%0 Journal Article
%A Morales Cámera, Matías M.
%A Dahlquist, Juan A.
%A Baldo, Edgardo G.
%A Alasino, Pablo H.
%A Moreno Moreno, Juan Antonio
%A Fuenlabrada Pérez, José Manuel
%A Basei, Miguel A.S.
%T Adakitic magmatism at the birth of the large Achala Intrusive Complex: Evidence of a thickened crust at the onset of Devonian foreland magmatism of SW Gondwana margin Author links open overlay panel
%D 2025
%@ 0024-4937
%U https://hdl.handle.net/20.500.14352/121280
%X The San Clemente satellite pluton (SCP), located on the eastern flank of the Achala Intrusive Complex (AIC) or Achala Batholith in southwestern Gondwana, represents a crucial record of Devonian foreland magmatism. This study integrates petrological and geochemical data, including whole-rock Sr–Nd and zircon Hf isotopes, as well as geochronological data (U–Pb in zircon and titanite), to constrain the petrogenesis of the SCP. The pluton consists of two main units: the San Clemente granodioritic unit (SCU) and the La Herradura monzogranitic unit (LHU), along with quartz-dioritic and tonalitic enclaves. Petrographic and field evidence suggest an incremental, east-to-west magmatic construction history, involving sequential and nearly synchronous emplacement of quartz-dioritic and tonalitic magmas, followed by the SCU and subsequently the LHU.U–Pb geochronological data indicate a protracted magmatic history for the satellite pluton and its enclaves, spanning from the Early to Middle Devonian. This activity is recorded in both antecrysts (∼404 Ma) and autocrysts (390–384 Ma), marking the onset of construction of the Achala Intrusive Complex. The presence of antecrysts points to early magmatic processes occurring in a deep crustal mush reservoir, whereas the autocryst ages reflect the development of a magma chamber at or near the final emplacement level.Petrological, geochemical, and isotopic data classify the SCU as High-SiO₂ Adakites (HSA) (SiO₂ = 68.7–70.7 %, K₂O/Na₂O = 0.4–0.6, A/CNK (molar percent Al2O3/[CaO + Na2O + K2O]) = 1.04–1.05, with high Sr/Y and LaN/YbN ratios, suggesting a source derived from the partial melting of a thickened mafic lower crust with limited input from the mantle (εNdt = −2.3 to −1.8; 87Sr/86Srt = 0.7047–0.7043; εHft = −9.0 to +2.2). The LHU exhibits hybrid compositions, combining peraluminous two-mica granites with adakitic affinities (SiO₂ = 71.9 %, K₂O/Na₂O = 1.12, ASI = 1.07, with high Sr/Y and LaN/YbN ratios), indicative of a dominant felsic crustal source with minor mafic contributions (εNdt = −4.6; 87Sr/86Srt = 0.7057; εHft = −12.0 to +2.2). The enclaves show geochemical affinities to primitive andesites and sanukitoids (SiO₂ = 56.1–57.4 %, MgO = 5.2–7.0 %, Mg# (molar percent 100 × MgO/(MgO+FeOt)) = 59–65, Cr = 124–151 ppm, Ni = 121–124 ppm, Ba = 235–1323 ppm, Sr = 501–753 ppm, Ce = 47–275 ppm), reflecting a metasomatized lithospheric mantle source with crustal contamination (εNdt = −2.8 to −3.0; 87Sr/86Srt = 0.7066–0.7091; εHft = −3.5 to +3.8).These findings indicate that the San Clemente pluton preserves key evidence that the formation of the AIC began with partial melting near the base of a thickened crust, followed by more extensive melting of the lower to middle crust, resulting in the formation of the voluminous, peraluminous A-type magmatism characteristic of the AIC.
%~