Structure of the Cobar Basin,New South Wales,based on seismic reflection profiling     

R. A. Glen  B. J. Drummond  B. R. Goleby  D. Palmer  K. D. Wake‐Dyster 《Australian Journal of Earth Sciences》2013,60(4):341-352

The Cobar Basin in central western New South Wales is a mineral‐rich Early Devonian basin typical of those that characterize the Siluro‐Devonian history of the Lachlan Orogen of southeastern Australia. One hundred and seventy kilometres of seismic profiling in three lines across the basin have shown it to be asymmetrical in shape with an east‐dipping western margin that is steeper than the moderately west‐dipping eastern margin. Maximum basin thickness is around 6 km, but there are significant thickness changes, especially from south to north, which reflect the effect of synsedimentary faulting. Seismic profiling suggests that the basin deformed by thin‐skinned tectonics; postulated strike‐slip effects were not visible on the sections. The seismic profiling has, for the first time, imaged the western synrift basin margin which is generally not exposed. Strain variations during deformation along this edge were taken up by the formation of a major jog ('dog‐leg') which has propagated into the basin as a tear fault. Intrabasinal tears, as well as thrusts, which link into one or more detachments, provide potential pathways for mineralizing fluids during basin inversion.  相似文献   

Analysis of the ferromagnetic contribution to the susceptibility by low field and high field methods in sedimentary rocks of the Southern Pyrenees and Northern Ebro foreland basin (Spain)     

Óscar Pueyo Anchuela  Antonio M. Casas‐Sainz  Emilio L. Pueyo  Andrés Pocoví Juan  Andrés Gil Imaz 《地学学报》2013,25(4):307-314

Magnetic susceptibility in rocks is the sum of the contributions of different magnetic particles (paramagnetic, diamagnetic and ferromagnetic s.l.). These contributions can be measured at variable temperatures or at variable fields (hysteresis loops). Both are time‐consuming techniques that cannot be routinely used in magnetic fabrics analysis. In this study, we propose a simplified method to determine the ferro‐ and paramagnetic contributions to the susceptibility, based on the discrete measurement of susceptibility at two different fields (near 0 and 2.5 T). The results obtained in samples from the Southern Pyrenees and Ebro Basin indicate that the ferromagnetic contribution vary considerably within homogeneous susceptibility values and within the expected range of paramagnetic values. Standard bulk susceptibilities higher than 200 10^?6 SI contribute significantly to the ferromagnetic fraction (>50% on average).  相似文献   

Linking a prolonged Neo‐Tethyan magmatic arc in South Asia: Zircon U‐Pb and Hf isotopic constraints from the Lohit Batholith,NE India     

Te‐Hsien Lin  Sun‐Lin Chung  Anil Kumar  Fu‐Yuan Wu  Han‐Yi Chiu  I‐Jhen Lin 《地学学报》2013,25(6):453-458

The Neo‐Tethyan subduction that operated before the India‐Asia collision resulted in an Andean‐type convergent margin in South Asia and was associated with extensive arc magmatism that formed the Transhimalayan batholiths. Magmatism in the Gangdese Batholith, the largest batholith exposed in the Lhasa terrane of southern Tibet, is considered to have lasted from the early Jurassic to Eocene. However, eastward correlation of the Gangdese Batholith is uncertain because it is truncated by the eastern Himalayan syntaxis. Here, we report new data from the Lohit Batholith, NE India, including: (i) zircon U‐Pb ages of five granitoids from ca. 148 to 96 Ma; and (ii) zircon Hf isotopes of these rocks that yield high and positive ε_Hf(T) values. We argue that the Lohit Batholith is the eastward extension of the Gangdese Batholith, and can be correlated southward to the Wuntho‐Popa arc in West Burma, thus linking a prolonged Neo‐Tethyan magmatic arc system from southern Tibet to Southeast Asia.  相似文献   

Deeply rooted glaciotectonism in western Denmark: geological composition,structural characteristics and the origin of Varde hill‐island     

A.‐S. HØYER  F. JØRGENSEN  J. A. PIOTROWSKI  P. R. JAKOBSEN 《第四纪科学杂志》2013,28(7):683-696

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Younger Dryas – early Holocene transition in the south‐eastern Iberian Peninsula: insights from land snail shell middens     

YURENA YANES  MAGDALENA GÓMEZ‐PUCHE  MARCO A. ESQUEMBRE‐BEBIA  JAVIER FERNÁNDEZ‐LÓPEZ‐DE‐PABLO 《第四纪科学杂志》2013,28(8):777-788

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Chloride transfer in cement‐based materials. Part 1. Theoretical basis and modelling     

K. Bourbatache  O. Millet  A. Aït‐Mokhtar  O. Amiri 《国际地质力学数值与分析法杂志》2013,37(11):1614-1627

In this first part of the work, we develop macroscopic models for migration and diffusion–migration of ionic species in saturated porous media, based on periodic homogenization. The prior application is chloride transport in cementitious materials. The dimensional analysis of Nernst–Planck equation lets appear to dimensionless numbers characterizing the ionic transfer in the porous medium. Using experimental data obtained from electrodiffusion tests on cement‐based materials (Part II), these dimensionless numbers are linked to the perturbation parameter ?. For a strong imposed electrical field, the asymptotic expansion of Nernst–Planck equation leads to a macroscopic model where the migration is predominant. For a weak imposed electrical field or in natural diffusion, we obtain a macroscopic model coupling diffusion and migration at the same order. In both models, the expression of the homogenized diffusion tensor is identical and only involves the geometric properties of the material microstructure. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献   

Phase equilibria constraints on melting of stromatic migmatites from Ronda (S. Spain): insights on the formation of peritectic garnet     

O. Bartoli  L. Tajčmanová  B. Cesare  A. Acosta‐Vigil 《Journal of Metamorphic Geology》2013,31(7):775-789

Stromatic metatexites occurring structurally below the contact with the Ronda peridotite (Ojén nappe, Betic Cordillera, S Spain) are characterized by the mineral assemblage Qtz+Pl+Kfs+Bt+Sil+Grt+Ap+Gr+Ilm. Garnet occurs in low modal amount (2–5 vol.%). Very rare muscovite is present as armoured inclusions, indicating prograde exhaustion. Microstructural evidence of melting in the migmatites includes pseudomorphs after melt films and nanogranite and glassy inclusions hosted in garnet cores. The latter microstructure demonstrates that garnet crystallized in the presence of melt. Re‐melted nanogranites and preserved glassy inclusions show leucogranitic compositions. Phase equilibria modelling of the stromatic migmatite in the MnO–Na₂O–CaO–K₂O–FeO–MgO–Al₂O₃–SiO₂–H₂–O₂–C (MnNCaKFMASHOC) system with graphite‐saturated fluid shows P–T conditions of equilibration of 4.5–5 kbar, 660–700 °C. These results are consistent with the complete experimental re‐melting of nanogranites at 700 °C and indicate that nanogranites represent the anatectic melt generated immediately after entering supersolidus conditions. The P–T estimate for garnet and melt development does not, however, overlap with the low‐temperature tip of the pure melt field in the phase diagram calculated for the composition of preserved glassy inclusions in garnet in the Na₂O–CaO–K₂O–FeO–MgO–Al₂O₃–SiO₂–H₂O (NCKFMASH) system. A comparison of measured melt compositions formed immediately beyond the solidus with results of phase equilibria modelling points to the systematic underestimation of FeO, MgO and CaO in the calculated melt. These discrepancies are present also when calculated melts are compared with low‐T natural and experimental melts from the literature. Under such conditions, the available melt model does not perform well. Given the presence of melt inclusions in garnet cores and the P–T estimates for their formation, we argue that small amounts (<5 vol.%) of peritectic garnet may grow at low temperatures (≤700 °C), as a result of continuous melting reactions consuming biotite.  相似文献   

Failure and size effect for notched and unnotched concrete beams     

D. Grégoire  L.B.  Rojas‐Solano  G. Pijaudier‐Cabot 《国际地质力学数值与分析法杂志》2013,37(10):1434-1452

Modelling failure in geomaterials, concrete or other quasi‐brittle materials and proper accounting for size effect, geometry and boundary effects are still pending issues. Regularised failure models are capable of describing size effect on specimens with a specific geometry, but extrapolations to other geometries are rare, mostly because experimental data presenting size effect for different geometries and for the same material are lacking. Three‐point bending fracture tests of geometrically similar notched and unnotched specimens are presented. The experimental results are compared with numerical simulations performed with an integral‐type non‐local model. Comparisons illustrate the shortcomings of this classical formulation, which fails to describe size effect over the investigated range of geometries and sizes. Finally, experimental results are also compared with the universal size effect law. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   

Mesozoic exhumation history of the Grenvillian Oaxacan Complex,southern Mexico     

Fanis Abdullin  Luigi Solari  Jesús Sol  Carlos Ortega‐Obregn 《地学学报》2021,33(1):86-94

We present the first fission‐track results from the Grenvillian Oaxacan Complex, southern Mexico. Time–temperature modelling of the data indicates that two significant Mesozoic cooling episodes are recorded in the Oaxacan Complex and these are interpreted as resulting from exhumation. The older cooling event took place from the Late Triassic to Middle Jurassic and is possible linked to the break‐up of Pangea (including the initial opening of the Gulf of Mexico during the Jurassic). The younger exhumation period in the Early Cretaceous is contemporaneous with the final stages of rifting of the Gulf of Mexico. Key stratigraphic records also provide independent evidence for these exhumation episodes. In our view, both Mesozoic rapid exhumation events were controlled by the activity of the Caltepec Fault Zone and the Oaxaca Fault. Our data suggest that both these large fault systems have remained active since, at least, the Late Triassic.  相似文献   

Increasing water losses from snow captured in the canopy of boreal forests: A case study using a 30 year data set          下载免费PDF全文

Nataliia Kozii  Hjalmar Laudon  Mikaell Ottosson‐Löfvenius  Niles J. Hasselquist 《水文研究》2017,31(20):3558-3567

Water losses from snow intercepted by forest canopy can significantly influence the hydrological cycle in seasonally snow‐covered regions, yet how snow interception losses (SIL) are influenced by a changing climate are poorly understood. In this study, we used a unique 30 year record (1986–2015) of snow accumulation and snow water equivalent measurements in a mature mixed coniferous (Picea abies and Pinus sylvestris ) forest stand and an adjacent open area to assess how changes in weather conditions influence SIL. Given little change in canopy cover during this study, the 20% increase in SIL was likely the result of changes in winter weather conditions. However, there was no significant change in average wintertime precipitation and temperature during the study period. Instead, mean monthly temperature values increased during the early winter months (i.e., November and December), whereas there was a significant decrease in precipitation in March. We also assessed how daily variation in meteorological variables influenced SIL and found that about 50% of the variation in SIL was correlated to the amount of precipitation that occurred when temperatures were lower than ?3 °C and to the proportion of days with mean daily temperatures higher than +0.4 °C. Taken together, this study highlights the importance of understanding the appropriate time scale and thresholds in which weather conditions influence SIL in order to better predict how projected climate change will influence snow accumulation and hydrology in boreal forests in the future.  相似文献