排序方式： 共有28条查询结果，搜索用时 15 毫秒
1.
Abstract A southwest dipping Mesozoic accretionary complex, which consists of tectonically imbricated turbiditic mudstone and sandstone, hemipelagic siliceous mudstone, and bedded cherts and basaltic rocks of pelagic origin, is exposed in northern North Island, New Zealand. Interpillow limestone is sometimes contained in the basaltic rocks. The grade of subduction‐related metamorphism increases from northeast to southwest, indicating an inverted metamorphic gradient dip. Three metamorphic facies are recognized largely on the basis of mineral parageneses in sedimentary and basaltic rocks: zeolite, prehnite‐pumpellyite and pumpellyite‐actinolite. From the apparent interplanar spacing d002 data for carbonaceous material, which range from 3.642 to 3.564 Å, the highest grade of metamorphism is considered to have attained only the lowermost grade of the pumpellyite‐actinolite facies for which the highest temperature may be approximately 300°C. Metamorphic white mica K–Ar ages are reported for magnetic separates and <2 µm hydraulic elutriation separates from 27 pelitic and semipelitic samples. The age data obtained from elutriation separates are approximately 8 m.y. younger, on average, than those from magnetic separates. The age difference is attributed to the possible admixture of nonequilibrated detrital white mica in the magnetic separates, and the age of the elutriation separates is considered to be the age of metamorphism. If the concept, based on fossil evidence, of the subdivision of the Northland accretionary complex into north and south units is accepted, then the peak age of metamorphism in the north unit is likely to be 180–130 Ma; that is, earliest Middle Jurassic to early Early Cretaceous, whereas that in the south unit is 150–130 Ma; that is, late Late Jurassic to early Early Cretaceous. The age cluster for the north unit correlates with that of the Chrystalls Beach–Taieri Mouth section (uncertain terrane), while the age cluster for the south unit is older than that of the Younger Torlesse Subterrane in the Wellington area, and may be comparable with that of the Nelson and Marlborough areas (Caples and Waipapa terranes). 相似文献
2.
Mathijs A. Booden Ian E.M. Smith Philippa M. Black Jeffrey L. Mauk 《Journal of Volcanology and Geothermal Research》2011,199(1-2):25-37
Latest Oligocene and Early Miocene volcanic rocks occur on the Northland Peninsula, New Zealand, and record the inception of Cenozoic subduction-related volcanism in the North Island that eventually evolved to its present manifestation in the Taupo Volcanic Zone. This NW-striking Northland Arc is continuous with the Reinga Ridge and comprises two parallel belts of volcanic centres ca. 60 km apart. A plethora of tectonic models have been proposed for its origins. We acquired new trace element and Sr–Nd isotope data to better constrain such models. All Northland Arc rocks carry an arc-type trace element signature, however distinct differences exist between rocks of the eastern and western belt. Eastern belt rocks are typically andesites and dacites and have relatively evolved isotope ratios indicating assimilated crustal material, and commonly contain hornblende. Additionally some eastern belt rocks with highly evolved isotope compositions show fractionated REE compositions consistent with residual garnet, and some contain garnetiferous inclusions in addition to schistose crustal fragments. In contrast, western belt rocks are mostly basalts or basaltic andesites with relatively primitive Sr–Nd isotope compositions, do not contain hornblende and show no rare earth element evidence for cryptic amphibole fractionation. Eastern and western belt rocks contain comparable slab-derived fractions of fluid-mobile trace elements and invariably possess an arc signature. Therefore the difference between the belts may be best explained as due to variation in crustal thickness across the Northland Peninsula, where western belt centres erupted onto a thinner crustal section than eastern belt rocks.The consistent arc signature throughout the Northland arc favours an origin in response to an actual, if short-lived subduction event, rather than slab detachment as proposed in some models. No Northland Arc rocks possess a convincing adakite-like composition that might reflect the subduction of very young oceanic lithosphere such as that of the Oligocene South Fiji Basin. Therefore we favour a model in which subduction of old (Cretaceous) lithosphere drove subduction. 相似文献
3.
Louisa S. Evans Philippa J. Cohen Agnetha Vave-Karamui Rosalie Masu Delvene Boso Senoveva Mauli 《社会与自然资源》2018,31(1):121-135
Environmental governance aims to reconcile an expanding set of societal objectives at ever-larger scales despite the challenges that remain in integrating conservation and development at smaller scales. We interrogate Solomon Islands’ engagement in the Coral Triangle Initiative on Coral Reefs, Fisheries and Food Security to contribute new insight on the scalar politics of multi-level marine governance. We show how regional objectives are re-interpreted and prioritized as they translate into national policy and practice. Our data suggest that enhanced coordination of finances and activities, integration of objectives in shared protocols and priority geographies, and a subtle shift in power relations between the state, donors, and implementation partners have resulted from processes of re-scaling. We discuss important procedural adjustments in cross-level and cross-scale governance across jurisdictional, institutional, and sectoral scales. We also reflect on the changing role of national governments in shifts toward large-scale, multi-national initiatives. 相似文献
4.
Philippa M. Black 《Contributions to Mineralogy and Petrology》1973,38(3):221-235
A Cretaceous to low-Tertiary sequence of interbedded pelites, cherts, basic and acidic volcanics and calcareous lenses has
been metamorphosed by an Oligocene event. A complete intergradational metamorphic sequence is exposed in the Ouégoa destrict.
The following metamorphic zones have been recognised: — (1) lowest-grade rocks consisting of quartz-sericite phyllites and
pumpellyite metabasalts (2) lawsonite zone, characterized by the association of lawsonite and albite (3) epidote zone, characterised
by epidote-omphacite-sodic hornblendealmandine bearing metabasalts and epidote-albite-almandine-glaucophane bearing metasediments;
calcareous metasediments may also carry omphacite. The epidote and lawsonite zones are separated by a narrow belt of transitional
rocks.
Garnets occur in metasediments throughout the lawsonite zone as rare tiny crystals (<0.03 mm diam.). Garnets first appear
in metabasalts in lawsonite-epidote transitional rocks. Garnets are widespread and abundant in epidote-zone metasediments
and metabasalts.
45 garnets from rocks representative of all lithologies and metamorphic grades have been analysed with an electron-probe microanalyser.
The garnets were consistently zoned. Garnets in lawsonite and low-grade epidote zones show a “bell-type” zoning with cores
enriched in Mn relative to Fe and rims enriched in Fe, Mg and frequently Ca. Garnets from high-grade epidote-zone metapelites
and metabasalts show, in addition, a shallow oscillatory zoning with complimentary variations in Mn and Fe equivalent to 5
mole- % spessartine and almandine. The Fe-for-Mn substitutional zoning, believed to be caused by a diffusion/saturation effect
similar to that of the Rayleigh fractional model (Hollister, 1966), appears to have had superimposed on it the effects of
parent-rock chemistry and metamorphic grade which control in a complex manner the composition of the cores and the rims of
garnets.
Garnets from different rock types and metamorphic grade are compositionally distinct. Garnets from lawsonite-zone rocks, irrespective
of parent-rock chemistry appear to be spessartine. Garnets from epidote-zone metaigneous rocks and most metasediments are
almandine. Garnets from epidote-zone metasediments with bulk-rock compositions which are manganiferous, or have high oxidation
ratios, or both, may be spessartine-rich. Garnets from metabasalts are consistently more pyropic in both core and rim compositions
than garnets from pelitic metasediments; the pyrope content of cores and rims of garnets from equivalent rock types and mineral
assemblages increases with increasing metamorphic grade. Cores of garnets from epidote-zone pelites are richer in grossular
than garnets from lower-grade pelites.
The reaction which brings almandine garnet into Ouégoa district blueschist assemblages simultaneously with the replacement
of lawsonite by epidote involves components of chlorites and sodic amphiboles and can be represented by the following simplified
equation: ferroglaucophane+Fe-rich chlorite+lawsonite → glaucophane+Mg-rich chlorite+epidote+almandine. 相似文献
5.
The Upper Oligocene to Lower Miocene Gore Lignite Measures of Eastern Southland accumulated in humid temperature to subtropical wet forest swamps in a coastal delta-plain paleoenvironment. The lignites have relatively low ash and low sulphur contents. They are xylitic, contain abundant resinite and range from poorly to strongly gelified. Petrographically, they are relatively uniform and dominated by humic macerals.The Eastern Southland Lignite Field can be divided into a southern (lower-rank) and a northern (higher-rank) area. The lower-rank lignites have bed moisture contents of 55–61% whereas the higher-rank lignites have bed moistures of 42–46%. In both areas the lignite seams are within 200 m of the surface but are probably separated by faults and have undergone separate burial and tectonic histories. Burial depths are believed to range from 250 m for lower-rank to 1100 m for higher-rank lignites. The rank increase from south to north is largely the result of compaction-induced reduction in porosity and consequent dewatering and is not accompanied by any notable increase in gelification. For these lignites, there is a linear relationship between bed moisture and fixed carbon but a significant shift away from the linear relationship between volatile matter and specific energy and bed moisture. Also, the higher-rank northern lignites have higher H:C and lower O:C atomic ratios than the southern lower-rank lignites. These geochemical changes are heat- and depth-related and represent changes in functional group composition that are independent of observed gelification. 相似文献
6.
7.
Periodically-harvested fisheries closures are emerging as a socially acceptable and locally implementable way to balance concerns about conserving ecosystem function and sustaining livelihoods. Across the Indo-Pacific periodically-harvested closures are commonly employed, yet their contribution towards more sustainable fisheries remains largely untested in the social and ecological context of tropical small-scale fisheries. To address this, we use an interdisciplinary approach to examine harvesting dynamics that would affect sustainability, namely, fishing effort, yield, gear and method use, periodicity of harvesting, controls placed on harvesting and resource owners’ decisions to open and close four fishing grounds in Solomon Islands. We compare these fishing patterns with those on surrounding, continuously open fishing grounds. Our study shows that total effort and total catch from periodically-harvested reef closures are low to moderate compared to reefs open to continuous fishing. When periodically-harvested closures were opened, effort in the closures was relatively intense, however, in most cases yield did not exceed annual benchmarks of sustainability described by previous studies. In some cases, harvesting during openings was restricted to a single taxon and single fishing gear and method, while in others there was unrestricted multi-species and multi-method harvesting. The duration and frequency of openings were highly variable, with open periods ranging from a single night to one month in duration, and occurring between one and 15 times per year. Fishing during openings was permitted for entire fishing communities in some cases, and only for specific rights-holding families in others. Decisions to open periodically-harvested closures tended to be based on immediate social or economic needs, and the openings provided a small boost to fish catch landed in communities. While periodically-harvested closures may alleviate fishing pressure in a small area of fishing grounds by reducing the opportunity to fish, openings of long duration or high frequency, combined with heavy or destructive exploitation, may lead to unsustainable harvesting within the area. 相似文献
8.
Susan Ringrose Philippa Huntsman-Mapila William Downey Stephan Coetzee Martin Fey Cornelis Vanderpost Bernard Vink Thebe Kemosidile Dikitso Kolokose 《Geomorphology》2008,101(4):544-557
This work considers the spatial distribution and ages of western MOZ basin siliclastic sediments prior to providing insights into the diagenesis of degraded dune and alluvial fan sands. Previously published and new TL/OSL ages imply that extensive over-washing of dune sands took place at least 100 ka ago while ages on Okavango floodplains imply that the fan was formed ca. 40 ka and has since undergone periods of higher and lower flood regimes. Sediment analyses indicate that both dune and fan sands contain a diagenetic matrix of clay-enhanced amorphous silica (CEAS) which bonds weakly formed aggregates. The time of formation of diagenetic matrix products is inconclusive but may have been accelerated during or shortly after events dated using OSL/TL techniques. Hence earlier dune over-washing may have led to greater porewater of an acidic to near neutral nature which in turn promoted smectite formation and silicic acid precipitation > 100 000 years ago. The relatively abundant CEAS matrix in floodplain sands implies more recent semi-continuous flood events again of an acidic-near neutral nature leading to the formation of smectite. In this case the floodplain sediments are dated as having been deposited around 40 and 11 ka, when porewater content may have accelerated clay formation and silica dissolution. The dual nature of the CEAS in the islands reflects a changing environment from smectite-dominated flooding events to sepiolite-dominated desiccation events. Flooding may also correspond to TL/OSL ages over the past 40 000 years which contributed to accelerated CEAS formation. The sepiolite is associated with a Ca-rich matrix implying desiccation which may relate to drying events over the 40 000 year period or to riparian tree root pumping and selective salt accumulation. This work shows that sedimentation in incipient rifts is complex and rarely explained totally in terms of primary depositional events. The implications of different stages of sand diagenesis may be significant in enhancing palaeo-environmental interpretations in semi-arid fluvial environments. 相似文献
9.
Philippa Hudson 《The Australian geographer》1989,20(1):54-64
The negative image created by a preoccupation with population losses in some rural areas and the decline in some economic and service functions in many small country towns has masked the considerable improvements which have occurred there. Insufficient attention has been given to the raised level of living in many rural locations which has increased the attraction of a rural lifestyle. Local shire councils have played an important role in enhancing the quality of local life through investment in new town facilities, and residents record a high level of community satisfaction. Although past social and economic roles are changing in rural locations, new functions are emerging in four settlements in New England, NSW, and this is facilitating their adaptation to a changing rural environment. 相似文献
10.
Timothy P. Wangler Alisa Stratulat Philippa Duffus Jean H. Prévost George W. Scherer 《Environmental Earth Sciences》2011,63(7-8):1565-1572
Many historically and culturally significant buildings have sandstones that contain swelling clay inclusions in the binding phase. Differential strains that evolve during wetting and drying cycles can generate stresses that are on the order of the strength of the stone, leading to degradation. Most damage observed in the field is surface delamination and buckling of the stone over a flaw, indicating that the damage is occurring during wetting. Classical buckling theory predicts buckling to occur at a particular aspect ratio, or flaw size. The results of this study confirm buckling theory experimentally. Through finite-element simulation and experiment, the study then explores a potential flaw propagation mechanism whereby nonuniform wetting patterns generate stress intensities capable of flaw propagation. As a result, small natural flaws can grow to the critical size necessary for buckling. 相似文献