排序方式： 共有48条查询结果，搜索用时 15 毫秒
21.
The Owen Conglomerate comprises coarse-grained siliciclastics that were deposited in response to Late Cambrian extension. The identification of normal faults that host thickened accumulations of siliciclastics is used here to support interpretation of syn-fill extension. Local mapping and section construction have identified a series of north-trending, en échelon, segmented normal faults that exhibit changes in along-strike polarity. The Late Cambrian faults are adjacent to sedimentary packages that define half-graben geometries, with an unconformity that defines basal contacts with underlying Mt Read Volcanics and onlap geometries onto the opposing basin margin. Faults that were active during deposition of the Owen Conglomerate were subsequently reversed during D1 Middle Devonian deformation, with reverse displacement controlling the development of inversion structures defined by north-trending fold structures. Pervasive northwest-trending D2 deformation extensively overprints earlier deformation features, and has led to the spectacular development of type 1 interference patterns that largely control outcrop distributions along the West Coast Range. Field evidence is documented in support for a simple structural history that accounts for geometries associated with Late Cambrian extension, prior to Middle Devonian inversion (D1) and subsequent shortening (D2). 相似文献
22.
Classification and regression techniques are among the most used tools by chemometricians.Withclassification,the two classic methods are discriminant analysis and SIMCA.In this paper we discuss theconnection between these two methods and introduce two new ones of the same family:DASCO(discriminantanalysis with shrunken covariances)and RDA(regularized discriminant analysis).We demonstrate on bothsimulated and real data sets that their performance is superior to the old favorites.This is especially truein small-sample/high-dimension settings typical in chemistry. 相似文献
23.
Time and tectonic processes involved in docking of the Argentine Precordillera (Cuyania terrane) against SW Gondwana has been a matter of much debate. A paleomagnetic study on the Early Caradoc Pavón Formation, exposed in the San Rafael block, province of Mendoza, Argentina, is presented. After detailed thermal and alternating field demagnetizations two geologically significant magnetic components were defined. A widespread post-tectonic component (A) is present in most sites of the Pavón Formation, with dual polarities, and is coincident with the characteristic remanence isolated from a Permo-Triassic rhyolitic dome intruding the sediments. Its pole position (83.7°S, 271.0°E, dp = 6.8°, dm = 9.0° N = 11 sites) falls on the Late Permian-Early Triassic South American reference poles suggesting that this component was acquired during the Choiyoi magmatic phase. A second component (B) also shows dual polarities and a positive fold test suggesting a primary origin. Unblocking temperatures and rock magnetic experiments indicate that B is carried either by hematite or magnetite at different sites. Anisotropy of magnetic susceptibility results suggest a depositional fabric and no remanence distortion due to deformation or compaction. A paleomagnetic pole computed from this remanence (PV) falls on 3.6°N, 346.4°E (dp = 2.9°, dm = 4.6° n = 22 samples). It indicates a paleolatitude around 26°S for deposition of Pavón sediments and constrains the paleogeographic evolution of Cuyania during the Ordovician, which was still at subtropical latitudes by the Early Caradoc. PV is consistent with the Laurentian Late Ordovician reference pole if Cuyania remains attached to SE Laurentia for the Early Caradoc, while it shows a significant cw rotation with no paleolatitude anomaly respect to the Gondwana reference pole when kept in its present position in SW South America. These comparisons are interpreted in three possible alternatives for the paleogeographic and tectonic setting of Cuyania in the Late Ordovician. 相似文献
24.
HSU Weibiao 《《地质学报》英文版》2004,78(5)
Coupled with a petrographical study, I carried out an ion probe study of rare earth element microdistributions in mineral phases of silicate inclusions from the Colomera ⅡE iron meteorite. Most mineral grains have homogeneous REEs, but show considerable inter-grain variations by a factor of 2 to 100. The whole rock REE abundances for Colomera, estimated by combining REE data with modal abundances, are relatively LREE-enriched with REEs of -10'CI, which suggest that Colomera silicates were highly differentiated and might represent a low degree partial melt (-10%) of a chondritic source. REE geochemistry of Colomera silicate inclusions points to an origin that involves differentiation, dynamic mixing, remelting, reduction, recrystallization, and subsequent rapid cooling near the surface of a planetary body. 相似文献
25.
应用烃类流体包裹体GOI和成分研究凝析气藏成藏过程：以准噶尔盆地莫索湾地区为例 总被引：1，自引：1，他引：1
The Grains containing Oil Inclusions(GOI)data in currently gas/condensate-beating Jurassic and Cretaceous reservoir sandstones of Well Pen 5(the Mosuowan area of central Junggar Basin,NW China)are generally greater than the empirical threshold line of 5%.This is consistent with the gas-condensate section originally containing a palaeo-oil column.In order to assess the origin of the oil trapped in the oil inclusion and its relationship to the free oil/gas-condensate,a detailed molecular geochemical study was carried out for correlation between the free and inclusion oils.The paleo oil is most likely sourced from the Lower Permian Fengeheng Formation,which generated hydrocarbons primarily during Late Triassic and the oils were later secondarily altered and dysmigrated along faults likely during Late Jurassic-Early Cretaceous.In contrast,the current reservoired oil/gas-condensate mainly derived from the Middle Permian Lower Wuerhe Formation,whose peak generation time last from Late Cretaceous even to the present.This paper showed that integrated oil-bearing fluid inclusion analyses have likely allowed a complex multi-phase charge history to be recognized and resolved with a high degree of confidence. 相似文献
26.
Detailed stratigraphic analyses of Late Emsian and Early Eifelian (Lower to Middle Devonian) carbonate-dominated strata in the northern Appalachian Basin indicate anomalous, locally varying relative sea level changes and inversions of topography. The distribution of a major basal-bounding unconformity, basinal pinnacle reefs, local absence of parasequences, and eastward migration of shallow marine carbonate lithofacies and related biofacies in the Onondaga Limestone and underlying strata mark the retrograde migration of an elongate, northeast-southwest-trending area of positive relief, bordered on its cratonward side by a similarly migrating basin of intermediate depth. These features are thought to represent the forebulge and back-bulge basin of the Appalachian foreland basin system as it developed during a time of relative quiescence within the Acadian Orogeny. However, the relatively small size of the bulgelike feature (ca. 80-100-km-wide, 20-50-m positive relief), its great distance from the probable deformation front (>400 km), and the lack of a well-developed foredeep immediately adjacent to the bulgelike feature may indicate that it represents a smaller-scale flexural high ("flexural welt") superposed over the cratonward edge of the larger-scale classical forebulge of the basin. Development of shallow-water reefs on the crest of the bulge during sea level lowstand, followed by migration of the bulge and widespread transgression, permitted growth of economically significant pinnacle reefs in the deep basin center. Further subsurface reef exploration should concentrate along the projected position of the bulge during the basal Onondaga lowstand. 相似文献
27.
Giorgio?RivalentiEmail author Alberto?Zanetti Maurizio?Mazzucchelli Riccardo?Vannucci Carlos?A.?Cingolani 《Contributions to Mineralogy and Petrology》2004,147(6):647-670
Amphibole ± phlogopite ± apatite-bearing mantle xenoliths at Gobernador Gregores display modal, bulk-rock and phase geochemical characteristics held as indicators of carbonatitic metasomatism. However, part of these xenoliths has high TiO2/Al2O3 and those displaying the most pronounced carbonatitic geochemical markers modally trend towards harzburgite. Bulk-rock, clinopyroxene and amphibole show Zr, Hf and Ti negative anomalies, which increase at decreasing Na2O and high field strength elements (HFSE) concentrations. Steady variation trends between xenoliths which have and do not have carbonatitic characteristics suggest a control by reactive porous flow of only one agent, inferred to be initially a ne-normative hydrous basalt (because of the presence of wehrlites) evolving towards silica saturation. Variation trends exhibit cusps when amphibole appears in the mode. Appearance of amphibole may explain the Ti anomaly variations, but not those of Zr and Hf. Numerical modelling [Plate Model (Vernières et al. in J Geophys Res 102:24771–24784, 1997)] gives results consistent with the observed geochemical features by assuming the presence of loveringite. Modest HFSE anomalies in the infiltrating melt may be acquired during percolation in the garnet-facies.In memory of Carlo Rivalenti 相似文献
28.
29.
通过分析阿尔金—龙门山地学断面的地震资料,建立了该剖面的地壳纵波速度结构。研究结果表明,阿尔金北侧的塔里木盆地地区莫霍面为50km,而在其南侧的祁连地块莫霍面突然加深至73km,在柴达木盆地莫霍面又抬升至58km左右,然后,在松潘甘孜地块莫霍面降至70km,并呈现为台阶状向龙门山方向抬升到60km左右,最低速层,而在其南部地区则没有低速层出现,推测低速层为地壳中部的局部熔融物质,阿尔金—龙门山剖面上的两个莫霍面坳陷区分别与祁连地块和松潘—甘孜地块上的两个莫霍面坳陷区相对应,指示出这个两个地块具有较深的山根,青藏高原北部的巨厚地壳很可能是由于中生代以来发生的印度板块与亚洲板块碰撞时受到来自东西及南北方向的挤压,使地壳缩短所致。 相似文献
30.
Mangrove forests can provide important cross-boundary subsidies of organic matter to adjacent habitats through the production, export, decomposition and assimilation of litter. We quantified two of these components in a temperate mangrove forest in Whangamata Harbour, New Zealand: 1) litter production; and 2) decomposition rates as a function of tidal elevation, sediment type and burial depth. Litter traps sampled monthly for a year measured an annual detrital input of 3.24–5.38 t DW ha?1, of which 77% occurred in summer. Decomposition rates depended on litter type, with leaves decomposing faster (63 d to decay by 50%) than pneumatophore and wood material (316 and 460 d, respectively). Buried leaf and wood litter decomposed 1.3–1.4 times slower than litter on the sediment surface; however, tidal elevation and sediment type (mud vs. sand) had no effect. The slow decay of litter (an order of magnitude slower than tropical mangrove litter) suggests that its incorporation into temperate marine food webs may be relatively slow. 相似文献