An Update on Tectonics

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/109300/1/eost2014EO420009.pd

CPCP: Colorado Plateau Coring Project — 100 Million Years of Early Mesozoic Climatic, Tectonic, and Biotic Evolution of an Epicontinental Basin Complex

Early Mesozoic epicontinental basins of western North America contain a spectacular record of the climatic and tectonic development of northwestern Pangea as well as what is arguably the world's richest and most-studied Triassic-Jurassic continental biota. The Colorado Plateau and its environs (Fig. 1) expose the textbook example of these layered sedimentary records (Fig. 2). Intensely studied since the mid-nineteenth century, the basins, their strata, and their fossils have stimulated hypotheses on the development of the Early Mesozoic world as reflected in the international literature. Despite this long history of research, the lack of numerical time calibration, the presence of major uncertainties in global correlations, and an absence of entire suites of environmental proxies still loom large and prevent integration of this immense environmental repository into a useful global picture. Practically insurmountable obstacles to outcrop sampling require a scientific drilling experiment to recover key sedimentary sections that will transform our understanding of the Early Mesozoic world

Assessing vertical axis rotations in large-magnitude extensional settings: A transect across the Death Valley extended terrane, California

Models for Neogene crustal deformation in the central Death Valley extended terrane, southeastern California, differ markedly in their estimates of upper crustal extension versus shear translations. Documentation of vertical axis rotations of range-scale crustal blocks (or parts thereof) is critical when attempting to reconstruct this highly extended region. To better define the magnitude, aerial extent, and timing of vertical axis rotation that could mark shear translation of the crust in this area, paleomagnetic data were obtained from Tertiary igneous and remagnetized Paleozoic carbonate rocks along a roughly east-west traverse parallel to about 36°N latitude. Sites were established in ∼7 to 5 Ma volcanic sequences (Greenwater Canyon and Brown's Peak) and the ∼10 Ma Chocolate Sundae Mountain granite in the Greenwater Range, ∼8.5 to 7.5 Ma and 5 to 4 Ma basalts on the east flank of the Black Mountains, the 10.6 Ma Little Chief stock and upper Miocene(?) basalts in the eastern Panamint Mountains, and Paleozoic Pogonip Group carbonate strata in the north central Panamint Mountains. At the site level, most materials yield readily interpretable paleomagnetic data. Group mean directions, after appropriate structural corrections, suggest no major vertical axis rotation of the Greenwater Range (e.g., D = 359°, I = 46°, α_(95) = 8.0°, N = 12 (7 normal (N), 5 reversed (R) polarity sites)), little post-5 Ma rotation of the eastern Black Mountains (e.g., D = 006°, I = 61°, α_(95) = 4.0°, N = 9 N, 6 R sites), and no significant post-10 Ma rotation of the Panamint Range (e.g., D = 181°, I = −51°, α_(95) = 6.5°, N = 9 R sites). In situ data from the Greenwater Canyon volcanic rocks, Chocolate Sundae Mountain granite, Funeral Peak basalt rocks, the Little Chief stock, and Paleozoic carbonate rocks (remagnetized) are consistent with moderate south east-side-down tilting of the separate range blocks during northwest directed extension. The paleomagnetic data reported here suggest that the Panamints shared none of the 7 Ma to recent clockwise rotation of the Black Mountains crystalline core, as proposed in recent models for transtensional development of the central Death Valley extended terrane

Thermochemical remanent magnetization in Jurassic silicic volcanics from Nevada, U.S.A.

Characteristic magnetizations from Middle Jurassic dacitic to andesitic subaerial volcanics (the Fulstone and Artesia Formations) in the Buckskin Mountain Range, western central Basin and Range Province, are well-grouped, generally display univectorial decays to the origin in demagnetization and have hematite blocking temperatures restricted almost entirely to above 620[deg]C. Petrographic, rock magnetic and electron microprobe investigations confirm that nearly pure hematite is the essential magnetic phase (up to about 10 vol. %) occurring as a replacement of coarse titaniferous magnetite phenocrysts and fine groundmass particles, as a secondary alteration product of ferromagnesian phenocrysts and as a mobilized phase filling cracks and other open spaces. The presence of antipodal directions in each flow unit and in interbedded volcanoclastic units (some having retained magnetite as a major magnetic phase) and magnetite-dominated remanences in time-equivalent intrusives cutting the flows indicates that the volcanics acquired their hematite remanence, a faithful record of the geomagnetic field, in high-temperature, deuteric oxidation during and following their emplacement, not during a later thermal event such as regional metamorphism. The remanence is probably a thermochemical remanent magnetization, although part may be of thermoremanent origin.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/23211/1/0000140.pd

Climatic, Tectonic, and Biotic Evolution in Continental Cores: Colorado Plateau Coring Project Workshop; St. George, Utah, 13-16 November 2007

A workshop was convened in St. George, Utah, to advance planning for the Colorado Plateau Coring Project (CPCP). The vast continental basins of the southwestern United States, particularly well exposed on the Colorado Plateau and its environs, contain one of the richest stratigraphic records of early Mesozoic age (between roughly 145 and 250 million years ago). This time period was punctuated by two of the major mass extinctions in the past 550 million years and witnessed the evolutionary appearance of the modern biota and dramatic climate changes on the continents. Since the mid-nineteenth century, classic studies of these basins, their strata, and their fossils have made this sequence instrumental in framing our context for the early Mesozoic world. Nonetheless, striking ambiguities in temporal resolution, uncertainties in global correlations with other early Mesozoic strata, and major doubts about latitudinal position still hamper testing of the major competing climatic, biotic, and tectonic hypotheses

Site Selected for Colorado Plateau Coring: Colorado Plateau Coring Project Workshop, Phase 2: 100 Million Years of Climatic, Tectonic, and Biotic Evolution From Continental Coring . . .

A workshop was convened in New Mexico to plan for the Colorado Plateau Coring Project (CPCP) and identify the target site for initial coring. The giant continental and near-shore to shallow marine epicontinental basins of the American Southwest are particularly well exposed on the Colorado Plateau and its environs and contain a rich record of early Mesozoic (~251-145 million years ago) strata. This time period was punctuated by two major mass extinctions and is notable for the evolutionary appearance of the modern biota and its apparent dramatic climate changes. Classic studies of these basins, their strata, and their fossils have made this sequence instrumental in framing the context for the early Mesozoic world. Ambiguities in temporal resolution, uncertainties in global correlations with other early Mesozoic strata, and major doubts about latitudinal position still hamper testing of competing climatic, biotic, and tectonic models for the evolution of western Pangea

Methyl 2-(8a-hy­droxy-4a-methyl-8-methyl­enedeca­hydro­naphthalen-2-yl)acrylate

The title compound, C16H24O3, was synthesized from ilicic acid which was isolated from the aerial part of Inula Viscosa­ (L) Aiton [or Dittrichia Viscosa­ (L) Greuter]. The mol­ecule contains two fused six-membered rings both in chair conformations. In the crystal, mol­ecules are linked into chains running parallel to the a axis by O—H⋯O hydrogen bonds

Empirical evidence for stability of the 405-kiloyear Jupiter-Venus eccentricity cycle over hundreds of millions of years

The Newark–Hartford astrochronostratigraphic polarity timescale (APTS) was developed using a theoretically constant 405-kiloyear eccentricity cycle linked to gravitational interactions with Jupiter–Venus as a tuning target and provides a major timing calibration for about 30 million years of Late Triassic and earliest Jurassic time. While the 405-ky cycle is both unimodal and the most metronomic of the major orbital cycles thought to pace Earth’s climate in numerical solutions, there has been little empirical confirmation of that behavior, especially back before the limits of orbital solutions at about 50 million years before present. Moreover, the APTS is anchored only at its younger end by U–Pb zircon dates at 201.6 million years before present and could even be missing a number of 405-ky cycles. To test the validity of the dangling APTS and orbital periodicities, we recovered a diagnostic magnetic polarity sequence in the volcaniclastic-bearing Chinle Formation in a scientific drill core from Petrified Forest National Park (Arizona) that provides an unambiguous correlation to the APTS. New high precision U–Pb detrital zircon dates from the core are indistinguishable from ages predicted by the APTS back to 215 million years before present. The agreement shows that the APTS is continuous and supports a stable 405-kiloyear cycle well beyond theoretical solutions. The validated Newark–Hartford APTS can be used as a robust framework to help differentiate provinciality from global temporal patterns in the ecological rise of early dinosaurs in the Late Triassic, amongst other problems

Paleomagnetism of Ordovician alkalic intrusives and host rocks from the Pedernal Hills, New Mexico: positive contact test in remagnetized rocks?

A set of thin dikes from central New Mexico, dated at 469 +/- 7 Ma (Rb-Sr; Loring and Armstrong, 1980), have yielded a virtual geomagnetic pole which lies on the Late Paleozoic segment of the North American apparent polar wander path. The remanence of the dikes appears to be a product of Late Paleozoic hydrothermal alteration. Paradoxically, however, the magnetization of the host rocks is most simply explained in terms of a positive contact test. Samples collected between 0.2 and 0.5 dike-widths from the contact contain a component of remanence parallel to the magnetization in the dikes, with unblocking temperatures which decrease with distance from the dikes. Host rocks from a distance of more than 1 dike-width show no evidence of the characteristic dike magnetization.There are two possible resolutions of this paradox: 1. (1) the magnetization of the host rocks is secondary, despite the apparent positive contact test, and is a product of hydrothermal fluid migration through the dikes or along the contact zones; or2. (2) the magnetization of the dikes is primary, but not representative of the Ordovician paleofield for North America.Possible reasons for inaccurate representation include: 1. (a) incomplete averaging of secular variation;2. (b) tectonic rotation with respect to the stable craton; or3. (c) erroneous age determination for the rocks.We argue that explanation (1) is the most likely.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/27358/1/0000383.pd

A rock-magnetic and geomagnetic secular variation record from late-Pleistocene Lake Estancia, New Mexico [abstract]

EXTRACT (SEE PDF FOR FULL ABSTRACT): Exposed sediments of Late Pleistocene Lake Estancia contain a high resolution record of regional climate variability for the period about 12,000 to 32,000 years. A detailed rock-magnetic study is being performed on this well-dated, well-preserved sedimentary sequence to determine how the magnetic signature of sediments responded to regional climate change