SHRIMP U–Pb geochronology and monazite EPMA chemical dating from the southeast Gawler Craton has constrained the timing of high-grade reworking of the Early Paleoproterozoic (ca 2450 Ma) Sleaford Complex during the Paleoproterozoic Kimban Orogeny. SHRIMP monazite geochronology from mylonitic and migmatitic high-strain zones that deform the ca 2450 Ma peraluminous granites indicates that they formed at 1725 ± 2 and 1721 ± 3 Ma. These are within error of EPMA monazite chemical ages of the same high-strain zones which range between 1736 and 1691 Ma. SHRIMP dating of titanite from peak metamorphic (1000 MPa at 730°C) mafic assemblages gives ages of 1712 ± 8 and 1708 ± 12 Ma. The post-peak evolution is constrained by partial to complete replacement of garnet–clinopyroxene-bearing mafic assemblages by hornblende–plagioclase symplectites, which record conditions of ∼600 MPa at 700°C, implying a steeply decompressional exhumation path. The timing of Paleoproterozoic reworking corresponds to widespread deformation along the eastern margin of the Gawler Craton and the development of the Kalinjala Shear Zone.
U‐Pb zircon geochronology and Nd isotope geochemistry have been used in the northwestern Yilgarn Craton region of Western Australia to map gneiss units of different ages and to provide a model for late Archean crustal evolution, despite the inherent difficulties of minimal exposure and variations in the appearance of units brought about by heterogeneous strain. The 3300–3730 Ma gneisses and intercalated metasedimentary units crop out in a ≤100 km wide tract, bounded on both sides by areas containing 2920–3000 Ma gneisses. Between 2750 and 2620 Ma, several generations of granitoids were emplaced throughout the region. Regardless of whether the granitoids intruded the 3300–3730 Ma or 2920–3000 Ma gneisses, modeling of their initial Nd isotopic compositions shows that they were most likely formed by partial melting of predominantly 2920–3000 Ma gneisses; only a minor input from early Archean sources is indicated for granitoids cutting the 3300–3730 Ma gneisses and intercalated metasediments. Some of the granitoids that intrude the 3300–3730 Ma gneisses contain 2920 Ma inherited zircons, supporting the Nd evidence that their source is dominated by 2920–3000 Ma gneisses. The 3300–3730 Ma gneisses are interpreted as belonging to an allochthonous terrain emplaced over a younger terrain comprising the 2920–3000 Ma gneisses. Subsequently, partial melting concentrated in the underlying 2920–3000 Ma terrain gave rise to the late Archean granitoids.
The East Greenland Caledonides occupy a crucial position in plate-tectonic reconstructions of the Late Mesoproterozoic to Early Neoproterozoic Grenville–Sveconorwegian belt. We present new field and isotopic data from the northern Stauning Alper which indicate that the 1050–930 Ma history of the area was characterized by deposition of extensive clastic sequences. Sources of detritus were dominated by rocks of Mesoproterozoic age, with only limited contributions from Archaean sources, suggesting deposition at a distance from the present Caledonian foreland. A Neoproterozoic granite (938±13 Ma) provides evidence for thermal perturbation at a time of extensional collapse and uplift recorded in NW Scotland, the Grenville Belt of Canada, Labrador and the Sveconorwegian of SW Sweden and southern Norway. Widespread anatexis in the northern Stauning Alper at c. 430–425 Ma resulted from both collisional melting and decompression melting on uplift contemporaneous with the early part of orogenic collapse of the Caledonian Fold Belt. Caledonian deformation was focused at the zone of most extensive granite emplacement. Isotopic evidence suggests that Caledonian granites, previously thought to be entirely post-kinematic, actually predate late Caledonian extension.
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