KINEMATICS OF JURASSIC RIFTING, MANTLE EXHUMATION, AND PASSIVE-MARGINFORMATION IN THE AUSTROALPINE AND PENNINIC NAPPES (EASTERN SWITZERLAND)

Citation
N. Froitzheim et G. Manatschal, KINEMATICS OF JURASSIC RIFTING, MANTLE EXHUMATION, AND PASSIVE-MARGINFORMATION IN THE AUSTROALPINE AND PENNINIC NAPPES (EASTERN SWITZERLAND), Geological Society of America bulletin, 108(9), 1996, pp. 1120-1133
Citations number
93
Language
INGLESE
art.tipo
Article
Categorie Soggetti
Geosciences, Interdisciplinary
ISSN journal
0016-7606
Volume
108
Issue
9
Year of publication
1996
Pages
1120 - 1133
Database
ISI
SICI code
0016-7606(1996)108:9<1120:KOJRME>2.0.ZU;2-4
Abstract
The Austroalpine and Upper Penninic nappes in eastern Switzerland repr esent a passive continental margin and the adjacent ocean of Jurassic- Cretaceous age, imbricated by Late Cretaceous-Tertiary orogenic shorte ning, Well-preserved, rift-related faults allow reconstruction of the passive margin and ocean-continent transition zone and yield new infor mation on the kinematics of rifting, Rifting evolved from pure-shear s tretching to detachment-controlled, asymmetric stretching and resulted in complete exhumation of subcontinental mantle rocks at the sea floo r. After precursory normal faulting in the Late Triassic, Jurassic rif ting occurred in two phases, During the first rifting phase (Hettangia n-Sinemurian), predominantly east-dipping normal faults developed in t he upper crust; their dips decreased in the middle to lower crust. whe re they probably graded into anastomosing shear zones in the lower cru st and mantle lithosphere. The resulting overall geometry approximated pure-shear stretching, During the second rifting phase (Toarcian-Midd le Jurassic), a system of west-dipping detachment faults formed, penet rating the whole lithosphere and accommodating asymmetric extension, D uring progressive stretching, subcontinental mantle rocks were tectoni cally exhumed and exposed at the sea floor in two areas, represented b y the Platta and Malenco nappes (Penninic). The intervening Margna and Sella continental nappes are interpreted as an extensional allochthon belonging to the Apulian margin, Finally, a mid-ocean ridge may have formed west of the Margna-Sella allochthon. The Austroalpine realm thu s represents the lower-plate margin-and the Brianconnais, the upper-pl ate margin-of the Piemont-Liguria ocean, This scenario is in qualitati ve agreement with the subsidence histories of the two margins.