长江河口主槽地貌形态观测与分析

人类活动可以改变流域至河口的泥沙输运与沉积。尽管一些近期的研究已经调查了长江河口的形态演变,然而,流域和河口工程如何影响河口河床的形态演变仍然是不清楚的。该文利用2010年至2015年多波束测深系统和浅地层剖面仪等先进现场测量仪器的长江口主槽走航测量资料,并结合主槽表层沉积物资料,分析了近年来人为强干扰下的长江河口主槽底床微地貌形态,以理解近期人类活动对河口的影响。结果显示:近年来长江河口主槽底床上除了存在平床、沙波、冲沟和冲刷痕等常见微地貌形态外,还存在着疏浚痕和凹坑等人为微地貌形态。在流域和河口大型工程的共同影响下,近年来南北港中上段、横沙通道和南槽上段均受到不同程度的冲刷,其主槽底床上呈现出不同程度冲沟和冲刷痕等侵蚀性微地貌。而由于疏浚工程的影响,南港下段、圆圆沙航槽和北槽航道底床上出现了大范围的疏浚痕和凹坑。近年来包括南槽上段、北槽主槽中段和下段的局部区域和北港拦门沙河段局部区域在内的长江河口最大浑浊带的河床沉积物有粗化趋势。南北港中上段和横沙通道的大部分区域均发育了大量沙波微地貌;总体上,长江河口沙波的波高在0.12~3.12 m,波长在2.83~127.89 m,波高/波长在0.003~0.136,长江河口中上段的沙波尺度(波高的均值为0.91 m,波长的均值为20.08 m)大于密西西比河下游(波高的均值为0.87 m,波长的均值为17.62 m),且两区域沙波的几何形态差异性较小。     

广西近海灾害地质因素及声学反射特征

利用高分辨率地球物理资料及相关历史资料,对北部湾北部的广西近海灾害地质因素进行了地质地球物理解译,识别出海底沙波、海底沙脊、塌陷洼地、冲刷沟槽、浅层气、残积砂体、地层间断、埋藏丘、埋藏古河道等多种灾害地质因素.根据它们出现的频率、规模及声学特征可知:浅层气和埋藏古河道是广西近海最为发育的灾害地质因素,其对海洋工程的施工与建设有较大的危害性.     

华南埃迪卡拉(震旦)系顶部地层划分及与寒武系界线FAD分子的选择

"雪球事件"以来,早期生命呈现多层次、大规模的加速演化,到寒武纪前夕,生命大爆发达到高潮;在生命剧烈演替的同时,地球环境标志也发生着响应,碳同位素剧烈漂移,并且与各个生命演化节点相对应。但是在划分最重要的地质界线,埃迪卡拉(震旦)系——寒武系界线及界线层型和点位("金钉子",GSSP)确立的问题上迄今仍存在着较大的分歧,以遗迹化石Treptichnus pedum作为该GSSP的标志化石,因其跨系、跨阶产出,生物延限长,因而在全球的生物地层划分对比中(特别在西伯利亚和中国华南地区)一直质疑声不断,而且以遗迹化石作为标志化石本身也具有一定的缺陷。中国华南地区两类古老的宏体化石——矿化管状的Cloudina和条带状的Shaanxilithes在全球范围内可以很好的对比,并且这两种实体化石的出现都对应着碳同位素的明显正漂移。本文通过研究华南震旦系顶部化石带的地层分布和地理分布,综合分析了其时空分布特点和系统演化意义,深入探讨了Cloudina和Shaanxilithes作为寒武系底界标志化石所具备的潜力,对埃迪卡拉(震旦)纪—寒武纪地层界线划分和层型选择提出了更为理想的标准。     

新疆乌鲁木齐东部早二叠世枕状玄武岩火山岩系的发现及大地构造意义

新疆乌鲁木齐东部野生动物园附近的下二叠统下部发育了一套以枕状玄武岩为代表的火山岩系。该玄武岩在公路上发育有两层,上部一层较厚,可达7～8m,下部一层2～3m。岩枕近圆形、肾状、枕状、条带状或蠕虫状等,多呈顶突底凹。岩枕长轴平行排列,长轴基本顺层面分布;有的岩枕中含大量海百合茎、珊瑚及腕足等生物化石。在TAS图中大部分样品位于玄武粗安岩,而在K_2O-SiO_2图上主要落在低K拉斑玄武岩区间。MnOTiO_2-P_2O_5图解显示以岛弧为主,常量元素的特征总体上更接近岛弧玄武岩。在Hf/3-Th-Ta图解上也以岛弧为主;在Zr/4-2Nb-Y图解显示以火山弧为主,常量元素的特点总体上更接近岛弧玄武岩。微量元素原始地幔标准化蛛网图表明为同源岩浆产物,具高度相似的演化过程,多种微量元素判别图揭示岛弧-弧后盆地环境;稀土总量明显较低,在稀土元素球粒陨石标准化图解上,其稀土分布曲线一致性较好,呈轻稀土富集右倾型,Eu为负异常,揭示了乌东玄武岩岩浆有一定分异。稀土元素配分曲线与弧后盆地玄武岩(BABB)具有很好的一致性。U-Pb和谐年龄为283±8Ma,结合地层及古生物资料推测乌东玄武岩喷发的时间为早二叠世早期。乌东枕状玄武岩-灰岩之下有一套(磨拉石)底砾岩,初定为石炭-二叠系的界限。底砾岩之下为下石炭统的中厚层灰岩,具有明显的喀斯特化,为不整合接触,揭示在两者之间发生了造山作用。通过对新疆乌东早二叠世早期的枕状玄武岩的地质特征、地球化学特征、形成环境和时代的研究,表明乌东一带早二叠世主要为一个岛弧和弧后盆地环境,进一步揭示了北天山北缘石炭-二叠世碰撞闭合造山之后又发生了松弛扩张形成了弧后盆地,海水再度大规模入侵。最终的闭合碰撞造山的时间最早可能在晚二叠世。由于乌东枕状玄武岩在喷出地表后受到了生物化石和陆源碎屑的污染,再加上侵入过程中地壳的污染,使其具有非常复杂的地球化学特点和多解性。乌东玄武岩的研究对于了解博格达山、甚至天山中段在晚古生代的构造沉积演化及造山作用具有重要意义,同时对准噶尔盆地、吐哈盆地及三塘湖盆地油气资源的形成与分布具有重要意义。     

Morphological and Phylogenetic Study Based on New Materials of Anchiornis huxleyi (Dinosauria,Theropoda) from Jianchang,Western Liaoning,China

Anchiornis huxleyi, which is a member of the Middle–Late Jurassic Yanliao Biota, is the smallest feathered dinosaur ever known. It has been described as a critical link between feathered dinosaurs and birds. Recent studies, including those of Anchiornis, Xiaotingia, Eosinopteryx and Aurornis, challenged Archaeopteryx as the most basal bird. The new Anchiornis huxleyi specimens that are described in this paper show some minor different characters compared to previously reported Anchiornis specimens, which has revised the character list of Anchiornis and indicates a different phylogenetic point from former opinions.     

Geochemical and Petrological Studies on the Early Carboniferous Sidingheishan Mafic–Ultramafic Iintrusion in the Southern Margin of the Central Asian Orogenic Belt, NW China

The Sidingheishan mafic-ultramafic intrusion is located in the eastern part of the Northern Tianshan Mountain, along the southern margin of the Central Asian Orogenic Belt in northern Xinjiang autonomous region of China. The Sidingheishan intrusion is mainly composed of wehrlite, olivine websterite, olivine gabbro, gabbro and hornblende gabbro. At least two pulses of magma were involved in the formation of the intrusion. The first pulse of magma produced an olivine-free unit and the second pulse produced an olivine-bearing unit. The magmas intruded the Devonian granites and granodiorites.An age of 351.4±5.8 Ma(Early Carboniferous) for the Sidingheishan intrusion has been determined by U-Pb SHRIMP analysis of zircon grains separated from the olivine gabbro unit. A U-Pb age of 359.2±6.4 Ma from the gabbro unit has been obtained by LA-ICP-MS. Olivine of the Sidingheishan intrusion reaches 82.52 mole% Fo and 1414 ppm Ni. On the basis of olivine-liquid equilibria, it has been calculated that the MgO and FeO included in the parental magma of a wehrlite sample were approximately10.43 wt% and 13.14 wt%, respectively. The Sidingheishan intrusive rocks are characterized by moderate enrichments in Th and Sm, slight enrichments in light REE, and depletions in Nb, Ta, Zr and Hf. The ε_(Nd)(t) values in the rock units vary from +6.70 to +9.64, and initial ~(87)Sr/~(86)Sr ratios range between 0.7035 and0.7042. Initial ~(206)Pb/~(204)Pb, ~(207)Pb/~(204)Pb and ~(208)Pb/~(204)Pb values fall in the ranges of 17.23-17.91,15.45-15.54 and 37.54-38.09 respectively. These characteristics are collectively similar to the Heishan intrusion and the Early Carboniferous subduction related volcanic rocks in the Santanghu Basin, North Tianshan and Beishan area. The low(La/Gd)_(PM) values between 0.26 and 1.77 indicate that the magma of the Sidingheishan intrusion was most likely derived from a depleted spinel-peridotite mantle.(Th/Nb)_(PM)ratios from 0.59 to 20.25 indicate contamination of the parental magma in the upper crust.Crystallization modeling methods suggest that the parental magma of the Sidingheishan intrusion was generated by flush melting of the asthenosphere and subsequently there was about 10 vol%contamination from a granitic melt. This was followed by about 5 vol% assimilation of upper crustal rocks. Thus, the high-Mg basaltic parental magma of Sidingheishan intrusion is interpreted to have formed from partial melting of the asthenosphere during the break-off of a subducted slab.     

A Preliminary Study on the Soft–Sediment Deformation Structures in the Late Quaternary Lacustrine Sediments at Tashkorgan, Northeastern Pamir, China

This study identified soft–sediment deformation structures(SSDS) of seismic origin from lacustrine sediments in the late Quaternary paleo–dammed lake at Tashkorgan, northeastern Pamir. The observed deformation structures include sand dykes, liquefied diapir and convolute structures, gravity induced SSDS, and thixotropic pillar and tabular structures. We conducted a preliminary study on the morphology, formation and trigger mechanisms of pillar and tabular structures formed by liquefaction of underlying coarse sand and thixotropy of the upper silty clay. The regional tectonic setting and distribution of lacustrine strata indicate that the most probable trigger for the SSDS in lacustrine sediments was seismic activity, with an approximate earthquake magnitude of M6.0; the potential seismogenic fault is the southern part of the Kongur normal fault extensional system. AMS 14 C dating results indicate that the SSDS were formed by seismic events occurring between 26050±100 yr BP and 22710±80 yr BP, implying intense fault activity in this region during the late Pleistocene. This study provides new evidence for understanding tectonic activity and regional geodynamics in western China.     

Cosmogenic 26Al/10Be Burial Dating of the Uplift Rate of Southern Qinling Mountains since the Middle Pleistocene

正Objective The Qinling Mountains(QM)in Central China is a natural barrier that corresponds to the boundary between the southern and northern climate and environment(Gong Hujun et al.,2017).Northern QM is relatively steep,and southern QM is in contrast relatively low and gentle.Investigations have shown that the average uplift rate of     

Mixing of Enriched Lithospheric Mantle-Derived and Crustal Magmas: Evidence from the Habo Cenozoic Porphyry in Western Yunnan

New zircon U–Pb ages, whole-rock geochemistry and zircon Hf isotopes from the Habo porphyry Western Yunnan, China, were determined to provide constraints on the timing of uplift of the Eastern Tibetan Plateau. The intrusive rocks consist of shoshonitic porphyry (syenite porphyry and monzonite porphyry). Zircon laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) U–Pb dating indicates coeval emplacement ages of ~35 Ma. The porphyries have alkaline affinities, enrichment in large ion lithophile elements (LILEs) and light rare earth elements (LREEs) (e.g., Rb, Th, U, Pb), with depletion of high field strength elements (HFSEs) (e.g., Nb, Ti, Ta) and weak Eu anomalies. They display uniform Lu–Hf isotopic compositions with negative zircon εHf(t) values ranging from -3.9 to -0.6. The chemical characteristics of the syenite porphyries indicated that they most likely originated from the lower crust, with mantle-derived material involved in their generation. Geochemically, the monzonite porphyries are similar to the syenite porphyries; however, the lower MgO contents suggest that they were produced by different degrees of partial melting of the same lower crust source. Combined with the geochemical and isotopic data in this paper, imply that the alkali-rich porphyries of the Habo polymetallic deposit were derived from the partial melting of lower crust, enriched by mantle magma, formed in a conversion stage from stress extrusion (a strike-slip shear process) to local stress relaxation (a strike-slip pull-apart process) at the Ailaoshao tectonic zone.