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Siravo, Gaia
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Siravo, Gaia
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57204856209
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- PublicationOpen AccessPaleomagnetic Evidence for Pre‐21 Ma Independent Drift of South Sardinia From North Sardinia‐Corsica: “Greater Iberia” Versus EuropeIt is unanimously acknowledged that the Corsica-Sardinia microplate rotated counterclockwise (CCW) by 40–50° between 21 and 15 Ma, synchronous with Liguro-Provençal Basin oceanic spreading. Conversely, 60–120° CCW rotations with respect to Europe from Sardinia (Permian dykes, volcanics and sediments, Mesozoic carbonates, and lower Eocene limestones) have been interpreted to be related to (a) late Permian intra-Pangea shear events, (b) Aptian Iberia rotation, and (c) Eocene Valais Ocean closure. We report paleomagnetic data from 31 red-bed sites from the mid-late Eocene (45–32 Ma) Cixerri Fm. exposed in SW Sardinia. Characteristic paleomagnetic directions from 25 dual polarity sites (240 samples) define an 86 ± 7° CCW rotation. We suggest that a S Sardinia block located NE of Balearic Islands rotated 30° CCW during the 30–21 Ma Liguro-Provençal rifting, and was decoupled from N Sardinia along the left-lateral Nuoro fault. After 21 Ma, Corsica-Sardinia underwent a drift-related 60° CCW rotation as a whole. A re-analysis of available paleomagnetic results shows that Permian data from N Sardinia-Corsica align with European directions considering a 60° CCW rotation, whereas Permian and mid Jurassic data from S Sardinia match European directions only after considering a ∼35° CCW Iberia rotation besides the 90° post-Eocene event. We suggest that S Sardinia was part of Iberia, and rotated CCW during both Aptian Iberia drift and Oligo-Miocene Liguro-Provençal opening. Our data, along with recent paleomagnetic results from Calabria, suggest that S Sardinia, Balearic Islands, Calabria, Peloritan, Kabylies, and Alboran were fragments of “Greater Iberia,” joined to Iberia before 30 Ma Liguro-Provençal rifting.
137 99 - PublicationRestrictedTranspression and the build-up of the Cordillera: the example of the Bucaramanga fault (Eastern Cordillera, Colombia)(2020)
; ; ; ; ; ; ; Widespread wrench tectonics have been described along the northern Andes. The Bucaramanga fault, described as sinistral strike-slip, bounds the high Santander Massif. We combine structural and thermochronological data from the centralsouthern portion of the fault to investigate the vertical displacement. The structural survey data show old phases of activity preserved in the host rocks along the fault trace, with the superimposition of different generations of slickenlines, and both strike-slip and dip-slip kinematics indicators. New and previous thermochronological data show that differential exhumation of the fault walls has been ongoing for the last 50 Ma. The hanging wall, the Santander Massif, records, in the central portion, decreasing exhumation rates from the early Miocene to the mid- to late Miocene and, in the southern portion, constant rates from the Late Oligocene to the Pliocene. Combining such observations, the thermochronological offset resulting from the relative motion of the two fault walls is comparable with the observed drop in elevation across the fault, suggesting that the present topography of the Santander Massif is related to vertical movement along the Bucaramanga fault. We infer that the fault has a significant Neogene reverse component, consistent with the present day horizontal global positioning system vector data, longterm exhumation rates and the structural assemblage.65 6 - PublicationRestrictedSlab flattening and the rise of the Eastern Cordillera, ColombiaThe topographic growth of a mountain belt is commonly attributed to isostatic balance in response to crustal and lithospheric thickening. However, deeper mantle processes may also influence the topography of the Earth. Here, we discuss the role of these processes in the Eastern Cordillera (EC) of Colombia. The EC is an active, double-vergent fold and thrust belt that formed during the Cenozoic by the inversion of a Mesozoic rift, and topography there has risen up to ∼5,000 m (Cocuy Sierra). The belt is located ∼500 km away from the trench where two separate portions of the Nazca plate subduct below the South American plate. North of 5◦N, the EC rises above a flat-slab subduction region. Volcanic arc migration implies slab shallowing by ∼10 Ma and flattening up to the present-day configuration at ∼6 Ma. The occurrence of a high vP/vSanomaly and clustered seismicity below the belt at ∼160 km depth delineates the slab geometry and has been related to dehydration of the slab, suggesting the presence of a hydrated mantle wedge. We compiled thermochronologic data and inverted for the exhumation history of the chain over the last 20 Ma using the age-elevation relationship and the different closure temperatures of multiple thermochronologic systems. Results indicate that exhumation rates increased during the Plio–Pleistocene at different wavelengths and amplitudes. The small wavelength and large amplitude signals could be related to shallow crustal deformation, whereas the source of the long wavelength and moderate amplitude signal has yet to be identified. Pulses of fast exhumation are found to be concomitant with the uplift that occurred from ∼7 Ma to the present-day. Previous studies suggested that the high topography of the chain cannot be achieved solely through isostatic adjustment. The highest residual topography is centered on the highest elevations of the EC, whereas the lowest residual topography corresponds to the Magdalena Valley, following the regional slab geometry. We propose that the recent uplift and exhumation events were triggered by the transition from regular to flat-slab subduction, along with the hydration of the mantle wedge above the slab. We test the dynamic feasibility of our hypothesis with a series of numerical models for the present-day state. Predicting the correct trends in elevation requires a flat-slab geometry, and a weak and buoyant mantle wedge.
56 3 - PublicationOpen AccessPaleomagnetism of the Peloritan Terrane (NE Sicily): From Greater Iberia to the Neo Apennine‐Maghrebide ArcCalabria and the Peloritan Mts. of NE Sicily are exotic terranes predominantly formed by Hercynian rocks interrupting the Meso-Cenozoic sediments exposed along Apennine-Maghrebide chains. Dual-polarity pre-tilting magnetization direction retrieved from 5 Jurassic, 5 upper Cretaceous-Eocene, and 4 upper Oligocene sedimentary sites from external-intermediate Peloritan nappes yield 99° ± 12°, 131° ± 15°, and 138° ± 12° (respectively) clockwise (CW) rotations with respect to Europe. Upper Cretaceous-Oligocene values are similar to the ∼130° CW late Miocene-Early Pleistocene rotation previously documented on internal Maghrebian nappes of W Sicily. Jurassic data imply a ∼30° Early Cretaceous counterclockwise (CCW) rotation, similar for sign, magnitude, and timing to Iberia rotation, proving that the Peloritan crust was part of Greater Iberia before its <30 Ma fragmentation and dispersal. Furthermore, 20 Jurassic-Oligocene sites yield post-tilting overprint direction (later rotated up to 60° CW) that was acquired synchronous to late Miocene-Pleistocene rotation. The Peloritan rotation is completely different from the 160° post-late Jurassic CCW rotation documented on NE Calabria, and demonstrates that the two terranes underwent independent drift histories. Lack of a Sardinian rotation fingerprint (90° CCW between 30 and 15 Ma) suggests that the Peloritan terrane lied S of the Calabria-Sardinia CCW rotating system, at the non-rotational apex of an Oligocene-early Miocene “Paleo Apennine-Maghrebide Arc.” The Peloritan terrane was stacked onto the African margin and incorporated in the Maghrebian chain in mid Burdigalian (18–17 Ma). Afterward, it formed the S limb of the “Neo Apennine-Maghrebide Arc,” and was passively carried on top of CW rotating Maghrebide nappes during late Miocene-Early Pleistocene (12–1 Ma).
20 1 - PublicationOpen AccessObsidians of Pantelleria (Strait of Sicily): A Petrographic, Geochemical and Magnetic Study of Known and New Geological Sources(2020-12)
; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; This paper provides new petrochemical and paleomagnetic data from obsidian sub-sources on the island of Pantelleria, exploited since the Neolithic. Data has been obtained from 14 obsidian samples from 4 locations: Fossa della Pernice (2 sites), Salto la Vecchia and Balata dei Turchi. Here, we aim to better characterize these obsidians using a cross-disciplinary and multi-analytical approach, to further understand their archaeological significance. Major element analyses (EMP) have enabled two compositional super-groups to be distinguished: (i) Fossa della Pernice, less peralkaline and (ii) Balata dei Turchi–Salto la Vecchia, distinctly more peralkaline and having almost identical chemical patterns. Trace element analyses (LA-ICP-MS) corroborate major element groupings, with the Balata dei Turchi–Salto la Vecchia super-group being further characterized by a pronounced negative europium anomaly. Glass H2O contents (FT-IR) reveal an overlap among all the sub-sources (H2O = 0.1–0.3 wt. %). Magnetic methods have refined the petrochemical groupings, permitting further distinction between Balata dei Turchi–Salto La Vecchia and the Fossa della Pernice super-groups. The occurrence of sub-microscopic (< 1 μm) ferromagnetic minerals results in different magnetic susceptibility and Natural Remanent Magnetization values and allows the best distinction among the products from the chosen sites. When compared with obsidian tools excavated from Bronze-age settlements on the island of Ustica (230 km NE of Pantelleria), 12% are distinctly peralkaline, indicating their provenance to be from the Balata dei Turchi sub-source.898 71 - PublicationOpen AccessFirst Pre‐Miocene Paleomagnetic Data From the Calabrian Block Document a 160° Post‐Late Jurassic CCW Rotation as a Consequence of Left‐Lateral Shear Along Alpine Tethys(2022)
; ; ; ; ; The Calabrian block, along with Alboran, Kabylies, and Peloritani form isolated and enigmatic igneous/metamorphic terranes (AlKaPeCa) stacked over the Meso-Cenozoic sedimentary successions of the Apennines and Maghrebides. They are commonly interpreted as fragments of the Hercynian chain rifted apart from Europe during Jurassic Alpine Tethys spreading, drifted southward during Neogene roll-back of (Neo) Tethyan slab fragments for hundreds of kilometers on top of nappe piles. We report on the paleomagnetism of upper Triassic-lower Miocene sedimentary rocks from the Longobucco succession that is transgressive over the crystalline Sila Massif (NE Calabria). Well-defined magnetization directions carried by hematite were isolated in 10 sites (122 samples) in Jurassic rocks. Nine Toarcian and one Tithonian Ammonitico Rosso sites yielded a dual polarity “A” magnetization component whit a direction over 40° from the geocentric axial dipole (GAD) field direction, that supports a positive fold test. Five sites yielded a “B” normal polarity component NE (<40°) of the GAD direction characterized by a negative fold test. We interpret the B component as a Miocene magnetic overprint later clockwise rotated by ∼20° during the well-known Pleistocene (1–2 Ma) rotation of Calabria. When corrected for such rotation, the A component defines a ∼160° counterclockwise (CCW) rotation of the Calabrian block with respect to Europe. Of these, ∼90° likely occurred along with Corsica-Sardinia block during its Eocene-Miocene rotation from the Provençal margin. Thus, the Calabrian block underwent an additional Cretaceous-Eocene 70° CCW rotation that we relate to Early-mid Cretaceous >500 km left-lateral transcurrent motion between Africa and Europe.391 44 - PublicationOpen AccessPaleomagnetic dating of pre-historic lava flows from the urban district of Catania (Etna volcano, Italy)(2022)
; ; ; ; ; ; ; ; ; ; ; Determining the ages of past eruptions of active volcanoes whose slopes were histori- cally inhabited is vitally important for inves- tigating the relationships between eruptive phenomena and human settlements. During its almost three-millennia-long history, Cata- nia—the biggest city lying at the toe of Etna volcano—was directly impacted only once by the huge lava flow emplaced during the A.D. 1669 Etna flank eruption. However, other lava flows reached the present-day Catania urban district in prehistoric ages before the founding of the city in Greek times (729/728 B.C., i.e., 2679/2678 yr B.P.). In this work, the Holocene lava flows of Barriera del Bosco, Larmisi, and San Giovanni Galermo, which are exposed in the Catania urban district, were paleomagnetically investigated at 12 sites (120 oriented cores). Paleomagnetic dat- ing was obtained by comparing flow-mean paleomagnetic directions to updated geo- magnetic reference models for the Holocene. The Barriera del Bosco flow turns out to rep- resent the oldest eruptive event and is paleo- magnetically dated to the 11,234–10,941 yr B.P. and 8395–8236 yr B.P. age intervals. The mean paleomagnetic directions from the San Giovanni Galermo and Larmisi flows overlap when statistical uncertainties are considered. This datum, along with geologic, geochemi- cal, and petrologic evidence, implies that the two lava flows can be considered as parts of a single lava field that erupted in a nar- row time window between 5494 yr B.P. and 5387 yr B.P. The emplacement of such a huge lava flow field may have buried several Neo- lithic settlements, which would thus explain the scarce occurrence of archaeological sites of that age found below the town of Catania.1279 21 - PublicationRestrictedTectonically driven drainage reorganization in the Eastern Cordillera, ColombiaHigh-elevation plateaus that are positioned in between topographic barriers are common orogenic features in the South American continent, formed under a range of evolving environmental conditions. For example, in the central Andes (Bolivia-Argentina), the Puna-Altiplano is arid and endorheic with a poorly developed fluvial system, while in the northern Andes (Colombia) the Chiquinquirà and Tunja highlands are characterized by a humid equatorial exorheic fluvial system. In addition to a plateau-like low-relief surface at 2500 m, the landscape of the northern Eastern Cordillera and SantanderMassif (northern Colombia) displays a lower elevation (~1500m) low-relief landscape (Mesas) comprising river captures, windgaps, and a disconnected alluvial fan that collectively record a transient state. This configuration has been achieved through a combination of compressive deformation and sub-crustal processes. The compressive shortening started to occur in the Paleogene and is still active, whereas regional surface uplift related to slab flattening andmantlewedge hydration startedintheLateMiocene/Pliocene.To disentangle the crustal vs sub-crustal forcing and to investigate the relative timing of drainage network evolutionwe combine the analysis of topography, hydrography (river longitudinal profiles, morphometric parameters, drainage divide stability), knickpoint migration (celerity model), paleo-longitudinal profile modeling, satellite images, and field observations. In particular, we show that during the development of the low-relief Mesas landscape the older Chiquinquirà highland was a closed drainage and that the lower portion of the Suárez River flowed northward into the Bucaramanga depression forced by the Los Cobardes Anticline topographic barrier. The Suárez River collected waters from the southern SantanderMassif and the upper reach of the Chicamocha River, which was draining the Tunja highland. An abandoned windgap deposit on the eastern edge of the Mesa de Barichara suggests that the lower portion of the Chicamocha Riverwas not yet formed. Subsequent to the Chiquinquirà highland drainage opening, two main tributaries of the Magdalena River, the Lebrija and Sogamoso, captured the Suárez River in a short temporal sequence. A knickpoint celerity model allows us to date the Lebrija capture of the Bucaramanga depression at ~260–270 ka and the subsequent Sogamoso capture at 190–220 ka. Only during this final stage, the lowermost Chicamocha River section formed and the drainage network developed to its present configuration. Finally,we suggest that the early Cenozoic rift inversion has controlled the drainage network pattern and the late Miocene sub-crustal-induced surface uplift has driven the main fluvial network reorganization.
37 11 - PublicationOpen AccessOrogen‐Parallel Transition From a Decoupled Fore‐Arc Sliver to Andean‐Type Mountain Chain: Paleomagnetic and Geologic Evidence From Southern Chile (37–39°S)(2020)
; ; ; ; ; ; ; The Chiloé fore‐arc sliver is an approximately N‐S elongated crust block detached from South America along the dextral intra‐arc Liquiñe‐Ofqui fault zone (LOFZ). The sliver is internally dissected by active NW‐SE sinistral faults whose relations with the LOFZ are speculative, also due to widespread fluvioglacial and volcanic blanket hiding the substratum. We focus on the northern LOFZ end and on the Biobio fault, supposedly the northernmost of the sinistral fault set, reporting on the results from field investigation and paleomagnetism of 48 (mostly Oligo‐Miocene) volcanic sites. We find that the Biobio fault is an old inherited crust discontinuity that did not yield significant block rotation and deformation during the Cenozoic, thus testifying the end of sinistral shear at about 38°S. At the same latitudes, a northward transition from pure strike‐slip to transpressive LOFZ deformation occurs. Intense tectonic deformation and >90° clockwise rotations characterize the main LOFZ strand. Conversely, a supposedly western LOFZ strand displays counterclockwise rotations, similar to the pattern previously documented in the forearc; thus, it does not represent a LOFZ segment. LOFZ and sinistral fault kinematics must be related, and we suggest that crust pushed northward west of the LOFZ escapes laterally toward the trench along the sinistral faults. We also speculate that the northward increasing age of the subducting Nazca plate implies a concomitant decrease of heat transfer on the upper plate, thus an increasing crust rigidity that eventually inhibits strain partitioning and sliver decoupling from 38°S.662 6 - PublicationOpen AccessSignificance of Northern Andes Terrane Extrusion and Genesis of the Interandean Valley: Paleomagnetic Evidence From the “Ecuadorian Orocline”(2021)
; ; ; ; ; ; ; GPS data suggest that the NW South America corner forms a semi-rigid block drifting NE- ward along the regional dextral strike-slip faults that bound an oceanic terrane accreted in Late Cretaceous times to W Ecuador and Colombia. However, the relevance of both strike-slip versus thrust tectonics during Cenozoic times and their relation with oceanic terrane accretion are unclear. Here we report on the paleomagnetism of 31 mid-upper Eocene to upper Miocene mainly volcanic sites from the Cordilleras Occidental and Real of southern Ecuador. Eleven sites show that the western Cordillera Occidental underwent a 24° ± 10° clockwise (CW) rotation with respect to South America after late Miocene times, while no rotation occurred further east. We relate the regional CW rotation to the emplacement of the Cordillera Occidental nappe onto the continental sediments of the Interandean Valley, blanketing the Cordillera's eastern margin. As rotation and continental sedimentation onset ages are similar, we interpret such tectonic depression as a narrow flexural basin formed ahead of the advancing nappe front. The 20°–30° CW Neogene rotation of the Cordillera Occidental is indistinguishable from the post-Cretaceous rotation of the Coastal forearc oceanic blocks, implying that the whole W Ecuador Andean chain was detached and rotated over a mid-crustal detachment during the last 10 Ma. Eocene- Miocene paleomagnetic inclination values are systematically consistent with those expected for South America, thus excluding latitudinal terrane drift. We suggest that the Andes of Ecuador and Peru form the “Ecuadorian Orocline”, formed by opposing orogenic rotations around the Amazonian craton indenter.433 74