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21.
The volcanic island of Milos, Greece, comprises an Upper Pliocene –Pleistocene, thick (up to 700 m), compositionally and texturally diverse succession of calc-alkaline, volcanic, and sedimentary rocks that record a transition from a relatively shallow but dominantly below-wave-base submarine setting to a subaerial one. The volcanic activity began at 2.66±0.07 Ma and has been more or less continuous since then. Subaerial emergence probably occurred at 1.44±0.08 Ma, in response to a combination of volcanic constructional processes and fault-controlled volcano-tectonic uplift. The architecture of the dominantly felsic-intermediate volcanic succession reflects contrasts in eruption style, proximity to source, depositional environment and emplacement processes. The juxtaposition of submarine and subaerial facies indicates that for part of the volcanic history, below-wave base to above-wave base, and shoaling to subaerial depositional environments coexisted in most areas. The volcanic facies architecture comprises interfingering proximal (near vent), medial and distal facies associations related to five main volcano types: (1) submarine felsic cryptodome-pumice cone volcanoes; (2) submarine dacitic and andesitic lava domes; (3) submarine-to-subaerial scoria cones; (4) submarine-to-subaerial dacitic and andesitic lava domes and (5) subaerial lava-pumice cone volcanoes. The volcanic facies are interbedded with a sedimentary facies association comprising sandstone and/or fossiliferous mudstone mainly derived from erosion of pre-existing volcanic deposits. The main facies associations are interpreted to have conformable, disconformable, and interfingering contacts, and there are no mappable angular unconformities or disconformities within the volcanic succession.Electronic Supplementary Material Supplementary material is available for this article at 相似文献
22.
A new approach to the parametrization of the cumulus-capped boundary layer is described. It combines a traditional higher-order turbulence closure, appropriate for boundary layers where the skewness of thermodynamic variable probability distributions is low (typically stratocumulus-capped), with non-local scaled similarity functions. These are introduced in order to represent explicitly that part of the distribution arising from skewed cumulus elements and the scalings are found to work very well against equilibrium shallow cumulus large-eddy simulations. Results from a wide range of single column model simulations, from stratocumulus to shallow cumulus to cumulus rising into stratocumulus, are presented that demonstrate the validity of the approach as a means of parametrizing the cloudy boundary layer. Sensitivity tests show that enhancement of the turbulence length scales and the buoyancy production of TKE are especially important. 相似文献
23.
Momo-iwa, Rebun Island, Hokkaido, Japan, is a dacite cryptodome 200–300 m across and 190 m high. The dome is inferred to have intruded wet, poorly consolidated sediment in a shallow marine environment. The internal structure of the dome is concentric, with a massive core, banded rim, and narrow brecciated border, all of which are composed of compositionally uniform feldspar-phyric dacite. Boundaries between each of the zones are distinct but gradational. The massive core consists of homogeneous coherent (unfractured) dacite and is characterized by radial columnar joints 60–200 cm across. The banded rim encircles the massive core and is 40 m wide. It is characterized by large-scale flow banding parallel to the dome surface. The flow banding comprises alternating partly crystalline and more glassy bands 80–150 cm thick. The outermost brecciated border is up to 80 cm thick, and consists of in situ breccia and blocky peperite. The in situ breccia comprises polyhedral dacite clasts 5–20 cm across and a cogenetic granular matrix. The blocky peperite consists of polyhedral dacite clasts 0.5–2 cm across separated by the host sediment (mudstone). The internal structures of the dome suggest endogenous growth involving a continuous magma supply during a single intrusive phase and simple expansion from the interior. Although much larger, the internal structures of Momo-iwa closely resemble those of lobes in subaqueous felsic lobe-hyaloclastite lavas. 相似文献
24.
Alice Recanati Yves Missenard Rmi Leprêtre Ccile Gautheron Jocelyn Barbarand Fatiha Abbassene Nachida Abdallah Aziouz Ouabadi Mohamed El Messaoud Derder Claire Boukari Rosella Pinna‐Jamme Frdric Haurine 《地学学报》2019,31(1):39-48
In North Africa, the Algerian margin is made of basement blocks that drifted away from the European margin, namely the Kabylia, and docked to the African continental crust in the Early Miocene. This young margin is now inverted, as dated Miocene (17 Ma) granites outcrop alongshore, evidencing kilometre‐scale exhumation since their emplacement. Age of inversion is actually unknown, although Pliocene is often considered in the offshore domain. To decipher the exhumation history of the margin between 17 and 5 Ma, we performed a coupled apatite fission track (AFT) and (U–Th–Sm)/He (AHe) study in the Cap Bougaroun Miocene granite. AFT dates range between 7 ± 1 and 10 ± 1 Ma, and mean AHe dates between 8 ± 2 and 10 ± 1 Ma. These data evidence rapid and multi‐kilometre exhumation during Tortonian times. This event cannot be related to slab break‐off but instead to the onset of margin inversion that has since developed as an in‐sequence north‐verging deforming prism. 相似文献
25.
Mario A. Aurelio Jocelyn B. Galapon Violet T. Hizon Dominic B. Sadsad 《Island Arc》2009,18(1):144-154
The structural signature in the area between the Baguio mineral district and Ansagan, Tuba, Benguet in the South Central Cordillera, northern Luzon, Philippines, is dominated by northeast- to ENE-trending faults, contained within a NNW–SSE-trending transtensional strip. This 50-km-long, 25-km-wide elongated tectonic zone is bounded to the west by the Pugo Fault and to the east by the Tebbo Fault, both being branches of the Philippine Fault System. Detailed structural geological (particularly microtectonic) analysis of fracture and mineral vein systems indicates strong conformity with the regional structural direction. Computed extensional stress axis σ3 directions are oriented N150° on average, sub-parallel to the strike of the bounding faults. The existence of known mineral deposits and prospects within the tectonic strip implies an intimate relationship between transtension and mineral occurrence. 相似文献
26.
Carlos J.P. Rosa Jocelyn McPhie Jorge M.R.S. Relvas 《Journal of Volcanology and Geothermal Research》2010
The Volcanic Sedimentary Complex (VSC) of the Iberian Pyrite Belt (IPB) in southern Portugal and Spain, comprises an Upper Devonian to Lower Carboniferous submarine succession with a variety of felsic volcanic lithofacies. The architecture of the felsic volcanic centres includes felsic lavas/domes, pyroclastic units, intrusions and minor mafic units that define lava–cryptodome–pumice cone volcanoes. The diversity of volcanic lithofacies recognized in different areas of the IPB mainly reflects variations in proximity to source, but also differences in the eruption style. The IPB volcanoes are intrabasinal, range in length from 2 km to > 8 km and their thickest sections vary from ∼ 400 m to > 800 m. These volcanoes are dominated by felsic lavas/domes that occur at several stratigraphic positions within the volcanic centre, however the pyroclastic units are also abundant and are spatially related to the lavas/domes. The intrusions are minor, and define cryptodomes and partly-extrusive cryptodomes. The hydrothermal systems that formed the Neves Corvo and Lousal massive sulfide ore deposits are associated with effusive units of felsic volcanic centres. At Neves Corvo, the massive sulfide orebodies are associated to rhyolitic lavas that overlie relatively thick fiamme-rich pyroclastic unit. In several other locations within the belt, pyroclastic units contain sulfide clasts that may have been derived from yet to be discovered coeval massive sulfide deposits at or below the sea floor, which enhances the exploration potential of these pyroclastic units and demonstrates the need for volcanic facies analysis in exploration. 相似文献
27.
Jocelyn Bell Burnell 《Astronomy& Geophysics》2004,45(6):6.10-6.14
Jocelyn Bell Burnell ponders the achievements and status of women in astronomy, past, present and future. 相似文献
28.
Abstract In this study, a 24‐h high‐resolution numerical prediction of a prefrontal squall line associated with the 14 July 1987 Montreal flood is employed to investigate the origin and role of mesoscale gravity waves in the development of the squall system. The 24‐h integration using an improved mesoscale version of the Canadian regional finite‐element model is first validated against available observations; then non‐observable features are diagnosed to reveal the relationship between deep convection and gravity wave events. It is shown that the model reproduces well many aspects of the squall line, such as the propagation and organization of the convective system, as well as its associated precipitation. It is found that gravity waves are first excited near Lake Erie, following the initiation of early convective activity. Then, these waves propagate eastward and northeastward at speeds of 20 and 35 m s‐1, respectively. As the waves propagate downstream, deep convection radiates rapidly behind the wave trough axis, forming a long line of squall convection. Because the squall line moves with the gravity waves in a “phase‐locked” manner, deep convection has a significant influence on the structure and amplitude of the gravity waves. The sensitivity of the wave‐squall prediction to various parameters in convective parameterization is also examined. 相似文献
29.
Tertiary basaltic pillow lobes at Cape Grim, northwestern Tasmania, Australia display well-preserved spreading cracks in the glassy crust. The spreading cracks are lens-shaped or rectangular in plan view. In cross section, they consist of a graben-like depression with a broad floor bounded by steep scarps. The floor of spreading crack contains an axial crack and a number of ridges that are arranged symmetrically with respect to the axial crack. The ridges within spreading cracks are inferred to have formed by the regular, repeated production and splitting of new crust at the centre of the spreading crack. This new interpretation of ridges in spreading cracks differs from the previous interpretation in which they are regarded as elongate normal fault blocks. Our interpretation provides new insight into the propagation mechanisms of pillow lavas. 相似文献
30.
In the Izu Peninsula (Japan), the Pliocene pumice-rich Dogashima Formation (4.55?±?0.87 Ma) displays exceptional preservation of volcaniclastic facies that were erupted and deposited in a below wave-base marine setting. It includes high-concentration density current deposits that contain clasts that were emplaced hot, indicating an eruption-fed origin. The lower part of the Dogashima 2 unit consists of a very thick sequence (<12 m) of massive grey andesite breccia restricted to the base of a submarine channel, gradationally overlain by pumice breccia, which is widespread but much thinner and finer in the overbank setting. These two breccias share similar mineralogy and crystal composition and are considered to be co-magmatic and derived from the destruction of a submarine dome by an explosive, pumice-forming eruption. The two breccias were deposited from a single, explosive eruption-fed, sustained, sea floor-hugging, water-supported, high-concentration density current in which the clasts were sorted according to their density. At the rim of the channel, localised good hydraulic sorting of clasts and stratification in the pumice breccia are interpreted to reflect local current expansion and unsteadiness rather than to be the result of hydraulic sorting of clasts during fall from a submarine eruption column and/or umbrella plume. A bimodal coarse (>1 m) pumice- and ash-rich bed overlying the breccias may be derived from delayed settling of pyroclasts from suspension. In Dogashima 1 and 2, thick cross- and planar-bedded facies composed of sub-rounded pumice clasts are intercalated with eruption-fed facies, implying inter-eruptive mass-wasting on the flank of a submarine volcano, and reworking and resedimentation by high-energy tractional currents in a below wave-base environment. 相似文献