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Crustal evolution of South American Platform based on Sm-Nd isotope geochemistry; Evolucao crustal da plataforma sul americana com base na geoquimica isotopica Sm-Nd

Abstract

Sm-Nd isotopic systematics is relevant to the topics of origin and evolution the of continental crust, where model ages refer to the time when crustal material was differentiated from the upper mantle. Alternative interpretations are due to a lack of adequate information on crustal processes and the variable composition of the mantle sources. The Sm-Nd methods are presented, and applied on rock materials from the South American Platform. The main conclusions indicate juvenile accretion with higher growth rates (peaks), around 3.7-3.5 Ga ({approx} 0.5% in volume), 3.1 - 2.9 Ga ({approx}16%), 2.7 - 2.6 ({approx} 9%), 2.2 - 1.9 (35%) and 1.3-1.0 (7%). The continental growth curve indicates that about 35 % of the crust was formed by 2.5 Ga, 88% by 1.8 Ga and 99% by 1.0 Ga, and the remaining {approx} 1 % was added in the Phanerozoic. Rapid crustal growth occurred between 2.2 and 1.9 Ga. The main period of continental crust formation occurred during the Paleoproterozoic, corresponding to 54 % in volume. Sm-Nd model ages, when compared with the crystallisation ages of granitoid rocks, furnish a rough estimate of juvenile vs. reworked material. Within the South American Platform about 45% of juvenile continental crust is still  More>>
Authors:
Publication Date:
Jul 01, 1998
Product Type:
Thesis/Dissertation
Report Number:
INIS-BR-4077
Resource Relation:
Other Information: TH: Tese (Ph.D.); refs., 146 figs., 58 tabs
Subject:
37 INORGANIC, ORGANIC, PHYSICAL AND ANALYTICAL CHEMISTRY; CONTINENTAL CRUST; EXPERIMENTAL DATA; GEOCHEMISTRY; GEOLOGIC AGES; ISOTOPE DATING; ISOTOPE RATIO; NEODYMIUM ISOTOPES; SAMARIUM ISOTOPES; SOUTH AMERICA
OSTI ID:
20799208
Research Organizations:
Sao Paulo Univ., SP (Brazil). Inst. de Geociencias
Country of Origin:
Brazil
Language:
Portuguese
Other Identifying Numbers:
TRN: BR0645713101368
Availability:
Available from INIS in electronic form
Submitting Site:
BRN
Size:
315 pages
Announcement Date:
Dec 22, 2006

Citation Formats

Sato, Kei. Crustal evolution of South American Platform based on Sm-Nd isotope geochemistry; Evolucao crustal da plataforma sul americana com base na geoquimica isotopica Sm-Nd. Brazil: N. p., 1998. Web.
Sato, Kei. Crustal evolution of South American Platform based on Sm-Nd isotope geochemistry; Evolucao crustal da plataforma sul americana com base na geoquimica isotopica Sm-Nd. Brazil.
Sato, Kei. 1998. "Crustal evolution of South American Platform based on Sm-Nd isotope geochemistry; Evolucao crustal da plataforma sul americana com base na geoquimica isotopica Sm-Nd." Brazil.
@misc{etde_20799208,
title = {Crustal evolution of South American Platform based on Sm-Nd isotope geochemistry; Evolucao crustal da plataforma sul americana com base na geoquimica isotopica Sm-Nd}
author = {Sato, Kei}
abstractNote = {Sm-Nd isotopic systematics is relevant to the topics of origin and evolution the of continental crust, where model ages refer to the time when crustal material was differentiated from the upper mantle. Alternative interpretations are due to a lack of adequate information on crustal processes and the variable composition of the mantle sources. The Sm-Nd methods are presented, and applied on rock materials from the South American Platform. The main conclusions indicate juvenile accretion with higher growth rates (peaks), around 3.7-3.5 Ga ({approx} 0.5% in volume), 3.1 - 2.9 Ga ({approx}16%), 2.7 - 2.6 ({approx} 9%), 2.2 - 1.9 (35%) and 1.3-1.0 (7%). The continental growth curve indicates that about 35 % of the crust was formed by 2.5 Ga, 88% by 1.8 Ga and 99% by 1.0 Ga, and the remaining {approx} 1 % was added in the Phanerozoic. Rapid crustal growth occurred between 2.2 and 1.9 Ga. The main period of continental crust formation occurred during the Paleoproterozoic, corresponding to 54 % in volume. Sm-Nd model ages, when compared with the crystallisation ages of granitoid rocks, furnish a rough estimate of juvenile vs. reworked material. Within the South American Platform about 45% of juvenile continental crust is still preserved within tectonic provinces of different ages. The remainder represents continental crust reworked in younger tectono-thermal events. In particular crustal reworking was predominating over juvenile accretion during Meso-Neoproterozoic. The Transbrasiliano Lineament is a megasuture, active in the Neoproterozoic, which separates a large northwestern mass, including the Amazonian and Sao Luis Cratons, from a southeastern mass, formed by a collage of cratonic fragments, of which the Sao Francisco and Rio de La Plata are the largest. The crustal evolutions of these two large continental masses are considered individually, and can be resumed following form: I - Old Archean rocks (>3.4 Ga) are found only within the south-eastern part (Gaviao Block, Contendas-Mirante Complex (Sao Francisco Craton) and Caldas Brandao Massif (Borborema Province); 2 - On both continental masses, crustal evolution between 3.0 and 1.7 Ga is very similar; 3 - During Meso and Neoproterozoic times, the northwestern mass (Amazonian and Sao Luis Cratons) remained virtually unaffected by tectono-orogenic events, while the southeastern mass is composed of smaller cratonic fragments, which later took part in the formation of two large supercontinents: Rodinia during the Mesoproterozoic, and Gondwana in the Neoproterozoic. (author)}
place = {Brazil}
year = {1998}
month = {Jul}
}