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Crustal stacking and expulsion tectonics during continental subduction: P‐T deformation constraints from Oman
Author(s) -
Agard Philippe,
Searle Michael P.,
Alsop G. Ian,
Dubacq B.
Publication year - 2010
Publication title -
tectonics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.465
H-Index - 134
eISSN - 1944-9194
pISSN - 0278-7407
DOI - 10.1029/2010tc002669
Subject(s) - geology , subduction , nappe , shear zone , geochemistry , ophiolite , continental margin , tectonics , petrology , eclogite , seismology
The northeastern continental margin of Oman in the Saih Hatat region is characterized by high‐pressure (HP) chloritoid‐ or carpholite‐bearing metasediments and highly deformed mafic eclogites and blueschists in a series of tectonic units bounded by high‐strain ductile shear zones. New data on the upper cover units of this HP nappe stack indicate that all of them underwent similar P conditions to the underlying Hulw structural unit (with a cooler exhumation pressure‐temperature path). Early SSW directed crustal thickening during ophiolite emplacement created recumbent folds and strong schistose fabrics in these Permian‐Mesozoic shelf carbonates and was followed by later NNE dipping normal sense shear zones and normal faults. The Mayh unit shows high strain in a 15–25 km long sheath fold that likely formed at carpholite grade pressures of 8–10 kbar. We show that there are no significant P differences across the Hulw shear zone (upper plate–lower plate discontinuity) or between the overlying Mayh, Yenkit‐Yiti, and Ruwi units. Postpeak metamorphic exhumation of the HP rocks was therefore accomplished by bottom‐to‐SSW (rather than top‐to‐NNE) active footwall extrusion beneath a fixed, static, passive hanging wall. Footwall uplift beneath these passive roof faults resulted in progressive expulsion of the HP rocks from depths of ∼80–90 km (eclogites) and mainly 30–35 km (blueschists and chloritoid‐/carpholite‐bearing units) during the Campanian–Early Maastrichtian. Oman thus provides a detailed record of how continental material (thick platform shelf carbonates) progressively jammed a subduction zone and emphasizes the contrasting behavior between cover units and their underlying basement.