Abstract

CERRON-SARCCO, John Franklin. Intrusive rocks of San Cristóbal, La Virgen, and Altillo Hills (Lima, Peru): petrogenetic processes and their local implications in the Coastal Batholith. Bol. cienc. tierra [online]. 2025, n.57, pp.7-21.  Epub Dec 11, 2025. ISSN 0120-3630.  https://doi.org/10.15446/rbct.n57.114144.

This study analyzed the petrogenetic processes and local implications of intrusive rocks in the San Cristóbal, La Virgen, and Altillo hills (Lima, Peru), belonging to the Patap and Santa Rosa Super Units. Geological mapping was conducted, along with the collection of 23 rock samples for petrographic, geochemical, and X-ray diffraction analysis. The results confirmed regional characteristics of igneous rocks, such as alkalinity, subduction environment, and magmatic arc type. Additionally, possible local processes were interpreted: (1) the Patap Super Unit, formed by oxidized magmatism in a low-energy environment, exhibited fractional crystallization, magma mixing, and pneumatolytic processes that produced xenoliths with phlogopite; (2) the Santa Rosa Super Unit, associated with reduced, high-energy magmatism, showed intense crustal assimilation, rapid crystal nucleation, and the release of hydrothermal fluids, which altered the rocks of the Patap Super Unit, forming actinolite, chlorite, epidote, and traces of pyrite.

Keywords : Coastal Batholith; X-ray diffraction; geochemistry; petrography; petrogenetic process; Patap Super Unit; Santa Rosa Super Unit.

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