The B isotopic signature of serpentine from obducted ophiolites: Mixing of fluids and tectonic implications

Exhumed Serpentinites and Their Tectonic Significance in Non‐Collisional Orogens

“…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). Thus, the Guachalá serpentinites most likely represent a northward extension of the ultramafic slivers along the Peltetec fault.…”

“…This may indicate that the different domains formed from successive fluids or that the minerals added to the domains shifted the B isotopic signature toward slightly positive values. These variable δ 11 B values have been documented on serpentinites from ophiolitic sequences, in which a mixture of seawater‐derived and subducted crust‐derived fluid is responsible for serpentinization (Lécuyer et al., 2002; Martin et al., 2016, 2023; Prigent et al., 2018). In the case of Aliso and Cosanga, overlapping antigorite δ 11 B values indicate serpentinization by similar metamorphic fluids, likely pointing to a common outcrop source.…”

“…However, in serpentinites with multiple serpentinization events, a whole-rock approach may not be suitable to discern potential differences in their isotopic signatures. In contrast, in-situ boron isotope studies (δ 11 B) allow to characterize each serpentine generation, providing insight into their origin and potential fluid mixing (Martin et al, 2015(Martin et al, , 2016(Martin et al, , 2020(Martin et al, , 2023. Boron, a highly fluid-mobile element (FME), with its two isotopes ( 10 B and 11 B) that have a large relative mass difference, is predicted to fractionate easily as a function of temperature, pH, phase partitioning, and potentially depth (Martin et al, 2020;Wunder et al, 2005).…”

“…In-situ boron isotope data of Cordillera Real serpentinites compared to published values in modern ocean basins, and exhumed terranes. Published data from C Boschi et al (2008Boschi et al ( , 2013,Harvey et al (2014),Lécuyer et al (2002),Martin et al (2016Martin et al ( , 2020Martin et al ( , 2023,Prigent et al (2018),Vils et al (2009), andYamada et al (2019)…”