Institute Geociencias

Madrid, Spain

Institute Geociencias

Madrid, Spain
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Egea-Gonzalez I.,Technical University of Cartagena | Egea-Gonzalez I.,University of Cádiz | Jimenez-Diaz A.,Complutense University of Madrid | Parro L.M.,Complutense University of Madrid | And 3 more authors.
Icarus | Year: 2017

The circum-Hellas area of Mars borders Hellas Planitia, a giant impact ∼4.0–4.2 Ga old making the deepest and broadest depression on Mars, and is characterized by a complex pattern of fracture sets, lobate scarps, grabens, and volcanic plains. The numerous lobate scarps in the circum-Hellas region mainly formed in the Late Noachian and, except Amenthes Rupes, have been scarcely studied. In this work, we study the mechanical behavior and thermal structure of the crust in the circum-Hellas region at the time of lobate scarp formation, through the modeling of the depth of faulting beneath several prominent lobate scarps. We obtain faulting depths between ∼13 and 38 km, depending on the lobate scarp and accounting for uncertainty. These results indicate low surface and mantle heat flows in Noachian to Early Hesperian times, in agreement with heat flow estimates derived from lithospheric strength for several regions of similar age on Mars. Also, faulting depth and associate heat flows are not dependent of the local crustal thickness, which supports a stratified crust in the circum-Hellas region, with heat-producing elements concentrated in an upper layer that is thinner than the whole crust. © 2017 Elsevier Inc.

Hollanda M.H.B.M.,Institute Geociencias | Archanjo C.J.,Institute Geociencias | Bautista J.R.,Institute Geociencias
Precambrian Research | Year: 2015

U-Pb ages of detrital zircons and neodymium (Nd) isotope compositions from two Neoproterozoic schist belts (Seridó and Lavras da Mangabeira) in the Borborema Province (NE Brazil) indicate a significant change of sediment provenance during the deposition of sands and conglomerates and the overlying graywacke-pelite sequences. The shift in provenance defines an unconformity in the Seridó Group characterized by a metadiamictite horizon that contains pebbles and cobbles of the Paleoproterozoic to Archean basement and recycled quartzites of the underlying Equador Formation. In Lavras da Mangabeira basin the change in provenance is defined by a cryptic internal disconformity that is characterized, as in the Seridó basin, by a time gap of c. 1.0Ga in the age of the detrital zircons. Nd compositions across these unconformities indicate that the pelites are very radiogenic (e{open}Ndpresent-day=-4 to -11) compared with the sandy deposits (e{open}Ndpresent-day=-22 to -31). The provenance of the metapelites at the top of the metasedimentary succession includes a prominent population of Cryogenian zircons with the youngest grains dated to between 0.64 and 0.62Ga. These zircons were deposited in a basin developed on continental basement that preserves remnants of near-shore to terrestrial deposits with no detrital zircons younger than 1.8Ga. This unconformity defines a useful stratigraphic horizon to correlate with other metasedimentary successions preserved in the Borborema Province. In the Seridó belt the unconformity documents the uplift of the orogenic hinterland, possibly during the continental collision, which preceded the deposition of the deep-water pelites. © 2014 Elsevier B.V.

Leao-Santos M.,Colorado School of Mines | Leao-Santos M.,Institute Geociencias | Li Y.,Colorado School of Mines | Moraes R.,University of Brasilia
Geophysics | Year: 2015

Strong hydrothermal alteration modifies rock physical properties in iron oxide-copper-gold deposits (IOCGs) and may result in characteristic signatures detectable in geophysical surveys. Magnetic data are commonly used in characterizing orebodies, and 3D inversions are often used to assist in interpretations. In areas with strong remanence and self-demagnetization, the total magnetization can have directions different from the inducing field direction. This deviation precludes the use of traditional inversion methods. Magnetic amplitude inversion offers one solution to this challenge because the amplitude data are weakly dependent on the magnetization direction. In addition, the low magnetic latitude also imposes difficulty in amplitude data calculation due to the instability in the component conversion in the wavenumber domain. To formulate a practical approach, we present a case study on applying the magnetic amplitude inversion to the Furnas southeast IOCG deposit at the low magnetic latitude in Carajás Mineral Province, Brazil, and demonstrate that the approach can reliably recover an interpretable distribution of effective magnetic susceptibility and identify massive magnetite from hydrothermal alterations associated with the high-grade ore. © 2015 Society of Exploration Geophysicists.

Rodriguez-Lopez J.P.,Complutense University of Madrid | Melendez N.,Complutense University of Madrid | Melendez N.,Institute Geociencias | de Boer P.L.,University Utrecht | And 2 more authors.
Aeolian Research | Year: 2013

During the Albian Iberia was under the influence of the Northern-Hemisphere Hot Arid Belt favouring the development of an extensive sandy desert system with a marine-erg margin where prograding aeolian dunes interacted with Tethyan waters. The interplay of different controls, such as synsedimentary tectonics, compaction of the underlying coal-bearing unit, eustatic sea-level variations, climate modulation, and the autodynamics of the different sedimentary subenvironments determined the character of bounding surfaces, which separate four erg sequences. These bounding surfaces, or supersurfaces, may display a different sedimentary expression in adjacent areas. Bounding surface 1 is a sand-drift surface (SDS) in the central-erg and a transgressive surface (TS) in the marine erg margin. Bounding surface 2 is associated with a basin re-configuration associated to active extension tectonics, followed by deflation. Bounding surface 3 marks the end of erg expansion, the start of its partial destruction and redeposition and reworking in restricted marine environments. Bounding surface 4 marks the return to more arid conditions and draa progradation into Tethyan waters. These bounding surfaces separate four erg sequences. On the basis of the relative role of allocyclic processes, two megasequences are defined. The first comprises erg sequences 1-3, and the second megasequence comprises erg sequence 4. Erg megasequence 1 developed while synsedimentary tectonic activity and substrate (peat) compaction were active. Erg megasequence 2 was mainly modulated by climate (change). A nomenclature for supersurfaces is proposed based on the types of external control. © 2013 Elsevier B.V.

Jimenez-Diaz A.,Complutense University of Madrid | Jimenez-Diaz A.,Institute Geociencias | Ruiz J.,Complutense University of Madrid | Perez-Gussinye M.,Royal Holloway, University of London | And 5 more authors.
Earth and Planetary Science Letters | Year: 2014

As a proxy for long-term lithospheric strength, the effective elastic thickness (Te) can be used to understand the relationship between lithospheric rheology and geodynamic evolution of complex tectonic settings. Here we present, for the first time, high-resolution maps of spatial variations of Te in Central America and surrounding regions from the analysis of the coherence between topography and Bouguer gravity anomaly using multitaper and wavelet methods. Regardless of the technical differences between the two methods, there is a good overall agreement in the spatial variations of Te recovered from both methods. Although absolute Te values can vary in both maps, the qualitative Te structure and location of the main Te gradients are very similar. The pattern of the Te variations in Central America and surrounding regions agrees well with the tectonic provinces in the region, and it is closely related to major tectonic boundaries, where the Middle American and Lesser Antilles subduction zones are characterized by a band of high Te on the downgoing slab seaward of the trenches. These high Te values are related to internal loads (and in the case of the southernmost tip of the Lesser Antilles subduction zone also associated with a large amount of sediments) and should be interpreted with caution. Finally, there is a relatively good correlation, despite some uncertainties, between surface heat flow and our Te results for the study area. These results suggest that although this area is geologically complex, the thermal state of the lithosphere has profound influence on its strength, such that Te is strongly governed by thermal structure. © 2014 Elsevier B.V.

Dominguez-Castro F.,University of Extremadura | Dominguez-Castro F.,National Polytechnic School of Ecuador | de Miguel J.C.,Archivo del Ministerio de Asuntos Exteriores y de Cooperacion | Vaquero J.M.,University of Extremadura | And 3 more authors.
Holocene | Year: 2014

From ad 711 to 1492, several regions in Iberia were under Muslim ruling. This Al-Andalus civilization generated a large amount of documentation during those centuries. Unfortunately, most of the documents are lost. The surviving Arabic documentary sources have never been studied from a climate perspective. In this paper, we present the first attempt to retrieve climate evidence from them. We studied all the Islamic chronicles (documents written by Islamic historians that narrate the social, political and religious history) available for the period ad 711-1010. It is shown that these sources recorded extreme events with a high temporal and spatial resolution. We identified three severe droughts, ad 748-754, ad 812-823 and ad 867-879, affecting Al-Andalus. We also noticed that the weather in Cordoba during the period ad 971-975 showed a higher frequency of snow and hail than current climate. The possibility of obtaining long continuous series from this type of source seems highly difficult. © The Author(s) 2014.

Abella J.,CSIC - National Museum of Natural Sciences | Alba D.M.,Institute Catala Of Paleontologia Miquel Crusafont | Robles J.M.,Institute Catala Of Paleontologia Miquel Crusafont | Robles J.M.,FOSSILIA Serveis Paleontologics i Geologics S.L. | And 7 more authors.
PLoS ONE | Year: 2012

The phylogenetic position of the giant panda, Ailuropoda melanoleuca (Carnivora: Ursidae: Ailuropodinae), has been one of the most hotly debated topics by mammalian biologists and paleontologists during the last century. Based on molecular data, it is currently recognized as a true ursid, sister-taxon of the remaining extant bears, from which it would have diverged by the Early Miocene. However, from a paleobiogeographic and chronological perspective, the origin of the giant panda lineage has remained elusive due to the scarcity of the available Miocene fossil record. Until recently, the genus Ailurarctos from the Late Miocene of China (ca. 8-7 mya) was recognized as the oldest undoubted member of the Ailuropodinae, suggesting that the panda lineage might have originated from an Ursavus ancestor. The role of the purported ailuropodine Agriarctos, from the Miocene of Europe, in the origins of this clade has been generally dismissed due to the paucity of the available material. Here, we describe a new ailuropodine genus, Kretzoiarctos gen. nov., based on remains from two Middle Miocene (ca. 12-11 Ma) Spanish localities. A cladistic analysis of fossil and extant members of the Ursoidea confirms the inclusion of the new genus into the Ailuropodinae. Moreover, Kretzoiarctos precedes in time the previously-known, Late Miocene members of the giant panda clade from Eurasia (Agriarctos and Ailurarctos). The former can be therefore considered the oldest recorded member of the giant panda lineage, which has significant implications for understanding the origins of this clade from a paleobiogeographic viewpoint. © 2012 Abella et al.

Perez-Zarate D.,National Autonomous University of Mexico | Santoyo E.,National Autonomous University of Mexico | Guevara M.,National Autonomous University of Mexico | Torres-Alvarado I.S.,National Autonomous University of Mexico | And 2 more authors.
Applied Thermal Engineering | Year: 2015

Water/Rock Interaction (WRI) experiments, Na-K geothermometry and geochemometrics modeling have been used for the study of the kinetic behavior of the volcanic rock dissolution under geothermal conditions. Ionic exchange reactions between Na-K and alkaline-feldspar minerals were monitored at 90°C and 150°C for a period of nearly 24 and 3 months, respectively. Na/K ratios (inferred from WRI experiments and Na-K geothermometers) and reaction times were used for estimating the most probable quasi-steady state conditions. A geochemometrics modeling was also performed to predict the reaction times required to achieve quasi-steady state conditions in the WRI experiments. This modeling was validated with WRI experimental data reported in the literature for which quasi-steady state conditions were known with accuracy. New WRI experiments were additionally carried out using batch reactors under controlled pressure and temperature conditions. Volcanic rock (basalt and dacites) crushed samples (500-1000 mm grain size) were reacted with distilled water at 90°C and 150°C using a W/R mass ratio of 5. Rock and fluid samples were collected and analyzed for major composition, before and after each experiment. The experimental results were subsequently used to calculate log(Na/K) values for describing the kinetic behavior of the alkaline-feldspar mineral dissolution. Values of log(Na/K) and reaction time at quasi-steady state conditions were reproduced with good accuracy by using the rational polynomial and logarithmic transformation regression models. These results were compared with those values inferred from the Na-K geothermometry, which theoretically assume deep geothermal equilibrium conditions. © 2014 Elsevier Ltd. All rights reserved.

After the adjustment of observations by the Least Squares Method (LSM), using statistical tests, it is possible to detect and identify non-random errors in the observations. The reliability theory makes use of appropriate measures to quantify the minimal detectable bias (error) in an observation, and its influence on the adjusted parameters, if not detected. The conventional reliability theory has been developed aiming at conventional testing procedures such as data snooping, which assumes that only one observation is contaminated by errors at a time. Recently, generalized measures of reliability were developed, relating to statistical tests that assumes the existence, simultaneous by, of multiple observations with errors (outliers). The goal of this paper is to present, discuss and apply the theory of reliability generalized for multiple outliers. Besides the theoretical formulation, this paper also presents experiments performed on a GPS network (Global Positioning System), where proposital errors were inserted in some observations and measures of reliability and statistical tests were calculated using the approach for multiple outliers. Comparisons with the conventional theory of reliability were also made. Finally, results were presented and discussed.

Vilalva F.C.J.,Institute Geociencias | Vlach S.R.F.,Institute Geociencias
Mineralogical Magazine | Year: 2010

Turkestanite, a rare Th- and REE-bearing cyclosilicate in the ekanite-steacyite group was found in evolved peralkaline granites from the Morro Redondo Complex, south Brazil. It occurs with quartz, alkali feldspar and an unnamed Y-bearing silicate. Electron microprobe analysis indicates relatively homogeneous compositions with maximum ThO2, Na2O and K2O contents of 22.4%, 2.93% and 3.15 wt.%, respectively, and significant REE 2O3 abundances(5.21 to 11.04 wt.%). The REE patterns show enrichment of LREE over HREE, a strong negative Eu anomaly and positive Ce anomaly, the latter in the most transformed crystals. Laser ablation inductively coupled plasma mass spectrometry trace element patterns display considerable depletions in Nb, Zr, Hf, Ti and Li relative to whole-rock sample compositions. Observed compositional variations suggest the influence of coupled substitution mechanisms involving steacyite, a Na-dominant analogue of turkestanite, iraqite, a REE-bearing end-member in the ekanite-steacyite group, ekanite and some theoretical end-members. Turkestanite crystals were interpreted as having precipitated during post-magmatic stages in the presence of residual HFSE-rich fluids carrying Ca, the circulation of which was enhanced by deformational events. © 2010 Mineralogical Society.

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