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The Compostela area is located in the western Trans‐Mexican Volcanic Belt, which consists of volcanic rocks that produced during the Pliocene to Recent volcanism. In this paper, we present petrography, whole‐rock major‐ and trace‐element concentrations, Ar–Ar ages, and Sr–Nd isotopic data of volcanic rocks from the Compostela area in the south of the city of Tepic, Nayarit, Mexico. These volcanic rocks are of intermediate composition and belong to the transitional series: basaltic trachyandesites [52.72–53.94 wt% SiO2; 0.69–2.53 wt% MgO] and subalkaline series: low‐Si [55.11–60.94 wt% SiO2; 0.79–2.74 wt% MgO] and high‐Si [61.60–62.71 wt% SiO2; 0.36–0.80 wt% MgO] andesites. The 40Ar/39Ar dating of two basaltic trachyandesites yields plateau ages of 1.05 ± 0.15 Ma and 1.07 ± 0.17 Ma and the andesites yielded a plateau age of 2.42 ± 0.36 Ma. These results indicate that the studied rocks were formed during the Pleistocene in two discrete episodes. The basaltic trachyandesites show enriched light rare earth elements patterns relative to high rare earth elements [(La/Yb)N = 5.81–8.07] with negligible Eu anomalies. The andesites display enriched large‐ion lithophile elements (Ba, K) with anomalies of Nb (Th/Ce) and Ti in the three groups identified in the subalkaline series. The basaltic trachyandesites appear in a tight cluster of initial 87Sr/86Sr ratios (0.703519–0.703882) as compared to the basaltic andesite 87Sr/86Sr (0.704073) and positive ɛNd(t) values of +5.6 to +3.4, respectively, indicating that the basaltic trachyandesites were derived from intermediate magmas from a shallow mantle source. Geochemical modelling reveals that both basaltic trachyandesite and andesite rocks were derived by a process of crystal fractionation accompanied by assimilation of crustal rocks at the lower or middle level. Geochemical ratios and multidimensional discrimination diagrams, combined with the cross‐section of the subduction zone indicates that basaltic trachyandesites were generated from a rift and/or Ocean Island Basalt‐type source, whereas andesites were generated from a slab‐derived source in a subduction environment. [ABSTRACT FROM AUTHOR]

The Mesa Virgen Calerilla (MVC) is located in the state of Zacatecas, Mexico. The most intense volcanism, which occurred during the Eocene, formed extensive ignimbrite deposits exposed in some parts as lava spills of rhyolitic (felsic) composition. This felsic volcanism may represent much of the MVC. This study describes whole‐rock geochemistry and mineralogy data from felsic volcanic rocks in the MVC to address their petrogenesis and tectonic setting. The MVC covers a compositional spectrum ranging from trachyte, dacite, to high‐silica rhyolite. The petrography and mineral assemblages indicate that the felsic rocks are composed of K‐feldspar (sanidine), quartz, plagioclase, and biotite. The felsic volcanic rocks have a composition of 64.08–78.17 wt% (SiO2)adj, 0.14–0.69 wt% (TiO2)adj, and 0.11–0.62 wt% (MgO)adj with 12–54 Mg number [Mg# = 100 × (Mg2+/[Mg2+ + Fe2+])]. These felsic volcanic rocks showed enrichment in light rare earth elements (LREE; [La/Sm]N = 3.80–7.19), and are depleted in heavy rare earth elements [HREE; (Tb/Yb)N ratios 0.35–1.84], along with negative Ba, Nb, Sr, P, Eu, and Ti anomalies. The geochemical characteristics and petrogenetic modelling indicate that felsic volcanic rocks are derived from partial melting process of an upper‐middle continental crust. The tectono‐magmatic model and multidimensional tectonic discrimination diagram indicate that an extensional‐related setting prevails for the MVC. [ABSTRACT FROM AUTHOR]

The Ahualulco Volcanic Complex (AVC) is situated in the north-central part of the San Luis Potosí Volcanic Field (SLPVF) that is found in the southern portion of the Mesa Central (MC). The Cúcamo, AVC is mainly composed of mafic and intermediate volcanic rocks. The present study focuses on understanding the evolution, origin, and magmatic processes and petrogenesis of mafic and intermediate rocks in the Cúcamo, AVC. The Quaternary mafic rocks have porphyritic textures with the mineral assemblage of olivine, and clinopyroxene. These volcanic rocks display high K calc-alkaline basaltic compositions with enrichment in light rare earth elements (LREEs) and incompatible elements. Geochemical modeling reveals that mafic magmas were derived through a partial melting process of a spinel lherzolite source at low degrees of melting (~2 to 15 %) in an extensional regime. The intermediate volcanic rocks show porphyritic and glomeroporphyritic textures with matrix formed by randomly oriented microlites. The main mineral assemblage consists of plagioclase, K-feldspar, and clinopyroxene. These volcanic rocks are characterized by calc-alkaline basaltic andesitic and andesite compositions with enrichment in light rare earth elements and incompatible elements. Geochemical modeling suggests that intermediate rocks were derived from high ratios of assimilation and fractional crystallization processes between mafic melts and continental crust in an extensional environment. [ABSTRACT FROM AUTHOR]

New major and trace element, and Sr, Nd and Pb isotope data for samples from the Volcán Tacaná, along with the published data from the Tacaná Volcanic Complex (TVC) and Chiapanecan Volcanic Belt (CVB), were used to better constrain the petrogenesis of the Pliocene to Holocene volcanism in southwestern Mexico. The TVC volcanic rocks sampled in this study were andesite, whereas the literature samples included, besides andesites, one subalkali basalt and a few dacites. The CVB housing the prominent El Chichón volcano, on the other hand, showed more alkalic magmatic products (trachyandesite and basaltic trachyandesite) but also included a few basalts and dacites. The enclaves and lithic fragments sampled from both TVC and CVB showed wide SiO 2 compositions similar to the volcanic products. The CVB rocks are more enriched in REE, LILE, and HFSE than the TVC. The combined data of volcanic rocks were evaluated through conventional multi-element diagrams as well as subduction- or crust-sensitive parameters. Although the TVC constitutes the northern end of the Central American Volcanic Arc (CAVA), some chemical differences were documented between them such as the TVC rocks have higher LILE, REE, HFSE, and combined ratio parameters. More importantly, the CVB seems to be significantly different from both TVC and CAVA as well as from other continental arcs such as higher LILE, REE, HFSE, and distinct isotopic signature, which may indicate that the origin of the CVB volcanism represents a direct action of the abundant strike-slip faults and extensional system prevalent in this area. Finally, the relationship of basic and evolved rocks from the CVB, especially on isotope-isotope diagrams, also suggests that the lower crust may have contributed to evolved magmas during the ascent of basic magmas through the crust. [ABSTRACT FROM AUTHOR]

The Pinos Volcanic Complex (PVC) is located in the San Luis Potosi Volcanic Field (SLPV) and southern region of the Mesa Central that includes Oligocene rhyolites and trachydacites. These felsic volcanic rocks are characterized by porphyritic textures with a main mineralogical arrangement of phenocrystals of quartz, potassium feldspar (sanidine), plagioclase and biotite embedded in a vitreous matrix with microcrystals of quartz. They display peraluminous, high-silica, alkaline (not peralkaline) composition, with flat heavy rare earth element concentrations and negative Eu anomalies values. They are enriched in large-ion lithophile elements (LILEs; Rb, Ba, K, Th, Ce) relative to highfield-strength elements (HFSE; Nb, Zr, P, Ti). Trace element ratios trend highlights variable degree of partial melting rather than the role of fractional crystallization. The petrogenetic modelling of trace elements reveal that the felsic volcanic rocks are consistent with their formation via partial melting of the middle/upper continental crust. Multi-dimensional tectonic discriminant diagrams and magmatic model indicate an extensional tectonic environment for the genesis of the felsic volcanic rocks. • The PVC is represented by mainly felsic volcanic rocks. • Partial melting of the middle-upper continental crust generated the felsic volcanic rocks. • Magmatic events occurred in the PVC during middle Oligocene in an extensional regime. [ABSTRACT FROM AUTHOR]

The southern part of the Mesa Central (MC) province, Mexico, is formed of several Cenozoic volcanic complexes. The Sierra de San Miguelito Complex (SSMC) is in the south-eastern part of the MC. The SSMC consists of: (1) mafic volcanic rocks of porphyritic texture and trachybasalt/basalt compositions; (2) intermediate volcanic rocks of porphyritic texture and basaltic-trachyandesite, basaltic andesite and andesite compositions; and (3) silicic volcanic rocks of porphyritic texture and rhyolite composition. New 40Ar/39Ar dating results, in combination with major- and trace-element data, and Sr-Nd-Pb isotope data, are used to investigate the petrogenesis and geodynamic evolution of SSMC. The 40Ar/39Ar radiometric age data constrains the magmatic events in the SSMC to between 34 and 21 Ma. Chondrite-normalized rare-earth element patterns are distinct for each volcanic succession; mafic and intermediate lavas have relatively flat light rare earth element (LREE) and large ion lithophile element (LILE) patterns, whereas the silicic volcanic rocks show enrichment in LREE and high field strength elements (HFSE). Within each volcanic phase, the total rare-earth element concentrations increase from mafic to silicic, and the size of the negative Eu anomalies progressively increase (Eu/Eu* from 0.02 to 1.04). The initial 87Sr/86Sr ratios are widely distributed (from 0.70344 to 0.71973) whereas the initial 143Nd/144Nd ratios are somewhat low and show a narrower range (0.51245 to 0.51287), indicating the mafic magmas derived from a slightly heterogeneous source. Geochemical modelling of the mafic volcanic rocks reveals two sources of magma: (1) a parental magmas generated from melting underlying lithospheric mantle; and (2) a second lithospheric melt contaminated by lower crust. Intermediate magmas evolved from assimilation and fractional crystallization (AFC) processes of both lithospheric melts, at shallower levels. The silicic volcanic rocks in the area, however, were probably derived from partial melting of sedimentary rocks within the upper–middle continental crust. New multidimensional tectonic discrimination diagrams, combined with the magmatic model, indicates that volcanic activities in the region were generated in an extensional environment. • The SSMC is represented by minor mafic and mainly intermediate and silicic rocks. • 40Ar/39Ar data show magmatic events occurred between 34 and 21 Ma in an extensional regime. • Partial melting of the lithospheric mantle generated the mafic volcanic rocks. • Intermediate rocks evolved through AFC processes of the lithospheric melts. [ABSTRACT FROM AUTHOR]

Paleogene−Neogene volcanic complexes are commonly found in the southern part of the Mesa Central province (MC), Mexico. The Sierra de San Miguelito Complex (SSMC) is located in the southeastern part of the MC and consists of two main phases of Oligocene and Miocene units as follows: (1) basaltic group of porphyritic texture of basalt/trachybasalt compositions; and (2) rhyolite-ignimbrite group of porphyritic texture of trachydacite/trachyte compositions. Chondrite-normalized rare-earth element patterns for the basaltic group display enrichment in light rare earth elements (LREE) and large ion lithophile elements (LILE), whereas the rhyolite-ignimbrite group shows enrichment in LREE and high field strength elements (HFSE). The Eu anomalies within the SSMC become progressively more negative from the basaltic group to the rhyolite-ignimbrite group (Eu/Eu* = 1.13 to 0.02) suggest upper crust (crustal contamination) participates during magma generation. Trace element modelling reveals that the basaltic group evolved through a mixing process between mafic and felsic end−members. In contrast, chondrite-normalized and multi-element models reveal that the rhyolite-ignimbrite group evolved by partial melting of the upper continental crust. New multi-dimensional discrimination diagrams along with the Nb–Ta anomalies reveal that the SSMC volcanic rocks were generated in an extensional environment. • The Sierra de San Miguelito Complex (SSMC) exposed during Oligocene–Miocene. • Basaltic group rocks are derived from mantle through crustal evolution. • Rhyolite–Ignimbrite group rocks evolved by partial melting of continental crust. • The SSMC volcanic rocks were generated in an extensional environment. [ABSTRACT FROM AUTHOR]