Petrogénesis > Metaultramáficas

Petrogénesis Metaultramáficas

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[Recristalización] [Composición y diagramas de fases] [Diagramas P-T] [Mg2SiO4 - SiO2 de J. Brady] [Desarrollo progrado] [Video desarrollo progrado] [Pseudosecciones] [Efecto composición del fluido] [Texturas] [Efecto del componente Al2O3: Clorita] [Relaciones de fases en el manto terrestre] [The Medellin Metaharzburgitic Unit (video & publicación)]

Recristalización metamórfica en metaultramafitas

Composición mineral y química y diagramas de fases composicionales

https://www.ugr.es/~agcasco/personal/rocasyminerales/Rocas/diapos/Diapositiva10.PNG

Diagramas P-T

Estabilidad de lizardita y antigorita, en el contexto de la mélange de subducción de la Sierra del Convento, E Cuba. Tomado de Cárdenas-Párraga, J., García-Casco, A., Proenza, J. A., Harlow, G. E., Blanco-Quintero, I. F., Lázaro, C., Villanova-de-Benavent, C., Núñez Cambra, K. (2017). Trace-element geochemistry of transform-fault serpentinite in high-pressure subduction mélanges (eastern Cuba): implications for subduction initiation. International Geology Review, 59(16), 2041–2064.

P-T diagram showing the metamorphic evolution of the serpentinite rocks of the Sierra del Convento and La Corea mélanges from the oceanic to the subduction environments. The red lines represent the reaction relationships in the CaO-MgO-SiO2-H2O system after Spear (1995) and Padrón-Navarta et al. (2012). The thick red reaction curves denote the calculated maximum stability of antigorite in the MgO-SiO2-H2O system. This reaction is almost coincident with the experimental stability limit of MSH antigorite (denoted as ‘MSH-Atg out (BP)’ in the figure, after Bromiley and Pawley 2003). Also shown is the experimental stability limit of Al-rich antigorite (denoted as ‘MASH-Atg out (UT)’ after Ulmer and Trommsdorff 1995). The orange shaded region encompasses additional experimental stability limits of antigorite with variable Al after Bromiley and Pawley (2003), Wunder and Schreyer (1997), and Wunder et al. (2001). The phase relations between lizardite and antigorite (green and blue reaction bands) are from Evans et al. (2013) and Schwartz et al. (2013). For reference, the thermal gradients of the top (slab–mantle interface) and bottom of the subducted oceanic crust in cold and warm subduction scenarios (Peacock and Wang 1999) and the wet basaltic solidus (Green 1982) are shown. The P-T paths of subducted MORB Grt-amphibolite blocks of the Sierra del Convento and La Corea mélanges followed counterclockwise P-T paths, reaching peak conditions appropriate for partial melting at ca. 750ºC at 15 kbar (García-Casco et al. 2008a; Lázaro et al. 2009; Blanco-Quintero et al. 2010, 2011e). Note that the related abyssal serpentinite from the down-going plate subducted at this stage would have been transformed into metaharzburgite/meta-olivine orthopyroxenite, which is lacking in the mélanges. The timing and P-T conditions of jadeitite formation in the Sierra del Convento mélange are after García- Casco et al. (2009) and Cárdenas-Párraga et al. (2012). Retrograde hydration of peridotite down to ca. 300ºC in the context of a transform-fault zone and the ensuing down-drag of the upper-plate serpentinite (which experienced limited subduction down to ca. 30 km, up to 450ºC after the onset of subduction) are indicated by deep-red arrows. Massive antigoritite formed at depths of ca. 15 kbar (Blanco-Quintero et al. 2011d). Exhumation of all types of blocks and serpentinite along the subduction channel allowed the formation of the mélanges with low-T serpentinite at <10 kbar in a fore-arc setting before the final collision-related exhumation during the latest Cretaceous (García-Casco et al. 2008b).