Some chemical data on members of the shoshonite association

Abstract

SUMMARY. A number of minerals and residual glasses from absarokites, shoshonites, and latites have been analysed by electron probe.Clinopyroxenes show very little iron-enrichment and these rocks are thus distinguished from thoteiites and alkali basalts.Glasses from this group are also distinct from tholeiites and alkali basalts and occupy a separate field on a CaO-Na20-K~O diagram.WHEN attention (Joplin, I965) was drawn to the close resemblance between certain lavas on the south coast of New South Wales, the absarokite-shoshonite-banakite series of Wyoming (Iddings, 1895), and the latites of Sierra Nevada (Ransome, I898), it was suggested that these rocks might be related to the alkali basalts or might even represent a distinct magma-type.A review of world occurrences of shoshonitic rocks (Joplin, I968) has shown that compositions may range from ultramafic absarokites to felsic toscanites and liparites and that there is little iron enrichment. Thus, the shoshonitic rocks have some affinities with the calcalkaline andesitic suite and the suggestion that they may be related to the alkali basalts is wrong.The range in composition from absarokites to liparites suggests that they belong to a differentiation series, but the andesite suite also shows a considerable range in composition and many petrologists consider that members of this suite arise by a complex process involving partial melting rather than by fractional crystallization or by contamination of a basaltic magma (Green and Ringwood, I968; Taylor et al., I969). The shoshonitic rocks may have a somewhat similar origin (Jake~ and White, I969). As the word 'series' seems to imply a differentiation series and it is unlikely that the shoshonitic rocks are the differentiates of a single magma, it is preferable to refer to them as members of the shoshonite association.In I965 it was also pointed out that shoshonitic lavas are associated with regions that were incompletely stabilized or only recently stabilized at the time of their extrusion. This is in harmony with their geographical distribution with regard to the andesites in the island arcs.Shoshonites and monzonites have a very similar composition and because many monzonites are associated with nepheline-and melanite-bearing rocks, with or without 9

Magmatic associations of the western part of the Aleutian island arc

“…The basalt-trachydolerite association of the Komandorskiy Islands is comparable in petrological-geochemical respects with the shoshonite associations ofthc present-day island arcs (Jakes and White, 1969; Joplin, 1968Joplin, , 1972Gill, 1970;Smith, 1972). The similarity is expressed in the increased amounts of such elements as K, Sr, and Ba, with a comparatively low content of Fe, and also the presence of titaniferous augite, a mineral typical of the alkalinebasaltoid and alkaline-gabbroid rocks.…”

Direct Associations Between Potassic Igneous Rocks and Gold-Copper Deposits in Volcanic Arcs

“…The igneous rocks have high K 2 O contents (4.00-5.84 wt%), and high K 2 O/Na 2 O ratios (0.92-1.54) which are typical for the shoshonite association (cf. Joplin et al 1972;Morrison 1980;Lu et al 2013). Molecular K/Na ratios for all unaltered samples are consistently >1 (i.e.…”

“…SiO 2 contents between 46.8 and 64.9 wt%), as shown in Table 6.6. The samples are characterized by high, but variable, Al 2 O 3 contents (13.4-19.9 wt %), very high K 2 O contents (up to 6.8 wt%) and high K 2 O/Na 2 O ratios (0.58-1.48) which are typical for the shoshonite association (Joplin et al 1972;Morrison 1980;Lu et al 2013). The rocks also have enriched LILE concentrations (e.g.…”

“…The rocks are generally unmetamorphosed, but are commonly gently folded with relatively gentle dips (Heithersay 1986;Heithersay et al 1990). Compositions of the igneous rocks, which are locally intruded by monzodiorite, monzonite and quartz-monzonite stocks, range from trachyandesitic to latitic, and they exhibit typical shoshonitic geochemistry (Joplin et al 1972;Morrison 1980). As discussed by previous workers, the Goonumbla igneous rocks are probably related to a former subduction event (Müller et al 1994;Blevin 2002).…”

Vulcanismo Basáltico De Afinidade Shoshonítica Em Ambiente De Arco Arqueano, Grupo Grão-Pará, Serra Dos Carajás - Pará

“…A abundância dos intercrescimentos granofiricos (geralmente 15 % em volume) e a presença de feldspato potássico parecem indicar magma original rico em potássio, rubídio e bário. Segundo Joplin et al (1972), o material intersticial mais importante das séries shoshoníticas é o feldspato potássico.…”