or collective redistirbution of any portion of this article by photocopy machine, reposting, or other means is permitted only with the approval of The approval portionthe ofwith any articlepermitted only photocopy by is of machine, reposting, this means or collective or other redistirbution This article has This been published in MOUNTAINS IN THE SEA Jasper Seamount SPOTLIGHT 2 30°26.40'N, 122°44.40'W Oceanography By Jasper G. Konter, Hubert Staudigel, and Jeffrey Gee , Volume 23, Number 1, a quarterly journal of The 23, Number 1, a quarterly , Volume Jasper Seamount is a submarine volcano D1 Dredge OBS -500 -1500 -2700 -3900 in the Fieberling-Guadalupe seamount -900 -2100 -3300 mbsl trail, located off the coast of Baja California, Mexico. It rises from the 4000-m-deep seafloor to a summit depth of 700 m (Figure 1). Detailed geophys- 30°30'N ical, geochemical, and geological studies D1 O there provide an in-depth geological D9 D2 ceanography understanding of a seamount that D14 D15 D11 00 0 approaches our knowledge of subaerial S -1 ociety. ociety. volcanoes. Active-source seismic experi- D12 D3 D18 © D4 00 ments at Jasper Seamount resulted in 30°25'N 0 The 2010 by D6 -2 00 the first seismic velocity models of an 0 D13 -3 intraplate seamount (Hammer et al., D19 O 1994). Marine gravity and magnetics D5 ceanography surveys, combined with analyses of D8 O ceanography ceanography the physical properties, geochemistry, S ociety. ociety. and geochronology of dredge samples, A enabled scientists to develop a detailed 122°45'W 122°40'W reproduction, systemmatic Republication, article for use and research. this copy in teaching to granted ll rights reserved. is Permission S model of its internal structure (Gee et al., ociety. Figure 1. Gridded multibeam bathymetry map of Jasper Seamount (adapted S 1988, 1991; Pringle et al., 1991). or Th e [email protected] to: correspondence all end from Konter et al., 2009). The seamount shows a slight northeast–southwest The resulting model of Jasper elongated summit and several small cones near the summit. Dredge hauls Seamount displays many similarities covered most of the seamount, and ocean bottom seismometers (OBSs) were to models of the formation of typical located around and across the seamount during the seismic experiment. Gravity and magnetics tows were performed in multiple passes (not shown). Hawaiian volcanoes, in particular, the stage-wise eruption of increasingly alkalic rocks (Figure 2). More than 90% of the volcano is made up of tholeiitic define two distinct stages: the flank throughout the mantle melting history to alkalic transitional basalts, defining alkalic series (FAS; 8.7–7.5 million years that brackets these three different O the flank transitional series (FTS) that ago) followed by the summit alkalic eruptive periods. Konter et al. (2009) ceanography erupted 11.5–10 million years ago. series (SAS; 4.8–4.1 million years ago). observed that the distinct evolutionary This volcanic foundation resembles At Jasper Seamount, the eruption of stages of Jasper also carry characteristic S ociety, P ociety, the shield-building phase of a typical volcanic rocks containing increasing mantle source signatures for Sr, Nd, Pb, Hawaiian oceanic intraplate volcano. fractions of alkalies at a given SiO and Hf isotopes that evolve in a way that O 2 Box 1931, Rockville, MD 20849-1931, Subsequent lavas erupted at Jasper concentration is interpreted to result resembles typical Hawaiian volcanoes Seamount are increasingly alkalic and from a decreasing relative melt fraction (Figure 3). The seamount’s foundation Jasper G. Konter ([email protected]) is Assistant Professor, Department of Geological Sciences, University of Texas at El Paso, El Paso, TX, USA. Hubert Staudigel is Research Geologist and Lecturer, Institute of Geophysics and Planetary Physics, Scripps Institution of Oceanography, University of California at San Diego, La Jolla, CA, USA. Jeffrey Gee is Professor and Department Head, Geosciences Research Division, Scripps Institution of Oceanography, University of California at San Diego, La Jolla, CA, USA. USA . 40 Oceanography Vol.23, No.1 10 (or shield) has isotopic mantle charac- PT teristics that are typical for long-term enriched incompatible element concen- 8 Alkali s trations (e.g., low 143Nd/144Nd), and basalts later stages appear to be more depleted TholeiiteTA 143 144 8 O (e.g., high Nd/ Nd). Altogether, 2 M SAS: 4.8-4.1Ma K 6 S: MGMG these similarities are likely to indicate A Lower degree melts FAS: 8.7-7.5Ma O + that processes generating magmas at 2 HWHW Na S:S 11.5-10 Jasper Seamount and Hawai`i are quite T FTS:FTS 11.5-10Ma similar, even though Jasper is a much 4 smaller volcano (690 km3) compared 3 to a Hawaiian volcano (~ 30,000 km ). Increasing crystallization This size difference is significant because 2 the most widely accepted model for the B origin of oceanic intraplate volcanoes 42 4466 5500 54 58 62 (OIV) is almost exclusively based on SiO2 studies of Hawai`i, which is the largest Figure 2. Major element composition of Jasper Seamount lavas showing that individual stages of the flank transitional series (FTS), OIV globally. Expanding the Hawaiian flank alkalic series (FAS), and summit alkalic series (SAS) are distinct evolutionary model to a much smaller in composition and likely represent smaller degrees of melting with seamount offers a rationale for the use of time. Within each stage, fractional crystallization creates a trend in the this model for this much more common data. Key for fields with rock types: B = basalt. HW = hawaiite. MG = mugearite. TA = trachy-andesite. PT = phonolitic tephrite. Adapted class of OIVs (see Wessel et al., 2010). It from Konter et al., 2009 suggests that the melting processes that produce the largest OIVs are actually .5134 similar to the processes that form much smaller seamounts. Pacific MORB .5132 REFERENCES Gee, J., L. Tauxe, J.A. Hildebrand, H. Staudigel, and Hawaii P. Lonsdale. 1988. Nonuniform magnetization PE SAS of Jasper Seamount. Journal of Geophysical Research 93:12,159–12,175. .5130 Gee, J., H. Staudigel, and J.H. Natland. 1991. Nd PS 144 Geology and petrology of Jasper Seamount. / FAS Nd FTS Journal of Geophysical Research 96:4,083–4,105. Hammer P.T.C, L.M. Dorman, J.A. Hildebrand, and 143 .5128 B.D. Cornuelle. 1994. Jasper Seamount struc- Austral ture: Seafloor seismic refraction tomography. S Journal of Geophysical Research 99:6,731–6,752. Konter, J.G., H. Staudigel, J. Blichert-Toft, .5126 B.B. Hanan, M. Polvé, G.R. Davies, N. Shimizu, and P. Schiffman. 2009. Geochemical stages Samoa at Jasper Seamount and the origin of intra- plate volcanoes. Geochemistry, Geophysics, Pitcairn Geosystems 10, Q02001, doi:10.1029/ 2008GC002236. 17.0 18.0 19.0 20.0 21.0 22.0 Pringle, M.S., H. Staudigel, and J. Gee. 1991. Jasper 206Pb/ 204Pb Seamount: Seven million years of volcanism. Figure 3. Pb-Nd isotope compositions of the flank transitional series Geology 19:364–368. (FTS), flank alkalic series (FAS), and summit alkalic series (SAS) are Wessel, P., D.T. Sandwell, and S.-S. Kim. distinct and vary significantly compared to the range in oceanic 2010. The global seamount census. basalts. In addition, the evolution in isotopic composition changes Oceanography 23(1):24–33. toward mid-ocean-ridge-basalt (MORB)-like compositions similar to the shield (S), post-shield (PS), and post-erosional (PE) stages in Hawai`i. Adapted from Konter et al., 2009 Oceanography March 2010 41.