Compositional Evolution of the Variscan Intra-Orogenic Extensional Magmatism in the Valencia del Ventoso Plutonic Complex, Ossa-Morena Zone (SW Iberia): A View from Amphibole Compositional Relationships
Metadatos
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Cambeses Torres, Aitor; Molina Palma, José Francisco; Morales López, Irene; González Montero, María Del Pilar; Bea Barredo, FernandoEditorial
MDPI
Materia
Amphibole compositional relationships Amphibole-plagioclase thermobarometry Postcollisional magmatism Magma mixing and hybridization Ossa-Morena Zone Iberia Variscan orogen
Fecha
2021Referencia bibliográfica
Cambeses, A.; Molina, J.F.; Morales, I.; Lázaro, C.; Moreno, J.A.; Montero, P.; Bea, F. Compositional Evolution of the Variscan Intra-Orogenic Extensional Magmatism in the Valencia del Ventoso Plutonic Complex, Ossa-Morena Zone (SW Iberia): A View from Amphibole Compositional Relationships. Minerals 2021, 11, 431. https://doi.org/10.3390/min11040431
Patrocinador
Ministerio de Economía y Competitividad (Gobierno de España), CGL2017-84469-PResumen
The Ossa-Morena Zone (OMZ), SW Iberia, has numerous Lower Carboniferous compositionally zoned plutons that formed in a Variscan intra-orogenic extensional setting. This magmatism
shows a wide compositional variation comprising alkaline, transitional, and calc-alkaline suites. The
calc-alkaline suite was produced by hybridization of alkaline magmas with felsic melts generated
by crustal anatexis related to the intrusion of mafic magmas in the middle crust. In this work, we
present a textural and mineralogical study of the Variscan Valencia del Ventoso main pluton from
the OMZ to track the compositional evolution of magmas during hybridization using constraints
from amphibole compositions and to determine the P-T conditions of emplacement using amphibolebased thermobarometry. This pluton exhibits reverse zoning with an inner facies containing alkaline
dolerites, gabbros, and quartz diorites, an intermediate facies with transitional diorites, and an outer
facies with calc-alkaline quartz diorites to monzogranites. Magmas from the intermediate and border
facies crystallized under oxidizing conditions at relatively low temperatures (range: 640–760 ◦C) and
ca. 280–300 MPa, implying near H2O-saturated conditions. These rock facies show mineralogical
evidence of hybridization between alkaline to mildly alkalic and calc-alkaline magmas. The former
is inferred from the occurrence of antecrysts of labradorite-andesine, high-Ti pargasite-hastingsite,
and biotite with deficiency in tetrahedral-site occupancy, a distinctive feature of biotite from the
inner facies alkaline dolerites. This contrasts with later crystallization from the calc-alkaline magma
of andesine-oligoclase, low-Ti magnesiohornblende-edenite, and biotite with full tetrahedral-site
occupancy. Constraints from amphibole-melt compositional relationships in antecrystic high-Ti
amphibole suggest that the alkaline magmatic component could have a high- to ultra-K affinity.