First Partial Melting Inversion Model for a Rift-Related Origin of the Sierra de Chichinautzin Volcanic Field, Central Mexican Volcanic Belt

Abstract

We present the geochemical and isotopic characteristics of Pleistocene to Holocene olivine-bearing mafic rocks from the Sierra de Chichinautzin (SCN) volcanic field, located in the central part of the Mexican Volcanic Belt (MVB). Some have geochemical characteristics of primary magmas, and their MORB-normalized patterns are similar to those displayed by extension-related mafic rocks. The SCN primary magmas show a limited range in 87 Sr/ 86 Sr (0.70348-0.70397; average (n = 7) = 0.70370 ± 0.00019), and 143 Nd/ 144 Nd (0.51279-0.51294; average (n = 6) = 0.51288 ± 0.00006).~New mineral and whole-rock chemical data allow estimation of eruption temperatures and assure the near-primary nature of the studied samples. Equilibrium temperatures for the primary magmas were in the range 1070-1150°C. Trace-element concentration data for near-primary magmas from the SCN are used to develop a partial melting inversion model, the first for any area of the MVB. The source composition calculated by this inversion method shows an enrichment in highly incompatible elements (e.g., [C La /C Yb ] n ~2.2), where [] n represents mande-normalized values), without a decou pling between LILE, REE, and HFSE. This relationship supports a rift-related origin for SCN volcanism. The calculated REE composition of the mantle source is comparable to that observed in mande xenoliths of central Mexico. Concentration ratios of incompatible elements have also been used to infer 7-16% as the approximate range in degree of partial melting of the mantle. These results reinforce the hypothesis that SCN mafic magmatism reflects partial melting of an enriched lithospheric mantle in an extensional tectonic setting, precluding participation of the subducted Cocos plate in the genesis of these magmas.

Continental Rift Setting for the Central Part of the Mexican Volcanic Belt: A Statistical Approach

“…In the C-MVB, in fact, seven different graben systems (Ajacuba, Pachuca, Zempoala, TlalliSanta Catarina, Chichinautzin-Izta-Malinche, Ciudad de México, and Acambay) have actually been mapped and documented [29,178]; most of these graben systems run approximately east-west, being sub-parallel to the MVB and are consistent with dominantly north-south extension. Extensional features and fault structures are not limited to the MVB, but they have been mapped throughout from the C-MVB to the Pacific coast [180,181].…”

“…Besides, the extensional tectonics in the western part of the MVB has played a significant role in the eruption of primitive magmas [35]. I, either alone [5,22,26,28,30,32,55,[69][70][71] or with colleagues [24,27,29,31,64,66,[182][183][184][185][186] published a series of papers on the MVB, involving major-and trace-elements and radiogenic isotopes. Some of them included petrogenetic modeling.…”

“…The geochemical data for some of them have been subjected to inverse modeling using the procedures proposed earlier [193][194][195][196][197][198][199]. Specifically, data from the Sierra de Chichinautzin in the C-MVB were modeled by [29]; these authors concluded that the primitive magmas represented partial melts from the underlying mantle without the involvement of the subducted slab. Later, I extended this work to the west-central to eastern MVB [32] and to the LTVF [13], ascertaining for these regions the same conclusion as that reached by us [29] for the Sierra de Chichinautzin.…”

“…For the sake of quantitative interpretation, this area was divided into two regions by arbitrarily setting a geographical limit for nearer to and farther away from the MAT. The prominent volcanic areas and structures corresponding to nearer the MAT (as arranged from west to east and from nearer to and farther from the MAT) were: Zitácuaro-Valle de Bravo [37][38][39][40]; Volcán Nevado de Toluca [41][42][43]; Tenango Volcanic Field [43,44]; Sierra de Chichinautzin and nearby areas [19,26,29,43,[45][46][47][48][49][50][51][52][53][54][55][56]; Valle de México [44,45,57]; Sierra Nevada and Río Frío [45,52,57]; Volcán Popocatépetl [45,[57][58][59][60][61][62][63]; and Volcán Iztaccíhuatl [45,49,52]. Similarly, the samples from areas farther from the MAT were taken from: Caldera de Amealco [64,65]; Volcán Zamorano [66]; Qu...…”

“…Although there is a consensus that the origin of the Guatemala to northwestern Costa Rica part of the CAVA is related to the subduction process [10][11][12], the origin of the MVB has been largely controversial [5], and a plethora of models have been proposed that vary from simple subduction relationship of the Cocos plate beneath the North American plate [7,[14][15][16][17][18][19], to the action of a mantle plume [20,21], to the ongoing rifting processes within the MVB [5,[22][23][24][25][26][27][28][29][30][31][32], and to hybrid or more complex tectonic models [33][34][35][36]. Therefore, given the complexity of the MVB more constraints are still required to eventually solve this controversy.…”