中国东部—西太平洋副热带季风和降水的气候特征及成因分析

利用1981—2000年候平均NCEP/NCAR再分析资料和CMAP全球降水资料,分析了从中国东部大陆到西太平洋副热带地区季风和降水季节变化的特征及其与热带季风降水的关系,探讨了季风建立和加强的原因。夏季东亚—西太平洋盛行的西南风开始于江南和西太平洋副热带的春初,并向北扩展到中纬度,热带西南风范围向北扩展的迹象不明显。从冬到夏,中国西部和西太平洋副热带的表面加热季节变化可以使副热带对流层向西的温度梯度反转比热带早,使西南季风在副热带最早开始;从大气环流看,青藏高原东侧低压槽的加强和向东延伸,以及西太平洋副热带高压的加强和向西移动,都影响着副热带西南季风的开始和发展;初夏江南的南风向北扩展与副热带高压向北移动有关,随着高原东侧低压槽向南延伸,槽前的偏南风范围向南扩展。随着副热带季风建立和向北扩展,其最大风速中心前方的低层空气质量辐合和水汽辐合以及上升运动也加强和向北移动,导致降水加强和雨带向北移动。热带季风雨季开始晚,主要维持在热带而没有明显进入副热带,江淮梅雨不是由热带季风雨带直接向北移动而致,而是由春季江南雨带北移而致。在热带季风爆发前,副热带季风区水汽输送主要来自中南半岛北部和中国华南沿海,而在热带季风爆发后,水汽输送来自孟加拉湾和热带西太平洋。     

气候平均场上西太平洋副热带高压双脊线过程可能成因的动力诊断分析

利用NCEP-DOE再分析数据集II,诊断分析了气候平均场上6次西太平洋副热带高压双脊线过程,借助一个两层半大气模式,从动力学上初步揭示了西太平洋热带大气准10天振荡（Quasi Ten-day Oscillation,简称QTO）向西北方向传播与季风槽东伸西撤之间的相互作用过程,探讨了气候平均场上西太副高双脊线可能的形成机制。分析表明季风槽准10天东西振荡是气候平均场上西太副高双脊线形成的主要原因,而季风槽东伸西撤与QTO传播密切相关。进一步分析发现,QTO向西北方向传播,东风切变作用于斜压辐散的经向梯度,在对流中心北侧生成正扰动涡度。QTO在季风槽东侧激发的气旋性扰动涡度,诱导季风槽东伸,侵入副高,造成副高外围变形,形成双脊线。因此,形成西太副高双脊线的主要原因之一可能是西太平洋热带大气QTO。尽管季风槽东伸直接引起副高双脊线发生,但是它只不过是受QTO影响的一种表现。本文仅为诊断结果,其结果还有待于模式敏感性试验的验证。     

鲁西新太古代济宁群含铁岩系形成时代——SHRIMP U-Pb锆石定年

济宁群以隐伏的地质体分布于华北克拉通鲁西地区,以往被划归古元古代。近年来在济宁群的钻探和地球物理研究中,发现存在较大规模条带状硅铁建造,其形成时代引起地学界极大关注。本文对济宁群变质碎屑沉积岩和长英质火山岩进行了锆石SHRIMP年龄测定。含砾绿泥绢云千枚岩的碎屑锆石年龄主要集中在～2.7Ga,可靠的最年轻碎屑锆石年龄为2.61±0.01Ga。变质长英质火山岩岩浆锆石年龄为2.56±0.02Ga。研究表明,济宁群形成于新太古代晚期,而不是以往认为的古元古代。华北克拉通条带状铁建造主要形成于新太古代晚期。济宁群在岩石组合、变质作用方面与鞍山、冀东以及五台地区同时代含硅铁建造的表壳岩系有差别,但是与本溪南芬铁矿的岩石组合有相似之处。这些可能为我国的隐伏太古宙BIF铁矿的研究与勘探提供了重要依据。     

U–Pb geochronology of the Western Channel Diabase,northwestern Laurentia: Implications for a large 1.59 Ga magmatic province,Laurentia's APWP and paleocontinental reconstructions of Laurentia,Baltica and Gawler craton of southern Australia

U–Pb baddeleyite ages of 1592 ± 3 and 1590 ± 4 Ma are reported for paleomagnetic sites in sheets and dykes of Western Channel Diabase (WCD) that intrude Proterozoic rocks of the flat-lying Hornby Bay Group in the Hornby Bay basin and the deformed volcanic-plutonic Great Bear Magmatic Zone of Wopmay orogen of northwestern Laurentia. A published WCD paleomagnetic pole at 9°N, 115°W (A₉₅ = 6°) has been demonstrated primary. The new ages indicate that the WCD pole falls midway in time between poles for the 1.74 Ga Cleaver dykes and 1.48–1.42 Ga Elsonian-aged plutons, filling an important gap in the Proterozoic apparent polar wander path (APWP) for Laurentia. The WCD pole can be compared with poles reported from similar-aged magmatic units on other cratons in order to test paleocontinental reconstructions. A comparison of the Laurentian WCD pole with primary ca. 1.63 Ga and ca. 1.575 Ga poles for Baltica, along with an earlier comparison of precisely dated 1.27–1.255 Ga poles for Laurentia and Baltica, suggests that the two cratonic blocks drifted as a single entity with Baltica adjacent to eastern Greenland during the ca. 1.59–1.27 Ga interval. On the basis of less well constrained ca. 1.84–1.83 Ga poles from Laurentia and Baltica, it is possible that this reconstruction existed as early as ca. 1.83 Ga. The WCD is the same age as Wernecke breccias of the Wernecke and Ogilvie Mountains of northwestern Laurentia and bimodal Gawler Range Volcanics (GRV) and related Olympic Dam breccias of the Gawler craton. It has been proposed by others that the Gawler craton lay adjacent to northwestern Laurentia at 1.59 Ga, with the Olympic Dam and Wernecke breccias forming a large hydrothermal province. The primary WCD pole provides an opportunity to test Laurentia–Gawler craton reconstructions at 1.59 Ga. A paleopole has been reported for the GRV, although its primary or secondary nature is open to interpretation. If primary, or if acquired as an overprint during the later stages of 1.60–1.58 Ga Hiltaba-GRV magmatism, then a position for the Gawler craton adjacent to northwestern Laurentia is permitted. If the GRV pole is a later secondary overprint then a reliable comparison with Laurentian poles cannot be made.     

西南天山特克斯科桑溶洞火山岩的锆石U-Pb年代学研究

新疆特克斯县乌孙山科桑溶洞火山-沉积岩剖面由变质岩、火山-沉积岩(中酸性火山熔岩、火山碎屑岩、生物碎屑灰岩)和侵入其中的花岗质岩石组成,花岗岩中保留着英安岩-安山岩顶垂体。夹在火山岩地层之间的厚层生物碎屑灰岩(其中发育溶洞)发生褶皱变形。在剖面多处见到逆冲构造,断裂带局部塑性变形。采自剖面下部英安岩样品的锆石232Th/238U比值为0.4～0.6,U-Pb谐和年龄368.3±1.7Ma(MSWD=1.5,n=15)。剖面上部流纹岩中锆石的232Th/238U比值为0.8～2.2,U-Pb谐和年龄为356.4±1.7Ma(MSWD=1.3,n=19)。大约12Ma的时差说明存在两次火山喷发事件,在这两次火山喷发的间歇形成了巨厚生物碎屑灰岩(1000m)。这种间歇性的火山喷发在西天山地区普遍发育,形成了规模巨大的滨海相火山-沉积盆地。剖面下部的英安岩与剖面上部的流纹岩的锆石具有不同的微量元素组成,预示着其岩浆源区性质的差异。     

基于多元统计和傅立叶和谱分析的土壤重金属的来源解析及其风险评价

分析珠江三角洲腹地佛山顺德区208个蔬菜地表层土样Cu、Ni、Cr、As、Pb、Zn、Cd和Hg等8种重金属的全量,结果表明,8种重金属的平均浓度高于广东省土壤背景值。Cd和Hg的最高浓度和变异系数分别为6.54mg/kg、115%和4.82mg/kg、151%,暗示Cd和Hg的人为来源。多元统计与傅立叶和谱分析的结合,解释了Cr、Ni和Cu的自然来源,Pb、Zn、As、Cd和Hg的人为来源;傅立叶和谱分析进一步阐释了Zn与Cu的双重来源,并推断土壤Hg来源于大气沉降。研究区内大约21.7%的土壤受重金属污染,表明需要调整该区的农业生产活动。     

Lateglacial and Holocene cosmogenic surface exposure age glacial chronology and geomorphological evidence for the presence of cold‐based glaciers at Nevado Sajama,Bolivia

Comparisons of palaeo‐equilibrium line altitudes between the Western and Eastern Cordilleras in the Central Andes are commonly based on the assumption that the tall outermost moraines visible in remotely sensed images of the Western Cordillera date to the Last Glacial Maximum (LGM). However, field investigation and geomorphic mapping at Nevado Sajama, Bolivia, indicates the tall moraines are relic features with shorter moraines overlying and in some cases extending beyond them. ³⁶Cl exposure ages from the shorter moraines suggest that they date to Lateglacial times ca. 16.9–10.2 ka. Although Lateglacial deposits have been found throughout the Central Andes, the extent of these deposits relative to LGM deposits varies both between the Western and Eastern Cordilleras and north‐to‐south along the Western Cordillera. In the Western Cordillera in the zone of easterly winds, the Lateglacial appears to be the most extensive glacial advance of the last glacial cycle. Geomorphic evidence also suggests that some Lateglacial moraines were deposited by cold‐based ice, a previously unreported finding in the tropical Andes. Retreat from other glacial features occurred at about 7.0–4.4 ka and 4.7–3.3 ka. These are the first directly dated Holocene glacial deposits in the Western Cordillera of Bolivia, and their presence suggests that the mid Holocene may not have been as warm and dry as previously thought. Copyright © 2008 John Wiley & Sons, Ltd.     

1998年夏季中国暴雨洪涝灾害的气象水文特征

文章分析了1998年夏季我国长江、嫩江、珠江流域发生的严重洪涝灾害的气象、水文特征及其成因。6月中、下旬珠江、长江、嫩江流域出现了持续性强降水, 局部地区下了大暴雨; 7月下旬长江流域出现了“二度梅”, 湖南、湖北和江西省普降暴雨; 8月上半月嫩江流域再次出现持续性强降水。频繁的强降水使长江、嫩江、华南西江等干、支流水位迅猛上涨, 支流河水不断涌入干流, 使得干流洪峰迭起。雨水和洪峰迭加, 引发了百年一遇的大洪水。1998年7月副热带高压南落是造成长江流域“二度梅”的主要原因。副热带高压、南海季风涌、中高纬冷空气和从青藏高原东移的中尺度对流系统 (MCS) 等4个因子的最佳组配, 有利于长江流域出现持续性强降水。     

珠江三角洲经济区行为主体特征分析

利用基本单位普查资料，采用定量方法，分析了珠江三角洲经济区行为主体的发育、结构和地域特征，并讨论了形成这些特征的主要原因，认为其反映了珠江三角洲经济区在中国的典型性和独特性。     

Mud volcanoes of the Orinoco Delta, Eastern Venezuela

Mud volcanoes along the northwest margin of the Orinoco Delta are part of a regional belt of soft sediment deformation and diapirism that formed in response to rapid foredeep sedimentation and subsequent tectonic compression along the Caribbean–South American plate boundary. Field studies of five mud volcanoes show that such structures consist of a central mound covered by active and inactive vents. Inactive vents and mud flows are densely vegetated, whereas active vents are sparsely vegetated. Four out of the five mud volcanoes studied are currently active. Orinoco mud flows consist of mud and clayey silt matrix surrounding lithic clasts of varying composition. Preliminary analysis suggests that the mud volcano sediment is derived from underlying Miocene and Pliocene strata. Hydrocarbon seeps are associated with several of the active mud volcanoes.Orinoco mud volcanoes overlie the crest of a mud-diapir-cored anticline located along the axis of the Eastern Venezuelan Basin. Faulting along the flank of the Pedernales mud volcano suggests that fluidized sediment and hydrocarbons migrate to the surface along faults produced by tensional stresses along the crest of the anticline. Orinoco mud volcanoes highlight the proximity of this major delta to an active plate margin and the importance of tectonic influences on its development. Evaluation of the Orinoco Delta mud volcanoes and those elsewhere indicates that these features are important indicators of compressional tectonism along deformation fronts of plate margins.