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101.
P. F. Carr C. L. Fergusson J. W. Pemberton G. P. Colquhoun S. I. Murray J. Watkins 《Australian Journal of Earth Sciences》2013,60(3):319-330
The Cape Hoskins volcanoes form part of the Quaternary volcanic island arc that extends from Rabaul in the east to the Schouten Islands in the west, and they overlie the northerly dipping New Britain Benioff Zone. The products of the volcanoes range in composition from basalt to rhyolite, and are normative in quartz and hypersthene. They contain phenocrysts of plagioclase and subordinate augite, hypersthene, and in most samples iron‐titanium oxides; some samples also contain olivine or quartz or both, and some pumice contains hornblende and, rarely, biotite. Chemical analyses of 29 volcanic rocks are presented; 22 were also analysed for 17 minor elements — Rb, Ba, Sr, Pb, Zn, Cu, Zr, Y, Ni, Co, Sc, Cr, V, Ga, B, U, and Th. Chemically the rocks have many of the characteristics of the ‘island arc tholeiitic series’, but do not show a pronounced relative enrichment in iron and appear to be relatively enriched in Sr. Compared with volcanic rocks from the northern part of the Willaumez Peninsula, they are lower in K (but not Na), Ti, Rb, Ba, Zr, Pb, Th, Ni, and probably also V, Cu, and Zn: these differences are attributed to the greater depth of the Benioff Zone beneath the Willaumez Peninsula. The more basic of the Cape Hoskins rocks are similar in most respects to lavas of comparable composition from Ulawun volcano to the east. 相似文献
102.
The southern part of the Sydney Basin of New South Wales is comprised mainly of Permian and Triassic marine to freshwater clastic sedimentary rocks. Within this sequence there are six latite extrusive units, several medium‐sized monzonite intrusions and a large number of small to medium‐sized basic to intermediate intrusions. Thin basaltic flows were extruded onto the Tertiary topographic surface. All of these rocks are relatively undeformed. Radiometric (K‐Ar) dating has previously been carried out on Mesozoic and Tertiary intrusions and flows of the southwestern portion of the Sydney Basin. However, relatively few Permian, and no post‐Permian, K‐Ar dates have been published for the southeastern portion of the basin. The present investigation provides nine K‐Ar dates from the latter area. Four extrusive and intrusive units have been confirmed as Permian in age (238 ± 6; 241 ± 4; 245 ± 6; and 251 ± 5 m.y.). Five post‐Permian (on stratigraphic criteria) intrusions yielded Tertiary ages (26.2 ± 3.0; 47.9 ± 2.5; 49.0 ± 4.0; 49.4 ± 2.0; and 58.8 ± 3.5 m.y.). The Permian ages agree with previously published K‐Ar data from the southeastern Sydney Basin, and the Tertiary ages complement and extend the data from the southwestern portion of the basin. However, no Mesozoic K‐Ar dates were obtained from the southeastern Sydney Basin. The Tertiary intrusions may have been emplaced as a result of rifting between Australia and New Zealand, or between Australia and Antarctica, or both. 相似文献
103.
New chemical, X‐ray and cell dimension data are presented for ferrian tourmaline in quartz‐tourmaline rock at three localities near Bungonia, New South Wales. The tourmaline is fine‐grained, normally euhedral, and forms up to 90% of the rock. It shows restricted solid solution between dravite and ferridravite, although some grains are zoned and others have an irregular, bipartite chemical variation. Tourma‐linisation is interpreted as being.related to late‐stage volatile emanations from the Marulan Batholith. 相似文献
104.
Arun M. Puthanpurayil Oren Lavan Athol J. Carr Rajesh P. Dhakal 《Bulletin of Earthquake Engineering》2016,14(8):2405-2434
To date, nonlinear dynamic analysis for seismic engineering predominantly employs the classical Rayleigh damping model and its variations. Though earlier studies have identified issues with the use of this model in nonlinear seismic analysis, it still remains the popular choice for engineers as well as for software providers. In this paper a new approach to modelling damping is initiated by formulating the damping matrix at an elemental level. To this regard, two new elemental level discrete damping models adapted from their global counterparts are proposed for its application in nonlinear dynamic analysis. Implementation schemes for these newly proposed models using Newmark incremental method and revised Newmark total equilibrium method is outlined. The performance of these proposed models, compared to existing models, is illustrated by conducting nonlinear dynamic analyses on a four story RC frame designed to Eurocodes. The incremental dynamic analysis study presented in the paper illustrates the fact that both the proposed models seem to produce more reliable results from an engineering perspective in comparison to the global models. It is also shown that the proposed elemental damping models lead to smaller and more realistic damping moments in the plastic hinges. Furthermore, these models could be easily included in existing software frameworks without adding noticeably to the computational effort. The computation time required for these models is approximately equivalent to the one required when using the tangent Rayleigh damping matrix with constant coefficients. 相似文献
105.
The reconstruction of former mountain glaciers has long been used to examine the implications of rapid climate shifts, for example at the last glacial–interglacial transition, and for evaluating asynchronous behaviour of mountain glaciers compared with mid‐latitude ice sheets during the Late Quaternary. Glacier reconstruction has also been used as a source of palaeoclimatic information, based on the recognition of empirical relationships between glaciers and climate. This paper reviews the application and implications of a recently revised method of glacier reconstruction (Carr and Coleman, 2007 ), based around glaciological principles of mass‐balance. This study examines how this approach can be used to test geomorphological interpretations of former mountain glaciation and also to infer precipitation fields at sites of former glaciation. Sites of Younger Dryas niche and icefield glaciation in the British Isles demonstrate how this method can verify interpretations of marginal glaciation and begin to understand the different behaviour of outlet glaciers within the same environmental regime. Examination of a site of former niche glaciation in Southern Africa demonstrates how glacier reconstruction may be used to infer annual and seasonal precipitation values and strongly supports the idea that winter precipitation in Lesotho and SE South Africa was substantially greater than present‐day values during the last glacial cycle. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
106.
Conditioning temperature‐index model parameters on synoptic weather types for glacier melt simulations 下载免费PDF全文
T. Matthews R. Hodgkins R. L. Wilby S. Guðmundsson F. Pálsson H. Björnsson S. Carr 《水文研究》2015,29(6):1027-1045
Temperature‐index models are widely favoured as a pragmatic means of simulating glacier melt because of their generally good performance, computational simplicity and limited demands for in situ data. However, their coefficients are normally treated as temporally stationary, unrealistically assuming a constancy of the prevailing weather. We address this simplification by prescribing model coefficients as a function of synoptic weather type, in a procedure that utilizes reanalysis data and preserves the minimal data requirements of temperature‐index models. Using a cross‐validation procedure at Vestari Hagafellsjökull, Iceland, and Storglaciären, Sweden, we demonstrate that applying transient model coefficients, for three temperature‐index models, results in statistically significant increases in the skill with which melt is modelled: Median simulation improvements in the Nash–Sutcliffe efficiency coefficient of 7.3 and 23.6% are achieved when hourly and daily melt totals are evaluated respectively. Our weather‐type modelling approach also yields insight to processes driving parameter variability, revealing dependence that is consistent with a priori considerations of the surface energy balance. We conclude that incorporating weather types into temperature‐index models holds promise for improving their performance, as well as enhancing understanding variability in coefficient values. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献
107.
Andrew S. Carr Arnoud Boom Brian M. Chase David L. Roberts Zoë E. Roberts 《Journal of Paleolimnology》2010,44(4):947-961
Pyrolysis–gas chromatography mass spectrometry (py-GC/MS) allows the characterisation of complex macromolecular organic matter.
In lakes and wetlands this can potentially be used to assess the preservation/diagenesis and provenance of sediment organic
matter. It can complement palaeoenvironmental investigations utilising ‘bulk’ sediment variables such as total organic carbon
(TOC) and TOC/total nitrogen ratios. We applied py-GC/MS analyses to a ~32,000-year sediment record from the southern Cape
coastline of South Africa. We used the results to evaluate the sources and extent of degradation of organic matter in this
semi-arid environment. Marked down-core changes in the relative abundance of multiple pyrolysis products were observed. Correspondence
analysis revealed that the major driver of this down-core variability in OM composition was selective preservation/degradation.
Samples comprising highly degraded OM are primarily confined to the lower half of the core, older than ~12,000 years, and
are characterised by suites of low-molecular-weight aromatic pyrolysis products. Samples rich in organic matter, e.g. surface
sediments, are characterised by products derived from fresh emergent or terrestrial vegetation, which include lignin monomers,
plant-derived fatty acids and long-chain n-alkanes. Pyrolysates from the late glacial-early Holocene period, approximately mid-way down the core are characterised by
distinct suites of long-chain n-alkene/n-alkane doublets, which may reflect the selective preservation of recalcitrant aliphatic macromolecules and/or enhanced inputs
of the algal macromolecule algaenan/polymerised algal lipids. Increased TOC, lower δ13C and increased abundance of more labile lignin and fatty acid products at the same depths suggest this period was associated
with increased lake primary productivity and enhanced inputs of terrestrial OM. TOC is the only ‘bulk’ parameter correlated
with the correspondence analysis axes extracted from the py-GC/MS data. Distinct fluctuations in TOC/total nitrogen ratio
are not explained by variation in organo-nitrogen pyrolysis products. Notwithstanding, the study suggests that py-GC/MS has
potential to complement palaeolimnological investigations, particularly in regions such as southern Africa, where other paleoenvironmental
proxy variables in sediments may be lacking or equivocal. 相似文献
108.
Godwin F. Mollel Carl C. Swisher III Lindsay J. McHenry Mark D. Feigenson Michael J. Carr 《Journal of African Earth Sciences》2009,54(5):127-143
Olmoti Crater is part of the Plio-Pleistocene Ngorongoro Volcanic Highland (NVH) in northern Tanzania to the south of Gregory Rift. The Gregory Rift is part of the eastern branch of the East African Rift System (EARS) that stretches some 4000 km from the Read Sea and Gulf of Aden in the north to the Zambezi River in Mozambique. Here, we (1) characterize the chemistry and mineral compositions of lavas from Olmoti Crater, (2) determine the age and duration of Olmoti volcanic activity through 40Ar/39Ar dating of Olmoti Crater wall lavas and (3) determine the genesis of Olmoti lavas and the relationship to other NVH and EARS volcanics and (4) their correlation with volcanics in the Olduvai and Laetoli stratigraphic sequences.Olmoti lavas collected from the lower part of the exposed crater wall section (OLS) range from basalt to trachyandesite whereas the upper part of the section (OUS) is trachytic. Petrography and major and trace element data reflect a very low degree partial melt origin for the Olmoti lavas, presumably of peridotite, followed by extensive fractionation. The 87Sr/86Sr data overlap whereas Nd and Pb isotope data are distinct between OLS and OUS samples. Interpretation of the isotope data suggests mixing of enriched mantle (EM I) with high-μ-like reservoirs, consistent with the model of Bell and Blenkinsop [Bell, K., Blenkinsop, J., 1987. Nd and Sr isotopic compositions of East African carbonatites: implications for mantle heterogeneity. Geology 5, 99–102] for East African carbonatite lavas. The isotope ratios are within the range of values defined by Oceanic Island Basalt (OIB) globally and moderate normalized Tb/Yb ratios (2.3–1.6) in these lavas suggest melting in the lithospheric mantle consistent with other studies in the region.40Ar/39Ar incremental-heating analyses of matrix and anorthoclase separates from Olmoti OLS and OUS lavas indicate that volcanic activity was short in duration, lasting 200 kyr from 2.01 ± 0.03 Ma to 1.80 ± 0.01 Ma. The age of Olmoti activity overlaps with ages reported for Ngorongoro Caldera, implying contemporaneous activity of multiple NVH volcanic centers during part of the eruption interval.Olmoti is considered the source for the bulk of interbedded volcanics and volcaniclastic deposits that comprise much of the upper Bed I section of nearby Olduvai Gorge, and part of the Laetoli sequence, both known for their well preserved fossils and archaeological remains. Age and chemical data reported here are compatible with those derived from tephra and lava interbedded in Bed I at Olduvai Gorge and from the Olpiro Beds at Laetoli. 相似文献
109.
The petrogenesis of Merensky Reef potholes at the Western Platinum Mine, Bushveld Complex: Sr-isotopic evidence for synmagmatic deformation 总被引:1,自引:0,他引:1
Potholes represent areas where the normally planar PGE-rich Merensky Reef of the upper Critical Zone of the Bushveld Complex
transgresses its footwall, such geometric relationships being unusual in layered intrusions. The recognition of vertical dykes
of Merensky pyroxenite in the footwall suggests downward collapse of crystal mush into pull-apart sites resulting from tensional deformation due to the loading effects of major new
magma additions. In contrast, crosscutting anorthosite veins display physical and isotopic evidence of upward emplacement. The Merensky Reef and its footwall have distinct initial Sr-isotope ratios (R
0 > 0.7066 and <0.7066, respectively), which may be used to constrain these processes related to pothole formation. Merensky
Reef in potholes (R
0 = 0.7069−0.7078) shows no isotopic evidence of assimilation of, or reaction with, footwall material. Discrete, discordant
replacement bodies of anorthosite extend from the footwall lithologies to cross-cut the Merensky Reef and its hanging wall.
The initial Sr-isotope ratio in these replaced rocks is totally reset to footwall values (R
0 = 0.7066), and immediately adjacent stratiform lithologies are slightly modified towards footwall values. In contrast, Neptunian
pyroxenitic (Merensky) dykes cross-cutting the footwall lithologies, with a large surface area to volume ratio, and low Sr
content, do not display footwall-like Sr-isotope initial-ratios (R
0 = 0.7077), and thus show no evidence for assimilation of or reaction with footwall material. Furthermore, pegmatoidal replacement
pyroxenite (“replacement pegmatoid”), at the base of the Merensky Reef within potholes, has a high initial-ratio (R
0 > 0.7071), and so models of pervasive metasomatism by footwall material are not applicable. This isotopic evidence indicates
that there was no active interaction of footwall material with the overlying magma during, or after, the formation of Merensky
Reef potholes, a basic tenet of existing pothole formation hypotheses involving footwall mass-transfer. In contrast, the isotopic
data are entirely consistent with an extensional model for pothole formation, with the more radiogenic Merensky magma migrating
laterally to fill extensional zones in the footwall layers.
Received: 11 October 1997 / Accepted: 21 December 1998 相似文献
110.