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

Publication Type  Journal Article
Year of Publication  2008
Authors  Tucholke, B. E.; Behn, M. D.; Buck, W. R.; Lin, J.
Journal Title  Geology
Volume  36
Issue  6
Pages  455-458
Journal Date  Jun
ISBN Number  0091-7613
Accession Number  ISI:000256389500006
Key Words  mid-ocean ridge; detachment fault; megamullion; oceanic core complex; oceanic magmatism; numerical modeling; mid-atlantic ridge; sea-floor generation; core complexes; morphology; accretion; modes

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, counterintuitivelly, that they may be associated with elevated magmatism. We present numerical models and geological data to show that these detachments occur when similar to 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.


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URL  <Go to ISI>://000256389500006
DOI  Doi 10.1130/G24639a.1