砂宝斯金矿区多矿物脉特征及其对砂岩的改造

砂宝斯矿区的成矿围岩为长石石英砂岩，砂岩被多期次的石英脉、方解石脉和高岭石脉所穿切，这些多矿物脉是热液流体运移的结果。矿物脉形成过程中对围岩进行了热改造，使砂岩发生了压溶作用、胶结作用和溶蚀作用，形成了蚀变砂岩。由于流体酸碱性和温压的变化，孔隙水介质的性质由酸性向碱性转变，在酸性成岩环境下形成的蚀变高岭石、伊利石将转变成绿泥石、绢云母等。绢云母的大量出现，石英次生加大和自生粘土矿物的形成均是热液流体活动的产物。     

伏牛山构造带变质流体脉变形特征及构造意义

伏牛山构造带由多条近平行的断裂带和夹持其间的变形岩片组成,洛南-栾川断裂带和瓦穴子-乔端断裂带为其中的两条主要断裂带。这两条断裂带虽遭受多期强烈构造活动的影响,但主造山期的构造特征至今仍然保存完好,并以中深层次的韧性剪切变形为主,形成了典型的糜棱岩和同构造期石英脉。本文从宏观、微观、超微观变形特征及年龄等方面对这些变质流体脉进行了研究,以探讨与其形成密切相关的构造活动特征、年代及其在秦岭造山带和华北板块南缘强变形带中的作用。石英脉中石英颗粒动态重结晶特征总体显示远离剪切带只有少量的膨凸式,靠近断裂带为亚颗粒式,形成核-幔结构,位错特征显示远离剪切带位错密度较小,靠近断裂带较大,位错形态显示瓦乔断裂带以挤压为主,洛南-栾川断裂带以剪切为主。两条断裂带石英脉的变形特征说明它们的糜棱岩化过程均为塑性变形中的晶质塑性变形,形成过程均为挤压在先,剪切在后。所测糜棱岩中石英脉的ESR年龄分别为372.9±30.0 Ma、275.0±20.0 Ma和218.0±20.0 Ma,真实地记录了晚加里东至中-晚海西期北秦岭的构造活动及所受影响。其中372.9±30.0 Ma是宽坪岩块向华北板块下的斜向俯冲汇聚和走滑的年代, 275.0±20.0 Ma是瓦乔断裂带的形成年龄。218.0±20.0 Ma的年龄则反映了华南、华北两大板块印支晚期全面闭合作用在秦岭造山带内部的影响。从以上3个年龄可以看出:北秦岭各构造带自北向南演化,时代上自北向南变新。     

Albite vein formation during exhumation of high-pressure terranes: a case study from alpine Corsica

The formation of late‐stage veins can yield valuable information about the movement and composition of fluids during uplift and exhumation of high‐pressure terranes. Albite veins are especially suited to this purpose because they are ubiquitously associated with the greenschist facies overprint in high‐pressure rocks. Albite veins in retrogressed metabasic rocks from high‐pressure ophiolitic units of Alpine Corsica (France) are nearly monomineralic, and have distinct alteration haloes composed of actinolite + epidote + chlorite + albite. Estimated P–T conditions of albite vein formation are 478 ± 31 °C and 0.37 ± 0.14 GPa. The P–T estimates and petrographic constraints indicate that the albite veins formed after the regional greenschist facies retrogression, in response to continued decompression and exhumation of the terrane. Stable isotope geochemistry of the albite veins, their associated alteration haloes and unaltered hostrocks indicates that the vein‐forming fluid was derived from the ophiolite units and probably from the metabasalts within each ophiolite slice. That the vein‐forming fluid was locally derived means that a viable source of fluid to form the veins was retained in the rocks during high‐pressure metamorphism, indicating that the rocks did not completely dehydrate. This conclusion is supported by the observation of abundant lawsonite at the highest metamorphic grades. Fluids were liberated during retrogression via decompression dehydration reactions such as those that break down hydrous high‐pressure minerals like lawsonite. Albite precipitation into veins is sensitive to the solubility and speciation of Al, which is more pressure sensitive than other factors which might influence albite vein formation such as silica saturation or Na:K fluid ratios. Hydraulic fracturing in response to fluid generation during decompression was probably the main mechanism of vein formation. The associated pressure decrease with fracturing and fluid decompression may also have been sufficient to change the solubility of Al and drive albite precipitation in fracture systems.     

Micro-environmental controls on biomineralization: superficial processes of apatite and calcite precipitation in Quaternary soils, Roussillon, France

Calcium hydroxyapatite and calcite precipitates around bacteria were observed in 2-week-old alluvial topsoil (Roussillon area, SE France). This observation prompted a laboratory study of Ca²⁺ and PO₄³⁻ incorporation into hydroxyapatite and Ca²⁺ into calcite mediated by bacteria using similar topsoil material, but free from apatite and calcite. Subsamples were prepared using three different grain sizes, and experiments were undertaken using sucrose and different contents of Ca²⁺ and PO₄³⁻. Mineralization experiments proceeded over 5 days. Calcium and PO₄³⁻ sorption onto clay influenced the Ca/P ratio in the solutions. Hydroxyapatite and calcite precipitation only occurred in unsterilized samples. The presence of clay minerals promoted biomineralization.     

Diagenesis or dire genesis? The origin of columnar spar in tufa stromatolites of central Greece and the role of chironomid larvae

Two Greek Pleistocene tufa stromatolites were examined petrographically and with stable isotope geochemistry to determine whether calcite spar is of primary or diagenetic origin. The younger (ca 100 ka) tufa from Zemeno primarily is micritic, with primary columnar calcite spar restricted to areas immediately above chironomid larval tubes. This relationship suggests that chironomid larval feeding behaviour is responsible for the development of Zemeno tufa columnar calcite, probably involving biological substances smeared onto the tufa surface. Most micritic crystals are not suitably oriented to allow later post‐depositional growth resulting in columnar fabrics. The older (ca 1 Ma) predominantly sparry tufa from Nemea contains some chironomid tubes and organic cyanobacterial filaments preserved in crystal fans but also contains many fabrics found in primary speleothem spar. Columnar spar here is unlikely to be the result of post‐depositional crystal growth. A comparison of stable isotopic trends between the two tufa deposits suggests that both contain interpretable seasonal trends and implies little or minor post‐depositional alteration of either tufa. Consequently, there is no basis for the common assumption that sparry tufa fabrics must be of diagenetic origin.     

方解石脉对中扬子地区沉湖土地堂复向斜油气保存单元的指示意义

野外观测表明,中扬子地区沉湖土地堂复向斜京山县城附近野外露头中二叠系和三叠系方解石脉主要是沿节理缝发育,脉体宽度较小。方解石脉的镜下微观的结晶特征、阴极发光特征、脉体穿插关系可以判断二叠系脉体大约有两期,三叠系脉体大约有三期。碳氧同位素值表明,三叠系方解石脉和围岩的氧同位素差值不大(Δδ18 O的差异范围为-0.19‰～4.12‰,平均值为1.9‰),二叠系方解石脉和围岩氧同位素差异较大(Δδ18 O的差异范围为4.07‰～12.03‰,平均值为7.3‰),三叠系脉体的流体直接来源于围岩,二叠系裂隙中方解石脉的形成过程中可能主要受到有机质的影响。方解石脉体中的流体包裹体均一温度在研究区建立的代表性虚拟井的埋藏史和热史基础上,推测二叠系方解石脉形成深度为3 000m～3 700m,形成深度约为2 000m～3 000m,两套地层中的方解石脉的形成时期为J3—K1燕山构造运动期。中扬子地区在多旋回的沉降和沉积过程中形成的上组合的区域性盖层(中三叠统—下侏罗统的泥质岩)在江汉平原区具有较好的封盖性。     

塔中上奥陶统方解石胶结物类型及其形成环境

通过对塔中地区上奥陶统数百块碳酸盐岩薄片和抛光面中各种方解石胶结物特征和成因的观察,并结合微量元素和碳、氧同位素分析,共识别出11种胶结物类型。详细描述了各胶结物的特征,并确定了胶结物的分布和形成次序。在此基础上对该区碳酸盐岩方解石胶结物形成环境进行了分析,共划分出海底成岩环境、大气水成岩环境和埋藏成岩环境。从而为该区孔隙演化史的建立和有利勘探目标预测提供了有力的依据。     

辽东半岛盖州市梁屯地区古元古代大理岩的碎屑锆石U--Pb定年及地质意义

通过地层对比、锆石LA--ICP--MS U--Pb定年及岩石地球化学研究限定胶—辽—吉活动带北东段辽东半岛盖州市梁屯地区一套碳酸盐岩建造的原岩形成时代、物质来源和地层归属等。其炭质方解大理岩锆石阴极发光(CL)图像显示碎屑锆石核部大都具有振荡环带,且其Th/U比值较高(Th/U=0. 15～2. 04),表明其为岩浆来源成因。锆石U--Pb年代学定年结果显示存在两个主要的年龄峰值,主要年龄峰值为新太古代晚期(2 560～2 500 Ma),次要峰值为古元古代中晚期(2 040～2 000 Ma),其沉积时限应晚于2. 0 Ga,与古元古代辽河岩群沉积时代一致。此外,该年龄与区域上的太古代基底和大量出露的辽吉花岗岩的年龄相一致,表明炭质方解大理岩物质来源于太古代基底和辽吉花岗岩。并通过岩相学、岩石地球化学、年代学和区域对比等研究,确认梁屯地区分布的这套富含炭质的大理岩建造(原岩为沉积石灰岩)可与辽河群高家峪岩组对比,而非前人认为的大石桥岩组。     

方解石负载羟基磷灰石复合材料去除水中铀离子的PRB活性介质研究

铀污染地下水分布于世界多国,其危害备受关注。本文基于溶胶-凝胶法制备方解石负载羟基磷灰石复合材料(CLHC),通过静态与动态对比试验,探讨了PRB活性介质对水中铀离子的吸附机理和去除效果。试验结果表明,制备的CLHC表面被羟基磷灰石覆盖,对铀离子具有较强的吸附能力。当U的初浓度为5.0 mg/L、试验周期为2 h、溶液pH值为4、CLHC用量为0.5 g/L时,CLHC可以吸附水中所有的铀离子。CLHC对铀离子的吸附过程可以用Langmuir等温吸附模型、粒子内扩散吸附动力学模型和准二级吸附动力学模型较好地进行描述。石英砂负载羟基磷灰石与CLHC相比,后者具有更强的吸附能力,而且具有更长的使用寿命。CLHC在吸附铀的过程中没有价态变化,其对铀离子的吸附主要为离子交换的化学吸附。本研究的成果可为可渗透反应墙被应用于铀污染地下水修复提供试验依据。     

致密砂岩层内强钙质胶结物成因机制及其意义——以鄂尔多斯盆地三叠系延长组长7油层组为例

通过岩心和薄片观察,利用荧光显微镜、阴极发光显微镜、同位素质谱仪、冷热台等设备,对鄂尔多斯盆地长7油层组强钙质胶结砂岩及其附近含油砂岩开展研究。结果表明：钙质胶结是致密砂岩储层含油非均质性的主要因素,胶结期次主要为一期;簇同位素揭示该期钙质胶结物的形成温度为18~42℃,对应地质时代为中晚三叠世—中侏罗世,为早成岩期产物,推测与盆地早期小规模构造运动相关;相邻的含油砂岩中油气包裹体伴生的同期盐水包裹体的均一化温度为90~120℃,结合盆地模拟揭示油气主要为一期充注,充注期为100~130 Ma,处于早白垩世;长7油层组不含油致密砂岩内钙质胶结物形成时间早于含油砂岩内石油的充注时间。