Volcanism In Mexico Research Articles

Barremian rift-related turbidites and alkaline volcanism in southern Mexico and their role in the opening of the Gulf of Mexico

The Chivillas Formation is the easternmost record of Mesozoic marine volcanism in Mexico. It consists of thick intervals of pillow lavas interbedded with siliciclastic turbidites, and debrites, containing clasts derived from metamorphic, sedimentary and volcanic sources. Clast composition and detrital zircon geochronology indicate a continental provenance, with sources located south of the studied rocks. Detrital zircon ages range from 1573 ± 60 to 125 ± 1.6 Ma. The probability curves have peaks at 124 to 130 Ma (mean 126 Ma); 188 Ma and 921–1236 Ma (the latter with peaks at ∼ 1022 and ∼ 1157 Ma). Subordinate peaks at 277, 419 and 535 Ma are also present. We interpret the youngest zircon population ∼ 126 Ma (Barremian), as the maximum depositional age. Other peaks suggest Grenvillian-type basement and Permo-Triassic arc sources. Late Jurassic detrital zircons were probably derived from the Sierra de Juárez Mylonitic belt. Pillow lavas are mostly alkaline basalts, with SiO 2 46%–53%, and alkali oxide (K 2O + Na 2O) 5–8 wt.%; all samples have low-TiO 2 (< 1.6 wt.%) and low V (180–242 ppm), with Ti/V between 30 and 50. 206Pb/ 204Pb isotopic ratios are 18.6–20.5, and 208Pb/ 204Pb are 38.4–40.3, within OIB and MORB ranges. Initial εNd(126) are 0.3 to 4.1, and T DM are 632–1520 Ma. Lava compositions are similar to alkaline basalts along the margins of the Atlantic Ocean, particularly to basalts from the Central Atlantic Magmatic Province (CAMP), and to the Cretaceous Peri-Atlantic Alkaline Pulse (PAAP). Volcano-sedimentary rocks from Chivillas Formation probably formed in a subsiding marine rift basin, at a ridge–transform intersection. This basin received sediments transported throughout longitudinal canyons along the major Jurassic–Cretaceous strike–slip fault. In this model, extension of the rift basin was controlled by right-lateral displacement of the strike–slip fault, which acted as a transform fault at this time. This rift is interpreted as a segment of the rift system of the Gulf of Mexico.

Volc�n Las Navajas, a Pliocene-Pleistocene trachyte/peralkaline rhyolite volcano in the northwestern Mexican volcanic belt

Volcan Las Navajas, a Pliocene-Pleistocene volcano located in the northwestern portion of the Mexican volcanic belt, erupted lavas ranging in composition from alkali basalt through peralkaline rhyolite, and is the only volcano in mainland Mexico known to have erupted pantellerites. Las Navajas is located near the northwestern end of the Tepic-Zacoalco rift and covers a 200-m-thick pile of alkaline basaltic lavas, one of which has been dated at 4.3 Ma. The eruptive history of the volcano can be divided into three stages separated by episodes of caldera formation. During the first stage a broad shield volcano made up of alkali basalts, mugearites, benmoreites, trachytes, and peralkaline rhyolites was constructed. Eruption of a chemically zoned ash flow then caused collapse of the structure to form the first caldera. The second stage consisted of eruptions of glassy pantellerite lavas that partially filled the caldera and overflowed its walls. This stage ended about 200 000 years ago with the eruption of pumice falls and ash flows, which led to the collapse of the southern portion of the volcano to form the second caldera. During the third stage, two benmoreite cinder cones and a benmoreite lava flow were emplaced on the northwestern flank of the volcano. Finally, the calc-alkaline volcano Sanganguey was built on the southern flank of Las Lavajas. Alkaline volcanism continued in the area with eruptions of alkali basalt from cinder cones located along NW-trending fractures through the area. Although other mildly peralkaline rhyolites are found in the rift zones of western Mexico, only Las Navajas produced pantellerites. Greater volumes of basic alkaline magma have erupted in the Las Navajas region than in the other areas of peralkaline volcanism in Mexico, a factor which may be necessary to provide the initial volume of material and heat to drive the differentiation process to such extreme peralkaline compositions.

Eolian deposition in the northeast Pacific Ocean: Cenozoic history of atmospheric circulation

The mass accumulation rate and grain size distribution of the total eolian component of North Pacific pelagic clays have been used to evaluate changes in eolian sedimentation and in the intensity of atmospheric circulation that have occurred during the past 70 m.y. Eolian deposition was relatively low, approximately 12 mg/cm2/1,000 yr, in the Late Cretaceous and Paleocene, reflecting an increasingly humid environment. A peak in accumulation rates across the Paleocene-Eocene boundary may be the result of episodic volcanism in Mexico. A sharp decrease in grain size across the Paleocene-Eocene boundary is not readily interpreted. Fine eolian grain size and the low accumulation rates, averaging 8 mg/cm2/1,000 yr, in the Eocene and early Oligocene are in agreement with low early Tertiary thermal gradients and less vigorous atmospheric circulation. Large increases in grain size between 37 and 30 m.y. ago, 20 and 10 m.y. ago, and 5 m.y. ago to the present suggest that atmospheric circulation intensified by a factor of 1.5, 1.8, and 1.4, respectively, at these times. Eolian accumulation rates increased from 8 mg/cm2/1,000 yr at the Eocene-Oligocene boundary to approximately 25 mg/cm2/1,000 yr at the end of the Miocene, with significant changes at 25 and 13 m.y. ago. Increased rates about 25 m.y. ago probably reflect movement of the core site into the influence of the westerlies, and the increase 13 m.y. ago appears to be a response to steepening thermal gradients and intensifying atmospheric circulation resulting from major expansion of Antarctic ice in the mid-Miocene along with a general increase in global aridity in the late Cenozoic. An order of magnitude increase in eolian accumulation rates (25 to 226 mg/cm2/1,000 yr) in Pliocene-Pleistocene time coincides with the onset of Northern Hemisphere glaciation and consequent climatic deterioration. The large increase in accumulation rates in Pliocene-Pleistocene time coincides with a relatively smal! increase in the intensity of atmospheric circulation compared to that in Oligocene and Miocene time, suggesting that the increased deposition rates were the result of an increase in global aridity in glacial times, rather than a further increase in the vigor of the global wind systems.

Volcanism in Mexico and Central America

Volcanism in Mexico and Central America

Geodynamics

Geodynamics

Volcanism in Mexico and Central America

Volcanism in Mexico and Central America

Geohistoric and paleogeographic data and evolution of volcanism in Mexico

Geohistoric and paleogeographic data and evolution of volcanism in Mexico

Geologic setting of Parícutin volcano

A wide belt of young volcanoes, more than 500 miles long, crosses Mexico approximately along the 19th parallel, separating a region of comparative stability to the north from one to the south marked by instability, strong seismicity, and negative anomalies of gravity. To this volcanic belt belong such giant cones as Orizaba, Popocatepetl, Nevado de Toluca, and Collma, as well as the recently active cone of Jorullo and the new volcano, Parícutin. During Early and Middle Tertiary times, volcanism in Mexico was much more wide‐spread, not only along the belt just mentioned but also to the north; during and since the Pliocene period, activity has been confined increasingly to this east‐west zone.