Structure of the southern Juan de Fuca Ridge from seismic reflection records

Morton, Janet L.; Sleep, Norman H.; Normark, William R.; Tompkins, Donald H.

doi:10.1029/jb092ib11p11315

Cited by 61 publications

(17 citation statements)

References 24 publications

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“…Axial highs have a small range of shallow depths for the magma lens, and rifted axial highs have a deeper magma lens that increases rapidly in depth with decreasing spreading rate. Ridges included are Reykjanes Ridge (RR) [ Sinha et al , 1997], Juan de Fuca Ridge (JdF) [ Morton et al , 1987], Costa Rica Rift (CRR) [ Mutter et al , 1995], Lau Basin (Lau) [ Collier and Sinha , 1990], Northern and Southern East Pacific Rise (NEPR, and SEPR) [ Detrick et al , 1987; Purdy et al , 1992; Carbotte et al , 1998], Galapagos Spreading Center (GSC) [ Detrick et al , 2002], and Southeast Indian Ridge (SEIR) (this paper). The SEIR data are also plotted in turquoise dots, representing the average depth to the magma lens for each segment.…”

Section: Discussionmentioning

confidence: 99%

Variations in upper crustal structure due to variable mantle temperature along the Southeast Indian Ridge

Baran

Cochran

Carbotte

et al. 2005

Geochem Geophys Geosyst

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[1] There is a systematic variation in axial morphology and axial depth along the Southeast Indian Ridge (SEIR) with distance away from the Australian Antarctic Discordance, an area of cold uppermost mantle. Since spreading rate (72-76 mm/yr) and mantle geochemistry appear constant along this portion of the SEIR, the observed variations in axial morphology and axial depth are attributed to a gradient in mantle temperature. In this study, we report results from a multichannel seismic investigation of on-axis crustal structure along this portion of the SEIR. Three distinct forms of ridge crest morphology are found within our study area: axial highs, rifted axial highs, and shallow axial valleys. Axial highs have a shallow ($1500 m below seafloor (bsf)) magma lens and a thin ($300 m) layer 2A along the ridge crest. Rifted axial highs have a deeper ($2100 m bsf) magma lens and thicker ($450 m) layer 2A on-axis. Beneath shallow axial valleys, no magma lens is imaged, and layer 2A is thick ($450 + m). There are step-like transitions in magma lens depth and layer 2A thickness with changes in morphology along the SEIR. The transitions between the different modes of axial morphology and shallow structure are abrupt, suggesting a threshold-type mechanism. Variations in crustal structure along the SEIR appear to be steady state, persisting for at least 1 m.y. Portions of segments in which a magma lens is found are characterized by lower relief abyssal hills on the ridge flank, shallower ridge flank depths, and at the location of along-axis Mantle Bouguer Anomaly (MBA) lows. The long-wavelength variation in ridge morphology along the SEIR from axial high segments to the west to axial valley segments to the east is linked to the regional gradient in mantle temperature. Superimposed on the long-wavelength trend are segment to segment variations that are related to the absolute motion of the SEIR to the northeast which influence mantle melt production and delivery to the ridge.Components: 10,963 words, 9 figures.

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Section: Discussionmentioning

confidence: 99%

Variations in upper crustal structure due to variable mantle temperature along the Southeast Indian Ridge

Baran

Cochran

Carbotte

et al. 2005

Geochem Geophys Geosyst

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“…1). In contrast to inferred large magma chambers of continental intrusions, only small magma chambers have been detected at mid-ocean ridges such as at the fast-spreading East Pacific Rise (Detrick et al, 1987(Detrick et al, , 1993aMutter et al, 1995), at the intermediate-spreading rate Juan de Fuca Ridge (Morton et al, 1987;Rohr et al, 1988) and at the Vala Fa Ridge Sinha, 1990, 1992). Mid-ocean ridge magma chambers are extremely small (ϳ1 km wide and ϳ100 m thick) and lens shaped (Kent et al, 1990), and their depths below the seafloor increase ( Fig.…”

Section: Introductionmentioning

confidence: 89%

Dependence of crustal accretion and ridge-axis topography on spreading rate, mantle temperature, and hydrothermal cooling

Chen¹

2000

Ophiolites and Oceanic Crust: New Insights From Field Studies and the Ocean Drilling Program

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New observations indicate that mantle temperature and hydrothermal cooling, in addition to spreading rate, play important roles in controlling the production of oceanic crust and ridge-axis topography at mid-ocean ridges. A complete crustal-genesis model is presented in this paper with the focus on the effects of anomalous mantle temperatures on crustal accretion and ridge-axis topography at mid-ocean ridges. Anomalous mantle temperatures are associated with either hotspots or regions of relatively cold mantle (''cold spots''). The contribution of this new model is that it integrates all three processes-melt production, melt migration, and melt injection-of oceanic crustal genesis into one simple, self-consistent model, whereas previous models have focused on only one of these processes. Calculations show that there exists a critical mantle temperature at which a small variation in mantle temperature causes a rapid transition from the presence of a crustal melt lens to the absence of such a melt lens beneath the ridge axis, resulting in a significant change in ridge-axis thermal structure and topography. Calculations also show that the sensitivity to the mantle-temperature anomaly is greatest at ridges having intermediate spreading rates, in agreement with observations along several such ridges. Since many ridges spreading at slow and intermediate rates are influenced by either a nearby hotspot or a relatively cold mantle anomaly (e.g., the Australian-Antarctic discordance at lat 49؇S, long 127؇E, so named because of its deviation from the global trend of seafloor topography), interaction between ridges and mantle having an anomalous temperature is important in controlling the crustal accretion and ridge-axis topography at mid-ocean ridges.

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“…In detail, the AMC between 9°17′N and the Clipperton FZ is segmented, with tapered AMC widths at the 9°17′N and 9°53′N devals, and at a small OSC at 9°35′N [Kent et al, 1993b;Smith et al, 2001]. Narrow "pinch outs" at these devals and OSCs may restrict along-axis magma mixing between tectonically segmented melt lenses each measuring ∼30 km along the axis [Morton et al, 1987;Harding et al, 1989]. [38] This concept of thin disconnected melt reservoirs along the EPR is supported by the spatially heterogeneous geochemical data.…”

Section: Short-term Small-scale Magmatic Processes At Fast Spreading Mormentioning

confidence: 99%

Geochemistry of lavas from the 2005–2006 eruption at the East Pacific Rise, 9°46′N–9°56′N: Implications for ridge crest plumbing and decadal changes in magma chamber compositions

Goss

Perfit

Ridley

et al. 2010

Geochem Geophys Geosyst

121

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[1] Detailed mapping, sampling, and geochemical analyses of lava flows erupted from an ∼18 km long section of the northern East Pacific Rise (EPR) from 9°46′N to 9°56′N during 2005-2006 provide unique data pertaining to the short-term thermochemical changes in a mid-ocean ridge magmatic system. mantle source over the spatial extent of the eruption and petrogenetic processes (e.g., fractional crystallization and magma mixing) operating within the crystal mush zone and axial magma chamber (AMC) before and during the 13 year repose period. Geochemical modeling suggests that the 2005-2006 lavas represent differentiated residual liquids from the 1991-1992 eruption that were modified by melts added from deeper within the crust and that the eruption was not initiated by the injection of hotter, more primitive basalt directly into the AMC. Rather, the eruption was driven by AMC pressurization from persistent or episodic addition of more evolved magma from the crystal mush zone into the overlying subridge AMC during the period between the two eruptions. Heat balance calculations of a hydrothermally cooled AMC support this model and show that continual addition of melt from the mush zone was required to maintain a sizable AMC over this time interval.

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Structure of the southern Juan de Fuca Ridge from seismic reflection records

Cited by 61 publications

References 24 publications

Variations in upper crustal structure due to variable mantle temperature along the Southeast Indian Ridge

Variations in upper crustal structure due to variable mantle temperature along the Southeast Indian Ridge

Dependence of crustal accretion and ridge-axis topography on spreading rate, mantle temperature, and hydrothermal cooling

Geochemistry of lavas from the 2005–2006 eruption at the East Pacific Rise, 9°46′N–9°56′N: Implications for ridge crest plumbing and decadal changes in magma chamber compositions

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