Direct measurement of magnetic reversal polarity boundaries in a cross‐section of oceanic crust

Tivey, Maurice A.; Johnson, H. Paul; Fleutelot, Corinne; Hussenoeder, Stefan A.; Lawrence, Róisin M.; Waters, Cheryl; Wooding, B.

doi:10.1029/98gl02752

Cited by 36 publications

(63 citation statements)

References 24 publications

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“…A number of lines of evidence suggest that block rotations of this type (resulting in inward-dipping lavas and outward-dipping dikes) may be common in intermediate-to fast-spread crust. These include paleomagnetic studies of oriented dike samples from Hess Deep [Hurst et al, 1994b] and ODP drill cores [Pariso and Johnson, 1989;Schouten and Denham, 2000], interpretations of axial magnetic anomalies [Schouten et al, 1999], and the inward-dipping trajectories of magnetic polarity boundaries along the Blanco Transform Fault [Tivey et al, 1998]. Hooft et al [1996] predicted a similar subsidence pattern based on the presence of a finite Figure 21.…”

Section: Geochemistry Geophysicsmentioning

confidence: 99%

Structure of uppermost fast‐spread oceanic crust exposed at the Hess Deep Rift: Implications for subaxial processes at the East Pacific Rise

Karson

Klein

Hurst

et al. 2002

Geochem Geophys Geosyst

118

178

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The uppermost 2 km of the oceanic crust created at the fast spreading (135 mm yr À1 , full rate) equatorial East Pacific Rise (EPR) is exposed for tens of kilometers along escarpments bounding the Hess Deep Rift. Mosaics of large-scale digital images from the remotely operated vehicle (ROV) Argo II and direct observations from the submersible Alvin document a degree of geological complexity and variability that is not evident from most studies of ophiolites or prevailing models of seafloor spreading. Dramatic variations in the thickness and internal structure are documented in both the basaltic volcanic and sheeted dike rock units. These rock units are characterized by extensive faulting, fine-scale fracturing, and rotations of coherent crustal blocks meters to tens of meters across. The uppermost basaltic lavas are essentially undeformed and have overall gently inclined flow surfaces. Through most of the basaltic lava unit, however, lava flow contacts dip (208-708W) toward the EPR and generally increase in dip downward in the section. Dikes cutting the lavas and in the underlying sheeted dike unit generally dip (908 -408E) away from the EPR. Deeper level gabbroic rocks show little evidence of the intense fracturing typical of the overlying units. We interpret this upper crustal structure as the result of subaxial subsidence within 1-2 km of the EPR that accommodated the thickening of the basaltic lava unit to $500 m. Variations in the thickness of lava and dike units and spatially related structures along the rift escarpments suggest temporal fluctuations in magma supply. These results indicate that substantial brittle deformation accompanied waxing and waning volcanism during the accretion of the crustal section exposed at the Hess Deep Rift. If this type of structure is typical of uppermost oceanic crust generated at the EPR, these processes may be common along fast spreading mid-ocean ridges.

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Section: Geochemistry Geophysicsmentioning

confidence: 99%

Structure of uppermost fast‐spread oceanic crust exposed at the Hess Deep Rift: Implications for subaxial processes at the East Pacific Rise

Karson

Klein

Hurst

et al. 2002

Geochem Geophys Geosyst

118

178

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“…[3] Tectonic windows into the oceanic crust provide the opportunity to directly investigate structural, magnetic, and compositional aspects of extensive exposures of the upper oceanic crust in situ from which to infer spreading processes [Francheteau et al, 1990;Karson, 1998;Tivey et al, 1998;Karson et al, 2002aKarson et al, , 2002bVarga et al, 2004;Larson et al, 2005;Pollock et al, 2005;Hayman and Karson, 2007]. Investigations of tectonic windows and drill cores confirm a generalized layered sequence of rock types for crust formed at intermediate to fast spreading rates that consists of basaltic lavas overlying a sheeted dike complex underlain by massive gabbro, and reveal similar structural relationships [Karson, 2002].…”

Section: Introductionmentioning

confidence: 99%

Paleomagnetic constraints on deformation of superfast-spread oceanic crust exposed at Pito Deep Rift

Horst¹,

Gee²,

Karson³

2011

J. Geophys. Res.

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[1] The uppermost oceanic crust produced at the superfast spreading (∼142 km Ma −1 , full-spreading rate) southern East Pacific Rise (EPR) during the Gauss Chron is exposed in a tectonic window along the northeastern wall of the Pito Deep Rift. Paleomagnetic analysis of fully oriented dike (62) and gabbro (5) samples from two adjacent study areas yield bootstrapped mean remanence directions of 38.9°± 8.1°, −16.7°± 15.6°, n = 23 (Area A) and 30.4°± 8.0°, −25.1°± 12.9°, n = 44 (Area B), both are significantly distinct from the Geocentric Axial Dipole expected direction at 23°S. Regional tectonics and outcrop-scale structural data combined with bootstrapped remanence directions constrain models that involve a sequence of three rotations that result in dikes restored to subvertical orientations related to (1) inward-tilting of crustal blocks during spreading (Area A = 11°, Area B = 22°), (2) clockwise, vertical-axis rotation of the Easter Microplate (A = 46°, B = 44°), and (3) block tilting at Pito Deep Rift (A = 21°, B = 10°). These data support a structural model for accretion at the southern EPR in which outcrop-scale faulting and block rotation accommodates spreading-related subaxial subsidence that is generally less than that observed in crust generated at a fast spreading rate exposed at Hess Deep Rift. These data also support previous estimates for the clockwise rotation of crust adjacent to the Easter Microplate. Dike sample natural remanent magnetization (NRM) has an arithmetic mean of 5.96 A/m ± 3.76, which suggests that they significantly contribute to observed magnetic anomalies from fast-to superfast-spread crust.

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“…The profiles were then inverted for magnetization using a modified Fourier transform approach for the analysis of dipping tabular bodies, assuming the semi-infinite source [Tivey, 1996;Tivey et al, 1998]. A band-pass wavelength filter from 0.5 km to 20 km was used to filter out short wavelength anomalies that presumably arise from local bathymetric sources and submersible motion and which do not affect the main magnetic signal that we seek.…”

Section: Data Processing and Resultsmentioning

confidence: 99%

“…The relatively steep geometry of these escarpments provides an excellent tectonic window to map the vertical magnetic structure and stratigraphy of oceanic lithosphere [e.g., Karson et al, 1992;Tivey, 1996;Tivey et al, 1998]. To demonstrate the vertical magnetic profile analysis approach, we assume the simplest geometry of a single fault with a monotonic slope and calculate the predicted anomaly that would arise for the north-facing Kane transform wall measurements.…”

Section: Vertical Magnetic Profile Analysismentioning

confidence: 99%

“…The vertical magnetic profiling (VMP) approach [Tivey, 1996;Tivey et al, 1998] is used to analyze the magnetic field data collected along transects up the Kane transform scarp where exposures of oceanic upper lithosphere are found. The relatively steep geometry of these escarpments provides an excellent tectonic window to map the vertical magnetic structure and stratigraphy of oceanic lithosphere [e.g., Karson et al, 1992;Tivey, 1996;Tivey et al, 1998].…”

Section: Vertical Magnetic Profile Analysismentioning

confidence: 99%

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Advanced geophysical studies of accretion of oceanic lithosphere in Mid-Ocean Ridges characterized by contrasting tectono-magmatic settings

Xu¹

2012

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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 degree of heterogeneity of the oceanic lithosphere, represented by two end-member models: the classical Penrose Model exemplified by layered magmatic crust formed along fast-spreading MORs, e.g., East Pacific Rise (EPR); and the recently defined Chapman Model describing heterogeneous mafic and ultramafic lithosphere formed in settings of oceanic detachment faulting common along slow-spreading MORs, e.g., Mid-Atlantic Ridge (MAR). This thesis is using advanced marine geophysical methods (including finite-difference wave propagation modeling, 3D multi-channel seismic reflection imaging, waveform inversion, streamer tomography, and near-bottom magnetics) to study lithospheric accretion processes in MORs characterized by contrasting tectono-magmatic settings: the magmatically dominated EPR axis between 9°30'-10°00'N, and the Kane Oceanic Core Complex (KOCC), a section of MAR lithosphere (23°20'-23°38'N) formed by detachment faulting. At the EPR study area, I found that the axial magma chamber (AMC) melt sill is segmented into four prominent 2-4-km-long sections spaced every ~5-10 km along the ridge axis characterized by high melt content (>95%). In contrast, within the intervening sections, the AMC sill has a lower melt content (41-46%). The total magma volume extracted from the AMC sill was estimated of ~46 × 10 6 m 3 , with ~24 × 10 6 m 3 left unerupted in the upper crust as dikes after 2005-06 eruption. At the KOCC, I used streamer tomography to constrain the shallow seismic velocity structure. Lithological interpretation of the seismic tomographic models provides insights into the temporal and spatial evolution of the melt supply at the spreading axis as the KOCC formed and evolved. Investigation of a magnetic polarity reversal boundary in crosssection at the northern boundary of KOCC suggests that the boundary (representing both a frozen isotherm and an isochron) dips away from the ridge axis along the Kane transform fault scarp, with a west-dipping angle of ~45° in the shallow (<1 km) crust and <20° in the deeper crust. Many thanks to my project advisors and cooperators, Brian Tucholke, RalphStephen, and Maurice Tivey, who have worked with me during the past five and a half years. These research experiences have greatly broadened my horizons on marine geology and geophysics, synthetic seismology, and geomagnetism. Brian introduced me into the geological world of detachment fault system, and his patience and insightful comments on our scientific paper on Kane oceanic core complex are greatly appreciated.I am very thankful for Ralph who introduced me to the world of time-domain finite difference (TDFD) synthetic seismology and Tom Bolmer for setting up the workstation for my TDFD calculations. Ralph's encouragement, enthusiasm, and interactions with me have inspired me to dig out more intere...

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Direct measurement of magnetic reversal polarity boundaries in a cross‐section of oceanic crust

Cited by 36 publications

References 24 publications

Structure of uppermost fast‐spread oceanic crust exposed at the Hess Deep Rift: Implications for subaxial processes at the East Pacific Rise

Structure of uppermost fast‐spread oceanic crust exposed at the Hess Deep Rift: Implications for subaxial processes at the East Pacific Rise

Paleomagnetic constraints on deformation of superfast-spread oceanic crust exposed at Pito Deep Rift

Advanced geophysical studies of accretion of oceanic lithosphere in Mid-Ocean Ridges characterized by contrasting tectono-magmatic settings

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