Abstract
Based on the LA-ICP-MS U-Pb zircon ages of four metamorphic samples, we discuss the geochronology and provenance of the Guadaiza nappe, an allochthonous unit that underlies the Ronda peridotites (Betic Cordilleras, Spain). The Guadaiza nappe is composed of Triassic marbles overlying a metapelitic sequence with schists and migmatites. Zircons from a quartzite interlayered with the marbles yield a maximum depositional age of ca. 289 Ma that supports the Triassic age. The idiomorphic morphology of these Paleozoic zircon crystals and the lack of late-Variscan metamorphism (ca. 300 Ma) supports a proximal source area, and suggests that the marbles were discordantly deposited over the metapelitic sequence, along the northern margin of the Alboran microplate. The zircon patterns from the metapelitic sequence mainly yield Paleoproterozoic (ca. 1.6–2.5 Ga), Tonian–Stenian (ca. 1000 Ma), Ediacaran–Cryogenian (ca. 600 Ma) and Paleozoic (ca. 500 Ma) age clusters. These results suggest provenance from areas within the triangle bound by the West African Craton, the Metasaharan Craton and the Hun Superterrane during the Paleotethys opening (Silurian–Devonian). A Silurian–Carboniferous deposition age for the schist protoliths is constrained by the youngest detrital zircon population (ca. 443 Ma) and the Variscan age of their migmatization by an additional peak of around 299 Ma in the migmatites.
Highlights
In the last decade, the technological improvement of the geochronological techniques (LA-ICP-MS, SHRIMP, SIMS, among others) and the facilities to acquire individual zircon data from sedimentary and metamorphic rocks, as the U-Pb age determination can supply the maximum depositional age or the tectonothermal events, means they have become the perfect geological tool to decipher the paleogeographic and geodynamic evolution of ancient terranes
It has been concluded that it conforms to a peri-Gondwanan terrane, e.g., [5–10], the scarcity of geochronological detrital zircon age data, the variable imprint of the Alpine tectonics that erased the vestiges of previous orogenic events, and, in other cases, the fact that the metamorphic rocks that form the basement have been dated as undifferentiated Paleozoic, makes its paleogeographic location still controversial
A more precise maximum depositional age of 443 ± 4 Ma can be obtained from the weighted average age that defines the youngest zircon population from four zircons of the metapelitic sequence, where the Variscan metamorphism would not lead to the spread of zircon recrystallization
Summary
The technological improvement of the geochronological techniques (LA-ICP-MS, SHRIMP, SIMS, among others) and the facilities to acquire individual zircon data from sedimentary and metamorphic rocks, as the U-Pb age determination can supply the maximum depositional age or the tectonothermal events, means they have become the perfect geological tool to decipher the paleogeographic and geodynamic evolution of ancient terranes. It has been concluded that it conforms to a peri-Gondwanan terrane, e.g., [5–10], the scarcity of geochronological detrital zircon age data, the variable imprint of the Alpine tectonics that erased the vestiges of previous orogenic events, and, in other cases, the fact that the metamorphic rocks that form the basement have been dated as undifferentiated Paleozoic, makes its paleogeographic location still controversial On this matter, some authors have suggested that during Cambrian and Ordovician times the Alboran microplate should be located in a central position of the Galatian Superterrane (formerly referred to as the Hun Superterrane, [5,11,12]), lying in between the Aquitaine and the intra-Alpine terranes [11,13]. Minerals 2022, 12, 325 other authors have suggested a westernmost starting localization of the Alboran microsuggested a westernmost starting localization of the Alboran microplate, in direct relaplate, inwith direct relationship with theIberian
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