scholarly journals White mica 40 Ar/39 Ar age spectra and the timing of multiple episodes of high-P metamorphic mineral growth in the Cycladic eclogite-blueschist belt, Syros, Aegean Sea, Greece

2016 ◽  
Vol 34 (5) ◽  
pp. 401-421 ◽  
Author(s):  
G. S. Lister ◽  
M. A. Forster
Keyword(s):  
Aegean Sea ◽  
White Mica ◽  
Mineral Growth ◽  
Metamorphic Mineral ◽  
Multiple Episodes

Evolution of regional metamorphism during back-arc stretching and subsequent crustal shortening in the 1.9 Ga Wopmay Orogen, Canada

1987 ◽  
Vol 321 (1557) ◽  
pp. 199-218 ◽  
Keyword(s):  
Regional Metamorphism ◽  
Thermal Relaxation ◽  
Time Interval ◽  
Magmatic Arc ◽  
Mineral Growth ◽  
Metamorphic Mineral ◽  
Mineral Assemblages ◽  
Continental Magmatic Arc ◽  
Uplift And Erosion ◽  
Structural Levels

The stratigraphic units, structural elements and metamorphic mineral assemblages of a regional metamorphic culmination in the 1.9 Ga Wopmay Orogen are exposed over greater than 30 km of composite structural depth, in a series of oblique sections produced by cross folding. Regional metamorphism developed continuously in three sequential, rapidly changing thermo-tectonic régimes within an evolving continental magmatic arc. At ca . 1900 Ma, stretching of intra-arc crust resulted in the accumulation of clastic sediment and bimodal volcanic rift-fill deposits. The onset (first stage) of regional metamorphism is marked by high- T low P mineral assemblages, condensed metamorphic zonal sequences and extensive areas of high-grade gneisses devoid of associated plutons. These features are interpreted in terms of a high thermal gradient related to stretching and thinning of the continental lithosphere. Five to ten million years after stretching, following deposition of a west-facing sedimentary prism, a suite of 1896—1878 Ma plutons was emplaced into the rift and margin deposits as they underwent subhorizontal shortening and deformation during the Calderian Orogeny. Thrusted and folded syn-orogenic foredeep deposits are also intruded by the syn-tectonic plutons. At high and intermediate structural levels, syn-tectonic metamorphic mineral growth and metamorphic zonal sequences which are spatially related to the plutons, document heat advection into the deforming marginal prism and mark a second stage of regional metamorphism related to the emplacement of the plutonic bodies. Inverted mineral isograds in autochthonous Proterozoic units beneath a basal décollement record downward thermal relaxation of isotherms following east-directed Calderian transport of the deformed, thickened, and still hot marginal prism over a relatively cold basement. Derivation of multi-point P - T trajectories from post-tectonic, poikiloblastic garnets charts metamorphic mineral growth during uplift and erosion of the internal zone, documenting the third (final) stage of regional metamorphism in Wopmay Orogen. The short erosional time interval (less than 11 Ma) between tectonic thickening and the end of uplift constrains the heat required for this last metamorphic stage to be inherited from the two preceding thermo-tectonic régimes: epicontinental stretching and the emplacement of the syn-tectonic plutonic suite.

scholarly journals 40Ar/39Ar thermochronology in the Ios basement terrane resolves the tectonic significance of the South Cyclades Shear Zone

2019 ◽  
Vol 487 (1) ◽  
pp. 291-313 ◽  
Author(s):  
Marnie Forster ◽  
Oleg Koudashev ◽  
Ruoran Nie ◽  
Sonia Yeung ◽  
Gordon Lister
Keyword(s):  
Shear Zone ◽  
High Vacuum ◽  
Aegean Sea ◽  
Potassium Feldspar ◽  
Ultra High Vacuum ◽  
The South ◽  
Directed Movement ◽  
Mineral Growth ◽  
Diffusion Parameters ◽  
Time Histories

AbstractWe conducted 39Ar diffusion experiments using potassium feldspar from the South Cyclades Shear Zone on Ios, in the Cyclades, Aegean Sea, Greece. Irradiated samples were step-heated in an ultra-high-vacuum resistance furnace attached to a mass spectrometer, thus also allowing 40Ar/39Ar geochronology. Conjoint inversion of these datasets allowed estimation of the relevant diffusion parameters, which were then used to forward model the effect of arbitrary temperature–time histories. Simulations used Monte Carlo methods to improve approximations to the observed age spectra. Two periods of rapid cooling could be inferred. The South Cyclades Shear Zone commenced operation during or shortly after the Eocene–Oligocene transition. Episodes of south-directed movement continued into Early Miocene time, however, with the footwall still hot enough to cause biotite ± garnet metamorphic mineral growth at the base of the overlying, already substantially exhumed, eclogite–blueschist unit. Since its footwall continued to cool, the South Cyclades Shear Zone was an extensional shear zone during both episodes of its operation.

The sources of metamorphic heat during collisional orogeny: the Barrovian enigma

2019 ◽  
Vol 56 (12) ◽  
pp. 1309-1317 ◽  
Author(s):  
Paul D. Ryan ◽  
John F. Dewey
Keyword(s):  
Rapid Heating ◽  
Regional Metamorphism ◽  
Thermal Relaxation ◽  
Geothermal Gradient ◽  
Medium Temperature ◽  
Mineral Growth ◽  
Metamorphic Mineral ◽  
Lithospheric Extension ◽  
Western Ireland ◽  
Collisional Orogeny

The problem of the observed very rapid advection of heat into metamorphic thrust stacks is reviewed. Conductive models relying on the thermal relaxation of a thickened crust will not produce the observed Barrovian (medium temperature, medium pressure) assemblages within some short-lived orogens (e.g., western Ireland and Timor). Studies of the rate and timing of metamorphic mineral growth suggest that this is commonly faster than predicted by thermal relaxation. Barrovian assemblages are localised in some orogens (e.g., the Alps) but extensive in others (e.g., the Himalayas). Metamorphic mineral growth brackets deformation; consequently, slow growth is inconsistent with the rapid uplift of many orogens. Thus, no single mechanism can account for the development of Barrovian assemblages during collisional orogeny. The only mechanisms that can supply large amounts of heat for regional metamorphism quickly (<10 Myr) are: rapidly thinning the lithosphere without stretching it (e.g., by plume thermal erosion, slab drop-off, or delamination); by emplacing magma into the crust (modest deep mafic underplate and (or) very large amounts of mafic and silicic magma emplaced into the middle and upper crust); or obducting hot nappes of arc with a thin ophiolite forearc (“hot iron” mechanism). Frictional and viscous heating produces local rapid heating but not fast regional heating. Back-arc or any kind of lithospheric extension increases the geothermal gradient and heat flow but does not heat rocks up. We suggest that magmatic advection of heat-associated lithospheric thinning or “hot iron” overthrusting of an arc/ophiolite are the primary sources of heat in short-lived orogens.

Same Address, Different Doors: Post-Heritage Deconstruction of the Heritage Household in Upstairs Downstairs in the 1970s and 2010s

2020 ◽  
Author(s):  
William Abbiss
Keyword(s):  
Final Section ◽  
Social Structures ◽  
The Third ◽  
The Past ◽  
War Narrative ◽  
Critical History ◽  
The Social ◽  
Fourth Series ◽  
History Of ◽  
Multiple Episodes

This article offers a ‘post-heritage’ reading of both iterations of Upstairs Downstairs: the LondonWeekend Television (LWT) series (1971–5) and its shortlived BBC revival (2010–12). Identifying elements of subversion and subjectivity allows scholarship on the LWT series to be reassessed, recognising occasions where it challenges rather than supports the social structures of the depicted Edwardian past. The BBC series also incorporates the post-heritage element of self-consciousness, acknowledging the parallel between its narrative and the production’s attempts to recreate the success of its 1970s predecessor. The article’s first section assesses the critical history of the LWT series, identifying areas that are open to further study or revised readings. The second section analyses the serialised war narrative of the fourth series of LWT’s Upstairs, Downstairs (1974), revealing its exploration of female identity across multiple episodes and challenging the notion that the series became more male and upstairs dominated as it progressed. The third section considers the BBC series’ revised concept, identifying the shifts in its main characters’ positions in society that allow the series’ narrative to question the past it evokes. This will be briefly contrasted with the heritage stability of Downton Abbey (ITV, 2010–15). The final section considers the household of 165 Eaton Place’s function as a studio space, which the BBC series self-consciously adopts in order to evoke the aesthetics of prior period dramas. The article concludes by suggesting that the barriers to recreating the past established in the BBC series’ narrative also contributed to its failure to match the success of its earlier iteration.

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