Geosciences

19063 KiB

Open AccessArticle

Geodynamic Reconstructions of the Australides—2: Mesozoic–Cainozoic

by Christian Vérard and Gérard M. Stampfli

Geosciences 2013, 3(2), 331-353; https://doi.org/10.3390/geosciences3020331 - 4 Jun 2013

Cited by 11 | Viewed by 8125

The present work, derived from a full global geodynamic reconstruction model over 600 Ma and based on a large database, focuses herein on the interaction between the Pacific, Australian and Antarctic plates since 200 Ma, and proposes integrated solutions for a coherent, physically [...] Read more.

The present work, derived from a full global geodynamic reconstruction model over 600 Ma and based on a large database, focuses herein on the interaction between the Pacific, Australian and Antarctic plates since 200 Ma, and proposes integrated solutions for a coherent, physically consistent scenario. The evolution of the Australia–Antarctica–West Pacific plate system is dependent on the Gondwana fit chosen for the reconstruction. Our fit, as defined for the latest Triassic, implies an original scenario for the evolution of the region, in particular for the “early” opening history of the Tasman Sea. The interaction with the Pacific, moreover, is characterised by many magmatic arc migrations and ocean openings, which are stopped by arc–arc collision, arc–spreading axis collision, or arc–oceanic plateau collision, and subduction reversals. Mid-Pacific oceanic plateaus created in the model are much wider than they are on present-day maps, and although they were subducted to a large extent, they were able to stop subduction. We also suggest that adduction processes (i.e., re-emergence of subducted material) may have played an important role, in particular along the plate limit now represented by the Alpine Fault in New Zealand. Full article

(This article belongs to the Special Issue Sedimentary Basins and Orogenic Belts)

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27194 KiB

Open AccessArticle

Geodynamic Reconstructions of the Australides—1: Palaeozoic

by Christian Vérard and Gérard M. Stampfli

Geosciences 2013, 3(2), 311-330; https://doi.org/10.3390/geosciences3020311 - 4 Jun 2013

Cited by 11 | Viewed by 8415

Abstract

A full global geodynamical reconstruction model has been developed at the University of Lausanne over the past 20 years, and is used herein to re-appraise the evolution of the Australides from 600 to 200 Ma. Geological information of geodynamical interest associated with constraints [...] Read more.

A full global geodynamical reconstruction model has been developed at the University of Lausanne over the past 20 years, and is used herein to re-appraise the evolution of the Australides from 600 to 200 Ma. Geological information of geodynamical interest associated with constraints on tectonic plate driving forces allow us to propose a consistent scenario for the evolution of Australia–Antarctica–proto-Pacific system. According to our model, most geodynamic units (GDUs) of the Australides are exotic in origin, and many tectonic events of the Delamerian Cycle, Lachlan SuperCycle, and New England SuperCycle are regarded as occurring off-shore Gondwana. Full article

(This article belongs to the Special Issue Sedimentary Basins and Orogenic Belts)

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7478 KiB

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Mesozoic–Cenozoic Evolution of the Western Margin of South America: Case Study of the Peruvian Andes

by O. Adrian Pfiffner and Laura Gonzalez

Geosciences 2013, 3(2), 262-310; https://doi.org/10.3390/geosciences3020262 - 4 Jun 2013

Cited by 61 | Viewed by 25541

Abstract

Based on the structural style and physiographic criteria, the Central Andes of Peru can be divided into segments running parallel to the Pacific coast. The westernmost segment, the Coastal Belt, consists of a Late Jurassic–Cretaceous volcanic arc sequence that was accreted to the [...] Read more.

Based on the structural style and physiographic criteria, the Central Andes of Peru can be divided into segments running parallel to the Pacific coast. The westernmost segment, the Coastal Belt, consists of a Late Jurassic–Cretaceous volcanic arc sequence that was accreted to the South American craton in Cretaceous times. The Mesozoic strata of the adjacent Western Cordillera represent an ENE-vergent fold-and-thrust belt that formed in Eocene times. Tight upright folds developed above a shallow detachment horizon in the West, while more open folds formed above a deeper detachment horizon towards the East and in the neighboring Central Highlands. A completely different style with steeply dipping reverse faults and open folds affecting the Neoproterozoic crystalline basement is typical for the Eastern Cordillera. The Subandean Zone is characterized by mainly NE-vergent imbricate thrusting which occurred in Neogene times. A quantitative estimate of the shortening of the orogen obtained from balanced cross-sections indicates a total shortening of 120–150 km (24%–27%). This shortening was coevel with the Neogene westward drift of South America, occurred at rates between 3 and 4.7 mm/year and was responsible for the high elevation of the Peruvian Andes. Full article

(This article belongs to the Special Issue Continental Accretion and Evolution)

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2165 KiB

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Preservation and Recycling of Crust during Accretionary and Collisional Phases of Proterozoic Orogens: A Bumpy Road from Nuna to Rodinia

by Kent C. Condie

Geosciences 2013, 3(2), 240-261; https://doi.org/10.3390/geosciences3020240 - 29 May 2013

Cited by 99 | Viewed by 11338

Abstract

Zircon age peaks at 2100–1650 and 1200–1000 Ma correlate with craton collisions in the growth of supercontinents Nuna and Rodinia, respectively, with a time interval between collisions mostly <50 Myr (range 0–250 Myr). Collisional orogens are two types: those with subduction durations <500 [...] Read more.

Zircon age peaks at 2100–1650 and 1200–1000 Ma correlate with craton collisions in the growth of supercontinents Nuna and Rodinia, respectively, with a time interval between collisions mostly <50 Myr (range 0–250 Myr). Collisional orogens are two types: those with subduction durations <500 Myr and those ≥500 Myr. The latter group comprises orogens with long-lived accretionary stages between Nuna and Rodinia assemblies. Neither orogen age nor duration of either subduction or collision correlates with the volume of orogen preserved. Most rocks preserved date to the pre-collisional, subduction (ocean-basin closing) stage and not to the collisional stage. The most widely preserved tectonic setting in Proterozoic orogens is the continental arc (10%–90%, mean 60%), with oceanic tectonic settings (oceanic crust, arcs, islands and plateaus, serpentinites, pelagic sediments) comprising <20% and mostly <10%. Reworked components comprise 20%–80% (mean 32%) and microcratons comprise a minor but poorly known fraction. Nd and Hf isotopic data indicate that Proterozoic orogens contain from 10% to 60% of juvenile crust (mean 36%) and 40%–75% reworked crust (mean 64%). Neither the fraction nor the rate of preservation of juvenile crust is related to the collision age nor to the duration of subduction. Regardless of the duration of subduction, the amount of juvenile crust preserved reaches a maximum of about 60%, and 37% of the volume of juvenile continental crust preserved between 2000 and 1000 Ma was produced in the Great Proterozoic Accretionary Orogen (GPAO). Pronounced minima occur in frequency of zircon ages of rocks preserved in the GPAO; with minima at 1600–1500 Ma in Laurentia; 1700–1600 Ma in Amazonia; and 1750–1700 Ma in Baltica. If these minima are due to subduction erosion and delamination as in the Andes in the last 250 Myr; approximately one third of the volume of the Laurentian part of the GPAO could have been recycled into the mantle between 1500 and 1250 Ma. This may have enriched the mantle wedge in incompatible elements and water leading to the production of felsic magmas responsible for the widespread granite-rhyolite province of this age. A rapid decrease in global Nd and in detrital zircon Hf model ages between about 1600 and 1250 Ma could reflect an increase in recycling rate of juvenile crust into the mantle; possibly in response to partial fragmentation of Nuna. Full article

(This article belongs to the Special Issue Continental Accretion and Evolution)

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8219 KiB

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The Role of Regional and Local Structure in a Late Ordovician (Edenian) Foreland Platform-to-Basin Succession Inboard of the Taconic Orogen, Central Canada

by Ruth Gbadeyan and George R. Dix

Geosciences 2013, 3(2), 216-239; https://doi.org/10.3390/geosciences3020216 - 21 May 2013

Cited by 9 | Viewed by 9936

Abstract

The Upper Ordovician (Edenian) Lindsay Formation of the Ottawa Embayment represents the final stage of carbonate platform development in the Taconic foreland periphery inboard of the northern Appalachian orogen. The succession overlies a narrow (~60 km) axis of a Neoproterozoic Laurentian rift extending [...] Read more.

The Upper Ordovician (Edenian) Lindsay Formation of the Ottawa Embayment represents the final stage of carbonate platform development in the Taconic foreland periphery inboard of the northern Appalachian orogen. The succession overlies a narrow (~60 km) axis of a Neoproterozoic Laurentian rift extending across the Grenville orogen. The Lindsay Formation consists of a lower heavily bioturbated skeletal limestone that represents a warm-water shoal facies following an underlying outer ramp stratigraphy, and an upper division of renewed deep-water deposition with organic-rich shale and fossiliferous lime mudstone. Pyritic deep-water black shale of the westerly advancing Taconic foreland basin disconformably overlies this platform succession. Stratigraphic correlation through the central embayment identifies likely synsedimentary faults and seaward-directed erosion bounding the Lindsay Formation in a region of older Ordovician faults and a change in the lithotectonic character of the crystalline basement. The Late Ordovician shallowing and localization of structural/erosional features are interpreted to record a structural hinge: a local accommodation to, first, foreland periphery uplift, then rapid subsidence related to westerly diachronous foreland subsidence through the platform interior. Spatial association of structures of differing ages suggests that reactivation of inherited weakened crust influenced Late Ordovician sedimentary patterns. Full article

(This article belongs to the Special Issue Sedimentary Basins and Orogenic Belts)

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10609 KiB

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Structural Evolution of the East Sierra Valley System (Owens Valley and Vicinity), California: A Geologic and Geophysical Synthesis

by Calvin H. Stevens, Paul Stone and Richard J. Blakely

Geosciences 2013, 3(2), 176-215; https://doi.org/10.3390/geosciences3020176 - 22 Apr 2013

Cited by 5 | Viewed by 14522

Abstract

The tectonically active East Sierra Valley System (ESVS), which comprises the westernmost part of the Walker Lane-Eastern California Shear Zone, marks the boundary between the highly extended Basin and Range Province and the largely coherent Sierra Nevada-Great Valley microplate (SN-GVm), which is moving [...] Read more.

The tectonically active East Sierra Valley System (ESVS), which comprises the westernmost part of the Walker Lane-Eastern California Shear Zone, marks the boundary between the highly extended Basin and Range Province and the largely coherent Sierra Nevada-Great Valley microplate (SN-GVm), which is moving relatively NW. The recent history of the ESVS is characterized by oblique extension partitioned between NNW-striking normal and strike-slip faults oriented at an angle to the more northwesterly relative motion of the SN-GVm. Spatially variable extension and right-lateral shear have resulted in a longitudinally segmented valley system composed of diverse geomorphic and structural elements, including a discontinuous series of deep basins detected through analysis of isostatic gravity anomalies. Extension in the ESVS probably began in the middle Miocene in response to initial westward movement of the SN-GVm relative to the Colorado Plateau. At ca. 3–3.5 Ma, the SN-GVm became structurally separated from blocks directly to the east, resulting in significant basin-forming deformation in the ESVS. We propose a structural model that links high-angle normal faulting in the ESVS with coeval low-angle detachment faulting in adjacent areas to the east. Full article

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1217 KiB

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Syracuse Limestone: From the Past a Prospect for Contemporary Buildings

by Alessia Giuffrida and Enrico Ciliberto

Geosciences 2013, 3(2), 159-175; https://doi.org/10.3390/geosciences3020159 - 11 Apr 2013

Cited by 8 | Viewed by 9389

Abstract

The conservation of the historic stone heritage has great importance when this material characterizes the image of a city, as it happens in Syracuse (Sicily). Its historical buildings are afflicted by a heavy state of deterioration due to the particular microclimate, to pollution [...] Read more.

The conservation of the historic stone heritage has great importance when this material characterizes the image of a city, as it happens in Syracuse (Sicily). Its historical buildings are afflicted by a heavy state of deterioration due to the particular microclimate, to pollution and to neglect endured over time. This article reports the investigations made on limestone samples from historic façades of the city and from the neighboring quarries still in operation, in order to understand the petrographic typology, the reaction to the degradation over time, the possible maintenance and recovery interventions, and the correct applications in buildings of new construction. For this aim, bulk and surface analysis have been made both on the quarry materials and on the corresponding aged materials. It is therefore possible to define the types of rock most suitable for the use in contemporary architecture guaranteeing criteria of perfect biocompatibility. In this way a natural material can be employed in traditional and innovative uses and ensure both the sustainability of the interventions and the continuity of a consolidated tradition. Full article

(This article belongs to the Special Issue Geoscience of the Built Environment)

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2214 KiB

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Spatial Evolution of the Chromium Contamination in Soils from the Assopos to Thiva Basin and C. Evia (Greece) and Potential Source(s): Anthropogenic versus Natural Processes

by Maria Economou-Eliopoulos, Ifigeneia Megremi, Cathy Atsarou, Christina Theodoratou and Charalambos Vasilatos

Geosciences 2013, 3(2), 140-158; https://doi.org/10.3390/geosciences3020140 - 9 Apr 2013

Cited by 31 | Viewed by 8037

Abstract

The investigation of the contamination in soil, plants and groundwater revealed a spatial evolution, with an increasing trend in the Cr, Fe, Ni, Mn and Co contents in soils from the Assopos to Thiva basin, followed by C. Evia and Ni-laterite deposits, suggesting [...] Read more.

The investigation of the contamination in soil, plants and groundwater revealed a spatial evolution, with an increasing trend in the Cr, Fe, Ni, Mn and Co contents in soils from the Assopos to Thiva basin, followed by C. Evia and Ni-laterite deposits, suggesting that the latter and their parent ophiolites are a potential source for these metals. In contrast, the contamination in groundwater by Cr(VI), ranging from 2 to 360 μg/L Cr, and a varying degree of salinization is probably due to both human activities and natural processes. A diverse source for the contamination of soil and groundwater in the Assopos-Thiva basins is consistent with the increasing trend of the Mg/Si ratio and Cr(VI) concentration in water. The use of deep karst-type aquifer instead of the shallow-Neogene one may provide a solution to the crucial environmental problem. The selective extraction by EDTA and alkaline solution showed that Cr and Fe are less available than Mn. The Cr contents in plants range from <1 to tens of mg/kg, due probably to the high resistance of chromite. However, the average Cr_total contents in plants/crops are higher than normal or sufficient values, whilst Cr_total accumulation [(% metals in plants × 100)/metal in soil] and Cr(VI) accumulation are relatively low. There is a very good positive correlation between accumulation factors for Cr and Fe (R² = 0.92), suggesting a similarity concerning their uptake. Full article

(This article belongs to the Special Issue Geoscience of the Built Environment)

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Geosciences, Volume 3, Issue 2 (June 2013) – 8 articles , Pages 140-353

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