Footwall rotation in an oceanic core complex quantified using reoriented Integrated Ocean Drilling Program core samples

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doi: 10.1016/j.epsl.2009.08.007
Author(s): Morris, A.; Gee, J. S.; Pressling, N.; John, B. E.; MacLeod, C. J.; Grimes, C. B.; Searle, R. C.
Author Affiliation(s): Primary:
University of Plymouth, School of Earth, Ocean and Environmental Sciences, Plymouth, United Kingdom
Scripps Institution of Oceanography, United States
University of Wyoming, United States
Cardiff University, United Kingdom
University of Wisconsin-Madison, United States
Durham University, United Kingdom
Volume Title: Earth and Planetary Science Letters
Source: Earth and Planetary Science Letters, 287(1-2), p.217-228. Publisher: Elsevier, Amsterdam, Netherlands. ISSN: 0012-821X CODEN: EPSLA2
Note: In English. 48 refs.; illus., incl. 1 table, sketch map
Summary: Oceanic core complexes expose lower crustal and upper mantle rocks on the seafloor by tectonic unroofing in the footwalls of large-slip detachment faults. The common occurrence of these structures in slow and ultra-slow spread oceanic crust suggests that they accommodate a significant component of plate divergence. However, the subsurface geometry of detachment faults in oceanic core complexes remains unclear. Competing models involve either: (a) displacement on planar, low-angle faults with little tectonic rotation; or (b) progressive shallowing by rotation of initially steeply dipping faults as a result of flexural unloading (the "rolling-hinge" model). We address this debate using palaeomagnetic remanences as markers for tectonic rotation within a unique 1.4 km long footwall section of gabbroic rocks recovered by Integrated Ocean Drilling Program (IODP) sampling at Atlantis Massif oceanic core complex on the Mid-Atlantic Ridge (MAR). These rocks contain a complex record of multipolarity magnetizations that are unrelated to alteration and igneous stratigraphy in the sampled section and are inferred to result from progressive cooling of the footwall section over geomagnetic polarity chrons C1r.2r, C1r.1n (Jaramillo) and C1r.1r. For the first time we have independently reoriented drill-core samples of lower crustal gabbros, that were initially azimuthally unconstrained, to a true geographic reference frame by correlating structures in individual core pieces with those identified from oriented imagery of the borehole wall. This allows reorientation of the palaeomagnetic data, placing far more rigorous constraints on the tectonic history than those possible using only palaeomagnetic inclination data. Analysis of the reoriented high temperature reversed component of magnetization indicates a 46°±6° anticlockwise rotation of the footwall around a MAR-parallel horizontal axis trending 011°±6°. Reoriented lower temperature components of normal and reversed polarity suggest that much of this rotation occurred after the end of the Jaramillo chron (0.99 Ma). The data provide unequivocal confirmation of the key prediction of flexural, rolling-hinge models for oceanic core complexes, whereby oceanic detachment faults initiate at higher dips and rotate to their present day low-angle geometries as displacement increases. Abstract Copyright (2009) Elsevier, B.V.
Year of Publication: 2009
Research Program: IODP Integrated Ocean Drilling Program
Key Words: 16 Structural Geology; 18 Geophysics, Solid-Earth; Atlantic Ocean; Atlantis; Atlantis Massif; Boreholes; Cenozoic; Characteristic remanent magnetization; Cores; Crust; Detachment faults; Electrical logging; Expeditions 304/305; Faults; Flexure; Foot wall; Formation MicroScanner; Gabbros; Geometry; IODP Site U1309; Igneous rocks; Integrated Ocean Drilling Program; Isostasy; Jaramillo Subchron; Low-angle faults; Lower Pleistocene; Lower crust; Magnetic inclination; Magnetization; Mantle; Mid-Atlantic Ridge; Mid-ocean ridges; Models; North Atlantic; Ocean floors; Oceanic core complexes; Paleomagnetism; Plate divergence; Pleistocene; Plutonic rocks; Quaternary; Remanent magnetization; Reversals; Rotation; Stereographic projection; Tectonics; Upper mantle; Well-logging
Coordinates: N301000 N301100 W0420600 W0420700
Record ID: 2010032446
Copyright Information: GeoRef, Copyright 2017 American Geosciences Institute. Reference includes data from CAPCAS, Elsevier Scientific Publishers, Amsterdam, Netherlands