Jill L. Karsten - Current Projects

I am presently working on four main projects:

Consequences of Ridge Subduction on Spreading Center Magmatism

This NSF-sponsored project, in collaboration with Sarah Sherman (UH) and Emily Klein (Duke), involves looking at the chemical variations observed in mid-ocean ridge basalts generated along the Southern Chile Ridge and eastern Woodlark Basin spreading centers. At both sites, the spreading center is being actively subducted at the nearby trench. Basalts dredged from the southern Chile Ridge in 1993 (Southern CROSS expedition) reveal unusual geochemical characteristics in many of the lavas - although major element variations are typical of mid-ocean ridge basalts (MORB), trace element variations show greater affinity with arc or continental materials. Thus, these lavas have chemical signatures which look more like arc or back-arc lavas, even though they occur in front of the subduction zone. We are currently conducting additional analyses of volatile and mobile element species in order to further constrain this unusual behavior.

The Role of Porosity and Seismic Velocity in Oceanic Crust

This ONR-funded study, in collaboration with Roy Wilkens and Gerard Fryer (UH), has invested the role of pore aspect ratio on the seismic velocity of oceanic crust and its evolution with crustal aging. Low aspect ratio cracks are found to have a pronounced effect on seismic velocities, in contrast with high aspect ratio (more spherical) voids. Since cracks seal preferentially during hydrothermal alteration of the crust, seismic velocities can increase rapidly, with very little change in total porosity. This study has been a multi-scale, multi-disciplinary study of the porosity structure of oceanic crust and has involved looking at cracks in thin section with SEM, mapping of outcrop scale porosity in the Troodos ophiolite, comparison of observed porosity with porosity inferred from physical property measurements, and synthetic modeling of oceanic crust velocity-porosity structure.

Origin of Enriched Mid-Ocean Ridge Basalts

This NSF-funded study has been investigating the possible origin of E-MORB from the Endeavour Segment, Juan de Fuca Ridge, by examining the spatial distribution of E-MORB relative to N-MORB and by investigating differences in crystallization histories, using Nomarsky Differential Imaging Contrast microscopy to document changes which might indicate fundamental differences in the magmatic history of N-MORB and E-MORB.

Evolution of Magmatic Systems at the Juan de Fuca Ridge

This NSF-funded work involves investigation of a) the thermal evolution of magmatic systems beneath a single ridge segment (Cleft) since passage of a propagating rift, using samples dredged from the Blanco Fracture Zone; b) along-axis variations of the Juan de Fuca ridge and its relationship to segmentation and hot spot interaction; and c) origin of the Heck, Heckle and Springfield seamount chains west of the Endeavour Segment. Papers on all of these projects are forthcoming.

Jill L. Karsten - Publications

Karsten, J.L., E.M. Klein, and S.B. Sherman (1995) Subduction zone geochemical characteristics in mid-ocean ridge basalts from the southern Chile Ridge: Implications of modern ridge subduction systems for the Archean, Lithos, in press.

Klein, E.M. and J.L. Karsten (1995) Ocean ridge basalts with convergent margin geochemical affinities from the Chile Ridge, Nature, 374: 52-57.

Shoberg, T., S. Stein, and J. Karsten (1991) Constraints on rift propagation history at the Cobb Offset, Juan de Fuca Ridge, from numerical modeling of tectonic fabric, Tectonophysics, 197: 295-308.

Wilkens, R.H., G.J. Fryer, and J.L. Karsten (1991) Evolution of porosity and seismic structure of the upper oceanic crust: Importance of aspect ratios, J. Geophys. Res., 96: 17,981-17,995.

Karsten, J.L., J.R. Delaney, J.M. Rhodes, and R.A. Liias (1990) Spatial and temporal evolution of magmatic systems beneath the Endeavour Segment, Juan de Fuca Ridge: Tectonic and Petrologic Constraints, J. Geophys. Res., 95: 19,235-19,256.

Karsten, J.L., and J.R. Delaney (1989) Hot spot-ridge crest convergence in the Northeast Pacific, J. Geophys. Res., 94: 700-712.

Karsten, J.L. (1988) Spatial and Temporal Variations in the Petrology, Morphology, and Tectonics of a Migrating Spreading Center: The Endeavour Segment, Juan de Fuca Ridge, Unpubl. Ph.D. Dissertation, Univ. of Washington, Seattle, WA, 329 pp.

Delaney, J.R., F.N. Spiess, S.C. Solomon, R. Hessler, J.L. Karsten, J.A. Baross, R.T. Holcomb, D. Norton, R.E. McDuff, F. Sayles, J. Whitehead, D. Abbott, and L. Olsen (1987) Scientific rationale for establishing long-term ocean bottom observatory/laboratory systems. In, Teleki, P.G., M.R. Dobson, J.R. Moore, and U.v. Stackelberg (eds.), Marine Minerals: Resource Assessment Strategies, pp. 389-411.

Davis, E.E., and J.L. Karsten (1986) On the cause of the asymmetric distribution of seamounts about the Juan de Fuca Ridge: Ridge crest migration over a heterogeneous asthenosphere, Earth Planet Sci. Letts., 79: 385-396.

Karsten, J.L., S.R. Hammond, E.E. Davis, and R.G. Currie (1986) Detailed geomorphology and neotectonics of the Endeavour Segment, Juan de Fuca Ridge: New results from Seabeam swath mapping, Geol. Soc. Am. Bull., 97: 213-221.

CASM (1985) Hydrothermal vents on an axis seamount of the Juan de Fuca Ridge, Nature, 313: 212-214.

Johnson, H.P., J.L. Karsten, J.R. Delaney, E.E. Davis, R.G. Currie, and R.L. Chase (1983) A detailed study of the Cobb Offset of the Juan de Fuca Ridge: Evolution of a propagating rift, J. Geophys. Res., 88: 2297-2315.

Lichtman, G.S., W.R. Normark, J.R. Delaney, J.L. Morton, H.P. Johnson, and J.L. Karsten (1983) Photogeology and evolution of the Juan de Fuca Ridge, U.S. Geol. Surv. Open File Rep: 83-464, 14 pp.

Johnson, H.P., J.L. Karsten, F.J. Vine, G. Smith, and G. Schonharting (1982) A low-level magnetic survey over a massive sulfide ore body in the Troodos ophiolite complex, Cyprus, J. Mar. Tech. Soc., 16: 76-80.

Karsten, J.L., J.R. Holloway, and J.R. Delaney (1982) Ion microprobe studies of water in silicate melts: Temperature-dependent water diffusion in obsidian, Earth Planet. Sci. Letts., 59: 420-428.

Delaney, J.R., H.P. Johnson, and J.L. Karsten (1981) The Juan de Fuca Ridge - hot spot - propagating rift system: New tectonic, geochemical, and magnetic data, J. Geophys. Res., 86: 11,747-11,750.

Delaney, J.R., and J.L. Karsten (1981) Ion microprobe studies of water in silicate melts: Concentration-dependent water diffusion in obsidian, Earth Planet. Sci. Letts., 52: 191-202.

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