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151.
1994年全球地震活动属于高水平,有4次大深震和4次浅源大地震。全球全年共发生6级以上地震134次,超过1993年。全球地震活动中心仍在太平洋西北边缘地震带。10月4日的千岛群岛地震是最大的浅源地震;6月9日的玻利维亚地震是最大的深源地震。1994年全球地震活动开始转折,揭开强烈活动期的序幕。各大地震带的A(b)值几乎按同一比例上升,显示全球地震整体性增强。全球地震A(b)值在6月和10月有两次高 相似文献
152.
153.
High-resolution climate variability of southwest China during 57-70 ka reflected in a stalagmite δ18O record from Xinya Cave 总被引:1,自引:0,他引:1
Li TingYong Yuan DaoXian Li HongChun Yang Yan Wang JianLi Wang XinYa Li JunYun Qin JiaMing Zhang MeiLiang Lin YuShi 《中国科学D辑(英文版)》2007,50(8):1202-1208
A 26-cm-long stalagmite (XY2) from Xinya Cave in northeastern Chongqing of China has been ICP-MS 230Th/U dated, showing a depositional hiatus at 2.3 cm depth from the top. The growth of the 2.3–26 cm interval determined by
four dates was between 57 ka and 70 ka, with a linear growth rate of 0.023 mm/a. We have analyzed 190 samples for δ
18O and δ
13C, mostly in the 2.3–26 cm part. The δ
18O and δ
13C values between 57 ka and 70 ka reveal decadal-to-centennial climatic variability during the glacial interval of Marine Isotope
Stage 4 (MIS4), exhibiting much higher resolution than that of the published Hulu and Dongge records during this interval.
Speleothem δ
18O in eastern China, including our study area can be used as a proxy of summer monsoon strength, with lighter values pointing
to stronger summer monsoon and higher precipitation, and vice versa. Two decreases in the δ
18O signature of XY2 record around 59.5 and 64.5 Ka are argued to correspond to the Dansgaard-Oeschger (D-O) events 17 and 18
respectively. The Heinrich event 6 (H6) can be identified in the record as a heavy δ
18O peak around 60 ka, indicating significant weakening of the monsoon in Chongqing during the cold period. The XY2 δ
18O record shows very rapid change toward to the interstadial condition of the D-O event, but more gradual change toward to
the cold stadial condition. This phenomenon found in the Greenland ice core records is rarely observed so clearly in previously
published speleothem records. According to SPECMAP δ
18O record, the glacial maximum of MIS 4 was around 64.5 ka with the boundary of MIS 3/4 around 60 ka. Unlike the marine record,
the speleothem record of XY2, China, exhibits much high frequency variations without an apparent glacial maximum during MIS
4. However, the timing of MIS 3/4 boundary seems to be around 60 ka when the H6 terminated, in agreement with the marine chronology.
The growth period of sample XY2 during glacial times probably reflects a local karstic routing of water, rather than having
climatic significance.
Supported by the National Natural Science Foundation of China (Grant Nos. 40672165, 90511004, 40672202) and the Academician
Special Project of Chongqing Science Committee (Grant No. 2003-7835) 相似文献
154.
155.
To understand the oxidation state and process of oxidation of lava domes, we carried out magnetic petrological analyses of lava samples obtained from domes and block-and-ash-flow deposits associated with the 1991–1995 eruption of Unzen volcano, Japan. As a result, we recognize three different types of magnetic petrology, each related to deuteric high-temperature oxidation during initial cooling. Type A oxides are characterized by homogenous titanomagnetite and titanohematite, indicating a low oxidation state and high titanomagnetite concentrations. Type B oxides are weakly exsolved and contain titanohematite laths and rutile lenses, indicating a higher oxidation state. Type C oxides, which represent the highest oxidation state, are completely exsolved and composed of Ti-poor titanomagnetite, titanohematite, rutile, and pseudobrookite, indicating high hematite concentrations. Some grains in Types A and B show indications of reduction, which was related to interaction with volcanic gases subsequent to high-temperature oxidation. In terms of geological occurrence, the oxidation processes probably differed for endogenous and exogenous domes. Endogenous dome lavas are oxidized concentrically and are classified into the three types according to their location within the dome: samples from the surface are strongly oxidized and classified as Type C, while the inner part is unoxidized and classified as Type A. Exogenous dome lavas are unoxidized and assigned to Type A. Some samples show signs of reduction, which may have occurred around fumaroles. We propose that location within the dome and the process of dome growth are the factors that control oxidation. 相似文献
156.
吐哈盆地十红滩铀矿床地质特征及控矿因素分析 总被引:1,自引:0,他引:1
李保侠 《华东地质学院学报》2002,25(4):292-300
叙述了吐哈盆地地质概况;十红滩铀矿区找矿目的层地质和砂体特征;重点对层间氧化带的纵横展布规律、地球化学分带性及前锋与铀矿化的关系作了阐述;对十红滩铀矿床南、北矿带的空间分布、形态、规模、物质成分、铀存在形式及南、北矿带差异做了研究。通过分析,最后得出十红滩铀矿床控矿因素是层间氧化带、鼻状隆起(南矿带)和北西向断裂构造(北矿带)、同时说明了局部铀矿化产出的决定因素。 相似文献
157.
砂岩型铀矿主要产在层间氧化带的尖灭地段 ,在地表无露头 ,因此有必要对层间氧化带尖灭地段的确定方法进行研究。为了能较为客观地反映铀矿的成矿环境 ,更准确地确定铀矿层间氧化带尖灭地段的位置 ,利用水岩体系Eh pH法在新疆伊犁 5 12砂岩型铀矿床中进行了研究。结果表明 ,Eh值在氧化带为高正值 ,在过渡带与还原带为低负值 ;pH值在氧化 还原过渡带接近中性 ;结合水 铀平衡区间图解 ,以水岩体系Eh值作为主要的分带指标 ,可以划分出层间氧化带的 4个分带的Eh值范围 ,从而可以精确地确定层间氧化带尖灭地段即铀矿石带的位置。该方法在国内砂岩型铀矿床中首次得到应用。 相似文献
158.
吐哈盆地水文地质条件研究 总被引:5,自引:1,他引:5
铀成矿层间氧化带的形成,发育与地下水的形成演化密切相关,本文采用古水文地质的分析方法,对吐哈盆地地下水的演化史进行了研究,定量确定了地静压力系统和水静压力系统对沉积水的改造作用,计算了压挤水和渗入水的水交替强度,指出了铀成矿层间氧化带发育的有利地区。 相似文献
159.
砂岩型铀矿的成矿地质条件与战略选区——以二连盆地和鄂尔多斯盆地为例 总被引:9,自引:0,他引:9
砂岩型铀矿是当前铀矿勘查的重点,按照其成矿特点,一般分为3种类型,即古河道型,层间氧化带型和潜水-层间氧化带型,本对这3种砂岩型铀矿产出地质条件的异同点进行了分析,初步总结了各种类型铀矿床的成矿模式,并以二连盆地和鄂尔多斯盆地例,对其成矿前景进行了宏观分析和评价。 相似文献
160.
碳硅泥岩型铀矿成矿特征,形成机理及找矿前景的讨论 总被引:2,自引:0,他引:2
伊勒门盆地是典型的中新生代山间盆地。文中分析了盆地盖层下白垩统巴彦花组的沉积体系特征及砂岩型铀矿找矿远景。认为辫状河、三解洲砾岩、砂砾央及砂岩层是寻找潜水层间氧化带砂岩型铀矿的有利层位,初步确定达来隆起带北西侧、查干台格布其狭长凹陷带及包林布其南部地区3片潜水层间氧化带砂岩型铀矿远景区。 相似文献