Accurate and Precise Silicon Isotope Analysis of Sulfur‐ and Iron‐Rich Samples by MC‐ICP‐MS

Silicon isotope determination of sulfur‐rich samples by MC‐ICP‐MS can be challenging because cation‐exchange chromatography used for Si purification does not efficiently remove anionic sulfur species. Results for pure Si standard solutions with addition of sulfate showed shifts of up to +1.04 ± 0.10‰ (2s) in δ³⁰Si. Doping of both standard solutions and samples with S to a fixed S/Si ratio can eliminate the relative change in instrumental mass fractionation due to variable S/Si in samples and also boosts the relative sensitivity of Si by up to 66%. Moreover, Fe hydroxide precipitation during sample processing adsorbs Si resulting in isotopic fractionations. Tests using Fe‐rich samples showed that this could be a major factor for observed shifts in δ³⁰Si. Acidification of the sample and standard solutions to a pH < 1 aggressively dissolved any Fe hydroxide precipitates, even in relatively Fe‐rich samples such as chondrite meteorites. The pH values of the sample solutions were subsequently adjusted to a range of 2–3 by adding ultra‐pure NaOH solutions. The combination of sulfur doping and the pH adjustment protocol ensured a full recovery of Si and proved to be an efficient and reliable method for Si isotope determination of S‐ and Fe‐rich materials.     

三维地震技术在沉积学研究中的应用

三维地震技术对沉积学的发展有着重要的推动作用,主要体现在分析方法和概念上.高精度的三维地震数据可以通过对沉积要素的直接成像来重建三维的沉积古环境,也可以通过对不同地质历史时期的古沉积环境进行成像来研究沉积演化史.地震数据联合测井数据也可以通过预测岩石性质分布来定量描述沉积岩的非均质性.在成岩作用分析工作中,高分辨率的地震成像用优于10 m的纵向分辨率在上千平方千米的范围内描述成岩界面的几何形态,是一种在整个盆地范围内研究成岩作用过程的新方法.应用三维地震技术解决沉积问题这一领域未来发展潜力巨大.对相关的方法、工作流程和研究实例进行了论述.     

碱性岩相关铜-金(钼)矿床的研究进展

由于超过20%的大型-超大型铜-金(钼)矿床与碱性岩浆有关,因此,该类矿床引起矿床学家的广泛关注。碱性岩有关的铜-金矿床的成矿岩体、物化条件及围岩种类各具特色,成矿成因类型多样,主要的成因类型为斑岩型铜-金(钼)、浅成低温热液脉型金-铜(钼)。总体上,该类矿床的矿化和蚀变具有一定的特征:该类矿床多产出在伸展环境下、均富碲化物矿化、有大量的钾质交代作用、含有氟矿物质和钒云母等,成矿蚀变亦有一定的规律。长英质岩石中经常发生钾长石蚀变,而绢云母、碳酸盐和钾长石的混合蚀变常出现在中基性侵入岩中,水热合成石英和酸性蚀变十分罕见。这种特征矿化可能与碱性岩浆流体演化有关,这种流体富含CO_2,且在高氧逸度、低硫逸度条件下释放。在伸展背景下的碱性-钙碱性省寻找此类矿床具有巨大的勘查潜力,尤其在碱性岩体中心及其外围可能形成勘探的靶区。在中国与碱性岩有关的金矿床亦有广阔的找矿前景,在借鉴国外寻找此类矿床经验的同时,仍需加强对与矿化作用有关的岩浆体活动的研究。     

湖北竹溪蔓荆沟碱性正长岩地球化学特征及其构造环境分析

在南秦岭造山带中发现的竹溪蔓荆沟碱性正长岩,呈透镜状侵入于辉绿岩体内,个别呈独立岩体侵入于早古生代地层中。单个正长岩体规模较小。通过对其进行岩相学及岩石地球化学特征研究,表明其为全碱(Na_2O~+K_2O)含量较高的钾质碱性正长岩;岩石中Mg~#值较低,明显低于原始岩浆Mg~#值,说明其为原始岩浆经历较高程度演化的产物;岩体中稀土元素总量ΣREE较高,轻稀土元素LREE富集明显,重稀土元素HREE亏损;通过微量元素构造环境判别分析认为,研究区正长岩形成于大陆裂谷环境,且形成于大陆裂谷早期阶段,其形成时代为早志留世。     

鄂尔多斯盆地苏77、召51区块山23段储层成岩作用与孔隙演化定量分析

利用扫描电镜、岩石薄片、高压压汞、X衍射等实验及物性分析资料,对鄂尔多斯盆地苏77、召51区块山23段储层基本特征、成岩作用类型及强度、孔隙演化模式进行研究。结果表明：储层主要岩石类型为成分成熟度较高、结构成熟度较低的石英砂岩和岩屑石英砂岩;孔隙类型以溶孔为主,残余粒间孔和晶间孔含量次之。储层在经历中等-强程度的压实,中等程度的胶结以及强烈的溶蚀作用后,处于中成岩阶段B期,局部处于晚成岩阶段。压实作用和胶结作用导致原生孔隙遭到破坏,孔隙度损失分别为1694％和1429％,晶间孔和溶蚀作用分别使孔隙度增加092％和564％,储层物性得以改善。孔隙空间经历原生孔隙减少→次生孔隙发育→次生孔隙减少→混合孔隙并存的复杂演化过程。     

云南省卓潘碱性杂岩体矿物学、地球化学特征及其地质意义

卓潘杂岩体是金沙江—哀牢山富碱侵入岩带的重要组成部分,位于兰坪盆地西部。岩体主要由辉长岩、辉石岩及正长岩组成,各岩石的K2O含量为096%～736%,Na2O含量为052%～662%,Na2O+K2O含量为198%～897%,K2O/Na2O比值介于035～1115之间,属于高钾、富碱的钾玄岩系列。岩石中的辉石为透辉石,长石主要为钠长石(An＜5)和正长石,黑云母为镁质黑云母。计算获得辉石的结晶温度范围介于1 070～1 490 ℃之间。各矿物成分特征表明卓潘杂岩体属于富铁、高氧逸度的岩浆体系,形成于后碰撞的挤压环境向伸展环境转换的构造背景。     

陆相碎屑岩成岩作用系统研究进展及发展趋势

文章围绕陆相碎屑岩成岩作用系统这一议题,概述了成岩作用系统研究的发展历程,总结近年来国内外成岩作用系统的研究进展,提出了未来的研究趋势。认为当前陆相碎屑岩成岩作用系统研究取得的进展包括5个方面:(1)原始沉积环境对成岩作用系统的影响,(2)成岩流体对成岩作用系统的影响,(3)构造作用对成岩作用系统的影响,(4)成岩系统的封闭性与成岩作用的关系,(5)层序控制下的成岩响应。未来成岩作用系统研究的趋势:各种实验手段的革新和综合利用、成岩系统过程恢复、成岩作用定量化研究及多学科交叉融合等方面将是未来成岩作用系统研究的主要方向,必将推动成岩作用系统研究进入新的阶段。     

Interactions between tectonics and fluid circulations in an inverted hyper-extended basin: Example of mesozoic carbonate rocks of the western North Pyrenean Zone (Chaînons Béarnais,France)

Interactions between fracturing, fluid circulations and fluid chemistry in hyper-extended margins are still poorly described as most of them are located offshore, buried underneath post-rift sediments. The southern Aquitaine basin and the northern Pyrenees constitute an appropriate case study to investigate these interactions since a model of hyper extended margin with mantle exhumation during the Lower Cretaceous subsequently inverted was recently proposed. From a field study, we here describe three main sets of fractures (set 1 to set 3). They are correlated with main stages of the geodynamic evolution of the basin corresponding to the Liassic rifting, the Aptian-Cenomanian hyper-extension, and the Pyrenean compression. Petrographic observations, Raman and micro-thermometry analysis on fluid inclusions, ICP-MS, and isotope analysis permitted to determine chemistries, temperatures, redox conditions, gas compositions, oxygen and carbon isotopic signatures, and REE contents of parent fluids for cements precipitated during each episode. In particular saddle dolomite and chlorite precipitated in set 2 fractures during the hyper-extension corresponding to the thermal peak at temperatures higher than 300 °C. The isotopic signature, the high CO₂ content, the occurrence of H₂S and the high salinity of parent fluids suggest ascending magmatic fluids percolating across Triassic evaporites. The late and post hyper-extensional phase is characterized by hydraulic brecciation in dolomitic formations, a decrease in temperature and salinity, a decrease in magmatic contribution in parent fluids, a closing of the diagenetic system during burial and a switch to reducing conditions during the precipitation of quartz, pyrite and calcite. The Pyrenean compressive phase associated with the third fracturing stage induced a reopening of the diagenetic system and favored a return to oxidizing conditions and infiltrations of meteoric fluids.     

引江济太对太湖水体碱性磷酸酶动力学参数的影响

采用野外定点采样、室内同步分析水体碱性磷酸酶活性及水化学指标的方法,研究引江济太调水对太湖各湖区水体碱性磷酸酶最大反应速率(v_max)、米氏常数(Km_m)值的影响。结果表明:在引江济太调水试验期间,各湖区水体中v_max及Km_m值时空分布存在差异性。调水稀释了各湖区蓝藻浓度,抑制了水体碱性磷酸酶v_max;贡湖区、西岸河口区及湖心区水体中Km_m值与入湖累积水量之间有显著的二次函数关系(p=0.007)。梅梁湖、竺山湖、贡湖及西岸河口区水体碱性磷酸酶v_max/Km_m随着总磷浓度升高而增加,但竺山湖、贡湖、草型湖、湖心及西岸河口区水体v_max/K随生物可利用磷(PO₃--P)浓度增加而下降。除草型湖区外,其它湖区水体v/K随叶绿素a浓度升高而增加。     

Diagenetic processes in carbonate mound sediments at the south‐west Rockall Trough margin

Cold water coral covered carbonate mounds at the south‐west margin of the Rockall Trough form ridges several kilometres long and up to 380 m high. Piston cores obtained at three mound crests reveal the complex internal structure of the mound build up, with alternating unlithified coral‐dominated intervals and lithified intervals. The most recent lithified interval is covered by corals embedded in a fine‐grained matrix, comprising ca 11 000 years of continuous mound evolution. Before this time ²³⁰Th/U dating shows the presence of several hiatuses in mound build‐up. Aragonitic coral material is absent or only present as mouldic porosity in the lithified intervals and coccoliths display widespread overgrowth. Downcore X‐ray fluorescence scanning, computer tomography scan images and petrographic observations indicate different degrees of diagenetic alteration. The upper boundary of the most recent lithified interval shows some erosional features, but petrographic observations indicate that initial lithification of the sediments is not related to this erosive event or to long‐term non‐sedimentation, but to earlier sub‐surface diagenesis. Organic matter oxidation and the subsequent lowering of the saturation state of the carbonate system drives dissolution of the unstable aragonitic coral skeletons. Depending on the openness of the system, this can lead to precipitation of a more stable low‐magnesium carbonate. A model is presented describing the sedimentary and diagenetic processes leading to the formation of lithified intervals.