After the subduction stopped at ca. 12.5 Ma off Baja California Peninsula, calc-alkaline volcanic... more After the subduction stopped at ca. 12.5 Ma off Baja California Peninsula, calc-alkaline volcanic activity vanished progressively, and the Comondú volcanic arc was replaced by a post-subduction diversified volcanism which derived from at least five distinct magmatic sources located beneath the Baja California Peninsula and the Gulf of California. New field data, 40K-40Ar datings and geochemical and petrological studies of
The data provided in this database were used to establish the temporality, composition and petrog... more The data provided in this database were used to establish the temporality, composition and petrogenetic aspects of the so-called Cretaceous-Eocene Mexican Magmatic Arc (CEMMA). This magmatic arc is continuous throughout western Mexico and its understanding is critical to elucidating the tectonics of southwestern North America. The data were carefully compiled from the literature, including published articles, thesis, internal reports from mining companies, and to a large extent come from unpublished information generated by the working group (CONACYT Research Grant 49528-F). Unreliable data in relation to the methodology used and those where the information was inconsistent were not included. The Cretaceous-Eocene Mexican Magmatic Arc: Conceptual framework from geochemical and geochronological data of plutonic rocks
The Arizpe sub-basin located in the northern part of the Rio Sonora basin is a Basin and Range ha... more The Arizpe sub-basin located in the northern part of the Rio Sonora basin is a Basin and Range half-graben that initiated during Late Oligocene time in north-central Sonora. Its ~2.1 km-thick, east- dipping volcanic and sedimentary fill assigned to the Baucarit Formation is divided, from base upwards, into the following informal members. The La Cieneguita member composed of interbedded conglomerate, siltstone and gypsum beds which unconformably overlay older Cenozoic volcanic rocks; the El Toro Muerto basalt composed of basalt flows, basalt breccia and subordinate conglomerate beds; the Arzipe conglomerate composed of three fining-upwards conglomerate sequences that interdigitates with flows of the Tierras Prietas basalt in its lower part and the Agua Caliente basalt in its upper part; the Bamori member is a coarsening-upward succession of siltstone, sandstone and conglomerate that unconformably overlies the Arizpe conglomerate and it is unconformably overlain by the sedimentary El ...
Abstract We present a study based on new and compiled geochronological and geochemical data to as... more Abstract We present a study based on new and compiled geochronological and geochemical data to assess the tectonomagmatic evolution of Mexico from the Late Cretaceous and Eocene (~90–40 Ma). review of the literature highlights the striking geological differences observed in southwestern US and Mexico and particularly south of the classical Laramide province. Current tectonic models for western Mexico indicate that the continental margin of Mexico was fully consolidated by ~90 Ma, with the final accretion of the Alisitos and Guerrero arc terranes. Since then, east-faced subduction with a regular lowering of the slab dip persisted up to ca. 40 Ma, when compression and calc-alkaline magmatism ceased along the entire Cordillera. The sustained magmatic arc activity along the herein defined “Cretaceous-Eocene Mexican Magmatic Arc” (CEMMA), leads us to recommend abandoning the use of the term “Laramide magmatism” in Mexico. We define the CEMMA as an arc that trends NW-SE along most of western Mexico, but scattered outcrops occur also in central and eastern Mexico. The CEMMA composition ranges from gabbro to alkali granite, but hornblende ± biotite granodiorites are by far the most abundant type of rocks. Coeval volcanic rocks have been deeply eroded, but andesite-dominated sequences are partially preserved in the eastern part of the arc, particularly below the Cenozoic volcanic rocks of the Sierra Madre Occidental. The geochemical database that we present include 729 samples and shows that the CEMMA formed in a typical continental magmatic arc environment (calc-alkaline–metaluminous signatures and #Mg’s Ta, Ti and P, coupled with positive anomalies of U, K and Pb. Initial values of 87Sr/86Sr and eNd range from 0.7031 to 0.7137 and from +6.2 to −8.3, respectively, suggesting mixing of variable proportions of crustal materials with the mantle-derived magmas. These elemental and isotopic features are typical of continental margin magmatic arcs. In this context, sustained generation of calc-alkaline magma under these conditions yielded outstanding conditions to form a diversity of metallic ores, particularly porphyry copper deposits, in the region of Arizona-New Mexico- Sonora, located just south of the classical Laramide province. Although the ages along the CEMMA can be roughly explained by partial melting of a metasomatized section of the mantle above the region of amphibole instability (~100 km), plutons with crystallization ages of ~90 Ma in eastern Sonora, and even more to the east in Durango and Zacatecas, are older than expected. We consider that these plutons were generated by more discrete magma pulses linked to the dehydration of the phlogopite deeper in the slab (~200 km).
Growing industrialization, including mining activity, dramatically increases environmental pollut... more Growing industrialization, including mining activity, dramatically increases environmental pollution. Exploitation of natural resources triggers landscape alteration, inputs of potentially toxic chemical elements to the environment and health diseases. In the case of mining activity, the measure of any associated environmental disturbance requires a geochemical background as a reference frame. Since in Mexico, there is a lack of this type of references in mining districts, the present study took a recent mining spill as an opportunity to establish the geochemical background of the upper Sonora river basin, which includes active and historical mining areas. The weighted average of elemental values was calculated using GIS tools. The data show that rocks have a similar geochemical behavior, which is characterized by pristine enrichment of Mn, Ca, P, Ba, Zn, As, Ag, Sb, W, Pb and Bi relative to the upper continental crust. Coefficients of variation values reveal that Sc, Y, Zr, Ce, Yb,...
After the subduction stopped at ca. 12.5 Ma off Baja California Peninsula, calc-alkaline volcanic... more After the subduction stopped at ca. 12.5 Ma off Baja California Peninsula, calc-alkaline volcanic activity vanished progressively, and the Comondú volcanic arc was replaced by a post-subduction diversified volcanism which derived from at least five distinct magmatic sources located beneath the Baja California Peninsula and the Gulf of California. New field data, 40K-40Ar datings and geochemical and petrological studies of
Five main petrologic and geochemical groups can be identified among the Middle to Late Miocene la... more Five main petrologic and geochemical groups can be identified among the Middle to Late Miocene lavas from the western part of Southern Baja California: calc-alkaline and K-rich andesites, adakites and associated niobium-rich basalts, tholeiitic basalts and basaltic andesites, magnesian andesites and basaltic andesites of adakitic affinity. These lavas, although spatially and temporally related, display very different geochemical signatures. Their trace
The Pacific margin of Baja California is one of the few examples of an active margin that evolved... more The Pacific margin of Baja California is one of the few examples of an active margin that evolved from a convergent margin (before 12 Ma) to a transform margin (12-5 Ma). The amount of motion along the transform zone, which mainly occurred along the Tosco-Abreojos fault, is still debated, as well as the time of the transfer of Baja California to the Pacific plate. During the FAMEX cruise (L'Atalante, April 2002), swath bathymetry data were acquired along the Baja California margin from 23N to 27N. Several seismic profiles were also collected across the margin, using 300 inch3 GI guns tuned in harmonic mode and a streamer with six 50m-long channels. The 10s pop-rate at a 10 knots speed allowed a 3-fold coverage with a record-length of 4s. One profile clearly evidence the flat top of the subducted slab that can be followed 20 km landward. The lower part of a large pre-Upper Miocene mass-wasting is missing from the paleo-trench fill, and there is no evidence for an accretionary pr...
el margen continental actuó como frontera transformante entre las placas Pacífi co y América del ... more el margen continental actuó como frontera transformante entre las placas Pacífi co y América del Norte. La zona de falla Tosco-Abreojos localizada a lo largo de dicho margen fue interpretada como el mejor candidato para acomodar este movimiento transformante antes del Plioceno. A principios del Plioceno la ruptura continental tierra adentro induce la
After the subduction stopped at ca. 12.5 Ma off Baja California Peninsula, calc-alkaline volcanic... more After the subduction stopped at ca. 12.5 Ma off Baja California Peninsula, calc-alkaline volcanic activity vanished progressively, and the Comondú volcanic arc was replaced by a post-subduction diversified volcanism which derived from at least five distinct magmatic sources located beneath the Baja California Peninsula and the Gulf of California. New field data, 40K-40Ar datings and geochemical and petrological studies of
The data provided in this database were used to establish the temporality, composition and petrog... more The data provided in this database were used to establish the temporality, composition and petrogenetic aspects of the so-called Cretaceous-Eocene Mexican Magmatic Arc (CEMMA). This magmatic arc is continuous throughout western Mexico and its understanding is critical to elucidating the tectonics of southwestern North America. The data were carefully compiled from the literature, including published articles, thesis, internal reports from mining companies, and to a large extent come from unpublished information generated by the working group (CONACYT Research Grant 49528-F). Unreliable data in relation to the methodology used and those where the information was inconsistent were not included. The Cretaceous-Eocene Mexican Magmatic Arc: Conceptual framework from geochemical and geochronological data of plutonic rocks
The Arizpe sub-basin located in the northern part of the Rio Sonora basin is a Basin and Range ha... more The Arizpe sub-basin located in the northern part of the Rio Sonora basin is a Basin and Range half-graben that initiated during Late Oligocene time in north-central Sonora. Its ~2.1 km-thick, east- dipping volcanic and sedimentary fill assigned to the Baucarit Formation is divided, from base upwards, into the following informal members. The La Cieneguita member composed of interbedded conglomerate, siltstone and gypsum beds which unconformably overlay older Cenozoic volcanic rocks; the El Toro Muerto basalt composed of basalt flows, basalt breccia and subordinate conglomerate beds; the Arzipe conglomerate composed of three fining-upwards conglomerate sequences that interdigitates with flows of the Tierras Prietas basalt in its lower part and the Agua Caliente basalt in its upper part; the Bamori member is a coarsening-upward succession of siltstone, sandstone and conglomerate that unconformably overlies the Arizpe conglomerate and it is unconformably overlain by the sedimentary El ...
Abstract We present a study based on new and compiled geochronological and geochemical data to as... more Abstract We present a study based on new and compiled geochronological and geochemical data to assess the tectonomagmatic evolution of Mexico from the Late Cretaceous and Eocene (~90–40 Ma). review of the literature highlights the striking geological differences observed in southwestern US and Mexico and particularly south of the classical Laramide province. Current tectonic models for western Mexico indicate that the continental margin of Mexico was fully consolidated by ~90 Ma, with the final accretion of the Alisitos and Guerrero arc terranes. Since then, east-faced subduction with a regular lowering of the slab dip persisted up to ca. 40 Ma, when compression and calc-alkaline magmatism ceased along the entire Cordillera. The sustained magmatic arc activity along the herein defined “Cretaceous-Eocene Mexican Magmatic Arc” (CEMMA), leads us to recommend abandoning the use of the term “Laramide magmatism” in Mexico. We define the CEMMA as an arc that trends NW-SE along most of western Mexico, but scattered outcrops occur also in central and eastern Mexico. The CEMMA composition ranges from gabbro to alkali granite, but hornblende ± biotite granodiorites are by far the most abundant type of rocks. Coeval volcanic rocks have been deeply eroded, but andesite-dominated sequences are partially preserved in the eastern part of the arc, particularly below the Cenozoic volcanic rocks of the Sierra Madre Occidental. The geochemical database that we present include 729 samples and shows that the CEMMA formed in a typical continental magmatic arc environment (calc-alkaline–metaluminous signatures and #Mg’s Ta, Ti and P, coupled with positive anomalies of U, K and Pb. Initial values of 87Sr/86Sr and eNd range from 0.7031 to 0.7137 and from +6.2 to −8.3, respectively, suggesting mixing of variable proportions of crustal materials with the mantle-derived magmas. These elemental and isotopic features are typical of continental margin magmatic arcs. In this context, sustained generation of calc-alkaline magma under these conditions yielded outstanding conditions to form a diversity of metallic ores, particularly porphyry copper deposits, in the region of Arizona-New Mexico- Sonora, located just south of the classical Laramide province. Although the ages along the CEMMA can be roughly explained by partial melting of a metasomatized section of the mantle above the region of amphibole instability (~100 km), plutons with crystallization ages of ~90 Ma in eastern Sonora, and even more to the east in Durango and Zacatecas, are older than expected. We consider that these plutons were generated by more discrete magma pulses linked to the dehydration of the phlogopite deeper in the slab (~200 km).
Growing industrialization, including mining activity, dramatically increases environmental pollut... more Growing industrialization, including mining activity, dramatically increases environmental pollution. Exploitation of natural resources triggers landscape alteration, inputs of potentially toxic chemical elements to the environment and health diseases. In the case of mining activity, the measure of any associated environmental disturbance requires a geochemical background as a reference frame. Since in Mexico, there is a lack of this type of references in mining districts, the present study took a recent mining spill as an opportunity to establish the geochemical background of the upper Sonora river basin, which includes active and historical mining areas. The weighted average of elemental values was calculated using GIS tools. The data show that rocks have a similar geochemical behavior, which is characterized by pristine enrichment of Mn, Ca, P, Ba, Zn, As, Ag, Sb, W, Pb and Bi relative to the upper continental crust. Coefficients of variation values reveal that Sc, Y, Zr, Ce, Yb,...
After the subduction stopped at ca. 12.5 Ma off Baja California Peninsula, calc-alkaline volcanic... more After the subduction stopped at ca. 12.5 Ma off Baja California Peninsula, calc-alkaline volcanic activity vanished progressively, and the Comondú volcanic arc was replaced by a post-subduction diversified volcanism which derived from at least five distinct magmatic sources located beneath the Baja California Peninsula and the Gulf of California. New field data, 40K-40Ar datings and geochemical and petrological studies of
Five main petrologic and geochemical groups can be identified among the Middle to Late Miocene la... more Five main petrologic and geochemical groups can be identified among the Middle to Late Miocene lavas from the western part of Southern Baja California: calc-alkaline and K-rich andesites, adakites and associated niobium-rich basalts, tholeiitic basalts and basaltic andesites, magnesian andesites and basaltic andesites of adakitic affinity. These lavas, although spatially and temporally related, display very different geochemical signatures. Their trace
The Pacific margin of Baja California is one of the few examples of an active margin that evolved... more The Pacific margin of Baja California is one of the few examples of an active margin that evolved from a convergent margin (before 12 Ma) to a transform margin (12-5 Ma). The amount of motion along the transform zone, which mainly occurred along the Tosco-Abreojos fault, is still debated, as well as the time of the transfer of Baja California to the Pacific plate. During the FAMEX cruise (L'Atalante, April 2002), swath bathymetry data were acquired along the Baja California margin from 23N to 27N. Several seismic profiles were also collected across the margin, using 300 inch3 GI guns tuned in harmonic mode and a streamer with six 50m-long channels. The 10s pop-rate at a 10 knots speed allowed a 3-fold coverage with a record-length of 4s. One profile clearly evidence the flat top of the subducted slab that can be followed 20 km landward. The lower part of a large pre-Upper Miocene mass-wasting is missing from the paleo-trench fill, and there is no evidence for an accretionary pr...
el margen continental actuó como frontera transformante entre las placas Pacífi co y América del ... more el margen continental actuó como frontera transformante entre las placas Pacífi co y América del Norte. La zona de falla Tosco-Abreojos localizada a lo largo de dicho margen fue interpretada como el mejor candidato para acomodar este movimiento transformante antes del Plioceno. A principios del Plioceno la ruptura continental tierra adentro induce la
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