砂岩稀土元素地球化学特征在沉积物源区分析中的应用——以中国东北漠河盆地中侏罗统为例

详细取样分析显示,漠河盆地中侏罗统砂岩具有如下稀土元素地球化学特征:(1)绣峰组、额木尔河组和开库康组砂岩的稀土元素球粒陨石标准化配分模式均表现出轻稀土富集、重稀土亏损但具变化平缓和明显的Eu负异常特征;二十二站组虽呈现轻稀土富集、重稀土亏损但变化平缓的特征,但没有明显的Eu负异常特征,反映了砂岩形成时的物源有差别。(2)漠河盆地中侏罗统的物源主要来自于上地壳长英质源区,源岩可能为花岗岩、变质岩和沉积岩的混合;但二十二站组和额木尔河组时期还可能有来自下地壳或幔源的深部物质（基性岩）加入导致物源发生了变化。(3)漠河盆地中侏罗统物源区的构造背景为活动大陆边缘的岛弧环境。(4)Ce/Ce*和Ceanom指数显示漠河盆地中侏罗统的古环境为还原环境,对油气生成十分有利。     

伊犁盆地南缘中下侏罗统碎屑岩地球化学特征及对物源制约

对可地浸砂岩铀矿找矿和评价而言,明确赋铀砂体的物源是关键。伊犁盆地南缘中下侏罗统为重要砂岩型铀矿赋矿层位。来自盆地南缘坎乡苏阿苏沟中下侏罗统剖面碎屑岩岩石学及地球化学特征分析,对该套碎屑岩物源区特征及构造环境进行研究。下侏罗统八道湾组以杂色砾岩、含砾粗砂岩为主,颗粒具有较差的分选性和磨圆度。砾岩中可见块状层理,正粒序层理,砂岩中可见大型板状层理,砂岩主要为岩屑砂岩,岩屑成分主要为硅质岩屑和流纹岩岩屑;下侏罗统三工河组以细砂岩,粉砂岩,泥岩为主,细粉砂岩中可见沙纹层理,泥岩中可见到水平层理;中侏罗统西山窑组主要发育含砾粗砂岩-砂岩-泥岩组合,砂岩中发育大型槽状层理,平行层理,泥岩可见水平层理;来自该剖面19件样品的地球化学测试数据显示,该套碎屑岩具有较高的SiO_2(53.01%~85.52%,平均值为71.22%)和Al_2O_3(7.45~23.83%,平均值为13.96%),低TFe_2O_3+MgO(0.95~10.77%,平均值为3.64%)和TiO_2(0.20~1.32%,平均值为0.74%),其微量元素和稀土元素组成与上地壳相似,轻稀土富集,重稀土较平坦,铕亏损较明显。微量元素和稀土元素特征显示其物源来源于上地壳长英质岩石,母岩沉积构造背景为与大陆岛弧相关沉积盆地。结合前人资料,认为伊犁盆地南缘中下侏罗统物源可能来源于石炭系大陆岛弧环境下形成的岩石。     

鸡西盆地白垩纪碎屑岩地球化学特征及其对物源的制约

鸡西盆地白垩系包括下白垩统滴道组、城子河组、穆棱组、东山组、猴石沟组及上白垩统海浪组等。白垩纪碎屑岩主量元素地球化学特征具有高SiO2、低Fe2O3、FeO、MgO的特点,说明白垩纪碎屑岩的源岩主要为长英质岩石。岩石的稀土元素具轻稀土元素富集,重稀土相对亏损,具弱的负Eu异常,其特征类似于上地壳特征。白垩纪碎屑岩微量元素的含量与上地壳微量元素的含量基本一致。综合分析砂岩的常量元素、微量元素和稀土元素的地球化学特征和构造判别图解,可以认为,城子河组砂岩主要反映被动大陆边缘的源区构造背景,穆棱组砂岩反映活动大陆边缘源区背景,猴石沟组砂岩反映的源区为大陆岛弧源区构造背景。结合古水流方向和岩屑所反映的源区岩性特点,认为小兴安岭—张广才岭造山带构造杂岩是鸡西盆地白垩纪沉积碎屑岩的主要物源。但随着物源区剥蚀深度的增加,基底古老变质岩也占有相当的比重。     

虎林盆地北部坳陷中、新生代碎屑岩源区构造背景与物源区分析

虎林盆地北部坳陷地层包括下白垩统裴德组、下云山组、上云山组、珠山组，渐新统虎林组和中新统富锦组。北部坳陷砂岩-泥岩由常量、微量和稀土元素组成，揭示早白垩世砂岩-泥岩源区构造背景为活动大陆边缘，渐新统斗新统砂岩-泥岩多呈现出从活动大陆边缘向大陆岛弧转换的地球化学特征。结合沉积相特征和岩屑所反映的源区岩性特点，认为早白垩世时期物源主要来自于坳陷北部完达山造山带和南部古隆起；渐新统物源则主要来自盆地东北部的完达山造山带，并且碎屑岩的原始物质均来自上地壳。     

西昆仑塔什库尔干下-中侏罗统龙山组沉积构造背景分析

新疆塔什库尔干地区下-中侏罗统龙山组,位于最新填绘的唐盖河-新迭村构造混杂岩带（康西瓦构造带）的南侧,总体为一套青灰色-灰色碳酸盐岩-碎屑岩沉积,主要以泥灰岩和杂砂岩为主,源区岩石没有经过充分的搬运、分选,成熟度比较低。稀土元素特征表现为轻稀土元素富集、重稀土元素相对平坦和Eu亏损明显的特征,与典型上地壳非常相似;而微量元素质量分数也接近于大陆上地壳值;说明下-中侏罗统龙山组物源来自上地壳。沉积环境综合分析表明,龙山组沉积环境为浅海陆棚-近滨-前滨环境,表现出进积特征,总体为一个海退序列,反映了寒冷干燥的气候条件下,海平面下降、残留海盆收缩的沉积构造环境。从物源区构造背景来看,龙山组以活动大陆边缘为主,兼具大陆岛弧性质。结合区域地质构造背景,龙山组为羌塘地块和昆仑地块拼合之后形成的残留洋边缘沉积,其主要物源来源于其北侧的康西瓦构造带。     

Tectonic Setting and Provenance Analysis of Late Paleozoic Sedimentary Rocks in the Ordos Basin

鄂尔多斯盆地周缘物源均来自上地壳,以长英质岩石为主,主要为太古宇、元古宇的各类变火山-沉积岩组成的古老变质岩系,同时具有一定量的花岗岩和碱性玄武岩的混合,但物源成分及南北源区构造背景有所差异.在常量元素及稀土元素组成上,盆地南北物源区的沉积岩在地区及层位之间存在差异,且该变化符合大洋岛弧→大陆岛弧→活动大陆边缘→被动大陆边缘常量元素、稀土元素以及负Eu异常的变化趋势.常量元素变化分析表明盆地北部物源主要来自板块俯冲碰撞地带,与被动大陆边缘环境和活动大陆边缘环境相关,少数为与活动大陆边缘相关的岛弧构造环境有关,到晚古生代中晚期才逐渐与被动大陆边缘环境和活动大陆边缘环境相关.稀土元素对比分析表明,盆地北部物源与太古宙、元古宙的花岗片麻岩、闪长片麻岩、二长花岗岩、变余岩屑砂岩及千枚岩具有亲源性;而盆地南部早—中二叠世长期受被动大陆边缘物源影响,具有高SiO2,低Na2O的特征,这与太古宙—元古宙的太华群、秦岭群、宽坪群等岩系的高SiO2含量,K2O/Na2O＞1的特征一致,到晚古生代后期,逐渐与活动大陆边缘物源相关.北秦岭晚古生代山间盆地具有快速混杂堆积的沉积特点,属于盆地外缘,并与鄂尔多斯盆地呈连续过渡的状况,物源上具有继承关系;盆地晚古生代沉积岩中Gd含量及(Gd/Yb)N比值具有随时间迁移的特征,分析表明北部物源区在太原期处于构造快速活动期,而南部物源从山西期才开始进入快速活动期,这与区域构造演化背景一致,即北部物源区抬升要早于南部.     

右江盆地中三叠统细碎屑岩地球化学特征及其对物源区、构造背景的指示

右江盆地位于华南板块西南缘与印支板块的结合部位,于中三叠世沉积了一套以细碎屑岩为主的巨厚浊积岩。研究区中三叠统细碎屑岩的主量、微量和稀土元素分析表明,细碎屑岩以杂砂岩和岩屑砂岩为主,其源岩来自大陆上地壳,物源区岩石类型主要为长英质沉积岩和火成岩,岩石风化程度中等偏高,构造背景为大陆岛弧和活动大陆边缘。综合细碎屑岩稀土元素特征及前人对该区中三叠统古流向和碎屑锆石U-Pb年代学研究,认为中三叠统碎屑物来源复杂,云开地区、江南造山带和越北地块是主要的物源区。     

中侏罗世漠河盆地南缘构造特征及地质意义

通过对漠河盆地南缘地层层序、构造特征等进行的实际地质调查,认为漠河盆地南部盖层主要为中侏罗统的河流相、河漫滩相、湖相沉积岩以及上侏罗统和白垩纪火山岩,盆地南部受拉张作用影响,正断层、铲形断裂发育,盆地南缘具断陷盆地特征,盆地形成时间较长.同时厘定出漠河盆地南部边界位于绣峰林场二支线附近.     

大别山东南麓中新生代碎屑岩地球化学特征及其对物源的制约

位于大别山东南麓的安庆-潜山地区中新生代碎屑岩比较发育,主元素分析表明,砂岩主要为杂砂岩,其次是岩屑砂岩和长石砂岩。根据主元素、微量元素和稀土元素特征值分析结果,中、上三叠统和下、中侏罗统的源岩来源广泛,属于大陆岛弧、活动大陆边缘和被动大陆边缘构造背景,可能反映了前陆盆地物源的二元特征。古近系源岩主要为活动大陆边缘和大陆岛弧构造环境,说明物源仅来自大别山造山带。稀土元素比值及相关系数分析揭示,中晚三叠世黄马青群的源岩主要为宿松群的长英质片岩、浅粒岩以及大别杂岩,侏罗纪磨山组大致类似于大别群的花岗片麻岩,罗岭组与大别群比较类似。显示大别山造山带在中晚三叠世已经隆升并遭受剥露。     

鄂尔多斯盆地东南部中侏罗统延安组物源分析

中侏罗统延安组是鄂尔多斯盆地东南部的一套重要的含油气层系.通过对砂岩中碎屑岩成分、重矿物组合、石英的阴极发光及其泥岩微量地球化学等特征的研究,结合露头剖面古水流方向的测定,分析了鄂尔多斯盆地东南部中侏罗统延安组物源区的母岩性质、物源方向及其构造环境.结果表明,研究区延安组古水流和主要物源方向来自北东、北西方向.母岩主要为北缘阴山、东北缘吕梁山和西北缘阿拉善地区太古代及早元古代的花岗岩类、片麻岩系和浅变质岩系,并且推断这些地区从晚古生代开始,就长期为全盆地的沉积提供稳定的物源.这将对盆地的油气进行进一步勘探及开发和周缘地质构造研究具有重要的意义.     

湘东南汝城盆地性质及其对华南燕山早期构造环境的启示

湘东南汝城盆地为一早侏罗世—中侏罗世初期的陆相盆地。下侏罗统心田门组和高家田组主要为内陆湖泊—沼泽相碎屑岩沉积,夹有明显受地壳混染并具低钾高钠特征的板内拉斑玄武岩,表明早侏罗世汝城盆地为同造山上隆伸展裂陷盆地。中侏罗统千佛岩组与下伏高家田组为平行不整合接触关系。千佛岩组下部具类磨拉石沉积特征,上部局部含高家田组玄武质火山碎屑,地层呈西倾单斜式,盆地西缘为逆断裂所压覆等,表明中侏罗世初期汝城盆地为挤压收缩盆地,形成于造山构造环境。结合中生代地质构造发展框架及燕山早期晚阶段后造山花岗岩的大量发育等,认为湘东南及湘粤赣边区早侏罗世—中侏罗世初期属陆内同造山构造环境,中侏罗世早期—晚侏罗世为后造山构造环境。汝城盆地性质的确定对深入研究华南地区中生代构造演化具有重要的启示意义。     

中、上扬子北部盆-山系统演化与动力学机制

中国南方中生代经历了中国大陆最终主体拼合的陆缘及其之后的陆内构造演化。晚古生代末期,在秦岭—大别山微板块与扬子板块之间存在向西张口的洋盆,即勉略古洋盆。中三叠世末期开始,扬子板块相对于华北板块发生自南东向北西的斜向俯冲碰撞作用,扬子北缘晚三叠世至中侏罗世发育陆缘前陆褶皱逆冲带与前陆盆地系统。晚侏罗世至早白垩世,中国东部的大地构造背景发生了重要的构造转变,中、上扬子地区处于三面围限会聚的大地构造背景。在这种大地构造格局下,中、上扬子地区晚侏罗世至早白垩世发育陆内联合、复合构造与具前渊沉降的克拉通内盆地系统。自中侏罗世末期开始,扬子北缘前陆带与雪峰山—幕阜山褶皱逆冲带经历了自东向西的会聚变形过程及盆地的自东向西的迁移过程和收缩过程。扬子北缘相对华北板块的斜向俯冲导致在中扬子北缘的深俯冲及超高压变质岩的形成。俯冲之后以郯庐断裂—襄广断裂围限的大别山超高压变质地块在晚侏罗世向南强逆冲,致使扬子北缘晚三叠世至中侏罗世前陆盆地被掩覆和改造。     

Geochemical characteristics of a pre-Middle Jurassic oceanic crust fragment from the Central Pontides in northern Turkey: Geodynamic implications on intra-oceanic subduction initiation

The Central Pontides (northern Turkey) is one of the key localities to understand the geodynamic evolution of the Palaeo- and Neotethyan oceans. It consists of the pre-Jurassic basement units, the Early Jurassic and the Early Cretaceous accretionary complexes, the widespread Middle Jurassic continental arc magmatics and the Late Jurassic to Tertiary cover units. The Early Cretaceous accretionary complex is represented by the Central Pontide Structural Complex and includes the Middle Jurassic oceanic units, which were metamorphosed during the Early Cretaceous. Apart from these oceanic units, a few metaophiolite and serpentinite fragments have been recognized within the basement units, which may represent the remnants of an older ocean. The pre-Middle Jurassic Devrekani Metaophiolite is the largest oceanic fragment and tectonically intercalated within/between the Devrekani Metamorphics and the Çangaldağ Metamorphic Complex. It is mainly composed of harzburgites, dunites with chromite veins and metagabbros, and cut by metabasaltic andesites and metadacites. Petrographically, the gabbro consists mainly of plagioclase and clinopyroxene, and displays phaneritic/porphyritic texture. In contrast, the metabasaltic andesite includes plagioclase and mica phenocrysts within a fine-grained groundmass. Also, the metadacite is composed predominantly of quartz, plagioclase, and mica minerals. Two different magmatic groups belonging to completely different tectono-magmatic settings have been geochemically determined based on the immobile trace element systematics. The metadacites and metabasaltic andesites are akin to continental arc magmatics and characterized by negative Nb and Ta anomalies and depleted HFSE relative to Th and La contents. However, the metagabbro samples display the geochemical signatures of boninitic rocks and characterized by highly depletion in HFSEs and REEs relative to N-MORB. The Devrekani Metaophiolite in the Central Pontides may represent another remnant of pre-Middle Jurassic oceanic crust generation and can be north-eastward continuation of the Permian-aged Almacık complex and the Boğazköy Metaophiolite fragment in the western Sakarya Composite Terrane. It may have been cut by intrusions of the extensive Middle Jurassic continental arc magmatism after its imbrication within the basement unit. The presence of pre-Middle Jurassic oceanic units may indicate that the Paleozoic ocean may have survived as the Jurassic Intra-Pontide Ocean between the Scythian Platform and Sakarya Composite Terrane during the Mesozoic time. Thus, the Intra-Pontide Suture may normally include the Palaeozoic and Mesozoic remnants of the long-lived northward subducting Tethyan ocean.     

Multiproxy Paleosol Evidence for Jurassic Paleoclimate Fluctuations in the Sichuan Basin, SW China

Paleoclimate reconstruction of continental environments has been hampered by the limited evidence. A thick sequence of Jurassic continental deposits in the Sichuan Basin, Southwest China yields abundant paleosols that may offer valuable insights regarding Jurassic climate scenarios. A succession of 169 paleosols belonging to Protosols, Calcisols, and Argillisols from 23 detailed stratigraphic sections was recognized and characterized macro- and micromorphologically and assessed for mineral and geochemical compositions. Quantitative paleoclimate reconstructions using bulk geochemical proxies, the depth to and the stable oxygen isotopic composition of paleosol carbonates indicated a predominant alternation of semiarid and arid cool/warm-temperate climatic conditions punctuated by several episodes of subhumid and humid climates that generally prevailed in the Sichuan Basin during the Jurassic. The estimated paleoatmospheric CO2 concentrations (pCO2) from calcic paleosols yielded a low range of ~104 ± 58 to ~610 ± 152 ppmv during the Middle Jurassic. The terrestrial paleotemperature changes in the Sichuan Basin coincided with the pCO2 variations, which probably resulted from global geological events (e.g., volcanic activities, magmatic and oceanic events, and the ephemeral caps development) in the Middle Jurassic. Jurassic climatic fluctuations in the basin were likely attributed to true polar wander due to global plate motion, megamonsoon effect linked to global and regional paleogeography, and regional paleotopography.     

中亚及中国西部侏罗纪沉积盆地的构造特征

侏罗纪是中亚和中国西部地区沉积盆地主要形成时期,这表现在两个方面:(1)先期存在的盆地在此阶段沉积范围持续扩大;(2)形成了许多新的侏罗纪沉积盆地.本文通过对劳亚大陆南部侏罗纪特提斯北带构造特征、诸盆地早-中侏罗世岩相古地理和构造样式的分析,表明中国西部与中亚地区在侏罗纪时虽然都处于新特提斯北部被动大陆边缘,但由于受帕米尔弧向北推挤的影响,以及昆仑构造带与塔拉斯-费尔干纳断裂和阿尔金大型走滑断裂的存在,这两个地区的侏罗纪盆地具有完全不同的构造起因.以塔拉斯-费尔干纳断裂为界,西南侧中亚地区的侏罗纪沉积盆地主要是由新特提斯北部大陆边缘的被动伸展形成;东北侧中国西部的侏罗纪沉积盆地则主要发育于区域性挤压构造背景之下,形成的主要机制是重力陷落.此外,沿塔拉斯-费尔干纳断裂还存在几个侏罗纪的走滑拉分盆地.中国西部与中亚地区侏罗纪盆地的不同成因特征对盆地的比较研究和寻找侏罗系烃源岩都具有重要意义.     

Tectonics of the Aga Zone,Mongolia-Okhotsk belt

The structure and tectonics of the Aga Zone are considered. It is shown that this zone is a system of tectonic nappes thrust over the Argun microcontinent. The zone is composed of two rock complexes related to the Variscan and Kimmerian structural stages. The Variscan stage (Silurian(?)-Early Carboniferous) comprises structural elements that correspond to the continental slope; the oceanic basin proper; the active continental margin, including an accretionary wedge; and an island arc and backarc basin. The Devonian age of the ophiolites of the Shilka Belt is specified. The formation of this set of tectonic units is related to the Middle Paleozoic pulse of the opening of the Mongolia-Okhotsk paleobasin. The Kimmerian stage (Middle Carboniferous-Early Jurassic) is characterized by a different style of structural evolution. A system of separate troughs filled with flyschoid sequences was formed on the Variscan basement. The unstable setting related to shortening and closure of the paleobasin brought about the spatial migration of sedimentation zones and the development of intraformational breaks in sedimentation, as well as unconformities. This stage was completed in the Lias by the general uplift of the territory and the formation of Jurassic and Cretaceous mollase along its periphery. The Aga allochthonous mass was ultimately formed in the Middle Jurassic. This event is recorded in emplacement of Middle-Late Jurassic granitic plutons that blocked the nappes. The granitic-metamorphic layer was formed in the Paleozoic and Early Mesozoic at the margin of the Aga Zone upon its conjugation with the adjacent continental masses; this layer is related to crustal anatexis. The bulk of the granitic rocks of the Aga Zone were generated in the Middle and Late Jurassic due to the collision of the North Asian continent with the Argun microcontinent.     

澳大利亚北波拿巴盆地东北部侏罗纪古地貌及沉积相特征

利用二维地震和钻井、测井资料探讨了北波拿巴盆地东北部侏罗纪各时期的古地貌和沉积相特征。整个侏罗纪时期,研究区整体处于裂陷作用的构造环境,发育由陆相至海相的5个三级层序。早侏罗世早期的古地貌主要受控于北西向构造格局,沉积中心主要是北西走向的凹陷和向斜。早侏罗世晚期开始,北东向构造开始发育,同时盆地整体剧烈沉降,北西和北东走向的构造单元发生切割和冲突,导致其内部的构造分区十分零碎。中侏罗世末期盆地北部发生大面积抬升形成Callovian不整合,之后的构造活动比较稳定,同时北东向构造基本形成,研究区进入缓慢拗陷时期。在此构造演化背景下,北波拿巴盆地东北部在早—中侏罗世主要是陆相的河流相和冲积扇沉积,中侏罗世主要是海陆过渡相的扇三角洲和三角洲沉积,而晚侏罗世则主要是浅海和滨岸沉积。     

藏南聂拉木北部喜马拉雅山主脊带侏罗系重解

通过野外调查和地层系统校正,认为前人在该区划分的侏罗纪地层系统存在偏差。下侏罗统在喜马拉雅山主脊带南北两侧岩相变化较大,普普嘎组可能穿时;中上侏罗统岩相变化较小;侏罗系总厚度不超过1400m。中侏罗统鲕粒铁质岩所对应的岩石地层单元按命名先后原则应为定结组,形成于外陆棚环境,可能与全球侏罗纪海泛时期洋流涌入有关,代表特提斯喜马拉雅地区中侏罗世晚巴通期一次沉积地质事件;晚侏罗世基末利期在特提斯喜马拉雅可能存在与欧洲同期的缺氧事件。     

东南大陆边缘早侏罗世火成岩特征及其构造意义

东南大陆边缘早侏罗世火成岩主要呈双峰式火山岩、基性超基性杂岩体及A型花岗岩等形态产出。本文运用岩石学探针技术,通过早侏罗世火成岩岩石学与地球化学研究,并与晚中生代火成岩作对比,提出早侏罗世火成岩的形成与南岭东段近EW向张性断裂活动有关,标志着印支挤压造山的结束;之后东南大陆进入晚中生代NE向活动大陆边缘俯冲造山阶段,经历了挤压造山—剪切拉张过程,并在晚白垩世末期进入又一轮后造山拉张裂解阶段,即中生代时东南大陆边缘经历了早中生代(三叠纪—早侏罗世)和晚中生代(中侏罗世—晚白垩世)两期造山事件,其中早侏罗世的区域拉张作用是特提斯构造域向滨太平洋构造域转换的前奏,构造域转换可能始于中侏罗世(165Ma)。