First evidence of a “Barrovian”-type metamorphic regime in the Ross orogen of the Byrd Glacier area, central Transantarctic Mountains

2007 ◽  
Vol 19 (4) ◽  
pp. 451-470 ◽  
Author(s):  
F.M. Talarico ◽  
E. Stump ◽  
B.F. Gootee ◽  
K.A. Foland ◽  
R. Palmeri ◽  
...  
Keyword(s):  
Early Stage ◽  
Regional Metamorphism ◽  
Structural Data ◽  
Boundary Crossing ◽  
Prograde Metamorphism ◽  
Geochronological Data ◽  
Metamorphic Overprint ◽  
First Order ◽  
Dyke Swarms ◽  
Tectonic Boundary

AbstractThe Selborne Group comprises two metamorphic rock units, the muscovite±dolomite bearing Madison Marble and the biotite-muscovite±quartz-calcite Contortion Schist, which contains thick lenses of variably deformed metabasalts and metaconglomerates. Petrological and structural data indicate a polyphase metamorphic evolution including: i) an early stage of upper greenschist regional metamorphism (P = ~0.15–0.3 GPa; T = ~380–450°C), ii) prograde metamorphism during D1 up to amphibolite facies peak conditions (P = 0.58–0.8 GPa, T = ~560–645°C), iii) syn-D2 unloading-cooling retrograde metamorphism, iv) a post-D2 contact metamorphic overprint at variable T between 450 and 550°C and ~0.2 GPa connected to the emplacement of granitic plutons and felsic dyke swarms. Geochronological data constrain the polyphase syn-D1/D2 evolution between ~ 510 and 492 Ma. A similar metamorphic path, including a medium P stage but at lower T conditions, is documented in greenschist facies metabasalts within the Byrd Group in the Mount Dick area. The metamorphic pattern and close lithostratigraphic matching between Selborne Group and Byrd Group sharply contrast with the high-grade Horney Formation that is exposed north of the Byrd Glacier and corroborate the hypothesis that the Byrd Glacier discontinuity marks a first-order crustal tectonic boundary crossing the Ross orogen.

Age and origin of the Dover Fault: tectonic boundary between the Gander and Avalon Zones of the northeastern Newfoundland Appalachians

1981 ◽  
Vol 18 (9) ◽  
pp. 1431-1442 ◽  
Author(s):  
R. D. Dallmeyer ◽  
R. F. Blackwood ◽  
L. Odom
Keyword(s):  
Fault Zone ◽  
Country Rock ◽  
Regional Metamorphism ◽  
Tectonic Activity ◽  
Small Scale ◽  
Present Position ◽  
History Of ◽  
Scale Structures ◽  
Tectonic Boundary ◽  
Small Scale Structures

The Dover Fault forms a tectonic boundary between northern portions of the Gander and Avalon Zones of the Newfoundland Appalachians. A systematic geochronological investigation across the mylonitic fault zone has been carried out to clarify the origin and history of tectonic activity along this important Appalachian structure.Zircon fractions from the mylonitic Lockers Bay Granite (Gander Zone) record individually discordant U–Pb dates, but yield a well-defined upper concordia intercept age of 460 ± 20 Ma. Hornblende (1 sample) and biotite (11 samples) from variably mylonitic Gander Zone lithologies (plutonic and metamorphic) adjacent to the fault zone record undisturbed 40Ar/39Ar age spectra with plateau ages of 395 and 365–383 Ma, respectively. Together with field and petrographic characteristics, the new geochronologic data suggest that the Lockers Bay Granite originated as an anatectic melt during high-grade regional metamorphism of the country rock terrane at approximately 460 Ma. The crystal-rich magma was subsequently emplaced into its present position thereby producing local discordance with small-scale structures in host gneisses.Following its emplacement, the Lockers Bay Granite and country rock terrane were maintained at elevated postmetamorphic temperatures for a prolonged interval until they underwent rapid strain during Acadian (Devonian) juxtaposing of the northern Gander and Avalon Zones along the Dover Fault. Sudden Acadian uplift along the fault is suggested because of the rapid cooling of the northern Gander Zone through temperatures required for argon retention in hornblende and biotite. Post-mylonite brecciation may have locally affected argon isotopic systems of phyllitic lithologies adjacent to the fault zone in the study area.

Mineral parageneses and metamorphic reactions in metasedimentary enclaves from the Archaean Gneiss Complex of north-west India

1984 ◽  
Vol 48 (347) ◽  
pp. 195-209
Author(s):  
Ram. S. Sharma ◽  
Brian F. Windley
Keyword(s):  
Regional Metamorphism ◽  
Recrystallization Temperature ◽  
Prograde Metamorphism ◽  
Basement Complex ◽  
North West ◽  
Gneiss Complex ◽  
Two Generations ◽  
Orogenic Cycle ◽  
Banded Gneissic Complex ◽  
Partial Resorption

AbstractThree metasedimentary enclaves up to a kilometre in length of contrasting compositions within the polymetamorphic Banded Gneissic Complex (> 2580Ma) have been studied for their mineral parageneses and metamorphic conditions. The largest enclave, consisting of kyanite-chloritoid-muscovite schist with quartz or corundum, and kyanite-fuchsite-corundum ± diaspore, was metamorphosed at most under lower amphibolite conditions, and is thus not isofacial with the surrounding schists and gneisses (of the ‘basement’ complex) which reached sillimanite-grade metamorphism in the last orogenic cycle (Aravalli: 1650–950Ma Orogeny) in Rajasthan.The second enclave is a calc-silicate rock which occurs as a small lens. The presence of two generations of wollastonite which formed during different metamorphic events in the calcite-quartz-grossularite-anorthite-clinopyroxene assemblage indicates polymetamorphism.The third enclave is a metabasic rock which records a complete polymetamorphic history in discontinuous zones in garnet coexisting with hornblende-chlorite-plagioclase-quartz±epidote. To explain the garnet zoning a model involving partial resorption of early garnet during the initial recrystallization stage of superimposed regional metamorphism is preferred to the alternative based on a single prograde metamorphism and retrogression.The mineralogy of the calc-silicate and metabasic enclaves gives a recrystallization temperature of c. 700°C and a pressure in the range of 8–3 kbar during the second metamorphism.

Chronology of the Red Wine alkaline province, central Labrador

1977 ◽  
Vol 14 (8) ◽  
pp. 1940-1946 ◽  
Author(s):  
Alan B. Blaxland ◽  
Laurence W. Curtis
Keyword(s):  
Red Wine ◽  
Early Stage ◽  
Regional Metamorphism ◽  
Strong Support ◽  
New Age ◽  
Igneous Rocks ◽  
Rift System ◽  
Alkaline Rocks ◽  
Plutonic Rocks ◽  
Basaltic Lavas

An 11-point Rb–Sr whole-rock isochron for the regionally metamorphosed Red Wine alkaline province gives an age of intrusion of 1345 ± 75 Ma (errors quoted at 2σ) and an initial 87Sr/86Sr ratio of (1.7021 ± 0.0103. Two 5-point mineral isochrons give ages of ~1000 Ma that represent metamorphic 'resetting' of the alkaline rocks. The whole-rock intrusion age compares closely with the early stage of magmatism in the Gardar Province of south Greenland where un-metamorphosed agpaitic igneous rocks, similar to those of the Red Wine Province, occur. In both provinces, alkaline plutonic rocks are associated, both spatially and chronologically, with thick sequences of continental sediments and basaltic lavas, and the new age data lend strong support to the supposition that the Gardar and Red Wine rocks are parts of the same pre-drift magmatic province and inferred rift system. The Gardar Province has, however, escaped the effects of the Grenville regional metamorphism which severely affected the Red Wine rocks.

scholarly journals Mapping Boreal Forest Spruce Beetle Health Status at the Individual Crown Scale Using Fused Spectral and Structural Data

Forests ◽  
2021 ◽  
Vol 12 (9) ◽  
pp. 1145
Author(s):  
Janice Cessna ◽  
Michael G. Alonzo ◽  
Adrianna C. Foster ◽  
Bruce D. Cook
Keyword(s):  
Bark Beetle ◽  
Boreal Forests ◽  
Tree Mortality ◽  
Early Stage ◽  
Forest Health ◽  
Structural Data ◽  
Point Clouds ◽  
Vertical Gradient ◽  
High Spectral Resolution ◽  
Single Crown

The frequency and severity of spruce bark beetle outbreaks are increasing in boreal forests leading to widespread tree mortality and fuel conditions promoting extreme wildfire. Detection of beetle infestation is a forest health monitoring (FHM) priority but is hampered by the challenges of detecting early stage (“green”) attack from the air. There is indication that green stage might be detected from vertical gradients of spectral data or from shortwave infrared information distributed within a single crown. To evaluate the efficacy of discriminating “non-infested”, “green”, and “dead” health statuses at the landscape scale in Alaska, USA, this study conducted spectral and structural fusion of data from: (1) Unoccupied aerial vehicle (UAV) multispectral (6 cm) + structure from motion point clouds (~700 pts m−2); and (2) Goddard Lidar Hyperspectral Thermal (G-LiHT) hyperspectral (400 to 1000 nm, 0.5 m) + SWIR-band lidar (~32 pts m−2). We achieved 78% accuracy for all three health statuses using spectral + structural fusion from either UAV or G-LiHT and 97% accuracy for non-infested/dead using G-LiHT. We confirm that UAV 3D spectral (e.g., greenness above versus below median height in crown) and lidar apparent reflectance metrics (e.g., mean reflectance at 99th percentile height in crown), are of high value, perhaps capturing the vertical gradient of needle degradation. In most classification exercises, UAV accuracy was lower than G-LiHT indicating that collecting ultra-high spatial resolution data might be less important than high spectral resolution information. While the value of passive optical spectral information was largely confined to the discrimination of non-infested versus dead crowns, G-LiHT hyperspectral band selection (~400, 675, 755, and 940 nm) could inform future FHM mission planning regarding optimal wavelengths for this task. Interestingly, the selected regions mostly did not align with the band designations for our UAV multispectral data but do correspond to, e.g., Sentinel-2 red edge bands, suggesting a path forward for moderate scale bark beetle detection when paired with suitable structural data.

scholarly journals Portable optically stimulated luminescence age map of a paleoseismic exposure

Geology ◽  
2022 ◽  
Author(s):  
Christopher B. DuRoss ◽  
Ryan D. Gold ◽  
Harrison J. Gray ◽  
Sylvia R. Nicovich
Keyword(s):  
Normal Fault ◽  
Sedimentary Facies ◽  
Soil Characteristics ◽  
Optically Stimulated Luminescence ◽  
Geochronological Data ◽  
First Order ◽  
Depositional Processes ◽  
Spatiotemporal Trends ◽  
History Of ◽  
Colluvial Wedge

The quality and quantity of geochronologic data used to constrain the history of major earthquakes in a region exerts a first-order control on the accuracy of seismic hazard assessments that affect millions of people. However, evaluations of geochronological data are limited by uncertainties related to inherently complex depositional processes that may vary spatially and temporally. To improve confidence in models of earthquake timing, we use a high-density suite of radiocarbon and optically stimulated luminescence (OSL) ages with a grid of 342 portable OSL samples to explore spatiotemporal trends in geochronological data across an exemplary normal fault colluvial wedge exposure. The data reveal a two-dimensional age map of the paleoseismic exposure and demonstrate how vertical and horizontal trends in age relate to dominant sedimentary facies and soil characteristics at the site. Portable OSL data provide critical context for the interpretation of 14C and OSL ages, show that geochronologic age boundaries between pre- and post-earthquake deposits do not match stratigraphic contacts, and provide the basis for selecting alternate Bayesian models of earthquake timing. Our results demonstrate the potential to use emergent, portable OSL methods to dramatically improve paleoseismic constraints on earthquake timing.

scholarly journals Oxygen isotopes in ophicalcites: an ever-lasting controversy?

2020 ◽  
Author(s):  
Daniel Bernoulli ◽  
Helmut Weissert
Keyword(s):  
Oxygen Isotope ◽  
Isotope Geochemistry ◽  
Regional Metamorphism ◽  
Hydrothermal Activity ◽  
Eastern Alps ◽  
Metamorphic Overprint ◽  
Rock Interaction ◽  
Sea Floor ◽  
Detachment Faults ◽  
Mid Atlantic Ridge

Abstract Tectono-sedimentary breccias, known as ophicalcites, overlie serpentinised peridotites at a Jurassic ocean–continent transition along the Penninic-Austroalpine transition in the Eastern Alps of Switzerland. Deformation of the exhumed mantle rocks and breccia formation occurred under decreasing temperatures and along low-angle detachment faults exposing the mantle rocks at the sea floor and was coupled with hydrothermal activity and carbonation of the serpentinites at shallow depth and/or at the sea floor. Carbon isotopes in the ophicalcites persistently show marine values; however, the interpretation of oxygen-isotope values remained controversial: are they related to Jurassic hydrothermal activity or do they reflect Alpine metamorphic overprint? Here we discuss recent interpretations that relate oxygen isotope values measured in ophicalcites exclusively to Jurassic hydrothermal activity; to this end we use data that we earlier obtained along a north–south profile across Graubünden (eastern Switzerland). We revisited the sites of controversial interpretation along a north–south profile in eastern Switzerland. Along this profile, oxygen isotope values in ophicalcites and overlying pelagic sediments, up to 25 my younger than the ophicalcites, show identical values and become systematically lower with increasing Alpine metamorphism; they strongly deviate from values in ophicalcites and pelagic sediments measured along the Mid-Atlantic Ridge or ancient Atlantic ocean-continent transitions as e.g. in the Iberia–Newfoundland transect. The oxygen-isotope values measured in Alpine ophicarbonates thus reflect isotopic resetting during the Alpine orogeny, related to fluid-rock interaction during regional metamorphism. Hydrothermal processes that accompanied the formation of ophicalcites are not disputed; however, they cannot be traced by oxygen isotope geochemistry.

scholarly journals Geological and geochemical implications of the genesis of the Qolqoleh orogenic gold mineralisation, Kurdistan Province (Iran)

Geologos ◽  
2015 ◽  
Vol 21 (1) ◽  
pp. 31-57 ◽  
Author(s):  
Batoul Taghipour ◽  
Farhad Ahmadnejad
Keyword(s):  
Shear Zone ◽  
Early Stage ◽  
Hanging Wall ◽  
Regional Metamorphism ◽  
Shear Zones ◽  
Northwestern Part ◽  
Type I ◽  
Two Phase ◽  
Mean Values ◽  
Calcite Veins

Abstract The Qolqoleh gold deposit is located in the northwestern part of the Sanandaj-Sirjan Zone (SSZ), within the NE-SW trending Qolqoleh shear zone. Oligocene granitoids, Cretaceous meta-limestones, schists and metavolcanics are the main lithological units. Chondrite-normalised REE patterns of the ore-hosting metavolcanics indicate REE enrichment relative to hanging wall (chlorite-sericite schist) and footwall (meta-limestone) rocks. The pattern also reflects an enrichment in LREE relative to HREE. It seems that the LREE enrichment is related to the circulation of SO42- and CO2-bearing fluids and regional metamorphism in the Qolqoleh shear zone. Both positive and negative Eu anomalies are observed in shear-zone metavolcanics. These anomalies are related to the degree of plagioclase alteration during gold mineralisation and hydrothermal alteration. In progressing from a metavolcanic protomylonite to an ultramylonite, significant changes occurred in the major/trace element and REE concentration. Utilising an Al-Fe-Ti isocon for the ore-hosting metavolcanics shows that Sc, Y, K, U, P, and M-HREE (except Eu) are relatively unchanged; S, As, Ag, Au, Ca, LOI, Rb and LREE are enriched, and Sr, Ba, Eu, Cr, Co and Ni decrease with an increasing degree of deformation. Based on geochemical features and comparison with other well-known shear zones in the world, the study area is best classified as an Isovolume-Gain (IVG) type shear zone and orogenic type gold mineralisation. Based on the number of phases observed at room temperature and their microthermometric behaviour, three fluid inclusion types have been recognised in quartz-sulphide and quartz-calcite veins: Type I monophase aqueous inclusions, Type II two-phase liquid-vapour (L-V) inclusions which are subdivided into two groups based on the homogenisation temperature (Th): a) L-V inclusions with Th from 205 to 255°C and melting temperature of last ice (Tm) from -3 to -9°C. b) L-V inclusions with higher Th from 335 to 385°C and Tm from -11 to -16°C. Type III three-phase carbonic-liquid inclusions (liquid water-liquid CO2-vapour CO2) with Th of 345-385°C. The mean values of the density of ore-forming fluids, pressure and depth of mineralisation have been calculated to be 0.79-0.96 gr/cm3, 2 kbar and 7 km, respectively. The δ18Owater and δD values of the gold-bearing quartz-sulphide veins vary from 7.2‰ to 8‰ and -40.24‰ to -35.28‰, respectively, which are indicative of an isotopically heavy crustal fluid and likely little involvement of meteoric fluid. The δ18Owater values of the quartz-calcite veins have a range of -5.31‰ to -3.35‰, and the δD values of -95.65‰ to -75.31‰, which are clearly lower than those of early-stage quartz-sulphide-gold veins, and are close to the meteoric water line. Based on comparisons of the D-O isotopic systematics, the Qolqoleh ore-mineralising fluids originated from metamorphic devolatilisation of Cretaceous volcano-sedimentary piles. Devolatilisation of these units occurred either synchronously with, or postdates, the development of penetrative (ductile) structures such as shear zones and during overprinting brittle deformation

Distribution study of a synthetic ACTH analogue in rat tissue

1981 ◽  
Vol 96 (4) ◽  
pp. 464-469 ◽  
Author(s):  
Masaharu Hirata ◽  
Shinya Futaguchi ◽  
Kunihiro Odaguchi ◽  
Ken Inouye ◽  
Akira Tanaka
Keyword(s):  
Small Intestine ◽  
Tissue Distribution ◽  
Early Stage ◽  
Thigh Muscle ◽  
First Order ◽  
Distribution Study ◽  
Tissue Weight ◽  
First Order Kinetics ◽  
Hypophysectomized Rats ◽  
Rat Tissue

Abstract. Tissue distribution of {Aib1, Lys17,18,19}-corticotrophin-(1-19)-nonadecapeptide amide (690024-S), iv injected to hypophysectomized rats, were surveyed by bioassay. Among the tissues examined, the largest amount of 690024-S was found in the liver during 3 h of search for the injection, while a higher concentration of the peptide per tissue weight was found in kidney. Though a small amount of 690024-S was detected in spleen, heart and lung at an early stage, it was not detectable in other tissues such as brain, stomach, small intestine, thigh muscle, fat or foetus. The peptide was found to be excreted into bile for the duration of about 2 h. It was also found that the elimination of 690024-S in blood followed biphasic first order kinetics.

Blueschist facies conditions in Tethyan passive margin metabasaltic rocks of the easternmost Lower Alpujarride Units (Internal Betic Zone, Spain)

2021 ◽  
Author(s):  
Eva Santamaría-Pérez ◽  
Idael Francisco Blanco-Quintero ◽  
Agustín Martín-Algarra ◽  
David Benavente ◽  
Juan Carlos Cañaveras ◽  
...  
Keyword(s):  
Thermal Gradient ◽  
Early Stage ◽  
Passive Margin ◽  
Geochemical Data ◽  
Geodynamic Setting ◽  
Low Grade ◽  
Alkaline Basalt ◽  
Metamorphic Overprint ◽  
Sedimentary Sequences ◽  
Basalt Composition

<p>Jurassic shallow-intrusive basic bodies within the Permian-Triassic Tethyan passive margin sedimentary sequences of the Lower Alpujarride units (Internal Betic Zone, Spain) locally show Alpine low-grade metamorphism in the greenschist and blueschist facies. A small sill-like mafic body near Redován town (Callosa Range) partially preserves igneous ophitic/subophitic texture and relics of augite, ferrohornblende-ferroedenite, kaersutite and K-feldspar (orthoclase). The metamorphic overprint corresponds to high-pressure and low-temperature mineral assemblages that comprise magnesioriebeckite, actinolite, albite, stilpnomelane, phengite and chlorite, with rutile, apatite and titanite as accessory minerals. Major and trace element geochemical data reveal igneous protoliths derived from magmas of alkaline basalt composition enriched in incompatible elements and E-MORB geochemical affinity. The intrusion emplacement occurred at shallow crustal levels in an extensional geodynamic setting (within-plate basalts) related to the breakoff of Pangea. Pressure-Temperature (P-T) conditions estimated by means of pseudosection calculations and the intersection of phengite (Si) and chlorite (Mg#) isopleths indicate a cold thermal gradient with calculated peak metamorphic conditions of ca. 8 kbar at 310 ºC. These conditions are consistent with metamorphism during burial down to ca. 24 km depth and a thermal gradient of ca. 13 ºC/km. Although the easternmost Lower Alpujarride units have been traditionally described as reaching only lower-greenschist to greenschist metamorphic peak conditions, the textures, mineral compositions and P-T conditions of the studied metagabbroic body reveal blueschist facies conditions that attest for a regional early stage (Eocene) of subduction of the lower Alpujarride units. This event predates the late Oligocene - early Miocene subduction-related metamorphism of the Intermediate and Upper Alpujarride units.</p>

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