麻粒岩的形成及其对大陆地壳演化的贡献

麻粒岩是地球中最重要的岩石类型之一，它的形成主要受地热条件的控制。麻粒岩的形成可以与大陆碰撞、大陆拉张以及大陆弧模式相联系。麻粒岩在某种程度上，还是下地壳的同义词。通过麻粒岩地体地及火山岩中麻粒岩捕虏体的研究，使人们对地球深部的物质组成和结构有了直接的了解。麻粒岩在陆壳的形成和演化中具有举足轻重的地位。陆核说、陆壳垂直增生或横向增生说，都以麻粒岩作为重要的岩石学依据。     

塔里木盆地北部深层风化壳储层的形成与分布

塔北地区碳酸盐岩风化壳岩溶储层发育,储层具有质量好、分布面积广、埋藏深等特点,并已在轮南、塔河和英买力等地区发现数个亿吨级规模以上的大型油气田.本文通过对塔北地区200多口重要井的钻井、录井、测井、试油等第一手资料的系统分析,结合大量的分析化验资料与岩心及镜下观察,精细研究了风化壳储层的成因特点、分布规律与评价预测等.研究认为,寒武系发育白云岩型风化壳储层,以孔洞型储层为主;奥陶系主要为灰岩型风化壳储层,储层的基质孔隙度较低,溶蚀孔洞、溶蚀扩大缝和构造缝是其主要的储集空间,储层以洞穴型储层和网状裂缝型储层为主.台地相发育的纯净碳酸盐岩、海西期构造运动导致地层的长期暴露剥蚀、断裂裂隙作用和晚期大气淡水淋溶等是控制塔北风化壳储层形成的的重要因素;并发现塔北地区风化侵蚀能够作用到的深度主要在140m以内.虽然风化壳储层基质孔隙较差,但是储层物性受埋深影响不大;在有利的古岩溶地貌和断裂发育区,即使在更大的埋藏深度,也可能发育规模较大、性能较好的储集体.     

Mineral deposit formation in Phanerozoic sedimentary basins of north-east Africa: the contribution of weathering

The intra- and epicontinental basins in north-east Africa (Egypt, Sudan) bear ample evidence of weathering processes repeatedly having contributed to the formation of mineral deposits throughout the Phanerozoic.The relict primary weathering mantle of Pan-African basement rocks consists of kaolinitic saprolite, laterite (in places bauxitic) and iron oxide crust. On the continent, the reaccumulation of eroded weathering-derived clay minerals (mainly kaolinite) occurred predominantly in fluvio-lacustrine environments, and floodplain and coastal plain deposits. Iron oxides, delivered from ferricretes, accumulated as oolitic ironstones in continental and marine sediments. Elements leached from weathering profiles accumulated in continental basins forming silcrete and alunite or in the marine environment contributing to the formation of attapulgite/saprolite and phosphorites.The Early Paleozoic Tawiga bauxitic laterite of northern Sudan gives a unique testimony of high latitude lateritic weathering under global greenhouse conditions. It formed in close spatial and temporal vicinity to the Late Ordovician glaciation in north Africa. The record of weathering products is essentially complete for the Late Cretaceous/Early Tertiary. From the continental sources in the south to the marine sinks in the north, an almost complete line of lateritic and laterite-derived deposits of bauxitic kaolin, kaolin, iron oxides and phosphates is well documented.     

化学蚀变指数(CIA)反映湿润亚热带风化壳型土壤风化强度的适用性探讨

风化壳型土壤剖面是记录"地球关键带"长期信息的重要载体。然而,目前对大范围的风化壳-土壤原位风化过程研究较少,化学风化指标能否指示其风化强度存在争议。本研究以广东省湿润亚热带气候主导区的6个花岗岩风化壳型土壤剖面为研究对象,结合土壤的常量元素地球化学和粒度数据来描述剖面的化学风化和物理变化,探讨CIA反映湿润亚热带风化壳型土壤风化强度的适用性。结果显示：在温带地区迁移作用微弱的惰性元素Fe、Al、Ti在亚热带风化剖面上层含量相对中下层较低;随着地区降水量的增加,CIA从剖面顶部到底部数值呈增加趋势,这与风化壳剖面自上而下风化强度减弱的理想风化趋势相悖;并且发现CIA指标与气候参数,尤其是降水之间存在良好的反相关关系（R2=0.77,P < 0.01,y=-0.0065x+104.01）。通过对该异常现象的探讨,得到以下认识：在湿润亚热带地区,风化壳表层土壤具有复杂的物理、化学变化,尤其是高降水量引起的物理侵蚀使得化学活动性弱的Fe、Al、Ti氧化物、以及粘粒被地表径流带走或者下渗到更深层土壤中,使得表层土壤的CIA值偏低,不能真实反映其化学风化强度。因此,在应用CIA指标反映湿润亚热带高降水地区风化壳土壤剖面的风化强度时应当谨慎。     

Uranium oxidation and probable subaerial weathering of phosphatized limestone from the Pourtales Terrace*

Phosphatized limestones from the Pourtales Terrace, Straits of Florida, have undergone fresh-water diagenesis, as shown by several selective petrologic features such as dissolution of aragonitic skeletal material and preservation and recrystallization of Mg-calcite. This interpretation is supported by the fact that greater than 94% of the uranium in these samples is in the U(VI) oxidation state. On the deeper Pourtales Escarpment, phosphatized limestones show no alteration features indicative of fresh-water diagenesis. The uranium in these samples is a mixture of U(IV) and U(VI) with oxidation-state ratios similar to other sea-floor phosphorites. Our interpretation of these data is that uranium in the terrace samples was oxidized when that area was emergent. The karsted surface of the terrace, therefore, is a result of subaerial exposure of this portion of the Floridan platform. The escarpment samples were never above sea level, and so more closely retain their original uranium oxidation-state ratios.     

Mineralogical and geochemical alteration of low-grade metamorphic black slates due to oxidative weathering

Low-grade metamorphic black slates of Silurian and Lower Devonian ages (from the Thüringisches Schiefergebirge in Germany) were investigated to identify mineralogical and geochemical alterations that occur during the oxidative weathering black slates.The slates exhibit an intense total organic carbon decrease (>90 wt%) due to oxidative weathering. The organic matter in black slate consists mainly of non-pyrolysable material with only minor portions of pyrolysable material. In contrast to the non-pyrolysable organic matter, the concentration of pyrolysable organic matter is not decreased during weathering. Heating experiments have yielded information about a potential protection of pyrolysable organic matter against weathering, which is probably caused by a structural configuration or the intergrowth of organic matter and illite.The slates consist mainly of illite. Iron oxide (goethite) and phosphate encrustations were formed on slate surfaces as a result of oxidative and acid weathering of both iron sulfide and monazite. Kaolinite often occurs as an older encrustation beneath the iron oxide encrustations. Encrustations of iron oxide and phosphate are major sinks for trace elements, released during oxidative weathering.     

塔巴庙地区奥陶系风化壳识别与结构分析

水平洞穴砂砾岩是识别多期次岩溶旋回水平岩溶带的标志,是岩溶旋回连接沉积旋回及周期性海平面变化的纽带,故塔巴庙地区奥陶系水平洞穴岩溶带产出的层位、厚度,以及井深,则是水平岩溶发育状况的体现。这里从地层学、岩石学、矿物学、钻井录井、测井、地球化学等标志识别风化壳,根据三个水平岩溶带特征确定三个水平岩溶带的分布,进而对其进行分析对比。确定出三个水平岩溶带差异性及成因,使保存好的风化壳作为油气水储集的有利场所。     

黔西北玄武岩风化壳稀土地球化学特征

黔西北玄武岩风化壳中的稀土矿是一个分布广泛、稀土含量较高的新类型稀土矿。本文主要通过岩相学、矿物学和地球化学的方法,系统研究了该稀土矿层的岩石组构、矿物组合及地球化学特征,探讨了该地区稀土迁移富集机理。结果显示该风化壳稀土矿层厚度大(单层厚度0.1～0.5 m,总厚度约5～15 m)。矿石中主要矿物为高岭石(60%～80%),次要矿物为蒙脱石(2%～8%)、赤铁矿(5%～20%)。稀土总量较高(144～2288×10-6),具轻稀土富集特征,并且稀土含量高的样品均为高岭石粘土岩。稀土配分模式图中显示明显负铕异常(0.22～0.85),铈异常变化较大(0.86～1.63)。综合分析认为玄武岩风化壳中的稀土元素的富集和高岭石的含量密切相关,稀土元素可能在偏还原的环境中被高岭石颗粒吸附。     

Ground air of the bauxite-bearing lateritic weathering crust (Republic of Guinea)

The ground air of the bauxite deposit in West Africa was tested for its chemical composition. The obtained data provide the first insight into the air effect on the mineralogical-geochemical zoning of the lateritic weathering profile. The air was tested in areas with different geomorphologic features, which allowed us to study the effect of relief and landscape on the ground-air formation.     

Geochemistry of eolian dust and its elemental contribution to Lake Qinghai sediment

Located at the midpoint of the Asian “airborne dust corridor”, Lake Qinghai receives substantial dust annually, which may impact the biogeochemical cycles of the system. In order to determine quantitatively the flux and chemical contributions of dust to Lake Qinghai sediment, dust samples were collected monthly at two sites surrounding the lake from June 2009 to May 2011. The results demonstrate similar chemical compositions of dust samples to the local loess, implying strong representativeness of regional dust. The average dust deposition flux is 265.7 ± 55.0 g/m²/a, constituting 56.6 ± 11.7% of the modern sediment, approximating to previous estimates (∼65%). Contributions of dust-derived elements in the sediment differ substantially, with a minimum of 16.7% for Sr and a maximum of 83.9% for Cu. Among these elements, the contribution of lithophile elements (Na, Al, K, Ti, Mn, Fe and Rb) is close to that of the bulk dust; the contributions of mobile elements (Mg, Ca and Sr) are low, only 16.7% (Sr)–26.1% (Mg), whereas potentially harmful metals (Cu, Zn and Pb) have high contributions (70.3–83.9%). Seasonal variations of elemental inputs indicate that springtime contributions dominate the annual dust fluxes for all elements into the sediment, in agreement with the high dust flux in spring. These observations not only quantify the contribution of dust to the sediment of Lake Qinghai, but also highlight the important role of dust in the accumulation of various elements in the sediment, especially for potentially harmful metals.     

苔藓结皮对碳酸盐岩的风化作用研究进展

岩溶地区碳酸盐岩裸露率高、土壤形成速率缓慢,是世界上石漠化最严重的地区之一。在岩溶石漠化地区,苔藓植物与裸露钙质岩石上的藻类、细菌和真菌共存,形成苔藓结皮。苔藓结皮依赖其独特的形态结构、生理生态和遗传机制在干旱贫瘠的岩石上生长,参与碳酸盐岩的风化、土壤的形成和发育,对岩溶地区退化生态系统的恢复具有不可替代的作用,被誉为“荒漠生态系统工程师”。文章尝试阐明苔藓结皮各组分（微生物、苔藓植物）参与的岩石风化成土过程以及在石漠化治理中的应用,为岩溶区石漠化治理提供理论依据。     

Elastic properties, fabric and seismic anisotropy of amphibolites and their contribution to the lower crust reflectivity

In this paper the elastic properties of amphibolites from the Serie dei Laghi and the Ivrea zone (Southern Alps, N-Italy) were investigated as a function of their mineralogical composition, microfabric and density.Three orthogonal cores were cut parallel and normal to foliation and lineation; from those, bulk and grain density were measured and the interconnected porosity was calculated. Bulk density varies from 2.75 to 3.07 g/cm³ and calculated porosity ranges from 0.02 to 0.88%.The same cores were also used to measure seismic velocity of ultrasonic waves at room temperature and at increasing confining pressure up to 300 MPa. At high pressure the matrix properties are separated from the crack-induced properties. P-wave velocity varies with respect to the direction of propagation: the slowest direction is always normal to foliation and the fastest parallel to the mineral lineation. The mineral lineation is typically defined by the elongation of amphibole crystals, in which the fastest Vp direction is parallel to the c axis, that is also the elongation axis. The Vp ranges between 6.76 and 7.54 km/s in the direction parallel to lineation and between 6.32 and 7.06 km/s in the direction normal to foliation. This defines a Vp anisotropy of up to 14%, whose shape varies from orthorhombic to axially symmetric (either prolate or flattened). It was observed that both Vp and Vp anisotropy increase with the amount of amphibole and decrease with the amount of plagioclase. Moreover, the c axis distribution of amphiboles is responsible of the Vp anisotropy intensity and shape, in agreement with observations from previous studies. The seismic properties calculated with the approach of Mainprice (1990), using the fabric data, the elastic constants and the modal composition, gave results in good agreement with the measurements.Exposed rocks in the Ivrea and Serie dei Laghi zones show that amphibolites are interlayered with metapelites on a scale from 1 to 100 m. Because of the very large acoustic impedance contrast (20.34 ± 1.75 for amphibolites, 17.16 ± 0.4 for metapelites), they represent a very reflective portion in the middle-lower crust.     

河南省钙红土风化壳型铝土矿沉积规律及找矿远景概论

河南省是我国第二产铝大省,采用目前已查明的75个大中型铝土矿床勘查资料和样品测试结果,通过铝土矿成矿物质来源;矿床沉积环境及形成方式;矿床成矿规律等三方面对河南省铝土矿沉积规律进行全面阐述.然后应用所得成果总结了河南省铝土矿的分布规律,运用六个影响铝土矿找矿的因素:①成矿时代找矿;②沉积环境找矿③古地理找矿;④古岛边缘的分布规律;⑤沉积盆地内的喀斯特地貌;⑥构造控矿条件.划出了进一步找矿中的三个大的重点找矿远景区.     

不同前处理方法对北方红色风化壳粒度测试影响的初步探讨

选取中国北方岩溶区红色风化壳为研究对象,首先用浓度为30%的H2O2去除样品中的有机质,然后用4种不同的前处理方法分别进行处理,其中方法A未用盐酸溶液处理,方法B、C、D均用盐酸溶液分解可能存在的残余碳酸盐和次生游离氧化物,以消除其对机械颗粒可能存在的胶结作用,此外方法C的HCl在煮沸的条件下反应,方法 B的HCl在常温条件下进行,方法D则更改了超声波振荡的时间。本文样品采用Beckman公司生产的LS13320 型激光衍射粒度测试仪进行测量。结果表明,样品前处理方法对中国北方红色风化壳粒度分析结果有影响,不同的前处理方法使样品的粒度值最大产生5%左右的变化;从实验的稳定性上考虑,4种方法的平行试验标准偏差最大达到6.78%。在现有的认识条件下,粒度测量结果的可重复性是最基本的要求。本文认为方法C的测量效果要好于其他方法。      

乌干达苏库卢碳酸岩风化壳成矿元素地球化学评价指标

碳酸岩是一种特殊的火成岩,常与多种成因类型的矿床密切相关,故引起国内外学者的广泛关注。笔者以乌干达苏库卢碳酸岩风化壳为研究对象,选取区内典型剖面AB和钻孔ZK14(W),应用剖面地球化学异常和钻孔地球化学异常的方法总结了矿床的成矿规律和成因。笔者提出采用[w(Nb_2O_5)*w(REO)*w(TFe)*1000]/w(P_2O_5)累乘比值作为矿体剥蚀的判别指标(K_1),得出:强风化区K_1500,半、弱风化区500K_1100,碳酸岩原岩K_1100。同时,本文首次尝试为地球化学勘查理论适用于风化壳矿床提供勘查实例。     

The Earth’s tungsten budget during mantle melting and crust formation

During silicate melting on Earth, W is one of the most incompatible trace elements, similar to Th, Ba or U. As W is also moderately siderophile during metal segregation, ratios of W and the lithophile Th and U in silicate rocks have therefore been used to constrain the W abundance of the Earth’s mantle and the Hf-W age of core formation. This study presents high-precision W concentration data obtained by isotope dilution for samples covering important silicate reservoirs on Earth. The data reveal significant fractionations of W from other highly incompatible lithophile elements such as Th, U, and Ta. Many arc lavas exhibit a selective enrichment of W relative to Th, U, and Nb-Ta, reflecting W enrichment in the sub-arc mantle via fluid-like components derived from subducting plates. In contrast, during enrichment by melt-like subduction components, W is generally slightly depleted relative to Th and U, but is still enriched relative to Ta. Hence, all arc rocks and the continental crust exhibit uniformly low Ta/W (ca. 1), whereas W/Th and W/U may show opposite fractionation trends, depending on the role of fluid- and melt-like subduction components. Further high-precision W data for OIBs and MORBs reveal a systematic depletion of W in both rock types relative to other HFSE, resulting in high Ta/W that are complementary to the low Ta/W observed in arc rocks and the continental crust. Similar to previous interpretations based on Nb/U and Ce/Pb systematics, our Ta/W data confirm a depletion of the depleted upper mantle (DM) in fluid mobile elements relative to the primitive mantle (PRIMA). The abundance of W in the depleted upper mantle relative to other immobile and highly incompatible elements such as Nb and Ta is therefore not representative of the bulk silicate Earth. Based on mass balance calculations using Ta-W systematics in the major silicate reservoirs, the W abundance of the Earth’s primitive mantle can be constrained to 12 ppb, resulting in revised ratios of W-U and W-Th of 0.53 and 0.14, respectively. The newly constrained Hf-W ratio of the silicate Earth is 25.8, significantly higher than previously estimated (18.7) and overlaps within error the Hf-W ratio proposed for the Moon (ca. 24.9). The ¹⁸²Hf-¹⁸²W model age for the formation of the Earth’s core that is inferred from the ¹⁸²W abundance and the Hf/W of the silicate Earth is therefore younger than previously calculated, by up to 5 Myrs after solar system formation depending on the accretion models used. The similar Hf/W ratios and ¹⁸²W compositions of the Earth and the silicate Moon suggest a strong link between the Moon forming giant impact and final metal-silicate equilibration on the Earth.