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51.
The identification of fresh basalt spectra plays an important role in lunar stratigraphic studies; however, the process can be time consuming and labor intensive. Thus motivated, we developed an empirically derived algorithm for the automated identification of fresh basalt spectra from Clememtine UVVIS data. This algorithm has the following four parameters and limits: BC Ratio=3(R950−R900)/(R900−R750)<1.1, CD Delta=(R1000−R950)/R750−1.09(R950−R900)/R750>0.003 and <0.06, B Slope=(R900−R750)/(3R750)<−0.012, and Band Depth=(R750−R950)/(R750−R415)>0.1, where R750 represents the unnormalized reflectance of the 750 nm Clementine band, and so on. Algorithm results were found to be accurate to within an error of 4.5% with respect to visual classification, though olivine spectra may be under-represented. Overall, fresh basalts identified by the algorithm are consistent with expectations and previous work in the Mare Humorum area, though accuracy in other areas has not yet been tested. Great potential exists in using this algorithm for identifying craters that have excavated basalts, estimating the thickness of mare and cryptomare deposits, and other applications. 相似文献
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53.
《Geodinamica Acta》2013,26(5):349-361
The most widespread blocks within the Cretaceous ophiolitic mélange (North Anatolian ophiolitic mélange) in Central Anatolia (Turkey) are pillow basalts, radiolarites, other ophiolitic fragments and Jurassic-Cretaceous carbonate blocks. The pillow basalts crop out as discrete blocks in close relation to radiolarites and ophiolitic units in Cretaceous ophiolitic mélange. The geochemical results suggest that analyzed pillow basalts are within-plate ocean island alkali basalts. The enrichment of incompatible elements (Nb, Ta, Light REE, Th, U, Cs, Rb, Ba, K) demonstrates the ocean island environment (both tholeiites and alkali basalts) and enriched MORB. Dated calcareous intrafills and biodetrital carbonates reveal an age span of Callovian—Early Aptian. The thin-shelled protoglobigerinids, belonging to the genus Globuligerina, in the calcareous intrafills between pillow basalt lobes indicates a Callovian—Barremian age interval, most probably, Valanginian to Late Barremian. The volcanic and radiolarite detritus-bearing orbitolinid—Baccinella biodetrital carbonates dated as Late Barremian-Early Aptian in age, were probably deposited around atolls and have a close relationship with the ocean island pillow basalts. The results collectively support the presence of a seamount on the Neo-Tethyan oceanic crust during the Valanginian—Late Barremian and atolls during the Late Barremian-Early Aptian interval. The presence of an oceanic crust older than that seamount along the Northern Branch of Neo-Tethys is conformable with the geodynamic evolution of the Tethys. 相似文献
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55.
塔里木盆地夏河南层状玄武岩的岩石地球化学特征及地质意义 总被引:1,自引:0,他引:1
塔里木盆地夏河南玄武岩露头以水平层状分布为最大特征,其玄武岩层和沉积夹层保持了较原始的产状,是研究塔里木盆地二叠纪多期次玄武质岩浆活动的理想场所,是对比盆地内其他玄武质岩浆活动的最佳剖面。本文通过详细的野外和遥感解译工作,报道了夏河南玄武岩的野外产状、岩相学特征和各层玄武岩的地球化学特征,探讨了夏河南玄武岩的岩浆源区和岩浆演化过程。研究认为夏河南玄武岩质岩浆来源于富集的岩石圈地幔,为尖晶石-石榴石二辉橄榄岩经历低程度部分熔融的产物,各层玄武岩的成分差异与部分熔融程度有关,单一层内玄武岩的岩浆演化以分离结晶为主,地壳混染程度较小。夏河南各层玄武岩来源于同一岩浆源区,其特征与柯坪玄武岩相似,可对应于柯坪地区开派兹雷克组的6层玄武岩。研究进一步明确了塔里木盆地早二叠世玄武岩的空间分布特征,证实塔里木早二叠世大火成岩省的玄武质岩浆作用可从柯坪地区延伸到夏河南、塔中、塔西南等地。 相似文献
56.
Surface sediment samples were collected from 5 pristine coastal areas and 1 potentially contaminated coastal site on Tutuila, the main island of American Samoa, an isolated island group in the South Pacific Ocean. Samples were analysed for total element analysis (15 elements) and mineralogy. The results indicated no evidence of trace element contamination at any site, including Pago Pago Harbour. Inter-site variations could be explained assuming the sediments consisted predominantly of coralline sand and rubble with varying quantities of basaltic materials derived from local catchments. 相似文献
57.
开展广泛的磁化率特征研究是目前中国南方红色风化壳环境磁学研究的一个重要内容。通过对昆明西山4个峨眉山玄武岩风化壳剖面进行系统的磁化率测定发现,所有剖面磁化率值都呈现自剖面底部向顶部增高的趋势,这一现象与以往流行的玄武岩风化壳磁化率值随风化成土过程的加深而减小的模式有较大出入。磁化率与频率磁化率的对比分析结果进一步表明风化过程中形成的超顺磁颗粒可能是本区玄武岩风化壳(至少顶部60 cm区域)磁化率增强的主要贡献者。 相似文献
58.
The Hvalfjördur area, 30 km north of Iceland’s capital Reykjavik, belongs to the sequence of Late Tertiary to early Quaternary flood basalts with minor intercalations of hyaloclastites and rhyolites. The basalts are affected by progressive low-temperature metamorphism, caused by the burial of the lava succession and higher heat flow from nearby central volcanoes. Low-grade zeolite facies metamorphism of basaltic lavas in the Hvalfjördur area results in two distinct mineral parageneses that can be correlated to events in the burial and hydrothermal history of the lava pile. Stage Ia represents syn-eruptive near-surface alteration in which celadonite and silica were precipitated along primary pores. During regional burial metamorphism (stage Ib), hydrolysis of olivine and glass led to the formation of mixed-layer chlorite/smectite clays. The chlorite content of stage Ib phyllosilicate vesicle rims increases with increasing burial depth and temperature. Stage II occurred after the burial and is marked by zeolite mineralization caused by higher heat flow from the Laxárvogur and Hvalfjördur central volcanoes. Altogether 11 different zeolites were found in the Hvalfjördur area: analcime, chabazite, epistilbite, heulandite, laumontite, levyne, mesolite, stilbite, stellerite, thomsonite and yugawaralite. In total, three separate depth and temperature-controlled “zeolite zones” occur in the Hvalfjördur area. 相似文献
59.
矿床分布于北西向地球化学急变带古火山口。受峨眉山玄武岩控制,赋存于硅质、沥青质、气孔熔岩中。矿化与沥青化、硅化、方解石化密切相关。应为峨眉山玄武岩型同生热液矿床。 相似文献
60.
Shallow plumbing systems for small-volume basaltic volcanoes 总被引:3,自引:3,他引:0
Gordon N. Keating Greg A. Valentine Donathon J. Krier Frank V. Perry 《Bulletin of Volcanology》2008,70(5):563-582
Eruptive dynamics in basaltic volcanoes are controlled, in part, by the conduit geometry. However, uncertainties in conduit
shape and dike-to-conduit transition geometry have limited our predictive capability for hazards assessments. We characterize
the subvolcanic geometry of small-volume basaltic volcanoes (magmatic volatile-driven eruptions, 0.1 to 0.5 km3) based on a synthesis of field studies of five basaltic volcanoes exposed to varying degrees by erosion and exhibiting feeder
dikes, conduits, and vent areas ≤250 m depth. Study areas include East Grants Ridge (New Mexico, USA), Basalt Ridge, East
Basalt Ridge, Paiute Ridge, and Southeast Crater Flat (Nevada, USA). Basaltic feeder dikes 250 to 100 m deep have typical
widths of 4–12 m, with smooth host-rock contacts (rhyolite tuff). At depths less than 100 m, heterogeneities in the host rock
form preferential pathways for small dike splays and sills, resulting in a 30-m effective width at 50 m depth. The development
of a complex conduit at depths less than 70 m is reflected in bifurcating dikes and brecciation and incorporation of the country
rock. The overall zone of effect at depths less than 50 m is ≤110 m wide (220 m elongated along the feeder dike). Based on
comparisons with theoretical conduit flow models, the width of the feeder dike at depths from 250 to 500 m is expected to
range from 1 to 10 m and is expected to decrease to about 1–2 m at depths greater than 500 m. The flaring shape of the observed
feeder systems is similar to results of theoretical modeling using lithostatic pressure-balanced flow conditions. Sizes of
observed conduits differ from modeled dimensions by up to a factor of 10 in the shallow subsurface (<50 m depth), but at depths
greater than 100 m the difference is a factor of 2 to 4. This difference is primarily due to the fact that observed eroded
conduits record the superimposed effects of multiple eruptive events, while theoretical model results define dimensions necessary
for a single, steady eruption phase. The complex details of magma-host rock interactions observed at the study areas (contact
welding, brecciation, bifurcating dikes and sills, and stoping) represent the mechanisms by which the lithostatic pressure-balanced
geometry is attained. The similarity in the normalized shapes of theoretical and observed conduits demonstrates the appropriateness
of the pressure-balanced modeling approach, consistent with the conclusions of Wilson and Head (J Geophys Res 86:2971–3001,
1981) for this type of volcano. 相似文献