Evidence for 2.35 to 2.30 Ga juvenile crustal growth in the northwest Borborema Province, NE Brazil
Published:January 01, 2009
Ticiano J. S. Dos Santos, Allen H. Fetter, W. Randall Van Schmus, Peter C. Hackspacher, 2009. "Evidence for 2.35 to 2.30 Ga juvenile crustal growth in the northwest Borborema Province, NE Brazil", Palaeoproterozoic Supercontinents and Global Evolution, S. M. Reddy, R. Mazumder, D. A. D. Evans, A. S. Collins
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The c. 600 Ma Brasiliano Borborema Province of NE Brazil comprises a complex collage of Precambrian crustal blocks cut by a series of continental-scale shear zones. The predominant basement rocks in the province are 2.1–2.0 Ga Transamazonian gneisses of both juvenile and reworked nature. U–Pb zircon and Sm–Nd whole-rock studies of tonalite-trondhjemite-granodiorite basement gneisses in the NW Ceará or Médio Coreaú domain in the northwestern part of the Borborema Province indicate that this represents a continental fragment formed by 2.35–2.30 Ga juvenile crust. This block has no apparent genetic affinity with any other basement gneisses in the Borborema Province, and it does not represent the tectonized margin of the c. 2.1–2.0 Ga São Luis Craton to the NW. The petrological and geochemical characteristics, as well as the Nd-isotopic signatures of these gneisses, are consistent with their genesis in an island arc setting. This finding documents a period of crustal growth during a period of the Earth's history which is known for its tectonic quiescence and paucity of crust formation.
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Palaeoproterozoic Supercontinents and Global Evolution
The Palaeoproterozoic era (2500–1600 Ma) was a critical period of Earth history, with dynamic evolution from the deep planetary interior to its surface environment. Several lines of geological evidence suggest the existence of at least one pre-Rodinia supercontinent, named Nuna or Columbia, which formed near the end of Palaeoproterozoic time. Prior to this assembly, there may have been an older supercontinent (Kenorland) or perhaps only independently drifting supercratons. The tectonic records of amalgamation and dispersal of these ancient landmasses provide a framework that links processes of the deep Earth with those of its fluid envelope. The sixteen papers in this volume present reviews and new analytical data that span the geological record of Palaeoproterozoic Earth and provide a current picture of Palaeoproterozoic research. The volume provides a useful reference book for students and professional geoscientists interested in this important period of global evolution.