Quaternary low-temperature serpentinization and carbonation in the New Caledonia ophiolite.

The low-temperature alteration (< 150 °C) of ophiolites by infiltrated meteoric waters removes atmospheric CO2 through mineral carbonation and is assumed to generate H2 and possibly CH4 according to so-called serpentinization reactions. This overall alteration pattern is primarily constrained by the chemical composition of alkaline springs that are issued in several ophiolites worldwide. Here we report on the fingerprint, as veinlet mineralization, of the reactive percolation of such meteoric waters in the New Caledonia ophiolite (Massif du Sud). The mineralization which resulted from carbonation and serpentinization reactions, is young (< 2 Ma) and formed at a temperature of ca. 95 °C. It is mainly composed of lizardite, dolomite, magnetite ± pyroaurite. Thermochemical simulation of mineral-water equilibria shows that the percolating aqueous fluid was alkaline and H2 bearing. The δ13C of dolomite is exceptionally high, between 7.1 and up to 17.3‰, and is interpreted as evidence of low-temperature methanogenesis. Overall, the percolating fluid had a chemical composition similar to that of the waters issued today in the (hyper)alkaline springs of the Massif du Sud. The studied veinlets are thus interpreted as a sample of the plumbing system that fed an ancient Quaternary alkaline spring in the area.

First Apatite (U-Th)/He and apatite fission-track thermochronology dataset from the Abancay Deflection (Eastern Cordillera, Southern Peru).

According to their respective temperature sensitivities, Apatite (U-Th)/He (AHe) and apatite fission-track (AFT) thermochronology records the thermal evolution of the upper crust (<5 km) and is a key for distinguishing between different exhumation mechanisms through time-evolving rock uplift, and landscape evolution. We applied these methods to extract the thermal evolution of the upper crust in the Abancay Deflection at the northern edge of the Altiplano (southern Peru). We present 120 single-crystal AHe ages (from 31 samples) and 27 AFT central ages obtained from magmatic bodies across the study area. AHe ages range from 0.6 ± 0.1 to 35.8 ± 2.9 Ma with a satisfactory reproducibility of single-crystal AHe ages with less than 10% averaged dispersion. AFT ages range from 2.6 ± 1.9 to 38.2 ± 4.4 Ma with P( χ 2) values >5%. This dataset allows exploring the crust evolution from the late-Eocene to the Quaternary. Data processed and interpreted in the related article published in Tectonics[6] are stored in PANGAEA repository (108 AHe single-grain ages and 27 AFT ages). We furthermore present in this article 12 extra single-grain AHe ages obtained after the related article publication. We also present the details of fission-track length measurements published in the related article. Thermochronological ages could be reused for testing He diffusion or fission track annealing processes or investigating the broader tectonic/geodynamic evolution of the Andes.