首页 | 本学科首页   官方微博 | 高级检索  
     检索      


Advances in SHRIMP geochronology and their impact on understanding the tectonic and metallogenic evolution of southern Brazil
Authors:L A Hartmann  J A D Leite  L C Da Silva  M V D Remus  N J McNaughton  D I Groves
Institution:1. Instituto de Geociencias , Universidade Federal do Rio Grande do Sul , Av. Bento Goncalves, 9500, Porto Alegre, RS, 91500-000, Brazil E-mail: afraneo@if.ufrgs.br;2. Departamento de Recursos Minerais , Universidade Federal do Mato Grosso , Cuiaba, MT, 78080-000, Brazil;3. Geological Survey of Brazil (CPRM) , Rua Banco da Provincia, 105, Porto Alegre, RS, Brazil;4. Centre for Global Metallogeny, Department of Geology and Geophysics , University of Western Australia , Nedlands, WA, 6907, Australia
Abstract:Significant improvements, both in understanding the evolution of zircons and in understanding the geotectonic and metallogenetic evolution of the complex terrain of southern Brazil, are obtained from a SHRIMP geochronology study and reviewed in this paper. The use of backscattered electron and cathodoluminescence images, prior to SHRIMP isotopic determinations, proved of enormous fundamental value for this technique. Zircon is a domainal open‐system mineral in many geological conditions; very old domains may be preserved, but the same crystal may show ages of younger tectonic events. Zircons may recrystallise inwards from the rims or outwards from the cores, and also along euhedral high‐U or metamict thin zones. Zircons also may be recrystallised during gold‐related hydrothermalism, phyllic alteration of granitic rocks. The precise dating of amphibolite dykes can be achieved by the identification and dating of magmatic zircons. Precambrian orogenies are identified along with the intervening intracratonic tectonic cycles of supercontinents in southern Brazil from 3300 to 470 Ma. Granulite protoliths were formed during the Jequié Orogeny (ca 2600 Ma), but extensive arc accretion occurred in the Palaeoproterozoic (ca 2250 Ma) Encantadas Orogeny. Late in the Transamazonian Cycle, granites were formed by crustal melting at about 2000 Ma in the Camboriú Orogeny. Both accretionary and collisional orogenies are also identified in the Neoproterozoic Brasiliano Cycle. These are the accretionary Passinho Orogeny (ca 900 Ma) and São Gabriel Orogeny (ca 700 Ma), that were succeeded by the collisional Dom Feliciano Orogeny (ca 600 Ma). Base‐metal and gold deposition occurred in juvenile island arcs and in late orogenic porphyry‐copper‐type magmatic‐hydrothermal settings during the Neoproterozoic.
Keywords:base metals  Brasiliano Cycle  geotectonics  gold  orogeny  SHRIMP  Transamazonian Cycle  zircon dating
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号