东海北部外陆架EY02—1孔磁性地层研究

对长达70.20m的东海浅钻EY02-1进行了岩石磁学和古地磁分析,证明沉积物的载磁矿物主要为低矫顽力的磁铁矿,磁性地层揭示了发生于9.62~8.58m的磁极性事件,结合钻孔上部的AMS14C测年证明它为全新世初期的哥德堡磁极性漂移,线性外推的时间是距今12681~10206Ma,为全新世开始时地磁场是否发生过短期的磁极性漂移提供了新证据;与东海高分辨率的浅地层地震剖面以及典型钻孔(中法联合东海地震调查和DZQ4钻孔)对比还揭示,在中更新世地层中也出现过两次磁倾角变化。在钻孔中下部54.00~50.94m(2271—2151号样品)出现一段磁倾角变小甚至变成负值,但是由于该段沉积物以粗颗粒的砂为主并且负向样品并不连续,依据研究的标准不作为反磁极性事件。第二个比较连续的负向样品段出现在最底部70.20~64.31m。虽然研究区域内不乏揭示中更新统地层的地震剖面,但至今没有足够长的钻孔在时间上予以佐证。根据东海地震相对比和沉积物中海侵和海退旋回的不同特征以及布容期以来报道的反磁极性事件发生的时间来推测下部地层的时代归属。由于钻孔最底部的沉积主要是粗颗粒的粉砂质砂和细砂,同时钻孔也穿透了倒数第二冰期的杂乱地震相地层和其下的平行透明海相层,所以推测下部的倒转可能为发生在MIS8晚期的CR0反磁极性事件(距今265~255ka)。     

非感应起电参数化方案的对比性研究

为进一步研究不同的非感应起电机制对模拟云内电场的可适用性,把3种不同的非感应起电参数化方案引入三维强风暴动力和电耦合数值模式,以2005年6月10日发生在长春的一次雹暴过程为例,模拟分析第一次闪电发生前云内电场的发展情况。结果表明,电荷的产生始于过冷水含量中心,并随着过冷水含量中心的向上发展而上移;在-20～-30 ℃层存在一电荷的累积区,雷达回波跃增出现后的10 min左右,电场迅速增长,且在4～8 min内由不足50 kV·m-1增长到110 kV·m-1以上。采用方案一形成的主电荷区为偶极性结构,而采用方案二和方案三形成的为比较常见的三极性结构。对比其他地区的观测资料及模拟结果,表明相同的云体宏微观条件下,不同方案中极性反转温度的不同对云内中低层电荷的分布存在较大的影响。考虑低层正电荷区的发展及冰相粒子与过冷水含量的配置关系,取极性反转温度为-10～-20 ℃,方案二的模拟结果与实际较一致。     

华西秋雨起止与秋冬季节大气环流转换

根据1961—2010年平均的逐候NCEP/NCAR再分析资料、1979—2008年平均的逐候CMAP降水资料以及1961—2010年逐候平均的中国553个台站降水资料,讨论了华西秋雨起止日期与秋冬季大气环流转换特征的关系。结果表明,华西地区降水年变化表现为明显的夏、秋双峰特征,8月4—8日(第44候)为双峰间的低谷,10月8—12日(第57候)以后降水降至年平均以下。由此,将华西秋雨建立和结束日期分别确定为8月9—13日(第45候)和10月8—12日(第57候)。华西秋雨的建立对应于东亚夏季风开始向冬季风转变,其标志性环流调整特征是江南地区的西南风转为东南风。东亚经向海平面气压梯度在8月9—13日(第45候)由南高北低转为南低北高,造成850 hPa江南地区的西南风转为东南风,该东南风与来自孟加拉湾的热带西南季风交汇于华西地区,形成风向和水汽的辐合,使得华西地区的降水在夏峰之后再次增强,华西秋雨由此建立。华西秋雨的结束则对应于孟加拉湾热带西南季风结束和东亚冬季风完全建立,其标志性环流调整特征是孟加拉湾地区的西南风转为东北风。随着东亚纬向海平面气压梯度由北向南依次发生东高西低向东低西高的转变,东亚冬季风也逐步向南推进,9月8—12日(第51候)东北冬季风到达江南地区,10月8—12日(第57候)进一步推进到南海地区,此时来自孟加拉湾的热带西南季风消失,造成华西地区完全受大陆冷高压控制,东亚季风经圈环流也转为冬季型哈得来环流,东亚冬季风完全建立,华西秋雨也随之结束。因此,华西秋雨起止可能与东亚夏季风、南亚夏季风向冬季风的转变时间不同步有关,东亚季风与南亚季风的共同作用使得华西秋雨成为亚洲夏季风在中国大陆上的最后一个雨季。     

地球磁极倒转与白垩纪超静磁带的非线性分析

地球磁场多次发生南北(正负)磁极位置的变换和白垩纪超静磁带(CNS)的异常现象,这已为大家所公认.但造成这种异常现象的原因,则是迄今未能很好解答的一个难题. 应用非线性理论对地球磁极倒转和白垩纪超静磁带进行了分析, 认为超静磁带事件意味着地球核幔相互作用和外核流体运动可能处于能量最低的状态,地球磁场系统通过不断地与外界交换物质和能量,维持一种空间或时间的有序结构.在121～83Ma期间,无外星撞击地球引起地磁极性倒转,可能是白垩纪超静磁带出现的原因之一.地球磁场极性的随机倒转具有混沌运动的自逆转特性,混沌理论给地磁极性倒转提出了一个简明的动力机制解释.     

Tectonic setting of porphyry Cu–Au, Mo and related mineralization associated with contrasted Neogene magmatism in the Western Sulawesi Arc

The Neogene Western Sulawesi Arc, from the south going northwards, can be divided into three magmatic provinces of K alkaline–shoshonitic (AK-SH), high-K calc-alkaline (KCA), and low-K–normal calc-alkaline (TH-CA) affinity, referred to, respectively, as South, Central and North Sulawesi. The origin of this magmatism in terms of subduction and collision processes is contentious. Four widely spaced Cu–Au porphyry, and one Mo porphyry district(s) occur along the Western Sulawesi Arc, with the North Sulawesi province being the most mineralized. This porphyry mineralization is part of a regional belt that extends north into the Philippines and possibly south to the Sunda Arc. In western Sulawesi, common features that define the porphyry belt are obscure because the porphyry districts cannot be simply related, either in terms of their magmatic affinity, nature of basement, or tectonic setting. Nevertheless, it can be suggested that the generation of porphyry Mo systems requires involvement of continental crust in terms of magma source, while Au-rich porphyry systems are independent of the nature of the crust, and are derived from a mantle source.     

The Effect of Cr2O3 on the Partial Melting of Spinel Lherzolite in the System CaO-MgO-Al2O3-SiO2-Cr2O3 at 1{middle dot}1 GPa

Chromium as Cr³⁺ substitutes for octahedrally coordinated Alin upper-mantle minerals, thereby reducing the activity of Al₂O₃in the system and hence the concentration of Al₂O₃ in partialmelts. The effect of Cr₂O₃ on melt compositions multiply saturatedwith the spinel lherzolite phase assemblage has been quantifiedin the system CaO–MgO–Al₂O₃–SiO₂–Cr₂O₃at 1·1 GPa as a function of 100 Cr/(Cr + Al) in the spinel(Cr#_sp). The decrease of Al₂O₃ in the melt with increasing Cr#_spis accompanied by increasing MgO and SiO₂, whereas CaO remainsalmost constant. Consequently, the CaO/Al₂O₃ ratio of the meltincreases with Cr#_sp, and the melt becomes richer in normativediopside, hypersthene and quartz. The effect may explain certainmantle melts with unusually high CaO/Al₂O₃ ratios. The concentrationof Cr₂O₃ in the melt remains low even at high Cr#_sp, which meansthat the strong effect of Cr₂O₃ on partial melting equilibriais not readily apparent from its concentration in the melt itself.The existence of a highly refractory major component such asCr₂O₃ nullifies simplified conclusions from the ‘inverseapproach’ in the experimental study of basalt petrogenesis,as there is insufficient information in the composition of thepartial melt to reconstruct the conditions of melting. KEY WORDS: basalt petrogenesis; partial melting; reversal experiment; spinel lherzolite; system CMAS–Cr₂O₃; CaO/Al₂O₃ of melt; effect of Cr₂O₃     

古地磁场研究:挑战与机遇

地磁场源于地核流体的运动,至少已有约35亿年历史。地磁场的起源及演化一直是地球科学研究的前沿领域之一,这是因为它既是地球宜居环境的重要保障,也是探究地球系统各圈层联系的重要途径。本文重点围绕保留在岩石中的"深时"古地磁场记录,分析在地球内部磁场的形成与维持、地磁场极性倒转、以及地磁场强度变化等古地磁场研究三个方面的主要进展及面临的挑战。同时,结合古地磁测试技术的革新,磁发电机实验和超算模拟的应用,生物磁学的发展,阐述古地磁与地质学多学科交叉研究有望在揭示古地磁场变化及其对生物演化方面的贡献。对古地磁场变化的研究不仅有助于理解地磁场的起源与演化规律,也对认识地球的早期演化,甚至其它行星的演化有重要意义。     

Effect of hydrogeomorphic setting on calcareous fen hydrology

Calcareous fens are species‐rich peatlands that are dependent on minerotrophic water sources for wetland functioning, with current conceptual models suggesting the water source is ubiquitously groundwater upwelling. By quantifying the water balance and subsurface water flow paths and fluxes over 3 growing seasons for calcareous fens in 3 different hydrogeomorphic settings (Riparian, Trough, and Basin), we show evidence that challenges this conceptual model. The Riparian Fen received an order of magnitude more water inputs than the Trough or Basin Fens and was dominated by stream recharge inputs and groundwater outputs. Precipitation and evaporation dominated the water balance of the Trough Fen whereas only the Basin Fen received sizeable groundwater inputs. Indeed, subsurface water fluxes were low at all fens due to weak hydraulic gradients and low saturated hydraulic conductivity in some areas of each wetland, though variations in growing season precipitation led to subsurface flow reversals in all 3 fens. Our results demonstrate the importance of understanding landscape position, or hydrogeomorphic setting, on calcareous fen hydrology for improving conservation, management, and restoration efforts of these important ecosystems.     

Kinematic hardening predictions of large stress-reversals in 3-D test on loose sand

A rotational kinematic hardening constitutive model with the capability of predicting the behavior of soil during 3-D stress-reversals has been developed. An existing elasto-plastic constitutive model, the Single Hardening Model, utilizing isotropic hardening serves as the basic framework in these formulations. To this framework is added the capability of handling cross-anisotropic behavior as well as the kinematic hardening mechanism to capture inherent anisotropy of the sand in addition to the large stress-reversals. The model involves thirteen parameters, which can be determined from simple laboratory experiments, such as isotropic compression, drained triaxial compression and triaxial extension tests. The results from a series of true triaxial tests with large stress-reversals performed on loose cross-anisotropic Santa Monica Beach sand are employed for comparison with predictions.