Volcanic arc magmas: implications of a melting-mixing model for element recycling in the crust-upper mantle system

Journal Article · Mon Sep 01 04:00:00 EDT 1980 · J. Geol.; (United States)

DOI:https://doi.org/10.1086/628541· OSTI ID:6034838

Kay, R W

In a model tested by mass balance calculations, residual periodotite (partly depleted in a basalt fraction) in a subducted lithospheric plate thermally equilibrates with the surrounding hotter mantle at depth beneath island arcs, and being less dense, rises as kilometer size diapires. The diapirs are modified by addiion of small proportions of melt or saline suprcritical fluid from the denser oceanic basalt (eclogite) and sediment. The diapire serves as a source for arc basalts. Mass balance calculations show that large proportions of the K, Rb, Pb, Ba and to a lesser extent Sr and light REE in island arc tholeiites are recycled continental crust material. Proportions are less for high-alumina basalts and shoshonites. High La/Sm basalts from volcanic arcs may be quite similar to their oceanic and intraplate counterparts. High La/Sm basalts are distinctly different. The model does not apply to magmas tha have been chemically modified during migration through the crust (e.g., some Andean andesites). Mass and element recycling rates can be calculated from the volcanic arc model, which gives the relative contributions of the melting components, and the magmatic production rates of arcs. Mantle-derived magmatism is forming new continental crust at arcs at a rate exceeding subduction of crustally-derived sediment at arcs. Thus, the crust appears to be growing, but at a rate that is perhaps half of the mean past rate. The K content of newly added continental crust, when corrected for recycling, is very much lower than the mean K content of the crust. Thus the dominant present mechanisms of crustal formation appears to yield a very different composition than past mechanisms which were responsible for formation of the bulk of the crust.

• Research Organization: Cornell Univ., Ithaca
• OSTI ID: 6034838
• Journal Information: J. Geol.; (United States), Journal Name: J. Geol.; (United States) Vol. 88:5; ISSN JGEOA
• Country of Publication: United States
• Language: English

Related Subjects

58 GEOSCIENCES
580202* -- Geophysics-- Volcanology-- (1980-1989)
580400 -- Geochemistry-- (-1989)
ALKALI METALS
ALKALINE EARTH METALS
BARIUM
BASALT
CHEMISTRY
EARTH CRUST
EARTH MANTLE
ELEMENTS
GEOCHEMISTRY
GEOLOGIC MODELS
GEOTHERMAL SYSTEMS
IGNEOUS ROCKS
LANTHANUM
LEAD
MAGMA
MAGMA SYSTEMS
MASS BALANCE
METALS
ORIGIN
PLATE TECTONICS
POTASSIUM
RARE EARTHS
ROCKS
RUBIDIUM
SAMARIUM
STRONTIUM
TECTONICS
VOLCANIC ROCKS
VOLCANISM