Planetary Sciences, Geodynamics, Impacts, Mass Extinctions, and Evolution: Developments and Interconnections

Research frontiers in geophysics are being expanded, with development of new fields resulting from technological advances such as the Earth observation satellite network, global positioning system, high pressure-temperature physics, tomographic methods, and big data computing. Planetary missions and enhanced exoplanets detection capabilities, with discovery of a wide range of exoplanets and multiple systems, have renewed attention to models of planetary system formation and planet’s characteristics, Earth’s interior, and geodynamics, highlighting the need to better understand the Earth system, processes, and spatio-temporal scales. Here we review the emerging interconnections resulting from advances in planetary sciences, geodynamics, high pressure-temperature physics, meteorite impacts, and mass extinctions

Paleomagnetic behavior of volcanic rocks from Isla Socorro, Mexico

The direction and magnitude of the geomagnetic field vary both spatially and temporally and undergo significant departures from that of a geocentric axial dipole. In order to properly characterize persistent behaviors, time-averaged field models must be based on the highest quality data. Here we present full-vector paleomagnetic data for volcanic units exposed in the southeast quadrant of the island of Socorro, Mexico. We carried out a joint expedition between the Scripps Institution of Oceanography and the Universidad Nacional Autónoma México to Isla Socorro in January of 2005 during which we collected oriented paleomagnetic samples from 21 sites, representing as many as 10 different volcanic units (the oldest of which is ∼540 ka). We subjected over 100 specimens to the most up-to-date paleointensity methods, and included the standard reliability checks. In an earlier study, Bohrson et al. (1996) proposed a series of widespread eruptive events, based on similarities of argon/argon dates. Paleointensity from specimens that conform to the strictest acceptance criteria are available from both the (unoriented) original sample collection and our fully oriented (but as yet undated) new collection. Correlation between the two collections is however problematic. The time-averaged direction from Socorro is consistent with that expected from a geocentric axial dipole, and the time-averaged intensity is 30.0±7.1 μT, equivalent to a virtual axial dipole moment (VADM) of 67.6±16.0 ZAm2

Late Paleozoic or early Mesozoic magnetizations in remagnetized Paleozoic rocks, State of Oaxaca, Mexico

Characteristics of the Oaxaca Terrane of southern Mexico suggest that the record of a complete Wilson cycle is present. The local basement is composed of high-grade rocks of the Oaxaca Complex, which is considered to have North American affinities based on Grenvillian lithologies and ages. In contrast, early Paleozoic sedimentary rocks in depositional contact with the Oaxaca Complex have very close faunal affinities with the Olenid-Ceratopygid trilobite province of Argentina. Late Paleozoic faunas indicate that by this time the Oaxaca Terrane was once again associated with North America. In an attempt to gain further insight into the drift history of this area, we have undertaken a paleomagnetic study of the Paleozoic sedimentary rocks of Oaxaca.The results of our study indicate that the entire Paleozoic section was remagnetized in the same paleomagnetic field at some time following late Paleozoic sedimentation, emplacement of an igneous complex, and the earlier of two folding events. Fold and conglomerate tests show that the remagnetization occurred prior to deposition and folding of overlying early Cretaceous sediments. The Oaxaca Paleozoic rocks were therefore remagnetized sometime between late Permian and early Cretaceous. Since the exact age of remagnetization is not known, we compare our result with data from cratonic North America for the bracketed range of magnetization ages. This analysis indicates that as much as 28[deg] of net counterclockwise rotation could have occurred between Oaxaca and cratonic North America subsequent to the Oaxaca remagnetization.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/27031/1/0000019.pd

Paleomagnetic results from Grenvillian-aged rocks from Oaxaca, Mexico: Evidence for a displaced terrane

In order to test the possibly displaced nature of the Proterozoic (`Grenville'-aged) Oaxaca terrane, a paleomagnetic study was carried out on gneissic and meta-igneous (anorthosite) rocks with metamorphic ages reported to be between 1100 and 900 Ma. Using alternating field (AF) and thermal demagnetization techniques, we have isolated two magnetic directions: a shallow and southerly direction (D = 155[deg], I = -1[deg]) and a very steeply down direction (D = 6[deg], I = +74[deg]). It seems likely that the shallow direction is a remagnetization associated with a slight reheating and cooling due to a nearby Permian-Triassic intrusion. The steep direction is interpreted as a magnetization acquired during uplift and cooling following the Oaxacan Orogeny, and gives a paleopole at 47[deg]N, 93[deg]W with an age of ~950 Ma. This pole is at least 40[deg] from the Grenville Loop of the North American apparent polar wander path and the observed paleolatitude of 60[deg]N is much higher than that predicted for Oaxaca if it had always belonged to North America in the same relative position it has today. The high paleolatitude obtained for the Oaxaca terrane does not preclude, however, that it was part of North America during Grenvillian times, but in that case its position would have been much closer to Ontario and Quebec than it is today.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/28036/1/0000475.pd

Concordant paleomagnetic directions from the Tehuantepec Isthmus: Constraints on the Neogene evolution of the North American-Caribbean plate boundary

We report paleomagnetic data for Miocene igneous rocks of the southeastern Tehuantepec Isthmus region, Mexico. Thermal and alternating field demagnetization reveal predominantly normal polarity magnetization, interpreted as primary TRM. The overall mean direction (Dec = 355.6[deg], Inc = 36.5[deg], K = 36.4, a95 = 9.3[deg], N = 8 sites) is statistically indistinguishable from the expected direction, calculated using the North American reference pole. This result indicates that significant rotation or displacement of the Tehuantepec region relative to the craton has not occurred since 13 Ma.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/31328/1/0000237.pd

Estudio aeromagnético del complejo volcánico de Colima, occidente de México - implicaciones tectónicas y estructurales

"Se reporta la interpretación cualitativa y cuantitativa de anomalías aeromagnéticas del complejo volcánico de Colima (CVC) y sus alrededores. La zona se caracteriza por anomalías magnéticas de distintas amplitudes y longitudes de onda asociadas con estructuras volcánicas y cuerpos intrusivos, incluyendo al CVC. Se identifican 24 dominios aeromagnéticos definidos por patrones característicos de anomalías en un área de aproximadamente 11,500 km2 alrededor del CVC. El Volcán de Colima y el Nevado de Colima se caracterizan por anomalías dipolares de gran amplitud. Se investiga la estructura profunda del complejo volcánico utilizando un modelo magnético dimensional 2¾ - D, encontrando que la fuente asociada a las anomalías de los volcanes se relaciona con una posible cámara magmática de forma alargada, con una longitud mayor a los 6.8 km en dirección N-S y espesor máximo de 5.6 km. En el Volcán de Colima, ésta se localiza a una profundidad de 4.8 km. Este cuerpo se extiende por una distancia del orden de 5.6 km hacia el sur del CVC con un espesor promedio del orden de 0.54 km. Bajo el volcán Nevado de Colima se interpreta una posible cámara magmática colapsada de forma alargada con una longitud en dirección N-S mayor a 5.6 km y con espesor máximo de 1.2 km con una profundidad del orden de los 5.2 km bajo el cráter del Nevado. Se documentan, por primera vez, nuevas estructuras geológicas asociadas a anomalías magnéticas sepultadas por productos volcánicos, comofallas y cuerpos intrusivos. En la mayor parte del mapa magnético reducido al polo, se observan anomalías monopolares de grandes dimensiones, amplitudes altas y longitudes de onda largas, asociadas a rocas intrusivas. A 47 km al NW de los volcanes Colima y Nevado de Colima se puede apreciar un cinturón formado por tres de estas anomalías. En la zona también existe una serie de anomalías magnéticas relacionadas con la presencia de yacimientos de mineral de hierro, como la mina El Encino ubicada a 48 km al SE y el área mineralizada de la Sierra de Manantlán a 42 km al ESE del volcán de Colima.""Results of qualitative and quantitative interpretation of aeromagnetic anomalies over the Colima volcanic complex (CVC) and surrounding areas are presented. The area is characterized by magnetic anomalies of distinct amplitude and wavelength associated with volcanic structures and intrusive bodies, including the CVC. We identified 24 aeromagnetic domains in an area of 11,500 km2 around the CVC. We identify, for the first time, new geological structures buried under volcanic products, like faults and intrusive bodies. High amplitude magnetic dipolar anomalies characterize the volcanic structures of Colima and Nevado de Colima volcanoes. CVC deep structure was investigated by using a 2¾ D magnetic model, finding that the source is related to a possible magmatic chamber of elongated shape, >6.8 km long, in north-south strike with maximum thickness of 5.6 km, which is located at 4.8 m depth beneath the Colima volcano. The body extends to 5.6 km south of the Colima volcano, with average thickness of about 0.54 km. Under Nevado de Colima volcano, we interpreted a collapsed magmatic chamber, with elongated shape, >5.6 km long and 1.2 km of maximum thickness at a depth of around 5.2 km below the Nevado summit. In most of the reduced to the pole magnetic anomaly map, we observed large monopolar anomalies, high amplitude, and long wavelengths associated to the intrusive bodies. Three of these anomalies form a 47 km long belt to the NW of the CVC. There are several magnetic anomalies related to iron-ore deposits, i.e., El Encino mine (48 km SE of CVC) and Sierra de Manantlán (42 km ESE of CVC).

Palaeomagnetism of Late Miocene to Quaternary volcanics from the eastern segment of the Trans-Mexican Volcanic Belt

A systematic palaeomagnetic study in the eastern part of the Trans-Mexican Volcanic Belt includes 39 Miocene, Pliocene and Quaternary volcanic rocks in the southeastern Mexico Basin (Sierra Nevada and Sierra de Rı´o Frı´o), the Altiplano area, and the Palma Sola Massif. A total of 430 samples have been selectively demagnetized using mostly alternating field demagnetizing methods, supplemented by thermal analyses. Most characteristic remanences are carried by low-Ti titanomagnetites, with occasional titanohematites or slightly maghemitized low-Ti titanomagnetites, of similar direction. Seven sites were discarded because they presented intermediate directions, hydrothermal alteration or were remagnetized by lightning strikes. The mean directions of 32 sites, together with 24 sites from Sierra de las Cruces in the western Mexico basin, indicate rocks older than 2 Ma are rotated some 10° counterclockwise with respect to Quaternary rocks, whereas there is no rotational difference between Miocene and Pliocene rocks. Statistical analyses between different regrouped populations confirm that the rotational pattern is due to the age of the volcanics rocks but not to their spatial distribution. The Quaternary mean direction from the three Mexico Basin ranges is consistent with the geographical reference pole. In contrast, the Pliocene mean direction from volcanic rocks of the Altiplano area and the Sierra de Las Cruces is slightly rotated some 10° westwards with respect to the reference direction from North America. No significant rotations have been observed in the eastern TMVB (from the western Mexico Basin to the border of the Altiplano), between late Miocene and late Pliocene times. It suggests that a very small, counterclockwise vertical-axis rotation may have been taken place in this segment of the TMVB between late Pliocene and Quaternary times. Comparisons of these results with a summary of the available palaeomagnetic data in the area indicate that the previously reported Quaternary rotations are of questionable reliability, and that the large counterclockwise rotations, reported in Cretaceous to Miocene rocks, probably took place before the late Miocene. These new palaeomagnetic data support the idea that the eastern TMVB since the late Miocene, has been a zone of extension with a little, left-lateral shear component

Solution pans and linear sand bedforms on the bare-rock limestone shelf of the Campeche Bank, Yucatán Peninsula, Mexico

A high-resolution, near-surface geophysical survey was conducted in 2013 on the Campeche Bank, a carbonate platform offshore of Yucatán, Mexico, to provide a hazard assessment for future scientific drilling into the Chicxulub impact crater. It also provided an opportunity to obtain detailed information on the seafloor morphology and shallow stratigraphy of this understudied region. The seafloor exhibited two morphologies: (1) small-scale (<2 m) bare-rock karstic features, and (2) thin (<1 m) linear sand accumulations overlying the bedrock. Solution pans, circular to oblong depressions featured flat bottoms and steep sides, were the dominant karstic features; they are known to form subaerially by the pooling of rainwater and dissolution of carbonate. Observed pans were 10–50 cm deep and generally 1–8 m wide, but occasionally reach 15 m, significantly larger than any solution pan observed on land (maximum 6 m). These features likely grew over the course of many 10's of thousands of years in an arid environment while subaerially exposed during lowered sea levels. Surface sands are organized into linear bedforms oriented NE-SW, 10's to 100's meters wide, and kilometers long. These features are identified as sand ribbons (longitudinal bedforms), and contained asymmetric secondary transverse bedforms that indicate NE-directed flow. This orientation is incompatible with the prevalent westward current direction; we hypothesize that these features are storm-generated