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| Titel: |
Geology and geochronology of the Balcooma area: Part of an early palaeozoic magmatic belt in North Queensland |
| Auteur: |
Withnall, I. W. Black, L. P. Harvey, K. J. |
| Verschenen in: |
Australian journal of earth sciences |
| Paginering: | Jaargang 38 (1991) nr. 1 pagina's 15-29 |
| Jaar: |
1991-02 |
| Inhoud: |
The Balcooma Metavolcanics, in the eastern part of the mainly Proterozoic Georgetown Province, consist mostly of felsic metavolcanic and metasedimentary rocks. They were intruded by small microgranite and granite plutons, and porphyry dykes and sills before being deformed. Amphibolite facies metamorphism accompanied D1 and D2. The Balcooma Mylonite Zone separates the Balcooma Metavolcanics from the Proterozoic Einasleigh Metamorphics to the west, but the type of movement is uncertain. The Balcooma Metavolcanics have been regarded as probably of Early Palaeozoic age, because of similar lithologies and mineralization (e.g. the Balcooma Cu-Zn-Pb deposit) to the Cambrian to Ordovician Seventy Mile Range Group near Charters Towers, but a Proterozoic age was not ruled out. New U-Pb isotopic data confirm the existence of Early Palaeozoic magmatism in the area. The data, obtained by ion-microprobe analysis of zircons from metaporphyry related to the Balcooma Metavolcanics, yield ages of 471 ± 4 Ma (206Pb/238U), 478 ± 5 Ma (207Pb/235U), and 507 ± 22 Ma (207Pb/206Pb). The age of 471 ± 4 Ma (Middle Ordovician) is somewhat younger than that of the Seventy Mile Range Group, whereas the older age (507 ± 22 Ma) is more consistent with a correlation. Other metavolcanic rocks in the eastern Georgetown Province are also probably Early Palaeozoic in age. Unmetamorphosed Early and Late Ordovician mafic to felsic volcanic rocks are present in the western part of the Broken River Province, immediately east of the Georgetown Province. These, together with the Balcooma Metavolcanics and Seventy Mile Range Group, suggest the existence of a magmatic belt along the cratonic margin in the northern part of the Tasman Orogen in the Early Palaeozoic. A Rb-Sr isochron age of 408 ± 6 Ma was obtained from metapelite in the Balcooma Metavolcanics, but its significance is uncertain. |
| Uitgever: |
Taylor & Francis |
| Bronbestand: |
Elektronische Wetenschappelijke Tijdschriften |
Details van artikel 3 van 10 gevonden artikelen
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