1,721,103 research outputs found
Metamorphic evolution of the Saka Unit (Central Pontides, Northern Turkey): new implications for the Mesozoic convergence-related processes in the Intra-Pontide suture zone
Full text linkIn Northern Turkey, the Intra-Pontide suture (IPS) zone represents an east-west trending belt of deformed and/or metamorphic rocks bounded by the Istanbul-Zonguldak Terrane (IZ) to the north and the Sakarya Composite Terrane (SK) to the south (e.g. Göncüoğlu et al., 1997). Despite its importance for the geodynamics reconstructions of the Black Sea and Eastern Mediterranean areas during the Mesozoic, the IPS zone has been poorly investigated; only recently the role of its metamorphic units during the syn-collisional evolution was explored (Marroni et al., 2014; Frassi et al., 2016; 2017)
In order to provide new insights on the Mesozoic-Tertiary geodynamic reconstruction of the southern margin of the Laurasia, we present new data from the Saka Unit from the eastern portion of the IPS. Using a multidisciplinary approach that includes lithological, structural, metamorphic and petrographic investigations, we constrained the P-T-t path during the Mesozoic subduction and consequent exhumation and accretion to Laurasia. Following the determination of mesostructures, we analysed a series of samples of metabasite and metapelite. Mineral chemistry of phases at equilibrium in the pervasive S2 foliation was determined, and PT determinations were performed through pseudosection calculation of three samples. PT conditions are within the epidote-amphibolite facies, with pressures of 1.2 ± 0.15 GPa and Temperatures 600 ± 50 °C, thus higher than those determined previously, suggesting that S2 could be a composite foliation where a progressive evolution acquired during onset of exhumation was recorded. A comparison with the PT evolutions of the nearby Daday and Domuz-Dag units, shows that they record lower T at D2 at different ages, and that the pre-D2 conditions, when they are preserved, are different in the three units.
References
Frassi C., Göncüoğlu M.C., Marroni M., Pandolfi L., Ruffini L. Ellero A., Ottria G. & Sayit K. 2016. The Intra-Pontide Suture Zone in the Tosya-Kastamonu area, Northern Turkey. J. of Maps. 12, 211-219
Frassi, C, Marroni, M., Pandolfi, L., Göncüoğlu, M. C., Ellero, A., Ottria, G., Sayit, K., McDonald, C.S., Balestrieri, M.L. & Malasoma, A. 2018. Burial and exhumation history of the Daday Unit (Central Pontides, Turkey): implications for the closure of the Intra-Pontide oceanic basin. Geol. Mag., 155, 356-376.
Göncüoğlu, M. C., Marroni, M., Sayit, K., Tekin, U. K., Ottria, G., Pandolfi, L. & Ellero, A., 2012. The Ayli Dag ophiolite sequence (central-northern Turkey): A fragment of middle Jurassic oceanic lithosphere within the Intra-Pontide suture zone. Ofioliti, 37, 77–91.
Marroni, M., Frassi, C., Göncüoğlu, C. M., Di Vincenzo, G., Pandolfi, L., Rebay, G., Ellero, A. & Ottria, G. 2014. Late Jurassic amphibolite-facies metamorphism in the Intra-Pontide Suture Zone (Turkey): an eastward extension of the Vardar Ocean from the Balkans into Anatolia? J. Geol. Soc., 171, 605–608
Polyorogenic deformation history recognized at very shallow structural levels: the case of the Antola Unit (Northern Apennine, Italy)
No full textThe Antola Unit is a Ligurian Unit occurring at the top of the nappe pile of the Northern Apennines (Italy). The performed structural analysis indicates that the Antola Unit has been involved in a complex polyphase deformation history characterized however by the lacking of any metamorphic overprint. The successive deformation phases belong to both the Alpine and Apenninic orogenic cycles. Therefore the Antola Unit can be regarded as a good example of polyorogenic tectonic unit deformed at very shallow structural level.
The older part of the structural evolution can be referred to the “Mesoalpine” tectonic stage and is characterized by two deformation phases (D1 and D2) showing opposite vergences. The D1 and D2 structures were sealed by the middle Eocene-Miocene deposits of the Tertiary Piedmont Basin. The younger part of the deformation history can be instead referred to the Northern Apennine tectonics, and consists of two phases (D3 and D4) both involving the Tertiary Piedmont Basin succession. The structural data indicate that the D1 deformations developed in mostly unlithified rocks, and that these structures can be related to the westward emplacement of the Antola Unit in the Alpine orogenic wedge. The D2 phase is characterized by sub-isoclinal folds and low-angle extensional faults, and is referable to a gravity-driven deformation. Both the D3 and D4 phases, characterized by folds and thrusts, are referable to the compressive regime related to the development of the Northern Apennine.
Polyorogenic tectonics; Antola Unit; Northern Apennine; Soft sediment and gravity driven deformations; Shallow structural level
Internal Liguride Units from Central Liguria, Italy: new constraints to the tectonic setting from white mica and chlorite studies
No full textThe Internal Liguride Units (ILU) of the Northern Apennines are interpreted as remnants of the Western Tethys oceanic lithosphere. In Late Cretaceous-Paleocene time, this lithosphere was underthrusted, underplated and later exhumed in an accretionary wedge related to an east-dipping, low-rate subduction zone. Until recently, only five IL units resulting from disruption of this lithosphere (namely Cravasco/Voltaggio, Figogna, Gottero, Colli/Tavarone and Bracco/Val Graveglia) have been recognized. A recent structural survey of the Valpolcevera-Valle Scrivia area (Central Liguria) revealed the existence of four more tectonic units: Bric Montaldo, Serra, Vallecalda and Ciaè units. Mineral assemblages, "crystallinity", polytypism and b cell parameter of illite, as well as the "crystallinity" of chlorite in metapelites from these units indicate that they have attained diagenetic to middle anchizonal grade and have experienced baric conditions approximating the intermediate-pressure facies series of Miyashiro (1961). Overall, the data on the metamorphic grade, together with the deformation character, indicate that the Valpolcevera-Valle Scrivia units belong to the ILU, but they were underplated at shallower levels than those reached by the westernmost, highest-grade units (Cravasco/Voltaggio and Figogna); their features point to metamorphic conditions similar to those of the easternmost units (Gottero, Colli/Tavarone and Bracco/Val Graveglia). This study shows the reliability of illite "crystallinity" as a tool to estimate thermal conditions over the entire very low-grade metamorphic zone; it appears sensitive enough to reveal even small differences in grade between different tectonic units
Deformation history of the blueschist-facies sequences from the Villa de Cura unit (Northern Venezuela)
Full text linkThe Serrania del Interior terrane is located in Northern Venezuela, that represents the southern margin of the Caribbean plate. This terrane includes the Villa de Cura unit, which mainly consists of multiple sub-units of metamorphosed and deformed Cretaceous volcano-sedimentary sequences. These sequences are commonly interpreted as generated in a supra-subduction zone setting. The structural history of the Villa de Cura blueschists-facies units includes four main deformational phases, from D1 to D4. The first D1 phase is mainly represented by a relict S1 schistosity developed under HP/LT conditions. The relic S1 schistosity is deformed by isoclinal to subisoclinal F2 folds showing similar geometry. The F2 folds are characterized by a continuous S2 crenulation cleavage developed under greenschist-facies metamorphism. The parallelism between the A2 axes and the related L2 mineral lineations suggests an interpretation of the F2 folds as sheath folds developed during non-coaxial deformation. The kinematic indicators suggest a top-to-W sense of shear for the D2 phase. The D3 phase is distinguished by asymmetric, parallel F3 folds with a S vergence. Finally, the D4 phase consists of F4 open, gentle folds with high-angle to sub-vertical axial planes. The collected data suggest a complex deformation history, characterized by coupling of strike-slip tectonics and shortening during the retrograde evolution of the blueschist-facies sequences
Tectono-metamorphic history of the Tacagua ophiolitic unit (Cordillera de la Costa, Northern Venezuela): insights in the evolution of the southern margin of the Caribbean plate
Full text linkThe southern margin of the Caribbean Plate is well exposed in the Cordillera de la Costa of northern Venezuela, where amalgamated terranes consisting of continental and oceanic units occur. In the Cordillera de la Costa, metamorphosed oceanic units crop out along the coast near Caracas. Among them, the Tacagua unit is characterized by metaserpentinites and metabasites showing mid-oceanic ridge basalt geochemical affinity.
These lithologies, representative of a disrupted ophiolite sequence, are associated with metasediments consisting of calcschists alternating with pelitic and psammitic schists, whose protoliths were probably represented by deep-sea hemipelagic and turbiditic deposits. In the Tacagua unit, a polyphase deformation history has been reconstructed, consisting of four folding phases from D1 to D4. Geological setting suggests an involvement of the Tacagua unit in the processes connected with a subduction zone. The following deformations (from D2 to D4) observed in the field might be related to the exhumation history of the Tacagua unit. The late deformation history consists of an alternation of deformation phases characterized by displacement parallel (D2 and D4 phases) and normal (D3 phase) to plate boundary between the Caribbean and South America Plates. All lines of geological evidence suggest that the whole evolution of the Tacagua unit was acquired in a setting dominated by oblique convergence, in which alternation of strike-slip and pure compressional or pure extensional tectonics occurred through time
Calcareous nannofossil biostratigraphy of the Antola Unit succession (Northern Apennines, Italy): new age constraints for the Late Cretaceous Helminthoid Flysch
No full textThe stratigraphic succession of the Helminthoid Flysch Antola Unit of the Northern Apennines has been dated through the analysis of the calcareous nannofossil assemblages. The results of this study indicate that the Antola Unit succession comprises the Late Cenomanian-Early Turonian (UC5-UC7 Nannofossil Zones) Montoggio Shale, the Early Campanian (UC14b, UC15b Zones) Gorreto Sandstone, the upper Early Campanian-Early Maastrichtian (from UC15b/15c to UC17 Zones) Mt. Antola Flysch, the Early Maastrichtian-lower Late Maastrichtian (UC18-UC19 Zones) Bruggi-Selvapiana Formation and the Late Maastrichtian-Late Paleocene (from UC20a to NP5 Zones) Pagliaro Shale. These data suggest a possible correlation with the Cassio Unit succession, another Helminthoid Flysch unit of the Northern Apennines. As a whole, the presented data provide a useful contribution to knowledge of the tectono-sedimentary evolution of Helminthoid Flysch successions and to the reconstruction of the Late Cretaceous-Tertiary palaeogeography and tectonics of the Helminthoid Flysch Basin.
Helminthoid Flysch; calcareous nannofossils; Late Cretaceous; Paleocene; Antola Unit; biostratigraphy; Northern Apennine
Le unità Liguri Interne della zona Valpolcevera – valle Scrivia (Appennino Settentrionale) e il loro grado metamorfico
No full text
Deformation history of the Coast belt ophiolitic unit (Cordillera de la Costa, Northern Venezuela).
No full text- …
