Role of melt supply in oceanic detachment faulting and formation of megamullions

Normal faults are ubiquitous on mid-ocean ridges and are expected to develop increasing offset with reduced spreading rate as the proportion of tectonic extension increases. Numerous long-lived detachment faults that form megamullions with large-scale corrugations have been identified on magma-poor...

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Bibliographic Details
Published in:Geology (Boulder) 2008-06, Vol.36 (6), p.455-458
Main Authors: Tucholke, Brian E, Behn, Mark D, Buck, W. Roger, Lin, Jian
Format: Article
Language:English
Subjects:
accretion
Atlantic Ocean
case studies
crust
detachment faults
extension
faults
fracture zones
Geology
Geophysics
Kane fracture zone
lineation
lithosphere
Magma
magmatism
Marine
Mathematical models
megamullions
melts
Mid-Atlantic Ridge
mid-ocean ridges
mullions
North Atlantic
numerical models
ocean floors
oceanic crust
oceanic lithosphere
Oceans
Plate tectonics
sea-floor spreading
solid Earth (tectonophysics)
spreading centers
structural analysis
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Summary:Normal faults are ubiquitous on mid-ocean ridges and are expected to develop increasing offset with reduced spreading rate as the proportion of tectonic extension increases. Numerous long-lived detachment faults that form megamullions with large-scale corrugations have been identified on magma-poor mid-ocean ridges, but recent studies suggest, counterintuitively, that they may be associated with elevated magmatism. We present numerical models and geological data to show that these detachments occur when approximately 30%-50% of total extension is accommodated by magmatic accretion and that there is significant magmatic accretion in the fault footwalls. Under these low-melt conditions, magmatism may focus unevenly along the spreading axis to create an irregular brittle-plastic transition where detachments root, thus explaining the origin of the enigmatic corrugations. Morphological and compositional characteristics of the oceanic lithosphere suggested by this study provide important new constraints to assess the distribution of magmatic versus tectonic extension along mid-ocean ridges.
ISSN:0091-7613
1943-2682
DOI:10.1130/G24639A.1