Changes of marine productivity and sedimentary environment recorded by biogenic components in the Antarctica Ross Sea since the last deglaciation

Journal of Oceanology and Limnology - Changes in the marine productivity and sedimentary environment since the last deglaciation in the Ross Sea are presented in this paper. Opal has replaced...     

Origin of the inconsistent apparent Re–Os ages of the Jinchuan Ni–Cu sulfide ore deposit,China: Post-segregation diffusion of Os

Apparent Re–Os ages of some magmatic sulfide ore deposits are older than the zircon and baddeleyite U–Pb ages which are interpreted as the formation age of the host intrusions. The Jinchuan Ni–Cu–PGE deposit of China, the world's third largest, is such a case. We report apparent Re–Os isochron ages of 1117 ± 67 Ma, 1074 ± 120 Ma and 867 ± 75 Ma with initial ¹⁸⁷Os/¹⁸⁸Os ratios of 0.120 ± 0.012, 0.162 ±0.017 and 0.235 ± 0.027 for disseminated ores, sulfides from the disseminated ores and massive ores from Jinchuan, respectively. Using these data and Re–Os ages from the literature, we find that the oldest apparent Re–Os age and lowest initial Os isotope ratio are from disseminated ores which contain small amounts of sulfide minerals, the highest initial Os isotope ratios and youngest apparent Re–Os ages, consistent with the zircon and baddeleyite U–Pb ages, are from massive ores containing 90–100 modal% sulfide, and net-textured ores with about 25 modal% sulfides yield apparent Re–Os ages and initial Os ratios intermediate between those of the disseminated and massive ores.Because Os diffusion between sulfides is inhibited by the intervening silicates even at high temperatures, re-equilibration did not occur in the disseminated ore and the samples retained the Os ratios of the contaminated magma, leading to geologically meaningless ages that are older than the formation age of the rocks. While Os-bearing sulfide minerals and magnetite show low closure temperatures of Os diffusion and the sulfide minerals in the massive ore are closely connected with each other, facilitating fast diffusion of Os, re-equilibration of Os was achieved during cooling of the ore from about 850 °C after the segregation to about 400 °C. Thus, an age corresponding to the formation time and an elevated initial Os ratio were yielded by the massive ore. Os isotopes in the net-textured ore behave in the way intermediate between the disseminated and massive ores. Pb isotope data support the Os results. Disseminated ores have heterogeneous Pb isotope ratios whereas Pb in the massive ores is more uniform, consistent with Pb isotopic equilibration in the massive ores, but not in the disseminated ores.     

The mass-balance characteristics and sensitivities to climate variables of Laohugou Glacier No. 12, western Qilian Mountains, China

Due to global warming, glaciers on the Tibetan Plateau(TP) are experiencing widespread shrinkage; however, the mechanisms controlling glacier variations across the TP are still rather unclear, especially on the northeastern TP. In this study, a physically based, distributed surface-energy and mass-balance model was used to simulate glacier mass balance forced by meteorological data. The model was applied to Laohugou No. 12 Glacier, western Qilian Mountains, China, during2010~2012. The simulated albedo and mass balance were validated and calibrated by in situ measurements. The simulated annual glacier-wide mass balances were-385 mm water equivalent(w.e.) in 2010/2011 and-232 mm w.e. in 2011/2012,respectively. The mean equilibrium-line altitude(ELA) was 5,015 m a.s.l., during 2010~2012, which ascended by 215 m compared to that in the 1970 s. The mean accumulation area ratio(AAR) was 39% during the two years. Climatic-sensitivity experiments indicated that the change of glacier mass balance resulting from a 1.5 °C increase in air temperature could be offset by a 30% increase in annual precipitation. The glacier mass balance varied linearly with precipitation, at a rate of130 mm w.e. per 10% change in total precipitation.     

Dinosaur Footprints of Early Cretaceous in Site 1 ,Yanguoxia ,Yongjing Country ,Gansu Province

ＡｆｔｅｒｔｈｅｒｅｐｏｒｔｏｆｄｉｎｏｓａｕｒｆｏｏｔｐｒｉｎｔｓｉｎｔｈｅＥａｒｌｙＣｒｅｔａ ｃｅｏｕｓｉｎ 2 0 0 0 (Ｌｉｅｔａｌ.,2 0 0 0 ) ,ｗｅｆｏｌｌｏｗｅｄｔｏｕｎｅａｒｔｈ ,ｉｎｖｅｓｔｉ ｇａｔｅａｎｄｒｅｓｅａｒｃｈｔｈｅｆｏｏｔｐｒｉｎｔｓｗｉｔｈｔｈｅｓｕｐｐｏｒｔｏｆＮａｔｉｏｎａｌＮａｔ ｕｒａｌＳｃｉｅｎｃｅＦｕｎｄａｔｉｏｎａｎｄＳｔａｄｈｏｌｄｅｒＦｕｎｄｏｆＧａｎｓｕＰｒｏｖｉｎｃｅ.Ａｔｐｒｅｓｅｎｔ ,ｔｈｅｒｅａｒｅｔｅｎｔｒａｃｋｓｉｔｅｓａｂｏｕｔ 2 86ｆｏ…     

长江下游地区地震的日月周期性

根据重力固体潮理论值公式,计算长江下游地区地震(M_s≥5.0,1900～1990)的各位相值,按Schuster检验和χ2检验进行判定,发现该地区的地震具有下述非随机的月亮和太阳的周期性:(1)半日周期,表现为太阳时角变化的半周期(P_R=0.023,χ2=7.576)和半日固体潮周期(P_R=0.017,χ2=8.167);(2)半月周期,表现为半个朔望月周期(P_R=0.011,χ2=8.985)和双周潮周期(P_R=0.061,χ2=5.588);(3)对M_s≥5.1地震,还显示出1年的周期,太阳黄经的P_R=0.035,χ2=6.712。对M_s≥5.2地震,还存在半个月球近地点黄经变化周期(P_R=0.043,χ2=6.309)。     

鄂尔多斯周缘地震带地震活动的分期和相关分析

利用最优分割法对鄂尔多斯周缘地震带(区)的地震活动进行了分期,并作了相关分析。结果表明,1000年以来汾渭地震带北段可划为4个活跃期,每个活跃期的中心间距约300年,最大地震为7级,天水—陕南地震带(区)近一、二百年的地震活动可分为持续约10年左右的几个地震簇。所有分期中,海原地震带能量释放最大,且最近仍很活跃。汾渭地震带和海原—银川地震带活跃期存在相关现象,且其南段往往先于北段活跃,目前活动水平较低。该带1900年以来地震还有与河套地震带地震相呼应的现象和沿构造带南北迁移的规律。根据分期和相关结果推测,鄂尔多斯周缘各地震带都存在中强地震背景。其中海原—银川地震带近期发生5—6级或更大地震的可能性较大,天水—陕南地震带近期也有发生中强地震的可能。汾渭地震带虽然存在孕育6级以上大震的背景,但近年还不会发生强震。     

南北地震带北段上地幔速度结构成象(Ⅲ)-应用和结果

根据地震波走时资料反演得出南北地震带北段地壳和上地幔速度结构,发现在该区上地壳存在三个近东西向的低速条带,其空间展布与该区内现今活动构速基本一致;上地幔速度分布显示在该区似有平行的北东和北西向低速条带相互穿插,总体呈现网状;海原—古浪断裂带在上下地壳及上地幔的速度结构中均表现出相应的低速带,表明它是切穿地壳的深大断裂。通过反演还发现青藏块体的东北部边界大致在天祝—兰州—静宁—千阳—略阳—江油一带。     

气压变化及其对地壳形变和深井水位的影响

根据北京塔院地区1984和1985年的微气压计记录采用频谱分析和调和分析两种方法得出了大气潮谱的详细结构;用负荷勒甫数代替潮汐勒甫数,仿照固体潮的有关公式,导出了大气潮引起的地壳应变和地倾斜公式;使用北京塔院井的水位观测资料结合当地的气压资料,分析了气压变化对深井水位的影响.理论计算和实测资料的分析结果基本相符,特别是两种结果都得出S₂大气潮引起的体膨胀约为S₂固体潮体膨胀的20％.     

地震预报中地电阻率高精度计算方法

本文利用回归分析、谐波分析和预测、理论研究了从大地电位差(Vsp)和人工电位差(ΔV)迭加的合成势差(E)中高精度分离ΔV的方法。实际计算表明:当Vsp变化规律较强时,该方法的精度比常规方法提高几倍至十几倍;当Vsp变化规律较弱时,该方法的精度一般高于或接近于常规方法的精度。     

Palaeogene Biostratigraphic Characteristics of Red Basins In Western Henan and Its Adjacent Areas, With an Outline of Palaeogene Palaeobiogeographic Provinces of China

This article is a preliminary summary of Paleogene biostratigraphy of the Liguanqiao, Tantou andYuanqu basins, with a new proposal for Paleogene paleobiogeographic provinces of China. On the basis of asynthetic analysis of the geological data, characters of the mammalian assemblages and their comparisons withother corresponding faunas, a new scheme on Paleogene biostratigraphic subdivision of the basins has been putforward here. Based on differences of biostratigraphic sequences, characteristics of mammalian assemblagesand directions of faults controlling Paleogene basins in China, six Paleogene paleobiogeographic provinces ofChina have been proposed in this paper, that is: Tianshan-Yinshan-Tumen Province; Tarim-North China Prov-ince; Kunlun-Qinling Province, Yangtze Province, Nanling and Southeastern Coastal Province, Qinghai andTibet Province.