In the case of a basaltic magma that is very rich in volatiles, or (much more commonly on Earth) in the case of a volatile-rich andesitic or rhyolitic magma
, fragmentation in a steadily erupting magma is very efficient, and most of the pyroclasts formed are small enough to be thoroughly entrained by the gas stream.
(2000 vv e know that a caldera resurgence that began during the SEE with conduit opening and alkaline trachytic to rhyolitic magma emission near the caldera margins, initial volcanism was not explosive in nature: magma could reach the surface after complete volatile release through conduit permeable walls, promoting anorthoclase and sanidine nucleation rate increment and amphibole and mica stability reduction, which generated corrosion and opatization borders in mafics.
(3) Mixing of trachytic and rhyolitic magmas and/or mixing of magmas of different alkalinity.
The Paipa volcano produced alkaline rhyolitic and trachytic to high-K calcalkaline rhyolitic magmas eruptions during the Pliocene.
This hypothesis is illustrated by a series of mathematical equations that Burnham (1983) used to model the energy released from the exsolution of water in rhyolitic magma. In silicic melts that contain more than a few tenths of 1 wt.
Only a few weight percent of water are required to make exsolution of water from a rhyolitic magma an instantaneous process (Fig.
An average rhyolitic magma undersaturated in water remains under lithostatic pressure until saturation is reached.
So, many authors consider it unlikely that such a process could, by itself, yield the vast volumes of andesitic and rhyolitic magmas that occur in matute arcs, even if magnetite were to appear on the liquidus to subdue iron enrichment trends.
Andesites formed either by mixing of basaltic and rhyolitic magmas, or by contamination of a more mafic parent by the continental crust commonly display textural evidence of disequilibrium (Eichelberger 1975) or field evidence of magma mixing or host rock assimilation (Wiebe et al.
Slip and normal NW trending faults interact with inverse NE trending regional structures and possibly create the volcanic conduits for trachytic to rhyolitic magmas of alkaline affinity (Cepeda & Pardo, 2004).
Second eruptive epoch (SEE): The caldera resurgence began with the emission of alkaline trachytic and rhyolitic magmas near the caldera margins (Figure 16 g); most of the eruptions occurred at one or several intracaldera vents formed at the headstream of Olitas Creek (Figure 16 h) as suggested by the presence of domes.