Basalt-rhyolite volcanism by MORB-continental crust interaction: Nd, Sr-isotopic and geochemical evidence from southern San Joaquin Basin, California

Mukul Sharma, Asish R. Basu, Ronald B. Cole, Peter G Decelles

Research output: Contribution to journalArticle

19 Citations (Scopus)

Abstract

The early miocene Tecuya volcanic center in the southern San Joaquin basin of California consists of flows and tuffs of basalt and rhyolite that erupted, closely spaced in time, in both submarine and subaerial conditions. The rhyolites are overlain by the basalts and constitute approximately 45% of a total of at least 180 km3 of the Tecuya volcanic rocks. The basalts have εNd(t) values of +2 to +6 and (87Sr/86Sr)i values between 0.7035 and 0.7052. These rocks show LREE enrichment [(La/Yb)N =2.4-5.5; La=28-150 times chondrite] and higher Th/U, Th/Ta, Rb/Ta, Ba/Ta, Cs/Rb but lower K/Rb ratios than MORB. Combined major- and trace-element, and Sr-Nd isotopic data suggest the involvement of subcontinental lithosphere, depleted upper mantle source (MORB), and local continental crust in the basalt petrogenesis. εNd(t) values in rhyolites vary from +1.5 to +3.7 while (87Sr/86Sr)i ratios range from 0.7051 to 0.7064. The rhyolites display LREE enrichment [(La/Yb)N=10; La=100 times chondrite] along with a distinct negative Eu anomaly (Eu/Eu*=0.75) and depletion of Ti and P. Mixing relations in (87/86Sr)i - εNd(t) space among basalts, rhyolites, and local continental crust indicate that the Tecuya rhyolites were produced by assimilation of variable amounts of continental crust by MORB-related magmas and subcontinental lithosphere-derived melts. This conclusion is supported by the synchroneity of Tecuya volcanism at 22 Ma with interaction of a segment of the East Pacific Rise along the southern California margin. The Tecuya volcanic rocks thus provide an example for the generation of rhyolitic melts owing to crustal assimilation by basaltic melts during mid-oceanic ridge-induced magmatism along a continental margin.

Original languageEnglish (US)
Pages (from-to)159-172
Number of pages14
JournalContributions to Mineralogy and Petrology
Volume109
Issue number2
DOIs
StatePublished - Dec 1991
Externally publishedYes

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rhyolite
mid-ocean ridge basalt
basalt
continental crust
volcanism
crusts
Volcanic rocks
volcanology
basin
chondrites
assimilation
melt
rocks
chondrite
lithosphere
interactions
volcanic rock
petrogenesis
Southern California
mid-ocean ridges

ASJC Scopus subject areas

  • Geophysics
  • Geochemistry and Petrology

Cite this

Basalt-rhyolite volcanism by MORB-continental crust interaction : Nd, Sr-isotopic and geochemical evidence from southern San Joaquin Basin, California. / Sharma, Mukul; Basu, Asish R.; Cole, Ronald B.; Decelles, Peter G.

In: Contributions to Mineralogy and Petrology, Vol. 109, No. 2, 12.1991, p. 159-172.

Research output: Contribution to journalArticle

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abstract = "The early miocene Tecuya volcanic center in the southern San Joaquin basin of California consists of flows and tuffs of basalt and rhyolite that erupted, closely spaced in time, in both submarine and subaerial conditions. The rhyolites are overlain by the basalts and constitute approximately 45{\%} of a total of at least 180 km3 of the Tecuya volcanic rocks. The basalts have εNd(t) values of +2 to +6 and (87Sr/86Sr)i values between 0.7035 and 0.7052. These rocks show LREE enrichment [(La/Yb)N =2.4-5.5; La=28-150 times chondrite] and higher Th/U, Th/Ta, Rb/Ta, Ba/Ta, Cs/Rb but lower K/Rb ratios than MORB. Combined major- and trace-element, and Sr-Nd isotopic data suggest the involvement of subcontinental lithosphere, depleted upper mantle source (MORB), and local continental crust in the basalt petrogenesis. εNd(t) values in rhyolites vary from +1.5 to +3.7 while (87Sr/86Sr)i ratios range from 0.7051 to 0.7064. The rhyolites display LREE enrichment [(La/Yb)N=10; La=100 times chondrite] along with a distinct negative Eu anomaly (Eu/Eu*=0.75) and depletion of Ti and P. Mixing relations in (87/86Sr)i - εNd(t) space among basalts, rhyolites, and local continental crust indicate that the Tecuya rhyolites were produced by assimilation of variable amounts of continental crust by MORB-related magmas and subcontinental lithosphere-derived melts. This conclusion is supported by the synchroneity of Tecuya volcanism at 22 Ma with interaction of a segment of the East Pacific Rise along the southern California margin. The Tecuya volcanic rocks thus provide an example for the generation of rhyolitic melts owing to crustal assimilation by basaltic melts during mid-oceanic ridge-induced magmatism along a continental margin.",
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