Hydrologic and geomorphic processes in the Colville River delta, Alaska

The Colville basin drains the North Slope of Alaska and is one of several large Arctic river systems located within permafrost. The timing and style of fluvial processes in the earth's permafrost regions differ from those occurring in midlatitude settings. Moreover, in comparison to temperate-zone systems, rivers located entirely within permafrost perform most of their work during relatively short periods of time. This paper examines river ice hydrology and the resulting geomorphic processes that occur within the Colville delta, Alaska. Fluvial processes and landform development within the Colville delta occur after the flood-pulse is initiated by the breakup of river ice. During this 4-month period, the geomorphic processes are largely influenced by the movement of ice. The flood-pulse and accompanying river ice influences erosional and depositional processes and results in unique styles of sediment transport, deposition, and riverbank erosion.     

五台山区太古宙/元古宙界线划分及其地球演化意义

太古宙/元古宙界线代表地球演化历史上的重大事件,如何准确标定和划分这一界线对认识早期演化历史具有重要意义。区域构造及同位素地质年代学研究表明,华北克拉通新太古代构造演化明显滞后于欧美澳等克拉通,成为有利于建立太古宙/元古宙界线的关键地区。山西五台山区保留了较完整的新太古代-古元古代地层记录。先前研究主要依据该区地层、区域构造、叠层石记录进行界线划分,并对界线争议较多。本文在五台山区长期野外研究的基础上,通过对磨拉石沉积、同构造花岗岩、裂解环境相关玄武岩的综合探讨,建议这一界线划分在东冶亚群与豆村亚群之间。初步的同位素年龄制约表明,这一界线的时代介于2549±22Ma到2450±10Ma之间,与早期大陆克拉通伸展裂解、隆升剥蚀相关,并涉及岩石圈、水圈、大气圈性质的重大变化。     

南海大洋钻探及海洋地质与地球物理前沿研究新突破

南海是西太平洋地区规模最大且具有代表性的边缘海盆地之一。经过近几十年的研究积累,尤其是通过实施5个国际大洋钻探航次(1999–2018年)与国家自然科学基金委“南海深海过程演变”重大研究计划(2011–2019年),我国科学家获得了大量宝贵的第一手资料,取得了一系列创新进展与重大突破,标志着南海海洋地质与地球物理研究正走向国际前沿。重要研究成果包括:(1)新提出南海是“板缘张裂”盆地,与经典的大西洋型陆缘模式不同;(2)大洋钻探首次获取了基底玄武岩样品,结合中国在南海首次深拖地磁测量实验,精确测定了南海海盆玄武岩年龄,揭示南海海盆从东向西分段扩张;(3)大洋钻探结果发现南海陆缘岩石圈减薄之初岩浆迅速出现,未发现缓慢破裂造成的蛇纹岩出露;(4)发现南海扩张结束后仍存在大量岩浆活动,可能受控于多种构造与地幔因素;(5)地球化学证据与地球动力学模拟都显示南海岩浆的形成受到周边俯冲带的影响。目前我国的海洋地球科学正在进入崭新的发展阶段,有望以南海为基点,开始拓展到周边大洋,通过主导大型研究计划以及建设我国大洋钻探平台,以提升我国在南海、西太平洋与印度洋海洋地质科学研究的实质性影响力与引领地位。     

海南三亚中元古代变质砾岩的发现及其对Columbia超大陆裂解的指示

海南岛中元古代沉积记录对于探讨华南陆块早期大陆演化过程起关键作用。对海南三亚三郎岭地区奥陶系干沟村组砂岩-板岩组合中的变砾岩形成时代进行了重新厘定。碎屑锆石U-Pb同位素年龄分析结果表明,65颗锆石207Pb/206U年龄范围为2691~1350 Ma,且分成2691~2444 Ma、1838~1632 Ma、1540~1350 Ma三组,形成约1699 Ma、约1440 Ma 2个主要峰值和约2461 Ma的1个次要峰值。基于最年轻锆石年龄为1350 Ma,且没有出现海南岛常见的1250~1100 Ma和1000~900 Ma年龄记录,将该套变质砾岩沉积时代限定在1350~1250 Ma,而并非前人划属的奥陶纪,这是海南岛首次发现中元古代的砾岩建造。该套变砾岩砾石成分成熟度高、结构成熟度中等,表现为裂谷盆地高密度的碎屑流沉积特征,是研究区Columbia超大陆裂解晚期的沉积响应。变质砾岩与劳伦大陆西部的Belt-Purcell超群下部沉积地层具有相似的碎屑锆石年龄组成和年龄谱特征,暗示中元古代哥伦比亚超大陆中,海南岛与劳伦西部靠近。     

Middle-high latitude N2O distributions related to the Arctic vortex breakup

The relationship of N2O distributions with the Arctic vortex breakup is first analyzed with a probability distribution function （PDF） analysis. The N2O concentration shows different distributions between the early and late vortex breakup years. In the early breakup years, the N2O concentration shows low values and large dispersions after the vortex breakup, which is related to the inhomogeneity in the vertical advection in the middle and high latitude lower stratosphere. The horizontal diffusion coefficient （Kyy） shows a larger value accordingly. In the late breakup years, the N2O concentration shows high values and more uniform distributions than in the early years after the vortex breakup, with a smaller vertical advection and Kyy after the vortex breakup. It is found that the N2O distributions are largely affected by the Arctic vortex breakup time but the dynamically defined vortex breakup time is not the only factor.     

The structure,depositional style and accumulation characteristics of continental margin with diachronous breakup in the northern South China Sea

ABSTRACT

A typical diachronous breakup developed in the South China Sea (SCS); the breakup has been unequivocally identified, and gradually decreases in age from NE to SW. To illustrate the influence of a diachronous breakup on hydrocarbon accumulation, we used seismic profiles from CNOOC, and analysed crustal extension characteristics, sedimentary style and source rock accumulation. The main conclusions are as follows: (1) Because of the diachronous breakup in the SCS, various tectonic units developed in different positions on the northern continental margin with different degrees of extension. The Pearl River Mouth Basin (PRMB) is closer to the central sea basin of the SCS and has been affected by regional tension stress for a longer time. Tectonic units of proximal domain, necking zone, and distal margin types developed, and the crust structure thinned from the land towards the sea. The Qiongdongnan Basin (QB) is closer to the Southwest Sub-basin. There are symmetrical proximal domains on the southern and northern sides of the QB, with a necking zone in the central part. It presents as an abandoned passive continental margin. (2) The PRMB exhibited rifted cells first, followed by canyon type extensional faulting and horizontal axial transportation, and then by a longitudinal shelf-slope sedimentary style. But the QB has only rifted cells and canyon type faulting stages, no longitudinal shelf-slope sedimentary stage. The major source rocks in the northern SCS become younger from east to west, and the sedimentary facies change from lacustrine facies to marine-continental transitional facies. (3) The diachronous breakup process ultimately affecting oil and gas migration and accumulation process. The PRMB is dominated by deep-water shelf break accumulation with deep-water fan reservoir bodies. The QB is dominated by canyon type accumulation with channels.     

Rodinia超大陆构造演化研究的新进展和主要目标

概略评述了1997年以来国际上有关Rodinia超大陆构造演化问题的研究成果，并提出今后工作的主要目标。Rodinia超大陆的聚合造山发生在1300－1000Ma，基本形式表现为早期弧一陆碰撞和晚期陆－陆碰撞，并在1000－900Ma继以伸展作用。Rodinia超大陆的裂解发生于830Ma之后，但其过程具有明显的时，空分布不均一性，地幔柱可能是导致超大陆裂解的主要机制，大火成岩省”是地幔柱发育的关键性标志，已经初步证实裂解过程影响地球大气圈和水圈中二氧化碳的循环，进而改变晚前寒武纪的全球气候，控制生物圈的兴衰和岩石圈表层的碳酸盐，铁，锰和磷等沉积，这些现象可用“雪球化地球”（Snowball Earth)模式概括。     

塔里木盆地西北缘新元古代震积岩的发现及其地质意义

震积岩是地层中记录古地震事件的关键岩石记录,通过震积岩的识别和发育序列的研究有助于认识盆地形成的构造背景和区域大地构造过程。在塔里木盆地西北缘的乌什南部地区新元古界中识别出臼齿构造、微同沉积断裂和液化卷曲变形等古地震引起的软沉积变形构造,发育典型的震积岩（震裂岩和震褶岩）以及震浊积岩、冰碛岩和薄层状钙质泥岩等沉积单元,并在南华系上部形成了深水浊流沉积—冰水混积—地震活动和背景沉积—地震活动等两期震积作用序列。塔里木西北缘南华系震积岩与同时期正断层紧密伴生,共同指示区域构造伸展背景,可能与新元古代罗迪尼亚超大陆裂解、大规模裂谷作用有关。     

陕西周户地区“秦岭群”的解体

根据区内传统秦岭群包含不同原岩建造、不同变质岩石组合以及变形变质、副矿物和微量元素特征的差异，将其解作为丹凤岩群、深成侵入体、浅成一超浅成侵入体、片麻岩套等5个部分，首次区分出两类不同性质的混合岩，确认了秦岭群在该区的存在。     

开河期冰盖横向冰缝形成机理

春季随着流量或水位增加,冰盖底部受水流上举力作用发生弯曲,首先在岸壁附近形成纵向冰缝,破坏冰盖与岸壁的冻结,导致冰盖体中间部分与岸壁脱落分离。采用弹性基础梁的理论及计算方法,通过对冰盖体弯矩及弯曲应力分析,针对平面弯曲和垂直弯曲两种弯曲形式导致冰盖体横向冰缝形成机理进行了研究,并提出了横向冰缝间距的计算表达式。计算结果得到了实测资料的验证。研究结果表明,横向冰缝间距与开河初期冰盖宽度、厚度、冰的抗弯强度及地貌特征有关。