Provenance analysis and tectonic setting of the Ordovician clastic deposits in the southern Puna Basin, NW Argentina   总被引：9，自引：0，他引：9  

Udo Zimmermann  Heinrich Bahlburg† 《Sedimentology》2003,50(6):1079-1104

Provenance studies on Early to Middle Ordovician clastic formations of the southern Puna basin in north-western Argentina indicate that the sedimentary detritus is generally composed of reworked crustal material. Tremadoc quartz-rich turbidites (Tolar Chico Formation, mean composition Q_t89 F7 L4) are followed by volcaniclastic rocks and greywackes (Tolillar Formation, mean Q_t33 F42 L25). These are in turn overlain by volcaniclastic deposits (mean Q_t24 F30 L46) of the Diablo Formation (late Arenig–early Llanvirn) that are intercalated by lava flows. All units were deformed in the Oclóyic Orogeny during the Middle and Late Ordovician. Sandstones of the Tolar Chico Formation are characterized by Th/Sc ratios > 1, La/Sc ratios ≈ 10, whereas associated fine-grained wackes show slightly lower values for both ratios. LREE (light rare earth elements) enrichment of the arenites is ≈ 50× chondrite, Eu/Eu* values are between 0·72 and 0·92, and flat HREE (heavy rare earth elements) patterns indicate a derivation from mostly felsic rocks of typical upper crustal composition. The ε_{Nd(t = sed)} values scatter around −11 to −9. The calculated Nd-T_DM residence ages vary between 1·8 and 2·0 Ga indicating contribution by a Palaeoproterozoic crustal component. The Th/Sc and La/Sc ratios of the Tolillar Formation are lower than those of the Tolar Chico Formation. Normalized REE (rare earth elements) patterns display a similar shape to PAAS (post-Archaean average Australian shale) but with higher abundances of HREEs. Eu/Eu* values range between 0·44 and 1·17, where the higher values reflect the abundance of plagioclase and feldspar-bearing volcanic lithoclasts. Average ε_{Nd(t = sed)} values are less negative at −5·1, and Nd-T_DM are lower at 1·6 Ga. This is consistent with characteristics of regional rocks of upper continental crust composition, which most probably represent the sources of the studied detritus. The rocks of the Diablo Formation have the lowest Th/Sc and La/Sc ratios, lower LREE abundances than the average continental crust and are slightly enriched in HREEs. Eu/Eu* values are between 0·63 and 1·17. The Nd isotopes (ε_{Nd(t = sed)} = −3 to −1; T_DM = 1·2 Ga) indicate that one source component was less fractionated than both the underlying Early Ordovician and the overlying Middle Ordovician units. Synsedimentary vulcanites in the Diablo Formation show the same isotopic composition. Our data indicate that the sedimentary detritus is generally composed of reworked crustal material, but that the Diablo Formation appears to contain ≈ 80% of a less fractionated component, derived from a contemporaneous continental volcanic arc. There are no data indicating an exotic detrital source or the accretion of an exotic block at this part of the Gondwana margin during the Ordovician.  相似文献   

Geology and Genesis of the Ta'ergou Skarn - Quartz Vein Tungsten Deposit in the North Qilian Caledonian Orogenic Belt, Northwest China     

Zuoheng Zhang    Jingwen Mao    Jianmin Yang    Zhiliang Wang  Zhaochong Zhang 《Resource Geology》2003,53(2):101-114

Abstract. The Ta'ergou tungsten deposit in Gansu province, northwestern China, is located in the western part of the North Qilian Caledonian orogen, and consists of scheelite skarn bodies and wolframite quartz veins. The tungsten‐bearing skarn developed by the replacement of carbonate layers intercalated in the Precambrian schist and amphibolite whereas wolframite‐quartz ore veins developed along a group of fractures that cut through horizontal skarns. The Ta'ergou tungsten deposit is genetically related to the Caledonian Yeniutan granodiorite intrusion and occurs ca. 500 m wide in the exo‐contact zone 300 ～ 500 m apart from the intrusion. The granodiorite displays a lower grade of differentiation, low content of SiO₂ and high contents of mafic components. There are three types of fluid inclusions in the wolframite‐quartz vein systems, i. e. aqueous, CO₂‐H₂O and CO₂‐rich. The homogenization temperature of aqueous inclusion ranges from 140 to 380d?C and their salinities from 6.4 to 17.4 equivalent wt% NaCl. Laser Raman spectroscopy shows that the inclusions contain a relatively high content of CO₂. The δ³⁴S values of skarn type sulfides range from +8.1 to +12.7 per mil and those of quartz vein sulfides from +9.3 to +14.9 per mil, similar to sulfides of the granodiorite with from +6.0 to +11.7 per mil. The δ¹⁸O values of quartz are between +10.5 and +13.3 per mil and those of wolframite between +3.4 and +5.1 per mil. The δ¹⁸O water values of ore forming fluids range from +0.6 to +6.4 per mil and suggest the mixture of magmatic fluids with meteoric water formed the ore‐forming fluids. It has been proved that Precambrian strata in the west sector of North Qilian region are enriched in tungsten. We propose the strata were remelted to be tungsten‐granitoid during subduction. The polymetallic tungsten was gradually accumulated into the roof pendants of the granite intrusion by fractional crystallization and then was deposited by hydrothermal fluids during metasomatism and infilling along fractures. On the other hand, the granite intrusion also acted as “heating machine” to make hydrothermal fluids leach out the metals from Precambrian strata and these metals joined the ore‐forming hydrothermal system.  相似文献   

硫同位素混合总体筛分   总被引：4，自引：1，他引：4       下载免费PDF全文

崔彬  赵磊  詹朝阳  和志军 《地球学报》2003,24(6):494-496

现代矿床学研究表明，绝大多数矿床的形成具有多来源、多阶段、多成因的特点。定量研究S同位素来源可将形成一个矿床的过程看作是多个总体的混合或叠加，在数学上这种混合或叠加可以用混合总体筛分的数学模型来描述。笔者在长江中下游地区和湖南东坡矿田中成功地应用混合总体筛分的数学模型，定量研究了S同位素来源的问题，这一问题的解决对于研究成矿物质来源和成矿机理具有重要的意义。  相似文献   

高放废物处置系统地下水同位素特征   总被引：4，自引：1，他引：4  

郭永海  刘淑芬  吕川河 《地球学报》2003,24(6):525-528

在高放废物处置库场地特性评价中，对于深地质处置方案而言，最有可能使放射性核素进入生物圈的机制是地下水的迁移，因此，水文地质研究是场址预选和评价中的一个重要内容。本文以甘肃北山预选区旧井地段为例，根据地下水同位素数据，结合所获得的地质、水文数据和信息，分析研究了研究区基岩地下水的起源、形成、演化和循环特征。研究表明，北山预选区旧井地段，深部地下水和浅部地下水均源自大气降水的补给，弱含水、低渗透、低流速是该区的主要水文地质特征。  相似文献   

Origin and Formational Environment of Noda-Tamagawa Manganese Ore, Northeast Japan: Constraints from Isotopic Studies     

Mohammed El Rhazi  Ken-ichiro Hayashi 《Chemie der Erde / Geochemistry》2003,63(2):149-162

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Paleoecology of two marine oxygen isotope stage 7 sites correlated by the Sheep Creek tephra, northwestern North America     

Charles E Schweger 《Quaternary Research》2003,60(1):44-49

Pollen analysis at two sites, correlated by the presence of the 190,000 yr-old Sheep Creek tephra, documents fluctuations in vegetation and climate consistent with this date and indicates that the records span marine oxygen isotope stage 7 and the stage 6/7 transition. Dawson Cut, near Fairbanks, Alaska, provides a 5.2-m-long pollen record of interglacial boreal forest succeeded by shrub tundra and then forest/tundra. Ash Bend, Stewart River, central Yukon, provides a 9.5-m-long record of interglacial boreal forest succeeded by forest/tundra, shrub tundra, and herbaceous tundra. The replacement of forest at both sites by more open or tundra vegetation indicates warm interglacial conditions giving way to cold and arid climate. It is not clear whether stage 7 was warmer than the present. The warm-cool-warm climate oscillation evident at both sites may correlate to Lake Baikal substages 7a, 7b, and 7c. Sheep Creek tephra fell on forest/tundra vegetation.  相似文献   

河北省黄壁庄水库坝基渗漏单井示踪试验研究     

杜国平  董巧云  冷元宝  崔琳 《地球物理学进展》2003,18(3):395-399

以河北省黄壁庄水库副坝坝基的渗漏塌坑为例，利用“九五”国家重点科技成果推广项目“智能化地下水动态参数测量仪”在天然流场下，测量出水库自然渗漏量地下水的渗透流速流向、垂直向流速流向，每米含水层的渗透系数等工程必须的水文地质参数。确定性地诊断和检测出黄壁水库坝基渗漏隐患出现的具体位置和高程，从而为大坝的渗漏处理和安全处理提供详细的现场测量数据。  相似文献   

大布苏湖沉积剖面碳酸盐含量氧同位素特征的古气候意义   总被引：10，自引：3，他引：10  

沈吉  吴瑞金  羊向东  潘红玺  安芷生 《湖泊科学》1997,9(3):217-222

对大布苏湖沉积剖面碳酸盐含量和氧同位素特征研究表明，湖区15000年以来经历了多期冷湿与暖干气候旋回，大约距今6700年左右，气候变干并进入稳定的温暖时期，湖水逐渐高度浓缩，形成了现今的盐碱湖。  相似文献   

利用洞穴石笋的δ~(18)O和δ~(13)C重建3000a以来北京地区古气候和古环境——石花洞研究系列之三   总被引：10，自引：0，他引：10       下载免费PDF全文

李红春  顾德隆  陈文寄  李铁英 《地震地质》1997,(1)

首次提出用石笋中稳定同位素记录重建由降雨量和降水气团同位素组成所反映的古气候历史，从而为研究高分辨率的古季风气候信息开辟了新的途径。利用Ｈｅｎｄｙ准则、洞穴温度、研究区水系的δ１８ＯＨ２Ｏ值以及温度公式，证实了同位素分析结果的可靠性，ＣａＣＯ３－Ｈ２Ｏ之间存在同位素平衡分馏。对采自石花洞的石笋样品进行了分辨率约为２５ａ的δ１８Ｏ和δ１３Ｃ的分析测量，从而得到３０００ａ以来，北京地区古气候和古环境的变化信息  相似文献   

Measurement of Carbon Dioxide Emissions Plumes from Prudhoe Bay, Alaska Oil Fields     

Steven B. Brooks  Timothy L. Crawford  Walter C. Oechel 《Journal of Atmospheric Chemistry》1997,27(2):197-207

Large carbon dioxide plumes with concentrations up to 45 ppm aboveambient levels were measured about 15 km downwind of the Prudhoe Bay, Alaskamajor oil production facilities, located at 70° N Lat. above the ArcticCircle. The measured emissions were 1.3 × 10³ metrictons (C) hour^-1 (11.4× 10⁶ metric tons(C) year^-1), six times greater than the combustion emissionsassumed by Jaffe and coworkers in J. Atmos. Chem. 20 (1995), 213–227,based on 1989 reported Prudhoe Bay oil facility fuel consumption data, andfour times greater than the total C emissions reported by the oil facilitiesfor the same months as the measurement time periods. Variations in theemissions were estimated by extrapolating the observed emissions at a singlealtitude for all tundra research transect flights conducted downwind of theoil fields. These 30 flights yielded an average emission rate of1.02 × 10³ metric tons (C) hour^-1 with astandard deviation of 0.33 × 10³. These quantity ofemissions are roughly equivalent to the carbon dioxide emissions of7–10 million hectares of arctic tussock tundra (Oechel and Vourlitis,Trends in Ecol. Evolution 9 (1994), 324–329).  相似文献