南海西北部珊瑚礁记录所反映的新构造运动*

珊瑚礁是发育于热带海洋环境中由生物作用和地质作用共同形成的地质体,具有独特的新构造运动意义。南海西北部珊瑚礁记录所反映的新构造运动主要有火山活动、地壳升降运动和地震活动等。珊瑚礁区第四纪火山活跃,到现代已停止活动,部分火山构成珊瑚礁的基座,个别出露海面为火山岛;地壳升降运动差异较大,雷州半岛西南部珊瑚礁呈上升趋势,上升率为0.02~0.05mm/a;西沙群岛等岛礁地壳运动则呈下降趋势,下降率为-0.07~-0.10mm/a,岛礁中的造礁石珊瑚生长率、礁顶和灰沙岛的堆积率均相当于或大于地壳下降率与现代海平面上升率的总和;南海西北部珊瑚礁区内地震活动较强,尤其是1994年12月31日和1995年1月10日在雷州半岛西南部海域发生了6.1级和6.2 级地震,这两次地震对该区珊瑚礁的发育有较大的影响。     

新疆准噶尔盆地西北部二叠纪玄武岩浆作用流体介质条件:流体化学组成及碳同位素制约

准噶尔盆地西北部深层分布着大量的二叠纪玄武岩,其发育的流体介质条件缺乏系统研究。本文采用二叠纪玄武岩岩心样品,对基质中的流体化学组成和碳同位素组成进行分步加热质谱法分析,结果表明二叠纪玄武岩的流体组成中H_2O的含量极高(平均13789mm3.STP/g),次要组分为CO_2、O_2、H_2S和N2等,CO_2和CH_4的δ~(13)C值(分别为-28.9‰~-15.8‰和-36.8‰~-21.9‰)位于地壳与甲烷氧化来源组分的范围内;CH_4、C_2H_6、C_3H_8和C_4H_(10)等甲烷同系物的碳同位素组成随碳数增高总体具有正序分布特征,400~800℃温度段释出CH_4的δ~(13)C值(-25‰左右)明显重于200~400℃的(-35‰左右),部分样品400~800℃的CH_4-C_3H_8存在碳同位素反序分布的特征,显示幔源流体挥发份特征,其中混入大量的沉积有机质热裂解成因烃类气体,应为俯冲蚀变大洋板片的沉积物脱出流体挥发份。大量的H_2O指示岛弧俯冲的再循环流体的加入,甲烷氧化来源特征的CO_2和CH_4碳同位素组成揭示经历了长期的风化过程,表明相关岩浆作用后遭受长期的抬升。     

A seismic source zone model for the seismic hazard assessment of the Italian territory

We designed a new seismic source model for Italy to be used as an input for country-wide probabilistic seismic hazard assessment (PSHA) in the frame of the compilation of a new national reference map.

We started off by reviewing existing models available for Italy and for other European countries, then discussed the main open issues in the current practice of seismogenic zoning.

The new model, termed ZS9, is largely based on data collected in the past 10 years, including historical earthquakes and instrumental seismicity, active faults and their seismogenic potential, and seismotectonic evidence from recent earthquakes. This information allowed us to propose new interpretations for poorly understood areas where the new data are in conflict with assumptions made in designing the previous and widely used model ZS4.

ZS9 is made out of 36 zones where earthquakes with M_w > = 5 are expected. It also assumes that earthquakes with M_w up to 5 may occur anywhere outside the seismogenic zones, although the associated probability is rather low. Special care was taken to ensure that each zone sampled a large enough number of earthquakes so that we could compute reliable earthquake production rates.

Although it was drawn following criteria that are standard practice in PSHA, ZS9 is also innovative in that every zone is characterised also by its mean seismogenic depth (the depth of the crustal volume that will presumably release future earthquakes) and predominant focal mechanism (their most likely rupture mechanism). These properties were determined using instrumental data, and only in a limited number of cases we resorted to geologic constraints and expert judgment to cope with lack of data or conflicting indications. These attributes allow ZS9 to be used with more accurate regionalized depth-dependent attenuation relations, and are ultimately expected to increase significantly the reliability of seismic hazard estimates.     

Heterogeneous aquitard properties in sedimentary successions in the Apennine chain: case studies in southern Italy

The aim of this study was to analyse the hydrogeologic role of siliciclastic deposits and marly‐clayey‐calcareous successions within the carbonate Apennine chain (southern Italy). The study was carried out along the northern part of the Matese carbonate massif through (1) the hydraulic characterization of siliciclastic rocks in a test site, by means of Lugeon tests, and (2) the identification of the groundwater flow system discharging at an important spring located within a marly‐clayey‐calcareous succession in a second test site, by means of isotopic investigations. The results showed that the investigated siliciclastic deposits and marly‐clayey‐calcareous successions may allow significant groundwater discharge from carbonate aquifers. Thus, they do not everywhere behave as aquitard, contrary to the previous model. Instead, groundwater flows through the upper part of these successions, where stress release fracturing enhanced rock permeability in the near‐surface bedrock. Thus, these successions may locally be a new groundwater source within the southern Apennine chain. Copyright © 2009 John Wiley & Sons, Ltd.     

Paleomagnetic Excursions Recorded in the Yanchi Playa in Middle Hexi Corridor, NW China Since the Last Interglacial

Paleomagnetic determinations on lithologieal profiles of two paralleled long drillin gcores covering the past 130 kyr B.P., GT40 and GT60,from the Yanchi Playa in the arid Northwestern China indicate that a series of pronounced paleomagnetic excursions have been documented. By correlating our results with published regional and worldwide reports 4 excursion events out of 10 apparent reversal signals (labeled from GT-1 to GT-10) were identified as excursion events coeval with the Mono Lake Event (28.4 kyr-25.8 kyr), Laschamp Event (43.3 kyr-40.5kyr), Gaotai Event (82.8 kyr-72.4 kyr) and the Blake Event (127.4 kyr-113.3 kyr), respectively. GT-9 correlates with the above-mentioned Gaotai Event,GT-7 and GT-6 correspond to two stages of the Laschamp Event and GT-5 to the Mono Lake Event. It is noteworthy that the so-called Gaotai Event has not been reported as a pronounced paleomagnetic excursion in the Northwestern China. Every magnetic excursion event corresponds to paleointensity minima, anteceding those established abrupt paleoclimatic change events, such as the Younger Drays and the Heinrich Events (H1-H6). Here, we tentatively propose that these geomagnetic excursions/reversals can be viewed as precursors to climate abruptness. During the transitional stages when the earth‘s magnetic field shifted between a temporal normal and a negative period, the earth‘s magnetic paleointensity fell correspondingly to a pair of minima. Although more precise chronology and more convincing rock magnetic parameter determinations are essentially required for further interpretation of their intricate coupling mechanism, these results may have revealed, to some extent, that the earth‘s incessantly changing magnetic field exerts an strong influence on the onset of saw-tooth shaped abrupt climate oscillations through certain feedback chains in arid Central Asia or even North Hemispheric high latitude regions.     

印度洋西北部海域鸢乌贼的触腕和腕足钓捕断裂强度

鱿鱼的腕足断裂强度是影响鱿钓脱钩率的重要因素。通过现场实测,分析了印度洋西北部海域鸢乌贼(Symplectoteuthis oualaniensis)的腕足断裂强度对手钓作业脱钩率产生的影响。结果表明,鸢乌贼的每根触腕仅能承受的拉力相当于体重的0.7倍,因此,钓捕过程中,因触腕断裂造成的脱钩率接近100%;而另外的第I-IV腕足的断裂强度分别是其体重的2.30、2.05、2.06和1.87倍;5对腕足整体的平均脱钩率接近10%。     

Structure of the satellitary accretion disk of Saturn

A detailed computation on the equilibrium structure of an accretion disk around Saturn from which the regular satellites presumably originated is reported. Such a disk is the predecessor of the self-dissipating disk that is formed when the mass infall stops (Cassen and Moosman, 1981, Icarus48, 353–376). When determining the disk structure local energy balance was assumed. Convention was taken into account by introducing local energy dissipation and, in an approximate manner, sonic convection. Changes in the disk structure were investigated by varying the free parameters, i.e., the external flux from both the protosun and the protoplanet, the abundance of dust and the strength of turbulence. It has been verified that the external energy flux does not play an important role in the evolution of the disk structure. Models characterized by either longer times (?3 10³ year) or a noticeable depletion of condensable elements (10^?2 times less than the solar value) have a total mass of the order of 0.34?0.1 times the mass of the regular satellites increased by the mass of the light elements. Low turbulence models (Reynolds critical number $\text{Re}{}^1\text{= 150}$) are characterized approximately by a total mass twice as large the mass of the regular satellites. All the studied models present a temperature distribution that allows the condensation of iron, silicate, and, in the outer regions, ice grains. All models but the one with 10^?2 of the solar value of condensable elements are characterized by a wide convective region that contains the formation zone of the regular satellites.     

Early to Middle Jurassic (ca. 182–164 Ma) fractionated granitoids in the Korean Peninsula: Implication for the tectonomagmatic history of East Asia

The Jurassic granitoids (200–164 Ma) are distributed in the Korean Peninsula due to the Paleo-Pacific plate subduction. Early Jurassic (200–182 Ma) granitoids are mainly distributed in the southern Korean Peninsula. By contrast, Early to Middle Jurassic (182–164 Ma) granitoids are distributed in the central Korean Peninsula. In this study, we report detailed petrology, zircon U–Pb ages, and whole-rock geochemistry from the Seoul–Uijeongbu and Pocheon–Gimhwa pluton units in the central Korean Peninsula. The Seoul–Uijeongbu unit is dominated by biotite granite, with minor porphyritic biotite and garnet-biotite granite while the Pocheon–Gimhwa unit consists of biotite granite and porphyritic biotite granite, garnet-biotite granite, and two-mica granite. Zircon U–Pb age from those granites gives 180–167 Ma. The granitoids in the Pocheon-Gimhwa unit formed through fractional crystallization from biotite granite and porphyritic biotite granite to garnet-biotite granite, and two-mica granite based on gradually decreasing their Nb/Ta, Zr/Hf, and Eu/Eu* ratios. The strongly fractionated granitoids are garnet-biotite granite and two-mica granite. The LILE enrichment, Ta–Nb, Sr–P, and Eu–Ti troughs, and Ba depletion in most granitoids are similar to those of granitoids due to the subduction in the arc environment. Thus, these Jurassic granitoids (180–167 Ma) are mainly peraluminous granites with moderate crystal fractionation corresponding to I-type granite. Alkali feldspar granite associated with ore mineralization occurs in the Gwanaksan pluton from the southwestern Seoul–Uijeongbu unit. The alkali feldspar granite displays distinct negative Eu anomaly with high contents of Rb, Hf, Cs, and Nb compared with other granites. These characteristics imply that alkali feldspar granite experienced strong hydrothermal activity leading to feldspar ore mineralization compared to the other granites. The formation of a wide range of moderately evolved peraluminous granitoids is presumed to be related to rapid flat-subduction during 182–164 Ma, and the mineralization-related alkali feldspar granite indicates the termination of Jurassic granitoid magmatism in the central Korean Peninsula.     

24万年来西昆仑山甜水海湖岩芯碳酸盐含量变化与气候环境演化

青藏高原现代气候与环境存在着明显的区域差异。高原西北部的西昆仑山甜水 海地区是高原上气候最干旱的区域。作者于１９９５年６月在该区海拔４８４０ｍ的湖盆首次打钻取芯（ＴＳ９５孔）,获得５７ｍ湖泊岩芯,经对样品的实验室测年和多项环境指标分析,表明,ＴＳ９５孔岩芯覆盖了距今２４０－１７ｋａ间的时间尺度。期间,经历了倒数第二次冰期,末次间冰期,末次冰期早期,末次冰期间冰阶和末次冰盛期几个气候变化阶段。岩芯中