U/Pb geochronology of Devonian and older Paleozoic beds in the southeastern Maya block, Central America: Its affinity with peri-Gondwanan terranes

Abstract

Supplementary data presented here include concentration and isotopic ratios for U/Pb zircon ages performed by Laser Ablation ICP-MS. An overview of the technique employed for the single crystal laser ablation ICP multicollector mass spectrometric technique (LA-ICP-MS) at the Arizona Laserchron Center is included. ANALYTICAL TECHNIQUES After crushing and pulverizing samples, zircon grains were concentrated by Wilfley ® shaking table, Frantz ® isodynamic separator, methylene iodide and hand picking. Final zircon concentrates were sieved and grains >40 μm were selected for analysis. Zircon unknowns and standards were mounted on the center of 1 inch phenolic Orings and polished to expose grain interiors. Analyzed detrital zircons were selected DR2009238 randomly. Each measurement cycle consisted of one 20s integration on every centered peak with the laser off for background counts, twenty 1s integrations during mineral blasting, and ~30s of purging. Zircons were ablated with a New Wave Research DUV193 ArF Excimer laser (wavelength = 193 nm). The laser beam was operated with ~32mJ energy (at 23kV), pulse rate of 9Hz, and spot size of 35μm or 50 μm depending on size and complexity of zircons. The generated pit was ~10 μm deep. Ablated material was carried in helium gas into an Isoprobe ICPMS from GV Instruments. U, Th and Pb isotopes were analyzed simultaneously in static mode using Faraday collectors for 238 U, 232 U, 208 Pb, 207 Pb and 206 Pb, and using an ion counter for 204 Pb. Contributions to the 204 mass by Hg were removed by subtracting background counts. Common Pb corrections were calculated from 204 Pb measurements and assuming an initial isotopic composition according to the Pb evolution curve by Stacey and Kramers (1975). Fragments of NIST 610 trace element glass were analyzed with every sample to determine concentrations of U and Th. Five Sri Lanka zircon standards (564±4 Ma, 2sigma error) were analyzed before each sample and once every five unknowns.

Geocronología de circones detríticos de diferentes localidades del Esquisto Granjeno en el noreste de México

“…Dicho pico se encuentra también presente, aunque sólo como una población menor representada por siete granos de edades entre 1363 Ma y 1430 Ma, en la muestra de Miquihuana. Esta población, que teóricamente podría corresponder con las provincias de magmas anorogénicos Peninsular Ranges o Maria Belt en el suroeste de Norteamérica (Barbeau et al, 2005), es a la vez comparable con edades reportadas en la Formación Santa Rosa del Paleozoico de Chiapas (Weber et al, 2006), y en algunas unidades de metasedimentos del Complejo Acatlán o como circones heredados en rocas magmáticas del Macizo de Chiapas o Chiapas Massive Complex (Weber et al, 2008) y de las Montañas Maya en Belice (Martens et al, 2010). Tales diferencias en las distintas muestras, que difícilmente pueden ser explicadas con la información existente hasta el momento, son, sin embargo, una notable evidencia de la variedad de los depósitos y sus procedencias de bloques que, posiblemente, sólo de manera temporal aportaron materiales clásticos hacia la cuenca.…”

U–Pb geochronological constraints on the Triassic–Jurassic Ayú Complex, southern Mexico: Derivation from the western margin of Pangea-A

“…8) are reported from plutons dated with U-Pb thermal ionization mass spectrometry by Steiner and Walker (1996). Further, Martens et al (2010) report a 406 + 7/−6 Ma rhyolite from the volcaniclastic Bladen Formation.…”

Study of melt and a clast of 546 Ma magmatic arc rocks in the 65 Ma Chicxulub bolide breccia, northern Maya block, Mexico: western limit of Ediacaran arc peripheral to northern Gondwana

“…Detrital zircons in Devonian and Pennsylvanian-Permian rocks are predominantly of ca. 1 Ga and Early Devonian age (Martens et al 2010). …”

“…Other data yielded an inheritance age of 1210 ± 136 Ma (upper intercept, U-Pb zircon data; Steiner and Walker 1996). These rocks are unconformably overlain by Lower Devonian-middle Permian shelf clastic, carbonate and volcanic rocks displaying folds accompanied by lower greenschist facies metamorphism (Steiner and Walker 1996;Martens et al 2010). Detrital zircons in Devonian and Pennsylvanian-Permian rocks are predominantly of ca.…”