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1.
西藏普兰地区拉昂错蛇绿岩中辉绿岩的锆石SHRIMP U-Pb年龄及其地质意义 总被引：15，自引：0，他引：15
蛇绿岩中的辉绿岩岩墙是洋脊扩张的产物,其形成年龄代表了扩张事件的时间,也代表了蛇绿岩的形成时代.对雅鲁藏布江缝合带西段拉昂错蛇绿岩中的辉绿岩岩墙进行锆石SHRIMP U-Pb定年,得出加权平均年龄为120.2Ma±2.3Ma,代表辉绿岩的结晶年龄.结合已有的关于雅鲁藏布江蛇绿岩的形成年龄(西段休古嘎布122.3Ma±2.4Ma,中段大竹卡126.0Ma±1.5Ma、吉定123.0Ma±1.8Ma,东段罗布莎162.9Ma±2.8Ma)的报道,表明拉昂错地区特提斯洋海底扩张的时代与休古嘎布地区一致,雅鲁藏布江西段与中段地区洋盆的形成时代一致,但晚于东段的发育时代.这意味着整个东提斯洋盆的发育时代存在东早西晚的特点. 相似文献
2.
蛇绿岩中的辉绿岩岩墙是洋脊扩张的产物．其形成年龄代表了扩张事件的时间,也代表了蛇绿岩的形成时代？对雅鲁藏布江缝合带西段拉昂错蛇绿岩中的辉绿岩岩墙进行锆石SHRIMPU—Pb定年,得出加权平均年龄为120．2Ma±2．3Ma,代表辉绿岩的结晶年龄。结合已有的关于雅鲁藏布江蛇绿岩的形成年龄（西段休古嘎布122．3Ma±2．4Ma,中段大竹卡126．0Ma±1．5Ma、吉定123．0Ma＋_1．8Ma,东段罗布莎162．9Ma±2．8Ma）的报道,表明拉昂错地区特提斯洋海底扩张的时代与体古嘎布地区一致．雅鲁藏布江西段与中段地区洋盆的形成时代一致,但晚于东段的发育时代。这意味着整个东提斯洋盆的发育时代存在东早西晚的特点。 相似文献
3.
西藏休古嘎布蛇绿岩中辉绿岩锆石SHRIMP定年及其地质意义 总被引：10，自引：8，他引：10
应用SHRIMPⅡ锆石U-Pb法,对西藏休古嘎布蛇绿岩中的辉绿岩墙进行了测年,获得辉绿岩形成年龄为122.3±2.4Ma。该年龄代表了休古嘎布-达巴特提斯洋盆的形成时代,与雅鲁藏布江缝合带中段洋盆形成时代(126±1.5Ma)相当,此结果对于确定研究区特提斯洋盆的古构造格局及其发育演化过程等提供了重要的年代学制约。 相似文献
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江错蛇绿岩位于班公湖-怒江缝合带中段, 位于切里湖蛇绿岩亚带的最东端, 南邻蓬湖西蛇绿岩.江错蛇绿岩岩石组合相对较全, 主要由变质橄榄岩、辉长岩和辉绿岩等组成.江错蛇绿岩辉长岩-辉绿岩与N-MORB相比具有较高的Mg#、低Ti、K、Na和P的特征, 富集大离子亲石元素Sr、Rb、Ba和亏损高场强元素Th、Hf、Ta、Nb, REE配分图总体显示为平坦型分布模式.通过地球化学元素分析认为江错蛇绿岩是形成于SSZ之上的弧后盆地扩张脊环境.对其进行辉长岩锆石SHRIMP U-Pb定年, 得出加权平均年龄为189.8±3.3 Ma(MSWD=0.97), 该结果代表了班公湖怒江缝合带中段江错地区特提斯洋的扩张时代, 与中段东巧地区蛇绿岩年龄一致, 但晚于东段洋盆发育时代且早于西段洋盆发育时代, 表明整个班公湖-怒江洋盆发育时代存在东早西晚的特点. 相似文献
6.
休古嘎布蛇绿岩位于雅鲁藏布江蛇绿岩带西段,属于SSZ型蛇绿岩。用Sm-Nd法测定了该蛇绿岩中辉长辉绿岩的结晶年龄,辉石、斜长石和两个全岩样品的等时线年龄为(126.2±9.1)Ma,代表新特提斯洋在该区俯冲消减的时限。同时,对辉长辉绿岩的Nd-Sr-Pb同位素的测定结果表明,辉长辉绿岩的初始εNd(t)值高(6.7～9.1),反映原始岩浆起源于强烈亏损的地幔源区,未受大陆地壳物质的混染;初始206Pb/204Pb比值较低(17.412～17.523),但初始208Pb/204Pb比值较高(37.352～37.706),并具有较高的ISr值(0.70278～0.70383),指示休古嘎布蛇绿岩源于印度洋MORB型地幔域。 相似文献
7.
青藏高原南部雅鲁藏布江蛇绿岩带的时空分布特征及地质意义 总被引：6，自引：0，他引：6
雅鲁藏布江缝合带是青藏高原上重要的缝合带之一,位于青藏高原南部,蛇绿岩是该带的主体。雅鲁藏布江缝合带按蛇绿岩的出露规模、岩石层序以及侵位时间,大致可以分为东段、中段和西段。在蛇绿岩出露规模上存在显著差异,东段规模较小,中段次之,西段最大,并且在西段分成两支蛇绿岩带;蛇绿岩岩石层序出露比较齐全的是中段日喀则和东段罗布莎,其他地方的蛇绿岩均被肢解,不能组成完整的蛇绿岩岩石剖面;在蛇绿岩的形成和侵位时间上,也有着不同的特点,东段和西段集中形成于晚侏罗世—早白垩世,而中段形成时间较早,时代从中三叠世一直持续到早白垩世,主要集中形成于晚侏罗世—早白垩世。笔者系统研究雅鲁藏布江缝合带蛇绿岩在东西方向上所表现出来的差异性,对更全面深刻地了解新特提斯洋的产生、俯冲及其消亡过程和演化历史具有重要意义。 相似文献
8.
西藏吉定蛇绿岩地球化学特征及其构造指示意义 总被引：3，自引：2，他引：1
吉定蛇绿岩位于雅鲁藏布江蛇绿岩带的中段,是该带保存较好的蛇绿岩之一,通过对该岩体的研究及与附近蛇绿岩剖面的对比有助于恢复早白垩世雅鲁藏布江蛇绿岩带的演化过程。吉定蛇绿岩包括玄武岩、辉绿岩、堆晶岩及地幔橄榄岩四个岩石单元。壳层岩石岩浆结晶顺序为:橄榄石→单斜辉石→斜长石,代表湿岩浆系统分异。吉定蛇绿岩壳层熔岩(玄武岩和辉绿岩)Ti O2含量为0.87%~1.45%,平均1.1%,与印度洋N-MORB玻璃(1.19%)相似。REE配分模式具有明显的LREE亏损特征,稀土配分模式与典型的大洋中脊玄武岩相似。但其微量元素蛛网图上表现为富集LILE,而亏损HFSE,并具有较高LILE/HFSE比值特征,与俯冲带上的(SSZ)蛇绿岩相似。蛇绿岩熔岩在岩石地球化学上表现出既亲MORB,又具部分IAB的特征。结合区域上大竹卡、得几等蛇绿岩岩石及地球化学资料对比分析,提出吉定蛇绿岩形成于在洋内俯冲带上发育起来的弧后盆地,并提出日喀则地区早白垩世洋壳演化的解释模式:雅鲁藏布江中段蛇绿岩至少包含三种组分特征的蛇绿岩体,其代表性剖面分别是吉定,得村和大竹卡,分别形成于近俯冲带的弧后盆地、弧前盆地和弧后盆地,这些洋壳共同组成早白垩世时期的与特提斯洋俯冲带斜交的一条分段发育的洋中脊。 相似文献
9.
西藏泽当蛇绿岩玄武岩SHRIMP锆石U-Pb年龄
及其地质意义 总被引：1，自引：0，他引：1
雅鲁藏布江缝合带中各蛇绿岩体的准确定年对待提斯洋演化和青藏高原隆升的研究具有重要意义.泽当蛇绿岩是雅鲁藏布江缝合带东段最大的蛇绿岩块体,关于其形成年龄目前仍存在不同的认识.通过SHRIMP锆石U-Pb测年得到蛇绿岩中玄武岩的形成年龄为154.9Ma±2.0Ma(95％置信度,MSWD=0.98).蛇绿岩中的玄武岩是洋脊扩张的产物,其形成年龄代表了扩张事件的时间,也代表了蛇绿岩的形成时代.结合已有的雅鲁藏布江缝合带蛇绿岩的形成年龄,该年龄进一步反映出雅鲁藏布江缝合带蛇绿岩形成时间具有东早西晚的特点.泽当蛇绿岩与含有埃达克质英云闪长岩的泽当岛弧火成岩基本为同期形成的.地球化学特征显示定年的玄武岩形成于俯冲带之上,且具有指示洋内俯冲环境的地球化学特征.因此,泽当SSZ型蛇绿岩可能形成于洋内俯冲机制. 相似文献
10.
藏南罗布莎蛇绿岩辉绿岩中锆石SHRIMP测年 总被引：32，自引：2，他引：32
罗布莎蛇绿岩是雅鲁藏布江蛇绿岩带东段出露较好,也是研究程度较高的蛇绿岩片之一。对该蛇绿岩的形成时代至今存在分歧。本文获得该蛇绿岩辉绿岩中的锆石SHRIMPU-Pb定年的结果为162.9±2.8Ma,表明该蛇绿岩的形成时代为中侏罗世,同时发现,在罗布莎地区新特提斯洋形成时,可能存在地幔熔融的岩浆在扩张脊上涌过程中俘获老洋壳或者深海沉积物中锆石的情况;并且在侵位过程中,在该蛇绿岩的局部由于蚀变而产生了变质锆石。 相似文献
11.
Experimentally determined mineral-melt partition coefficients for Sc,Y and REE for olivine,orthopyroxene, pigeonite,magnetite and ilmenite 总被引：6，自引：0，他引：6
Roger L. Nielsen William E. Gallahan Florence Newberger 《Contributions to Mineralogy and Petrology》1992,110(4):488-499
Our current lack of understanding of the partitioning behavior of Sc, Y and the REE (rare-earth elements) can be attributed directly to the lack of a sufficiently large or chemically diverse experimental data set. To address this problem, we conducted a series of experiments using several different natural composition lavas, doped with the elements of interest, as starting compositions. Microprobe analyses of orthopyroxene, pigeonite, olivine, magnetite, ilmenite and co-existing glasses in the experimental charges were used to calculate expressions that describe REE partitioning as a function of a variety of system parameters. Using expressions that represent mineral-melt reactions (versus element ratio distribution coefficients) it is possible to calculate terms that express low-Ca pyroxene-melt partitioning behavior and are independent of both pyroxene and melt composition. Compositional variations suggest that Sc substitution in olivine involves either a paired substitution with Al or, more commonly, with vacancies. The partitioning of Sc is dependent both on melt composition and temperature. Our experimentally determined olivine-melt REE Ds (partition coefficients) are similar to, but slightly higher than those reported by McKay (1986) and support their conclusions that olivines are strongly LREE depleted. Y and REE mineral/melt partition coefficients for magnetite range from 0.003 for La to 0.02 for Lu. Ilmenite partition coefficients range from 0.007 for La to 0.029 for Lu. These experimental values are two orders of magnitude lower than many of the published values determined by phenocryst/matrix separation techniques. 相似文献
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Regional landslide-hazard assessment for Seattle, Washington, USA 总被引：13，自引：6，他引：13
Rex L. Baum Jeffery A. Coe Jonathan W. Godt Edwin L. Harp Mark E. Reid William Z. Savage William H. Schulz Dianne L. Brien Alan F. Chleborad Jonathan P. McKenna John A. Michael 《Landslides》2005,2(4):266-279
Landslides are a widespread, frequent, and costly hazard in Seattle and the Puget Sound area of Washington State, USA. Shallow
earth slides triggered by heavy rainfall are the most common type of landslide in the area; many transform into debris flows
and cause significant property damage or disrupt transportation. Large rotational and translational slides, though less common,
also cause serious property damage. The hundreds of landslides that occurred during the winters of 1995–96 and 1996–97 stimulated
renewed interest by Puget Sound communities in identifying landslide-prone areas and taking actions to reduce future landslide
losses. Informal partnerships between the U.S. Geological Survey (USGS), the City of Seattle, and private consultants are
focusing on the problem of identifying and mapping areas of landslide hazard as well as characterizing temporal aspects of
the hazard. We have developed GIS-based methods to map the probability of landslide occurrence as well as empirical rainfall
thresholds and physically based methods to forecast times of landslide occurrence. Our methods for mapping landslide hazard
zones began with field studies and physically based models to assess relative slope stability, including the effects of material
properties, seasonal groundwater levels, and rainfall infiltration. We have analyzed the correlation between historic landslide
occurrence and relative slope stability to map the degree of landslide hazard. The City of Seattle is using results of the
USGS studies in storm preparedness planning for emergency access and response, planning for development or redevelopment of
hillsides, and municipal facility planning and prioritization. Methods we have developed could be applied elsewhere to suit
local needs and available data. 相似文献
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David W. Valentino Jeffrey R. Chiarenzelli 《Proceedings of the Geologists' Association. Geologists' Association》2014
Structural, petrographic, and geochemical criteria are applied in combination to determine the petrologic origins of slaty rocks in polydeformed metasedimentary terranes. Multiple lines of evidence suggest that the Peach Bottom slate (PBs), mined over several centuries, is an ultraphyllonite. It occurs within an Alleghanian dextral retraining bend within the Appalachian Piedmont, as a segment of the Pleasant Grove-Huntington Valley shear zone system (>200 km long). The PBs differs markedly from other slates, in that, it contains abundant, micro-scale remnant porphyroclasts of higher-grade minerals. The PBs has major, trace and rare earth element geochemistry and 147Sm/143Nd ratios that are similar to the surrounding pelitic rocks. When compared to average slates, the geochemistry of the PBs exhibits depletion in alkali earth and alkali elements. 相似文献
14.
A new conceptual model for release rate of radionuclides from the proposed repository for high level nuclear waste located at Yucca Mountain, Nevada is developed. The model predicts that heat generated from radioactive decay combined with the unsaturated environment will lead to an inward flow system that, under many relevant conditions, will slow the release of and sometimes sequester radionuclides at locations of higher heat release and lower water percolation. The amount of protection will be greatest for more concentrated waste forms such as spent fuel and less for glass waste forms. The redistribution and concentration of the radionuclides is anticipated to significantly delay radionuclide release and create a tendency towards gradual release over time that is independent of localized penetrations of metallic barriers. 相似文献
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Kumasaka Osamu Bronen Robin Harrington Elise Knox-Hayes Janelle Laska Shirley Naquin Albert Patrick Andy Peterson Kristina Tom Stanislaus 《GeoJournal》2021,87(2):307-327
Efforts in the United States to plan or implement relocation in response to climate risks have struggled to improve material conditions for participants, to incorporate local knowledge, and to keep communities intact. Mixed methodologies of community geography provide an opportunity for dialogue and knowledge-sharing to collaboratively diagnose the challenges of climate adaptation led by communities. In this article, we advance a participatory practice model for the co-creation of knowledge initiated during a two-day workshop with members from the Biloxi-Chitimacha-Choctaw Tribe from Isle de Jean Charles in Louisiana, Yup’ik people from Newtok Village in Alaska, and researchers from the MIT Resilient Communities Lab. Building on prior scholarship of indigenizing climate change research, this article shares the experience of the workshop to support knowledge exchange and dialogue, with the goal of understanding how to build participatory and non-extractive community-academic partnerships. We reflect on the community values and principles used to guide this workshop to inform more inclusive and co-produced research partnerships, and pedagogies that can improve and assist the self-determination of groups impacted by climate change. Workshop presentations and discussions highlight interconnected themes of resources, systems & structures, regulatory imbalance, and resilience that underpin climate resettlement. We reflect on the narratives presented by members of both Indigenous tribes and NGO partners that illustrate the shortcomings of resettlement planning practices past and present as perpetuating existing inequality. In response to this structured knowledge exchange, we identify potential roles for community-academic partnerships that aim to improve the equity of existing resettlement models. We propose approaches for incorporating traditional knowledge into the pedagogy, discourse, and practice of academic planning programs.
相似文献17.
在沙泉子铜镍矿上方,开展土壤微细粒全量测量、金属活动态(粘土吸附态)测量及地电化学测量的试验工作。试验结果显示,三种方法圈定的成矿元素地球化学异常分布范围与深部隐伏矿体较为吻合,表明土壤微细粒全量测量、粘土吸附态测量和地电化学测量可以有效地指示隐伏铜镍矿体,可作为该区寻找隐伏铜镍矿的有效手段。 相似文献
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The London-Victoria lode-type Au deposit near Parkes, New South Wales, was discovered in 1863 and became the subject of modern exploration in 1980 after about 75 years of little or no activity. The deposit lies within Palaeozoic tuffaceous, andesitic rocks. Soil geochemistry was the main technique used to define drill targets, and the deposit is now at an advanced state of assessment for probable development.Rock geochemistry is being investigated as an aid in drill-core interpretation in the search for extensions to the London-Victoria deposit and other similar deposits in the district.At an early stage of the rock-geochemical work it became clear that minor basemetal mineralization was also present in the structural hanging wall at between 30 and 70 m from the lode Au deposit. Interpretation of the geochemical signatures for major elements (Ca, Mg, Na, K, Fe) and trace elements (Cu, Pb, Zn, Mn) is confused by an overlap and merging of responses from the Au and base-metal mineralization. The measurement of bromine-soluble Sb, As, Bi, and Te, together with the more conventional major and trace elements, permits discrimination between geochemical halos related to the Au and those resulting from minor base metal mineralization.The results demonstrate the use of rock geochemistry for Au exploration, its usefulness in drawing attention to geological features, and the utility of bromine-soluble trace elements commonly associated with gold mineralization. 相似文献
19.
Tom Myers 《Hydrogeology Journal》2013,21(3):655-671
Extensive phosphate mining in the Blackfoot watershed of Idaho (USA) has substantially increased the selenium (Se) concentration in the river during both snowmelt and baseflow when groundwater discharge dominates. Phosphate mines create a linkage between Se-laden shale that occurs in the Phosphoria Formation and the underlying regional Wells Formation aquifer. Using a reconnaissance-level transport model, mines in the watershed were prioritized for remediation and for comparing the results of simulations of remediation scenarios with a baseline of no remediation, for which Se concentration in the river will exceed the aquatic standard along an extensive length. An accurate simulation of recharge distribution around the watershed and simulated flux to the river is essential. Remediation of mines north of the river will substantially decrease the size of the Se plume, although significant Se will continue to discharge to the river. Similarly, remediation of three mines south of the river would decrease the Se discharge to the river but allow substantial amounts to remain stored in the groundwater north and far south of the river. A lack of calibration data is not a reason to forgo remediation, but rather ongoing data collection can be used to fine-tune plans as they are implemented. 相似文献
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