Stratigraphy,structure and geochronology of ore leads in the Matsitama Schist belt of Northern Botswana

The Matsitama schist belt in northeastern Botswana comprises an area of metasediments, notably quartzites, limestones, shales and amphibolites that are bounded by granites and gneisses. The belt lies southwest of the Rhodesian cration and north of the Limpopo mobile belt.Stratigraphic, structural and lead isotopic evidence indicates that the Matsitama metasediments are equivalent to the Shashi metasediments in the Limpopo belt. There is strong evidence that the Matsitama and Shashi metasediments stratigraphically underlie volcanic rocks of the Tati belt which have been correlated with Archaean schist belts of about 2700 Ma of Rhodesia. Therefore, the Matsitama and Shashi rocks are at least as old as the schist belts of the Rhodesian craton and may represent a shallow-water facies that occurs only in the Limpopo area.There is no structural evidence that the Matsitama and Shashi metasediments were deposited unconformably on basement rocks, although the presence of gneiss, amphibolite and ironstone pebbles in a Matsitama conglomerate, as well as the presence of orthoquartzites, shows the existence of a basement source region. However, the surrounding granites intrude the Matsitama and Shashi metasediments and all underwent several deformation phases.The structural history of the Matsitama rocks can be described in terms of five phases of deformation. The main cleavage-producing deformation phase, F₂, folded the rocks into a major synform and intensely deformed them. Before this, however, the rocks had been folded and thrust so that part of the succession shows downward-facing F₂ structures and there are possibly repetitions of the stratigraphy due to imbrication. Structures of the F₃ and F₄ phases fold the main cleavage but locally are sufficiently intense to modify the shape of the finite strain ellipsoid. There is a major ductile shear zone of F₄ age, south of which F₄ folds are tight, while to the north, F₄ deformation is negligible. All of these structures can be correlated with deformation phases in the Tati schist belt to the east and in the northern part of the Limpopo mobile belt.Lead isotope evidence suggests that mineralization in the Matsitama metasediments occurred at least 2200 Ma ago, and that leads from Dihudi/Thakadu and Messina, in the centre of the Limpopo belt, underwent a two-stage history of events at 2600–2700 Ma and 2000–2100 Ma ago, agreeing with other geochronological evidence. The leads from Matsitama and Messina are isotopically distinct from leads from the Rhodesian schist belts, which show evidence of transfer to the crust some 3500 Ma ago. The absence of this 3500 Ma-old lead from the Matsitama and Messina environments may indicate different crustal conditions and possibly the absence of the Rhodesian-type early basement.     

Disequilibrium in co-existing clinopyroxene and garnet from blueschist-facies Fe-rich eclogites, Voltri Group, Italy

Abstract Clinopyroxenes and garnets from 11 blueschist-facies Fe-rich eclogite samples from the Voltri Group show a wide range of chemical compositions. Detailed analyses of single pyroxene and garnet grains show wide and scattered chemical inhomogeneity, the K_D(K_D= (Fe₂₊/Mg)^Gt/(Fe²⁺/Mg)^Cpx) ranges from 20 to 87 based on rim analyses only. The data obtained indicate that the mineral pairs never attained equilibrium under uniform P-T conditions and that the compositions of the metamorphic minerals were influenced mainly by the composition of the pre-metamorphic minerals and by topotactical reactions.     

青藏高原东部黄土沉积元素地球化学示踪

青藏高原东部广泛分布着典型黄土沉积,对气候变化有着敏感的响应。对青藏高原东部地区典型表土、黄土、古土壤以及砂样,进行系统的常量、微量元素组成分析,结果显示,高原东部黄土常量元素氧化物主要为SiO₂、Al₂O₃、Fe₂O₃和CaO,黄土中SiO₂和CaO含量差别较大;Rb、Sr、Ba、Zr、V含量占了微量元素含量的大部分,表土、黄土、古土壤微量元素含量差别不一。与高原东部的风沙沉积、黄土高原黄土、河西走廊黄土的对比结果表明,青藏高原东部黄土组分的常量元素之间的比值（SiO₂/Al₂O₃、TiO₂/Al₂O₃）、常量与微量元素之间的比值（Zr/Al、Zr/Ti）、常量元素三角图（Ca-Mg-K、Ca-Mg-Na）等与其他地区黄土有明显差异,而青藏高原东部黄土与高原表土沉积物及河流砂、风成砂样品比较接近。这些异同点指示青藏高原东部黄土与黄土高原黄土的物源不同;其物源可能主要来自于青藏高原内部,高原内部的河流沉积物、冰碛物等粉尘物质可能为青藏高原东部黄土的主要物源。     

重庆石柱二叠纪栖霞组地球化学特征及其环境意义

在对重庆市石柱县二叠纪栖霞组地层野外露头沉积特征研究的基础上,结合室内薄片观察,根据碳酸盐岩样品的元素含量、比值及相关性,探讨了栖霞组沉积地球化学特征与古环境意义.用于古环境分析的10件栖霞组样品SiO₂、MgO含量低,且两者具有较好的正相关性,Sr含量高,平均为1 751×10-6,Mn/Sr<0.1,Fe/Sr<1,δ18O_PDB>-10‰,表明成岩过程中样品几乎不受硅化及白云岩化作用的影响,未发生化学性质上的改变,可作为古环境分析的可靠对象.栖霞组碳酸盐岩CaO含量高,平均为53.81%,接近纯灰岩的理论化学组成,陆源元素Al₂O₃、TiO₂含量很低,平均值分别为0.17%与0.012%,表明其形成于陆源碎屑影响微弱的稳定古海洋环境.古气候指标MgO/CaO比值极低,平均为0.026,古盐度指标100×(MgO/Al₂O₃)比值高,平均为1 241,古水深判别指标Sr/Ba、1000×(Sr/Ca)比值高,平均值分别为286和4.54,指示了栖霞组碳酸盐岩为潮湿气候下的陆表海(远岸)沉积.古氧相地球化学指标U/Al、V/Al、Mo/Al、Cr/Al、Co/Al、V/(V+Ni)和U/Th特征一致表明栖霞组碳酸盐岩沉积于贫氧—缺氧环境.垂向上,陆源元素∑(Al₂O₃+TiO₂)含量逐渐降低,古水深指标Sr/Ba、1000×(Sr/Ca)比值逐渐增大,表明栖霞组沉积过程中离岸渐远、陆源供给逐步减少、水体持续加深.     

冀东秦家峪中元古界高于庄组锰矿成因: 来自矿物学和地球化学的制约

冀东秦家峪锰矿赋存于中元古界蓟县系高于庄组二段底部含锰岩系内,其成因尚不明确.以秦家峪锰矿ZK58-2钻孔样品为研究对象,通过显微薄片观察、电子探针分析及全岩地球化学分析等方法,探讨了高于庄组锰矿的锰质来源和沉积环境对成矿的贡献.显微薄片观察、电子探针分析表明,原生矿带中含锰矿物主要为菱锰矿、铁镁菱锰矿、钙菱锰矿、锰方...     

The Asama igneous complex, central Japan: An ultramafic-mafic layered intrusion in the Mikabu greenstone belt, Sambagawa metamorphic terrain

The Asama igneous complex comprises layered mafic and ultramafic plutonic rocks exposed over about 500×6000 m in the Mikabu greenstone belt, Sambagawa metamorphic terrain of Mie Prefecture; its margins terminate by faults, and there is no trace of chilled rocks. The exposed layered sequence is about 460 m thick, and includes dunite, plagioclase wehrlite, olivine gabbro and two-pyroxene gabbro. The crystallization sequence of essential cumulus minerals is olivine, followed by plagioclase and clinopyroxene together, and finally the appearance of orthopyroxene. Olivine systematically varies in composition from Fo₈₉ to Fo₇₈ with stratigraphic height in the lower to middle portion of the layered sequence. The composition of clinopyroxene changes from Ca₄₉Mg₄₆Fe₅ to Ca₄₀Mg₄₇Fe₁₃ upward in the layered sequence; cumulus orthopyroxene, which occurs at the top of the exposed layered sequence, has a composition of Ca₂Mg₇₄Fe₂₄. Cumulus chromite occurs as disseminated grains in peridotitic rocks, and tends to increase its Fe³⁺/(Cr+Al+Fe³⁺) ratio with stratigraphic height. The most aluminous chromite [Cr/(Cr+Al) = 0.48] occurs in dunite that crystallized shortly before plagioclase began to separate as an essential phase. The Cr/(Cr+Al) ratio of the most aluminous chromite, coupled with the crystallization order of essential minerals, suggests that the Asama parental magma was moderately enriched in plagioclase and clinopyroxene components in the normative mineral diagram plagioclase-clinopyroxene-orthopyroxene. It was similar to a Hawaiian tholeiite and different from the Bushveld and Great “Dyke” parental magmas that were more enriched in orthopyroxene component; it also differed from mid-oceanic ridge basalts that are more depleted in the orthopyroxene component. The Asama clinopyroxene and chromite show characteristically high TiO₂ contents and are also similar to those in Hawaiian tholeiites. The Asama igneous complex probably resulted from the crystallization of a magma of a Hawaiian (oceanic-island) tholeiite composition and formed in an oceanic island regime.     

不同成因类型煤型气地球化学特征及其判识意义

通过数理统计前人公开发表的国内外21个盆地或地区的324组煤型气地化数据, 分析不同成因类型煤型气地层分布和稳定碳、氢同位素组成及空间分布特征, 提出多个煤型气成因类型判识图版, 并以实例论证这些图版的可行性.研究结果表明: 与煤层相关的生物成因气不同于常规生物气, 最显著区别在于前者δ13C(CH₄)上限值低, 即生物成因气δ13C(CH₄)＜-60‰, 热成因气δ13C(CH₄)＞-40‰, 混合成因气δ13C(CH₄)介于二者之间.随着有机质演化程度增强, 从生物成因气至热成因气, δ13C(CH₄)、δ13C(CO₂-CH₄)、δ13C(C₂H₆-CH₄)及CH₄/(C₂H₆+C₃H₈)具有变重趋势且相关性明显, δ13C(CH₄)与δ13C(CO₂-CH₄)、δ13C(CH₄)与δ13C(C₂H₆-CH₄)及δ13C(CH₄)与CH₄/(C₂H₆+C₃H₈)是划分煤型气成因类型最可靠的图版.      

辽河盆地煤系地层中特高含量的二萜类及其地质意义

从辽河盆地东部凹陷下第三系沙三段煤系烃源岩中检出了特高含量的海松烷,脱氢松香烷等三环二萜烷和扁枝烷等四环二萜烷类化合物,此外还检测到了奥利烯、乌散烯等罕见的三萜类。上述三类化合物尽管出现在同一套地层中,但它们的主要来源并不完全相同,其中三环二萜和四环二萜类分别以裸子植物和蕨类植物为主要来源,而五环三萜类则主要来源于被子植物。说明辽河盆地下第三系沙三段煤系地层中母质输入的多样性和复杂性。     

Geochemical variations within a laminated evaporite deposit: evidence for brine composition during formation of the Permian Castile Formation, Texas and New Mexico, USA

The Upper Permian Castile Formation of the Delaware Basin in northwest Texas and New Mexico consists of up to 600 m of evaporites and is subdivided into units of anhydrite overlain by halite. The Castile Formation has commonly been interpreted as a deep-water, deep-basin deposit in which sediments were laid down in several hundred metres of water or brine. Recent textural observations within anhydrite units, in which the thick-bedded anhydrite horizons have been interpreted as being of shallow-water origin, have challenged this assumption. This geochemical study of the oldest anhydrite unit in the Castile Formation (the Anhydrite 1 Member) attempts to resolve some of the problems regarding brine depth and evolution in the basin. The Anhydrite 1 Member has been subdivided into five major cycles on the basis of the distribution of stratigraphic units of thick-bedded anhydrite.

Stable isotopic analyses of sulphur from anhydrite, and oxygen and carbon from calcite show that the basin waters were chemically homogeneous during precipitation of anhydrite, and do not indicate any significant input of meteoric, continental-derived waters. Throughout the section studied progressive enrichment of ¹⁸O upwards within cored intervals indicates continuous evaporation of the water body. Carbon isotopes appear to indicate fluctuations in organic activity within the cycles. Trace elemental analyses of Fe, Mg, Sr, Mn, Al, Ba, Zn, Pb and Cu from the sulphate fraction of the samples show a very high variability. There is a distinct increase in trace elemental abundances at the tops of cycles which may indicate variations in precipitation kinetics. Analyses of texturally defined cycles show that up-core trends for many of the trace elements correlate with changes in δ¹⁸O, indicating a progressive increase in the influence of evaporation. In addition, cyclical variations in trace elemental composition indicate changes in basin conditions with around a 350-year cyclicity. These changes are independent of δ¹⁸O values. The geochemical data do not provide conclusive proof of water depth during deposition of the Castile Formation. The data are interpreted as reflecting small-scale changes in conditions of deposition, despite the fact that water input remained essentially constant in terms of chemical composition.     

页岩解吸气地球化学特征及其影响因素分析——以四川盆地焦石坝地区JYA井为例

通过对焦石坝地区JYA井五峰-龙马溪组页岩岩心样品进行现场解吸，计算页岩的总含气量，同时分时段采集解吸气样品进行气组分和稳定碳同位素测定.研究结果表明：1）研究区含气量较高，成分以甲烷为主，为典型干气，含气量主要受控于矿物组成、有机碳含量和含水饱和度等；2）页岩解吸气组分随着解吸时间呈规律性变化，CH₄和C₂H₆含量逐渐升高，CO₂含量先降低后升高，N₂含量逐渐降低；3）解吸气中δ¹³C₁和δ¹³C₂会出现不同程度的分馏现象，主要受控于吸附-解吸过程；4）不同岩相页岩气解吸过程存在差异，在一阶解吸阶段，富泥硅质混合页岩样品的δ¹³C₁由重变轻，而富硅质页岩样品由轻变重，这可能由于富泥硅质混合页岩无机孔占主导，孔径较大，游离气占总含气量比例较大.     

页岩解吸气地球化学特征及其影响因素分析 ——以四川盆地焦石坝地区JYA井为例

通过对焦石坝地区JYA井五峰-龙马溪组页岩岩心样品进行现场解吸,计算页岩的总含气量,同时分时段采集解吸气样品进行气组分和稳定碳同位素测定.研究结果表明：1）研究区含气量较高,成分以甲烷为主,为典型干气,含气量主要受控于矿物组成、有机碳含量和含水饱和度等;2）页岩解吸气组分随着解吸时间呈规律性变化,CH₄和C₂H₆含量逐渐升高,CO₂含量先降低后升高,N₂含量逐渐降低;3）解吸气中δ¹³C₁和δ¹³C₂会出现不同程度的分馏现象,主要受控于吸附-解吸过程;4）不同岩相页岩气解吸过程存在差异,在一阶解吸阶段,富泥硅质混合页岩样品的δ¹³C₁由重变轻,而富硅质页岩样品由轻变重,这可能由于富泥硅质混合页岩无机孔占主导,孔径较大,游离气占总含气量比例较大.     

天然气运移地质色层效应机理和指标探讨

笔者采集了四川盆地威远和中坝气田沿水平方向剖面分布的气井中天然气、凝析油样品,进行了色谱和色谱-质谱分析表明,大部分组分参数向构造圈闭顶部递增,少数呈现递减趋势。认为这种组分分布是天然气（凝析油）渗流运移过程中地质色层效应的结果。笔者着重从分子极性、分子量和分子直径（体积）的角度探讨了参数递增或递减的机理。经过对化和筛选,认为凝析油ABI₁,参数和天然气△R₃参数是较理想的渗流运移专属性指标.     

Re–Os geochronology of organic rich sediments: an evaluation of organic matter analysis methods

Rhenium and osmium in organic-rich sedimentary rocks are dominantly hydrogenous, but any nonhydrogenous component will influence the accuracy and precision of the Re–Os date obtained. To minimize the influence of any nonhydrogenous Re and Os, we evaluate analysis of isolated organic matter from the whole rock, together with whole rock analysis using a CrO₃–H₂SO₄ digestion medium instead of inverse aqua regia, for a black shale unit of the Exshaw Formation, Canada. This unit previously returned a whole rock Re–Os date of 358±10 Ma (Model 3) [Geochim. Cosmochim. Acta (2002)] using inverse aqua regia dissolution. Organic matter isolated from the whole rock matrix using the HF–BF₃ technique [Org. Geochem. 20 (1993) 249] yields scattered data and a Re–Os date of 449±220 Ma (Model 3, MSWD=616). The organic matter analyses show similar ¹⁸⁷Os/¹⁸⁸Os values, but significantly lower ¹⁸⁷Re/¹⁸⁸Os values in comparison to the whole rock analyses. We show that the Re–Os systematics of organic matter are altered during chemical isolation, and as such we suggest that the HF–BF₃ method should not be used for Re–Os analysis of organic matter. Whole rock Re–Os analysis using a CrO₃–H₂SO₄ digestion medium yields significantly better regression analysis compared with the inverse aqua regia method, and the Re–Os data identify two distinct initial ¹⁸⁷Os/¹⁸⁸Os values for the sample set. Separate regressions of these data yield precise dates [366.1±9.6, MSWD=2.2 and 363.4±5.6 Ma, MSWD=1.6 (Model 3)], which are indistinguishable from the age constraints for this formation (363.4±0.4 Ma, U–Pb monazite). Comparison of the Re–Os dates obtained from aqua regia and CrO₃–H₂SO₄ methods suggests that the former may contain nonhydrogenous Re and Os, whereas the CrO₃–H₂SO₄ method dominantly liberates hydrogenous Re–Os from organic matter, allowing for better stratigraphic age determinations and evaluation of the Os isotope composition of seawater.     

Pipes of mafic pegmatite in the stratiform Fiskenaesset anorthosite complex, southwest Greenland

Pipes of hornblende gabbro and ultramafite cut across cumulate layering in the lower part of the Fiskenaesset complex. The pipes form irregular networks in which all vertical portions are massive and pegmatitic, whereas some horizontal portions are layered. Two kinds of layering occur: mineral-graded layers formed by precipitation of plagioclase and hornblende, and comb layers formed by the upward growth of tabular hornblende crystals. Alternations of these layers show that magma with plagioclase phenocrysts was flushed through the pipes in pulses, perhaps associated with erratic propagation of cracks and magmatic drilling.     

The late Cretaceous lithospheric mantle beneath the Central Andes: Evidence from phase equilibria and composition of mantle xenoliths

Temperature estimates and chemical composition of mantle xenoliths from the Cretaceous rift system of NW Argentina (26°S) constrain the rift evolution and chemical and physical properties of the lithospheric mantle at the eastern edge of the Cenozoic Andean plateau. The xenolith suite comprises mainly spinel lherzolite and subordinate pyroxenite and carbonatized lherzolite. The spinel lherzolite xenoliths equilibrated at high-T (most samples >1000 °C) and P below garnet-in. The Sm–Nd systematics of compositionally unzoned clino- and orthopyroxene indicate a Cretaceous minimum age for the high-T regime, i.e., the asthenosphere/lithosphere thermal boundary was at ca. 70 km depth in the Cretaceous rift. Major elements and Cr, Ni, Co and V contents of the xenoliths range between values of primitive and depleted mantle. Calculated densities based on the bulk composition of the xenoliths are <3280 kg/m³ for the estimated P–T conditions and indicate a buoyant, stable upper mantle lithosphere. The well-equilibrated metamorphic fabric and mineral paragenesis with the general lack of high-T hydrous phases did not preserve traces of metasomatism in the mantle xenoliths. Late Mesozoic metasomatism, however, is obvious in the gradual enrichment of Sr, U, Th and light to medium REE and changes in the radiogenic isotope composition of an originally depleted mantle. These changes are independent of the degree of depletion evidenced by major element composition. ¹⁴³Nd/¹⁴⁴Nd_i ratios of clinopyroxene from the main group of xenoliths decrease with increasing Nd content from >0.5130 (depleted samples) to ca. 0.5127 (enriched samples). ⁸⁷Sr/⁸⁶Sr_i ratios (0.7127–0.7131, depleted samples; 0.7130–0.7134, enriched samples) show no variation with variable Sr contents. Pb_i isotope ratios of the enriched samples are rather radiogenic (²⁰⁶Pb/²⁰⁴Pb_i 18.8–20.6, ²⁰⁷Pb/²⁰⁴Pb_i 15.6–15.7, ²⁰⁸Pb/²⁰⁴Pb_i 38.6–47) compared with the Pb isotope signature of the depleted samples. The large scatter and high values of ²⁰⁸Pb/²⁰⁴Pb_i ratios of many xenoliths indicates at least two Pb sources that are characterized by similar U/Pb but by different Th/Pb ratios. The dominant mantle type in the investigated system is depleted mantle according to its Sr and Nd isotopic composition with relatively radiogenic Pb isotope ratios. This mantle is different from the Pacific MORB source and old subcontinental mantle from the adjacent Brazilian Shield. Its composition probably reflects material influx into the mantle wedge during various episodes of subduction that commenced in early Paleozoic or even earlier. Old subcontinental mantle was already replaced in the Paleozoic, but some inheritance from old mantle lithosphere is represented by rare xenoliths with isotope signatures indicating a Proterozoic origin.     

Nd, O and Sr isotopic constraints on the origin of Precambrian rocks, Southern Black Hills, South Dakota

The Nd, O and Sr isotopic characteristics of Precambrian metasedimentary, metavolcanic and granitic rocks from the Black Hills of South Dakota are examined. Two late-Archean granites (2.5-2.6 Ga) have T_dm ages of 3.05 and 3.30 Ga, suggesting that at least one of the granites was derived through the melting of significantly older crust. Early-Proterozoic metasedimentary rocks have T_dm ages that range from 2.32 to 2.45 Ga. These model ages, in conjunction with probable stratigraphic ages ranging from 1.9 to 2.2 Ga, indicate that mantle-derived material was added to the continental crust of this region during the early-Proterozoic. Previous studies of the Harney Peak Granite complex have reported U-Pb and Rb-Sr ages of about 1.71 Ga and most granite samples examined in this study have Sr isotopic compositions consistent with that age. Two granite samples taken from the same sill, however, give two-point Rb-Sr and Sm-Nd ages of 2.08 ±0.08 and 2.20 ±0.20 Ga (∑²²⁰⁰_Nd = −15.5), respectively. In addition, whole-rock and apatite samples of the spatially associated Tin Mountain pegmatite give a Sm-Nd isochron age of 2000 ±100 Ma (∑²²⁰⁰_Nd = −5.8 ±1.8).

The Sm-Nd, O and Rb-Sr isotopic systematics of these granitic rocks have been complicated to some degree by both crystallization and post-crystallization processes, and the age of the pegmatite and parts of the Harney Peak Granite complex remain uncertain. Processes that probably complicated the isotopic systematics of these rocks include derivation from heterogeneous source material, assimilation, mixing of REE between granite and country rock during crystallization via a fluid phase and post-crystallization mobility of Sr. The Nd isotopic compositions of the pegmatite and the Harney Peak Granite indicate that they were not derived primarily from the exposed metasedimentary rocks.     

塔里木东北缘坡十Ni矿化侵入体中橄榄石和铬尖晶石对成岩成矿及源区特征的约束

坡十Ni矿化超镁铁侵入体的矿化岩相主要为第二侵入期次的（斜长）单辉橄榄岩、（斜长）二辉橄榄岩、 纯橄岩等岩相。坡十超镁铁岩的橄榄石成分变化范围较大, 橄榄石的Fo值在76.8～89.6之间, Ni含量为767×10^-6～4 580×10^-6。铬尖晶石的Mg^#值和Cr^#值变化范围分别为19.4～41.9和49.8～64.8, 原生铬尖晶石中Cr₂O₃和Al₂O₃表现为负相关, 蚀变改造的铬尖晶石则表现为正相关。橄榄石成分剖面显示坡十母岩浆处于一个动态的岩浆系统中, 成分稳定的新鲜岩浆的补给、 持续向上的动力及浅部橄榄石快速分离结晶,造成了不同深度橄榄石成分的不同变化。坡十侵入体母岩浆估算结果为MgO=14.49％, FeO=10.01％,模拟结果显示橄榄石中Ni含量的变化主要受橄榄石结晶分异和硫化物不混溶作用共同控制,其中橄榄石与硫化物熔体发生明显的Fe-Ni交换反应。坡十母岩浆中橄榄石分离结晶造成的硫饱和,是坡十硫化物熔离的重要因素。橄榄石高Fo值、母岩浆高MgO、超镁铁岩中斜长石发育、矿物高结晶温度和铬尖晶石成分的弧岩浆特征显示,塔里木东北缘坡十侵入体是俯冲交代的岩石圈地幔部分熔融形成的母岩浆的产物,表现出低压高温的演化特征,其中源区熔融机制可能与塔里木二叠纪地幔柱提供的热源或该区大规模拆沉作用造成的软流圈上涌有关。     

高温高压下超临界二氧化碳作用对花岗岩力学性质影响的试验研究

为了研究二氧化碳基增强型地热系统核心及邻近区域中超临界二氧化碳(ScCO₂)作用对岩石力学性能的影响,设计了纯ScCO₂与干燥花岗岩作用,ScCO₂、水蒸气与干燥花岗岩作用,ScCO₂与在水中浸泡了24 h后的花岗岩作用3种试验条件,每种试验条件下均开展了210、240、270℃温度下的试验。对ScCO₂作用后的岩样以及一个未经处理的对比样先后开展纵波波速测试以及单轴压缩试验,获得了岩石的纵波波速、单轴抗压强度以及弹性模量。纵波波速试验结果表明,在上述3种试验条件下,花岗岩样的波速会都会发生一定程度的降低。单轴压缩试验结果表明,ScCO₂作用后的岩石单轴抗压强度及弹性模量都几乎没有受到影响,但是从破坏模式看,未经处理的岩石以张拉破坏为主,处理后的岩石以剪切破坏为主,并且随着温度的升高剪切破坏越明显。试验结果说明,在不存在水或者仅有微量水存在的情况下,ScCO₂的作用对岩石产生轻微损伤,岩样的刚性减弱、塑性增强,导致其纵波波速有少量的下...     

辽西地区北票组烃源岩生物标志化合物特征的差异性

北票组是辽西地区重要的一套煤系地层,被认为是该区油气勘探的重要目的层.坤头营子剖面和卧龙剖面是该区较为有代表性的北票组地层剖面,对于研究北票组的沉积环境、有机质来源等具有重要意义.采用气相色谱-质谱（GC-MS）等技术对2个剖面的烃源岩样品进行了分析测试,结果显示两组样品表现出不同的地球化学特征.坤头营子剖面的烃源岩样品抽提物正构烷烃的质量色谱图均为单峰态,主峰碳数以C₁₉为主,姥鲛烷/植烷比值（Pr/Ph）在3.0~4.0之间;甾烷系列中以C₂₉甾烷为优势,C₂₃三环萜烷含量相对较低,伽马蜡烷指数低（平均0.08）.取自卧龙剖面的样品质量色谱图大部分呈现双峰态,Pr/Ph值低;甾烷系列中C₂₇占优势,萜烷系列中C₂₃三环萜烷含量高,具有较高的伽马蜡烷含量（平均0.23）,且各项生标成熟度参数均已达到异构平衡化阶段.结合样品的全岩分析显微组分分析结果,认为两者主要差异可能是剖面附近的侵入岩造成,北票组烃源岩有机质具有陆源高等植物和低等水生生物双重来源,以陆源高等植物为主.     

南沙海区曾母盆地地层系统

曾母盆地是南沙海区研究和勘探程度较高的盆地, 其地层系统一直是建立整个南沙海区地层系统的重要依据.然而由于盆地沉积厚度大和横向相变快等原因, 对曾母盆地的分层方案和地层时代的认识存在很大分歧.为了给曾母盆地甚至南沙海区的油气勘探中地层划分对比和地震剖面的解释提供基础依据, 在搜集整理和分析国外有钻井控制的地震剖面和分层方案的基础上, 提出了一个实用的、便于与南海北部盆地对比的曾母盆地地层划分对比方案.将中海油对南海北部诸盆地制定的一套地层界面编号系统和地矿部广州海洋地质局对曾母盆地地层的命名结合起来, 并根据国外在曾母盆地获得的钻探和联井地震测线资料对界面的时代作了一定调整, 将曾母盆地基底以上的地层划分为4组1群(曾母组、立地组、海宁组、南康组、北康群), 之间由5个重要不整合面(T_g、T₆₀、T₄₀、T₃₂、T₃₀) 相分隔.还将该方案与国内外其他方案进行了对比和讨论, 以供阅读有关资料时参考.为了方便将这套地层系统应用于地震剖面的解释和分析, 用实例显示了同一地层中由于地层相变而造成的地震相的巨大变化, 以及各重要不整合面的特征及其在地震剖面上的表现.