Early to Middle Jurassic history of the southern Siberian continent (Transbaikalia) recorded in sediments of the Siberian Craton: Sm-Nd and U-Pb provenance study

2017 ◽  
Vol 188 (1-2) ◽  
pp. 8 ◽  
Author(s):  
Elena I. Demonterova ◽  
Alexei V. Ivanov ◽  
Ekaterina M. Mikheeva ◽  
Anastasia V. Arzhannikova ◽  
Andrei O. Frolov ◽  
...  
Keyword(s):  
Middle Jurassic ◽  
Sedimentary Rocks ◽  
Orogenic Belt ◽  
Bulk Rock ◽  
Irkutsk Basin ◽  
Short Time Span ◽  
History Of ◽  
Juvenile Crust ◽  
Detrital Zircon Ages ◽  
Short Time

The deposition of Jurassic continental sedimentary rocks in the southern part of the Siberian continent (Transbaikalia) reflects the intensification of tectonomagmatic processes in this region. The most likely cause of this intensification was associated with the formation and development of the Mongol-Okhotsk orogenic belt. The latter was controlled in its turn by the closure of the Mongol-Okhotsk Ocean, for which the timing of its closure, as well as the formation of a collisional orogeny and its subsequent collapse are still under debate. We address this question by studying sediments of the Irkutsk Basin, which were deposited in a short time span in the Middle Jurassic, most likely during the Aalenian. The Sm-Nd data for bulk-rock sandstones demonstrate that the youngest samples of the Irkutsk Basin are characterized by a prominent contribution from a source within the juvenile crust of the Mongol-Okhotsk orogenic belt. U-Pb detrital zircon ages concur with the Sm-Nd data and show that the amount of material derived from local cratonic sources decreased in time whereas material from the remote Transbaikalian sources increased. Our data provide evidence that mountain growth in Transbaikalia intensified rapidly close to the Early and Middle Jurassic boundary.

Provenance of Jurassic sedimentary rocks of south-central Quesnellia, British Columbia: implications for paleogeography

2004 ◽  
Vol 41 (1) ◽  
pp. 103-125 ◽  
Author(s):  
Nathan T Petersen ◽  
Paul L Smith ◽  
James K Mortensen ◽  
Robert A Creaser ◽  
Howard W Tipper
Keyword(s):  
Detrital Zircon ◽  
Middle Jurassic ◽  
Sedimentary Rocks ◽  
Source Area ◽  
Lower Jurassic ◽  
Early Jurassic ◽  
Late Triassic ◽  
Nd Isotopes ◽  
South Central ◽  
History Of

Jurassic sedimentary rocks of southern to central Quesnellia record the history of the Quesnellian magmatic arc and reflect increasing continental influence throughout the Jurassic history of the terrane. Standard petrographic point counts, geochemistry, Sm–Nd isotopes and detrital zircon geochronology, were employed to study provenance of rocks obtained from three areas of the terrane. Lower Jurassic sedimentary rocks, classified by inferred proximity to their source areas as proximal or proximal basin are derived from an arc source area. Sandstones of this age are immature. The rocks are geochemically and isotopically primitive. Detrital zircon populations, based on a limited number of analyses, have homogeneous Late Triassic or Early Jurassic ages, reflecting local derivation from Quesnellian arc sources. Middle Jurassic proximal and proximal basin sedimentary rocks show a trend toward more evolved mature sediments and evolved geochemical characteristics. The sandstones show a change to more mature grain components when compared with Lower Jurassic sedimentary rocks. There is a decrease in εNdT values of the sedimentary rocks and Proterozoic detrital zircon grains are present. This change is probably due to a combination of two factors: (1) pre-Middle Jurassic erosion of the Late Triassic – Early Jurassic arc of Quesnellia, making it a less dominant source, and (2) the increase in importance of the eastern parts of Quesnellia and the pericratonic terranes, such as Kootenay Terrane, both with characteristically more evolved isotopic values. Basin shale environments throughout the Jurassic show continental influence that is reflected in the evolved geochemistry and Sm–Nd isotopes of the sedimentary rocks. The data suggest southern Quesnellia received material from the North American continent throughout the Jurassic but that this continental influence was diluted by proximal arc sources in the rocks of proximal derivation. The presence of continent-derived material in the distal sedimentary rocks of this study suggests that southern Quesnellia is comparable to known pericratonic terranes.

scholarly journals VIOLATING THE BASIC TENETS OF CARE – LOOKING BACK ON YEARS OF EVIDENCE BASED MEDICINE FROM AN ONCOLOGIST'S VIEWPOINT

2020 ◽  
pp. 86-88
Author(s):  
Bishan Basu
Keyword(s):  
Medical Practice ◽  
Evidence Based Medicine ◽  
Healthcare Systems ◽  
Evidence Based ◽  
Short Time Span ◽  
Short Period ◽  
History Of ◽  
Pros And Cons ◽  
Short Time ◽  
Based Medicine

Evidence-Based Medicine (EBM) came into fashion nearly three decades ago. However, over this short period, this system of medical philosophy has come to dominate the medical practice worldwide. Never in the history of medicine could a single way of medical practice could dominate the healthcare systems of diverse countries like EBM did, that too within such short time span. But, it is high time we should ponder over the pros and cons of EBM and if this way of medical practice is to be allowed to continue, we should consider integration of additional inputs from the traditional ways of medicine. Though article focusses upon the cancer care, the conclusions derived can be applied to any other disciplines of healthcare.

scholarly journals The western Hayfork terrane: Remnants of the Middle Jurassic arc in the Klamath Mountain province, California and Oregon

Geosphere ◽  
2020 ◽  
Vol 16 (4) ◽  
pp. 1058-1081
Author(s):  
Calvin G. Barnes ◽  
Melanie A. Barnes
Keyword(s):  
Trace Element ◽  
Middle Jurassic ◽  
Regional Metamorphism ◽  
Sedimentary Rocks ◽  
Trace Element Analysis ◽  
Arc Magmatism ◽  
Bulk Rock ◽  
Element Analysis ◽  
Mountain Province ◽  
Klamath Mountain

Abstract Arc magmatism was widespread in the Cordillera of North America during Middle Jurassic time. The predominant representative of this arc magmatism in the Klamath Mountain province is the western Hayfork terrane (WHT). This terrane is primarily metasedimentary, consisting mainly of crystal-lithic arenite, argillitic sediments and lahar deposits, rare lavas, and sparse quartz-rich arenite. Because lavas are rare, petrologic study using bulk-rock compositions is restricted to analysis of cobbles in lahar deposits. Moreover, the WHT underwent greenschist-facies regional metamorphism with consequent modification of bulk-rock compositions. However, many of the sandstones preserve igneous clinopyroxene and calcic amphibole, which were phenocrysts in the original volcanic rocks. Major- and trace-element compositions of the magmatic pyroxene and amphibole permit reconstruction of the range of rock types eroded from the arc, specifically scant basalt, volumetrically dominant basaltic andesite and andesite, and smaller but significant amounts of dacite and rhyodacite. Eruptive temperatures reached ∼1180 °C and may have been as low as ∼800 °C on the basis of pyroxene and amphibole thermometry, with most eruptive temperatures >1000 °C. On the basis of augite compositions, WHT magmatism is divided into two suites. One features high-Mg augite with high abundances of Cr and Sr, high Sr/Y and Nd/Yb values, and low Y and heavy rare-earth elements (REE). These compositions are typical of high-Mg andesite and dacite suites in which garnet is a residual mineral, most probably in a metasomatized upper mantle setting. The other suite contains augite with lower Sr, Sr/Y, and Nd/Yb; these features are typical of normal calc-alkaline magmas. Augite from a coeval pluton emplaced inboard of the western Hayfork outcrop belt is similar to augite from the low-Sr group of WHT samples. In contrast, augite from the Ironside Mountain pluton, previously considered the plutonic equivalent of WHT sediments, is Fe-rich, with low Cr and Sr and relatively high Zr and REE. Previous suggestions that the Ironside Mountain pluton is correlative with the WHT are not supported by these data. The magmatic diversity of the WHT is typical of the modern Aleutian and Cascade arcs, among others, and could reflect subduction of relatively young oceanic lithosphere or fragmentation of the subduction slab. Although we favor the former setting, present data cannot rule out the latter. The presence of scant quartz-rich sedimentary rocks within the predominantly volcanogenic WHT is consistent with deposition as a sedimentary apron associated with a west-facing magmatic arc with late-stage input from cratonal sources. The results of this study indicate that detailed petrographic study of arc-derived sedimentary rocks, including major- and trace-element analysis of preserved magmatic phases, yields information about magmatic affinities, processes, and temperatures.

The Mont Saint Hilaire plutonic complex: occurrence of excess 40Ar and short intrusion history

1986 ◽  
Vol 23 (7) ◽  
pp. 948-958 ◽  
Author(s):  
Lisa A. Gilbert ◽  
K. A. Foland
Keyword(s):  
Heating Temperature ◽  
Sedimentary Rocks ◽  
Time Interval ◽  
Crustal Assimilation ◽  
Crustal Rocks ◽  
Short Time Span ◽  
Plutonic Complex ◽  
Widespread Phenomenon ◽  
Short Time ◽  
Western Half

Mont Saint Hilaire is an approximately 10 km2 alkaline plutonic complex in the Monteregian petrographic province of Quebec. The complex consists of an older, western half of alkali gabbros and an eastern portion of nepheline syenites and magmatic breccias. The intrusives were emplaced at depths of no more than a few kilometres into Paleozoic sedimentary rocks through the underlying Grenville basement. 40Ar/39Ar analyses of amphibole yield complex age spectra in which the apparent ages decrease with increasing heating temperature. Conventional K–Ar analyses of amphibole, pyroxene, and feldspar yield anomalously old dates. These data indicate the presence of small yet significant amounts (up to 8 × 10−11 mol/g) of excess 40Ar. The quantities of excess argon are variable between rocks and minerals from the same rock. In contrast, biotites yield concordant plateaus and consistent ages ranging only from 124.1 to 124.6 Ma. These data define the age of the complex (124.4 ± 1.2 Ma) and imply a short time span of emplacement of about 0.5 Ma or less. The restricted time interval suggests the various lithologies are cogenetic. The nature of the amphibole 40Ar/39Ar spectra indicates that excess 40Ar was acquired after crystallization. The 40Ar could have been present in the initial magma either from crustal assimilation or from a mantle source. Alternatively, it could have been derived from outgassing of older crustal rocks. The occurrence of excess 40Ar in epizonal plutons may be a more widespread phenomenon than commonly recognized.

Chilliwack composite terrane in northwest Washington: Neoproterozoic–Silurian passive margin basement, Ordovician–Silurian arc inception

2010 ◽  
Vol 47 (10) ◽  
pp. 1347-1366 ◽  
Author(s):  
E. H. Brown ◽  
G. E. Gehrels ◽  
V. A. Valencia
Keyword(s):  
Volcanic Rocks ◽  
Sedimentary Rocks ◽  
Complex Problem ◽  
Late Ordovician ◽  
Detrital Zircons ◽  
Passive Margin ◽  
Early Paleozoic ◽  
Intrusive Rocks ◽  
History Of ◽  
Detrital Zircon Ages

The Chilliwack composite terrane in northwest Washington is part of an assemblage of mid-Paleozoic arc terranes extending from California to Alaska. Some terranes bear evidence of exotic origin, whereas others apparently formed proximal to western Laurentia, posing a complex problem in unraveling the Paleozoic accretionary history of the Cordillera. In our proposed broader definition, the Chilliwack composite terrane includes the volcanic and sedimentary East Sound and Chilliwack groups, and the plutonic and metamorphic Turtleback and Yellow Aster complexes. New zircon ages indicate that the plutonic and volcanic rocks are mutually related as parts of the same arc complex and that its inception was as old as Late Ordovician to Silurian, older than most other parts of the mid-Paleozoic terrane assemblage. Basement to the arc complex is a passive margin assemblage of metamorphosed quartzose sandstone and calc-silicate rock of the Yellow Aster Complex, bracketed in age by ca. 1000 Ma detrital zircons and 418 Ma intrusive rocks. This association of paragneiss basement and overlying and (or) intruding arc resembles that of older parts of the extensive Yukon–Tanana terrane in the northern Cordillera. Detrital zircon ages support a western Laurentian pericratonic origin for the paragneiss basement and the overlying arc. However, an early to mid-Paleozoic connection of this assemblage to the exotic outboard Alexander terrane is also indicated, based on (1) Mesoproterozoic and early Paleozoic detrital zircons in Devonian sedimentary rocks of the arc, and also in certain other pericratonic Devonian terranes and strata of the miogeocline; (2) Late Ordovician – Silurian igneous ages; and (3) an earliest Devonian or older metamorphic age of the basement paragneiss.

scholarly journals On the Short Time Scale Evolutionary History of the Contact Binary VW Cephei

1998 ◽  
Vol 11 (1) ◽  
pp. 396-396
Author(s):  
I. Pustylnik
Keyword(s):  
Evolutionary History ◽  
Light Curves ◽  
Published Data ◽  
Short Time Scale ◽  
Flare Activity ◽  
Considerable Portion ◽  
History Of ◽  
Contact Binary ◽  
Elongation Phase ◽  
Short Time

We study the short-time evolutionary history of the well-known contact binary VW Cep. Our analysis is based partly on the numerous UBV lightcurves obtained at Tartu Observatory, IUE spectra, and samples from the published data. Special attention is given to the effects of asymmetry of the light curves. A higher degree of asymmetry outside the eclipses along with the significant displacements of the brightness maxima in respect to the elongation phase is interpreted as evidence that a considerable portion of the flaring source is concentrated close to the neck connecting the components. We discuss the nature of asymmetry in terms of possible mass exchange and the flare activity and compare the results of our model computations with the record of orbital period variations over the last 60 years.

scholarly journals ‘Scrupulous and Timid Conformism’: Ireland and the Reception of the Liturgical Changes of Vatican II

Religions ◽  
2021 ◽  
Vol 12 (7) ◽  
pp. 545
Author(s):  
Gary Carville
Keyword(s):  
Vatican Ii ◽  
Time Span ◽  
Second Vatican Council ◽  
The People ◽  
Vatican Council ◽  
Short Time Span ◽  
Irish Catholics ◽  
Catholic Tradition ◽  
Short Time ◽  
The Church

The Second Vatican Council and, in particular, its Constitution on the Sacred Liturgy, changed much in the daily life of the Church. In Ireland, a country steeped in the Catholic tradition but largely peripheral to the theological debates that shaped Vatican II, the changes to liturgy and devotional practice were implemented dutifully over a relatively short time span and without significant upset. But did the hierarchical manner of their reception, like that of the Council itself, mean that Irish Catholics did not receive the changes in a way that deepened their spirituality? And was the popular religious memory of the people lost through a neglect of liturgical piety and its place in the interior life, alongside what the Council sought to achieve? In this essay, Dr Gary Carville will examine the background to the liturgical changes at Vatican II, the contribution to their formulation and implementation by leaders of the Church in Ireland, the experiences of Irish Catholic communities in the reception process, and the ongoing need for a liturgical formation that brings theology, memory, and practice into greater dialogue.

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