The Peltetec ophiolitic belt (Ecuador): a window to the tectonic evolution of the Triassic margin of western Gondwana

Exhumed Serpentinites and Their Tectonic Significance in Non‐Collisional Orogens

“…In contrast, peak metamorphic ages for the Agoyán (∼235 Ma), Cuyuja (∼135 Ma), and potentially Upano unit (Late Cretaceous‐Paleocene) argue for at least three events. Additionally, new radiometric data in the Peltetec ophiolitic belt yielded a zircon U‐Pb crystallization age of ∼228 Ma, different from the c. 135 Ma (Ar‐Ar on plagioclase) initially proposed for this possible suture zone (Spikings et al., 2015; Villares et al., 2021).…”

“…The large abundance of mafic volcanic sequences with arc or ophiolitic affinities was the main argument for the collisional model (Litherland et al., 1994). However, Triassic mafic rocks in Ecuador and Colombia (e.g., Piedras, Peltetec, Monte Olivo, Santa Elena, Aburrá) have been linked to widespread peraluminous granites and migmatites (e.g., Moromoro, Sabanillas, Tres Lagunas, Cajamarca) formed from slab breakoff/crustal thinning and anatexis in the Ecuadorian Amotape block, or trench retreat and slab rollback in the Cordillera Real domain during eastward migration of South America caused by rifting during the Pangea continental break up (Cochrane et al., 2014a; Riel et al., 2013; Villares et al., 2021). In the northern Colombian Andes, serpentinites within the Medellín metaharzburguitic unit have been associated with the Triassic Aburrá ophiolite and interpreted as a fragment of oceanic lithospheric mantle formed at a back‐arc basin (Garcia‐Casco et al., 2020; Ibañez‐Mejia et al., 2020).…”

“…This location is adjacent to the northern section of the Peltetec fault. In the central segment of this major structural feature, serpentinites occur in the Guarguallá River valley (Figure 2) between the Triassic Peltetec ophiolitic belt and the recently described Precambrian-Cambrian Guarguallá mafic-ultramafic unit (Spikings et al, 2021;Villares et al, 2021). Additionally, the boron isotopic signature of the two analyzed serpentinites yields similar results, with an δ 11 B range between ∼ 4.5 and +1.9‰ (Figure 8), resembling serpentinites from ophiolitic slivers within the northern section of the Guatemala Suture Zone (GSZ) (Martin et al, 2023).…”

“…Additionally, in the slab rollback scenario, the relative divergence between the downgoing slab and the upper plate can create the space or reduce the downgoing shear stress and enhance exhumation in the forearc (Brun & Faccenna, 2008). The back-arc tectonic scenario suggested for the Peltetec ophiolitic belt (Villares et al, 2021) can also be extended to other Triassic mafic-ultramafic complexes within the Cordillera Real (Zumba, Monte Olivo). In this context, the Quebrada Soledad serpentinites and the Agoyán metapelites should represent exhumed slivers along the forearc.…”

“…The southernmost sliver occurs near the locality of Zumba, where serpentinites are associated with pyroxenites and gabbros, likely of Triassic age (Litherland et al., 1994). In the central Cordillera Real, a serpentinite sliver is sandwiched between Precambrian‐Cambrian metagabbros and Triassic metabasalt and metasedimentary sequences defined as the Guarguallá unit and the Peltetec ophiolitic belt, respectively (Spikings et al., 2021; Villares et al., 2021). Further north, two serpentinite slivers were described by Litherland et al.…”