NDLI: Los diques comendíticos de Papachacra (Catamarca): magmatismo peralcalino en sierras Pampeanas orientales

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Los diques comendíticos de Papachacra (Catamarca): magmatismo peralcalino en sierras Pampeanas orientales

Content Provider	Semantic Scholar
Author	Colombo, Fernando Elias Lira, Raúl Oleary, María Sol Tassinari, Colombo Celso Gaeta
Copyright Year	2010
Abstract	The comenditic dikes from Papachacra (Catamarca): peralkaline magmatism in Eastern Sierras Pampeanas. In Papachacra (Cata- marca Province, NW Argentina) there is a pluton composed of several different A-type granitoids that show alkaline affi- nities. The latest rocks are peralkaline rhyolites (comendites), which form dikes up to 50 cm thick cross-cutting the gene- tically unrelated El Portezuelo granite. They have porphyritic texture and are composed of K feldspar (Or 97-98 Ab 2-3 ) and aegirine (Ac94-98) phenocrysts in an aphanitic groundmass of quartz, K feldspar, albite, aegirine and Li-bearing amphibole chemically related to fluor-ferro-leakeite. Minor accessory phases include ilmenite, magnetite, pyrochlore-group minerals, REE-rich epidote, zircon (interstitial), monazite-(Ce) and an unidentified Nb-Y-Fe oxide. Their SiO 2 content ranges bet- ween 68.28 and 69.33%, with very low Mg, Ca, Ba, Sr and Eu, and high concentrations of Nb (399-409 ppm), Ta (16-34 ppm), Th (46-84 ppm), Y (101-192 ppm), Zn (280-320 ppm), Ga (42-47 ppm) and especially Zr (2324-3000 ppm). The co- mendites were intruded during a distensive magmatic event. A reconnaissance Rb-Sr isotopic study performed on related rocks indicates an age of 295 + 8 Ma, with an initial 87 Sr/ 86 Sr ratio of ca. 0.7041, pointing to a source from the sublithos- pheric mantle or the base of the lower crust. These rocks belong to the A 1 class of A-type granites, suggesting an origin related to rifting or hot spots, and their trace element ratios show affinities with melts related to oceanic island basalts. In this respect, they are different from all the post-Devonian A-type granites described in Eastern Sierras Pampeanas.
Starting Page	194
Ending Page	205
Page Count	12
File Format	PDF HTM / HTML
Volume Number	66
Alternate Webpage(s)	http://www.scielo.org.ar/pdf/raga/v66n1-2/v66n1-2a19.pdf
Language	English
Access Restriction	Open
Content Type	Text
Resource Type	Article

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