Geochemical constraints on the petrogenesis of Triassic alkaline basalts of Sierra de Valle Fértil, Western Sierras Pampeanas, Argentina: implications for their origin, evolution and tectonic setting

Triassic-Jurassic thermal evolution and exhumation of the western Gondwana foreland: Thermochronology and basalt thermobarometry from the Argentine Sierras Pampeanas

“…However, few differences are observed when considering a cutoff of MgO > 6 wt% (see Table SM3). The few reported olivine data (Castro et al, 2019), in turn, indicate that the Ni content is low, similar to the most evolved MORBs (cf., Sobolev et al, 2005), suggesting a peridotitic rather than a pyroxenitic mantle source for the selected mafic rocks. We assumed a H2O content of 0.5%, typical of alkaline magmas and consistent with the calculated Ne-normative mineralogy J o u r n a l P r e -p r o o f (Castro et al, 2019).…”

“…The few reported olivine data (Castro et al, 2019), in turn, indicate that the Ni content is low, similar to the most evolved MORBs (cf., Sobolev et al, 2005), suggesting a peridotitic rather than a pyroxenitic mantle source for the selected mafic rocks. We assumed a H2O content of 0.5%, typical of alkaline magmas and consistent with the calculated Ne-normative mineralogy J o u r n a l P r e -p r o o f (Castro et al, 2019). Before performing the thermobarometric calculations, the basalt compositions were corrected for olivine fractionation by 0.001% incremental addition of olivine until obtaining a Fo 90 olivine composition using an Fe-Mg olivine-melt partition coefficient of 0.3 and a Fe 3+ /Fe* ratio of 0.15.…”

“…We used the Si and Mg thermobarometer of Plank and Forsyth (2016) that, in addition, allowed us calculating the melting depth, which is a key parameter to understand the response of the lower part of the lithosphere to stretching and changes of lithospheric thickness. Geochemical data (Table SM3) are from the southernmost Ischigualasto basin in the Sierra de Valle Fertil (Castro et al, 2019;Fig 1a) and Cuyo basin (Orellano et al, 2019;Ramos and Kay, 1991 and our sample), located close to the Andean belt. Only samples with MgO > 7 wt% (or mg# [molar MgO/(MgO + FeO*) x 100] > 55) were used for modeling to avoid major clinopyroxene fractionation and crustal contamination (mg# is the Mg-number and FeO* is the total Fe).…”

“…According to geochemical compositions, the Triassic basalts of western Sierras Pampeanas are mantle derived without a strong influence of crustal contamination (Ramos and Kay, 1991;Castro et al, 2019). Such types of basalts provide a good record of the pressure and temperature conditions during mantle melting (Herzberg et al, 2007).…”

Gondwanan Inheritance on the Building of the Western Central Andes (Domeyko Range, Chile): Structural and Thermochronological Approach (U‐Pb and40Ar/39Ar)

“…Interestingly, a similar correlation to the Triassic paleotrench distance is observed in the geochemistry of the Triassic volcanism. Thus, purely intraplate alkaline affinities are recorded in basaltic rocks from the eastern portion of the Ischigualasto basin, (Castro de Machuca et al., 2019) whereas in the western margin of the Cuyo basin, alkaline to subalkaline basalts coexist with calc‐alkaline silicic volcanism (Orellano et al., 2019). The mixed affinity of the Cuyo basin volcanism has been explained as crustal assimilation during an intraplate rifting unrelated to subduction (Orellano et al., 2019).…”