扬子克拉通古元古代变质演化——来自黄陵穹窿石榴斜长角闪岩的证据

为探讨扬子克拉通古元古代变质作用特征及其形成的构造背景,对黄陵穹窿北部石榴斜长角闪岩开展了岩相学、地球化学和年代学研究。结果表明,石榴斜长角闪岩中主要矿物有石榴子石、斜长石、角闪石、单斜辉石、石英、钛铁矿等,其中保留有3个阶段的不同变质期次的矿物组合,进变质矿物组合为角闪石+斜长石+石英+钛铁矿,峰期矿物组合为石榴子石+角闪石+斜长石+单斜辉石+石英+钛铁矿,退变质矿物组合为石榴子石+角闪石+斜长石+石英+钛铁矿。石榴斜长角闪岩原岩为亚碱性玄武岩,属于拉斑系列,Mg^#较低,表明其原岩经历了一定程度的分异作用。使用传统地质温压计计算不同变质阶段的温压条件分别为：进变质阶段,t=596～625℃,p=0.70～0.82 GPa;峰期变质阶段,t≈760℃,p≈1.35 GPa;退变质阶段,t=692～738℃,p=0.68～0.74 GPa,并建立了一条顺时针的p-t轨迹,显示出先升温升压至峰期阶段,随后发生近等温减压的过程。这一p-t轨迹体现了汇聚板块边缘俯冲-碰撞的构造背景,对石榴斜长角闪岩中的锆石进行U-Pb定年,获得了2 008±11 Ma的谐和年龄,并结合该...     

Zircon U-Pb ages and provenance characteristics of the Zhiluo Formation sandstones and the formation background of the uranium deposit in Huangling area,Ordos Basin,China

The newly discovered medium-scale Huangling uranium deposit is located in the Shuanlong area of the southeast Ordos Basin. This paper presents the systematic geochemical and zircon U-Pb studies on the Zhiluo Formation sandstones in the Huanling area. The data obtained play an important role in deducing the provenance and tectonic setting of the source rocks. The results show that the lower part of the Zhiluo Formation is mainly composed of felsic sedimentary rocks. The source rocks originated from a continental island arc environment in terms of tectonic setting. U-Pb ages of detrital zircons obtained can be roughly divided into three groups: 170–500 Ma, 1600–2050 Ma, and 2100–2650 Ma. Based on the characteristics of trace elements and rare earth elements (REE) and the zircon U-Pb dating results, it is considered that the Cryptozoic Edo provenance of the Zhiluo Formation mainly includes magmatic rocks (such as granodioritic intrusions) and metamorphic rocks (such as gneiss and granulite) in the orogenic belts on the northern margin of the North China Plate and in the Alxa Block. Based on sedimentological and petrological results, it can be concluded that the provenance of clastic sediments in the Zhiluo Formation was in north-south direction. The preconcentration of uranium is relatively low in the Lower Zhiluo Formation in the Huangling area. Meanwhile, the paleocurrent system in the sedimentary period is inconsistent with the ore-bearing flow field in the mineralization period, which restricts the formation of large-scale and super-large-scale uranium deposits and ore zones in the southeast Ordos Basin. The understanding of provenance directions will provide crucial references for the Jurassic prototype recovery and paleo-geomorphology of the Ordos Basin and the prediction of potential uranium reservoirs of the basin.©2021 China Geology Editorial Office.     

鄂西地区陡山沱组页岩储层孔隙特征及影响因素

页岩储层孔隙结构是评价页岩气资源潜力的基础。本文基于有机碳含量、沥青反射率、X射线衍射、场发射扫描电镜(FE-SEM)及低温氮气吸附等方法,探讨鄂西地区震旦系陡山沱组页岩沉积组成、孔隙结构及其控制因素。结果表明:(1)陡山沱组为硅质和钙质页岩,TOC介于3.29%～6%,主要为I型干酪根,处于高-过成熟阶段;(2)陡山沱组页岩有机孔发育程度较低,无机孔提供主要储集空间,包括脆性矿物和黏土矿物的粒间孔、层间孔和部分溶蚀孔,以及少量微裂缝;(3)孔径分布范围为1.1～284nm,总孔体积平均为0.034ml/g,微孔、介孔和大孔体积分别为0.005ml/g、0.023ml/g和0.006ml/g,以介孔为主;(4)陡山沱组页岩TOC与孔体积无明显相关性,表明有机孔对孔体积贡献较小。硅质矿物和黏土矿物含量与页岩孔体积正相关性较好,表明矿物组成是陡山陀组页岩孔隙发育的主要控制因素。鄂西地区陡山沱组页岩具有良好的物质条件、生烃条件和页岩气储集空间,是潜在的页岩气勘探开发层系。     

Tectonic evolution of the Huangling dome and its control effect on shale gas preservation in the north margin of the Yangtze Block,South China

Significant breakthroughs of shale gas exploration have been made in Lower Cambrian and Sinian shale in the north margin of the Yangtze Block, South China. The drill wells with industrial gas flow located in the southern margin of the Huangling dome. Base on the geological survey, 2D seismic, geochronological and drill wells data, the tectonic evolution history of Huangling dome was studied, and its control effect on the preservation condition of shale gas was discussed. The result shows that the Huangling dome might undergo four tectonic stages: (1) About 800 Ma, granite intrusion in the Huangling dome basement, primarily of granites replaced metamorphism rocks; (2) 800–200 Ma, no significant tectonic movement with slowly buried history; (3) From 200 Ma, multi-phase uplift and the sedimentary rocks was eroded in the core of the Huangling dome. Shale gas in the Cambrian and Sinian strata was well preserved in the margin of the Huangling dome as the following reasons: (1) The Sinian shale was buried about 7.8 km in-depth during Middle Jurassic, source rocks have a suitable thermal maturity for shale gas; (2) The rigid basement of the Huangling dome was mainly composed by homogeneity granite, without intensive deformation. As the main challenges of the widely distributed Lower Cambrian and Sinian shale are high-maturity and intensive deformation, a geological unit with a dome probably is a favorable zone for the old age shale gas. Therefore, it indicates that the adjacent zone of the Xuefengshan, Shennongjia and Hannan are the geological units with a dome and probably have potentials for the exploration of shale in the Lower Cambrian and Sinian.     

长江三峡黄陵花岗岩与莲沱组凝灰岩的锆石SHRIMPU—Pb年龄及其构造地层意义

华南古陆普遍发育新元古代花岗岩,其时代、成因及其对华南新元古代的构造演化具有标识意义。该类型的花岗岩与华南克拉通的破坏及雪球事件的启动相关,其年代学研究一直备受关注,高质量的锆石SHRIMPU—Pb定年是确定其相互关系的基础。黄陵花岗岩体中的岩浆锆石的SHRIMPU—Pb加权平均年龄为837Ma±7Ma,另获得莲沱组顶部层凝灰岩较年轻的一组岩浆锆石SHRIMPU—Pb加权平均年龄724Ma±12Ma。前者表明黄陵花岗岩与桂北的三防、元宝山和云南的峨山花岗岩体侵位的时间相同,后者确定了莲沱组顶界的时代。这为确定南华系的年代地层学框架提供了重要的科学依据。     

角闪石全铝压力计对黄陵岩体古隆升速率的研究

采用矿物化学分析和角闪石全铝压力计方法,得到黄陵岩体中黄陵庙花岗闪长岩和三斗坪英云闪长岩的结晶压力为4.23×108 Pa和4.60×108 Pa,对应的侵位深度为14.6 km和15.8 km;结合已有的岩石年龄资料,可以得到新元古代黄陵岩体的古隆升速率约为0.09 km/Ma.结果表明,黄陵岩体在形成过程中,基底伴随有缓慢的隆升剥露.     

黄陵地区基性岩墙群的地球化学特征及其地质意义

黄陵地区的基性岩墙群主要由辉绿岩脉和辉绿玢岩脉组成, 走向主要为NEE向, 少量为NNW向.元素地球化学显示其为形成于板内拉张环境下的亚碱性玄武岩特征, 其很低的Mg# 指示为岩浆高度演化的产物, 同时Nb、Ta的亏损和Pb的富集表明其受到地壳物质的混染, 这说明可能是在拉张环境下由先前被俯冲带流体交代的地幔源重熔的结果.根据前人的年代学研究结果, 它形成于770Ma左右, 可能跟Rodinia超级古陆裂解构造背景相关.      

扬子板块北缘新元古代构造属性的岩浆事件制约

黄陵地区新元古代侵入杂岩可为研究扬子板块北缘新元古代构造演化过程及其深部动力学机制提供关键信息。依据岩石组合及分布特征,可将黄陵杂岩划分为黄陵庙岩套、三斗坪岩套、大老岭岩套和晓峰岩套四个单元。本文以黄陵杂岩的围岩崆岭杂岩中花岗片麻岩、黄陵庙黑云母花岗岩和三斗坪闪长岩为研究对象,在系统的野外地质和岩石学研究基础上,开展了LA-ICP-MS锆石U-Pb年代学分析。结果表明,崆岭杂岩花岗片麻岩原岩年龄为1978±13 Ma,且记录了2.5 Ga的构造-热事件。黄陵庙黑云母花岗岩和三斗坪闪长岩分别形成于815±9 Ma和813±6 Ma,与黄陵庙岩套和三斗坪岩套的侵位时限基本一致。综合分析本次研究结果与前人资料,认为黄陵杂岩主要形成于863～794 Ma,为新元古代早期岩浆活动的产物。通过综述区域地质和地球化学研究资料,认为黄陵杂岩形成于新元古代早期活动大陆边缘的构造环境,提出扬子板块北缘在新元古代早期经历了长期的俯冲-增生造山过程。     

黄陵二号煤矿充水因素分析

通过对黄陵二号煤矿充水因素的分析,结合矿井实际涌水量,认为矿井在开采延安组2号煤层时,延安组中部含水层为矿井的直接充水含水层,直罗组下段含水层为矿井主要的间接充水含水层;上部的洛河组砂岩水是矿井井筒充水的主要水源,也是矿井充水的间接充水含水层;矿井的主要充水通道为开采沉陷裂隙,充水方式为顶板进水。最后指出,该矿井开采2号煤层的最大隐患是直罗组下段砂岩顶板突水和井筒洛河组砂岩涌水。     

黄陵矿区2^#煤层煤岩及煤相特征分析

应用煤岩学与地球化学相结合的研究方法,探讨了黄陵矿区2#煤层的煤岩学特征及煤相类型。研究表明：2#煤层显微煤岩组分以镜质组为主,煤层从底部到顶部煤相由潮湿森林沼泽向开放沼泽过渡,包含五个次级演化层序,潮湿森林泥炭沼泽相是煤层煤相类型的主体,水动力条件较弱,成煤植物以木本植物为主,形成环境整体上为潮湿—覆水环境。