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   

Hydrous olivine alteration on Mars and Earth     

Zoltn Vci  Carl B. Agee  Christopher D. K. Herd  Erin Walton  Oliver Tschauner  Karen Ziegler  Vitali B. Prakapenka  Eran Greenberg  Sylvia Monique‐Thomas 《Meteoritics & planetary science》2020,55(5):1011-1030

Hydrous alteration of olivine macrocrysts in a Martian olivine phyric basalt, NWA 10416, and a terrestrial basalt from southern Colorado are examined using SEM, EPMA, TEM, and µXRD techniques. The olivines in the meteorite contain linear nanotubes of hydrous material, amorphous areas, and fluid dissolution textures quite distinct from alteration identified in other Martian meteorites. Instead, they bear resemblance to terrestrial deuteric alteration features. The presence of the hydrous alteration phase Mg‐laihunite within the olivines has been confirmed by µXRD analysis. The cores of the olivines in both Martian and terrestrial samples are overgrown by unaltered rims whose compositions match those of a separate population of groundmass olivines, suggesting that the core olivines are xenocrysts whose alteration preceded crystallization of the groundmass. The terrestrial sample is linked to deep crustal metasomatism and the “ignimbrite flare‐up” of the Oligocene epoch. The comparison of the two samples suggests the existence of an analogous relatively water‐rich magmatic reservoir on Mars.  相似文献   

Combining IR and X‐ray microtomography data sets: Application to Itokawa particles and to Paris meteorite     

Zelia Dionnet  Rosario Brunetto  Alice Alon‐Toppani  Stefano Rubino  Donia Baklouti  Ferenc Borondics  Anne‐Ccile Buellet  Zahia Djouadi  Andrew King  Tomoki Nakamura  Alessandra Rotundi  Christophe Sandt  David Troadec  Akira Tsuchiyama 《Meteoritics & planetary science》2020,55(7):1645-1664

In the near future, a new generation of sample return missions (Hayabusa2, OSIRIS‐REx, MMX, etc.) will collect samples from small solar system bodies. To maximize the scientific outcome of laboratory studies and minimize the loss of precious extraterrestrial samples, an analytical sequence from less destructive to more destructive techniques needs to be established. In this work, we present a combined X‐ray and IR microtomography applied to five Itokawa particles and one fragment of the primitive carbonaceous chondrite Paris. We show that this analytical approach is able to provide a 3‐D physical and chemical characterization of individual extraterrestrial particles, using the measurement of their 3‐D structure and porosity, and the detection of mineral and organic phases, and their spatial co‐localization in 3‐D. We propose these techniques as an efficient first step in a multitechnique analytical sequence on microscopic samples collected by space missions.  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