TY - JOUR
T1 - Late Mesoproterozoic Deformation of SW Amazonia (Rondônia, Brazil) : Geochronological and Structural Evidence for Collision with Southern Laurentia
AU - Tohver, Eric
AU - Van Der Pluijm, B.A.
AU - Scandolara, J.E.
AU - Essene, E.J.
PY - 2005
Y1 - 2005
N2 - Proposed assembly of the Rodinia supercontinent in the late Mesoproterozoic involved the collision of the Amazon craton with some portion of the southern or eastern margin of cratonic North America. Previously reported paleomagnetic data from the SW Amazon craton suggest a paleogeographic link between “Grenvillian” deformation of the SW Amazon craton and late Mesoproterozoic tectonometamorphism in southern Laurentia. A structural, geochronological, and petrological investigation of the western Amazon basement rocks (Rondônia, Brazil) was carried out in order to document evidence of a Grenvillian collision connecting the Amazon to Laurentia. Integration of 40Ar/39Ar data and feldspar thermometry data from regionally extensive strike‐slip mylonitic shear zones (Ji‐Paraná shear zone network) indicates that deformation took place at 450°–550°C between 1.18 and 1.15 Ga. An older, ca. 1.35‐Ga event found exclusively in less‐deformed basement rocks is interpreted as recording cooling from an earlier metamorphic episode (650°–800°C indicated by feldspar thermometry) unrelated to the Grenville collision. The style of deformation in the SW Amazon craton contrasts with that observed in southern Laurentia, where extensive crustal thickening accommodated by deep‐seated thrust sheets resulted in widespread thermal resetting of isotopic systems during exhumation and postorogenic cooling. In contrast, the predominantly strike‐slip activity observed in the Amazon resulted in age resetting through strain‐induced recrystallization, not regional‐scale thermal resetting. Consequently, the ages recorded by hornblende in the SW Amazon craton are slightly older than the cooling ages preserved in southern Laurentia. Differences in structural style and geochronological record are interpreted as indicative of an exhumed, asymmetric crustal structure similar to that of modern orogens.
AB - Proposed assembly of the Rodinia supercontinent in the late Mesoproterozoic involved the collision of the Amazon craton with some portion of the southern or eastern margin of cratonic North America. Previously reported paleomagnetic data from the SW Amazon craton suggest a paleogeographic link between “Grenvillian” deformation of the SW Amazon craton and late Mesoproterozoic tectonometamorphism in southern Laurentia. A structural, geochronological, and petrological investigation of the western Amazon basement rocks (Rondônia, Brazil) was carried out in order to document evidence of a Grenvillian collision connecting the Amazon to Laurentia. Integration of 40Ar/39Ar data and feldspar thermometry data from regionally extensive strike‐slip mylonitic shear zones (Ji‐Paraná shear zone network) indicates that deformation took place at 450°–550°C between 1.18 and 1.15 Ga. An older, ca. 1.35‐Ga event found exclusively in less‐deformed basement rocks is interpreted as recording cooling from an earlier metamorphic episode (650°–800°C indicated by feldspar thermometry) unrelated to the Grenville collision. The style of deformation in the SW Amazon craton contrasts with that observed in southern Laurentia, where extensive crustal thickening accommodated by deep‐seated thrust sheets resulted in widespread thermal resetting of isotopic systems during exhumation and postorogenic cooling. In contrast, the predominantly strike‐slip activity observed in the Amazon resulted in age resetting through strain‐induced recrystallization, not regional‐scale thermal resetting. Consequently, the ages recorded by hornblende in the SW Amazon craton are slightly older than the cooling ages preserved in southern Laurentia. Differences in structural style and geochronological record are interpreted as indicative of an exhumed, asymmetric crustal structure similar to that of modern orogens.
U2 - 10.1086/428807
DO - 10.1086/428807
M3 - Article
VL - 113
SP - 309
EP - 323
JO - Journal of Geology
JF - Journal of Geology
SN - 0022-1376
IS - 3
ER -