Correlated geophysical, geochemical, and volcanological manifestations of plume‐ridge interaction along the Galápagos Spreading Center

Abstract

[1] As the Galápagos hot spot is approached from the west along the Galápagos Spreading Center there are systematic increases in crustal thickness and in the K/Ti, Nb/Zr, 3 He/ 4 He, H 2 O, and Na 2 O content of lavas recovered from the spreading axis. These increases correlate with progressive transitions from rift valley to axial high morphology along with decreases in average swell depth, residual mantle Bouguer gravity anomaly, magma chamber depth, average lava Mg #, Ca/Al ratio, and the frequency of point-fed versus fissure-fed volcanism. Magma chamber depth and axial morphology display a ''threshold'' effect in which small changes in magma supply result in large changes in these variables. These correlated variations in geophysical, geochemical, and volcanological manifestations of plume-ridge interaction along the western Galápagos Spreading Center reflect the combined effects of changes in mantle temperature and source composition on melt generation processes, and the consequences of these variations on magma supply, axial thermal structure, basalt chemistry, and styles of volcanism.Components: 6355 words, 4 figures, 1 table.

Chemistry of hot springs along the Eastern Lau Spreading Center

“…The thinnest crust along the ELSC is found north of 2030'S where there is no magma-lens reflector. These changes contrast with those in response to increasing magma supply along the near-constant (45-56 mm/yr) intermediate spreading rate Galapagos Spreading Center (GSC) as it approaches the Galapagos hotspot (Detrick et al, 2002). As magma supply increases along the GSC, the magma lens becomes shallower, layer 2a becomes thinner, but overall crustal thickness increases.…”

Tectonic and magmatic segmentation of the Global Ocean Ridge System: a synthesis of observations

“…MCS data have been acquired along the ridge axis from c. 958W to 91820 ′ W and reveal a crustal magma body beneath most of the ridge axis east of 94820 ′ W ( Fig. 7g; Detrick et al 2002;Blacic et al 2004). Although there is a 15 km-long break in the continuity of the AML at the 93815 ′ W OSC, this discontinuity is not a significant boundary in magma lens properties as might be expected if regional upwelling centres fed the adjoining second-order segments.…”

“…The available seismic data from the western GSC show breaks in continuity and changes in the depth of the AML at several of these small offsets (93853 ′ W, 92840 ′ W, 91833 ′ W; Fig. 7g; Detrick et al 2002;Blacic et al 2004), suggestive of separate magmatic systems beneath the adjacent segments. Furthermore, some of these small offsets also mark major regional boundaries in other ridge properties.…”

Composition of the Oceanic Crust

“…Figure 20 Regional averages of seismically determined crustal thickness versus Na 8.0 (the Na 2 O content of basalts normalized to 8 wt% MgO; Klein and Langmuir, 1987). Sources for seismic determinations of crustal thickness are from Klein and Langmuir (1987), augmented and/or superseded by the following: Smallwood and White (1998), Navin et al (1998), Darbyshire et al (2000), Detrick et al (2002), Muller et al (1999), Hooft et al (2000), Fowler and Keen (1979), Canales et al (1998), McClain andLewis (1982), Kodaira et al (1997), Klingelhöfer et al (2000), Jokat et al (2003), Michael et al (2003), Holmes et al (2008 Crustal thickness (km) Figure 21 Relationship between axial depth and seismically determined crustal thickness along mid-ocean ridges. The thickest crust, and by implication the greatest extents of melting, occur at the shallowest axial depths.…”