Neogene exhumation and relief evolution in the eastern Betics (SE Spain): Insights from the Sierra de Gador          下载免费PDF全文

Marianne Janowski  Nicolas Loget  Cécile Gautheron  Jocelyn Barbarand  Nicolas Bellahsen  Jean Van Den Driessche  Julien Babault  Bertrand Meyer 《地学学报》2017,29(2):91-97

The Betics are a key area to study an orogenic landscape disrupted by late‐orogenic extension. New low‐temperature thermochronology (LTT) data (AHe and AFT) coupled with geomorphic constraints in the Sierra de Gador (Alpujarride complex) are used to reconstruct the cooling history and evolution of relief during the Neogene. We document three stages: (1) a fast cooling event between 23 and 16 Ma associated with the well‐known extensive tectonic exhumation of the Alpujarride unit, (2) a period of slow cooling between 16 and 7.2 Ma related to a planation event and (3) a post‐7.2 Ma surface uplift associated with the inversion of the Alboran domain undetected by LTT. The planation event followed by this late uplift can explain the occurrence of inherited low‐relief surfaces overlain by Tortonian–Messinian platform deposits at the top of the range. Finally, we propose that the Sierra de Gador is a more transient landscape than the nearby Sierra Nevada.  相似文献   

Emplacement of Semail–Emirates ophiolite at ridge–trench collision          下载免费PDF全文

Adolphe Nicolas  Françoise Boudier 《地学学报》2017,29(2):127-134

The Oman‐Emirates is the largest and best‐exposed ophiolite; consequently, it has attracted significant interest among scientists, together with serious conflicts. Most geologists regard this ophiolite as having formed in an intra‐oceanic subduction zone before being accreted to the Arabian continent. Here, we propose an alternative scenario, supported by detailed field observations and integrated geophysics. The smaller Emirates part of the ophiolite was forced into a nearby continent, in the pre‐collision stage of Tethyan closure. The contraction led to the exhumation of the mantle floor of segmented basins accreted in a rifted system similar to the present‐day Gulf of California. The implied high temperature–high pressure metamorphism and the range of geochemical signatures were introduced during the process of rifting, whereas the larger Oman ophiolite was emplaced by obduction onto and along the subducting continental shore. This Ridge–Trench–Transform system might call for a new process to obduct over continents in particular Tethyan ophiolites.  相似文献   

Possible long-term decline in impact rates: 1. Martian geological data     

Cathy Quantin  Nicolas Mangold  Pascal Allemand 《Icarus》2007,186(1):1-10

Quantin et al. [Quantin, C., Allemand, P., Mangold, N., Delacourt, C., 2004a. Icarus 172, 555-572] tabulated crater count data for 56 landslides along the walls of Valles Marineris. Under the assumption of a constant cratering rate after about 3 Gyr ago, as used in the 1999-2005 iterations of the crater chronology isochron system of Hartmann, and in the Hartmann and Neukum system, these data indicate a regularly increasing rate of landslides, which would be difficult to explain. We suggest that these data may support a decline in inner Solar System cratering rates by about a factor of 3 since 3 Gyr ago, not unlike predictions based on asteroid belt collision models. Such a decline is also supported by our review of data on lunar impact melts and glass spherules in a companion paper [Hartmann, W.K., Quantin, C., Mangold, N., 2007. Icarus 186, 11-23]. Such models produce not only a more uniform rate of landslides over the last 3 Gyr, but also a more uniform rate of resurfacing processes which also had an apparent increase under the assumption of a constant cratering rate.  相似文献   

Closure of a hyperextended system in an orogenic lithospheric pop‐up,Western Pyrenees: The role of mantle buttressing and rift structural inheritance     

Nicolas Saspiturry  Ccile Allanic  Philippe Razin  Benoit Issautier  Thierry Baudin  Eric Lasseur  Olivier Serrano  Sophie Leleu 《地学学报》2020,32(4):253-260

The Early Cretaceous hyperextended Mauléon rift is localized in the north‐western Pyrenean orogen. We infer the Tertiary evolution of the Mauléon basin through the restoration of a 153‐km‐long crustal‐scale balanced cross‐section of the Pyrenean belt, which documents at least 67 km (31%) of orogenic shortening in the Western Pyrenees. Initial shortening, accommodated through inversion of inherited crustal structures, led to formation of a pop‐up structure, in which the opposite edges underwent similar shortening with different tectonic reactivation styles, localized versus. distributed. Underthrusting of the Iberian margin accommodated further convergence, forming the Axial Zone antiformal stack of crustal nappes within a lithospheric pop‐up. Thin‐skinned and thick‐skinned structures propagated outward from the heart of this pop‐up, a block of strong mantle acting as a buttress inhibiting complete inversion of the Mauléon rift basin.  相似文献   

Moving beyond the catchment scale: Value and opportunities in large-scale hydrology to understand our changing world     

Daniel G. Kingston  Nicolas Massei  Bastien Dieppois  David M. Hannah  Andreas Hartmann  David A. Lavers  Jean-Philippe Vidal 《水文研究》2020,34(10):2292-2298

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Hydrological regimes in a tropical valley of New Caledonia (SW Pacific): Impacts of wildfires and invasive fauna     

Caroline Marie Clémence Tramier  Pierre Genthon  Quentin Réginald Camille Paul Delvienne  Nicolas Luc Sauvan  Jean-Jérôme Olivier Cassan  Etienne Ebrard  Pascal Sébastien Dumas  Yann Queffélean 《水文研究》2021,35(3):e14071

In New Caledonia wildfires and invasive mammals (deer and wild pigs) constitute the major agents of land surface degradation. Our study reveals the linkage between land cover and water balance on the northeast coast of New Caledonia (2400 mm annual rainfall) located on a micaschist basement. The hydrological regime of characteristic and representative land surfaces is assessed using a 1-year record from three 100 m² plots each, located in a forest area degraded by an invasive fauna, in a woody savannah which is regularly burned, and in a healthy forest area. The three plots present highly contrasting hydrological regimes, with annual and maximum runoff/rain ratios during a rain event of, respectively, 0.82, 0.16, 0.03, and 2.7, 0.7, 0.2, for the degraded forest, the savannah and the healthy forest. Such results suggest that subsurface flow originating from the contributing area above the degraded forest plot should exfiltrate inside the plot. A conceptual model for the degraded forest plot shows that water exfiltrating inside the plot represents 61% of the observed runoff. In savannahs, water should mainly be transferred downstream by subsurface flow within a thick organic soil layer limited by an impervious clay layer at a 20–30 cm depth. Savannahs are generally located above forests and generate the transfer of rainwater to downslope forests. Exfiltration into the forests can be the result of this transfer and depends on the thickness and permeability of the forest topsoils and on topographic gradients. Water exfiltration in forest areas highly degraded by pigs and deer enhances erosion and increases further degradation. It probably also limits percolation in the areas located downstream by increasing the amount of superficial runoff concentrated in gullies.  相似文献   

On the prevalence of forest fires in Spain     

Boccard  Nicolas 《Natural Hazards》2022,114(1):1043-1057

Natural Hazards - We study the prevalence of forest fires in Spain in the long run by computing the probability that a forest tree, as opposed to shrub or bush, will be lost to fire over the course...  相似文献   

Electrical interferences observed in the Cassini CIRS spectrometer     

Cheong Chan  Shane Albright  Nicolas Gorius  John Brasunas  Don Jennings  F. Michael Flasar  Ronald Carlson  Ever Guandique  Conor Nixon 《Experimental Astronomy》2015,39(2):367-386

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Radio observations of Comet 9P/Tempel 1 before and after Deep Impact     

Nicolas Biver  Dominique Bockelée-Morvan  Jacques Crovisier  Alain Lecacheux  Gabriel Paubert  Matthew Sumner  Åke Hjalmarson  Anders Winnberg  Aage Sandqvist 《Icarus》2007,187(1):253-271

Comet 9P/Tempel 1 was the target of a multi-wavelength worldwide investigation in 2005. The NASA Deep Impact mission reached the comet on 4.24 July 2005, delivering a 370-kg impactor which hit the comet at 10.3 km s⁻¹. Following this impact, a cloud of gas and dust was excavated from the comet nucleus. The comet was observed in 2005 prior to and after the impact, at 18-cm wavelength with the Nançay radio telescope, in the millimeter range with the IRAM and CSO radio telescopes, and at 557 GHz with the Odin satellite. OH observations at Nançay provided a 4-month monitoring of the outgassing of the comet from March to June, followed by the observation of H₂O with Odin from June to August 2005. The peak of outgassing was found to be around between May and July. Observations conducted with the IRAM 30-m radio telescope in May and July 2005 resulted in detections of HCN, CH₃OH and H₂S with classical abundances relative to water (0.12, 2.7 and 0.5%, respectively). In addition, a variation of the HCN production rate with a period of 1.73±0.10 days was observed in May 2005, consistent with the 1.7-day rotation period of the nucleus. The phase of these variations, as well as those of CN seen in July by Jehin et al. [Jehin, E., Manfroid, J., Hutsemékers, D., Cochran, A.L., Arpigny, C., Jackson, W.M., Rauer, H., Schulz, R., Zucconi, J.-M., 2006. Astrophys. J. 641, L145-L148], is consistent with a rotation period of the nucleus of 1.715 days and a strong variation of the outgassing activity by a factor 3 from minimum to maximum. This also implies that the impact took place on the rising phase of the “natural” outgassing which reached its maximum ≈4 h after the impact. Post-impact observations at IRAM and CSO did not reveal a significant change of the outgassing rates and relative abundances, with the exception of CH₃OH which may have been more abundant by up to one order of magnitude in the ejecta. Most other variations are linked to the intrinsic variability of the comet. The Odin satellite monitored nearly continuously the H₂O line at 557 GHz during the 38 h following the impact on the 4th of July, in addition to weekly monitoring. Once the periodic variations related to the nucleus rotation are removed, a small increase of outgassing related to the impact is present, which corresponds to the release of ≈5000±2000 tons of water. Two other bursts of activity, also observed at other wavelengths, were seen on 23 June and 7 July; they correspond to even larger releases of gas.  相似文献   

Latitudinal librations of Mercury with a fluid core     

Julien Dufey  Benoît Noyelles  Nicolas Rambaux 《Icarus》2009,203(1):1-12

In the framework of the space missions to Mercury, an accurate model of rotation is needed. Librations around the 3:2 spin-orbit resonance as well as latitudinal librations have to be predicted with the best possible accuracy. In this paper, we use a Hamiltonian analysis and numerical integrations to study the librations of Mercury, both in longitude and latitude. Due to the proximity of the period of the free libration in longitude to the orbital period of Jupiter, the 88-day and 11.86-year contributions dominate Mercury’s libration in longitude (with the Hermean parameters chosen). The amplitude of the libration in latitude is much smaller (under 1 arcsec) and should not be detected by the space missions. Nevertheless, we point out that this amplitude could be much larger (up to several tens of arcsec) if the free period related to the libration in latitude approaches the period of the Jupiter-Saturn Great Inequality (883 years). Given the large uncertainties on the planetary parameters, this new resonant forcing on Mercury’s libration in latitude should be borne in mind.  相似文献