Cenozoic multiphase orogenic deformations in Northern Calabria Arc: hints from geological mapping in the Longobucco Basin

2020 ◽  
Author(s):  
Giulia Innamorati ◽  
Simone Fabbi ◽  
Massimo Santantonio
Keyword(s):  
Late Cretaceous ◽  
Sedimentary Cover ◽  
Shear Zones ◽  
Geological Mapping ◽  
Ductile Deformation ◽  
Original Position ◽  
Tyrrhenian Sea ◽  
Block Rotation ◽  
Discrete Events ◽  
Mass Transport Deposits

<p>The Meso/Cenozoic geodynamic evolution of the Calabria Peloritani Arc (CPA) has been, and is still, hotly debated, this sector of the Apennine chain being an exotic continental ribbon scraped off from its original position (European Plate) during the south-eastward migration of the Apenninic slab.</p><p>The Southern sector of the Arc (Peloritani Mts.) has been analysed using a multidisciplinary approach. An analysis of pre-, syn- and late-orogenic siliciclastic deposits (Militello Fm, Frazzanò Flysh, Capo d’Orlando Fm) is essential for our understanding of how orogenic phases developed through the Late Cretaceous and Palaeogene. Biostratigraphical constraints reveal a multi-step compressive history, with discrete events (Alpine phase – Balearic phase – Apenninic phase)</p><p>The Northern sector of the Arc is conversely less well known, namely with regards to its pre-Serravallian history, due to the lack of continuous exposures of the Meso/Cenozoic sedimentary cover. One remarkable exception is the Longobucco Basin (Sila Greca, CS), where a Meso/Cenozoic succession covers unconformably the igneous and metamorphic Hercynian basement.  A geological mapping project of the Longobucco Basin is proving instrumental in constraining the Cenozoic dynamics of this sector of the Arc. In particular, the Paludi Fm has been analysed. This is a multifaceted lithostratigraphic unit, made of conglomerates/breccias, reddish marls and arenaceous turbidites, whose composition testifies the dismantling of an orogen. This unit is in turn crosscut and deformed by north eastward verging thrusts dated as Burdigalian by Vignaroli and co-authors (2014), therefore it also apparently predates a younger tectonic phase (see the Frazzanò Flysch in Southern CPA for an analogy).</p><p>Despite the regional importance of this Unit, its age is highly debated in the literature, ranging from the Late Cretaceous to the Aquitanian, according to different Authors. In this light, a biostratigraphic study of this unit ( nannoplancton, micro- and macroforaminifer)a, has been performed.</p><p>Field mapping has revealed a wealth of sedimentary structures ascribable to ductile and or/brittle-ductile deformation, typical of mass transport deposits (i.e. slumps, non-tectonic thrusts, pseudo sigma structures, asymmetric rootless folds and ductile shear zones). The occurrence of olistostromes, with evidence of syn-emplacement deformation, has been mapped. These plastically deformed bodies are Late Cretaceous in age (Aptian to Maastrichtian). They document lost parts of the succession, eroded during the uplift phases and cannibalized within a younger part of the succession, which must therefore be post-Cretaceous.</p><p>Being the age obtained from micropaleontological data comprised between the Eocene and the Oligocene, we must preliminarily ascribe the emplacement stage to an alpine phase. The Burdigalian thrusting event predates the opening of the Tyrrhenian sea and the detachment of the CPA from the Corsica-Sardinia block. It cannot therefore be ascribed to an Apenninic s.s. phase. We attribute this thrusting event to an earlier phase (Balearic phase) related to the Corsica-Sardinia block rotation.     </p><p>Vignaroli G., Minelli L., Rossetti F., Balestrieri M.L. & Faccenna C. (2012) - Tectonophysics, 538, 105-119.</p>

scholarly journals Midcrustal shear zones in postorogenic extension: Example from the northern Tyrrhenian Sea

1998 ◽  
Vol 103 (B6) ◽  
pp. 12123-12160 ◽  
Author(s):  
Laurent Jolivet ◽  
Claudio Faccenna ◽  
Bruno Goffé ◽  
Massimo Mattei ◽  
Federico Rossetti ◽  
...  
Keyword(s):  
Shear Zones ◽  
Tyrrhenian Sea

scholarly journals Remote predictive geological mapping as a tool for the reconstruction of the complex geodynamic evolution of Melanesia

2020 ◽  
Author(s):  
Philipp Brandl ◽  
Anna Kraetschell ◽  
Justin Emberley ◽  
Mark Hannington ◽  
Margaret Stewart ◽  
...  
Keyword(s):  
Large Scale ◽  
Solomon Islands ◽  
Sedimentary Cover ◽  
Complete Information ◽  
Geological Mapping ◽  
Geophysical Data ◽  
Geodynamic Evolution ◽  
Predictive Mapping ◽  
Lithostratigraphic Units ◽  
Geological Map

<p>The offshore regions of Eastern Papua New Guinea and the Solomon Islands include several active and remnant arc and backarc systems that formed in response to complex plate tectonic adjustments following subduction initiation in the Eocene. Although there has been extensive exploration for offshore petroleum resources, and more than 54 research cruises have investigated or transited the region since 1993, a comprehensive regional geological map, including the deep marine areas, has not been available at a scale that permits quantitative analysis of the basin history. We present the first map that depicts interpreted assemblage- and formation-level lithostratigraphic units correlated across the marine basins and adjacent land masses. The mapped assemblages and large-scale formations are based on a compilation of land-based geological maps, marine geophysical data (hydroacoustics, magnetics, and gravity) integrated with the results of geological sampling, ocean drilling, seismic surveys, and seabed observations.</p><p>More than 400,000 km<sup>2 </sup>of the map area covered by ship-based multibeam and other geophysical data were inspected to derive the offshore geological units. In areas with limited data, the units were extrapolated from well-documented formations in adjacent regions with more complete information, including on land. This approach follows closely the techniques used for remote predictive mapping in other regions of the Earth where geological information is sparse. Geological boundaries were constrained by ship-based multibeam data reprocessed at 35-m to 50-m resolution and integrated with the Global Multi-Resolution Topography (GMRT) gridded at 100 m. Lithotectonic assemblages were assigned on the basis of plate structure, crustal type and thickness, age, composition, and sedimentary cover and further refined by bathymetric and geophysical data from the literature and cruise reports. The final compilation is generalized and presented here at 1:1 М. Our new approach integrates conventional mapping on land with remote predictive mapping of the ocean floor.</p><p>The newly compiled geological map illustrates the diversity of assemblages in the region and its complex geodynamic evolution. The resolution of our map allows to perform quantitative analyses of area-age relationships and thus crustal growth. Further geoscientific analyses may allow to estimate the regional mineral potential and to delineate permissive areas as future exploration targets.</p>

Revised stratigraphy of the Mesozoic rocks of southern Cyprus

1980 ◽  
Vol 117 (6) ◽  
pp. 547-563 ◽  
Author(s):  
R. E. Swarbrick ◽  
A. H. F. Robertson
Keyword(s):  
Oceanic Crust ◽  
Continental Margin ◽  
Late Cretaceous ◽  
Sedimentary Cover ◽  
Igneous Rocks ◽  
Late Triassic ◽  
Metamorphic Rocks ◽  
Southern Cyprus

SummaryRecent resurgence of interest in the Mesozoic rocks of SW and southern Cyprus necessitates redefinition of the Mesozoic sedimentary and igneous rocks in line with modern stratigraphical convention. Two fundamentally different rocks associations are present, the Troodos Complex, not redefined, a portion of late Cretaceous oceanic crust, and the Mamonia Complex, the tectonically dismembered remnants of a Mesozoic continental margin. Based on earlier work, the Mamonia Complex is divided into two groups, each subdivided into a number of subsidiary formations and members. The Ayios Photios Group is wholly sedimentary, and records the evolution of a late Triassic to Cretaceous inactive continental margin. The Dhiarizos Group represents Triassic alkalic volcanism and sedimentation adjacent to a continental margin. Several other formations not included in the two groups comprise sedimentary mélange and metamorphic rocks. The Troodos Complex possesses an in situ late Cretaceous sedimentary cover which includes two formations of ferromanganiferous pelagic sediments, radiolarites and volcaniclastic sandstones. The overlying Cainozoic calcareous units are not redefined here.

Deformation mechanisms in naturally-deformed blueschist facies metabasalts: constraints from exhumed subduction complexes in Greece and California

2021 ◽  
Author(s):  
Carolyn Tewksbury-Christle ◽  
Alissa Kotowski ◽  
Whitney Behr
Keyword(s):  
Electron Backscatter Diffraction ◽  
Shear Zones ◽  
Ductile Deformation ◽  
Interface Shear ◽  
Dislocation Glide ◽  
Dislocation Activity ◽  
Metasedimentary Rocks ◽  
Temperature Conditions ◽  
Low Viscosity ◽  
Lower Temperature

<p>The strength, or viscosity, of the subduction interface is a key parameter in subduction dynamics, influencing both long-term subduction plate speeds and short-term transient deformation styles. Fossil subduction interfaces exhumed from downdip of the megathrust record ductile deformation accommodated by diverse lithologies, including metasedimentary and metamafic rocks. Existing flow laws for quartz-rich rocks predict relatively low viscosities, in contrast to high viscosities predicted for basalt and eclogite, but the rheological properties of blueschists representative of metamorphosed oceanic crust of the down-going slab are poorly constrained. Two key questions remain: 1) are there significant viscosity contrasts between blueschists and quartz- or mica-rich metasedimentary rocks, and 2) what are the microscale mechanisms for creep in naturally deformed blueschists and how do they vary with pressure and temperature? To address these questions, we characterized deformation in natural samples from the Condrey Mountain Schist (CMS) in northern California, USA, and the Cycladic Blueschist Unit (CBU) on Syros Island, Cyclades, Greece, using outcrop-scale structural observations, optical microscopy, and Electron Backscatter Diffraction. The CMS and CBU record pressure-temperature conditions of 0.8-1.1 GPa, 350-450°C and 1.4-1.8 GPa, 450-550°C, respectively. </p><p>In the field, blueschists form m- to km-scale lenses that are interfolded with quartz schists, ultramafics, and, in the CBU, eclogites and marbles. At the outcrop scale in both localities, quartz-rich schists and blueschists each exhibit strong foliations and lineations and planar contacts at lithological boundaries. At the thin section scale, the prograde foliation and mineral lineation in blueschists are commonly defined by Na-amphiboles elongated in the lineation direction. Crystallographic preferred orientations in Na-amphibole in all samples have c-axes parallel to lineation and a-axes predominantly defining point-maxima perpendicular to the foliation, suggesting some component of dislocation activity for all temperature conditions in our sample suite. Microtextures in lower temperature CMS samples suggest strain accommodation primarily by dislocation glide and kinking in Na-amphibole, with extremely high-aspect-ratio grains and limited evidence for climb-controlled dynamic recrystallization. Some higher temperature CBU samples show large porphyroclasts with apparent ‘core-and-mantle’-type recrystallization textures and subgrain orientation analyses consistent with the (hk0)[001] slip systems. In contrast, epidote grains accommodate less strain than Na-amphibole, via some combination of rigid rotation, brittle boudinage, and minor intracrystalline plasticity.</p><p>Observations of evenly-distributed strain, despite lithological heterogeneity, suggest low viscosity contrasts and comparable bulk strengths of quartz schists and blueschists. Our microstructural observations suggest that Na-amphibole was the weakest phase and accommodated the majority of strain in mafic blueschists. Dislocation activity, and not just rigid-body-rotation or diffusional processes, accommodated some component of strain and possibly transitioned with increasing temperature from glide- to climb-controlled. Although effective viscosities appear to be similar, subduction interface shear zones dominated by blueschists may exhibit a power-law rheology consistent with dislocation activity, in contrast to the common inference of Newtonian creep in metasediments. Complementary experimental work on CMS and CBU rocks will also be presented at this meeting (see Tokle et al. and Hufford et al.).</p>

Ductile deformation and microstructures

2021 ◽  
pp. 58-85
Author(s):  
Jean-Luc Bouchez ◽  
Adolphe Nicolas
Keyword(s):  
Plastic Deformation ◽  
Grain Size ◽  
Elastic Deformation ◽  
Applied Stress ◽  
Deformation Mechanism ◽  
Chemical Elements ◽  
Shear Zones ◽  
Ductile Deformation ◽  
Deformation Mechanisms ◽  
Solid Materials

In contrast to the elastic deformation, which is reversible, usually neglected by field geologists but important for geophysicists working in seismology, ductile deformation is irreversible. This chapter is restricted to solid materials. Materials containing a melt fraction will be examined in Chapter 7. In the geological literature, ‘ductile’ is often used as a synonym for ‘plastic’. The latter is rather used, and will be used to specify deformation mechanisms that dominantly involve the action of dislocations. In contrast to brittle deformation, which by essence is discontinuous and highly localized (see Chapter 3), ductile deformation is generally continuous and affects large volumes of rock. However, ductile deformation may be concentrated into restricted rock volumes (or domains). Such localization is common in shear zones and/or when superplastic deformation mechanism is involved. Plastic deformation mechanisms naturally depend on temperature, magnitude of the applied stress, mineral nature and grain-size of the rocks. In upper parts of the crust, fluids are able to carry chemical elements over large distances and influence the deformation mechanisms. Micrographs of several microstructural types as well as deformation maps for olivine and calcite are given at the end of this chapter.

scholarly journals Engineering Geological and Geotechnical Approaches for the Construction of Powerhouse Cavern of Tehri Pumped Storage Plant (1000 MW) - A Case Study

2019 ◽  
Vol 24 ◽  
pp. 35-44
Author(s):  
Rajeev Prasad ◽  
Nishith Sharma
Keyword(s):  
Underground Structure ◽  
Shear Zones ◽  
Structural Features ◽  
Geological Mapping ◽  
Left Bank ◽  
Rock Composition ◽  
Northern India ◽  
Set Up ◽  
Pumped Storage

Construction of underground Cavern in the Himalayan region is full of challenges and uncertainties. Experience has shown that construction in Himalayan regions requires good understanding of geology, adequate site investigations, proper design and selection of suitable construction methodology and technology. The most commonly encountered geological problems during excavation of underground structure in Hydroelectric Projects are, Fault/Thrust/Shear Zones squeezing and swelling, wedge block failure etc. Tehri Pumped Storage Plant (PSP) is located at the left bank of river Bhagirathi in the state of Uttarakhand in Northern India. This case study indicates about the geological challenges faced and their remedial measures during the construction of Tehri PSP Powerhouse Cavern having dimension of 203m x 24m x 58m.3D-geological mapping with 1:100 scales was carried out in excavated central drift of powerhouse to evaluate the rock composition, behavior of rock mass, structural features and further investigation to finalize the layout and orientation. During the investigation Sheared Phyllite with bands of thinly Phyllite Quartzite rock were encountered in the end portion of central drift of powerhouse which had posed a mammoth challenge in designing the powerhouse cavern. Keeping in view the recommendations of geotechnical experts and the design consultants, decision were made to shift the cavern further by 50 m to avoid Sheared Phyllite bands. The shifting of cavern led to the reorientation of structures like control room, service bay and location of units etc. This paper briefly describes the Engineering Geological and Geotechnical set up of powerhouse with proper investigation approaches and excavation sequences highlighting the importance of orientation and Sheared Phyllite Zone.

Deformation textures in pyrite from the Vangorda Pb-Zn-Ag deposit, Yukon, Canada

1993 ◽  
Vol 57 (386) ◽  
pp. 55-66 ◽  
Author(s):  
D. Brown ◽  
K. R. McClay
Keyword(s):  
Grain Boundary ◽  
Boundary Migration ◽  
Shear Zones ◽  
Grain Boundary Sliding ◽  
Ductile Deformation ◽  
Mining District ◽  
Strain Partitioning ◽  
Triple Junctions ◽  
Brittle Deformation ◽  
Deformation Textures

AbstractThe Vangorda Pb-Zn-Ag orebody is a 7.1 M tonne, polydeformed stratiform massive sulphide deposit in the Anvil mining district, Yukon, Canada. Five sulphide lithofacies have been identified within the desposit with a typical mineralogy of pyrite, sphalerite, galena, and barite. Pyrrhotite-sphaleritemagnetite assembalges are locally developed. Etched polished sections of massive pyrite ores display relict primary depositional pyrite textures such as colloform growth zoning and spheroidal/framboidal features. A wide variety of brittle deformation, ductile deformation, and annealing textures have been identified. Brittle deformation textures include thin zones of intense cataclasis, grain indentation and axial cracking, and grain boundary sliding features. Ductile deformation textures include strong preferred grain shape orientations, dislocation textures, grain boundary migration, dynamic recrystallisation and pressure solution textures. Post deformational annealing has produced grain growth with lobate grain boundaries, 120° triple junctions and idioblastic pyrite porphyroblasts. The distribution of deformation textures within the Vangorda orebody suggests strong strain partitioning along fold limbs and fault/shear zones, it is postulated that focussed fluid flow in these zones had significant effects on the deformation of these pyritic ores.

scholarly journals A revised map of volcanic units in the Oman ophiolite: insights into the architecture of an oceanic proto-arc volcanic sequence

2019 ◽  
Author(s):  
Thomas M. Belgrano ◽  
Larryn W. Diamond ◽  
Yves Vogt ◽  
Andrea R. Biedermann ◽  
Samuel A. Gilgen ◽  
...  
Keyword(s):  
Subduction Zones ◽  
Sedimentary Cover ◽  
Phase 1 ◽  
Volcanic Rocks ◽  
Shear Zones ◽  
Magma Ascent ◽  
Upper Crust ◽  
Vms Deposits ◽  
Geochemical Analyses ◽  
Semail Ophiolite

Abstract. Recent studies have revealed genetic similarities between Tethyan ophiolites and oceanic proto-arc sequences formed above nascent subduction zones. The Semail ophiolite (Oman–U.A.E.) in particular can be viewed as an analogue for this proto-arc crust. Though proto-arc magmatism and the mechanisms of subduction-initiation are of great interest, insight is difficult to gain from drilling and limited surface outcrops in submarine fore-arcs. In contrast, the Semail ophiolite, in which the 3–5 km thick upper-crustal succession is exposed in an oblique cross-section, presents an opportunity to assess the architecture and volumes of different volcanic rocks that form during the protoarc stage. To determine the distribution of the volcanic rocks and to aid exploration for the volcanogenic massive sulphide (VMS) deposits that they host, we have re-mapped the volcanic units of the Semail ophiolite by integrating new field observations, geochemical analyses and geophysical interpretations with pre-existing geological maps. By linking the major element compositions of the volcanic units to rock magnetic properties, we were able to use aeromagnetic data to infer the extension of each outcropping unit below sedimentary cover, resulting in in a new map showing 2100 km2 of upper-crustal bedrock. Whereas earlier maps distinguished two main volcanostratigraphic units, we have distinguished four, recording the progression from early spreading-axis basalts (Geotimes) through to axial to off-axial depleted basalts (Lasail), to post-axial tholeiites (Tholeiitic Alley) and finally boninites (Boninitic Alley). Geotimes (Phase 1) axial dykes and lavas make up ~55 vol% of the Semail upper crust, whereas post-axial (Phase 2) lavas constitute the remaining ~ 45 vol % and ubiquitously cover the underlying axial crust. The Semail boninites occur as discontinuous accumulations up to 2 km thick at the top of the sequence and constitute ~ 15 vol % of the upper crust. The new map provides a basis for targeted exploration of the gold-bearing VMS deposits hosted by these boninites. The thickest boninite accumulations occur in the Fizh block, where magma ascent occurred along crustal-scale faults that are connected to shear zones in the underlying mantle rocks, which in turn are associated with economic chromitite deposits. Locating major boninite feeder zones may thus be an indirect means to explore for chromitites in the underlying mantle.

Chapter 3 Archean (>2.6 Ga) and Paleoproterozoic (2.5–1.8 Ga), pre- and syn-orogenic magmatism, sedimentation and mineralization in the Norrbotten and Överkalix lithotectonic units, Svecokarelian orogen

2020 ◽  
Vol 50 (1) ◽  
pp. 27-81 ◽  
Author(s):  
Stefan Bergman ◽  
Pär Weihed
Keyword(s):  
Variable Temperature ◽  
Tectonic Setting ◽  
Active Continental Margin ◽  
Volcanic Rocks ◽  
Shear Zones ◽  
Ductile Deformation ◽  
Fe Oxide ◽  
Ductile Shear Zones ◽  
Three Stages ◽  
Felsic Volcanic

AbstractTwo lithotectonic units (the Norrbotten and Överkalix units) occur inside the Paleoproterozoic (2.0–1.8 Ga) Svecokarelian orogen in northernmost Sweden. Archean (2.8–2.6 Ga and possibly older) basement, affected by a relict Neoarchean tectonometamorphic event, and early Paleoproterozoic (2.5–2.0 Ga) cover rocks constitute the pre-orogenic components in the orogen that are unique in Sweden. Siliciclastic sedimentary rocks, predominantly felsic volcanic rocks, and both spatially and temporally linked intrusive rock suites, deposited and emplaced at 1.9–1.8 Ga, form the syn-orogenic component. These magmatic suites evolved from magnesian and calc-alkaline to alkali–calcic compositions to ferroan and alkali–calcic varieties in a subduction-related tectonic setting. Apatite–Fe oxide, including the world's two largest underground Fe ore mines (Kiruna and Malmberget), skarn-related Fe oxide, base metal sulphide, and epigenetic Cu–Au and Au deposits occur in the Norrbotten lithotectonic unit. Low- to medium-pressure and variable temperature metamorphic conditions and polyphase Svecokarelian ductile deformation prevailed. The general northwesterly or north-northeasterly structural grain is controlled by ductile shear zones. The Paleotectonic evolution after the Neoarchean involved three stages: (1) intracratonic rifting prior to 2.0 Ga; (2) tectonic juxtaposition of the lithotectonic units during crustal shortening prior to 1.89 Ga; and (3) accretionary tectonic evolution along an active continental margin at 1.9–1.8 Ga.

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