期刊
INTERNATIONAL JOURNAL OF EARTH SCIENCES
卷 93, 期 5, 页码 860-885出版社
SPRINGER
DOI: 10.1007/s00531-004-0423-6
关键词
Cadomian; geochronology; Garnet-bearing diorite; geochemistry; Merida
Diorites and related rocks in the Merida area of northern Ossa-Morena (SW Iberia) are intrusive into Precambrian metavolcanic and metasedimentary sequences. Cumulate products from the H2O-rich magmas are amphibole-rich gabbros to hornblendites. Major and trace element compositions, including Sr and Nd isotope data, allow the definition of a calc-alkaline series likely formed in relation to an immature arc setting. Crystallization of the intrusives has been established between ca. 570 and 580 Ma by U-Pb dating of constituent zircons. Garnet growth in dioritic rocks reflects a tectono-thermal overprint dated by Sm-Nd internal isochrons at around 555 Ma. Older Sm-Nd and Lu-Hf results between ca. 593 and 637 Ma on the same rocks suggest an earlier stage of regional metamorphism within the arc environment. The northern Ossa-Morena composite batholith and related metamorphic units have been tectonized and dismembered in the course of subsequent low-grade events during final stages of the Cadomian orogeny and the Variscan cycle. The units studied represent a well preserved segment of the arc region that evolved in Neoproterozoic times along the western border of Gondwana to conform the Cadomian-Avalonian basement of the Hercynian realm.
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