FRANÇAIS: La cornéenne est un matériau lithique fréquemment retrouvé sur les sites archéologiques... more FRANÇAIS: La cornéenne est un matériau lithique fréquemment retrouvé sur les sites archéologiques préhistoriques du Québec méridional. On l’associe généralement aux occupations de l’Archaïque post-laurentien (4500–3000 A.A.), mais cette étude montre que l’utilisation de ce matériau n’est pas exclusive à cette période. Les analyses physico-chimiques présentées ici permettent d’identifier une source potentielle et vraisemblablement principale de ce matériau, la cornéenne du mont Royal. La pétrologie de ce type de roche indique un métamorphisme essentiellement thermique opérant dans l’environnement immédiat de massifs intrusifs. Il faut donc considérer la cornéenne présente sur les autres collines montérégiennes en tant que sources potentielles, même si celles-ci sont à ce jour non documentées par l’archéologie.
ENGLISH: Hornfels is a lithic material frequently discovered on prehistoric sites in southern Quebec. It is commonly associated with Terminal Archaic (or “post-laurentian” Archaic [4500–3000 B.P.]) occupations, but this study demonstrates that such an association can be misleading. The results of the physical and chemical analyses presented here also indicate that Mont Royal, a small hill located in the city of Montreal, is the most probable source of hornfels used in prehistoric times. Outcrops of hornfels exist on some other Monteregian Hills, but to this day there are no archaeological indications that they were exploited by aboriginal groups.
The São Francisco shield is one of the major cratonic units forming the backbone of the South Ame... more The São Francisco shield is one of the major cratonic units forming the backbone of the South American continent. The Quadrilátero Ferrífero area, in the south of the shield, is underlain by three major units: granitic-gneissic terrains with a minimum age of 2860 Ma; the Rio das Velhas greenstone belt, emplaced at 2772–2780 Ma; and the Minas Supergroup-Itacolomi Group Paleoproterozoic sedimentary sequences. The 207Pb206Pb and UPb ages of more than 400 detrital zircons obtained by Laser ablation-ICPMS and isotope dilution lead to the following conclusions: (1) the Rio das Velhas greenstone belt contains exclusively cratogenic sediments and developed on, or proximal to, old, evolved continental crust with a minimum age of ca. 2.85 Ga; (2) the lower detrital sequence of the Minas Supergroup was supplied with sediments derived from both the granite-greenstone terrain and the surrounding older crust; (3) the upper unit of the Minas Supergroup (Sabará Formation) contains 2125 Ma zircon and the overlying Itacolomi Group contain zircons with minimum ages of ca. 2.06 Ga, identical to the ages of regional metamorphism. Together with other considerations, these ages lead to the novel proposal that the tectogenic sedimentation represented by these units occurred in a foreland basin of the Transamazonian orogen. Basin evolution was closely associated with the tectonic development of the orogen and uplift of basement complexes between 2125 Ma and 2030 Ma.The scarcity of 2.6-2.4 Ga zircons in the Proterozoic units of the Quadrilátero Ferrífero confirms previous results for the São Francisco shield and is symptomatic of the absence of magmatic-metamorphic activity in that period of time.
FRANÇAIS: La cornéenne est un matériau lithique fréquemment retrouvé sur les sites archéologiques... more FRANÇAIS: La cornéenne est un matériau lithique fréquemment retrouvé sur les sites archéologiques préhistoriques du Québec méridional. On l’associe généralement aux occupations de l’Archaïque post-laurentien (4500–3000 A.A.), mais cette étude montre que l’utilisation de ce matériau n’est pas exclusive à cette période. Les analyses physico-chimiques présentées ici permettent d’identifier une source potentielle et vraisemblablement principale de ce matériau, la cornéenne du mont Royal. La pétrologie de ce type de roche indique un métamorphisme essentiellement thermique opérant dans l’environnement immédiat de massifs intrusifs. Il faut donc considérer la cornéenne présente sur les autres collines montérégiennes en tant que sources potentielles, même si celles-ci sont à ce jour non documentées par l’archéologie.
ENGLISH: Hornfels is a lithic material frequently discovered on prehistoric sites in southern Quebec. It is commonly associated with Terminal Archaic (or “post-laurentian” Archaic [4500–3000 B.P.]) occupations, but this study demonstrates that such an association can be misleading. The results of the physical and chemical analyses presented here also indicate that Mont Royal, a small hill located in the city of Montreal, is the most probable source of hornfels used in prehistoric times. Outcrops of hornfels exist on some other Monteregian Hills, but to this day there are no archaeological indications that they were exploited by aboriginal groups.
The São Francisco shield is one of the major cratonic units forming the backbone of the South Ame... more The São Francisco shield is one of the major cratonic units forming the backbone of the South American continent. The Quadrilátero Ferrífero area, in the south of the shield, is underlain by three major units: granitic-gneissic terrains with a minimum age of 2860 Ma; the Rio das Velhas greenstone belt, emplaced at 2772–2780 Ma; and the Minas Supergroup-Itacolomi Group Paleoproterozoic sedimentary sequences. The 207Pb206Pb and UPb ages of more than 400 detrital zircons obtained by Laser ablation-ICPMS and isotope dilution lead to the following conclusions: (1) the Rio das Velhas greenstone belt contains exclusively cratogenic sediments and developed on, or proximal to, old, evolved continental crust with a minimum age of ca. 2.85 Ga; (2) the lower detrital sequence of the Minas Supergroup was supplied with sediments derived from both the granite-greenstone terrain and the surrounding older crust; (3) the upper unit of the Minas Supergroup (Sabará Formation) contains 2125 Ma zircon and the overlying Itacolomi Group contain zircons with minimum ages of ca. 2.06 Ga, identical to the ages of regional metamorphism. Together with other considerations, these ages lead to the novel proposal that the tectogenic sedimentation represented by these units occurred in a foreland basin of the Transamazonian orogen. Basin evolution was closely associated with the tectonic development of the orogen and uplift of basement complexes between 2125 Ma and 2030 Ma.The scarcity of 2.6-2.4 Ga zircons in the Proterozoic units of the Quadrilátero Ferrífero confirms previous results for the São Francisco shield and is symptomatic of the absence of magmatic-metamorphic activity in that period of time.
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ENGLISH: Hornfels is a lithic material frequently discovered on prehistoric sites in southern Quebec. It is commonly associated with Terminal Archaic (or “post-laurentian” Archaic [4500–3000 B.P.]) occupations, but this study demonstrates that such an association can be misleading. The results of the physical and chemical analyses presented here also indicate that Mont Royal, a small hill located in the city of Montreal, is the most probable source of hornfels used in prehistoric times. Outcrops of hornfels exist on some other Monteregian Hills, but to this day there are no archaeological indications that they were exploited by aboriginal groups.
ENGLISH: Hornfels is a lithic material frequently discovered on prehistoric sites in southern Quebec. It is commonly associated with Terminal Archaic (or “post-laurentian” Archaic [4500–3000 B.P.]) occupations, but this study demonstrates that such an association can be misleading. The results of the physical and chemical analyses presented here also indicate that Mont Royal, a small hill located in the city of Montreal, is the most probable source of hornfels used in prehistoric times. Outcrops of hornfels exist on some other Monteregian Hills, but to this day there are no archaeological indications that they were exploited by aboriginal groups.