萨拉乌苏组沉积时代的重新厘定

重新认识我国北方地区晚更新世河湖相标准地层--萨拉乌苏组的形成时代，对于萨拉乌苏组与马兰黄土的关系，与冰期气候对比等具有重要意义。笔者近年来根据野外层位对比和地层沉积相的划分，采用绝对年代控制，并结合黄土－古土壤序列研究的最新成果，初步建立了可以与黄土、深海沉积记录和冰期气候波动对比的萨拉乌苏组地层序列。认为河湖相沉积的萨拉乌苏组形成于约１４００００～７００００ａ.Ｂ.Ｐ.的末次间冰期，大致与深海氧同位素第５阶段对应，与黄土高原古土壤Ｓ１发育同期。城川组风成细砂形成于约７００００～１００００ａ.Ｂ.Ｐ的末次冰期，与黄土高原的马兰黄土是同期异相地质体.     

关于侵入岩体中金矿床成因研究若干问题的讨论

各时代、不同类型侵入岩中的金矿床是金矿的主要类型。关于金矿床与岩体的成因关系目前尚存在不同的看法，但传统的岩浆热液成因观点仍居统治地位，其原因往往在于不少研究者把岩液热液成因当成了固定模式应用于具体矿床的研究，而不是建立在综合研究的基础之上。本文结合近年来金矿的研究进展，强调侵入岩中金矿床的研究的研究要综合考虑成岩成矿的时代与时差，成矿流体和成矿物质的来源等各方面因素。金矿床定年的进展研究表明，矿     

Mineralization Ages of the Jiapigou Gold Deposits,Jilin

The Jiapigou gold deposits are typical vein type deposits associated withArchaean greenstone belts in China. According to the crosscutting relationships between dykesand auriferous veins, single hydrothermal zircon U-Pb dating and quartz K-Ar,~(40)Ar-~(39)Ar andRb-Sr datings, the main mineralization stage of the Jiapigou deposit has been determined to be2469-2475 Ma, while mineralization superimposition on the gold deposit occurred in1800-2000 Ma and 130-272 Ma. They form a mineralization framework of one oldermetallogenic epoch (Late Archaean-Early Proterozoic) and one younger metallogenic epoch(Mesozoic) of gold deposits in Archaean greenstone belts in China.     

巴楚-伽师Ms6.8地震地磁异常特点分析

通过分析、比较1996--2003年喀什地震台站记录到的新疆伽师及附近地区发生的多次6级地震的地磁前兆异常特征，发现在这几组地震活动过程中喀什地震台的地磁表现出不同的异常特征，说明与地震破裂特征有更深层次的相关性，且地磁响应比异常和总强度差值异常在一定程度上反映了台站周围小范围的震源区介质电性结构的变化。巴楚-伽师6．8级地震前地磁异常特征并不十分突出，有别于1996—1998年伽师强震群震前地磁异常量较丰富的特点。     

Seasonal and Diurnal Variation of Surface Ozone and a Preliminary Analysis of Exceedance of its Critical Levels at a Semi-arid Site in India

The mixing ratios of surface O₃ were measured at St. John's College, Agra, an urban and traffic influenced area for the period of 2000–2002. The monthly averaged O₃ mixing ratios ranged between 8 to 40 ppb with an annual average of 21 ppb. Strong diurnal and seasonal variations in O₃ mixing ratios were observed throughout the year except for monsoon season. The mixing ratios of O₃ follow the surface temperature cycle and solar radiation (r = 0.72 and r = 0.65 with temperature and solar radiation, respectively). Concentrations were higher with winds associated with NE and NW direction indicating the impact of pollution sources on surface O₃ concentration. Exceedance of ozone critical level was calculated using the AOT 40 index and found to be 840 ppb.h and 2430 ppb.h for summer and winter seasons, respectively. The present O₃ exposures are lower than the critical level of O₃ and suggest that the present level of O₃ does not have any impact on reduction in crop yields.     

GEOLOGICAL MARKS OF A POSSIBLE EXTRATERRESTRIAL IMPACT EVENT ON THE BOUNDARY BETWEEN SINIAN/CAMBRIAN IN TIANMENSHAN IN WESTERN HUNAN

Geologic marks related to extraterrestrial impact events, such as impact split gravels, impact brecciate layers, impact dikes, microirghizites, microtektites, especially meteoritic residues, were discovered on the boundary between Sinian/Cambrian at Tianmenshan of Western Hunan, which may possibly demonstrate that an extraterrestrial impact event has ever occurred there on the S/C boundary.     

Timing and geochemical characters of the Sanchazi magmatic arc in Mianlüe tectonic zone, South Qinling

The Sanchazi mafic-ultramafic complex in Mianlue tectonic zone, South Qinling can be subdivided into two blocks, i.e. Sanchazi paleo-magmatic arc and Zhuangkegou paleo-oceanic crust fragment (ophiolite). The Sanchazi paleo-magmatic arc is mainly composed of andesite, basaltic and basalt-andesitic gabbro (or diorite), andesitic dyke, plagiogranite and minor ultramafic rocks, which have typical geochemical features of island arc volcanic rocks, such as high field strength element (e.g. Nb, Ti) depletions and lower Cr, Ni contents. The Light rare earth element (LREE) and K enrichments of these rocks and zircon xenocrystals of 900 Ma from plagiogranite suggest that this magmatic arc was developed on the South active continental margin of the South Qinling micro-continent. The U-Pb age of (300 ± 61)Ma for zircons from plagiogranite indicates that the Mianlue paleo-oceanic crust was probably subducted underneath the South Qinling micro-continent in Carboniferous. This is consistent with the formation time (309Ma) of the Huwan eclogite originating from oceanic subduction in Dabie Mountains, suggesting that the Mianlue paleo-ocean probably extended eastward to the Dabie Mountains in Carboniferous. The high-Mg adakitic rocks in Sanchazi paleo-magmatic arc suggest that the subducted oceanic crust was relatively young (＜25Ma) and hot.     

K–Ar geochronology of the temporal change of eruptive style in the eastern Izu peninsula, central Japan

Abstract   A recent K–Ar study elucidated that eruptive style in the eastern Izu peninsula changed from polygenetic to monogenetic volcano at 0.3–0.2 Ma. To narrow down the time of change, we determined 10 K–Ar ages on Togasayama Andesite of Amagi volcano, the youngest polygenetic volcano in the area, and Togasayama Monogenetic Volcano, one of the oldest monogenetic volcanoes in the area, which overlies a part of the Togasayama Andesite. Dating results showed that the Togasayama Andesite effused at least from 0.34 to 0.20 Ma, whereas the Togasayama Monogenetic Volcano erupted at 0.26–0.29 Ma, suggesting that the northern part of the Togasayama Andesite effused after the eruption of the Togasayama Monogenetic Volcano. Considering previous data, it is therefore inferred that change of eruptive style in the eastern Izu area occurred during the period 0.29–0.20 Ma, with considerable overlap of both polygenetic and monogenetic volcanism.     

Global scale annual and semi-annual variations of daytime NmF2 in the high solar activity years

The annual and semi-annual variations of the ionosphere are investigated in the present paper by using the daytime F2 layer peak electron concentration (NmF2) observed at a global ionosonde network with 104 stations. The main features are outlined as follows. (1) The annual variations are most pronounced at magnetic latitudes of 40–60° in both hemispheres, and usually manifest as winter anomalies; Below magnetic latitude of 40° as well as in the tropical region they are much weaker and winter anomalies that are not obvious. (2) The semi-annual variations, which are usually peak in March or April in most regions, are generally weak in the near-pole regions and strong in the far-pole regions of both hemispheres. (3) Compared with their annual components, the semi-annual variations in the tropical region are more significant.In order to explain the above results, we particularly analyze the global atomic/molecular ratio of [O/N2] at the F2 layer peak height by the MSIS90 model. The results show that the annual variation of [O/N2] is closely related with that of NmF2 prevailing in mid-latitudes and [O/N2] annual variation usually may lead to the winter anomalies of NmF2 occurring in the near-pole region. Moreover, NmF2 semi-annual variations appearing in the tropical region also have a close relationship with the variation of [O/N2]. On the other hand, the semi-annual variations of NmF2 in the far-pole region cannot be simply explained by that of [O/N2], but the variation of the solar zenith angle may also have a significant contribution.     

Matuyama-Brunhes reversal and Kamikatsura event on Maui: paleomagnetic directions, Ar/Ar ages and implications

Eighty-nine basaltic lava flows from the northwest wall of Haleakala caldera preserve a concatenated paleomagnetic record of portions of the Matuyama-Brunhes (M-B) reversal and the preceding Kamikatsura event as well as secular variation of the full-polarity reversed and normal geomagnetic field. They provide the most detailed volcanic record to date of the M-B transition. The 24 flows in the transition zone show for the first time transitional virtual geomagnetic poles (VGPs) that move from reverse to normal along the Americas, concluding with an oscillation in the Pacific Ocean to a cluster of VGPs east of New Zealand and back finally to stable polarity in the north polar region. All but one of the 16 Kamikatsura VGPs cluster in central South America. The full-polarity flows, with ⁴⁰Ar/³⁹Ar ages spanning a total of 680 kyr, pass a reversal test and give an average VGP insignificantly different from the rotation axis, with standard deviation consistent with that for other 0-5 Ma lava flows of similar latitude. Precise ⁴⁰Ar/³⁹Ar dating consisting of 31 incremental heating experiments on 12 transitional flows yields weighted mean ages of 775.6±1.9 and 900.3±4.7 ka for the M-B and Kamikatsura transitional flows, respectively. This Matuyama-Brunhes age is ∼16 kyr younger than ages for M-B flows from the Canary Islands, Tahiti and Chile that were dated using exactly the same techniques and standards, suggesting that this polarity transition may have taken considerably longer to complete and been more complex than is generally believed for reversals.