Age, Origin and Cooling History of the Coronel Joao Sa Pluton, Bahia, Brazil

In north-east Brazil, Archean and Paleoproterozoic cratonicblocks are enclosed within a network of Brasiliano-age (0·7–0·55Ga) metasedimentary foldbelts. The unfoliated Coronel JoãoSá granodiorite pluton, which contains magmatic epidoteand strongly resorbed clinopyroxene, intrudes the SergipanoFoldbelt. Zircons yield a concordant U–Pb crystallizationage of 625 ± 2 Ma; titanite ages are approximately 621Ma. Discordant zircons suggest inheritance from at least twomagma sources of ages <1·8 and >2·2 Ga.Model calculations based on diffusion parameters and Rb–Srisotope data from separated minerals indicate that the plutoncooled at a rate of 36°C/Myr. Whole-rock element compositionsand initial Sr–Nd isotopic compositions that are heterogeneouson all length scales suggest magma mixing. Trace-element concentrationsand Nd isotope data argue against a contribution from a contemporaneousmantle-derived magma. Values of magmatic _Nd (at 625 Ma) resemblecontemporary _Nd for local supracrustal rocks and basement, compatiblewith anatexis of a crustal source. In north-east Brazil, cratonicblocks could have amalgamated with foldbelts that originatedas: (1) a mosaic of island arcs and arc basins (traditionalallochthonous model), or as (2) extensional continental sedimentarybasins (but not oceanic crust) later involved in collision (autochthonousmodel). The Coronel João Sá isotopic and chemicaldata support an autochthonous origin. KEY WORDS: Brasiliano Orogeny; granodiorite pluton; Rb–Sr isotopes, Sm–Nd isotopes; U–Pb isotopes, magma cooling rate     

华北克拉通东部含金刚石金伯利岩的侵位年龄和Sr-Nd-Hf同位素地球化学特征

本文首次报道了我国华北克拉通内部金伯利岩中金云母巨晶的Ar-Ar同位素年龄和含金刚石金伯利岩的Hf同位素组成特征,并结合金伯利岩的Sr-Nd同位素组成特征对华北金伯利岩的岩石成因及其构造背景进行了探讨.金伯利岩中金云母巨晶的年代学分析显示华北克拉通内部的蒙阴和复县金伯利岩具有一致的侵位年龄,约465±2 Ma.这与以前发表的金伯利岩中钙钛矿的U-Pb年龄和金云母的Rb-Sr等时线年龄一致.Sr-Nd同位素结果表明蒙阴和复县金伯利岩皆具有很小的Nd同位素变化范围（εNd分别为-0.4～0.2和-3.4～-2.3）.然而,这些金伯利岩却具有极大的Sr同位素组成范围（ISr分布为-0.2～28.1和0～75）.其中复县比蒙阴金伯利岩具有较低的Nd同位素和更宽的Sr同位素组成.Hf同位素分析结果表明蒙阴和复县两岩区内部各金伯利岩岩管具有非常一致的铪同位素组成,类似于Nd同位素组成特征,其中蒙阴金伯利岩的^176Hf/^177Hf初始值为0.282474～0.282416,相应的εHf值为-2.37～-0.30;复县金伯利岩的^176Hf/^177Hf初始值为0.282305～0.282369;相应的εHf值为-6.29～-4.04.这说明蒙阴金伯利岩与复县金伯利岩相比具有较高的Hf同位素组成.结合Sr-Nd同位素组成,暗示蒙阴和复县金伯利岩的Hf同位素组成的不同可能反映金伯利岩岩浆形成时软流圈、岩石圈地幔以及俯冲的洋壳物质参与比例的不同.Sr-Nd-Hf同位素特征说明我国华北古生代金伯利岩的形成同样与华北周边的古大洋岩石圈向华北内部俯冲作用有关.     

Origin of sulphate in the unsaturated zone and groundwater of a loess aquifer

The use of the sulphate mass balance (SMB) between precipitation and soil water as a supplementary method to estimate the diffuse recharge rate assumes that the sulphate in soil water originated entirely from atmospheric deposition; however, the origin of sulphate in soil and groundwater is often unclear, especially in loess aquifers. This study analysed the sulphur (δ³⁴S-SO₄) and oxygen (δ¹⁸O-SO₄) isotopes of sulphate in precipitation, water-extractable soil water, and shallow groundwater samples and used these data along with hydrochemical data to determine the sources of sulphate in the thick unsaturated zone and groundwater of a loess aquifer. The results suggest that sulphate in groundwater mainly originated from old precipitation. When precipitation percolates through the unsaturated zone to recharge groundwater, sulphates were rarely dissolved due to the formation of CaCO₃ film on the surface of sulphate minerals. The water-extractable sulphate in the deep unsaturated zone (>10 m) was mainly derived from the dissolution of evaporite minerals and there was no oxidation of sulphide minerals during the extraction of soil water by elutriating soil samples with deionized water. The water-extractable concentration of SO₄ was not representative of the actual SO₄ concentration in mobile soil water. Therefore, the recharge rate cannot be estimated by the SMB method using the water-extractable concentration of SO₄ in the loess areas. This study is important for identifying sulphate sources and clarifying the proper method for estimating the recharge rate in loess aquifers.     

Organic matter origin and distribution in suspended particulate materials and surficial sediments from the western Adriatic Sea (Italy)

In this study, organic carbon (OC), total nitrogen (TN), stable carbon isotopic (δ¹³C_OC) and CuO reaction product compositions were used to identify the sources of organic matter (OM) and to quantify the relative importance of allochthonous and autochthonous contributions to the western Adriatic Sea, Italy. Suspended particulate material (195 samples) and surficial sediments (0–1 cm, 70 samples) from shallow cross-shelf transects were collected in February and May 2003, respectively. Vertical water column profiles were acquired along the same transects. Data include depth, potential temperature, salinity, density and chlorophyll fluorimetry.Along the western Adriatic shelf in the near-shore region, the phytoplankton growth was influenced by dynamics of the buoyant plumes from the Po and Appennine rivers. A small amount of very fine terrigenous material remained suspended within the coastal current and was exported southward along the shelf to the slope. High variability in the bulk composition was detected in the Po prodelta surficial sediments, whereas the western Adriatic shelf, although a larger area, exhibited a narrower range of values.A significant decoupling was observed between suspended particles in the water column and surficial deposits. The organic material collected in the water column was compositionally heterogeneous, with contributions from marine phytoplankton, riverine–estuarine phytoplankton and soil-derived OM. Frequent physical reworking of surficial sediments likely leads to the efficient oxidation of marine OC, resulting in the observed accumulation and preservation of refractory soil-derived OC delivered by the Po and Appennine rivers.     

云南降水中稳定同位素变化的模拟和比较

利用MUGCM的模拟,云南地区日、月、年时间尺度下降水中稳定同位素的变化、降水量效应以及δD/δ18O之间的关系被分析。无论是在日时间尺度下还是在月、年时间尺度下,降水同位素均存在显著的降水量效应。与实测结果相比,模拟的降水中δ18O与降水量之间具有更强的相关性。对于单站而言,蒙自站和腾冲站的大气水线被较好地模拟。但在思茅站和昆明站,模拟结果未能准确再现实际降水中δD与δ18O的关系,模拟的大气水线斜率比实测结果偏高。这意味着,在云南这个特殊的地区,模式可能高估了HDO的贫化。     

松潘—甘孜造山带中巴西金-矽卡岩矿床成矿热液系统演化的(REE、Sr、O)证据

本文通过对巴西典型金-矽卡岩矿床的解剖，探讨了成矿流体来源、组成演化，以及流体和岩石之间的质量转移程度和机理的信息，揭示金成矿过程中成矿流体演化的规律。研究认为，成矿作用两阶段的成矿流体分别为变质流体和大气降水，它们在开放系统中水岩质量比分别为0．02，2．11，并且获得矽卡岩可能是由围岩转向岩体方向的变质流体交代形成的认识。     

胶东邢家山钼钨矿床辉钼矿Re-Os同位素测年及其地质意义

邢家山矿床是胶东地区一特大型矽卡岩-斑岩型钼钨矿床,构造位置上处于华北板块东南缘与扬子板块对接地带,在成因上与幸福山似斑状含角闪二长花岗岩密切相关,归属于该区与燕山早期花岗质岩浆作用有关的特大型、大型和中型铜钼多金属矿床成矿系列。本文对该矿床透辉石榴矽卡岩中的辉钼矿进行了Re-Os同位素测年,结果显示,辉钼矿Re-Os同位素模式年龄范围为156.91±1.78Ma至160.70±1.66Ma,加权平均值为158.91±1.91Ma,对应的Re-Os等时线年龄为158.70±2.06Ma;这些年龄数据与区域上的燕山早期花岗岩锆石U-Pb年龄(158.53±0.79Ma)相近,指示区域上该期铜钼多金属矿化与区内花岗岩具有密切的时间和成因关系。中、晚侏罗世华北东部广泛的地壳增厚作用和地壳重熔导致的大规模地壳重熔型花岗质岩浆活动为该区钼钨多金属矿成矿提供了主要成矿物质和流体。结合已有的研究成果,认为胶东地区中生代以来岩浆活动及相应的成矿作用可能主要存在4期,即:约165～155Ma的铜钼多金属矿化期、约137～110Ma的金矿化期、约120～110Ma的铜钼铅锌多金属矿化期、和约100～75Ma的金银铅锌多金属矿化期,分别对应于燕山早期-燕山晚期的各期次花岗质岩浆活动。     

江南造山带东段旌德岩体锆石LA-ICPMS年龄和Nd-Sr-Hf同位素地球化学

提要：旌德花岗质杂岩体位于安徽南部,由花岗闪长岩和二长花岗岩组成。本研究得到岩体中锆石U-Pb年龄为(141.0±1.0) Ma,认为该年龄代表岩体的侵位年龄。岩体全岩主量元素特征显示出中偏酸性 (SiO2＝66.01%~70.87%),富Al (Al2O3＝14.91%~16.24%),富碱 (alk = 6.64%~8.01%),K2O/Na2O变化范围在0.78~1.04,镁、铁含量较低,MgO：0.68%~1.06%,TFe2O3 (2.0%~3.34%),以及低磷 (P2O5 =0.10%~0.14%)的特点;微量元素主要富集Sr (189×10-6~452×10-6),贫Nb、Ta、P、Ti、Y、Yb,高Sr/Y比值 (23~66)和 (La/Yb)N (13~58),Eu有轻微的负异常到弱的正异常 (δEu＝0.81~1.18)。旌德岩体的地球化学特征与中国东部中生代埃达克质岩相似。ISr＝0.7096~0.7101, εNd(t)＝-6.28~-7.32,εHf(t)值变化于-6.5~-1.1,两阶段模式年龄 tDM2=1.4~1.5 Ga。较年轻的Nd同位素模式年龄、较高的εNd(t)值和εHf(t)值,以及岩体中发育有岩浆混合成因的暗色包体,指示源区可能有地幔物质的贡献。幔源岩浆底侵使下地壳发生部分熔融,并发生了岩浆混合作用,形成了旌德岩体。     

湖泊碳酸盐在过去环境变化研究中的应用

国内外的研究成果表明,湖泊沉积碳酸盐矿物及其微量元素、同位素分布特征记录了全球或区域古气候环境演变历史,可以从中提取大量定量化的古气候参数。因此,可以根据湖泊碳酸盐矿物的含量和碳、氧同位素变化等信息推知其形成时期的气候环境,重建古环境,揭示气候环境演变的规律。湖泊碳酸盐是一种研究古环境演化重要的代用指标,在过去气候环境变化研究中有广阔的应用前景。     

Upwelling signals in radiocarbon from early 20th-century Peruvian bay scallop (Argopecten purpuratus) shells

We quantified Δ¹⁴C, δ¹⁸O, and δ¹³C cycles along ontogeny within four bay scallop (Argopecten purpuratus) shells collected from Callao Bay, Salaverry, and Sechura Bay, Peru following the 1907–1908 non-El Niño years and the 1925–1926 El Niño. Δ¹⁴C and δ¹³C generally covary; Δ¹⁴C and δ¹⁸O vary inversely. Simultaneous decreases in Δ¹⁴C and increases in δ¹⁸O in non-El Niño shells are followed by constant Δ¹⁴C and gradually decreasing δ¹⁸O, which we interpret as evidence for discrete marine upwelling events followed by warming of the initially cold upwelled water. Upwelling changes from El Niño events are detectable with difficulty in mollusk shell Δ¹⁴C.