What tectonic processes were operating in the Archean, and whether they were similar to the “modern-style” plate tectonics seen operating today, is a fundamental question about Archean geology. The Superior Province is the largest piece of preserved Archean crust on Earth. As such it provides an excellent opportunity to study Archean tectonic processes. Much work has been completed in the southern part of the Superior Province. A well-documented series of discrete, southward younging orogenies related to a series of northward dipping subduction zones, has been proposed for amalgamating this part of the Superior Province. The tectonic evolution in the northwestern Superior Province is much less constrained, and it is unclear if it is related to the series of subduction zones in the southern part of the Superior Province, or if it is related to an entirely different process. Such ideas need to be tested in order to develop a concise model for the Meso – and Neoarchean tectonic evolution of the northwestern Superior Province. To this end, a field mapping, U-Pb geochronology, Nd isotope, and lithogeochemistry study was undertaken in the Island Lake greenstone belt. This granite-greenstone belt is part of the northern margin of the North Caribou terrane, a larger reworked Mesoarchean crustal block located in the northwestern Superior Province. U-Pb TIMS zircon geochronology data shows that the Island Lake greenstone belt experienced a long and complex geological history that included the deposition of three distinct volcanic assemblages at ca. 2897 Ma, 2852 Ma, and 2744 Ma, as well as a younger clastic sedimentary group, the Island Lake group. All of these volcanic assemblages include felsic and mafic volcanic rocks, as well as a suite of contemporaneous plutonic rocks. The U-Pb data set shows that the Savage Island shear zone, a regional fault structure that transects the Island Lake greenstone belt, is not a terrane-bounding feature as correlative supracrustal assemblages are observed on both sides of it. The Nd isotope data shows that the volcanic assemblages and contemporaneous plutons have been variably contaminated by an older ca. 3.0 Ga crustal source. The mafic volcanic rocks in the assemblages have two distinct geochemical signatures, and show a pattern of decreasing crustal contamination with decreasing age. Together these data suggests that the Meso – and Neoarchean volcanic assemblages are part of an intact primary volcanic stratigraphy that were built on the same ca. 3.0 Ga basement and have autochthonous relationships with each other. This basement is the North Caribou terrane. The youngest sedimentary group in the belt, the Island Lake group, was deposited between 2712 Ma and 2699 Ma. It consists of “Timiskaming-type” sedimentary rocks, and is the youngest clastic sedimentary package in the belt. A detailed study of detrital zircons in units from the stratigraphic bottom to the top of the sedimentary group indicates an age pattern of detrital zircons that is most consistent with a scenario in which sediments were deposited in inter-diapiric basins created by diapirism and sagduction (i.e., vertical tectonic) processes. During the diapiric ascent of the felsic material, inter-diapiric basins were formed in the synclines between adjacent domes, into which sediments were deposited. U-Pb zircon TIMS geochronology identified two ages of deformation in the Island Lake greenstone belt. Two dykes that crosscut an older, D1 foliation place a minimum age of ca. 2723 Ma on the D1 deformation, and two syn-kinematic dykes date movement along two transpressional shear zones to 2700 Ma. Together all these data indicate that the tectonic evolution in the Island Lake greenstone belt and in the northwestern Superior Province took place in three main stages. The first two stages involved the generation of Meso – and Neoarchean volcanic assemblages and contemporaneous plutonic rocks due to southward dipping subduction under the North Caribou micro-continent. The third stage involved the deposition of late “Timiskaming-type” sediments during vertical tectonic processes in conjunction with horizontal tectonic movement along late transpressional shear zones at ca. 2.70 Ga. At the end of this process the North Superior superterrane was terminally docked to the North Caribou terrane along the North Kenyon fault. This study shows that while a version of horizontal or “modern” style plate tectonics were operating in the Archean, vertical tectonic processes were also occurring and that these processes operated synchronously in the Neoarchean.

What tectonic processes were operating in the Archean, and whether they were similar to the “modern-style” plate tectonics seen operating today, is a fundamental question about Archean geology. The Superior Province is the largest piece of preserved Archean crust on Earth. As such it provides an excellent opportunity to study Archean tectonic processes. Much work has been completed in the southern part of the Superior Province. A well-documented series of discrete, southward younging orogenies related to a series of northward dipping subduction zones, has been proposed for amalgamating this part of the Superior Province. The tectonic evolution in the northwestern Superior Province is much less constrained, and it is unclear if it is related to the series of subduction zones in the southern part of the Superior Province, or if it is related to an entirely different process. Such ideas need to be tested in order to develop a concise model for the Meso – and Neoarchean tectonic evolution of the northwestern Superior Province. To this end, a field mapping, U-Pb geochronology, Nd isotope, and lithogeochemistry study was undertaken in the Island Lake greenstone belt. This granite-greenstone belt is part of the northern margin of the North Caribou terrane, a larger reworked Mesoarchean crustal block located in the northwestern Superior Province. U-Pb TIMS zircon geochronology data shows that the Island Lake greenstone belt experienced a long and complex geological history that included the deposition of three distinct volcanic assemblages at ca. 2897 Ma, 2852 Ma, and 2744 Ma, as well as a younger clastic sedimentary group, the Island Lake group. All of these volcanic assemblages include felsic and mafic volcanic rocks, as well as a suite of contemporaneous plutonic rocks. The U-Pb data set shows that the Savage Island shear zone, a regional fault structure that transects the Island Lake greenstone belt, is not a terrane-bounding feature as correlative supracrustal assemblages are observed on both sides of it. The Nd isotope data shows that the volcanic assemblages and contemporaneous plutons have been variably contaminated by an older ca. 3.0 Ga crustal source. The mafic volcanic rocks in the assemblages have two distinct geochemical signatures, and show a pattern of decreasing crustal contamination with decreasing age. Together these data suggests that the Meso – and Neoarchean volcanic assemblages are part of an intact primary volcanic stratigraphy that were built on the same ca. 3.0 Ga basement and have autochthonous relationships with each other. This basement is the North Caribou terrane. The youngest sedimentary group in the belt, the Island Lake group, was deposited between 2712 Ma and 2699 Ma. It consists of “Timiskaming-type” sedimentary rocks, and is the youngest clastic sedimentary package in the belt. A detailed study of detrital zircons in units from the stratigraphic bottom to the top of the sedimentary group indicates an age pattern of detrital zircons that is most consistent with a scenario in which sediments were deposited in inter-diapiric basins created by diapirism and sagduction (i.e., vertical tectonic) processes. During the diapiric ascent of the felsic material, inter-diapiric basins were formed in the synclines between adjacent domes, into which sediments were deposited. U-Pb zircon TIMS geochronology identified two ages of deformation in the Island Lake greenstone belt. Two dykes that crosscut an older, D1 foliation place a minimum age of ca. 2723 Ma on the D1 deformation, and two syn-kinematic dykes date movement along two transpressional shear zones to 2700 Ma. Together all these data indicate that the tectonic evolution in the Island Lake greenstone belt and in the northwestern Superior Province took place in three main stages. The first two stages involved the generation of Meso – and Neoarchean volcanic assemblages and contemporaneous plutonic rocks due to southward dipping subduction under the North Caribou micro-continent. The third stage involved the deposition of late “Timiskaming-type” sediments during vertical tectonic processes in conjunction with horizontal tectonic movement along late transpressional shear zones at ca. 2.70 Ga. At the end of this process the North Superior superterrane was terminally docked to the North Caribou terrane along the North Kenyon fault. This study shows that while a version of horizontal or “modern” style plate tectonics were operating in the Archean, vertical tectonic processes were also occurring and that these processes operated synchronously in the Neoarchean.

The oldest dated rocks from the Acasta gneisses of the western Slave Province, Canada present an igneous age of ~4030 Ma. Following this the detrital zircons from the Jack Hills, Narryer Gneiss Terrane, Yilgarn Craton, Western Australia are identified as 4404 ±8 Ma. These discoveries suggest that crustal formation started as early as the Priscian Eon. Hitherto the Earth has gone through a series of interactions involving the atmosphere, hydrosphere, crust, mantle and core. However, only limited remnants of these early processes remain on the accessible crust due to extensive crustal reworking. The Southern Granulite Terrane (SGT) in the southern part of India represents the most extensive exposure of lower crustal granulite terranes in the world. This study mainly focuses on the characteristics of Archean (~2500 Ma) tectonics and nature of subsequent crustal growth, which led to the formation of Archean Nilgiri Block. Detailed fieldwork in this terrane and subsequent petrographic analysis revealed charnockites, hornblende-biotite gneiss, metagabbro/mafic granulite, websterite, amphibolite, Grt-Ky metasediment, metatuff and banded iron formation as the main rock types in this terrane. Field and petrographic results show a regional trend with garnet-orthopyroxene-biotite-quartz-plagioclase-K- feldspar bearing charnockites in the southern part which gets subsequently enriched in clinopyroxene that forms garnet-absent two pyroxene granulites consisting of orthopyroxene-clinopyroxene-quartz-plagioclase-K-feldspar towards the central part. Further north, metagabbro/mafic granulite is enriched in garnet-clinopyroxene-plagioclase assemblage. Websterite, amphibolite, metasediment, metatuff and banded iron formation are stacked and closely associated within this mafic belt in the north. The metagabbro represents peak P-T conditions of ~850°C and ~14kbar compared to the charnockites, which recorded a peak P-T of ~850°C and 9-10kbar. Petrographic results of oxide minerals show that the southern charnockitic part is abundant in rutile-ilmenite association represent reduced conditions compared to the oxidized magnetite-hematite-ilmenite associations in the mafic rocks. This oxidation trend is followed by pyrrhotite-chalcopyrite enriched southern charnockitic region that transforms to pyrite rich northern mafic belt. Ilmenite¬titanite association with no sulphides characterizes the hornblende-biotite gneiss in the entire Nilgiri Block. The geochemical variations of major, trace and rare earth elements show that the granulite-amphibolite grade felsic rocks evolved in an arc magmatic process leaving behind mafic magma, which later intruded into these rocks, in a subduction related arc magmatic process. The U-Pb LA-ICPMS and SHRIMP dating of charnockite, hornblende-biotite gneiss and met gabbros shows ca. 2550 Ma formation age and ca. 2450 Ma metamorphism in this terrane.