贵州兴旺煤矿开采地表塌陷预测方法探讨

以贵州六枝特区兴旺煤矿地表塌陷为例,采用概率积分法作为地表移动及变形预测的模式,选取下沉系数、主要影响角、主要影响半径和水平移动系数为地表移动参数,计算得出井田开采后地表最大下沉值为1425．3mm,影响面积约1．85km^2。并比较说明除移动参数外各类煤柱的留设也是其中需要考虑的因素。     

新疆阿吾拉勒山西段穷布拉克铜矿床流体包裹体和碳氧硫同位素研究

穷布拉克铜矿床是新疆阿吾拉勒铁铜成矿带西段规模最大的一个铜矿床.本文对该矿床Ⅰ号矿体3种矿石中的方解石脉开展了流体包裹体和稳定同位素研究,结果表明:3种矿石的包裹体均为气液两相包裹体,流体体系为NaCl-H2O体系.包裹体的均一温度为85～343℃,盐度范围为(1.57～17.79) wt％NaCl eq.,密度为0.7～1.05 g/cm3.方解石的δ 13C值为-3.2‰～-6.5‰,平均-4.08‰,显示出幔源的特征.成矿流体的δ18O值为0.45‰～4.44‰.硫化物δ 34S值变化范围较大,为-10.5‰～5.5‰.Ⅰ号矿体与矿区内的火山热液型矿体具有相似的流体包裹体和稳定同位素特征,沉积特征不明显,并非沉积-改造型,与其他矿体具有相同的成因类型.成矿流体由火山热液和参与了水-岩反应的大气水两种流体混合而成,以火山热液占主导地位.矿物沉淀主要与流体混合后缓慢降温有关,但混合后的稀释作用以及水-岩反应导致pH值升高可能也起到了一定作用.     

云县-景谷火山弧带大中河晚志留世火山岩的发现及其地质意义

云县-景谷火山弧带大中河地区新识别出一套晚志留世中基性-中酸性火山岩组合,其LA-ICPMS锆石U-Pb年龄为421.2±1.2Ma和417.6±5.1Ma。该套火山岩具有富铝(12.73%～16.63%)、富钠(K₂O/Na₂O=0.56～0.99)和高Mg^#(46.0～50.0)的特征,属于钙碱性系列岩石;同时富集轻稀土,Eu具有不同程度的弱亏损,亏损高场强元素(Nb、Ta、Ti),具有正ε_Nd(t)值(3.86～4.39)和较高的Th/Ta比值(15～17),显示与活动大陆边缘岛弧型火山岩相似的地球化学性质。大中河晚志留世火山岩很可能是俯冲沉积物流体交代地幔楔物质部分熔融的产物,并在岩浆上升过程中经历了一定的分离结晶作用和浅部地壳物质的同化混染;结合区域同期(410～420Ma)岩浆活动及相关的高压变质事件分析,应为原-古特提斯洋在早古生代末期向东俯冲消减作用的产物,从而为扬子陆块西部边缘晚古生代"三江"多岛弧盆系的形成演化提供了前锋弧发育的岩石学证据及其动力学机制。     

浙江衢州新路火山岩盆地西段热点作用及其对铀成矿的控制作用

新路火山岩盆地是浙江省重要的产铀基地。文章通过对该区热点作用的研究,解释了该区铀矿床(点)的形成机制,以期获得该区铀矿找矿的新突破。地球物理资料显示,该区深部40 km处存在相对低速体的塑性体(地幔柱冠状体之上的幔枝构造),在其上部地层存在相对高速体的岩浆侵入体;中生代以来发育4次岩浆旋回;地层结构表现出下部为变质基底,中部为滑脱层,上部为上叠火山岩和白垩纪沉积盆地的三层式结构。热点作用的地质、地球物理特征明显。流体包裹体研究表明,成矿热液的温度为317~420℃,盐度w(NaCleq)为39.76%~49.68%,其成分为CO2及含碱、H2O、卤素、氮和一些金属元素,地幔流体特征明显,与铀矿伴生的微量元素及成矿同期的硫同位素也指示出成矿流体来源于上地幔或下地壳。地球物理和地球化学特征均指示出该区存在热点成矿作用,据此建立了该区的热点活动模式。文章认为,热点对该区铀成矿的控制主要表现为:①当深部基性岩浆运移至上地壳时,使硅铝质岩石发生部分熔融,形成酸性岩浆,喷出地表形成了新路火山岩,侵入时则形成次火山岩体和各类酸性侵入岩体,为成矿准备了有利的赋矿层位或有利围岩;②地幔柱上隆作用,形成或复活了一系列断裂构造,完善或形成了成矿所需的导矿构造和储矿构造;③地幔柱上隆时,提供了成矿所需的大量热能,造成围岩蚀变,从而萃取了围岩中的部分铀源;④随着酸性岩浆的不断分异结晶,岩浆中有用组分浓度不断增高,提供了深部热液中的成矿物质。     

吉林红旗岭1号和7号岩体中含矿超镁铁质岩的矿物化学特征:对岩浆演化过程以及铜镍硫化物矿床形成机制的约束

本文对吉林红旗岭1号和7号岩体中含矿超镁铁质岩的主要造岩矿物进行了详细研究。两岩体的主要造岩矿物为贵橄榄石、古铜辉石、单斜辉石、斜长石、角闪石和金云母。岩浆的暗色矿物结晶顺序为:橄榄石→斜方辉石→单斜辉石→角闪石→黑云母,与镜下实际观察一致,是岩浆在不同深度结晶的产物。原始岩浆来自上地幔,两岩体进入高位岩浆房中的熔体的MgO含量分别13.98%和14.22%、Mg#值分别为72.22和71.05,为含水的高镁的苦橄质玄武岩浆。深部岩浆房深度距地表约26～27km,岩浆房内的结晶温度介于1280～1379℃之间,即结晶于下地壳中。岩浆由深部上升到高位(浅部)岩浆房中的过程是近绝热的,也是快速完成的。岩浆可能经历了两次岩浆房的演化过程,岩浆在上升到高位岩浆房之前,在深部曾经历了较短时间的橄榄石和少量辉石的分离结晶作用;但在高位岩浆房中混染了地壳物质,与此同时,还经历了同源岩浆混合作用以及岩浆过冷却作用,这些都有利于岩浆体系中成矿元素含量增高以及硫达到饱和状态,使金属硫化物熔离并晶出,从而使岩体发生铜镍矿化作用。     

粤东地区早白垩世花岗质岩浆作用及其成因演化

粤东地区出露有大埔黑云母花岗岩、大埔黑云母钾长花岗岩和揭西黑云母钾长花岗岩3种岩石类型,大埔黑云母花岗岩和揭西黑云母钾长花岗岩的LA-ICP-MS锆石U-Pb年龄分别为136.3±0.6Ma和134.9±0.4Ma,属于晚中生代早白垩世,而非前人认为的晚侏罗世;3种岩石在主量元素上总体具有富硅、铝,碱含量中等,贫铁、镁、钙、钛、磷的特征,属于高钾钙碱性的弱过铝质岩石;大埔黑云母花岗岩的δEu负异常中等,具略向右倾的轻稀土富集模式,可能是由时代相当于元古宙的富砂屑岩部分熔融形成的;大埔黑云母钾长花岗岩、揭西黑云母钾长花岗岩具有中等—强的δEu负异常,稀土配分模式为海鸥型,二者在野外分布上紧密共生,时间上比较接近,在地球化学上表示出连续变化的趋势,具有相似的同位素组成,可能是由时代相当于元古宙的陆壳富泥质变质沉积岩部分熔融形成的,是同一岩浆演化到不同阶段的产物.     

青海东昆仑南坡成矿带铜钴矿预测中的主要科技问题

青海省东昆仑南坡金铜铅锌多金属成矿带经历了漫长而复杂的地质构造演化历史,产有丰富的金、铜、铅、锌、钼等金属矿产,但在铜钴矿预测中仍存在一些关键科学问题需进一步研究解决。本文在详述了区域地层、侵入岩、变质岩、构造、矿产等区域成矿地质背景的基础上,分析了青海东昆仑南坡成矿带地质工作程度低、研究程度低、成矿预测的基础科学问题不清、矿产勘查项目所引用的基础资料与研究工作所引用的基础资料明显不一致和主要矿床类型及预测方向等主要科学技术问题,探讨了该成矿带铜钴矿产预测现状与预测思路,从而提出了青海东昆仑南坡成矿带开展铜钴矿预测的工作方向。     

准噶尔盆地中拐地区石炭-二叠纪火山岩特征及构造环境分析

中拐地区位于准噶尔盆地西北缘,是在石炭纪-早二叠世挤压应力场作用下形成的宽缓鼻状古隆起。石炭-二叠纪火山岩是主要的含油层系之一,到目前为止已发现了多个油气藏和出油气点,显示出良好的勘探前景。根据系统、精细的地震资料解释,中拐地区在石炭-二叠纪时期主要存在4期构造运动,分别对应4个不整合面: 1)石炭系与二叠系之间; 2)二叠系佳木河组与下乌尔禾组之间; 3)二叠系下乌尔禾组与上乌尔禾组之间; 4)二叠系上乌尔禾组与三叠系百口泉组之间。通过对中拐地区石炭-二叠纪火山岩的全岩元素分析表明,该区域主要为中-酸性的安山岩、英安岩和流纹岩及火山角砾岩和凝灰岩为主,其中SiO₂的含量普遍较高,平均含量达到了67％,判定中拐地区的石炭-二叠纪火山岩喷发环境应位于岛弧体系的大陆内侧,在喷发过程中经历过陆壳的熔融作用。结合前人对周缘火山岩的研究,认为石炭-二叠纪时期中拐地区由岛弧环境逐渐进入陆内演化阶段,三叠纪开始进入稳定的沉积演化时期。     

Stratigraphic records of the dynamic uplift of the Emeishan large igneous province

Abstract

Fluid dynamical and numerical modelling predicts a large-scale regional domal uplift prior to basalt eruptions in large igneous provinces, which can be readily measured when a plume head rises below a shallow marine sedimentary basin. Research on the sedimentology, biostratigraphy, and isotopic chronology of the Emeishan large igneous province demonstrates that the sedimentary environment in the Maokou stage is not uniform carbonate platform facies, but rather sedimentary facies with a north–south linear alignment and west–east different distribution controlled by the syn-depositional normal faulting of the Changhai and Xiaojiang faults, which are the result of underwater dynamic uplift induced by deep mantle activity. The dynamic uplift started in the Maokou stage. Thus, thinning of the Maokou limestone was the product of the difference in the initial depositional thickness caused by the underwater uplift and post-depositional surface uplift and erosion, but post-depositional uplift was much less than kilometre scale. Sedimentary facies differentiation and tectonic–sedimentary evolution in the Maokou stage provide a constraint for the time of the initial eruption and eruption environment before and during the Emeishan basalt eruption. Small-scale magmatic activity might have already begun in the middle of the Maokou stage, whereas submarine and terrestrial sedimentary environments coexisted before and during Emeishan basalt eruption.     

Characteristics and genesis of diachronous Carboniferous volcano-sedimentary sequences: insights from geochemistry,petrology and U–Pb dating in the North Junggar basin,China

ABSTRACT

The subduction of oceanic lithosphere during the Carboniferous Period contributed to the formation of widely distributed subduction-related volcanic rocks within the Junggar basin. These volcanic rock associations contain significant clues for understanding the subduction of the Keramaili oceanic lithosphere and the filling of the remnant oceanic basin. Here, we report regional gravity and magnetic data, petrology, geochemistry, and U–Pb dating for Carboniferous volcanic rocks from the North Junggar basin (NJB). Using samples from well Y-1, we distinguish upper and lower volcanic sequences on the basis of selected geochemical data. An isochronous stratigraphic framework of Carboniferous volcano-sedimentary sequences is then constructed and the petrogenesis of these volcanic rocks is discussed. Finally, we propose an explanation for the genesis of these diachronous Carboniferous volcano-sedimentary sequences. The results show that various volcanic rocks are distributed in different areas of the NJB, and mainly consist of calc-alkaline basalt–andesite–dacite assemblages and alkaline basalt–basaltic andesite–andesite assemblages. The geochemical data also demonstrate a binary nature of the Carboniferous volcanic rocks. In the eastern NJB, the lower and upper volcanic sequences are formed during the early and late Carboniferous, respectively. However, all of these volcano-related sequences in the western of the NJB are formed during the late Carboniferous. These volcano-sedimentary sequences exhibit a ‘ladder-style’ of temporospatial evolution from east to west. The geochemical results also indicate that the upper volcanic rocks include island arc components formed in an extensional setting, whereas the lower volcanic rocks were derived from deep crustal cycling metasomatism by various mantle components in a continental arc environment. Earlier closure of the Keramaili oceanic basin and slab roll-back of the Junggar oceanic lithosphere in eastern versus western Junggar basin led to the formation of these diachronous volcano-sedimentary sequences.