Bimodal back-arc alkaline magmatism after ridge subduction: Pliocene felsic rocks from Central Patagonia (47°S)期刊界 All Journals 搜尽天下杂志传播学术成果专业期刊搜索期刊信息化学术搜索

按检索

Bimodal back-arc alkaline magmatism after ridge subduction: Pliocene felsic rocks from Central Patagonia (47°S)

Authors:	Felipe Espinoza Diego Morata Mireille Polv Yves Lagabrielle Ren C Maury Christle Guivel Joseph Cotten Herv Bellon Manuel Surez

Institution:	^aDepartamento de Geología, Universidad de Chile, Casilla 13518, Correo 21, Santiago, Chile ^bLMTG, Université de Toulouse, CNRS, IRD, OMP Avenue E.douard Belin 31400 Toulouse, France ^cUMR 5243 Géosciences Montpellier, Université de Montpellier 2, Place Eugène Bataillon, CC 60, 34095 Montpellier Cedex 5, France ^dUMR 6538 Domaines océaniques, Université de Bretagne Occidentale, 6 avenue le Gorgeu, C.S. 93837, 29238 Brest Cedex 3, France ^eUMR 6112 Laboratoire de Planétologie et Géodynamique, Pétrologie Structurale, Université de Nantes, 2 rue de la Houssinière, B. P. 92208, 44322 Nantes Cedex 03, France ^fServicio Nacional de Geología y Minería, Avenida Santa María 0104, Santiago, Chile

Abstract:	Volumetrically minor microsyenites, alkali microgranite and related trachytic dykes intrude early Pliocene OIB-like alkali basaltic and basanitic flows of the Meseta del Lago Buenos Aires in Central Patagonia (47°S–71°30′W), and occur together with scarce trachytic lava flows. Whole-rock K–Ar ages between 3.98 and 3.08 Ma indicate that the emplacement of these felsic rocks occurred more or less synchronously with that of the post-plateau basaltic sequence that they intrude, during a bimodal mafic–felsic magmatic episode devoid of intermediate compositions. Chemically, these rocks have A₁-type granitoid affinities and are characterized by high silica and alkali contents (60–68 wt.% SiO₂; 8.7–10.8 wt.% Na₂O + K₂O), major and trace elements patterns evidencing evolution by low-pressure fractional crystallization, and Sr and Nd isotopic signatures similar to those of coeval basalts ((⁸⁷Sr/⁸⁶Sr)_o = 0.70488–0.70571; (¹⁴³Nd/¹⁴⁴Nd)_o = 0.512603–0.512645). Nevertheless, some of them have the most radiogenic Sr values ever reported for a magmatic rock in the Meseta and even in the whole Neogene Patagonian Plateau Lavas province ((⁸⁷Sr/⁸⁶Sr)_o = 0.70556–0.70571; (¹⁴³Nd/¹⁴⁴Nd)_o = 0.512603–0.512608). In addition, very high contents of strongly incompatible elements in the most evolved rocks, together with Sr isotopic ratios higher than those of coeval basalts, suggest the occurrence of open-system magmatic processes. Continuous fractional crystallization from a primitive basaltic source, similar to post-plateau coeval basalts, towards alkali granites combined with small rates of assimilation of host Jurassic tuffs (AFC) in a shallow magmatic reservoir, best explains the geochemical and petrographic features of the felsic rocks. Therefore, A₁-type magmatic rocks can be generated by open-system crystallization of deep asthenospheric melts in back-arc tectonic settings. In Central Patagonia, these 3–4 Ma old alkaline intrusions occur aligned along a N160–170 trending lineament, the Zeballos Fault Zone, stacking the morphotectonic front of one segment of the Patagonian Cordillera. Intrusion along this fault zone occurred during the onset of a new transtensional or extensional event in the area, related to major regional tectonics occurring in possible relation with the collision of one segment of the Chile Spreading Ridge with the trench.

Keywords:	Mafic–felsic alkaline magmatism Syenites Central Patagonia back-arc Pliocene Chemical modeling
本文献已被 ScienceDirect 等数据库收录！

设为首页 | 免责声明 | 关于勤云 | 加入收藏