The transition from Pangea amalgamation to fragmentation: Constraints from detrital zircon geochronology on West Iberia paleogeography and sediment sources

Abstract

Detrital zircon U-Pb geochronology data from late Carboniferous to Triassic clastic sedimentary rocks in SW Iberia were used to investigate the regional paleogeography during the transition from Pangea amalgamation to breakup. The major U-Pb zircon age peaks are middle Devonian to Carboniferous (~390-300 Ma), CambrianOrdovician (~530-440 Ma), Cryogenian-Ediacaran (~750-540 Ma), Stenian-Tonian (~1.2-0.9 Ga) and Paleoproterozoic (~2.3-1.8 Ga). Rapid exhumation of Variscan crystalline rocks at the contact between the South Portuguese zone and Ossa Morena Zone, explains the abundance of late Paleozoic ages in the upper Carboniferous-lower Permian continental successions. The U-Pb zircon data constrain the maximum depositional age of the Santa Susana Basin to c. 304 Ma and the Viar Basin to c. 297 Ma. The Triassic sequences, despite being c. 100 Ma younger than the Variscan tectonothermal events, contain low proportions of late Paleozoic zircon. The major peaks in all zircon spectra closely resemble those found in the adjacent basement rocks, indicating small source areas, mainly located near the rift shoulders. Longer travelled fluvial systems are postulated for the eastern portions of the Algarve Basin, which was closer to the westward advancing Tethys Ocean than the rift basins of West Iberia. Sequences that contain significant proportions of~1.2-0.9 Ga zircon are probably recycled from post-collisional Carboniferous-Permian continental deposits that were more extensive than those found today.

Revisiting the Intermediate Sediment Repository Concept Applied to the Provenance of Zircon

“…The quantitative analysis presented in this study was based on a compilation of detrital zircon U-Pb ages from Holocene beach sands [16] and their potential metasedimentary and sedimentary sources [16,28,29,33,34,[39][40][41], as well as igneous zircon ages from Sines plutons [16,30]. LA-ICP-MS measurements, 90-110% concordant 206 Pb-238 U ages for grains younger than 1.0 Ga, and 207 Pb- 206 Pb ages for older grains [41] were used to compare the distinct populations of zircon U-Pb ages obtained.…”

“…LA-ICP-MS measurements, 90-110% concordant 206 Pb-238 U ages for grains younger than 1.0 Ga, and 207 Pb- 206 Pb ages for older grains [41] were used to compare the distinct populations of zircon U-Pb ages obtained. The geochronological methods are described in [16,28,29,34,39,40]. Table 1 presents a summary of the zircon U-Pb ages obtained.…”

“…Numbers in bold with a p-value > 0.05 indicate zircon populations or age groups that are not significantly different; D-values using error in the CDF are indicated by underlined values. [16,28,29,34,39,40]). Age intervals are based on LA-ICP-MS results with 90-110% concordance.…”

“…As for the provenance of Pliocene-Pleistocene siliciclastic rocks and Holocene beach sand, the MDS diagram suggests significant derivation from the erosion of Cretaceous syenites and Carboniferous and Triassic siliciclastic rocks, which are statistically distinguishable. [16,28,29,34,39,40]).…”

The Beni Bousera marbles, record of a Triassic-Early Jurassic hyperextended margin in the Alpujarrides-Sebtides units (Rif belt, Morocco)

“…Stenian-Tonian dates could reveal the erosion of primary sources such as the coeval NW-Gondwanian mafic intrusions (Ikenne et al, 2017) or, more likely, that of proximal secondary sources from the shoulder of the Triassic rift (cf. Dinis et al, 2018), such as Carboniferous metasediments of the Variscan belt of the Moroccan Meseta, which contain 1260-800…”