Temporal and spatial variability in the composition of lavas exposed along the Western Blanco Transform Fault

Pollock, Meagen; Klein, E. M.; Karson, Jeffrey A.; Tivey, Maurice A.

doi:10.1029/2005gc001026

Cited by 10 publications

(17 citation statements)

References 53 publications

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“…JDF, Juan de Fuca Ridge; WBD, West Blanco Depression; EBD, East Blanco Depression; PP, Parks Plateau; IPF, inner pseudofault. lavas have major and trace element compositions comparable with near 'zero-age' lavas sampled at the surface along the southern Cleft Segment of the Juan de Fuca Ridge [Pollock et al, 2005;Stakes et al, 2006]; these similarities suggest that magmatic processes along the Cleft Segment have remained relatively stable over the past ∼1 Ma [Pollock et al, 2005].…”

Section: Geochemistry Of Btf North Wall Lavas and Dikesmentioning

confidence: 70%

“…Ridge‐parallel lineations and abyssal hills can be followed to within ∼5 km of the BTF (Figure 3b), and the sedimentary layer at the top of the BTF north wall is essentially undeformed except by local slumping [ Karson et al , 2002b]. Major and trace element compositions are similar for BTF north wall lavas and near zero‐age lavas sampled at the surface along the southern Cleft segment of the Juan de Fuca Ridge [ Pollock et al , 2005; Smith et al , 1994; Stakes et al , 2006]. This suggests that magmatic processes in the region have not changed significantly in the past ∼1 Ma.…”

Section: Discussionmentioning

confidence: 99%

“…Lavas sampled along the BTF north wall are incompatible element depleted normal mid‐ocean ridge basalts that were derived from a slightly heterogeneous mantle source [ Pollock et al , 2005]. Lavas with relatively primitive compositions are predominantly sampled shallower than more evolved lavas, and thus Pollock et al [2005] argue that the upper lavas along the BTF north wall may have been erupted off‐axis while the lower lavas represent axial flows that have subsided and been progressively buried as the crust was formed. The BTF north wall lavas have major and trace element compositions comparable with near ‘zero‐age’ lavas sampled at the surface along the southern Cleft Segment of the Juan de Fuca Ridge [ Pollock et al , 2005; Stakes et al , 2006]; these similarities suggest that magmatic processes along the Cleft Segment have remained relatively stable over the past ∼1 Ma [ Pollock et al , 2005].…”

Section: Geologic Backgroundmentioning

confidence: 99%

“…[10] Lavas sampled along the BTF north wall are incompatible element depleted normal mid-ocean ridge basalts that were derived from a slightly heterogeneous mantle source [Pollock et al, 2005]. Lavas with relatively primitive compositions are predominantly sampled shallower than more evolved lavas, and thus Pollock et al [2005] argue that the upper lavas along the BTF north wall may have been erupted off-axis while the lower lavas represent axial flows that have subsided and been progressively buried as the crust was formed. The BTF north wall [Juteau et al, 1995;Karson et al, 2002b;Tivey et al, 1998], Hess Deep Rift Scarp [Francheteau et al, 1990[Francheteau et al, , 1992Karson et al, 1992Karson et al, , 2002a, ODP/DSDP Hole 504B [Alt and the Leg 148 Scientific Party, 1993;Anderson et al, 1982;Becker et al, 1982], and IODP/ODP Hole 1256D [Expedition 309 and 312 Scientists, 2006].…”

Section: Geochemistry Of Btf North Wall Lavas and Dikesmentioning

confidence: 99%

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Mapping of seismic layer 2A/2B boundary above the sheeted dike unit at intermediate spreading crust exposed near the Blanco Transform

Christeson

Karson

McIntosh

2010

Geochem Geophys Geosyst

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[1] We present results from a study mapping the seismic layer 2A/2B boundary in young ocean crust located adjacent to the north wall of the Blanco Transform Fault (BTF). We review seafloor features, geochemical and petrologic data, seismic imaging, and seismic structure and conclude that the BTF seismic study region is representative of crust formed at the intermediate spreading Juan de Fuca Ridge. The mean layer 2A two-way travel time beneath the seafloor is 0.37 ± 0.10 s for the 42 × 12 km seismic survey area. Several regions are observed where layer 2A is consistently thin or thick over lateral distances of 5-10 km, both in a ridge-parallel and ridge-perpendicular direction. Layer 2A thicknesses appear more variable in the ridge-parallel (isochron) direction than the ridge-perpendicular (flow line) direction. There is no systematic pattern of layer 2A thickness variability with distance from the BTF, nor is there a correlation between seafloor topography and layer 2A thickness. Calculated mean layer 2A thickness for the seismic study region is 485 ± 135 m assuming an interval velocity of 2.65 km/s. The imaged layer 2A/2B boundary projects on average ∼600-650 m above the top of the sheeted dike complex mapped on the adjacent BTF north wall. We argue that the geologic context of the layer 2A/2B boundary will vary as competing processes of magmatic construction and fracturing (increasing porosity) and crustal thickening, compaction, dike intrusion, and hydrothermal sealing (decreasing porosity) vary as the crust spreads laterally from the ridge axis to ridge flanks.Components: 12,415 words, 15 figures.

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Section: Geochemistry Of Btf North Wall Lavas and Dikesmentioning

confidence: 70%

Section: Discussionmentioning

confidence: 99%

Section: Geologic Backgroundmentioning

confidence: 99%

Section: Geochemistry Of Btf North Wall Lavas and Dikesmentioning

confidence: 99%

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Mapping of seismic layer 2A/2B boundary above the sheeted dike unit at intermediate spreading crust exposed near the Blanco Transform

Christeson

Karson

McIntosh

2010

Geochem Geophys Geosyst

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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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Influence of the oceanic crust structure on marine magnetic anomalies: Review and forward modelling

Zhang

Jiang

et al. 2022

Geological Journal

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Handling Editor: CHANDRAKALA. KOTESWARA Marine magnetic anomaly strips are important for plate tectonic studies, thereby promoting the development of the geoscience revolution. Most previous studies typically consider a lava layer with vertical polarity boundaries as a simplified magnetic source layer. However, it cannot accurately explain the observed magnetic anomaly data; thus, complex oceanic crusts with multiple magnetic source layers, such as lava, dike, and gabbro layers, and various polarity boundary dip angles should be considered. To date, there is a lack of systematic understanding about how the dike and gabbro layers affect the total marine magnetic anomalies, particularly the effect of lava layers with different boundary inclinations on the intensity and polarity boundary of the magnetic anomaly. This study aimed to confirm the significance of these factors. Hence, we systematically simulated and analysed the magnetic anomaly characteristics with different inclination and magnetization settings for each layer using the forward modelling method and determined the impact of the complexity of the magnetic structure of the oceanic crust on the magnetic anomaly. Our results showed that the contributions of the dike and gabbro layers to the magnetic anomalies was up to 10%-30% and cannot be ignored. Moreover, the polarity transition point may shift with the inclination of the lava, dike, and gabbro layers but is insensitive to the magnetization of each layer. This study emphasizes the significance of the dike and gabbro layers and the inclination variations of different layers, which should be thoroughly studied. This study facilitates a reasonable interpretation of the magnetic structure of the oceanic crust and further refines the boundary of the magnetization zone with alternative polarity.

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Temporal and spatial variability in the composition of lavas exposed along the Western Blanco Transform Fault

Cited by 10 publications

References 53 publications

Mapping of seismic layer 2A/2B boundary above the sheeted dike unit at intermediate spreading crust exposed near the Blanco Transform

Mapping of seismic layer 2A/2B boundary above the sheeted dike unit at intermediate spreading crust exposed near the Blanco Transform

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

Influence of the oceanic crust structure on marine magnetic anomalies: Review and forward modelling

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