铁矿床深部矿体定位预测的一种新途径 ———以西藏恰功铁矿为例

恰功铁矿是近几年新发现的矿山,矿体的形态、大小、位置、产状、边界等几何特征还没有清楚的认识,为了弄清这些问题,文章首先通过小渡多尺度分析方法将恰功铁矿磁异常资料进行了位场信号分离,然后应用欧拉反褶积方法反演了异常与其场源深度的对应定量关系,最后把位场分离后的异常场源深度叠加起来,就可以对矿山深部找矿提供一种全新的思路.     

河南桐柏围山城金银成矿带成矿物质来源: 铅同位素证据

围山城金银成矿带出露有破山银矿床、银洞坡金矿床和银洞岭银矿床等三个大型金银矿床,均受地层和构造的双重控制,赋矿地层为新元古界歪头山岩组,河前庄背斜是成矿带的主要控矿构造.围岩地层歪头山岩组的铅同位素组成具有整体富Th亏U、低μ高ω的特征,与围山城金银成矿带的矿石铅整体富Th亏U、低μ高ω的特征一致.经过年龄校正后,把成矿带内的围岩地层和岩体的全岩铅同位素样品与矿石铅同位素对比分析发现,围岩歪头山岩组与矿石关系最为接近,其次为燕山期梁湾花岗岩体.成矿带的矿石铅具有混源特征.可以认为围岩歪头山岩组和梁湾花岗岩体共同为成矿带提供了铅源及成矿物质.     

潍北平原地区全新世以来的海侵与海岸线变迁

末次冰期后,在全新世大暖期及区域沉降的影响下,渤海湾沿岸普遍发育海侵现象,位于莱州湾南岸的潍北平原区在经历全新世最大海泛面后,海水退却过程中留下了数条古海岸线,形成了多处贝壳堤、牡蛎礁等海岸带遗迹。研究区内新发现常家村、后柳家2处牡蛎礁,其14C年龄分别为（5130±30）a B.P.和（6030±30） a B.P.;通过对区内全新世海陆交互相沉积关系及海相地层分布规律的研究,结合已有测年数据与近现代遥感影像数据,对潍北平原区全新世以来的海陆变迁进行了总结,恢复了自6000 a B.P.至公元1989年间的6条海岸线。     

Soil erosion and sediment transport in Tanzania: Part I – sediment source tracing in three neighbouring river catchments

Water bodies in Tanzania are experiencing increased siltation, which is threatening water quality, ecosystem health, and livelihood security in the region. This phenomenon is caused by increasing rates of upstream soil erosion and downstream sediment transport. However, a lack of knowledge on the contributions from different catchment zones, land-use types, and dominant erosion processes, to the transported sediment is undermining the mitigation of soil degradation at the source of the problem. In this context, complementary sediment source tracing techniques were applied in three Tanzanian river systems to further the understanding of the complex dynamics of soil erosion and sediment transport in the region. Analysis of the geochemical and biochemical fingerprints revealed a highly complex and variable soil system that could be grouped in distinct classes. These soil classes were unmixed against riverine sediment fingerprints using the Bayesian MixSIAR model, yielding proportionate source contributions for each catchment. This sediment source tracing indicated that hillslope erosion on the open rangelands and maize croplands in the mid-zone contributed over 75% of the transported sediment load in all three river systems during the sampling time-period. By integrating geochemical and biochemical fingerprints in sediment source tracing techniques, this study demonstrated links between land use, soil erosion and downstream sediment transport in Tanzania. This evidence can guide land managers in designing targeted interventions that safeguard both soil health and water quality.     

Sediment organic matter source estimation and ecological classification in the semi-enclosed Batan Bay Estuary,Philippines

The large organic matter flow in tropical coastal areas is recognized as an important process in the global carbon(C)cycle.However,the nature of organic matter flow in semi-enclosed tropical estuaries remains unclear due to the various environmental processes(tidal change,river flow,waves from the sea,and internal circulation)and organic matter sources therein.Thus,sediment organic matter(SOM)sources,and their distribution pattern,are key to understanding ecosystem material flow.Our research in the Batan Bay Estuary,Philippines,a semi-enclosed estuary under large mangrove deforestation,was conducted to determine ecosystem properties through analysis of C and nitrogen stable isotope ratios and environmental factors.First,we determined that mangrove litter,microphytobenthos,and phytoplankton are the main SOM sources in the Batan Bay Estuary.Second,the estuary was classified into three ecological zones(the Bay zone,Back-barrier zone,and River zone).In addition,we estimated SOM source ratios using the Stable Isotope Analysis in R package and determined different organic matter sources in different zone.The high ratios of mangrove litter as SOM indicate that a large amount of terrestrial plant organic matter remains despite the heavy mangrove deforestation that has occurred since the 1980s,and that the Back-barrier zone consists of a different type of ecosystem that promotes accumulation of C from mangrove litter and microphytobenthos.     

The δ13C–δ18O variations in marble in the Hida Belt,Japan

Marble has a great potential to understand a history of various geological events occurring during tectonic processes. In order to decode metamorphic–metasomatic records on C–O isotope compositions of marble at mid-crustal conditions, we conducted a C–O–Sr isotope study on upper amphibolite-facies marbles and a carbonate–silicate rock from the Hida Belt, which was once a part of the crustal basement of the East Asian continental margin. Carbon and oxygen isotope analyses of calcite from marbles (Kamioka area) and a carbonate–silicate rock (Wadagawa area) show a large variation of δ¹³C [VPDB] and δ¹⁸O [VSMOW] values (from −4.4 to +4.2 ‰ and +1.6 to +20.8 ‰, respectively). The low δ¹³C values of calcites from the carbonate–silicate rock (from −4.4 to −2.9 ‰) can be explained by decarbonation (CO₂ releasing) reactions; carbon–oxygen isotope modeling suggests that a decrease of δ¹³C strongly depends on the amount of silicate reacting with carbonates. The occurrence of metamorphic clinopyroxene in marbles indicates that all samples have been affected by decarbonation reactions. All δ¹⁸O values of calcites are remarkably lower than the marine-carbonate values. The large δ¹⁸O variation can be explained by the isotope exchange via interactions between marble, external fluids, and/or silicates. Remarkably low δ¹⁸O values of marbles that are lower than mantle value (~+5 ‰) suggest the interaction with meteoric water at a later stage. Sr isotope ratios (⁸⁷Sr/⁸⁶Sr = 0.707255–0.708220) might be close to their protolith values. One zircon associated with wollastonite in a marble thin-section yields a U–Pb age of 222 ± 3 Ma, which represents the timing of the recrystallization of marble, triggered by H₂O-rich fluid infiltration at a relatively high-temperature condition. Our isotope study implies that the upper amphibolite-facies condition, like the Hida Belt, might be appropriate to cause decarbonation reactions which can modify original isotope compositions of marble if carbonates react with silicates.     

俯冲带中大理岩与榴辉岩的Mg-Fe-C-O同位素迁移

碳酸盐岩和碳酸盐化岩石是俯冲带中碳的主要地质载体.俯冲-折返的超高压变质岩记录了俯冲隧道中流体-岩石的相互作用与元素迁移,是研究地球内部元素循环的重要媒介.本文采集了大别造山带罗家岭互层状产出的大理岩和榴辉岩,建立了横跨岩性界面的矿物组成、显微结构和Mg-Fe-C-O同位素剖面.大理岩中主要组成矿物为白云石,其次为方解...     

扬子地台西南缘早三叠世层序地层格架

扬子地台西南缘早三叠世地层被划分为4个沉积层序。通过综合研究已取得的牙形石生物地层资料,与Haq等人提出的三叠纪牙形石生物时带进行了对比,初步定出了各沉积层序及体系域的界面年龄(层序1底界年龄251Ma;层序2底界年龄245.2Ma;层序3底界年龄243Ma;层序4底界年龄240.5Ma,顶界年龄239.4Ma),从而建立了区内分辨率较高的早三叠世地层格架。格架中层序组合特征在碳酸盐岩台地边缘显示得非常清楚,其中,层序1-层序2高水位体系域的台地边缘依次向陆后退,呈退积或超覆(overlap)型组合关系;层序3-层序4高水位体系域的台地边缘则依次向海推进,呈进积或退覆(offlap)型组合关系。这种组合特征主要受沉积盆地的构造沉降及2级海平面升降亚旋回的海面变化的控制,构造沉降加速和海面上升期形成的层序呈退积型组合关系;构造沉降平缓及海面下降期形成的层序呈进积型组合关系。此外,还研究了斜坡地带(贵阳改毛)层序1-层序3底部的碳氧同位素组成变化规律:海侵体系域-高水位体系域碳、氧同位素组成变化不大,δ13C主要为正值,但在高水位体系域顶部明显负向偏移;低水位体系域碳、氧同位素组成变化剧烈,且均为负值。这为地层划分提供了地球化学方面的依据。     

金属矿床的同位素直接定年方法

矿床的直接定年就是直接对成矿流体或矿石矿物进行同位素定年 ,这样确定的年龄就直接代表了成矿年龄。目前主要有石英和闪锌矿中流体包裹体的Rb Sr同位素定年、黄铁矿和石英中包裹体的Ar Ar同位素定年、金属硫化物的Rb Sr同位素定年、金属硫化物和氧化物的Sm Nd同位素定年、金属硫化物的Re Os同位素定年 ,以及单个矿石矿物的Pb逐步淋滤法定年     

西藏南部康马岩体岩石类型及其同位素测年

康马岩体位于西藏南部康马县城北侧 ,其内部可划分出 5种不同的岩石类型 :(1)片麻状黑云二长花岗岩 ;(2 )眼球状黑云二长花岗岩 ;(3)片麻状二云母二长花岗岩 ;(4 )弱片麻状细粒黑云二长花岗岩 ;(5 )变质的暗色辉长辉绿岩。前两类为康马岩体的主体岩石类型 ,侵位时代为加里东早期 (约4 78～ 4 6 1Ma) ;其余均呈脉状产出 ,其中片麻状二云母二长花岗岩与康马岩体主体岩石类型属于同期产物 ,弱片麻状细粒黑云二长花岗岩形成于海西早期 ((339.0± 1.2 )Ma) ,暗色辉长辉绿岩的形成时代目前还不十分清楚。不同类型的岩石其Ar Ar冷却年龄约为 18～ 14Ma。