Gravity study of an Archaen crustal segment near Thunder Bay, Ontario / by Scott Philip Cheadle. --

A gravity survey in an area involving portions
\nof the Quetico and Shebandowan subprovinces of the
\nSuperior structural province resulted in the establishment
\nof 350 new gravity stations in addition to 50
\npreviously established stations.
\nFor the purposes of this study the bedrock was
\ndivided into 4 major units including the metavolcanic
\nrocks* metasedimentary rocks, assorted gneissic rocks
\nand a group of intrusive igneous bodies.
\nBased on gravity modeling of these principal
\nunits, the following subsurface structure results. The
\nmetavolcanic rocks vary in depth extent from 6 km to
\n12 km and typically occupy a trough-shaped structure
\nflanked by a domical feature of granitoid gneisses to
\nthe south. To the north of the metavolcanic unit, the
\nmetasedimentary rocks form a basin-like structure of
\nvariable depth extent. The contact between these two
\nunits is modeled as dipping steeply southward.
\nThe Quetico granitoid gneisses to the north of
\nthe metasedimentary unit form a southward dipping wedge
\nwhich extends to depths of 10 km in the model structure
\nprofiles. These gneisses are modeled as being underlain
\nby a denser substratum representative of more basic
\ngneiss and amphibolite. The basal surface of this
\nunit is gently convex upward, and the unit as a whole
\nthickens toward the north and dips toward the south
\nin a tapered wedge extending to a depth of 10 km.
\nThis unit is inclined slightly from east to west, and
\nis exposed at the present erosion surface in the
\neastern portion of the study area only.
\nA number of quartz monzonite plutons have been
\nemplaced near the northern portion of the metasedimentary
\nunit and outcrops above the southern most edge of the
\ndense substratum underlying the Quetico gneisses.
\nA tectonic model put forward synthesizes the
\navailable information regarding Archean crustal
\nevolution and the data from this study. The proposed
\nmodel consists of a basin-like structure (Quetico
\nsubprovince) which received sedimentary and volcanic
\ndebris from a mature volcanoplutonic terrane to the
\nnorth (Wabigoon subprovince). Additional sedimentation
\ninto the basin was provided from the less mature
\nvolcanoplutonic terrane to the south (Shebandowan
\nsubprovince). Subsequent deformation accompanied by
\nhigh grade metamorphism resulted in a general upwarping
\nof the basin, producing the structures now observed in
\nthis part of the Quetico subprovince.

Récupéré en direct depuis OpenAlex et désinversé. Les résumés ne sont pas conservés dans cette base de données : les index inversés représentent 8,6 Go des 9,3 Go de texte de la base, et le serveur dispose de 13 Go libres.