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Titolo:
THE CERRO-MENCENARES VOLCANIC CENTER, BAJA-CALIFORNIA-SUR - SOURCE AND TECTONIC CONTROL ON POSTSUBDUCTION MAGMATISM WITHIN THE GULF-RIFT
Autore:
BIGIOGGERO B; CHIESA S; ZANCHI A; MONTRASIO A; VEZZOLI L;
Indirizzi:
UNIV MILAN,DIPARTIMENTO SCI TERRA,VIA MANGIAGALLI 34 I-20133 MILAN ITALY CNR,CTR STUDIO GEODINAM ALPINA & QUATERNARIA I-20133 MILAN ITALY
Titolo Testata:
Geological Society of America bulletin
fascicolo: 9, volume: 107, anno: 1995,
pagine: 1108 - 1122
SICI:
0016-7606(1995)107:9<1108:TCVCB->2.0.ZU;2-D
Fonte:
ISI
Lingua:
ENG
Soggetto:
ROCKS; GEOCHEMISTRY; MEXICO; SUBDUCTION;
Tipo documento:
Article
Natura:
Periodico
Settore Disciplinare:
Science Citation Index Expanded
Citazioni:
40
Recensione:
Indirizzi per estratti:
Citazione:
B. Bigioggero et al., "THE CERRO-MENCENARES VOLCANIC CENTER, BAJA-CALIFORNIA-SUR - SOURCE AND TECTONIC CONTROL ON POSTSUBDUCTION MAGMATISM WITHIN THE GULF-RIFT", Geological Society of America bulletin, 107(9), 1995, pp. 1108-1122

Abstract

At the end of active subduction along the North American plate (12.5 Ma), in the Baja California peninsula are magmatism was replaced mainly by alkali-rich high-Mg basaltic andesites and andesites with peculiar and unusually high K/Rb, Sr/Rb, and LREE/HREE ratios defined ''bajaite'' by Rogers et al. (1985) and ''Baja alkalic suite'' by Sawlan (1991). Two interesting features of this magmatic change are represented by (i) emplacement of transitional, high-g calc-alkaline andesites thatpreceded, in places, the Baja alkalic suite magmatism and (ii) subduction unrelated medium-K calc-alkaline magmatism in Baja California Sur, active in areas within the Gulf of California Rift, for example, Tres Virgenes-Reforma caldera, Isla Coronado. A previously unknown example of this calc-alkaline activity was studied in the area of Cerro Men-cenares located north of Loreto, Baja California Sur. The Mencenares volcanic complex is located along the Gulf coast, east of the main Gulfescarpment. Activity of the Mencenares volcanic complex occurred in three stages: (i) an initial phase of rhyolitic dome emplacement; (ii) andesitic to dacitic volcanism that produced the Mencenares stratovolcano; (iii) late-stage emplacement of silicic domes and flows, mostly dacite and rhyolite, along north-south-trending normal faults. Tephra and lava flows interfinger with marine sediments of the Pliocene LoretoBasin and the youngest volcanic products were probably emplaced during Quaternary times. This volcanism is coeval with the Baja alkalic suite magmatism west of the Gulf escarpment. In the latter areas, Baja alkalic suite magmas ascended rapidly with only limited differentiation. In the Mencenares volcanic complex, a complex tectonic framework favored the formation of crustal magma chambers where more complex phenomena such as extensive differentiation and mixing could take place. A change from medium-g calc-alkaline toward Baja alkalic suite-like chemical characteristics is present in the younger products of the Mencenares volcanic complex and mixing possibly occurred between medium-g calc-alkaline and Baja alkalic suite magmas. Magma evolution in the Loreto area suggests that (i) Baja alkalic suite and medium-K calc-alkaline magmas can coexist in time and interact in the same volcanic field; (ii) if a relic, subduction-related component is the main cause of medium-g or high-g calc-alkaline volcanism then this component appears to decrease from east to west; and (iii) although prior calc-alkaline magmatism may not be unquestionably considered a necessary condition for the generation of Baja alkalic suite magmas, episodes of medium-g or high-K calc-alkaline melt extraction from mantle sources precede or accompany Baja alkalic suite magmatism in many instances.

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Documento generato il 23/09/20 alle ore 06:25:49