U–Pb ages and tectonic significance of late Archean alkalic magmatism and nonmarine sedimentation: Timiskaming Group, southern Abitibi belt, Ontario

Abstract

The paper presents U-Pb ages for zircons of the calc-alkalic to alkalic igneous suite and associated alluvial-fluvial sedimentary rocks of the Timiskaming Group in the late Archean Abitibi greenstone belt, Superior Province. The Timiskaming Group rests unconformably on pre-2700 Ma komatiitic to calc-alkalic volcanic sequences and is the expression of the latest stages of magmatism and tectonism that shaped the greenstone belt. An age of 2685 ? 3 Ma for the Bidgood quartz porphyry, an age of about 2685-2682 Ma for a quartz-feldspar porphyry clast in a conglomerate, and ages ranging from 2686 to 2680 Ma for detrital zircons in sandstones appear to reflect an early stage in the development of the Timiskaming Group. The youngest detrital zircons in each of three sandstones at Timmins, Kirkland Lake, and south of Larder Lake define maximum ages of sedimentation at about 2679 Ma; the latter sandstone is cut by a porphyry dyke dated by titanite at 26772; Ma, identical to the 2677 * 2 Ma age for a volcanic agglomerate of the Bear Lake Formation north of Larder Lake. Similar ages have previously been reported for syenitic to granitic plutons of the region. The dominant period of Timiskaming sedimentation and magmatism was thus 2680-2677 Ma. Xenocrystic zircons found in a porphyry and a lamprophyre dyke have ages of 2750-2720 Ma, which correspond to the ages of the oldest units in the belt, predating the volumetrically dominant ca. 2700 Ma greenstone sequences. The presence of these xenocrysts and the onlapping of the Timiskaming Group on all earlier lithotectonic units of the southern Abitibi belt support the concept that the 2700 Ma ensimatic sequences were thrust onto older assemblages during a phase of compression that culminated with the generation of tonalite and granodiorite at about 2695-2688 Ma. Published geochemical data for the Timiskaming igneous suite, notably the enrichments in large-ion lithophile elements and light rare-earth elements and the relative depletion of Nb, Ta, and Ti compare with the characteristics of suites at modem convergent settings such as the Eolian and the Banda arcs and are consistent with generation of the melts from deep metasomatized mantle in the final stages of, or after cessation of, subduction. Late-and post-Timiskaming compression caused north-directed thrusting and folding. Turbiditic sedimentary units of the Larder Lake area which locally structurally overly the alluvial-fluvial sequence and were earlier thought to be part of the Timiskaming Group, appear to be older "flyschoid" sequences, possibly correlative with sedimentary rocks deposited in the Porcupine syncline at Timmins between 2700 and 2690 Ma. Nous prtsentons des Lges U-Pb sur zircons d'un cortbge de roches ignees, calco-alcalines a alcalines, et de roches stdimentaires alluviales-fluviales assocites du Groupe de Timiskaming dans la ceinture archtene de roches vertes de 1' Abitibi, province du lac Superieur. Le Groupe de Timiskaming repose en discordance sur des stquences de volcanites, komatiitiques a calcoalcaline...

Molecular evidence of Late Archean archaea and the presence of a subsurface hydrothermal biosphere

“…Additionally, four interbedded basalt flows were sampled to monitor postdepositional alteration and contamination. The Porcupine Assemblage is unconformably topped by fault-controlled, clastic sediments of the Timiskaming Sequence that range from 2,676 to 2,670 Ma (27). No other sedimentary units are known from this area.…”

Geological classification of Canadian gold deposits

“…The deposit is largely hosted by a steeply plunging composite stock of syenite, augite syenite, and syenite porphyry GSC 1999-016E, GSC 1999 intruding Timiskaming Group conglomerate, wacke, and Tracadie tuff. This sedimentary sequence, dated between 2680 ± 3 Ma and 2677 ± 3 Ma (Corfu et al, 1991) unconformably overlies mafic volcanic rocks of the Kinojevis Group which predate 2700 Ma. In the south, the deposit is separated from ultramafic and mafic flows of the Larder Lake Group, dated at 2705 ± 2 Ma (Corfu, 1993), by the Larder Lake-Cadillac fault zone (Fig.…”

Depositional Gaps in Abitibi Greenstone Belt Stratigraphy: A Key to Exploration for Syngenetic Mineralization

“…At South Porcupine, east of Timmins, the lower contact of the Timiskaming assemblage is a sharp erosional angular unconformity with the underlying Porcupine assemblage, with no evidence of subaerial weathering (Born, 1995). In the Timmins, Kirkland Lake, and Larder Lake area, the Timiskaming assemblage ranges in age from 2677 to 2670 Ma, based on U-Pb detrital and magmatic zircon age determinations (Corfu et al, 1991;Ayer et al, 2005). Conglomerates and alkaline volcanic rocks in the northern Abitibi greenstone belt, such as the Matagami Group and the Haüy Formation, were previously assigned to older episodes between 2715 to 2705 Ma (Mueller and Donaldson, 1992b).…”