Provenance of the Upper Triassic Silves Sandstones of the Algarve Basin (Portugal) based on U-Pb detrital zircon and apatite data
Four samples from the Upper Triassic Silves Sandstones of the Algarve Basin were collected for U-Pb detrital apatite and zircon dating. The basin is bisected by the São Marcos da Serra-Quarteira Fault (SMSQF). Sample TL1 is located in the western part of the basin whereas samples CM2, SC1 and QR1 are located in the eastern part of the basin.
U-Pb detrital zircons analyses were undertaken on sample CM2. Two populations are evident: one within a 204-633 Ma age interval, with peaks at 269, 435 and 577 Ma while the older population shows a broad range of detrital zircon ages with peaks at 920 and 1666 Ma. The Permian zircons correspond to 15% (13 grains) of all zircons analysed. Sample TL1 yielded a well defined zircon population in the 308-322 Ma age interval (34 grains) with a peak at 312 Ma. The remaining zircons yielded ages older than 322 Ma, with minor peaks at 585 and 969 Ma. Permian ages are absent in this sample.
Six apatite grains were analysed in sample CM2, giving a mean 207Pb-corrected age of 371±82 Ma. Eight apatite grains from sample SC1 gave a mean 207Pb-corrected age of 315±18 Ma. In sample QR1 six apatite grains yielding 207Pb-corrected ages ranging from 214 to 518 Ma. In Sample TL1 twenty-six grains were analysed, yielding 207Pb-corrected ages ranging from 277 to 910 Ma.
The detrital apatite and zircon U-Pb data indicate multiple sources. Since apatites are unlikely to survive more than one sedimentary cycle, rocks ranging from Cambrian to Permian age were exposed and contribute to the Silves Sandstone basin located in the eastern part of the Algarve basin. This is also supported by the detrital zircon age data. The SMSQF may have acted as a drainage basin divide, due to the lack of Permian detrital zircon ages west of this fault and the presence of both zircon and apatites of Precambrian age.
AAPG Datapages/Search and Discovery Article #90226 © 2015 European Regional Conference and Exhibition, Lisbon, Portugal, May 18-19, 2015