Paleoproterozoic Multistage Metamorphic Ages Registered in the Precambrian Basement Rocks at the Southeastern Margin of the North China Craton and Their Geological Implications

The Precambrian basement rocks in the Bengbu and neighboring areas, located at the southeastern margin of the North China Craton, occur as granulite terrains and xenoliths in the Mesozoic dioritic porphyry.

Crystallization Conditions and Petrogenesis of the Paleoproterozoic Basement Rocks in Bangladesh:An Evaluation of Biotite and Coexisting Amphibole Mineral Chemistry

The Paleoproterozoic （-1.73 Ga） basement rocks from Maddhapara, Bangladesh show a large range of chemical variations including diorite, quartz diorite, monzodiorite, quartz monzonite and granite. These are composed of varying proportions of quartz＋plagioclase＋K-feldspar＋biotite＋ hornblende±epidote＋titanite＋magnetite＋apatite and zircon. Amphibole and biotite, dominant ferro- magnesian minerals, have been analyzed with an electron microprobe. The biotite, Mg-dominant trioc- tahedral micas, is classified as phlogopitic nature. Relatively high Mg （1.33-1.53 pfu）, Mg^# （0.52-0.59） and low AIw （0.13-0.25 pfu） contents in the biotite reflect slightly fractionated magma, which might be a relative indicator for the origin of the parental magma. Biotite is also a very good sensor of oxidation state of the parental magma. Oxygen fugacity of the studied biotites estimate within the QFM and HM buffers and equilibrate at about -12.35 and -12.46, which exhibit the source materials were relatively higher oxidation state during crystallization and related to arc magmatism. Whereas, calcic amphi- boles, a parental member of arc-related igneous suite, display consistent oxygen fugacity values （-11.7 to -12.3）, low Al^# （0.16-0.21） with H2Omelt （5.6 wt.%-9.5 wt.%） suggest their reliability with the typical values of calc-alkaline magma crystallization. The oxygen fugacity of magma is related to its source material, which in turn depends on tectonic setting. Discrimination diagrams and chemical indices of both biotite and amphibole of dioritic rocks reveal calc-alkaline orogenic complexes; mostly I-type suite formed within subduction-related environments. Moreover, igneous micas are used as metal- logenic indicator. The biotites with coexisting amphibole compositions show an apparent calc-alkaline trend of differentiation. The study suggests that the trend of oxidized magmas is commonly associated with compressive tectonic and convergent plate boundaries.

The oldest basement rock in the Yangtze Craton revealed by zircon U-Pb age and Hf isotope composition

Here we report an integrated study of zircon U-Pb age and Hf isotope composition for a gneiss sample from the Kongling terrain in the Yangtze Craton. CL imaging reveals that most zircons are magmatic, and a few of them have thin metamorphic rims. The magmatic zircons gave a weighted mean U-Pb age of 3218±13 Ma, indicating the gneiss is the oldest basement rock in the Yangtze Craton found to date. They have εHf(t) value of -2.33±0.51,and two-stage Hf model age of 3679±49 Ma,indicating that the gneiss was derived from partial melting of >3.6 Ga crustal rock. The metamorphic rims yielded an age of 2732±16 Ma, implying that the metamorphic event occurred in the Neoarchean era, which may be also a major tectono-thermal event in the Yangtze Craton.

Petrology and Geochemical Features of Crystalline Rocks in Ora-Ekiti,Southwestern Nigeria

This research investigates and reports on the petrology and geochemical characteristics of crystalline basement rocks in Ora-Ekiti,Southwestern Nigeria.Exhaustive geological investigation reveals migmatite,banded gneiss,gran­ite gneiss and biotite gneiss underlie the area.In reducing order of abundance,petrographic examination reveals that migmatite contains quartz,muscovite and opaque minerals.Banded geniuses contain quartz,biotite,plagioclase,and opaque minerals.Granite geniuses contain quartz,plagioclase,biotite,microcline and opaque;while biotite geniuses contain biotite,plagioclase,opaque minerals,and quartz.Silica contents in migmatite(69.50%-72.66%;ca.71.23%),banded gneiss(71.66%-77.1%;ca.75.23%),biotite gneiss(72.32%-76.18%;ca.73.83%)and granite gneiss(69.82%-73.15%;ca.71.95%)indicate the rocks are siliceous.High alumina contents in migmatite(12.18%),banded gneiss(10.28%),biotite gneiss(11.46%)and granite gneiss(9.97%)are comparable to similar rocks in the basement com­plex.All the rocks show Ba,Sr and Rb enrichment.Harker diagrams of Al_(2)O_(3)versus SiO_(2)and CaO versus SiO_(2)show negative trends while Na_(2)O versus SiO_(2),K_(2)O versus SiO_(2)and TiO_(2)versus SiO_(2)plots showed positive trends.This var­iation probably depicts extensive crystal fractionation in the magmatic systems that produced the rocks prior to meta­morphism or partial melting of the precursor rock.SiO_(2)versus(Na_(2)O+K_(2)O)classifies the rocks as granite to granodi­orite.The rocks are high K-calc-alkaline and calc-alkalic on SiO_(2)-K_(2)O plot.This shows the rocks are potassic meaning that they are formed from a potassium-rich source.The plot of Al_(2)O_(3)/(Na_(2)O+K_(2)O)versus Al_(2)O_(3)/(CaO+Na_(2)O+K_(2)O)reveals the crystalline rocks are orogenic and originated from granitoid with meta luminous affinity.The rocks consist of gneisses of no economic minerals,but the petrology reveals them as common rocks typical of metamorphic terrains and geochemical features of the rocks reveal they are felsic and of granitic composition.

塔里木盆地东北缘吐格尔明背斜和阳北断裂带构造分析

吐格尔明背斜和阳北断裂位于塔里木盆地北缘,南天山山前库车褶皱冲断带的东段,两者均为基底卷入型构造。阳北断裂是一个反转构造,其变形历史可以追溯到侏罗纪—白垩纪的正断层;新生代构造反转,发生了多期冲断变形加速期,分别发生于白垩纪末—古近纪初、古近纪末—新近纪初、中新世早期、上新世和第四纪。吐格尔明背斜构造带是阳北断裂中新世早期及以后的冲断作用派生出来的一个次级基底卷入型构造变形带。它由吐格尔明背斜及其南、北两条呈背冲关系的逆冲断层组成。背斜核部元古宇变质岩出露地表;中、新生界直接不整合于变质岩之上,缺失全部古生界,说明研究区可能属于一个长期存在的古生代古隆起。

基底变质岩深部潜山储层构造裂缝发育特征及主控因素——以渤海湾盆地渤中B区块为例

构造裂缝是改善基底变质岩潜山储层物性、提高油气产能的关键因素,但对于基底变质岩潜山储层构造裂缝的发育特征及主控因素的多尺度综合研究较少。以渤海湾盆地渤中B区块为例,综合利用薄片、岩心和成像测井资料,系统总结了基底变质岩潜山储层构造裂缝的特征,明确了主控因素,揭示了构造裂缝有效性影响因素和发育模式。研究区构造裂缝主要发育剪性裂缝,张性缝次之,斜交缝和直立缝较发育;裂缝整体充填程度高,主要充填物为泥质,其次为碳酸盐类;识别出近EW向、NE—SW向、NW—SE向和NNW—SSE向四组构造裂缝,其中近EW向裂缝较为发育,说明印支早期的强挤压作用环境是裂缝大规模发育的关键时期。研究区构造裂缝主要受岩石力学性质、构造作用、风化作用、储层物性和岩性控制。构造裂缝有效性主要受控于最大水平主应力方向与构造裂缝走向的夹角、构造运动、裂缝充填以及溶蚀作用等因素。纵向上基底变质岩深部潜山的构造裂缝随着深度增加所受风化作用减弱,在内幕带中沿断层局部发育溶蚀孔隙;不同岩石力学性质的岩石发育裂缝程度不同,脆性指数较大的岩石裂缝发育程度较高。横向上背斜核部的构造裂缝线密度大于翼部,当储层孔隙度和渗透率处于合适范围时有利于构造裂缝发育。

Optimizing the Interpretation of Sub-surface Resistivity in Relation with Borehole Productivity in Basement Area Applied to Seno Province （Burkina Faso）

This study aims at identifying possible correlations between shapes, types of geophysical anomalies and borehole productivity according to geological and hydrogeotogical contexts. The methodology adopted was a two-pronged one--the first step sought to： （1） interpret the electrical resistivity values from horizontal profiling and vertical electrical sounding implemented in Seno province that preceded the drilling of 513 boreholes; （ii） interpret data from pumping tests carried out on boreholes having a discharge superior to 1 m3/h （＂positive borehole＂） by using Cooper-Jacob＇s method. In the second step, according to geology, authors tried to identify possible correlations between each of the qualitative geophysical parameters： ~shape of anomaly〉〉, tttype of anomaly〉〉 and ~〈type curve〉〉 on the one hand, and hydrogeological parameters such as discharge, alteration thickness, transmissivity and saturated level on the other. The results of this study have shown that the chances of having a positive borehole in Seno province are higher when the type of anomaly is TCC （80%）, shape of anomaly is ＂W＂ and when type curve is ＂H＂ （80%） for all geological formations. Granitic formations are those that record higher discharges while schists record high transmissivity values.

Timing of Metamorphism and Provenance of the Metamorphic Basement of the Xiangshan Uranium Orefield, Jiangxi Province, China

The origin, age and evolution of the Precambrian metamorphic basement of southern China provide useful insights into early crustal development. Here, we present new laser ablation-inductively coupled plasma-mass spectrometry （LA-ICP-MS） U-Pb age data for detrital zircons from five samples of the Precambrian metamorphic basement of the Xiangshan uranium orefield. Two of these samples, from the northern Xiangshan volcanic basin, yielded a total of 140 U-Pb ages that cluster within the Neoproterozoic （773-963 Ma; 79.3% of data points）, with the rest being scattered through the Paleoproterozoic and Mesoproterozoic, along with a single Archean age. These ages indicate that this basement material is associated with the Cathaysia Block. In comparison, the 172 concordant ages from the other three samples from the southern part of the Xiangshan volcanic basin cluster within the Neoproterozoic （767-944 Ma; 59.8%） as well as the Proterozoic （37.8%） and the Archean （2502-2712 Ma; 14.5%）. These samples are also free of zircons with Grenvillian ages, indicating that these units are associated with the southeastern Yangtze Block. Combining these data with the geochemistry of these units, which suggests that the metamorphosed sedimentary rocks within the northern and southern parts of the Xiangshan basin have a common component from a magmatic island arc that formed during the early Neoproterozoic, we infer that the basin was located along the boundary between the Cathaysian and Yangtze blocks. In addition, the zircons within the samples from the southern and northern parts of the Xiangshan basin show different pre-Neoproterozoic （963 Ma） age populations but similar post- Neoproterozoic zircon populations, indicating that the amalgamation of the Cathaysian and Yangtze blocks occurred after the Neoproterozoic （960 Ma）, with magmatism peaking at 830 Ma and rifting starting at -770 Ma, leading to the subsequent deposition （from bottom to top） of the Shenshan, Kuli, and Shangshi formations.

Metamorphism of the Basement of the Qilian Fold Belt in the Minhe-Ledu Area, Qinghai Province, NW China

The basement of the central Qilian fold belt exposed along the Minhe-Ledu highway consists of psammitic schists, metabasitic rocks, and crystalline limestone. Migmatitic rocks occur sporadically among psammitic schist and metabasitic rocks. The mineral assemblage of psammitic schist is muscovite + biotite + feldspar + quartz ± tourmaline ± titanite ± sillimanite and that of metabasitic rocks is amphibole + plagioclase + biotite ± apatite ± magnetite ± pyroxene ± garnet ± quartz. The migmatitic rock consists of leucosome and restite of various volume proportions; the former consists of muscovite + alkaline feldspar + quartz ± garnet ± plagioclase while the latter is either fragments of psammitic schist or those of metabasitic rock. The crystalline limestone consists of calcite that has been partly replaced by olivine. The olivine was subsequently altered to serpentine. Weak deformations as indicated by cleavages and fractures were imposed prominently on the psammitic schists, occasionally on metabasitic rocks, but not on migmatitic rocks. The basement experienced metamorphism up to temperature 606-778± and pressure 4.8-6.1 kbar (0.48-0.61 GPa), equivalent to amphibolite-granulite facies. The peak of the metamorphism is marked by a migmatization which occurred at several localities along the studied route 587-535 Ma ago. The basement also recorded a retrograde metamorphism of greenschist facies, during which biotite, garnet, amphibole, and pyroxene were partly altered to chlorite.

Fluid interaction mechanism and diagenetic reformation of basement reservoirs in Beier Sag, Hailar Basin, China

Based on analysis of core observation, thin sections, cathodoluminescence, scanning electron microscope(SEM), etc., and geochemical testing of stable carbon and oxygen isotopes composition, element content, fluid inclusions, and formation water, the fluid interaction mechanism and diagenetic reformation of fracture-pore basement reservoirs of epimetamorphic pyroclastic rock in the Beier Sag, Hailar Basin were studied. The results show that:(1) Two suites of reservoirs were developed in the basement, the weathering section and interior section, the interior section has a good reservoir zone reaching the standard of type I reservoir.(2) The secondary pores are formed by dissolution of carbonate minerals, feldspar, and tuff etc.(3) The diagenetic fluids include atmospheric freshwater, deep magmatic hydrothermal fluid, organic acids and hydrocarbon-bearing fluids.(4) The reservoir diagenetic reformation can be divided into four stages: initial consolidation, early supergene weathering-leaching, middle structural fracture-cementation-dissolution, and late organic acid-magmatic hydrothermal superimposed dissolution. Among them, the second and fourth stages are the stages for the formation of weathering crust and interior dissolution pore-cave reservoirs, respectively.

四川盆地东部寒武系油气跨层成藏及天然气勘探意义

四川盆地东部发育下寒武统筇竹寺组泥页岩烃源岩,其生成的油气向上能否穿越中下寒武统膏盐岩区域盖层,并在中上寒武统洗象池群储层聚集成藏(即油气跨层成藏),一直缺乏清晰的认识。为此,开展了洗象池群储层固体沥青和中下寒武统膏盐岩区域盖层封盖性等研究,探讨了油气跨层成藏及其天然气勘探意义。四川盆地东部洗象池群储层固体沥青主要来源于筇竹寺组泥页岩烃源岩;中下寒武统膏盐岩区域盖层封闭性良好,但在中二叠世至中三叠世,复活的基底断裂和新形成的规模较大的断裂使其封盖完整性遭受一定程度的破坏,为寒武系油气跨层成藏提供了重要的垂向运移通道。该区寒武系油气成藏经历了盐下早期古油藏(S_(3)—P_(1))、油气跨层成藏(P_(2)—T_(2))和古气藏(T_(3)—K_(1))等演化阶段;油气跨层成藏是多旋回叠合盆地油气成藏的重要特征,中二叠世至中三叠世复活的基底断裂和新形成的规模较大的断裂是寻找洗象池群原生古气藏的重要线索。确定和评价原生古气藏将是今后研究区洗象池群天然气勘探的重点和难点。

尖北气田基岩构造裂缝特征及其对储层的影响

裂缝是影响基岩气藏高效开发的关键因素。综合岩芯、薄片及成像测井资料,分析了尖北基岩气田构造裂缝分布规律,探讨了裂缝对储层质量的控制作用。构造裂缝以直立-高角度半充填-未充填缝为主,开启缝占比63.3%;裂缝走向主要包括近EW向、NW-SE向、NE-SW向和近SN向4组;上部层位以近EW向为主(占比80%),裂缝密度高、开度大,下部层位的裂缝多为NW-SE向和NE-SW向,裂缝发育不均,开度一般偏小;背斜高部位裂缝最发育,其次为构造斜坡和鞍部,断层控制区有效裂缝发育差。构造裂缝促进基岩风化淋滤作用,有效沟通次生孔隙,提升储层渗透率1~2个数量级,在基岩不整合面之下形成厚约40~150 m的优质储层。综合分析认为,构造高部位优质储层厚度大,控制了气井高产,是勘探开发部署的有利区,基岩不整合面下40 m之内风化淋滤作用强,是水平井钻探的有利靶区。

顺层岩质边坡动力响应及地基水平抗力研究

建立了坡顶存在高层建筑的顺层岩质边坡数值模型,以研究边坡地基对建筑地下室侧向约束作用。分析了岩质边坡地基在水平地震工况下的加速度响应规律、边坡变形机制以及地下室侧壁受力特征等。通过控制变量法分别分析地下室临坡距、边坡坡高、坡角以及结构面强度参数等因素对地下室约束作用的影响,并采用归一法对岩石边坡地基水平抗力系数进行敏感性分析。结果表明:在确保岩质边坡不产生沿外倾结构面发生滑动破坏的前提下,结构面强度参数对水平抗力系数影响较小,岩质边坡地基水平抗力系数主要影响因素的程度排序为:坡高>临坡距>坡角。

岩石地基地下室上浮事故原因分析及加固

聚焦于建筑物地下结构上浮问题,本文以某一建筑物的岩石地基地下室为上浮破坏工程案例,从工程施工工况和地下结构检测鉴定的角度,展开上浮事故原因分析及加固方案实施。结果表明,岩石地基的复杂性使之成为良好的渗流路径,加之提前停止降水、群锚破坏等因素,共同造成了建筑物上浮、构件开裂、结构受损等问题。加固时应严格按照设计和规范要求采取降水措施,合理布置抗浮措施,并应加强后期观测,避免造成更大的经济损失和社会影响。研究结果具有较好的科学意义和工程应用前景,可为类似的地下室上浮处理及抗浮锚杆施工提供参考。

露天煤矿顺倾软岩基底超前内排技术研究

针对顺倾软岩基底露天煤矿因边坡失稳引发的采剥失衡、采排失序等问题,选取蒙东地区典型软岩边坡露天煤矿作为研究对象,采用理论分析、数值模拟、稳定性验算等方法,对条带控制开采超前内排工艺展开研究。结果表明:条带控制开采区域上部开口宽度确定为65~70 m;条带控制开采区域下部开口宽度为25~30 m;内排土场超前内排后单台阶平盘宽70 m,坡面角45°,单台阶高12~24 m,并采用自下而上的逆序排土方式,停排高度为602 m;。

豫西地区金钼铅锌银矿集区成矿规律研究

豫西地区金钼铅锌银矿集区是我国多金属矿产资源的重要产地,属于东秦岭大型成矿带的东段。以金矿床及银铅矿为代表阐述了金钼铅锌银热液矿床的成矿规律(包括分布规律、矿床物质来源、矿床成因及花岗岩的成矿作用等内容),分析了矿床与构造的关系、地层物质组成的关系及与花岗岩之间的关系等,得出矿床的分布具丛聚性,而且矿集区具有小岩体成大矿的规律(金堆城钼矿、南泥湖钼矿、东沟钼矿、文峪金矿、东闯金矿),矿床成矿物质均来源于基底地层。燕山期花岗岩是各种矿产的高温高压热源的提供者,岩浆期后含矿热液为成矿物质向围岩及构造进行广泛充填、交代和沉淀成矿的关键载体。

内蒙古白云鄂博地区基底岩石锆石年代学及对构造背景的指示

白云鄂博地区的克拉通基底岩石主要由糜棱岩化花岗片麻岩(2588±15Ma),正长岩、花岗闪长岩(2018±15Ma)和黑云母花岗片麻岩、含石榴石蓝晶石花岗片麻岩(～1890Ma)等组成,白云鄂博超大型稀土矿床就位于华北克拉通太古代基底之上。太古代克拉通基底在早元古代中晚期(2.0Ga)又经历了一次强烈的碰撞造山运动,造成了闪长质与花岗质岩浆侵位,以及1.9Ga片麻岩相变质事件。

基岩油气藏的形成与分布

与成层性良好的沉积岩油气藏相比,基岩油气藏属于特殊类型的油气藏。在前人研究的基础上,结合辽河坳陷所发现的基岩油气藏,界定了基岩油气藏的内涵,梳理了全球基岩油气藏的分布特征,研究了基岩油气藏的形成条件与控制因素,提出了目前面临的问题。基岩油气藏包括基岩顶部风化壳油气藏和内幕油气藏2种类型,与构造特征明显的潜山相比较,其更强调岩性特征;全球已超过30个盆地中发现了基岩油气,主要发育在构造活动强烈的裂陷盆地、走滑盆地和前陆盆地;基岩油气来源于周围毗邻多洼陷的烃源岩层段,储层的储集空间分为顶部风化壳溶蚀孔洞和内幕网状裂缝系统,后者主要遵循"岩性优势序列"发育,圈闭发育存在纵向上的多重性和空间上的普遍性特点,源储接触方式分为垂向直接接触、侧向直接接触和间接接触3种类型,并依此建立3种油气成藏模式,受到多洼陷的烃源岩条件、多期次的断裂活动、广布性的圈闭条件和内外结合的沟通条件等控制;强调了基岩油气藏在内幕储层形成机制、油气成藏和油气水分布规律等方面存在的问题,为下一步基岩油气藏勘探指明了方向。

煤层渗透率影响因素综述与分析

文章详细地讨论了诸因素对煤层渗透率的影响 ,指出在常规情况下 ,有效应力、基质收缩等在煤层绝对渗透率诸影响因素中占据主导地位 ;并在以上分析的基础之上 ,提出了煤层气勘探开发的施工工艺中应该尽量避免渗透率的损失 ,或者尽量采用强化措施 ,对煤层进行改造 ,以提高渗透率 ,从而提高其开发能力。同时也指出了应加强对煤层孔隙度、渗透率的测定方法的研究以及煤层割理、孔隙发育机理的研究 ,为储层评价提供更为充分的依据。

华南基底变质岩的Sm-Nd同位素及其对花岗岩类物质来源的制约

华南地区存在两种类型变质基底。Sm-Nd同位素数据的研究结果表明,它们可分别代表华南两种类型元古代地壳端员。华夏地块区副变质岩代表成熟度较高的(早)元古代地壳端员,^(147)Sm/^(144)Nd=0.1198,^(143)Nd/^(144)Nd=0.511822;江南古岛弧区副变质岩代表成熟度较低的(中—晚)元古代地壳端员,^(147)Sm/^(144)Nd=0.1246,^(143)Nd/^(144)Nd=0.512170。根据上述数据得出了华南元古代地壳Sm-Nd同位素演化域,进而对华南不同时代花岗岩类的物质来源作了进一步的讨论。