Inherited Palaeozoic and Mesozoic Rb-Sr isotopic signatures in Neogene Calc-alkaline volcanics, Alboran volcanic province, SE Spain

H. P. Zeck, A. B. Kristensen, E. Nakamura

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Abstract

A pyroxene andesite unit within the post-Alpine Alboran volcanic province has a Neogene extrusion age; however, its Rb-Sr isotopic relations define a regression line of 509 ± 62(2σ) Ma (Early Palaeozoic). There are two concordant data point clusters on the regression line, one of which is well constrained, defining a secondary regression line of 202 ± 30(2σ) Ma (Early Mesozoic). Considering the mineralogy of the andesites-plagioclase, Ca-poor and Ca-rich pyroxene, and Ti-magnetite-and the presence of restilic aggregates comprising these same four minerals, recent dehydration melting experiments suggest an origin by anatexis of an amphibolite-dominated source rock complex. Inherited zircon ion-microprobe ages in the range of 500-1800 Ma, an Sm-Nd isochron age of 1.5 ± 0.4(2σ) Ga, T(CHUR)(Nd) crustal derivation ages from ~0.75 to 1.05 Ga and ε(Nd)(0) values of -4 to -7 support a complex petrogenesis, involving large-scale reworking of older material. 87Sr/86Sr vs 1/Sr and 143Nd/144Nd vs 1/Nd indicate a heterogeneous source rock complex showing two-component mixing. The data favour volcano-sedimentary source rock complex parent material which at ~500 Ma underwent a diagenetic or hydrothermal event, which regionally reset Rb-Sr isotope systematics. Subsequently, at ~200 Ma the complex went through local diagenetic or hydrothermal re-equilibration, which created domains with slightly different 87Sr/86Sr ratios, before undergoing Alpine high-grade metamorphism and subsequent anatexis. Roughly coeval, restile-rich cordierite dacites show similar, ~200 Ma, high-age Rb-Sr isotopic relations, which are interpreted as the age of diagenesis of its sedimentary parent material. This is supported by inherited zircon ion-microprobe ages of 300-400 Ma upwards. Also for these rocks 87Sr/86Sr vs 1/Sr shows linear trends, which are explained analogically by sedimentary component mixing in the parent material of the anatectic source rock complex rather than by magmatic stage mixing or contamination. A sinking slab model is suggested for the regional setting of the crustal anatectic regime, melting being supported by fast uplift (of isotherms) and diapiric underplating by high-temperature asthenospheric mantle.

Original languageEnglish
Pages (from-to)511-524
Number of pages14
JournalJournal of Petrology
Volume40
Issue number4
DOIs
Publication statusPublished - Apr 1999

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Keywords

  • Crustal anatexis
  • Inherited isochrons
  • Post-collisional magnatism
  • Restite-melt repartition

ASJC Scopus subject areas

  • Geophysics
  • Geochemistry and Petrology

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