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Cox R Lowe DR 《Journal of sedimentary research. Section A, Sedimentary petrology and processes : an international journal of SEPM (Society for Sedimentary Geology)》1996,66(3):548-558
Most studies of sandstone provenance involve modal analysis of framework grains using techniques that exclude the fine-grained breakdown products of labile mineral grains and rock fragments, usually termed secondary matrix or pseudomatrix. However, the data presented here demonstrate that, when the proportion of pseudomatrix in a sandstone exceeds 10%, standard petrographic analysis can lead to incorrect provenance interpretation. Petrographic schemes for provenance analysis such as QFL and QFR should not therefore be applied to sandstones containing more than 10% secondary matrix. Pseudomatrix is commonly abundant in sandstones, and this is therefore a problem for provenance analysis. The difficulty can be alleviated by the use of whole-rock chemistry in addition to petrographic analysis. Combination of chemical and point-count data permits the construction of normative compositions that approximate original framework grain compositions. Provenance analysis is also complicated in many cases by fundamental compositional alteration during weathering and transport. Many sandstones, particularly shallow marine deposits, have undergone vigorous reworking, which may destroy unstable mineral grains and rock fragments. In such cases it may not be possible to retrieve provenance information by either petrographic or chemical means. Because of this, pseudomatrix-rich sandstones should be routinely included in chemical-petrological provenance analysis. Because of the many factors, both pre- and post-depositional, that operate to increase the compositional maturity of sandstones, petrologic studies must include a complete inventory of matrix proportions, grain size and sorting parameters, and an assessment of depositional setting. 相似文献
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加拿大地盾麻粒岩区的含金铁建造：一个太古代的深部金成矿体系 总被引：1，自引：0，他引：1
在加拿大地盾的苏必利尔省东部，金产于混合岩化副片麻岩区的变质铁建造之中。位于距英云闪长岩入体１００ｍ的主要金矿点，经受了类矽卡岩的变质作用，该变质作用出现于麻粒岩级变质作用的晚期。尽管矿化作用产于高级变质围岩之中，但它具有许多低级太古宙绿岩带金矿化作用的特征，例如：（１）富Ａｕ、Ａｓ、Ｓ、Ｓｂ、Ｗ、Ｕ和ＦｅＯ；（２）贱金属／金比值低；（３）金在毒砂中作为包体存在；（４）位于长英质侵入体附近；（５）富铁的碎裂围岩；（６）相近的成矿时间（大约２６５０Ｍａ）。这种金矿化出现于变质作用的峰期附近，并代表了晚太古代广泛发育的地壳深部成矿作用体系。本文的主要结论是太古代金矿化作用的主要特征与深部地壳地质作用有关，而不是与上部地层如绿岩带的淋滤作用有关。 相似文献
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Ｗｏｌｙｕ矿床是Ｙｏｕｎｇｄｏｎｇ地区最大的脉状低温热液Ａｕ－Ａｇ矿床之一，也是朝鲜第一个赋存于硫银锗矿物之中的富锗Ａｕ－Ａｇ矿床。穿切晚石炭纪凝灰岩和石英斑岩（８１．５±１．８Ｍａ）的矿脉（７８．９±１．２Ｍａ）由分属三个矿化阶段的石英和碳酸盐组成。第一矿化阶段的石英和碳酸盐中含有黄铁矿、贱金属和金银矿。第Ｉ矿化阶段的Ａｇ－Ａｕ－Ｇｅ矿脉的矿物组合随着时间演化发生系统的变化：①石英＋黄铁矿；②石英十黄铁矿＋银金矿十辉银矿＋闪锌矿；③碳酸盐十石英＋闪锌矿＋银金矿十辉银矿；④碳酸盐＋自然金＋辉银矿＋银硫矿＋硫银锗矿＋闪锌矿。温度和硫离子活度的计算值为：组合①３６０～２８０℃，１０￣（－７）～１０￣（－１０）；组合②２８０～２１０℃，１０￣（－１０）～１０￣（－１４）；组合③２１０～１８０℃，１０￣（－１４）～１０￣（－１６）；组合④１８８～１５５℃，１０￣（－１７）～１０￣（－１８）。上述数据、金与硫化物紧密共生以及蚀变带中黄铁矿的大量存在都说明了硫离子活度降低和冷却在金的沉淀中起了重要的作用。随着时间演化成矿流体中氢、氧同位素均显示出系统的变化。在主要的Ａｇ－Ａｕ－Ｇｅ成矿过程中，随着石英向碳酸盐的转变δＤ 相似文献
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钾质火成岩,橄榄粗玄岩与金矿的直接与间接的联系 总被引：3，自引：0，他引：3
世界上许多低温到中温热液和斑岩型Ａｕ±Ｃｕ产出与钾质火成岩和橄榄粗玄岩相关或产于其中。容矿岩体多以高卤族元素如Ｃｌ和Ｆ、大离子亲石元素和贫高场强元素为特征。与钾质火成岩套有关的成矿作用往往限于三类构造环境：晚期大洋岛弧、大陆弧和后碰撞弧。晚期大洋岛弧的实例有巴布亚新几内亚Ｌｉｌｉｒ岛中更新世的Ｌａｄｏｌａｍ金矿床，斐济ＶｉｔｉＬｅｖｕ上新世的Ｅｍｐｅｒｏｒ金矿和澳大利亚新南威尔士奥陶纪Ｇｏｏｎｕｍｂｌａ斑岩铜金矿床。大陆弧的实例包括中生代一新生代智利安第斯山脉的许多低温金和斑岩型Ｃｕ－Ａｕ矿床。后碰撞弧的一个实例是中新世巴布亚新几内亚的Ｐｏｒｇｅｒａ金矿床。对于这些晚期大洋岛弧、大陆弧和后碰撞弧中与金一铜矿床有关的钾质火成岩，其云母斑晶中ＣＬ的含量与同构造环境非高钾岩石相比特别高。大洋岛弧中矿化钾质火成岩的云母斑晶中似乎以十分高的ＣＬ和Ｆ为特征。 相似文献
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Heat and bromide were compared as tracers for examining stream/ground water exchanges along the middle reaches of the Santa Clara River, California, during a 10-hour surface water sodium bromide injection test. Three cross sections that comprise six shallow (<1 m) piezometers were installed at the upper, middle, and lower sections of a 17 km long study reach, to monitor temperatures and bromide concentrations in the shallow ground water beneath the stream. A heat and ground water transport simulation model and a closely related solute and ground water transport simulation model were matched up for comparison of simulated and observed temperatures and bromide concentrations in the streambed. Vertical, one-dimensional simulations of sediment temperature were fitted to observed temperature results, to yield apparent streambed hydraulic conductivities in each cross section. The temperature-based hydraulic conductivities were assigned to a solute and ground water transport model to predict sediment bromide concentrations, during the sodium bromide injection test. Vertical, one-dimensional simulations of bromide concentrations in the sediments yielded a good match to the observed bromide concentrations, without adjustment of any model parameters except solute dispersivities. This indicates that, for the spatial and temporal scales examined on the Santa Clara River, the use of heat and bromide as tracers provide comparable information with respect to apparent hydraulic conductivities and fluxes for sediments near streams. In other settings, caution should be used due to differences in the nature of conservative (bromide) versus nonconservative (heat) tracers, particularly when preferential flowpaths are present. 相似文献
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The Queensland Environmental Protection Agency monitored water quality at 133 sites in North Queensland waterways between Cooktown and Bundaburg from 1992 to 2001. Condition of the waterways was rated by comparing recent data with the Queensland Water Quality Guidelines. Long-term trends were analysed using a censored regression technique that incorporates the effects of flow, temperature, seasonality and allows for long-term non-linear trends. Many sites were in good condition; those in poor condition were usually impacted by point source discharges; those in moderate condition were usually impacted by agricultural land use. There were no consistent long-term trends across the whole region. Recommendations for future programs include incorporating pressure indicators, ensuring high standards of quality assurance, including covariates such as rainfall in trend assessment and continuing programs over more than 10 years to allow detection of trends due to changes in land-use. 相似文献
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塔里木地块上石炭统的古地磁研究 总被引：3，自引：1，他引：2
本文对塔里木地块西北缘柯坪地区的3条上石炭统康克林组剖面进行了古地磁研究。95个定向岩心样品的逐步热退磁和交变退磁揭示出3个磁性组分,第一个是具有低解阻温度谱或低矫顽力谱在现代地磁场作用下形成的粘滞剩磁A(D=10°;I=56°,α95=4°);第二个是红色石英砂岩的具有反极性的高温组分B(D=217°,I=-43°,λ=56°,Φ=184°E;A25=6°详细研究表明,该分量受附近晚二叠世脉岩侵入的重磁化;第三个是灰岩高矫顽力谱的反极性组分C（D=241°、I=-51°,λ=41°N,Φ=160°E,A（?）=4°）。这一分量通讨倾斜检验,在95%概率水平上明显不同于塔里木地块目前已有的石炭纪以后的古地磁方向,它代表了原生剩磁。研究结果表明:（1）晚石炭世塔里木地块已和哈萨克斯坦地块、苏联西天山地块以及西伯利亚地块发生碰撞:（2）苏联西天山地块相对塔里木地块曾逆时针旋转了70°（欧拉极位置λ=8°N,Φ=69°E）,而塔里木地块则相对西伯利亚地块逆时计旋转了21°（欧拉极位置λ=20°N,Φ=34°E）。从该区已有的晚古生代至早三叠世占地磁数据看,这些地块之间的相对旋转运动发生于早三叠世之后。 相似文献
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由英国剑桥大学R.S.White和D.P.Mackenzie写的两篇新论文“裂谷带的岩浆作用”和“裂谷带的火山活动”(分别见J.GeO.Phy.Res.94,7685—7730,1989和Scient.American,261,62—67,1989,)是目前最令人满意的论文之一,其中将最近几年开展的综合地质研究进行了全面总结。 至少在过去250Ma的时期内,每30Ma左右大陆区就遭受一次剧烈的火山作用,形成所谓大陆溢流玄武岩区,这些地区包括北大西洋区、埃塞俄比亚、印度德干高原、南非干燥荒原(Karoo)和南美洲的巴拉那 相似文献