期刊
INTERNATIONAL JOURNAL OF EARTH SCIENCES
卷 103, 期 5, 页码 1203-1218出版社
SPRINGER
DOI: 10.1007/s00531-013-0939-8
关键词
Whole-rock geochemistry; Sm-Nd and Rb-Sr isotopes; ID-TIMS zircon U-Pb geochronology; Early Cambrian granitoids; Ossa-Morena Zone; North Gondwana magmatism
资金
- IGME [348]
- Spanish Ministry of Education and Science [CGL2009-07073, CGL2008-03046/BTE]
- GONDWANA project by Fundacao para a Ciencia e Tecnologia Portugal [PTDC/CTE-GIX/110426/2009]
- GOLD project by Fundacao para a Ciencia e Tecnologia Portugal [PTDC/GEO-GEO/24462012]
- project IGCP (UNESCO-IUGS) [597]
- Fundação para a Ciência e a Tecnologia [PTDC/CTE-GIX/110426/2009] Funding Source: FCT
Two distinct Cambrian magmatic pulses are recognized in the Ossa-Morena Zone (SW Iberia): an early rift-(ER) and a main rift-related event. This Cambrian magmatism is related to intra-continental rifting of North Gondwana that is thought to have culminated in the opening of the Rheic Ocean in Lower Ordovician times. New data of whole-rock geochemistry (19 samples), Sm-Nd-Sr isotopes (4 samples) and ID-TIMS U-Pb zircon geochronology (1 sample) of the Early Cambrian ER plutonic rocks of the Ossa-Morena Zone are presented in this contribution. The ER granitoids (Barreiros, Barquete, Calera, Salvatierra de los Barros and Tablada granitoid Massifs) are mostly peraluminous granites. The Sm-Nd isotopic data show moderate negative epsilon Ndt values ranging from -3.5 to +0.1 and TDM ages greatly in excess of emplacement ages. Most ER granitoids are crustal melts. However, a subset of samples shows a transitional anorogenic alkaline tendency, together with more primitive isotopic signatures, documenting the participation of lower crust or mantle-derived sources and suggesting a local transient advanced stage of rifting. The Barreiros granitoid is intrusive into the Ediacaran basement of the Ossa-Morena Zone (S,rie Negra succession) and has yielded a crystallization age of 524.7 +/- A 0.8 Ma consistent with other ages of ER magmatic pulse. This age: (1) constrains the age of the metamorphism developed in the Ediacaran back-arc basins before the intrusion of granites and (2) defines the time of the transition from the Ediacaran convergent setting to the Lower Cambrian intra-continental rifting in North Gondwana.
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