Petrology of Baby Bare and Mama Bare lavas

• Published in: Geophysical research letters Vol. 25; no. 1; pp. 117 - 120
• Main Authors: Karsten, J. L., Becker, N., Mottl, M. J., Wheat, C. G.
• Format: Journal Article
• Language: English
• Published: Washington, DC Blackwell Publishing Ltd 01-01-1998; American Geophysical Union
• Subjects: Crystalline rocks; Earth sciences; Earth, ocean, space; Exact sciences and technology; Experimental petrology; Geochemistry; Marine; Soil and rock geochemistry; Juan de Fuca Ridge; East Pacific Rise; INE, Pacific, Juan de Fuca Ridge, Endeavor Segment; INE, Pacific, Baby Bare; INE, Pacific, Momma Bare; INE, Pacific, Papa Bare; petrology; hydrothermal circulation; fractional crystallization; mid-ocean ridges; volcanic rocks; upper mantle; igneous rocks; submarine volcanism; partial melting; volcanic glass; Pacific Ocean; major-element analyses; oceanic crust; electron probe data
• ISSN: 0094-8276; 1944-8007
• DOI: 10.1029/97GL53564

The Three Bares are small volcanoes that host the only‐known hydrothermal vents active in oceanic crust older than 2 Ma. Major element data for Baby and Mama Bare lavas indicate formation by low extents of partial melting of a depleted mantle source, with limited cooling and crystallization prior to eruption. These lavas are compositionally unlike all lavas produced at the adjacent spreading center, but resemble a subset of lavas from small seamounts nearby. We conclude that the Three Bares represent off‐axis volcanism rather than normal crustal accretion. Such off‐axis volcanism increases basement roughness locally, and thus plays an important role in hydrothermal circulation in sedimented ridge flank settings.