中扬子地区显生宙构造演化及其对油气系统的影响

中扬子地区作为南方海相油气勘探的重点战略区块 ,自基底形成至今 ,陆块南北经历了多期造山活动。其中 ,古生代以来的后四期造山作用控制与发育了区内海陆相四套含油气系统 ,加里东及印支早期造山作用利于原生海盆含油气系统的发育与形成 ;印支晚期—喜山期造山作用对其具有改造和破坏作用 ,但利于陆相含油气系统的形成。研究区海盆发育期形成的古隆起及其周缘斜坡带是海相残留盆地油气运聚与保存的有利场所     

Phanerozoic Paleomagnetism Characteristics of the Qomolangma Area in Tibet

This paper conducts systematic test research on the 2920 paleomagnetic directional samples taken from Ordovician-Paleogene sedimentary formation in the north slope of Qomolangma in south of Tibet and obtains the primary remanent magnetization component and counts the new data of paleomagnetism the times. Based on the characteristic remanent magnetization component, it calculates the geomagnetic pole position and latitude value of Himalaya block in Ordovician-Paleogene. According to the new data of paleomagnetism, it draws the palaeomagnetic polar wander curve and palaeolatitude change curve of the north slope of Qomolangma in Ordovician-Paleogene. It also makes a preliminary discussion to the structure evolution history and relative movement of Himalaya bloc. The research results show that many clockwise rotation movements had occurred to the Himalaya block in northern slope of Qomolangmain the process of northward drifting in the phanerozoic eon. In Ordovician-late Cretaceous, there the movement of about 20.0° clockwise rotation occurred in the process of northward drifting. However, 0.4° counterclockwise rotation occurred from the end of late Devonian epoch to the beginning of early carboniferous epoch; 6.0° and 8.0° counterclockwise rotation occurred in carboniferous period and early Triassic epoch respectively, which might be related with the tension crack of continental rift valley from late Devonian period to the beginning of early carboniferous epoch, carboniferous period and early Triassic epoch. From the Eocene epoch to Pliocene epoch, the Himalaya block generated about 28.0° clockwise while drifting northward with a relatively rapid speed. This was the result that since the Eocene epoch, due to the continuous expansion of mid-ocean ridge of the India Ocean, the neo-Tethys with the Yarlung Zangbo River as the main ocean basin closed to form orogenic movement and the strong continent-continent collision orogenic movement of the east and west Himalayas generated clockwise movement in the mid-Himalaya area. According to the calculation of palaeolatitude data, the Himalaya continent-continent collusion orogenic movement since the Eocene epoch caused the crustal structure in Indian Plate-Himalaya folded structural belt-Lhasa block to shorten by at least 1000 km. The systematic research on the paleomagnetism of Qomolangma area in the phanerozoic eon provides a scientific basis to further research the evolution of Gondwanaland, formation and extinction history of paleo-Tethys Ocean and uplift mechanism of the Qinghai-Tibet Plateau.     

显生宙碳酸盐岩中燧石结核的几种成因模式

显生宙以来,碳酸盐岩地层中有燧石结核产出的现象十分普遍。现有研究认为,硅质生物壳体是燧石结核最主要的硅质来源,随着地质历史上主要硅质生物类型的演变,燧石结核的产出环境逐渐从浅水变为深水。不同地区不同层位的燧石结核往往具有一些共同特征,包括呈孤立分散的结核状产出、硅质选择性交代方解石颗粒而保留晶形完好的白云石、硅质矿物具有隐晶硅质-微晶石英-粗晶石英的规律性变化等。基于上述主要特征及不同研究实例的特点,前人总结出了有机质氧化模式、半透膜模式、混合水硅化模式、重结晶应力控制交代模式等燧石结核成因模式,从不同角度对燧石结核的典型特征进行了解释。然而由于燧石结核成因的复杂性及其可形成于沉积-成岩的不同阶段,各个成因模式均存在一定的局限性,只可用于解释部分地质特征。鉴于燧石结核对研究区的沉积环境、成岩历史等具有很好的指示作用,对其成因的研究具有重要意义,尽管上述模式的提出时间较早,但针对特定问题的研究非常深入,在以后的研究中应加以借鉴。     

东北及内蒙古东部地区显生宙构造演化的有关问题

以国家油气资源战略选区项目研究成果为基础,结合近年来该区积累的大量区域地质调查资料和已发表的数据,对东北及内蒙古东部地区早古生代以来的大地构造性质及其演化进行综合对比分析。东北地区晚古生代以来的构造演化以稳定的大陆地块为主体,而非两大板块间多岛洋演化形成的造山带。东北地区的各地块均具有前寒武纪—早前寒武纪、甚至是太古宙的古老基底,它们在早古生代早期(490～510Ma)同时遭受了区域变质作用和花岗质岩浆侵入。350～450Ma,各地块均处于相对稳定的构造环境,以普遍缺失这一时期的花岗质岩浆活动记录为标志。从早古生代晚期开始,东北及内蒙古东部地区至少已存在2个早古生代早期固结的微陆块,即额尔古纳—兴安微陆块和松嫩—佳木斯微陆块,这2个微陆块向北分别与俄罗斯境内的额尔古纳微陆块和布列亚微陆块相连。二者在早石炭世沿北北东向展布的开鲁—嫩江—黑河—诺拉—索霍提(Nora-Soukhotin)一线碰撞拼合,形成统一的东北亚晚古生代大陆板块。西拉沐伦河断裂西端被北北东向构造所截,向东延至开鲁—嫩江断裂,并没有延伸到松辽盆地内,说明西拉沐伦河断裂可能与开鲁—嫩江碰撞带的形成有关。从晚石炭世开始,东北亚大陆板块整体处于伸展构造背景,至少在中国境内具有北陆南海的构造-沉积古地理格局,早期发育以火山岩为主的断陷盆地,到中二叠世演化成一个规模巨大的海相沉积盆地。中生代以来,东北地区的构造体制转换及物质成分演化不仅仅是古亚洲洋构造域和西太平洋构造域叠加转换的结果,蒙古—鄂霍茨克构造域的演化对该区现今构造体制的形成也具有重要影响。地质和地球物理综合证据显示,大兴安岭北部的得尔布干断裂、内蒙古中部的贺根山断裂和黑龙江省东部的跃进山断裂可能并不是具有一定深度规模的构造分区断裂。东北地区的中、新生代盆地之下并非都是变质结晶基底,而是存在一个规模巨大的晚古生代海相沉积盆地。     

The Paleoceanography during the Time with High δ13C of Phanerozoic marine carbonates

Carbon isotopic composition of marine carbonates is a record for various important geological events in the process of earth development and evolution. The carbonates of Carboniferous, Permian and Triassic, as the transition from Paleozoic to Mesozoic-Cenozoic have very high ¹³C value. Taking this as the main point, and combined with the oxygen, strontium isotopic composition in carbonates, distribution of carbonate basin area through geologic time, the correlation of carbon isotopic composition of marine carbonates to sea level change, organic carbon burial flux, exchange of CO₂ content in atmosphere and ocean, and long cycle evolution of the earth ecosystems were approached. The results are shown as follows: ①The interval of ¹³C >3‰ during Phanerozoic was concentrated in Carboniferous, Permian and the beginning of Triassic, but the beginning of Triassic was characterized by higher frequency and larger fluctuations in ¹³C value during a short time, whereas the Carboniferous-Permian presented a continuously stable high ¹³C value, indicating a larger amount of organic carbon accumulation in this time interval. Relatively high ¹⁸O values during this time was also observed, showing a long time of glaciations and cold climate, which suggest a connection among rapid organic carbon burial, cold climate, as well as pCO₂ and pO₂ states of atmosphere. ②The over consumption of atmosphere CO₂ by green plants during the time with high ¹³C of seawater forced CO₂ being transferred from ocean to atmosphere for the balance, but the decrease in the seawater amount and water column pressure caused by the global cooling could weaken dissolution capacity of CO₂ in seawater and carbon storage of marine carbonates, and also reduce the carbonate sedimentary rate and decrease the carbonate basin area globally from Devonian to Carboniferous and Permian. During the middle-late Permian carbonate was widely replaced by siliceous sediments even though in shallow carbonate platform, which resulted in the decrease of marine invertebrates, suggesting the Permian chert event should be global. ③The Phanerozoic ⁸⁷Sr/⁸⁶Sr trend of seawater showed a sharp fall in Permian and drop to a minimum at the end of the Permian, indicting input of strontium from the submarine hydrothermal systems (mantle flux). Such process should accompany with a supplement of CO₂ from deep earth to atmosphere and ocean system, but the process associated with widespread volcanism and rises of earth’s surface temperature pricked up the mass extinction during the time of end Permian. ④Cold climate and increase of continental icecap volume, the amalgamation of northern Africa and Laurentia continentals were the main reasons responsible for the sea level drop, but the water consumption result from the significantly increased accumulation of organic carbon should also be one of the reasons for the sea level drop on the order of tens of meters. ⑤The mass extinction at the end Permian was an inevitable event in the process of earth system adjustment. It was difficult for marine invertebrates to survive because of the continuously rapid burial of organic carbon, and of the decrease of sea water amount and its dissolution ability to CO₂. At last, at the end of Paleozoic, the supplement of CO₂ to atmosphere and ocean by widely magma activities resulted in a high temperature of earth surface and intensified mass extinction.     

年轻造山带洋板块地层*

重点分析和总结了由显生宙增生复合体和造山带混杂岩重建的年轻造山带洋板块地层--太平洋洋板块地层,也简要介绍了东古印度洋(东新特提斯洋)和古亚洲洋洋板块地层的重建情况。通过对阿拉斯加南部中生代增生地体、俄罗斯远东和中国东北侏罗纪-早白垩世增生复合体、日本二叠纪-侏罗纪-白垩纪等不同时期的增生复合体、菲律宾侏罗纪增生复合体和美国加州海岸山脉中侏罗世-古新世弗朗西斯卡杂岩体等不同单元的岩石学特征、古生物地层学、年代地层学、因逆冲导致的构造叠置和混杂失序特征及演化阶段的分析,重建了太平洋洋板块地层。其中加州海岸山脉中侏罗世-古新世弗朗西斯卡杂岩体的研究比较深入,对该区俯冲带上叠蛇绿岩(大峡谷群弧前盆地蛇绿岩)和弗朗西斯卡北部马林海岬杂岩体(原岩为洋中脊玄武岩)进行了有效区分,不仅还原了太平洋板块的俯冲碰撞过程,还厘清了与之伴生的弧前盆地裂陷和扩张过程。另外,板块俯冲的滞留和幕式增生在活动时间较短的板块俯冲体系中可能不容易识别。     

造山带金矿研究现状与存在的问题

造山带金矿是当前矿床学和大地构造学研究热点,Groves等(1998)、Goldfarb等(2001)基于太古"地壳连续模式"(Groves,1993)的研究工作以涉及资料量大、应用成果新、考虑地质因素多而居于这一领域前沿.但是,目前众多研究对前寒武地质与显生宙地质的宏观差异、世界金矿一些总体规律及若干具体大地构造背景等尚认识不足.显生宙缺乏太古代大规模火成活动,已知金矿中很少同变质深成型(hypozonal),以浅变质岩为围岩的金矿区中没有相当的中-深变质岩为围岩的金矿."太古绿岩带"金矿区同样也缺乏浅变质岩为围岩的金矿.华北地块周边金矿主要形成在侏罗-白垩纪,明显晚于大兴安岭造山带和秦岭-大别山造山带,而与欧亚陆缘近南北向燕山期岩浆弧有关.距俯冲带较远、缺乏蛇绿混杂岩与大规模变质作用、发育大量中-新生代盆地及广泛地壳减薄等表明,中国东部与北美科迪勒拉(Cordillera)造山带晚中生代地质存在宏观差异,燕山期岩浆弧可能形成于一个以伸展为主导的环境,大量以花岗岩为围岩或相对太古变质围岩后生成因金矿及其成矿的大地构造背景值得深入研究,弄清各类显生宙金矿与造山带的关系是推进造山带金矿研究的关键.     

显生宙全球海水化学成分演化及其对蒸发岩沉积的约束

通过搜集显生宙以来不同地质时期内海相碳酸盐岩鲕粒及胶结物矿物成分、钾盐矿床矿物种类及组合特征、蒸发岩盆地中石盐流体包裹体成分,并利用这些资料与人工海水模拟实验得到的石盐中Br分配特征的对比,得出海水成分在5.5亿年以来的显生宙期间,经历了五个阶段:其中晚元古代至寒武纪早期、二叠纪早期至中生代早期、新生代早期至现今,这些时期的原始海水组成特征系数m(SO_4~(2-))+m(HCO_3~-)/2m(Ca~(2+)),为Na-Mg-K-SO_4-Cl型海水,此期间沉积的钾盐矿床的钾镁盐矿物主要为钾盐镁矾、无水钾镁矾、杂卤石、硫酸镁石等含MgSO_4矿物,海相鲕粒和碳酸盐胶结物矿物成分为文石;而寒武纪早期至石炭纪、中生代早期至新生代早期,原始海水组成特征系数m(Ca~(2+))m(SO_4~(2-))+m(HCO_3~-)/2,为Na-Mg-KCa-Cl型海水,此期间沉积的钾镁盐矿物主要为光卤石和钾石盐,甚至含有溢晶石,海相鲕粒和碳酸盐胶结物矿物成分为方解石。根据石盐流体包裹体成分计算得出:显生宙期间,海水K+含量大部分时间变化幅度较小,为9.3～11.5mmol/kg H_2O(除了石炭纪和晚元古代),平均为10.55mmol/kg H_2O。Mg~(2+)含量在早寒武世≥67mmol/kg H_2O、晚志留世至中泥盆世31～41mmol/kg H_2O、晚古生代≥48mmol/kg H22O、晚白垩世34mmol/kg H_2O和现代55.1mmol/kg H_2O。Ca~+含量在晚元古代至古生代早期≤11mmol/kg H_2O、古生代早期至石炭纪22～35mmol/kg H_2O、石炭纪至中生代早期≤17mmol/kg H_2O、中生代早期至新生代早期19～39mmol/kg H_2O及新生代早期至今7～21mmol/kg H_2O。SO_4~(2-)含量在晚元古代至古生代早期≥23mmol/kg H_2O、古生代早期至石炭纪5～17mmol/kg H_2O、石炭纪至中生代早期13～22mmol/kg H_2O、中生代早期至新生代早期5～19mmol/kg H_2O及新生代早期至今12～29.2mmol/kg H_2O。海水Ca~(2+)与SO_4~(2-)含量的相对变化是控制海相钾盐矿床钾镁盐矿物类型的基本因素。同时,利用以上数据计算得到的显生宙各时期海水[m(Mg~(2+))+m(SO_4~(2-))]/[m(K~+)+m(Ca~(2+))]的变化与各时期海相蒸发岩系石盐层底部的Br含量变化具有同步性,进一步验证了显生宙期间海水成分是不断变化的,是约束海相蒸发岩钾盐矿物类型的主要因素。海水成分变化的控制因素为洋中脊热液和陆地水,其中洋中脊热液起主要作用,而控制这些因素变化的根本原因为板块构造运动。     

Were the hydraulic parameters of Precambrian rivers different?

Palaeohydraulic estimates have been made using time-tested standard empirical formula involving channel dimensions, especially channel depth, in four Indian Proterozoic fluvial formations. These are the Mesoproterozoic Ramdurg, younger Mesoproterozoic Muchkundi and Neoproterozoic Cave Temple Arenite in Karnataka, and Upper Rewa Sandstone in central India. The basic data came from direct measurement of decompacted thicknesses of completely preserved channel-fills or bedforms, and more commonly of cross-sets. The result, in combination with data derived by others in a similar way from a few other Precambrian fluvial formations helps to provide a new insight into the palaeohydraulics of Precambrian rivers.River gradients appear to have been steeper during the Precambrian; the possibly continuous range of variation in river gradients from alluvial fans to the plains, as a whole shifted to higher values during the Precambrian epoch. The likely reason is a greater possibility of sediment bypassing on vegetation-free land. Concomitant downstream increase in discharge was enhanced in Precambrian rivers due to lack of withdrawal of groundwater through biogenic activity. Precambrian rivers were commonly ephemeral, but downstream the ephemerality index was reduced and some rivers might have been perennial where they debouched into standing bodies of water. The Precambrian river deposits studied generally had smaller width and depth with respect to Phanerozoic and modern rivers, possibly due to unstable substratum causing surface run-off tended to be impelled along multiple independent minor channels.