全球白垩系烃源岩分布及沉积环境*

烃源岩是油气生成的物质基础,白垩系烃源岩以29%的比例居全球各层系之首。通过古地磁与地理信息数据耦合,以及对所有白垩系烃源岩层位数据的统计和对比,恢复了白垩系烃源岩的分布特征,分析了其发育环境。结果表明：(1)白垩系烃源岩主要发育于阿普特阶—土伦阶(占白垩系烃源岩的52 63%)。(2)白垩系烃源岩主要发育于2种构造、沉积环境：陆表海环境(非典型被动陆缘)和裂谷环境。(3)白垩纪早期,烃源岩干酪根以Ⅰ型为主;白垩纪中期,烃源岩干酪根过渡为以Ⅱ型为主,Ⅰ型较少;白垩纪晚期,Ⅲ型干酪根烃源岩迅速增多。(4)白垩纪大陆裂解边缘出现富有机质沉积,上升流促进生物繁盛,高温、干旱的气候使陆表浅海区盐度较高,其还原环境有利于烃源岩的保存。     

Cretaceous tectonic evolution of the Neo-Tethys in Central Iran:Evidence from petrology and age of the Nain-Ashin ophiolitic basalts

The Nain and Ashin ophiolites consist of Mesozoic melange units that were emplaced in the Late Cretaceous onto the continental basement of the Central-East Iran microcontinent(CEIM).They largely consist of serpentinized peridotites slices;nonetheless,minor tectonic slices of sheeted dykes and pillow lavas-locally stratigraphically associated with radiolarian cherts-can be found in these ophiolitic melanges.Based on their whole rock geochemistry and mineral chemistry,these rocks can be divided into two geochemical groups.The sheeted dykes and most of the pillow lavas show island arc tholeiitic(IAT)affinity,whereas a few pillow lavas from the Nain ophiolites show calc-alkaline(CA)affinity.Petrogenetic modeling based on trace elements composition indicates that both IAT and CA rocks derived from partial melting of depleted mantle sources that underwent enrichment in subduction-derived components prior to melting.Petrogenetic modeling shows that these components were represented by pure aqueous fluids,or sediment melts,or a combination of both,suggesting that the studied rocks were formed in an arc-forearc tectonic setting.Our new biostratigraphic data indicate this arc-forearc setting was active in the Early Cretaceous.Previous tectonic interpretations suggested that the Nain ophiolites formed,in a Late Cretaceous backarc basin located in the south of the CEIM(the so-called Nain-Baft basin).However,recent studies showed that the CEIM underwent a counter-clockwise rotation in the Cenozoic,which displaced the Nain and Ashin ophiolites in their present day position from an original northeastward location.This evidence combined with our new data and a comparison of the chemical features of volcanic rocks from different ophiolites around the CEIM allow us to suggest that the Nain-Ashin volcanic rocks and dykes were formed in a volcanic arc that developed on the northern margin of the CEIM during the Early Cretaceous in association with the subduction,below the CEIM,of a Neo-Tethys oceanic branch that was existing between the CEIM and the southern margin of Eurasia.As a major conclusion of this paper,a new geodynamic model for the Cretaceous evolution of the CEIM and surrounding Neo-Tethyan oceanic basins is proposed.     

辽东石庙沟岩体岩石地球化学特征、锆石U-Pb年龄、Hf同位素及其地质意义

辽东石庙沟地区位于华北陆块东部的辽吉造山/活动带上,该带经历了十分复杂的构造演化过程,记录了多期岩浆-构造-变质事件。石庙沟岩体为花岗斑岩,富SiO₂、Na₂O和K₂O,贫CaO、MgO及Al₂O₃,亏损高场强元素（Nb、Ti、Ta、P）,富集大离子亲石元素（K、Rb、Ba、U）,A/CNK值大于1,REE配分曲线呈"海鸥"式分布,以具有显著的负Eu异常为特征,高Ga/Al值,与典型A型花岗岩特征一致。花岗斑岩中锆石的LA-ICP-MS U-Pb测年结果表明其成岩年龄为（123.0±1.6）Ma,为早白垩世。锆石Hf同位素分析表明,ε_Hf（t）值均为负值,介于-15.72~-12.85之间,平均值为-14.14,二阶段模式年龄（T_DM2）在2 164~1 989 Ma之间,平均为2 067 Ma,反映源岩以大陆壳成分为主。结合花岗斑岩高SiO₂,低Mg、Co、Cr、Ni,且富集LREE和LILE,亏损HFSE等特征,表明早白垩世花岗斑岩岩浆应为大陆地壳物质熔融的产物。根据年代学和岩石地球化学研究认为,早白垩世花岗斑岩是古太平洋板块向欧亚大陆板块俯冲所形成的活动大陆边缘弧花岗岩。研究区早白垩世花岗斑岩的形成主要受太平洋构造域的影响,形成环境受板块俯冲造山后伸展作用和下地壳拆沉作用的联合制约,是辽东地区岩石圈减薄的直接证据。     

鄂尔多斯盆地白垩系沙漠相沉积特征及其水文地质意义

白垩纪鄂尔多斯盆地在燕山期抬升-沉降及气候演变的背景条件下,受水力、风力等地质作用,经历了早白垩世宜君-洛河期→环河期与罗汉洞期→泾川期两个沙漠沉积演化阶段。其中,洛河期和罗汉洞期是沙漠发育的两个主要时期,形成了旱谷、沙丘、丘间及沙漠湖等多类型沙漠亚相碎屑岩沉积。沙丘沉积砂岩作为白垩系沙漠相最主要的沉积岩石,具有分布稳定、厚度巨大、含盐量低、孔隙空间发育、储水性和透水性强等特点,不但具有良好的地下水赋存和循环条件,而且一般赋存着水质较好的地下水。     

北祁连造山带东段老虎山石英闪长岩成因及其地质意义

以北祁连造山带东段老虎山石英闪长岩体为研究对象，进行了锆石U-Pb年龄及全岩元素与Sr-Nd同位素组成的系统 测定，据此探讨了岩石的成因及其对北祁连构造演化的启示。锆石LA-ICP-MS U-Pb定年结果表明，石英闪长岩体的形成 年龄为440 Ma。岩石具有亚碱、准铝以及贫钙、镁、铁的特征，碱铝指数（AKI值） 均低于0.85，铝饱和指数（A/NKC 值） 多小于1.0，属钙碱性I型花岗岩类岩石。在稀土和微量元素组成上，岩石富集轻稀土和大离子亲石元素（如Rb、Cs、 Th和U），亏损高场强元素（如Nb和Ta），显示弧岩浆岩的地球化学特征。岩体具有相对均一的Sr-Nd同位素组成，初始Sr同 位素值为0.7058~0.7071，εNd(t)值为-1.06~-0.31。综合分析表明，老虎山石英闪长岩应起源于玄武质下地壳物质的部分熔 融，并在成岩过程中有少量幔源物质的混入。对区内火成岩地质地球化学特征与产出背景的全面分析，表明受北祁连洋俯 冲及随后岛弧与祁连—柴达木陆块碰撞拼贴影响，弧后盆地的北向俯冲消减作用可能是诱发民乐窑沟和老虎山弧岩浆岩以 及导致毛藏寺—老虎山花岗岩带内埃达克质岩石侵位的基本动力机制。     

Changes of Late Mesozoic Tectonic Regimes around the Ordos Basin (North China) and their Geodynamic Implications

A synthesis is given in this paper on late Mesozoic deformation pattern in the zones around the Ordos Basin based on lithostratigraphic and structural analyses. A relative chronology of the late Mesozoic tectonic stress evolution was established from the field analyses of fault kinematics and constrained by stratigraphic contact relationships. The results show alternation of tectonic compressional and extensional regimes. The Ordos Basin and its surroundings were in weak N-S to NNE-SSW extension during the Early to Middle Jurassic, which reactivated E-W-trending basement fractures. The tectonic regime changed to a multi-directional compressional one during the Late Jurassic, which resulted in crustal shortening deformation along the marginal zones of the Ordos Basin. Then it changed to an extensional one during the Early Cretaceous, which rifted the western, northwestern and southeastern margins of the Ordos Basin. A NW-SE compression occurred during the Late Cretaceous and caused the termination of sedimentation and uplift of the Ordos Basin. This phased evolution of the late Mesozoic tectonic stress regimes and associated deformation pattern around the Ordos Basin best records the changes in regional geodynamic settings in East Asia, from the Early to Middle Jurassic post-orogenic extension following the Triassic collision between the North and South China Blocks, to the Late Jurassic multi-directional compressions produced by synchronous convergence of the three plates (the Siberian Plate to the north, Paleo-Pacific Plate to the east and Lhasa Block to the west) towards the East Asian continent. Early Cretaceous extension might be the response to collapse and lithospheric thinning of the North China Craton.     

CFCs法在鄂尔多斯白垩系地下水盆地浅层地下水年龄研究中的应用

鄂尔多斯白垩系地下水盆地是中国重要的能源基地,利用CFCS方法对鄂尔多斯白垩系地下水盆地年轻地下水年龄进行测定,取得了比较准确的结果。结果表明,盆地地下水系统可以分为局部地下水系统、中间地下水系统和区域地下水系统。地下水盆地内局部地下水系统地下水循环更替快,年龄为20 a左右,地下水年龄随深度增加而增加;中间地下水系统和区域地下水系统地下水循环更替相对较慢,年龄大于70 a,可以寻求14C等其他同位素方法确定准确年龄。     

华北板块北缘勃隆克A型花岗岩锆石U-Pb定年及其地质意义

内蒙古翁牛特旗勃隆克岩体位于华北板块北缘,侵位于上侏罗系火山岩地层中。详细的岩相学研究显示,勃隆克花岗岩具有粒状结构、蠕虫结构和文像结构,块状构造,部分斜长石已绢云母化、泥化。对勃隆克花岗岩进行了LA-ICP-MS锆石U-Pb定年,获得134.0±1.8Ma和134.9±4.1Ma的侵位年龄,表明其形成于早白垩世。地球化学特征显示,花岗岩属于高钾钙碱性系列,有较高的SO2(74.1%~75.6%)、Na2O+K2O(8.98%~9.2%)、Rb(210×10-6~225×10-6)含量和10000×Ga/Al(2.69~2.80)、Rb/Sr(5.8~18.9)值,具有较低的CaO、MgO、Ba和Sr含量。铝饱和指数A/CNK=0.99~1.03,属于偏铝质或过铝质A型花岗岩。稀土元素球粒陨石标准化图解显示,轻稀土元素相对富集,负Eu异常明显;在原始地幔标准化图解上,Ba、Sr、Nb、Ta、P、T强烈亏损,富集Rb、Th、K、Hf等元素,与华北板块北缘早白垩世A型花岗岩类似。结合区域构造演化,认为勃隆克花岗岩形成于伸展构造背景。晚中生代,华北板块北缘构造体制经历了重大的转变,地壳从挤压体制转为岩石圈减薄和地壳伸展体制,软流圈物质上涌导致上覆地壳长英质物质的部分熔融形成勃隆克A型花岗岩。     

松辽盆地白垩纪地层时代划分

松辽盆地经多年来地质生产和科研活动,已经建立了一套完整的地层层序,由下往上为：沙河子组、营城组、登娄库组、泉头组、青山口组、姚家组、嫩江组、四方台组、明水组等９组２７个岩性段。白垩系的上限在明水组和依安组之间,相当于马斯特里赫特阶的顶界,同位素年龄为６６Ｍａ。白垩系的下限在沙河子组和火石岭组之间,相当于贝利亚斯阶的底界,同位素年龄为１４４Ｍａ。松辽盆地白垩系属陆相地层,三分性明显,自然划分为下、中、上三统,这种划分方案正被更多的地质工作者所接受。     

祁连山中段白垩纪以来阶段性构造抬升过程的磷灰石裂变径迹证据

祁连山作为青藏高原的东北边界,是研究青藏高原隆升和扩展的重要区域,利用磷灰石裂变径迹分析反映的祁连山地区白垩纪以来阶段性隆升和扩展新认识对理解青藏高原的隆升过程有重要的意义。分别采自南祁连陆块、疏勒南山—拉脊山缝合带、中祁连陆块和北祁连缝合带22个样品的磷灰石裂变径迹年龄介于(124±11)Ma与(13±2)Ma之间,平均径迹长度介于(13.6±2.3)μm和(10.3±1.8)μm之间。时间-温度反演模拟结果表明祁连山地区至少经历了3个重要构造活动阶段:1)白垩纪早期((129±14)~(115±17)Ma)祁连山隆升,南祁连陆块和疏勒南山—拉脊山缝合带的冷却速率及剥蚀速率均较大,并且祁连山南部可能率先抬升而初步构成高原的东北边界;2)白垩纪中晚期—中新世((115±17)~(25±7)Ma)祁连山构造平静,南祁连陆块和疏勒南山—拉脊山缝合带冷却速率及剥蚀速率均较低;3)中新世以来祁连山由南向北逐渐扩展,构造活动强烈而最终形成盆-山构造地貌格局。祁连山白垩纪早期的快速冷却过程可能是受拉萨地块和羌塘地块碰撞的影响;中新世以来向北扩展则主要是受印度—欧亚板块碰撞的影响。