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11.
Gianluca Vignaroli Claudio Faccenna Federico Rossetti 《International Journal of Earth Sciences》2009,98(5):1077-1093
Geological mapping coupled with structural investigations carried out in the Voltri Massif (eastern Ligurian Alps, Italy)
provide new data for the interpretation of the tectonic context controlling main fabric development during exhumation of its
high-pressure core. The Voltri Massif is here interpreted as a c. 30 km-long eclogite-bearing, asymmetric dome formed by the
progressive verticalisation of the regional, second-phase mylonitic foliation developed during retrogressive greenschist metamorphic
conditions. In this light, the exhumation history is driven by a ductile-to-brittle extensional process, operating through
low-angle, top-to-the-W multiple detachment systems. A Late Eocene–Early Oligocene age for this extensional episode is proposed
on the basis of structural correlations, stratigraphic and radiometric constraints. In this scenario, the Voltri Massif is
interpreted as an extensional domain developed to accommodate the Late Eocene–Early Oligocene arching of the Western Alps–Northern
Apennines orogenic system. 相似文献
12.
VINCENZO GIANFRANCO DI; ANDRIESSEN PAUL A. M.; GHEZZO CLAUDIO 《Journal of Petrology》1996,37(5):1175-1206
Detailed petrographic and geochemical data and Sr and Nd isotopecompositions of enclaves and host-granite are reported for oneof the largest strongly peraluminous cordierite-bearing intrusionsof the Hercynian Sardinia-Corsica Batholith: the San BasilioGranite. Compared with other peraluminous series, the San BasilioGranite has a ‘non-minimum melt’ composition andshows variations primarily owing to fractionation of early-crystallizedplagioclase, quartz and biotite. Crystallization age is constrainedat 305 Ma, by Rb-Sr whole-rock age [30523 Ma with (87Sr/86Sr)i= 0.711050.00041], and occurred during late Hercynian tectonicevents. Nd(305Ma) values range from –7.8 to –7.5.The San Basilio Granite contains both magmatic and metamorphicenclaves. Magmatic enclaves, similar to mafic microgranularenclaves common in calc-alkaline granitoids, are tonalitic incomposition and show a variation in silica content from 60.3to 67.7 wt % correlating with a variation in (87Sr/86 Sr) (305Ma)and Nd (305 Ma) from 0.7092 to 0.7109 and from –6.6 to–7.4, respectively. Together with petrographic and othergeochemical data, the Sr and Nd isotopic data record differentstages in a complex homogenization process of an unrelated maficmagma with a crustal melt. A process of simple mixing may accountfor the variations of nonalkali elements and, to some extent,of Sr and Nd isotopes, whereas the distribution of alkali elementsrequires diffusioncontrolled mass transfer. Petrographic andmineralogical data on metamorphic enclaves and geochemical modellingfor trace elements in granite indicate melt generation by high-degreepartial melting involving biotite breakdown of a dominantlyquartzo-feldspathic protolith at about T>750–800Cand P>6 kbar leaving a granulite facies garnet-bearing residue,followed by emplacement at 3 kbar. Nd(305Ma) values of thegranite fall within the range defined by the pre-existing metamorphicrocks but (87Sr/86Sr) (305Ma) ratios are lower, indicating involvementof at least two distinct components: a dominant crustal componentand a minor well-mixed mafic end-member. These data point toa decoupling between the Sr-Nd isotope systematics and majorand trace element compositions, suggesting that the effect ofthe mafic component was minor on granite major and trace elementconcentrations, but significant on Sr and Nd isotopes. The studyof the magmatic enclaves and the isotopic evidence demonstratethat unrelated mafic magmas, probably derived from the mantle,had a close spatial and temporal association with the productionof ‘on-minimum melt’ strongly peraluminous granites,and support the proposal that heat from the mafic magma contributedto crustal melting. KEY WORDS: cordierite-bearing granite; enclaves; felsic-mafic interaction; Sardinia-Corsica Batholith; Sr and Nd isotopes
*Corresponding author. 相似文献
13.
STEFANO ANDREUCCI MARK D. BATEMAN CLAUDIO ZUCCA SELIM KAPUR İHSAN AKŞIT ADAM DUNAJKO VINCENZO PASCUCCI 《Sedimentology》2012,59(3):917-938
A multi‐disciplinary approach was followed to investigate two thick palaeosol strata that alternate with wind‐blown dominated deposits developed along the Alghero coast (North‐west Sardinia, Italy). Optically stimulated luminescence ages reveal that both palaeosols were developed during cooler drier periods: the first one at around 70 ka Marine Isotope Stage 4 and the latter around 50 ka (Marine Isotope Stage 3). In contrast, the pedological features indicate that the palaeosols underwent heavy weathering processes under warm humid to sub‐humid conditions, characteristic of the Sardinian climate during the last interglacial stage (Marine Isotope Stage 5e). To reconcile this apparent data discrepancy, a range of sedimentological and pedological analyses were conducted. These analyses reveal that the palaeosols possess a complex history, with accumulation and weathering occurring during Marine Isotope Stage 5e, and erosion, colluviation and final deposition taking place during the following cold stages. Thus, even if these reddish palaeosols were last formed during the glacial period, the sediments building up these strata probably record the climate of the last interglacial stage (Marine Isotope Stage 5e). Trace element and X‐ray diffraction analyses, together with scanning electron microscope images, reveal the presence of Saharan dust in the parent material of the palaeosols. However, no evidence of any far‐travelled African dust has been observed in the Marine Isotope Stage 4–3 aeolian deposits. It is possible to conclude that in the West Mediterranean islands, Saharan dust input, even if of modest magnitude, is preserved preferentially in soils accumulated and weathered during interglacial stages. 相似文献
14.
Role of the backstop-to-cover thickness ratio on vergence partitioning in experimental thrust wedges
The ratio between the thickness of the sedimentary sequences offscraped from the subducting plate ( H c ) and the average thickness of the backstop ( H b ) is expected to significantly influence vergence partitioning in thrust wedges. A series of simple sandbox experiments was performed to study the role of the H c / H b ratio in model thrust wedges. The results obtained show that thrust wedges with H c / H b values lower than 1 are essentially pro-ward verging, with minor retro-ward faulting; H c / H b values greater than 1 imply an increase of vergence partitioning. When a threshold value is exceeded, fully partitioned, doubly vergent thrust wedges develop. Comparison with natural submarine thrust wedges suggests that these experimental results may provide useful insights on the evolution of structural architecture at convergent margins. 相似文献
15.
Marco Maffione Fabio Speranza Claudio Faccenna Eduardo Rossello 《Earth and Planetary Science Letters》2010,289(1-2):273-286
The southernmost segment of the Andes of southern Patagonia and Tierra del Fuego forms a ～ 700 km long orogenic re-entrant with an interlimb angle of ～ 90° known as Patagonian orocline. No reliable paleomagnetic evidence has been gathered so far to assess whether this great orogenic bend is a primary arc formed over an articulated paleomargin, or is due to bending of a previously less curved (or rectilinear) chain. Here we report on an extensive paleomagnetic and anisotropy of magnetic susceptibility (AMS) study carried out on 22 sites (298 oriented cores), predominantly sampled in Eocene marine clays from the external Magallanes belt of Tierra del Fuego. Five sites (out of six giving reliable paleomagnetic results) containing magnetite and subordinate iron sulphides yield a positive fold test at the 99% significance level, and document no significant rotation since ～ 50 Ma. Thus, the Patagonian orocline is either a primary bend, or an orocline formed after Cretaceous–earliest Tertiary rotations. Our data imply that the opening of the Drake Passage between South America and Antarctica (probably causing the onset of Antarctica glaciation and global climate cooling), was definitely not related to the formation of the Patagonian orocline, but was likely the sole consequence of the 32 ± 2 Ma Scotia plate spreading. Well-defined magnetic lineations gathered at 18 sites from the Magallanes belt are sub-parallel to (mostly E–W) local fold axes, while they trend randomly at two sites from the Magallanes foreland. Our and previous AMS data consistently show that the Fuegian Andes were characterized by a N–S compression and northward displacing fold–thrust sheets during Eocene–early Miocene times (50–20 Ma), an unexpected kinematics considering coeval South America–Antarctica relative motion. Both paleomagnetic and AMS data suggest no significant influence from the E–W left-lateral Magallanes–Fagnano strike–slip fault system (MFFS), running a few kilometres south of our sampling sites. We thus speculate that strike–slip fault offset in the Fuegian Andes may range in the lower bound values (～ 20 km) among those proposed so far. In any case our data exclude any influence of strike–slip tectonics on the genesis of the great orogenic bend called Patagonian orocline. 相似文献
16.
17.
We have performed 3-D scaled lithospheric experiments to investigate the role of the gravitational force exerted by a subducting slab on the deformation of the subducting plate itself. Experiments have been constructed using a dense silicone putty plate, to simulate a thin viscous lithosphere, floating in the middle of a large box filled with glucose syrup, simulating the upper mantle. We examine three different plate configurations: (i) subduction of a uniform oceanic plate, (ii) subduction of an oceanic-continental plate system and, (iii) subduction of a more complex oceanic-continental system simulating the asymmetric Africa-Eurasia system. Each model has been performed with and without the presence of a circular weak zone inside the subducting plate to test the near-surface weakening effect of a plume activity. Our results show that a subducting plate can deform in its interior only if the force distribution varies laterally along the subduction zone, i.e. by the asymmetrical entrance of continental material along the trench. In particular, extensional deformation of the plate occurs when a portion of the subduction zone is locked by the collisional process. The results of this study can be used to analyze the formation of the Arabian plate. We found that intraplate stresses, similar to those that generated the Africa-Arabia break-up, can be related to the Neogene evolution of the northern convergent margin of the African plate, where a lateral change from collision (Mediterranean and Bitlis) to active subduction (Makran) has been described. Second, intraplate stress and strain localization are favored by the presence of a weakness zone, such as the one generated by the Afar plume, producing a pattern of extensional deformation belts resembling the Red Sea-Gulf of Aden rift system. 相似文献
18.
J. Martinod F. Funiciello C. Faccenna S. Labanieh V. Regard 《Geophysical Journal International》2005,163(3):1137-1150
19.
Gianluca Vignaroli Claudio Faccenna Laurent Jolivet Claudia Piromallo Federico Rossetti 《Tectonophysics》2008,450(1-4):34-50
The controversial relationship between the orogenic segments of the Western Alps and the Northern Apennines is here explored integrating recently published 3D tomographic models of subduction with new and re-interpreted geological observations from the eclogitic domain of the Voltri Massif (Ligurian Alps, Italy), where the two belts joint each other. The Voltri Massif is here described as an extensional domain accommodating the opposing outward migration of the Alpine and Apennine thrust fronts, since about 30–35 Ma. Using tomographic images of the upper mantle and paleotectonic reconstructions, we propose that this extensional setting represents the surface manifestation of an along strike change in polarity of the subducted oceanic slab whose polarity changed laterally in space and in time. Our tectonic model suggests that the westward shift of the Alpine thrust front from the Oligocene onward was the consequence of the toroidal asthenospheric flow induced by the retreat of the Apenninic slab. 相似文献
20.
Claudio Faccenna Michele Soligo Andrea Billi Luigi De Filippis Renato Funiciello Claudio Rossetti Paola Tuccimei 《Global and Planetary Change》2008,63(4):299-308
The depositional and erosional history of the Lapis Tiburtinus endogenic travertine located circa 25 km to the east of Rome, Central Italy, near the Colli Albani quiescent volcano, is interpreted through three-dimensional stratigraphy and uranium-series geochronology. Analyses of large exposures located in active quarries and of cores obtained from 114 industrial wells reveal that the travertine deposit is about 20 km2 wide and 60 m thick on average. The travertine thickness is over 85 m toward its western N–S-elongated side, where thermal springs and large sinkholes occur aligned over a seismically-active N-striking fault. The travertine age was calculated using the U/Th isochron method. Results constrain the onset and conclusion of travertine deposition at about 115 and 30 ka, respectively. The three-dimensional study of the travertine shows that this deposit is characterized by a succession of depositional benches grown in an aggradational fashion. The benches are separated by five main erosional surfaces, which are associated with paleosols, conglomerates, and karstic features. This evidence shows that the travertine evolution was mostly controlled by water table fluctuations. Chronological correlations between travertine evolution and paleoclimate indicators suggest that the travertine deposition was partly modulated by climate conditions. Other influencing factors may have been fault-related deformation and volcanic events. 相似文献