Tensile fracturing and expansion possible relating to tectonic activity and faulting have in part controlled the emplacement of alkali feldspar rich rocks in Heronian sediments at Lake La Cloche, south of Massey, Ontario. The rocks include
1.
albitite - composed almost entirely of low albite (Dr2-Abg95-An3) and minor dispersed hematite.
2.
perthosite - containing separate phases of microcline and albite with mutual replacement textures.
The seem to be physically separate but show similarities in spatial, textural and chemical aspects. They have been emplaced chiefly within a fracture zone at the top of the Mississagi quartzite. Perthosite is intimately related with
3.
tuffisite - a somewhat mineralogically and modally variable rock emplaced as matrix within an irregular breccia pipe north of the fracture zone. The overall mineral assemblage is microcline + albite + perthite + epidote + chlorite + sericite+ hematite. Texturally it is reminiscent of crystal cuffs. Phenoclasts of the alkali feldspars (rounded, abraded) float in a hydrous silicate background. These phenoclasts are replicas of those in perthosite. Fragments of perthosite (phenoclast poor) were also found in tuffisite in one local. Tuffisite ranges from alkali feldspar poor to feldspar rich varieties. It is typically a silica poor alumina, lime, iron arid potash-rich rock.
Tuffisite was probably emplaced as a fluidized mass. Some similarities to known fluidized bodies are present. These include rounding, attrition and fretting of the host rock, extensive penetration and exploitation of joints, bedding and planar weaknesses, internal sculpturing of the host rock, evidence for both mechanical and chemical emplacement.
It may also be classed as a hydrothermalite. This refers to crytallization under submagmatic conditions, the pneumatolytic to hydrothermal range, hydroxyl minerals commonly developing. In this respect and others it is comparable with weilbergites, alkali feldspar-chlorite rocks within the Lahn region of Germany.
Certain nearby breccia pipes and red feldspar rocks have been associated with alkalic igneous activity. (An alkaline rock province has been postulated along the North Shore of Lake Huron) Specif1cally soda rich fenite breccias are present at Nemag and Kusk lakes, 12 miles southwest of Sudbury.
The red feldspar rock albitite is common along the North Shore.
It is often adjacent or spatially related to diabase and has been interpreted accordingly in terms of genesis. Some albitites are not related spatially to di abase bodies and their emplacement has been controlled fracture systems. Their origin is more hazy.
The author suggests two alternative interpretations dependent on whether alkali feldspars in tuffisite are considered to be primarily on- allochthonous.
Alternative One - (Alkali feldspars primary): Perthosite and albitite are special fractionates, concentrated initially within the proto-tuffisite magma aj an al kali-volatile rich phase. These juvenile liquids were emplaced within a fracture zone at the top of the Mississagi. At about the same time tuffisite was emplaced within an irregular breccia pipe.
The author throws open for argument the possibility that tuffisite
is an upper crustal altered fenite breccia with associated red feldspar rock emplacement la fracture zones.
Alternative Two-(Alkali feldspars allochthonous);Tuffisite is a
hybrid rock type akin to a weilbergites (also interpreted as hybrid). Crystallization of red feldspar rocks within the pneumatolytic stage involved contamination in part by mafic material (possibly diabase). The resultant mechanical, chemical mixture was emplaced as a fluidized mass-tuffisite.
More work needs to be done in determining which alternative is valid and what the exact relationships and sources of albitite, perthosite and tuffisite are. / Thesis / Bachelor of Science (BSc)
| Identifer | oai:union.ndltd.org:mcmaster.ca/oai:macsphere.mcmaster.ca:11375/29252 |
| Date | 05 1900 |
| Creators | Legun, Andy |
| Source Sets | McMaster University |
| Language | English |
| Detected Language | English |
| Type | Thesis |
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