Magmatism along the high Paraguay River at the border of Brazil and Paraguay: A review and new constraints on emplacement ages

Comin-Chiaramonti, P., Gomes, C.B., De Min, A., Ernesto, M. and Gasparon, M. (2015) Magmatism along the high Paraguay River at the border of Brazil and Paraguay: A review and new constraints on emplacement ages. Journal of South American Earth Sciences, 58 72-81. doi:10.1016/j.jsames.2014.12.010


Author Comin-Chiaramonti, P.
Gomes, C.B.
De Min, A.
Ernesto, M.
Gasparon, M.
Title Magmatism along the high Paraguay River at the border of Brazil and Paraguay: A review and new constraints on emplacement ages
Journal name Journal of South American Earth Sciences   Check publisher's open access policy
ISSN 0895-9811
1873-0647
Publication date 2015-03
Year available 2015
Sub-type Article (original research)
DOI 10.1016/j.jsames.2014.12.010
Open Access Status
Volume 58
Start page 72
End page 81
Total pages 10
Place of publication Oxford, United Kingdom
Publisher Pergamon
Collection year 2016
Language eng
Formatted abstract
The magmatic rocks from Alto Paraguay (High Paraguay River extensional lineament), western Apa craton, mainly consist of several major circular alkaline complexes and some rhyolitic domes and ignimbrites. The former are characterized by intrusive Na–alkaline rock-types (nepheline syenites and syenites and effusive equivalents) topped by lava flows and ignimbrites. Two main evolved suites were defined using petrochemical and Sr– isotope data: an agpaitic suite in the north and a miaskitic suite in the south. The domes of subalkaline rhyolitic lavas and ignimbrites occur to the north of the alkaline complexes, along the Paraguay River, near the town of Fuerte Olimpo.

The emplacement ages of the alkaline complexes were constrained using the K–Ar, Ar–Ar, Rb–Sr and Sm–Nd dating methods on whole rocks and/or mineral separates (amphibole, alkali feldspar and biotite). Ages are quite variable (Upper Permian to Middle Triassic), with average K–Ar and Ar–Ar ages of 248.8 ± 4.8 and 241.8 ± 1.1 Ma, respectively, and Rb–Sr and Sm–Nd age data giving best values from 248 ± 4 to 244 ± 27 Ma and from 256 ± 3 to 257 ± 3 Ma, respectively. In contrast, the Fuerte Olimpo volcanics show a Mesoproterozoic age (1.3 Ga, K–Ar and Ar–Ar radiometric methods; and 1.42 ± 0.24 to 1.30 ± 0.03 Ga, Rb–Sr and Sm–Nd methods, respectively).

Rb–Sr systematics (87Sr/86Sr initial ratios ≤ 0.7038) highlight a relatively “primitive” character of the Na–alkaline magmatic source(s), in contrast with the “crustal” values (87Sr/86Sr initial ratio ∼ 0.7105) of the Fuerte Olimpo rhyolites. Thus, magmatism in the Alto Paraguay area is related to two extensional events: a younger event corresponding to the Permian–Triassic alkaline rocks, and an older event connected to the Precambrian volcanic acidic rocks.
Keyword Alto Paraguay
Apa craton
Na-sodic complexes
Triassic Age
Fuerte Olimpo volcanics
Mesoproterozoic Age
Q-Index Code C1
Q-Index Status Confirmed Code
Institutional Status UQ

Document type: Journal Article
Sub-type: Article (original research)
Collections: School of Earth Sciences Publications
Official 2016 Collection
 
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