Rhyolite-basalt complex on Gardiner River, Yellowstone Park, Wyoming

Magma Mixing: History and Dynamics of an Eruption Trigger

“…Although Bowen did not explicitly deny the possibility of magma mixing, he reinterpreted field evidence of magma mixing rather as immiscibility of liquids (e.g., Bowen 1928). In 1944, Wilcox published a work on the Gardner River complex (Yellowstone, USA; Wilcox 1944) which is now considered a milestone for evidence of magma mixing, even if at that time it received strong comments from Fenner and remained one of the few papers on the topic. Only in the 1970's geoscientists started to deeply investigate magma mixing, recorded as a plethora of unequivocal evidence in both plutonic and volcanic rocks, as a major petrogenetic process (e.g., Eichelberger 1978Eichelberger , 1980Blundy and Sparks 1992;Wiebe 1994;Wilcox 1999).…”

“…In order to provide possible classification of magma mixing structures, the evidence of mechanical mixing in igneous rocks can be roughly divided into three different groups: (i) flow structures, (ii) magmatic enclaves and (iii) physico-chemical disequilibria in melts and crystals (e.g., Walker and Skelhorn 1966;Didier and Barbarin 1991;Hibbard 1995;Flinders and Clemens 1996;Wilcox 1944Wilcox , 1999Perugini et al 2002Perugini et al , 2003Streck 2008;Perugini and Poli 2012;Morgavi et al 2016). Flow structures can be readily recognized in field outcrops as they show alternating light and dark coloured bands constituted by magmas with different compositions.…”

“…The term magmatic enclave is used to identify a discrete portion of a magma occurring within a host magma with a different composition (e.g., Wilcox 1944;Walker and Skelhorn 1966;Bacon 1986, Didier andBarbarin 1991). Generally, enclaves display quite sharp contacts with the host rock, although it is not rare to observe that some enclaves display engulfment and disruption of their boundaries due to infiltration of the host magma.…”

A field trip guide to the petrology of Quaternary volcanism on the Yellowstone Plateau

“…Later, Fenner (1938Fenner ( , 1944 concluded that the rhyolite flow intruded and dissolved deeply eroded older basalt. Using a combination of detailed mapping and petrography, Wilcox (1944) concluded that the rhyolitic and basaltic components of the complex were both liquid at the time of their joint eruption. He showed that the basalt was chilled against the rhyolite, but never the reverse.…”

“…Additionally, Wilcox showed that quartz and sanidine xenocrysts in the basalt, interpreted to be derived from the rhyolitic component, occur away from the contact with the rhyolite, indicating the basalt was liquid or at least partly liquid when the two magmas mixed. Hawkes (1945) proposed a model similar to Wilcox (1944), but proposed that mixing occurred on the surface. Boyd (1961) and Struhsacker (1978) concluded that the basaltic and rhyolitic melts variably mixed in a composite feeder, because microphenocrysts in the basaltic portions of the unit are aligned with flow banding and minerals in the rhyolitic groundmass.…”