Paleozoic and Mesozoic stratigraphic sequences in the Puerto Libertad area, NW Sonora, Mexico, are intruded by Laramide granitic plutons with dominantly alkaline affinity. We conducted a petrogenetic study of these bodies across a north-south 35 km long transect at oriented NW-SE which includes the Sierra Picú (SP), El Destierro (ED), Sierra Tordilla (ST) and Sierra Los Mochos (SLM). The intrusive bodies display abundant Mafic Microgranular Enclaves (MME) and are intruded by aplitic and pegmatitic dike swarms. U/Pb zircon dates of the intrusive rocks yield crystallization ages between 71.9 and 74.9 Ma. Granodioritic and mozogranitic rocks dominate the SP and ED, while syenogranitic rocks dominate the ST and SLM regions. In addition, these rocks show notable effects, by normal and listric faults which includes cataclastic rocks. Geothermobarometry data from amphiboles and plagioclase of the granodiorites suggest that the temperatures and pressures reached 711–740 °C and 1.67–2.43 kb. respectively, and were emplaced at depths between ∼5 and 6 km. Geochemically, this magmatism shows a relatively high silica content (56–75 wt%), values of Sr/Y = 29–50, La/Yb = 26–39, Sr up to 600 ppm and Ba up to 1400 ppm and depleted in highfield strength elements. Collectively these geochemical traits accentuate the adakite signature of these rocks. This work raises the current problems related to the petrogenetic and tectonic aspects for the generation of calc-alkaline and adakitic magmas while proposing ternary discrimination diagrams to aid in the discrimination from classic calk-alkaline, adakites and adakitic affinity magmatism.
Bibliographical noteFunding Information:
The authors extend special thanks to the following projects and institutions: (1) Vicerrectoría UNISON for geochronology founding; (2) We are thankful to James Hagadorn and patrons from the Denver Museum of Nature & Science for funding for EMPA; (3) CONACYT Project 180784 ″Geodynamic Evolution of the Proto-Gulf of California: Emphasis on the volcanic remains of the Miocene in Sonora, Mexico”/Dr. Jesus Roberto Vidal Solano for the financing of field work; and (4) Geology Department at UNISON and Igneous Petrology students who collaborate in fieldwork. (5) We are also thankful to K. Domanik for the EMPA support and Aimé Orcí Romero for the thin section fabrication at ERNO-UNAM. (6) Irene Pérez Casillas, Concepción Arredondo de la Rosa from CarMinLab are acknowledge for their help with zircon mineral separation and CL imagining. (7) We are thankful with the suggestions of four anonymous reviewers which greatly help to improve this manuscript.
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- Geochemical adakite signature
- Laramide continental arc
- Puerto libertad
- U–Pb zircon geochronology