Morphological and microtectonic analysis of Quaternary deformation from Puná and Santa Clara Islands, Gulf of Guayaquil, Ecuador (South America)

This paper presents the neotectonic study of Santa Clara and Puná Islands sited in the Gulf of Guayaquil eastern part. Both islands are located on the south-western segment of the fault zone bounding to the east the North Andean Block. Fault motion and morphostructural analysis were carried out from Pleistocene age terrain. A two step deformation characterises the South Puná tectonics. The first step involves the Zambapala Cordillera uplift that post-dates Pleistocene sediments and pre-dates a marine terrace correlated with the M.I.S. 11 or 13 (440–550 ka). The second step is the formation of a pull-apart that shows evidence of 2.9 km dextral offset since the M.I.S. 11 or 13, giving an offset mean rate of 5.3 to 6.6 mm/yr. This rate is higher than the one calculated on the Pallatanga Fault northeast of the study area, in the Western Andean Cordillera, suggesting that deformation is split in different fault segments from the Gulf of Guayaquil to the continent. The Zambapala Cordillera uplift and transpression deformation requires a compressive event that may have been induced by the subduction process during the early Pleistocene.     

An interpretation and catalogue of paleoseismicity in Sweden

Paleoseismic data provide a long-term record of seismic activity to predict hazards for periods longer than one to a few centuries. In Sweden, the analysis reveals there was a drastic change in dominant seismic mode from a high to super-high deglacial mode to a low to moderately low mode in present and Late Holocene time. Paleoseismic criteria and characteristics include numerous different sources of information; viz. primary faults, bedrock deformation, sedimentary deformation, rock and sediment slides, liquefaction, sorting by shaking, tsunamis, differing geomorphic expressions, disordering and ordering of magnetic particles. By applying multiple criteria, it was possible to identify 44 paleoseismic events, including 23 events of estimated M 6–7, 12 events of M 7–8 and 6 events of M > 8. Varve-dating often allows a precision as to a single year, in one case even to the season of a year. The key for paleoseismic reconstruction and testing is the application of multiple criteria.     

青藏高原晚始新世干旱化事件：改则盆地康托组碳酸盐岩碳氧同位素的记录

改则盆地位于青藏高原腹地,盆地内沉积物记录了高原古环境变化的重要信息。本文对改则盆地康托组碳酸盐岩碳氧同位素进行研究,结果显示改则盆地中-晚始新世的演化分为两个阶段:1中始新世湿润气候下开放湖盆阶段:虽然碳酸盐岩δ~(18)O值在43层处向正值偏移,但整体~(18)O和~(13)C强烈亏损,并且该时期碳酸盐岩δ~(18)O值和δ~(13)C变化相关系数为R~2=0.082。表明该阶段的研究区虽然经历过短期蒸发作用增强或补给水减少,但整体是气候湿润条件下补给水丰富的开放型湖盆。2晚始新世干旱气候下封闭湖盆阶段:经过中新世晚期(63层)气候和湖泊水文状态的过渡,晚始新世~(18)O和~(13)C同位素富集,δ~(18)O值和δ~(13)C值变化相关系数为R~2=0.7762。表明该阶段气候干旱,蒸发作用强烈,湖盆萎缩成为封闭湖盆。综合前人研究,认为青藏高原腹地及北缘、东北缘在晚始新世存在明显的区域性干旱化事件。对比分析青藏高原隆升、全球气候记录、全球海水Sr和大气CO_2记录,认为青藏高原腹地和北部的干旱化事件主要受青藏高原隆升的影响。     

鲁西隆起和济阳拗陷耦合关系分析

通过分析鲁西隆起和济阳拗陷的地壳结构特征,结合二者的空间分布、时间演化及构造上的相关性,发现同处于伸展构造环境且相邻的鲁西隆起和济阳拗陷在地壳结构特征存在明显不同.济阳拗陷表现为地壳均衡的镜像结构特征,不同于地壳呈向上隆起状的鲁西隆起,说明鲁西隆起和济阳拗陷在成因上存在明显差异.济阳拗陷的伸展过程并非由地幔物质主动上涌造成,应是鲁西隆起在隆升过程对济阳拗陷地壳的拖拽作用,鲁西隆起和济阳拗陷的地壳结构特征反映出它们在成因上具有明显的耦合性.     

青藏高原新生代古高度研究：现状与展望

青藏高原新生代古高度研究是地球系统科学研究中的一个热点、难点和重点,它是解决地球深部动力学、地貌地形演化和气候变化等各部分相互关系的一个关键突破口。目前以古生物和氧同位素为代表的各种古高度计被用来重建青藏高原新生代的古高度历史,但是不同的研究方法所得到的结果并不一致,关于青藏高原何时隆升到现在的海拔高度存在晚上新世、晚中新世和始新世等不同认识。因为古高度结果的差异,所以对于青藏高原新生代的构造隆升过程和动力机制也存在大的争议。本文首先详细的阐述了部分古高度计的应用原理及其各自的优缺点,收集总结了78条青藏高原古高度研究的成果,梳理了目前青藏高原新生代古高度研究的历史和现状。然后在此基础上讨论了目前高原古高度研究的特点和存在的问题,即地层年代学、氧同位素和古生物古高度计结果的协调、“以点带面”、区域研究程度差异较大、替代性指标的多解性、古纬度影响、地质时期温度递减率的不确定性、全球气候变化的影响等特点和问题。最后就存在的特点和问题指出在恢复青藏高原新生代古高度时所需要完善和注意的方面,其中最重要的是注重地层年代学的可靠性。     

中国海相油气田勘探实例之五塔中奥陶系大型凝析气田的勘探和发现

塔中奥陶系碳酸盐岩的勘探始于1989年,直至2005年发现塔中Ⅰ号坡折带奥陶系碳酸盐岩凝析气田,探明加控制石油地质储量1.5×108t(油当量),是我国目前发现的第一个奥陶系生物礁型大油气田。油气的主力产层位于上奥陶统良里塔格组上部,储层为受坡折带控制的陆棚边缘礁滩体石灰岩。油气沿坡折带呈带状展布,为整体含油的大型准层状岩性油气藏。论述了塔中碳酸盐岩大油气田的勘探历程、主要地质特征,以及对海相碳酸盐岩勘探的启示。     

构造和气候共同控制下的藏南热隆盆地中更新世以来的演化

热隆盆地是亚东－谷露裂谷系南部, 由宁金抗沙西麓断裂控制的断陷盆地, 根据野外地质调查、 遥感(RS)和数字高程模型(DEM)分析, 盆地内发育有三期洪积扇, 形成时代分别在中更新世中期(第一期)、 中更新世中期至晚更新世早期(第二期)、 晚更新世晚期(第三期)。 这三期洪积扇的发育分别对应于间冰期和间冰阶的高温大降水时期, 表明在第四纪以来, 由于间冰期与间冰阶期的到来, 温度升高, 降雨量增加, 地表径流作用增强, 先成洪积扇被破坏, 新洪积扇形成。 盆地内自中更新世中晚期以来剥蚀程度自北向南减弱, 表明在整体抬升的背景下, 由于宁金抗沙西麓断裂的活动, 使得盆地北部基岩抬升速率大于南部, 形成自北向南的掀斜。     

东海陆架外缘区构造特征及其成因机制

东海陆架边缘的构造特征记录了有关冲绳海槽张裂过程的关键信息,对于进一步理解海槽的形成演化以及弧后张裂与弧-陆碰撞之间的相互作用至关重要。本文基于多道地震和重磁资料,分析了东海陆架边缘的地形和构造特征,并对冲绳海槽早期张裂过程、北西向断裂带的分隔控制作用、钓鱼岛隆起带南北构造差异和冲绳海槽的向西前展等问题进行了探讨。结果表明,冲绳海槽西侧陆坡存在的分段性,各分段在地形地貌、地层展布和构造特征等方面的不同,体现了其构造演化和现今构造活动性的差异。冲绳海槽中—北段的张裂始于陆架前缘坳陷,在晚中新世向东扩展至整个海槽,晚中新世至今以分散式张裂为主。北西向断裂带对东海陆架边缘不同分段的构造特征和构造活动起到了分隔控制和转换协调作用,控制了不同类型陆坡的形成和发育。受冲绳海槽在全宽度上向西前展的影响,钓鱼岛隆起带南段的基底隆起及其支撑的陆架边缘发生了破坏和沉降,形成基底起伏较大、地形崎岖不平的陆坡。     

Research achievements of the Qinghai-Tibet Plateau based on 60 years of aeromagnetic surveys

The Qinghai-Tibet Plateau (also referred to as the Plateau) has long received much attention from the community of geoscience due to its unique geographical location and rich mineral resources. This paper reviews the aeromagnetic surveys in the Plateau in the past 60 years and summarizes relevant research achievements, which mainly include the followings. (1) The boundaries between the Plateau and its surrounding regions have been clarified. In detail, its western boundary is restricted by West Kunlun-Altyn Tagh arc-shaped magnetic anomaly zone forming due to the arc-shaped connection of the Altyn Tagh and Kangxiwa faults and its eastern boundary consists of the boundaries among different magnetic fields along the Longnan (Wudu)-Kangding Fault. Meanwhile, the fault on the northern margin of the Northern Qilian Mountains serves as its northern boundary. (2) The Plateau is mainly composed of four orogens that were stitched together, namely East Kunlun-Qilian, Hoh-Xil-Songpan, Chamdo-Southwestern Sanjiang (Nujiang, Lancang, and Jinsha rivers in southeastern China), and Gangdese-Himalaya orogens. (3) The basement of the Plateau is dominated by weakly magnetic Proterozoic metamorphic rocks and lacks strongly magnetic Archean crystalline basement of stable continents such as the Tarim and Sichuan blocks. Therefore, it exhibits the characteristics of unstable orogenic basement. (4) The Yarlung-Zangbo suture zone forming due to continent-continent collisions since the Cenozoic shows double aeromagnetic anomaly zones. Therefore, it can be inferred that the Yarlung-Zangbo suture zone formed from the Indian Plate subducting towards and colliding with the Eurasian Plate twice. (5) A huge negative aeromagnetic anomaly in nearly SN trending has been discovered in the middle part of the Plateau, indicating a giant deep thermal-tectonic zone. (6) A dual-layer magnetic structure has been revealed in the Plateau. It consists of shallow magnetic anomaly zones in nearly EW and NW trending and deep magnetic anomaly zones in nearly SN trending. They overlap vertically and cross horizontally, showing the flyover-type geological structure of the Plateau. (7) A group of NW-trending faults occur in eastern Tibet, which is intersected rather than connected by the nearly EW trending that develop in middle-west Tibet. (8) As for the central uplift zone that occurs through the Qiangtang Basin, its metamorphic basement tends to gradually descend from west to east, showing the form of steps. The Qiangtang Basin is divided into the northern and southern part by the central uplift zone in it. The basement in the Qiangtang Basin is deep in the north and west and shallow in the south and west. The basement in the northern Qiangtang Basin is deep and relatively stable and thus is more favorable for the generation and preservation of oil and gas. Up to now, 19 favorable tectonic regions of oil and gas have been determined in the Qiangtang Basin. (9) A total of 21 prospecting areas of mineral resources have been delineated and thousands of ore-bearing (or mineralization) anomalies have been discovered. Additionally, the formation and uplift mechanism of the Plateau are briefly discussed in this paper.©2021 China Geology Editorial Office.     

迁安紫苏花岗岩的~(40)Ar/~(39)Ar年龄谱

对采自河北省迁安县水厂地区的紫苏花岗岩中的黑云母和紫苏辉石进行了~(40)Ar/~(39)Ar年龄测定,分别给出了18.7亿年和19.6亿年的~(40)Ar保存年龄。这两种矿物的年龄谱的视年龄的梯度变化表明,紫苏花岗岩形成后是缓慢冷却的。3.9亿年左右的一次热事件,造成了放射成因~(40)Ar的丢失。根据热历史和封闭温度的研究,从27亿年(侵入到该区紫花岗岩中的花岗闪长岩的锆石U-Pb年龄)到19.6亿年,紫苏花岗岩岩体的抬升速率为6.5m/Ma,但从19.6亿年到18.7亿年,其抬升速率高达111m/Ma,具有明显的构造抬升作用。