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11.
Large, magnesium-rich olivines are plentiful in several Holocenecinder cones within 20 km of Mt. Shasta Summit. Glasses (formerlysilicate melts) included in the olivines are high alumina basalts(tholeiites and olivine tholeiites). In the most magnesian olivinesthe glass inclusions have large vapor bubbles. Surrounding someof the glass inclusions are broad Fe-rich zones and ghost outlines.These facts indicate crystallization of major proportions ofolivine from the initial trapped melts. The initial melts containedan inferred 24 per cent of MgO and were rich in volatiles. Theinferred entrapment temperature of the initial melt is 1410°C. The initial liquid is a possible mantle derived parentof Mt. Shasta basalts and andesites and of some hidden alpineperidotite. 相似文献
12.
R. SCOTT ANDERSON GEORGE L. JACOBSON JR. RONALD B. DAVIS ROBERT STUCKENRATH 《Boreas: An International Journal of Quaternary Research》1992,21(4):359-371
Gould Pond sediments are unusual in North America in that they include a continuous record of change from marine to freshwater conditions during the late-glacial period, with a wide array of micro- and macrofossils deposited during a period of high sedimentation rate. Marine waters, much colder than those in the present Gulf of Maine, covered the site at the time of deglaciation (c. 13,200 BP). Plants characteristic of modem tundra grew on nearby uplands. Marine recession, due to isostatic rebound of the land, occurred from c . 12,800–12,200 BP. The lake water was completely freshened by 12,000 BP. A sparse shrub-herb tundra became established around Gould Pond as marine waters receded. Subsequent to 11,300 BP, sedges and other herbs became more abundant, and willow and Dryas less abundant, signifying increased warmth and decreased frost action. At least six tree species, all now common in the area, arrived around Gould Pond between c . 10,800 and 10,500 BP. This rapid transition was coincident with the most rapid major non-anthropogenic change of vegetation at sites across eastern North America during the postglacial period. 相似文献
13.
A structural map of Oscar II Land compiled using black and white, stereo-pair air photos and other available information sources suggests the existence of three structural zones within the deformed platform cover strata. The western zone consists of basement involved overthrusts of complex geometry in the north large-scale folds of platform cover strata with a stepped, down to the east profile in the south. The central zone consists primarily of folds within Kapp Starostin Fm. and overlying Triassic strata that likely formed above a subhorizontal décollement within Gipshuken Fm. strata. Farther to the east thrusts emplace Permian Kapp Starostin Fm. strata over Triassic strata. This zone probably represents stratigraphic climb of the basal decollement. Conservative estimates of shortening for the central and eastern zones are in the 15-25% range. The contribution of the western zone structures to overall Tertiary shortening depends on the geometry of faults underlying the stepped folds and is uncertain at present.
Changes along strike are in part due to differential levels of erosion and changes in transport direction, but also probably important was variable thickness of the platform cover strata involved (less to the north) and the availability of incompetent horizons along which thrust-fiats could form. Two areas with anomalous structural trends may represent oblique ramps. 相似文献
Changes along strike are in part due to differential levels of erosion and changes in transport direction, but also probably important was variable thickness of the platform cover strata involved (less to the north) and the availability of incompetent horizons along which thrust-fiats could form. Two areas with anomalous structural trends may represent oblique ramps. 相似文献
14.
The laterally persistent but thin, Jurassic age (Bathonian-Callovian) Brentskardhaugen bed is poorly sorted (often with mud to cobble size), and is crudely normally and/or reversely graded without internal discontinuities. These traits may indicate a short-lived depositional event, and are inconsistent with an origin as a basal, transgressive gravel lag formed in a terrestrial or shoreline setting. Mega-storm events on a shallow marine shelf with an underlying condensed section may account for the poor sorting, grading, stratigraphic position and remanie character of the bed. 相似文献
15.
The South African midwater trawl fishery targets adult horse mackerel Trachurus capensis. The bulk of the catch is taken by a single freezer-trawler, the biggest fishing vessel operating in South African waters. As fishing takes place off the south coast in ecologically sensitive areas, there are concerns about the potential impacts of this fishing operation on non-target species. Fishing behaviour and bycatch of this fishery from 2004 to 2014 were investigated by analysing observer records with regard to catch composition, volume and temporal and spatial patterns. The midwater trawl fishery was estimated to have caught 25 415 tonnes annually, with a bycatch of 6.9% of the total catch, by weight. There are species overlaps with various fisheries, namely the demersal trawl, small-pelagic, line, shark longline and squid fisheries, yet the total bycatch estimates from this fishery are generally small relative to catches taken in the target fisheries. Bycatch species with the highest average annual catches were chub mackerel Scomber japonicus, redeye roundherring Etrumeus whiteheadi, ribbonfish Lepidopus caudatus and hake Merluccius spp. Large-fauna bycatch species included sunfish Mola mola as well as a number of CITES II- and IUCN-listed species, such as Cape fur seal Arctocephalus pusillus, dusky shark Carcharhinus obscurus, smooth hammerhead shark Sphyrna zygaena and thresher sharks Alopias spp. The 97.9% observer coverage is high and the 6.9% bycatch rate low compared to other South African fisheries; however, due to the large size of the individual hauls (average of 46.3 t), the average sampling rate of 1.56% is low. Our analyses suggest that bycatch in the South African midwater trawl fishery has been lower than in other South African fisheries and similar fisheries elsewhere, but due to the combination of high catch volumes and low sampling rates, estimation errors for rare species are high and there is a substantial risk of incidental unmonitored bycatch of rare large fauna and aggregations of small fauna. This could be mitigated by spatio-temporal management of this fishery, to avoid fishing in high-risk areas, and the introduction of an electronic monitoring programme. 相似文献
16.
G Minton JR Kema Kema A Todd L Korte PB Maganga JR Migoungui Mouelet 《African Journal of Marine Science》2017,39(4):423-433
Private industry, the Government of Gabon and two international NGOs collaborated to conduct marine surveys off the coast of Gabon, Central Africa. Surveys addressed multiple objectives of surveillance and monitoring, the documentation of the distribution of and threats to the marine megafauna, and capacity-building among government agents and local early-career scientists. During 22 days of survey effort over a two-year period, observers documented humpback whales Megaptera novaeangliae, bottlenose dolphins Tursiops truncatus, Atlantic humpback dolphins Sousa teuszii and common dolphins Delphinus delphis. Humpback whale presence was limited to the months of July to November. Bottlenose dolphins were present year-round and photo-identification of individuals indicated a closed, resident population, with an abundance estimate of 118 (CV = 21.6%, 95% CI 78–180). Small open-decked fishing vessels with gillnets were observed concentrated around river mouths within 2 km of shore, while commercial trawlers were at least 10 km offshore; all were confirmed to be registered and legal. Observations of marine turtles, flocks of marine birds, and floating logs and other debris were sparse. This multi-stakeholder collaboration to conduct a marine survey can serve as an effective model by which funding and logistic support from private industry paired with technical expertise from NGOs and academic institutions can benefit marine and coastal conservation. 相似文献
17.
WILLIAM JAMES SMITH JR 《The Geographical journal》2008,174(3):251-268
Many least-wealthy, rural, remote and resource-poor small island communities are unlikely to benefit from high-profile global water improvement initiatives. Their small landmasses, geologic composition, geography, social and technological isolation, colonial history, and weak educational and financial resources constitute significant barriers to improving access to safe drinking water. This paper discusses the relatively unique position of such island societies in the international community, providing a case study of the Federated States of Micronesia that integrates data and information pertaining to water resources management and governance, spanning from the island village to national scale. A vision is offered regarding the interaction between small island human and biophysical water systems, manifesting ways to pursue water resource development to improve public health which are constructed to be economically, physically and culturally sustainable. 相似文献
18.
Keisuke ISHIDA Shigeyuki SUZUKI Carla DIMALANTA Graciano YUMUL JR. Karlo QUEA?O Decibel FAUSTINO-ESLAVA Edanjarlo MARQUEZ Noelynna RAMOS Rolando PE?A 《地球学报》2012,33(S1):29-31
The basement of the Philippine Mobile Belt (PMB) is mainly composed of ophiolites that are mostly overlain by Paleogene to Miocene turbidites in central Luzon. To clarify the geological development of the PMB with respect to the initial stage of the arc volcanism (eg. Yumul et al., 2003, 2008; Dimalanta and Yumul, 2003; Suzuki et al., 2011), radiolarian dating was examined in siliceous sediments associated with the ophiolites and turbidites. The samples were collected from sites identified with the Zambales and Montalban ophiolites, basic tuff phyllites in NW Din-galan, and their overlying formations. 相似文献
19.
Adakitic lavas in the Central Luzon back‐arc region,Philippines: lower crust partial melting products? 总被引:6,自引:0,他引:6
Graciano P. Yumul JR Carla Dimalanta Herve Bellon Decibel V. Faustino Joel V. De Jesus Rodolfo A. Tamayo JR Ferdinand T. Jumawan 《Island Arc》2000,9(4):499-512
Abstract Volcanism in the back-arc side region of Central Luzon, Philippines, with respect to the Manila Trench is characterized by fewer and smaller volume volcanic centers compared to the adjacent forearc side-main volcanic arc igneous rocks. The back-arc side volcanic rocks which include basalts, basaltic andesites, andesites and dacites also contain more hydrous minerals (ie, hornblende and biotite). Adakite-like geochemical characteristics of these back-arc lavas, including elevated Sr, depleted heavy rare earth elements and high Sr/Y ratios, are unlikely to have formed by slab melting, be related to incipient subduction, slab window magmatism or plagioclase accumulation. Field and geochemical evidence show that these adakitic lavas were most probably formed by the partial melting of a garnet-bearing amphibolitic lower crust. Adakitic lavas are not necessarily arc–trench gap region slab melts. 相似文献
20.
Abstract The basement complex of Bohol Island consists of the Southeast Bohol Ophiolite Complex (SEBOC), Cansiwang Melange and Alicia Schist. The SEBOC is a complete, but dismembered ophiolite with outcrops generally trending northeast– southwest and dipping north-west. The harzburgite units of the SEBOC are almost always observed to be thrusted onto the Cansiwang Melange, which in turn is thrusted onto the Alicia Schist. Bouguer gravity values on Bohol range from about +60 mGal in the west to +120 mGal in the east, in the region to the north-east of the SEBOC outcrops. Based on the present distribution of the SEBOC units and their thrust fault relationship with the Cansiwang Melange and Alicia Schist, it is proposed that the SEBOC was emplaced by onramping towards the south-eastward direction. However, the orientation of the Bouguer highs suggests that the thrusting direction of the ophiolite units is towards the south-west and not towards the south-east. 相似文献