TY - JOUR
T1 - U-Pb geochronology of felsic volcanic rocks hosted in the Gafo formation, South Portuguese zone
T2 - The relationship with Iberian pyrite belt magmatism
AU - Rosa, D.R.N.
AU - Finch, A.A.
AU - Andersen, T.
AU - Inverno, C.M.C.
PY - 2008/10
Y1 - 2008/10
N2 - Felsic volcanic rocks exposed in the Frasnian Gafo Formation, in the Azinhalinho area of Portugal, display very similar geochemical signatures to volcanic rocks from the Iberian Pyrite Belt (IPB), located immediately to the south. The similarities include anomalously low high field-strength elements (HFSE)concentrations, possibly caused by low-temperature crustal melting, which translate into classification problems. A geochronological study, using laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) analyses of zircon grains from these rocks, has provided concordia ages of 356±1.5 Ma and 355±2.5 Ma for two samples of rhyodacite porphyry, and 356±1.4 Ma for a granular rhyodacite. These results show that volcanism at Azinhalinho was broadly contemporaneous with IPB volcanism, widely interpreted as being of Famennian to Visean age. Considering that the host rocks of the Azinhalinho volcanic rocks are Frasnian, and therefore deposited synchronously with the Upper Devonian Phyllite-Quartzite Group sedimentation in the IPB basin, the radiometric ages imply that the Azinhalinho felsic rocks are intrusive and likely represent conduits or feeders to the volcanism of the IPB.
AB - Felsic volcanic rocks exposed in the Frasnian Gafo Formation, in the Azinhalinho area of Portugal, display very similar geochemical signatures to volcanic rocks from the Iberian Pyrite Belt (IPB), located immediately to the south. The similarities include anomalously low high field-strength elements (HFSE)concentrations, possibly caused by low-temperature crustal melting, which translate into classification problems. A geochronological study, using laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) analyses of zircon grains from these rocks, has provided concordia ages of 356±1.5 Ma and 355±2.5 Ma for two samples of rhyodacite porphyry, and 356±1.4 Ma for a granular rhyodacite. These results show that volcanism at Azinhalinho was broadly contemporaneous with IPB volcanism, widely interpreted as being of Famennian to Visean age. Considering that the host rocks of the Azinhalinho volcanic rocks are Frasnian, and therefore deposited synchronously with the Upper Devonian Phyllite-Quartzite Group sedimentation in the IPB basin, the radiometric ages imply that the Azinhalinho felsic rocks are intrusive and likely represent conduits or feeders to the volcanism of the IPB.
KW - Geochronology
KW - Iberian pyrite belt
KW - LA-ICP-MS
KW - U-Pb
KW - Zircon
UR - http://www.scopus.com/inward/record.url?scp=64549131744&partnerID=8YFLogxK
U2 - 10.1180/minmag.2008.072.5.1103
DO - 10.1180/minmag.2008.072.5.1103
M3 - Article
AN - SCOPUS:64549131744
VL - 72
SP - 1103
EP - 1118
JO - Mineralogical Magazine
JF - Mineralogical Magazine
SN - 0026-461X
IS - 5
ER -