Magmatic and tectonic extension at mid-ocean ridges : 2. Origin of axial morphology
MetadataShow full item record
We investigate the origin of mid-ocean ridge morphology with numerical models that successfully predict axial topographic highs, axial valleys, and the transition between the two. The models are time-dependent, simulating alternating tectonic and magmatic periods where far-field extension is accommodated by faulting and by magmatism, respectively. During tectonic phases, models predict faults to grow on either side of the ridge axis and axial height to decrease. During magmatic phases, models simulate magmatic extension by allowing the axial lithosphere to open freely in response to extension. Results show that fault size and spacing decreases with increasing time fraction spent in the magmatic phase F M . Magmatic phases also simulate the growth of topography in response to local buoyancy forces. The fundamental variable that controls the transition between axial highs and valleys is the “rise-sink ratio,” (F M /F T )(τ T /τ M ), where F M /F T is the ratio of the time spent in the magmatic and tectonic periods and τ T /τ M is the ratio of the characteristic rates for growing topography during magmatic phases (1/τ M ) and for reducing topography during tectonic phases (1/τ T ). Models predict the tallest axial highs when (F M /F T )(τ T /τ M ) ≫ 1, faulted topography without a high or valley when (F M /F T )(τ T /τ M ) ∼ 1, and the deepest median valleys when (F M /F T )(τ M /τ T ) < 1. New scaling laws explain a global negative correlation between axial topography and lithosphere thickness as measured by the depths of axial magma lenses and microearthquakes. Exceptions to this trend reveal the importance of other behaviors such as a predicted inverse relation between axial topography and spreading rate as evident along the Lau Spreading Center. Still other factors related to the frequency and spatial pervasiveness of magmatic intrusions and eruptions, as evident at the Mid-Atlantic and Juan de Fuca ridges, influence the rise-sink-ratio (F M /F T )(τ T /τ M ) and thus axial morphology.
Author Posting. © American Geophysical Union, 2008. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Geochemistry Geophysics Geosystems 9 (2008): Q09O12, doi:10.1029/2008GC001970.
Suggested CitationArticle: Ito, Garrett T., Behn, Mark D., "Magmatic and tectonic extension at mid-ocean ridges : 2. Origin of axial morphology", Geochemistry Geophysics Geosystems 9 (2008): Q09O12, DOI:10.1029/2008GC001970, https://hdl.handle.net/1912/3276
Showing items related by title, author, creator and subject.
Advanced geophysical studies of accretion of oceanic lithosphere in Mid-Ocean Ridges characterized by contrasting tectono-magmatic settings Xu, Min (Massachusetts Institute of Technology and Woods Hole Oceanographic Institution, 2012-02)The structure of the oceanic lithosphere results from magmatic and extensional processes taking place at mid-ocean ridges (MORs). The temporal and spatial scales of the variability of these two processes control the ...
Behn, Mark D.; Ito, Garrett T. (American Geophysical Union, 2008-08-02)We use 2-D numerical models to explore the thermal and mechanical effects of magma intrusion on fault initiation and growth at slow and intermediate spreading ridges. Magma intrusion is simulated by widening a vertical ...
Magmatic focusing to mid-ocean ridges : the role of grain-size variability and non-Newtonian viscosity Turner, Andrew J.; Katz, Richard F.; Behn, Mark D.; Keller, Tobias (John Wiley & Sons, 2017-12-06)Melting beneath mid-ocean ridges occurs over a region that is much broader than the zone of magmatic emplacement that forms the oceanic crust. Magma is focused into this zone by lateral transport. This focusing has typically ...