Zonal structure of the Perth Road monzonite, Grenville Province, Ontario

Abstract

The Perth Road pluton is a lenticular, grossly conformable body emplaced in metasedimentary rocks of the Grenville series during a period in which the enclosing gneisses deformed by plastic flow. The body is zoned and from the center outward comprises gabbro, diorite, monzonite (the dominant rock-type), quartz monzbnite, and granite. The change from one rocktype to the next is gradual and the progressive acidification toward all the contacts, without regard to the type of enclosing gneiss, is taken as an indication of cogenesis of the plutonic assemblage; modal mineral variations of quartz, alkali-feldspar, plagioclase, and color index demonstrate this mineral progression.The enclosing crystalline metasedimentary rocks have been metamorphosed to the hornblende granulite facies, and although recrystallization has kept pace with deformation some cahclasis pervades all rocks. The pluton occupies a flattened crestal position of a doubly plunging fold, and all folds show a combination of fold-styles depending on the relative competence of the various rock-types. Flow models demonstrate that Ihe early magmatic precipitates collected in regions of maximum velocity of the magma during folding of the enclosing envelope of gneisses and that syntectonic differentiation in this manner obtains for the Perth Road and other plutons in the area.

A nested diapir model for the reversely zoned Turtle Pluton, southeastern California

“…KEY WORDS: early Cretaceous, mafic enclaves, magma mixing, Mojave Desert, source rocks Of the compositionally zoned plutons described in the literature, relatively few are composed of a more felsic rim and a more mafic core (Ermanovics 1970;Ayuso 1984;Fridrich & Mahood 1984;Nabelek et al 1986;Bourne & Danis 1987;Wernicke 1987;Nironen 1989); these are termed reversely zoned in contrast to the "normal" case of mafic rims and felsic cores. Whereas in situ fractional crystallisation through sidewall crystallisation and solidification is commonly invoked as the principal mechanism that produces normally zoned plutons, this model cannot be applied to reversely zoned plutons particularly as the minerals with the highest crystallisation temperatures reside in the core.…”

Field relations, crystallization, and petrology of reversely zoned granitic plutons in the Bottle Lake Complex, Maine

“…The Perth Road pluton (Ermanovics, 1970) and the Loon Lake pluton (Dostal, 1975) in the province of Ontario (Canada) are zoned bodies resulting from flow differentiation. Ermanovics (1970) described the zonation of the Perth Road pluton from gabbro at the center to granite at the margins. He interpreted the zonation as a result of flow differentiation in a chamber undergoing folding.…”