Dacite Petrogenesis on Mid-Ocean Ridges: Evidence for Oceanic Crustal Melting and Assimilation

Wanless, V. D.; Perfit, Michael R.; Ridley, W. I.; Klein, E. M.

doi:10.1093/petrology/egq056

Cited by 119 publications

(137 citation statements)

References 96 publications

Supporting

Mentioning

125

Contrasting

Order By: Relevance

“…While early models used measurements from one or two axial lavas to calculate the ages of older lavas (e.g., Goldstein et al, 1994), at 9117′-9154′N EPR there are now enough young axial lavas of known age that form coherent trends of 238 U-230 Th-226 Ra disequilibria (Sims et al, 2002 such that this technique is ever more robust Waters et al, 2011). Elkins et al, 2011;Lundstrom et al, 1995;Waters et al, 2011 (Table 1), within analytical uncertainties, and are consistent with isotopic compositions previously reported for east limb lavas (Wanless et al, 2010) and basalts from 9117′N-9154′N EPR (Goss et al, 2010;Sims et al, 2002Sims et al, , 2003Waters et al, 2011). This isotopic homogeneity indicates that their time-integrated parent/daughter Rb/Sr and Sm/Nd are uniform, suggesting that these lavas either come from a homogeneous mantle source that is similar to the mantle source for lavas from 9117′-9154′N EPR, or that any melts derived from compositional heterogeneities are diluted and masked by thorough mixing (cf.…”

Section: Dating Lavas With U-th-ra Disequilibriasupporting

confidence: 82%

“…222 Rn accumulates and decays to 210 Pb in a smaller volume of basaltic magma, producing 210 Pb excesses in basaltic froth. Density instability due to accumulation of this buoyant bubble-rich basaltic magma froth beneath dacitic magma may facilitate magma mixing between basalt and dacite magma end members, which has been suggested to explain the wide range of intermediate compositions erupted at the 9103′N OSC (Wanless et al, 2010).…”

Section: Discussionmentioning

confidence: 98%

“…Samples were then hand-picked by microscope for a second time to assure clean glass devoid of visible alteration. Sample splits (~1-3 g) were then dissolved, aliquotted, spiked and then U, Th, and Ra were separated using chemical techniques outlined in Sims et al (2008aSims et al ( , 2008b Wanless et al, 2010). Sr isotopic analyses have internal precision of 5-10 ppm, and after adjusting to 0.71024 (NBS SRM 987), external precision is estimated at 15-30 ppm.…”

Section: U-series Disequilibriamentioning

confidence: 99%

“…We selected 22 of these samples for 238 U-230 Pb isotopic age dating. These samples span a range of tholeiitic volcanic rock compositions, including ferrobasalt, basaltic andesite (or basaltic icelandite), andesite (or icelandite; cf., Carmichael, 1964), and dacite (Wanless et al, 2010(Wanless et al, , 2011; and, tectonic settings including the axial graben, the ridge flank, and the large, axis-parallel pillow ridge and flat-topped seamount that overlie the westernmost extent of the wide melt lens (Fig. 1).…”

Section: Introductionmentioning

confidence: 99%

“…2, and sample descriptions and compositional variations are given in Supplemental Table 1. Sample major and trace element compositions have been published elsewhere (Wanless et al, 2010(Wanless et al, , 2011.…”

Section: Introductionmentioning

confidence: 99%

See 4 more Smart Citations

Sill to surface: Linking young off-axis volcanism with subsurface melt at the overlapping spreading center at 9°03′N East Pacific Rise

Waters

Sims

Klein

et al. 2013

Earth and Planetary Science Letters

View full text Add to dashboard Cite

a b s t r a c tNo young, off-axis, mid-ocean ridge lavas have yet been directly linked to underlying off-axis melt bodies. In this study, we present new measurements of 238 U-230 Th-226 Ra-210 Pb isotope compositions for a suite of lavas from the overlapping spreading center (OSC) at 9103′N on the East Pacific Rise (EPR). These lavas span a large range of compositions, from basalt to dacite, and include both axial and off-axis samples recovered from a prominent, axis-parallel pillow ridge and a flat-topped seamount that overlie the westernmost extent of a 4-km-wide melt lens (Kent et al., 2000). We report 210 Pb excesses in axial basalts and basaltic andesites, which we suggest results from gas-magma fractionation of 222 Rn from 226 Ra beneath dacite magmas. In addition, our U-series ages agree with visual observations, indicating that while most recent volcanic activity occurs at the spreading axis, active volcanism also occurs away from the axis. Specifically, the off-axis pillow ridge and seamount samples overlying the off-axis subsurface melt body have eruption ages of less than 8 ka, and likely as young as 1 ka, despite being located on crust that has a spreading age of~75 ka. The young ages of these lavas, combined with existing geological, geochemical and geophysical constraints, provide evidence for a genetic link between the pillow ridge and seamount lavas and the seismically imaged, underlying off-axis melt lens. This link demonstrates that off-axis volcanism does not necessarily come from a sub-axial magma body and can be sourced directly from off-axis magma bodies.

show abstract

Section: Dating Lavas With U-th-ra Disequilibriasupporting

confidence: 82%

Section: Discussionmentioning

confidence: 98%

Section: U-series Disequilibriamentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 3 more Smart Citations

Sill to surface: Linking young off-axis volcanism with subsurface melt at the overlapping spreading center at 9°03′N East Pacific Rise

Waters

Sims

Klein

et al. 2013

Earth and Planetary Science Letters

View full text Add to dashboard Cite

show abstract

Seafloor photo‐geology and sonar terrain modeling at the 9°N overlapping spreading center, East Pacific Rise

Klein

White

Nunnery

et al. 2013

Geochem Geophys Geosyst

View full text Add to dashboard Cite

[1] A fundamental goal in the study of mid-ocean ridges is to understand the relationship between the distribution of melt at depth and seafloor features. Building on geophysical information on subsurface melt at the 9 N overlapping spreading center on the East Pacific Rise, we use terrain modeling (DSL-120A side scan and bathymetry), photo-geology (Jason II and WHOI TowCam), and geochemical data to explore this relationship. Terrain modeling identified four distinct geomorphic provinces with common seafloor characteristics that correspond well to changes in subsurface melt distribution. Visual observations were used to interpret terrain modeling results and to establish a relative seafloor age scale, calibrated with radiometric age dates, to identify areas of recent volcanism. On the east limb, recent eruptions in the north are localized over the margins of the 4 km wide asymmetric melt sill, forming a prominent off-axis pillow ridge. Along the southern east limb, recent eruptions occur along a neovolcanic ridge that hugs the overlap basin and lies several kilometers west of the plunging melt sill. Our results suggest that long-term southward migration of the east limb occurs through a series of diking events with a net southward propagation direction. Examining sites of recent eruptions in the context of geophysical data on melt distribution in the crust and upper mantle suggests melt may follow complex paths from depth to the surface. Overall, our findings emphasize the value of integrating information obtained from photo-geology, terrain modeling, lava geochemistry and petrography, and geophysics to constrain the nature of melt delivery at mid-ocean ridges.Components: 13,950 words, 12 figures.

show abstract

Effect of latent heat of freezing on crustal generation at low spreading rates

Sleep

Warren

2014

Geochem Geophys Geosyst

View full text Add to dashboard Cite

Lithospheric structure changes at low spreading rates (<40 mm a 21 ), such that steady state molten rock cannot exist above the normal Moho depth of 6 km. Dredge statistics of recovered lithologies indicate that the percentage of basalt is significantly decreased compared to faster ridges and that the mode of crust generation is variable. One important effect on lithospheric structure is the latent heat released when basaltic magma freezes within the mantle, instead of being transported all the way to the surface. Using thermal models, we show that freezing of melt at mantle depths buffers temperature due to the latent heat of crystallization. Two quasi-stable seafloor-spreading patterns are imposed on the model: (1) upwelling of magma along a narrow axial zone and (2) pure shear extension over a broad zone. The variability in crustal structure predicted by these models explains variability observed in dredge lithology statistics at eight slow to ultraslow spreading ridge segments. For example, the Gakkel Eastern Volcanic Zone and Sparsely Magmatic Zone are both spreading at 12 mm a 21 , but the former is composed of 7% peridotite, whereas the latter is 46% peridotite. This difference can be explained by a change from a narrow axis regime with 2 km thick crust to a wide axis regime with a crust-mantle mix. Overall, dredge statistics and thermal models suggest that some, but not all, latent heat of ascending magmas is released at mantle depths and that various ridge axial morphologies can occur.

show abstract

Dacite Petrogenesis on Mid-Ocean Ridges: Evidence for Oceanic Crustal Melting and Assimilation

Cited by 119 publications

References 96 publications

Sill to surface: Linking young off-axis volcanism with subsurface melt at the overlapping spreading center at 9°03′N East Pacific Rise

Sill to surface: Linking young off-axis volcanism with subsurface melt at the overlapping spreading center at 9°03′N East Pacific Rise

Seafloor photo‐geology and sonar terrain modeling at the 9°N overlapping spreading center, East Pacific Rise

Effect of latent heat of freezing on crustal generation at low spreading rates

Contact Info

Product

Resources

About