Geochemistry of Laramide granitic rocks across the Southern margin of the Paleozoic North American continent, Central Sonora, Mexico

Martin Valencia-Moreno, Joaquin Ruiz, Jaime Roldan-Quintana

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Abstract

The geochemistry of Laramide granitic rocks from central Sonora was studied to relate possible compositional variations to the assimilation of different crustal sources. Most of the studied rocks are granodiorites collected near the southern boundary of the Paleozoic North American continent. North of this boundary, the Laramide plutons intruded a thick section of Upper Proterozoic and Paleozoic miogeoclinal strata, whereas south of it, the intrusives were emplaced in Lower Ordovician to Permian eugeoclinal rocks accreted to the continental margin between Late Permian and Middle Triassic times. Whole-rock Na2O, TiO2, and P2O5 contents are slightly higher in plutons intruded in cratonic and miogeoclinal rocks, whereas MgO and CaO seem to be higher in plutons emplaced in eugeoclinal rocks. The samples located in the north are characterized by steeper chondrite-normalized REE slopes and generally well developed negative europium anomalies, whereas the group of granitoids in the south have flatter REE slopes and generally smaller negative europium anomalies. Available isotope data show 87Sr/86Sr initial ratios above 0.7070, and ε(Nd) initial values between -4.6 and -4.2 in plutons to the north. In a narrow E-W region just south of the Paleozoic continental margin, the samples yielded similar 87Sr/86Sr ratios but unexpectedly low ε(Nd) values between -5.4 and -5.1. South of this region, the isotope signatures are slightly more primitive, with 87Sr/86Sr initial ratios between 0.7067 and 0.7057 and initial ε(Nd) values between -3.9 and -3.7. The results of this study suggest that the nature of the assimilated crust may have influenced the final composition of the Laramide granitic rocks of central Sonora.

Original languageEnglish (US)
Pages (from-to)845-857
Number of pages13
JournalInternational Geology Review
Volume41
Issue number9
StatePublished - Sep 1999

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Paleozoic
geochemistry
pluton
rock
europium
continental margin
Permian
rare earth element
isotope
anomaly
continent
granodiorite
chondrite
Ordovician
Proterozoic
Triassic
crust

ASJC Scopus subject areas

  • Geology

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Geochemistry of Laramide granitic rocks across the Southern margin of the Paleozoic North American continent, Central Sonora, Mexico. / Valencia-Moreno, Martin; Ruiz, Joaquin; Roldan-Quintana, Jaime.

In: International Geology Review, Vol. 41, No. 9, 09.1999, p. 845-857.

Research output: Contribution to journalArticle

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