Late Cretaceous-Oligocene magmatic record in southern Mexico: The case for a temporal slab window along the evolving Caribbean-North America-Farallon triple boundary

Abstract

Continental magmatism in southern Mexico is expected to record the eastward displacement of the Farallon-North America-Caribbean triple junction. However, a trench-transversal belt of magmatism in the central western Guerrero State does not fit into a regular pattern of arc migration and reorientation following the formation of the WSW trending Acapulco trench in the Cenozoic. We revised the magmatic pattern of southern Mexico using an updated database and new laser ablation inductively coupled plasma-mass spectrometry sensitive high-resolution ion microprobe, Ar-Ar ages, and geochemical and geologic data for the coastal part of the anomalous Guerrero belt. Our data reveal a persistent magmatic activity between~75 and 35 Ma, with a changing character at the Paleocene-Eocene boundary (circa 56 Ma). Late Cretaceous-Paleocene granitoids have an adakitic signature imprinted by stable garnet in the source and show no plagioclase fractionation, indicative of wet and oxidized magmas. Eocene rocks consist of an almost bimodal suite of plutonic bodies covered by a succession of mafic lavas. Granitic plutons show plagioclase fractionation and flat middle rare earth element-heavy rare earth element; gabbros have a tholeiitic character, indicative of dryer and more reduced magmas. They appear later and were emplaced at shallow depth in an extensional sedimentary basin. We interpret the magmatic record of the Guerrero belt as the response to two concurrent processes: (1) a temporal window in the Farallon slab induced by the concurrent subduction along the two noncollinear trench segments of southern Mexico (WNW trending) and of the Chortís block (NNW trending) and (2) a scissor-like transtensional rifting associated to counterclockwise rotation and eastward motion of the Chortís block.

Thermal metamorphism of mantle chromites and the stability of noble-metal nanoparticles

“…Along the contact between ultramafic and mafic rocks, a lens-like body that containing troctolites and hornblende pegmatites have yielded 40 Ar/ 39 Ar ages of ~38 Ma, consistent with resetting due to the intrusion of the Eocene granites ( Fig. 1; Ferrari et al 2014).…”

Paleomagnetism and Geochronology of the Early Cretaceous Dipilto Batholith (NW Nicaragua): Chortís Block Large Rotation With Respect to SW North America

“…Penecontemporaneously, the convergent system of NW of Mexico (Baja California) was undergoing the Alisitos arc assembly and formation of an accretionary complex, as a result of the Farallon plate subduction below NAM (Alsleben et al, ; Boschman et al, ; Schmidt et al, ). On the other hand, the accretionary complex is absent it the southwestern part of Mexico (i.e., SW of the Guerrero Terrane) and was probably truncated by geodynamics of the Farallon‐Cocos‐NAM plates or the Chortís block (Ferrari et al, ; Schaaf et al, ).…”

Description of the Geology of the Tecolotlan Graben, Jalisco, Mexico

“…Age probability diagram for dated volcanic rocks in the Tepic-Zacoalco and Colima grabens. Data from Allan (1986), Moore et al (1994), Nieto-Samaniego et al (1999), Ferrari et al ( , 2013Ferrari et al ( , 2014, Frey et al (2004Frey et al ( , 2007, Centeno-García et al (2011), Valencia et al (2013, Duque-Trujillo et al (2015).…”

“…Ferrari et al (2014) showed that igneous rocks 93-70 Ma in western Mexico are virtually restricted to the Jalisco block; they relate the magmatism to subduction of the Farallon plate to the east beneath Mexico. The Cretaceous igneous suite of the Tecolotlan graben very similar to other Cretaceous to Paleogene magmatic rocks of Jalisco as compiled by Ferrari et al (2014). They are notably different than a Cretaceous to Paleocene suite of adakitic rocks found to the SE.…”

“…They have deeper Nb anomalies, lower concentrations of LREE and Y, positive Sr anomalies (even in the felsic rocks), and signifi cantly higher Sr/Y and La/Y ratios. Ferrari et al (2014) interpret these distinctive magmas to have formed when a tear and slab window developed and the basaltic/ eclogitic oceanic crust partially melted.…”