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Author Abad, Isabel ♦ Nieto, Fernando ♦ Gutiérrez Alonso, Gabriel ♦ Murphy, J. Brendan ♦ Braid, James A. ♦ Rodríguez Navarro, Alejandro B.
Source SpringerLink
Content type Text
Publisher SP Birkhäuser Verlag Basel
File Format PDF
Copyright Year ©2012
Language English
Subject Domain (in DDC) Natural sciences & mathematics ♦ Earth sciences
Subject Keyword Anchizone ♦ Appalachian orogen ♦ Crystal-chemical parameters ♦ Hollow Fault ♦ Kübler Index ♦ Orientation analysis ♦ Geology
Abstract The Lower Silurian—Lower Devonian Arisaig Group (Antigonish Highlands) in the Canadian Appalachians is a sequence of shallow marine strata deposited after the accretion of Avalonia to Baltica during the closure of the Iapetus Ocean. Deformation of the strata is widely attributed to the Devonian Acadian orogeny and produced shallowly plunging regional folds and a cleavage of varying penetrativity. Phyllosilicate minerals from the finest-grained rocks exhibit very low-grade (diagenetic-anchizone) metamorphic conditions. X-ray diffraction study reveals that the sampled rocks contain quartz, K-white mica, chlorite, and feldspars; illite–smectite and chlorite–smectite mixed-layers are common but Na–K mica and kaolinite occur only in some samples. The identification of illite–smectite mixed-layers in diagenetic samples, with Kübler Index >0.50 Δ°2θ and the highly heterogeneous b-cell dimension of the K-white micas are in agreement with the variable chemical composition of dioctahedral micas, which present low illitic substitution and variable phengitic content. The spatial variation in the above crystal-chemical parameters was plotted along a NW–SE composite cross section across the regional folds. No correlation was found between the metamorphic conditions and either the stratigraphic depth or the strain values measured by phyllosilicates orientation analyses, as a function of the penetrativity of the cleavage. However, the metamorphic grade generally increases towards the Hollow Fault, and is highest in samples located within a 1 km corridor from the fault surface. Incipient cleavage is observed in the anchizonal samples located in the vicinity of the Hollow Fault and in some of the diagenetic samples, indicating cleavage development under low temperatures (<200 ºC). These relationships, together with regional syntheses, suggest low-grade metamorphism post-dated regional folding and was coeval with Late Carboniferous dextral movement along the Hollow Fault. Fluid circulation associated with movement along this major fault may be the driving mechanism for the increasing metamorphism towards it.
ISSN 16618726
Age Range 18 to 22 years ♦ above 22 year
Educational Use Research
Education Level UG and PG
Learning Resource Type Article
Publisher Date 2012-08-01
Publisher Place Basel
e-ISSN 16618734
Journal Swiss Journal of Geosciences
Volume Number 105
Issue Number 2
Page Count 15
Starting Page 283
Ending Page 297


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Source: SpringerLink