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UPb geochronology of Labradorian and later events in the Grenville Province, eastern Labrador

1996; Elsevier BV; Volume: 80; Issue: 3-4 Linguagem: Inglês

10.1016/s0301-9268(96)00017-4

1872-7433

Sandra L. Kamo, Hardolph A. Wasteneys, Charles F. Gower, T. E. Krogh,

High-pressure geophysics and materials

UPb dating of selected rock units in the Hawke River and Groswater Bay terranes of the Grenville Province in eastern Labrador has refined the timing of metamorphism and magmatism during the Labradorian Orogeny (1710-1620 Ma). In the northern part of the Hawke River terrane, a major migmatization event is confirmed between 1671+4−3 Ma for a tonalitic gneiss and a newly determined age of 1662 ± 3 Ma for a granite dyke that cross-cuts the migmatized fabric of its host. This event can be correlated with similar coeval activities in the Lake Melville terrane to the south and Labradorian thrusting at the Grenville front. In the Paradise metasedimentary gneiss belt, high-grade metamorphism has been dated in two localities: in pillowed mafic volcanic flows associated with the metasedimentary gneisses which produced new zircon growth at 1645 Ma in a garnet-amphibolite assemblage, and in pegmatitic melt pods hosted in high-grade pelitic gneiss at 1638+11−3 Ma. The time of this metamorphic event places a minimum depositional age on the supracrustal assemblage in the Paradise metasedimentary gneiss belt that conflicts with a previously reported age for sedimentation at ≤ 1627 Ma. The 1645 Ma metamorphic event was coeval with emplacement of a layered mafic intrusion (1644 ± 2 Ma) in the Groswater Bay terrane, a large granite body between the Groswater Bay terrane and the Hawke River terrane (1645+7−5 Ma), which is a minimum age for juxtaposition of the two terranes (but inferred from other data to be 1665 Ma), and leucogabbro from the White Bear Arm complex (≥ 1640 Ma), which is adjacent to the Paradise metasedimentary gneiss belt. The faulted contact between the White Bear Arm complex and the Paradise metasedimentary gneiss belt is intruded by the ∼100-km-long Paradise Arm pluton at 1639 ± 2 Ma, indicating contact between the two domains at this time. Pegmatitic phases in the White Bear Arm complex indicate later magmatism at 1629+3−2 Ma. Current geological models argue for accretion of terranes (never widely separated) at 1665 Ma followed by crustal thickening and uplift between 1645 and 1639 Ma. Deformation in the Hawke River terrane during the Pinwarian event (ca. 1500-1470 Ma) is suggested by complex data for monazite and baddeleyite from the White Bear Arm complex and from titanite data for rocks elsewhere in the Hawke River terrane. Grenvillian metamorphic effects are present in the region but do not appear to have had a major impact.