珠江口盆地惠州凹陷新近系珠江组K22陆架砂脊沉积成因分析*

通过分析珠江口盆地惠州凹陷新近系珠江组NE—SW向平行于古岸线展布的K22条带状砂体外部地震反射特征、内部反射结构及平面展布规律,并运用层序地层学方法和理论,结合海平面变化特点,对K22条带状砂脊沉积成因进行了研究。结果显示:K22条带状砂脊为发育在陆架区古构造高带、受控于强制性海退过程的再沉积产物,其物源来自于早期的三角洲,沉积水动力条件多样,主要为海退过程中的潮汐流和波浪作用;同时,沿岸流也对砂脊形态的形成起到了关键作用,这些砂脊后期得益于快速的海侵而保留下来。留存下来的沙脊沉积被包裹在海相泥岩背景中,可形成良好的岩性圈闭。     

Influence of igneous processes and serpentinization on geochemistry of the Logatchev Massif harzburgites (14°45′N,Mid-Atlantic Ridge), and comparison with global abyssal peridotites

We acquired bulk-rock analyses of Mid-Atlantic Ridge (MAR) harzburgites in order to understand the influence of submarine igneous and metamorphic processes on the distribution of incompatible elements (especially rare Earth elements or REEs) in abyssal peridotites. The geochemical characteristics of these Logatchev Massif serpentinized and talc-altered harzburgites, and spatially associated metagabbros were then compared with a compilation of global abyssal peridotites. The Logatchev harzburgites show light rare earth element (LREE) enrichments (average La _N /Yb _N = 2.81), positive correlations between LREEs (e.g. La, Ce, Pr, and Nd) and high field strength elements (HFSEs; e.g. Nb and Zr), and positive correlations between HFSEs and Th. Most global abyssal peridotites show similar trends. We suggest that the systematic enrichment of incompatible elements probably reflects a post-partial fusion magmatic refertilization. The compositional scatter exhibited by some serpentinized peridotites in Nb-LREE diagrams is probably due to the elimination of diopside during partial melting and significant impregnation by a melt produced in the Opx–Ol–Sp melting field rather than to later hydrothermal alteration. The correlation between Pb and Nd observed for most global abyssal peridotites, including the Logatchev harzburgites, indicates magmatic generation. The scatter of Pb in some rocks suggests that lead is likely mobile during serpentinization or weathering. Low to moderate water/rock (W/R) ratios in the harzburgites calculated from Sr isotopic compositions (5.98–26.20 for a close system and 1.66–2.72 for an open system), and the low abundance of REEs in Logatchev hydrothermal fluids indicate that the REE contents of abyssal peridotites probably were little influenced by hydrothermal alteration. Compared to this later alteration, the presence of small proportions of gabbroic melt (from 1:30 to 1:3 in our sample) that crystallized in the residual harzburgites modified their REE patterns significantly by elevating the LREEs.     

Identification of Archaean plate tectonic processes from multidimensional discrimination diagrams and probability calculations

We applied our group's previously published multidimensional diagrams in 2006–2012 and corresponding probability estimates in 2011–2012 to geochemical data for Archaean rocks compiled from cratons in Australia, South Africa, Brazil, Canada, and India. Tectonic processes similar to present-day plate tectonics evidently were active at least since the Palaeoarchaean (?3570 Ma). This seems to be true in spite of a presumably hotter Earth at that time. For the eastern part of the Pilbara craton (Australia), a Palaeoarchaean (3570–3450 Ma) and Mesoarchaean (2900 Ma) continental arc setting apparently evolved to a collision (Col) setting during the Neoarchaean (2600 Ma). We infer an island arc (IA) environment for Kambalda (Australia) during the Neoarchaean (2700 Ma). For the Barberton belt (South Africa), a transition from a mid-ocean ridge regime during the older part of the Palaeoarchaean (3470 Ma) to an IA setting during the younger part (3300–3260 Ma) is likely. We inferred an arc environment for the São Francisco craton (Brazil) and the Rio Maria terrane (Brazil) during the Mesoarchaean (3085–2983 Ma and 2870 Ma, respectively), whereas a within-plate setting is clearly indicated for the Carajás metallogenic province (Brazil) during the Neoarchaean (2740–2700 Ma). We also recognize an IA regime for the Mesoarchaean (3000 Ma) North Caribou and Neoarchaean (2700 Ma) Abitibi greenstone belts (Canada), and for the Gadwal greenstone belt (India) during the Neoarchaean (2700–2500 Ma). A Col setting was inferred for the Archaean sanukitoid suite (Canada) and the Kolar suture zone (India) during the Neoarchaean (2700–2660 Ma and 2630–2520 Ma, respectively).     

山东莱州浅滩地区沉积特征与沉积作用

通过系统采集海底表层沉积样品进行粒度测试分析,对现代莱州浅滩地区的沉积类型、粒度特征、泥沙搬运方式、运移趋势及沉积动力、沉积机制进行了研究。结果表明,莱州浅滩是形成于松散碎屑堆积海岸岬角岸外的砂砾质水下沙洲／沙脊,它的形成深刻改变了浅滩地区原有的沉积动力和机制,在浅滩两侧海域各自形成了大致对称的潮余环流,分别与两个主要...     

Dynamics of multiple intertidal bars over semi‐diurnal and lunar tidal cycles,North Lincolnshire,England

Multiple intertidal bars are common features of wave‐dominated sandy beaches, yet their short‐term (<1 month) and small‐scale (<1 km) morphology and dynamics remain poorly understood. This study describes the morphodynamics of multiple intertidal bars in North Lincolnshire, England, during single and lunar tidal cycles under two contrasting conditions – first when significant wave height was <0·5 m and second when significant wave height frequently exceeded 1 m. The relative importance of swash, surf and shoaling processes in determining morphological change was examined using detailed field observations and a numerical model. The beach featured four intertidal bars and both cross‐shore and longshore bar morphology evolved during the field investigation, particularly under medium to high wave‐energy conditions. Numerical modelling suggests shoaling processes are most common on the seaward two bars under calm wave conditions (H_s < 0·5 m) and that surf zone processes become more common during neap tides and under more energetic (H_s < 0·5 m) conditions. Surf processes dominate the inner two bars, though swash influence increases in a landward direction. The numerical modelling results combined with low tide survey data and high‐resolution morphological measurements strongly suggest changes in the intertidal bar morphology are accomplished by surf zone processes rather than by shoaling wave or swash processes. This is because shoaling waves do not induce significant sediment transport to have any morphological effect, whereas swash action generally does not have enough scope to act as the swash zone is much narrower than the surf zone. It was found, however, that the absolute rate of morphological change under swash action and surfzone processes are of similar magnitudes and that swash action may induce a significant amount of local morphological change when the high tide mark is located on the upper bar, making this process important for bar morphodynamics. Copyright © 2007 John Wiley & Sons, Ltd.     

库姆塔格沙漠大尺度风场特征分析

利用美国NCEP/NCAR1979—2006年27 a地面10 m高度的日平均风场再分析-2资料以及46 a的地面常规气象站观测资料和1 a的沙漠中自动气象站观测资料,对库姆塔格沙漠地区风场进行了统计与诊断分析。结果表明：沙漠地区,一年四季北风和东北风为近地面主要存在的风向,春季风速最强,夏季次之,秋冬季最弱;在夏秋冬季节,由于北风的逐渐减弱,加上受到南侧阿尔金山和青藏高原风场的影响,南下的气流在沙漠南侧分为三支,分别流入新疆、青海和甘肃。春夏季节在沙漠北侧基本都是以东北风或者西北风吹向库姆塔格沙漠,秋冬季节,沙漠地区出现西南风。根据沙漠周围6个气象站风场风速显示,库姆塔格沙漠地区风速存在明显的周期变化,在过去的10多年中库姆塔格沙漠周围风场风速处于一个低谷期,但最近几年风速有不断加强的趋势。     

应用卫星影像系列海图叠合法分析沙洲动态变化——以江苏东沙为例

利用1973~2000年9个时相的卫片、海图,提出了卫星影像系列——海图叠合分析法来分析辐射沙洲中大沙洲的动态变化,并将之运用到东沙的动态趋势分析中。研究结果表明:(1)通过卫星影像系列——海图叠合分析法,可避开了不同时相卫片的潮位校正难点,揭示了沙洲的冲蚀淤长变化。(2)东沙北缘向南移动;沙洲东缘向东移动;在沙洲西部遭受侵蚀,边缘东移,但幅度不大。     

西南印度洋中脊斜向扩张分段特征及构造成因探讨

斜向扩张是超慢速扩张洋中脊独特的构造特征,其地形分段特征明显区别于经典的快速-慢速端元洋中脊模型,是理解超慢速扩张洋中脊地质过程的重要切入点.基于西南印度洋中脊Indomed-Gallieni和Shaka-DuToit段多波束地形数据,分析了不同斜向扩张角度(α)洋中脊的地形分段样式.其中,46.5°～47.5°E(α...     

Geodynamic Information in Peridotite Petrology

Systematic differences are observed in the petrology and majorelement geochemistry of natural peridotite samples from thesea floor near oceanic ridges and subduction zones, the mantlesection of ophiolites, massif peridotites, and xenoliths ofcratonic mantle in kimberlite. Some of these differences reflectvariable temperature and pressure conditions of melt extraction,and these have been calibrated by a parameterization of experimentaldata on fertile mantle peridotite. Abyssal peridotites are examplesof cold residues produced at oceanic ridges. High-MgO peridotitesfrom the Ronda massif are examples of hot residues producedin a plume. Most peridotites from subduction zones and ophiolitesare too enriched in SiO₂ and too depleted in Al₂O₃ to be residues,and were produced by melt–rock reaction of a precursorprotolith. Peridotite xenoliths from the Japan, Cascades andChile–Patagonian back-arcs are possible examples of arcprecursors, and they have the characteristics of hot residues.Opx-rich cratonic mantle is similar to subduction zone peridotites,but there are important differences in FeO_T. Opx-poor xenolithsof cratonic mantle were hot residues of primary magmas with16–20% MgO, and they may have formed in either ancientplumes or hot ridges. Cratonic mantle was not produced as aresidue of Archean komatiites. KEY WORDS: peridotite; residues; fractional melting; abyssal; cratonic mantle; subduction zone; ophiolite; potential temperature; plumes; hot ridges