Evaluating Complex Magma Mixing via Polytopic Vector Analysis (PVA) in the Papagayo Tuff, Northern Costa Rica: Processes that Form Continental Crust

Abstract

Over the last forty years, research has revealed the importance of magma mixing as a trigger for volcanic eruptions, as well as its role in creating the diversity of magma compositions in arcs. Sensitive isotopic and microchemical techniques can reveal subtle evidence of magma mixing in igneous rocks, but more robust statistical techniques for bulk chemical data can help evaluate complex mixing relationships. Polytopic vector analysis (PVA) is a multivariate technique that can be used to evaluate suites of samples that are produced by mixing of two or more magma batches. The Papagayo Tuff of the Miocene-Pleistocene Bagaces Formation in northern Costa Rica is associated with a segment of the Central American Volcanic Arc. While this segment of the arc is located on oceanic plateau, recent (<8 Ma) ignimbrites bear the chemical signatures of upper continental crust, marking the transition from oceanic to continental crust. The Papagayo Tuff contains banded pumice fragments consistent with one or more episodes of mixing/mingling to produce a single volcanic deposit. The PVA solution for the sample set is consistent with observations from bulk chemistry, microchemistry and petrographic data from the rocks. However, without PVA, the unequivocal identification of the three end-member solution would not have been possible

Late Cenozoic tephrostratigraphy offshore the southern Central American Volcanic Arc: 1. Tephra ages and provenance

“…The <8–2.02 Ma old Bagaces Formation contains the Carbonal lava flow (8.05 ± 0.09 Ma), Alto Mirador Ignimbrite (4.87 ± 0.07 Ma), Lower Sandillal Ignimbrite (4.15 ± 0.02 Ma), Upper Sandillal Ignimbrite (4.1 ± 0.02 Ma), Pan de Azúcar Ignimbrite (3.64 ± 0.066 Ma), Abomal Fall (3.21 ± 0.06 Ma), Abomal Ignimbrite (2.97 ± 0.03 Ma), Río Colorado Ignimbrite (2.08 ± 0.01Ma), and Cañas Ignimbrite (2.06 ± 0.02 Ma). The Papagayo Tuff [ Szymanski et al ., ] (Papa correlation field in Figures e, g, h, S1, and S2), a welded ignimbrite with basal contact to the Carbonal lava flow (∼8 Ma; Figure ) [ Alvarado and Gans , ]), may correspond to the Río Colorado Ignimbrite.…”

“…[], Szymanski et al . [], and Stoppa []. See Figure 2 for tephra acronyms and MP = ignimbrite close to Meco Plantel Bagaces; UCanal and LCanal = upper and lower flow units of the Canal/Tenorio ignimbrite; LEI = La Ese Ignimbrites; Papa = Papagayo Tuff).…”

“…A number of Quaternary widespread, voluminous tephras, mostly ignimbrites, are known from Costa Rica (Figure ) [ Alvarado and Gans , ]. Prominent are the ∼0.6–1.6 Ma Liberia Formation and the ∼2 to ∼8 Ma Bagaces Formation, both dominantly composed of voluminous silicic ignimbrites that may be related to now mostly hidden older caldera structures (Cañas Dulces and Guayabo calderas) identified by geothermal drilling (Figure ) [ Vogel et al ., ; Alvarado and Gans , ; Chiesa , ; Zamora et al ., ; Szymanski et al ., ].…”

Magmatic consequences of the transition from orthogonal to oblique subduction in Panama

“…The amphibole crystals do not show evidence of breakdown rims and appear to grow synchronously with feldspar. The occurrence of both hydrous and anhydrous mafic phases is consistent with observations of modern ignimbrites further north in Costa Rica [ Vogel et al ., ; Deering et al ., ; Szymanski et al ., ].…”

“…Pumice clasts are well‐preserved in the Gatun deposits and can be gray or banded, which we interpret as mixing/mingling between the evolved high SiO 2 magma and more primitive mafic lavas [e.g., Hannah et al ., ; Szymanski et al ., ]. Most pumice is sparsely porphyritic and dominated by glass (Figure a).…”