）开发井生产异常,导致同一缝洞单元相邻井出现相应动态变化;（4）注水井的示踪剂注入,检测邻近井检测示踪剂的含量、受效时间等,判断井间的连通级别;（5）不通缝洞单元的流体组分、密度和粘度等存在差异。结合塔河油田实际资料,共划分了42个缝洞单元,认为缝洞储集体的分布与岩溶古地貌、古水系和断裂带有一定的吻合性。     

Source and mobility of minor and trace elements in a volcanic aquifer system: Mt. Vulture (southern Italy)

In this paper we provide a geochemical investigation on 34 groundwater samples in the Mt. Vulture volcanic aquifer representing one of the most important groundwater resources of the southern Italy pumped for drinking and irrigation supply. The present study includes the first data on the abundance and mobility of minor and trace elements and the thermodynamic considerations on water–rock interaction processes in order to evaluate the conditions of alkali basalt weathering by waters enriched in magma-derived CO₂. The results highlight the occurrence of two hydrofacies: bicarbonate alkaline-earth and alkaline waters deriving from low-temperature leaching of volcanic rocks of Mt. Vulture, and bicarbonate-sulfate-alkaline waters (high-salinity waters) related to prolonged water circulation in alkali and feldspathoids-rich pyroclastic layers interbedded with clay deposits. The Al-normalized relative mobility (RM) of metals in Vulture's aquifer varies over a wide range (10^− 1 < RM < 10⁴), confirming that the basalt weathering is not a congruent and isochemical process. Chemical equilibrium studies show that the bicarbonate alkaline-earth and alkaline waters, having a short interaction with silicate minerals, plot very close to the kaolinite–smectite stability boundary, whereas the high-salinity waters fall in the stability field of smectite and muscovite because of prolonged interaction with alkali and feldspathoids-rich pyroclastic layers. Overall, for the bicarbonate alkaline-earth and alkaline waters, the release of toxic metals in solutions is related to the spatial variation of host-rock geochemistry, the high-salinity waters, collected near urban areas, show values higher than legal limits for Ni and As, likely as a consequence of anthropogenic contribution.     

Trace elements and REE fractionation in subsoils developed on sedimentary and volcanic rocks: case study of the Mt. Vulture area,southern Italy

There is an increasing interest in the distribution of rare earth elements (REEs) within soils, primarily as these elements can be used to identify pedogenetic processes and because soils may be future sources for REE extraction, despite much attention should be paid to the protection and preservation of present soils. Here, we evaluate the processes that control the distribution of REEs in subsoil horizons developed over differing lithologies in an area of low anthropogenic contamination, allowing estimates of the importance of source rocks and weathering. Specifically, this study presents new data on the distribution of REEs and other trace elements, including transition and high-field-strength elements, in subsoils developed on both Quaternary silica-undersaturated volcanic rocks and Pliocene siliciclastic sedimentary rocks within the Mt. Vulture area of the southern Apennines in Italy. The subsoils in the Mt. Vulture area formed during moderate weathering (as classified using the chemical index of alteration) and contain an assemblage of secondary minerals that is dominated by trioctahedral illite with minor vermiculite. The REEs, high-field-strength elements, and transition metals have higher abundances in subsoils that developed from volcanic rocks, and pedogenesis caused the Mt. Vulture subsoils to have REE concentrations that are an order of magnitude higher than typical values for the upper continental crust. This result indicates that the distribution of REEs in soils is a valuable tool for mineral exploration. A statistical analysis of inter-elemental relationships indicates that REEs are concentrated in clay-rich fractions that also contain significant amounts of low-solubility elements such as Zr and Th, regardless of the parent rock. This suggests that low-solubility refractory minerals, such as zircon, play a significant role in controlling the distribution of REEs in soils. The values of (La/Yb)_N and (Gd/Yb)_N fractionation indices are dependent on the intensity of pedogenesis; soils in the study area have values that are higher than typical upper continental crust ratios, suggesting that soils, especially those that formed during interaction with near neutral to acidic organic-rich surface waters, may represent an important source of both light REEs and medium REEs (MREEs). In comparison, MREE/heavy REE fractionation in soils that form during moderate weathering may be affected by variations in parent rock lithologies, primarily as MREE-hosting minerals, such as pyroxenes, may control (La/Sm)_N index values. Eu anomalies are thought to be the most effective provenance index for sediments, although the anomalies within the soils studied here are not related to the alteration of primary minerals, including feldspars, to clay phases. In some cases, Eu/Eu* values may have a weak correlation with elements hosted by heavy minerals, such as Zr; this indicates that the influence of mechanical sorting of clastic particles during sedimentary transport on the Eu/Eu* values of siliciclastic sediments needs to be considered carefully.     

Use of molecular approaches in hydrogeological studies: the case of carbonate aquifers in southern Italy

Waterborne pathogens represent a significant health risk in both developed and developing countries with sensitive sub-populations including children, the elderly, neonates, and immune-compromised people, who are particularly susceptible to enteric infections. Annually, approximately 1.8 billion people utilize a faecally contaminated water source, and waterborne diseases are resulting in up to 2.1 million human mortalities globally. Although groundwater has traditionally been considered less susceptible to contamination by enteric pathogens than surface water due to natural attenuation by overlying strata, the degree of microbial removal attributable to soils and aquifers can vary significantly depending on several factors. Thus, accurate assessment of the variable presence and concentration of microbial contaminants, and the relative importance of potentially causative factors affecting contaminant ingress, is critical in order to develop effective source (well) and resource (aquifer) protection strategies. “Traditional” and molecular microbiological study designs, when coupled with hydrogeological, hydrochemical, isotopic, and geophysical methods, have proven useful for analysis of numerous aspects of subsurface microbial dynamics. Accordingly, this overview paper presents the principal microbial techniques currently being employed (1) to predict and identify sources of faecal contamination in groundwater, (2) to elucidate the dynamics of contaminant migration, and (3) to refine knowledge about the hydrogeological characteristics and behaviours of aquifer systems affected by microbial contamination with an emphasis on carbonate aquifers, which represent an important global water supply. Previous investigations carried out in carbonate aquifers in southern Italy are discussed.     

Magma-derived gas influx and water-rock interactions in the volcanic aquifer of Mt. Vesuvius, Italy

We report in this paper a systematic investigation of the chemical and isotopic composition of groundwaters flowing in the volcanic aquifer of Mt. Vesuvius during its current phase of dormancy, including the first data on dissolved helium isotope composition and tritium content. The relevant results on dissolved He and C presented in this paper reveal that an extensive interaction between rising magmatic volatiles and groundwaters currently takes place at Vesuvius.Vesuvius groundwaters are dilute (mean TDS ∼ 2800 mg/L) hypothermal fluids ( mean T = 17.7°C) with a prevalent alkaline-bicarbonate composition. Calcium-bicarbonate groundwaters normally occur on the surrounding Campanian Plain, likely recharged from the Apennines. δD and δ¹⁸O data evidence an essentially meteoric origin of Vesuvius groundwaters, the contribution from either Tyrrhenian seawater or ¹⁸O-enriched thermal water appearing to be small or negligible. However, the dissolution of CO₂-rich gases at depth promotes acid alteration and isochemical leaching of the permeable volcanic rocks, which explains the generally low pH and high total carbon content of waters. Attainment of chemical equilibrium between the rock and the weathering solutions is prevented by commonly low temperature (10 to 28°C) and acid-reducing conditions.The chemical and isotope (C and He) composition of dissolved gases highlights the magmatic origin of the gas phase feeding the aquifer. We show that although the pristine magmatic composition may vary upon gas ascent because of either dilution by a soil-atmospheric component or fractionation processes during interaction with the aquifer, both ¹³C/¹²C and ³He/⁴He measurements indicate the contribution of a magmatic component with a δ¹³C ∼ 0‰ and R/R_a of ∼2.7, which is consistent with data from Vesuvius fumaroles and phenocryst melt inclusions in olivine phenocrysts.A main control of tectonics on gas ascent is revealed by data presented in this paper. For example, two areas of high CO₂ release and enhanced rock leaching are recognized on the western (Torre del Greco) and southwestern (Torre Annunziata-Pompeii) flanks of Vesuvius, where important NE-SW and NW-SE tectonic structures are recognized. In contrast, waters flowing through the northern sector of the volcano are generally colder, less saline, and CO₂ depleted, despite in some cases containing significant concentrations of magma-derived helium. The remarkable differences among the various sectors of the volcano are reconciled in a geochemical interpretative model, which is consistent with recent structural and geophysical evidences on the structure of Somma-Vesuvius volcanic complex.     

Platform margin collapses and sequence stratigraphic organization of carbonate slopes: Cretaceous–Eocene,Gargano Promontory,southern Italy

We describe the sequence stratigraphic organization and the associated sedimentological characteristics of Cretaceous to Eocene slope and base-of-slope carbonate successions. The study area is located in the Gargano Promontory which belongs to the stable foreland of southern Italy. The succession consists of three superimposed depositional sequences separated by major unconformities. The upper two sequences are clear examples of sequence stratigraphic organization; in fact, they both start with huge megabreccia wedges (LST) followed upward by thin pelagic units (TST) and a thick package of calciturbidites and debrites that alternate with pelagic mudstone (HST). The Cretaceous highstand systems tract is clearly arranged in a number of coarsening-upward cycles while the Eocene one which also comprises a toplap shallow water unit, is not. The Gargano stratigraphic palimpsest and the entire margin of the Apulia Platform show remarkable similarities with present-day carbonate platform margins and slopes where irregular, convex-bankward embayments suggest large-scale failures. It is clear that classic sequence stratigraphic organization can result from simple platform dismantling, having no or little time relation with global sea-level fluctuations. In fact, as the margin failure (LST) interrupts the carbonate production, a period of starvation (TST) along the entire slope and base-of-slope follows necessarily. Finally, when the margin once again becomes active and productive, sediment exportation starts again and the system begins to prograde (HST).     

Trace element and isotopic variations from Mt. Vulture to Campanian volcanoes: constraints for slab detachment and mantle inflow beneath southern Italy

New Sr–Nd–Pb isotopic ratios and trace element data for volcanic mafic rocks outcropping along a E–W transect in southern Italy, from Mt. Vulture to Neapolitan volcanoes, are reported. The variation of LILE/HFSE, HFSE/HFSE and radiogenic isotopes along this transect indicates that all of these volcanoes contain both intra-plate and subduction-related signatures, with the former decreasing from Mt. Vulture to Campanian volcanoes. New data are also reported for the Paleocene alkaline rocks from Pietre Nere (Apulia foreland), which show isotopic ratios mostly overlapping the values for Mediterranean intra-plate volcanoes as well as the Eocene–Oligocene alkaline mafic lavas from the northern Adria plate. Pietre Nere provides evidence for an OIB mantle composition of FOZO-type, free of subduction influences, that is present beneath the Adria plate (Africa) before its collision with Europe. After this collision, and formation of the southern Apennines, westward inflow of mantle from the Adria plate to the Campanian area occurred, as a consequence of slab break off. Interaction of subduction components with inflowing Adria mantle generated hybrid sources beneath the Vulture–Campania area, which can explain the compositional features of both Mt. Vulture and the Campanian mafic rocks. Therefore, mafic magmas from these volcanoes represent variable degrees of mixing between different mantle components.     

巴楚地区碳酸盐岩中深成侵入岩特征及其对储层发育的影响

为了深入探讨深部岩浆活动对碳酸盐岩储层发育的影响,文中通过显微鉴定、地球化学分析以及流体包裹体测试,对巴楚地区和3井奥陶纪钻遇的火成岩进行了详细研究。和3井碳酸盐岩中的火成岩是紫苏辉长岩,为深成侵入岩体,辉长岩的w(SiO2)介于44.89%～45.39%,w(K2O+Na2O)为4.04%～4.67%,w(Na2O)/w(K2O)为2.16～4.23,属钠质碱性系列,形成于板内构造环境。微量元素分配模式以Ba富集Sr亏损为特征。∑REE介于163.43×10-6～215.99×10-6,LREE/HREE介于5.14～5.58,LaN/YbN介于5.192～5.980,δEu介于0.926～1.002,稀土配分模式属轻稀土富集型,通过对和3井碳酸盐岩孔隙度、渗透率以及其中流体包裹体的分析,孔隙度和渗透率的变化与辉长岩的分布有关,流体包裹体温度介于62～161℃,和3井碳酸盐岩受到过热事件的影响,辉长岩的侵入改善了和3井碳酸盐岩的储层物性。     

评价页岩压裂形成缝网能力的新方法

页岩储层的“体积压裂”,使美国页岩气产业取得巨大成功,有效评价压裂裂缝网络形成的难易程度,是压裂开采的首要目标,目前国内外尚未发现有效的评价方法,为此开发了一种新的测试方法。针对10种岩芯,测试岩石力学参数,并对比分析常用的3种页岩脆性评价方法。采用压后裂隙结构面迹长分布的分维值和面密度对裂缝进行定量表征,并对压后崩落碎块进行对比分析。通过实验认为,杨氏模量和泊松比判别法与塑性系数判别法用于评价岩石脆性,精确度更高;脆性岩石通常表现为高杨氏模量或（和）低泊松比的特征,与单轴抗压强度、抗张强度和压入硬度没有对应关系;压裂裂缝的分布具有统计意义上的分形特征,分维可用于定量评价压后裂缝网络复杂度;硬度越高,压后裂缝密度越小;脆性越强,压后裂缝密度越大。新方法是岩石脆性、硬度和天然裂缝系统（和沉积层理）特征的综合体现,用于评价页岩压后形成缝网的能力,不仅直观可靠,而且简单有效,有利于现场推广应用,对于今后页岩气或致密砂岩气开发的理论研究和现场应用具有一定的指导意义。     

塔北哈拉哈塘奥陶系碳酸盐岩岩溶储层发育特征及主要岩溶期次

位于塔北隆起中部的哈拉哈塘地区,具有良好的油气成藏条件,是近期塔北油气勘探的突破新区,勘探的主要目标是奥陶系碳酸盐岩岩溶储层。本文通过对区域沉积、构造演化背景的分析,利用钻井、岩芯、地震等资料,对本区岩溶型储层的沉积和成岩作用特征进行了研究,探讨了储层发育的主要岩溶阶段、岩溶模式及主控因素。结果表明哈拉哈塘地区奥陶系碳酸盐岩岩溶储层的主体在一间房组和鹰山组一段,储集空间主要为近层状分布的溶蚀孔洞/洞穴和裂缝,岩溶储层的发育主要受控于一间房组沉积末期的准同生期岩溶和志留系沉积之前的表生期(潜山+顺层)岩溶。前一期岩溶具有区域分布较均匀、规模较小的特点;后一期岩溶在前期岩溶的基础上发育,并根据古地貌的差异在平面上分为4个区:北部Ⅰ区一间房组直接暴露,发育古潜山岩溶;Ⅱ区一间房组之上覆盖了厚度不等的吐木休克组、良里塔格组和桑塔木组,岩溶主要受控于河流和断裂的下切及由北部Ⅰ区地表水补给的地下水顺层岩溶;南部的Ⅲ区和Ⅳ区发育顺层及沿断裂的岩溶和淡水与南部海水的混合水岩溶。在以上两期主要岩溶作用的影响下,哈拉哈塘一间房组和鹰山组一段地层发育近层状岩溶洞穴、孔洞、角砾孔和裂缝,形态多变,具有极强的非均质性。     

Petrogenesis and evolution of Mt. Vulture alkaline volcanism (Southern Italy)

Summary The Late Pleistocene Mt. Vulture strato-volcano developed at the intersection of NE-SW and NW-SE lithospheric fault systems, on the easternmost border of the Apennine compressional front overthrust onto the Apulian foreland. The initial phase of the volcanic activity is represented by pyroclastic deposits, including lava blocks, and subordinate eccentric domes, mostly phonolitic in composition. The later stages of activity formed the bulk of the strato-volcano (pyroclastic products and subordinate lavas), mostly tephritic in composition, with minor intercalations of basanite, mela-foidite and melilitite lavas and dikes. Variations in rock and mineral composition suggest that the volumetrically predominant basanite-tephrite (foidite)-phonotephrite-phonolite series can be accounted for by fractional crystallization processes starting from basanitic parental magmas, in agreement with the remarkably constant ⁸⁷Sr/⁸⁶Sr isotopes (0.70586–0.70581). Mass-balance calculations indicate that the variably differentiated magmas may have been produced by removal of wehrlite, clinopyroxenite and syenite cumulates, some of which are occasionally found as cognate xenoliths in the volcanics. Fractionation processes probably developed in multiple-zoned magma chambers, at depths of 3–5 km, corresponding to the tectonic discontinuity between the allochthonous Apennine formations and the underlying Apulian platform. Highly differentiated phonolitic magmas capping the magma chambers and their conduits thus appear to have fed the initial volcanic activity, whereas dominantly tephritic products were erupted in later stages. The least evolved mafic magmas, namely basanites, mela-foidites and melilitites, are characterized by diverse Na/K ratios and critical SiO₂-undersaturation, which indicate their derivation as independent melts generated from distinct, heterogeneously enriched mantle sources and by variable partial melting degrees. Primitive mantle-normalized incompatible element patterns of Vulture mafic lavas invariably share analogies with both orogenic subduction-related magmas (high Low Field Strength Elements/High Field Strength Elements ratios, K, Rb and Th contents and marked Ti and Nb negative anomalies) and alkaline lavas from within-plate and rift settings (high Light Rare Earth Elements, P, Zr, Nb and Na). These geochemical features may be accounted for by magma generation from deep lithospheric mantle sources, enriched in Na-alkali silicate/carbonatite anorogenic components, subsequently affected by orogenic subduction-related K-metasomatism, analogous to that which modified magma sources of the Roman Magmatic Province along the internal Apennine Chain. Received April 12, 2000; revised version accepted June 7, 2001     

Exploratory seismic site response surveys in a complex geologic area: a case study from Mt. Etna volcano (southern Italy)

A preliminary study targeting to evaluate the local seismic response was performed in the eastern flank of Mt. Etna (southern Italy) using ambient noise measurements. The obtained spectral ratios were subdivided through cluster analysis into different classes of fundamental frequency permitting to draw an iso-frequency contour map. The analysis set into evidence the extreme heterogeneity of lava sequences, which makes difficult to identify a single seismic bedrock formation. Another important outcome, concerning the local seismic effects in terms of frequency and azimuth, is the important role played by the fracture fields associated with the main structural systems of the area. The existence of two zones with strong directional effects striking WNW–ESE and NW–SE, nearly orthogonal to the orientation of the main fracture fields, corroborate such hypothesis.

     

Exploratory seismic site response surveys in a complex geologic area: a case study from Mt. Etna volcano (southern Italy)

A preliminary study targeting to evaluate the local seismic response was performed in the eastern flank of Mt. Etna (southern Italy) using ambient noise measurements. The obtained spectral ratios were subdivided through cluster analysis into different classes of fundamental frequency permitting to draw an iso-frequency contour map. The analysis set into evidence the extreme heterogeneity of lava sequences, which makes difficult to identify a single seismic bedrock formation. Another important outcome, concerning the local seismic effects in terms of frequency and azimuth, is the important role played by the fracture fields associated with the main structural systems of the area. The existence of two zones with strong directional effects striking WNW–ESE and NW–SE, nearly orthogonal to the orientation of the main fracture fields, corroborate such hypothesis.     

容城地热田雾迷山组碳酸盐岩热储层裂缝主控因素及成因机制

容城地热田雾迷山组是华北地区典型的低孔隙度碳酸盐岩热储层,也是地热流体勘探的主要目标。裂缝对研究区地热流体的富集和产能有重要影响。本文通过对研究区岩心、薄片和成像测井等资料的分析,确定了裂缝的发育特征、控制因素和形成期次。结果表明容城地热田雾迷山组碳酸盐岩热储层裂缝多为未充填的高角度斜交缝,11.8%的裂缝被方解石和石英脉充填。裂缝开度主要集中在0~2 mm,靠近断裂的D19井开度最大（均值为3.65 mm）,孔隙度也最大（均值为0.752 3%）,裂缝孔隙度随开度的增大线性增加。裂缝在断裂附近或者构造应力场较大的区域更为发育,受构造作用影响最明显。在同一构造环境和应力场下,岩性是控制研究区裂缝发育的主导因素。容城地热田雾迷山组碳酸盐岩热储层裂缝大致分为3组,印支期形成的NNE-SSW与NW-SE向“X”型共轭剪裂缝,燕山晚期形成的NEE-SWW向剪裂缝,以及喜马拉雅期形成的近E-W向张裂缝。

     

The Early Cretaceous drowning unconformities of the Apulia carbonate platform (Gargano Promontory, southern Italy): local fingerprints of global palaeoceanographic events.

Drowning successions which cap carbonate platforms and flanks bear palaeoenvironmental information which is useful for genetic stratigraphy; they constitute predictive key-markers in regional to global correlations. An Early Cretaceous platform-to-basin transition has been investigated in Apulia (southern Italy) and two drowning unconformities, dated as early Valanginian and late early Aptian, have been documented. They occur at the base of thick pelagic tongues wedging toward the platform and mark the base of two depositional sequences showing distinct transgressive–regressive cycles. Timing of drowning processes, based on biostratigraphy and dynamic stratigraphy, allows the correlation of unconformities with global-scale palae- oceanographic events marked, among others, by positive spikes of well-established δ¹³C curves. Drowning signatures in the Apulia carbonates fit the stratigraphic, palaeoecological and possibly geochemical evidence found in global records at the same stratigraphic levels. Moreover, it is proposed that the observed drowning events were caused by palaeoceanographic crises affecting factory productivity.