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Sample records for age metamorphic history

  1. High-precision UPb ages of metamorphic rutile: application to the cooling history of high-grade terranes

    USGS Publications Warehouse

    Mezger, K.; Hanson, G.N.; Bohlen, S.R.

    1989-01-01

    Metamorphic rutiles occurring in granulite and upper amphibolite facies metapelitic rocks of the Archean Pikwitonei granulite domain (Manitoba) and the Proterozoic Adirondack terrane (New York) give concordant and near concordant UPb ages. The Pb concentrations in rutile range from 2.85 to 168 ppm, U concentrations range from 10.9 to 390 ppm and the measured 206Pb 204Pb ratios range from 182 to 22,100 corresponding to 238U 204Pb ratios of 398-75,100. The proportions of radiogenic 208Pb are very low, ranging from 0.0 to 6.9% of total radiogenic Pb. The habits of the rutile crystals range from stubby to acicular, the physical properties vary from opaque/black to transparent/reddish-brown. Separate batches of black and reddish-brown rutile grains from the same samples have similar U and Pb concentrations, Pb-isotope ratios, and yield the same U Pb ages within analytical uncertainty. No correlation of U concentration and 206Pb 204Pb ratios with morphology or color of the rutiles was observed among the samples analyzed. Most rutiles yield concordant UPb ages which are reproducible within analytical uncertainty, i.e. generally ??2 Ma. The UPb ages for prograde rutile are younger than the time of peak metamorphism given by UPb ages for garnet and zircon, and also younger than UPb ages for sphene and monazite, and 40Ar 39Ar and KAr ages for hornblende but older than 40Ar 39Ar and KAr ages for biotite from the same area. This suggests that the rutile ages reflect cooling below closure temperatures. Within a single hand-specimen, and thus for an identical thermal history, larger rutile grains give older ages than do smaller grains. This suggests that volume diffusion is the most probable mechanism responsible for the ages being younger than the time of peak metamorphism. It also suggests that the dimensions for such diffusion are directly related to the dimensions of the rutile crystal and not to the dimensions of sub-grain domains, as is the case for Ar diffusion in

  2. U-Pb garnet, sphene, monazite, and rutile ages: Implications for the duration of high-grade metamorphism and cooling histories, Adirondack Mts. , New York

    SciTech Connect

    Mezger, K.; Rawnsley, C.M.; Hanson, G.N. ); Bohlen, S.R. )

    1991-05-01

    Garnet ages for the Lowlands range from 1,168-1,127 Ma, those from the central and southern Highlands from 1,154-1,013 Ma. Metamorphism in the Highlands may not have occurred as a single event but rather in several discrete thermal pulses. An age of 1,153 {plus minus} 3 Ma was determined for garnets in the syn-regional metamorphic contact aureole of the Diana syenite, consistent with that of the syenite intrusion, 1 155 {plus minus} 4 Ma. Garnets just outside the contact aureole give an age of 1,168 {plus minus} 6 Ma. In the Lowlands, monazite yielded an age of 1,161 {plus minus} 1 Ma, rutiles yielded ages of 1,005 {plus minus} 2 Ma and 953 {plus minus} 4 Ma, and sphene ages range from 1,156 to 1,103 Ma. In the Highlands, monazite yielded an age of 1,033 {plus minus} 1 Ma, rutiles yielded ages of 911 {plus minus} 2 Ma and 885 {plus minus} 2 and sphenes from 1,033 Ma to 991 Ma. The rutile and monazite ages indicate that both terranes cooled at time-integrated rates of ca. 1.5C/Ma for at least 150 Ma following the last phase of high-grade metamorphism. The Lowlands cooled to ca. 400C by ca. 1,000 Ma and the Highlands by ca. 900 Ma. The mineral ages indicate that metamorphic pressures and temperatures recorded by thermobarometry correspond to conditions attained polychronically over 150 Ma or more. Mineral ages combined with temperature estimates for peak metamorphism indicate that the closure temperature for the U-Pb system is >800C in garnet, 640-730C in monazite, and 500-670C in sphene.

  3. Cathodoluminescence of diamond as an indicator of its metamorphic history

    NASA Astrophysics Data System (ADS)

    Kopylova, Maya; Bruce, Loryn; Longo, Micaela; Ryder, John; Dobrzhinetskaya, Larissa

    2010-05-01

    Diamond displays a supreme resistance to chemical and mechanical weathering, ensuring its survival through complex and prolonged crustal processes, including metamorphism and exhumation. For these reasons, volcanic sources and secondary and tertiary collectors for detrital placer diamonds, like Ural or Bingara diamonds, may be difficult to determine. If metamorphic processes leave their marks on diamond, they can be used to reconstruct crustal geologic processes and ages of primary diamondiferous volcanics. Four diamond suites extracted from metamorphic rocks have been characterized using optical CL, infrared and CL spectroscopy, and photoluminescence at the liquid nitrogen temperature. The studied diamonds are from the ~2.7 Ga sedimentary conglomerate and lamprophyric breccia metamorphosed in the greenschist facies (Wawa, Northern Ontario, Canada) during the 2.67 Ga Kenoran orogeny, and from the ultra-high pressure (UHP) terranes of Kokchetav (Kazakhstan) and Erzgebirge (Germany) exhumated in the Paleozoic. Wawa diamonds (Type IaAB and Type II) displayed green, yellow, orange, and red CL colours controlled by the CL emittance at 520, 576 nm, and between 586 and 664 nm. The UHP terranes diamonds show much weaker CL; few luminescent stones display CL peaks at 395, 498, 528 nm and a broad band at 580-668 nm. In contrast, most common diamonds found in unmetamorphosed rocks, i.e. octahedrally grown Type IaAB stones, luminescence blue emitting light at ~415-440 nm and 480-490 nm. There is a noticeable difference between cathodoluminescence of these diamonds and diamonds in metamorphic rocks. The studied diamonds that experienced metamorphism show a shift of CL emission to longer wavelengths (above 520 nm) and to green, yellow and red CL colours. Photoluminescence has the high resolution necessary to assign luminescence to specific optical centers of diamond. Diamonds in metamorphic rocks contain H3 (pairs of substitutional nitrogen atoms separated by a vacancy) and NVo

  4. Thermal history of a metamorphic core complex

    NASA Technical Reports Server (NTRS)

    Dokka, R. K.; Mahaffie, M. J.; Snoke, A. W.

    1985-01-01

    Fission track (FT) thermochronology studies of lower plate rocks of the Ruby Mountains-East Humbolt Range metamorphic core complex provide important constraints on the timing an nature of major middle Tertiary extension of northeast Nevada. Rocks analyzed include several varieties of mylonitic orthogneiss as well as amphibolitic orthognesses from the non-mylonitic infrastructural core. Oligocene-age porphyritic biotite granodiorite of the Harrison Pass pluton was also studied. The minerals dated include apatite, zircon, and sphene and were obtained from the same rocks that have been previously studied. FT ages are concordant and range in age from 26.4 Ma to 23.8 Ma, with all showing overlap at 1 sigma between 25.4 to 23.4 Ma. Concordancy of all FT ages from all structural levels indicates that the lower plate cooled rapidly from temperatures above approx. 285 C (assumed sphene closure temperature (2)) to below approx. 150 C (assumed apatite closure temperature) near the beginning of the Miocene. This suggests that the lower plate cooled at a rate of at least approx. 36 deg C/Ma during this event. Rapid cooling of the region is considered to reflect large-scale tectonic denudation (intracrustal thinning), the vertical complement to intense crustal extension. FT data firmly establish the upper limit on the timing of mylonitization during detachment faulting and also coincide with the age of extensive landscape disruption.

  5. Organic matter and metamorphic history of CO chondrites

    NASA Astrophysics Data System (ADS)

    Bonal, Lydie; Bourot-Denise, Michèle; Quirico, Eric; Montagnac, Gilles; Lewin, Eric

    2007-03-01

    The metamorphic grades of a series of eight CO3 chondrites (ALHA77307, Colony, Kainsaz, Felix, Lancé, Ornans, Warrenton and Isna) have been quantified. The method used was based on the structural grade of the organic matter trapped in the matrix, which is irreversibly transformed by thermal metamorphism. The maturation of the organic matter is independent with respect to the mineralogical context and aqueous alteration. This metamorphic tracer is thus valid whatever the chemical class of chondrites. Moreover, it is sensitive to the peak metamorphic temperature. The structural grade of the organic matter was used along with other metamorphic tracers such as petrography of opaque minerals, Fa and Fs silicate composition in type I chondrules, presolar grains and noble gas (P3 component) abundance. The deduced metamorphic hierarchy and the attributed petrographic types are the following: ALHA77307 (3.03) < Colony (3.1) < Kainsaz (3.6) < Felix (3.6 (1)) < Ornans (3.6 (2)) < Lancé (3.6 (3)) < Warrenton (3.7 (1)) < Isna (3.7 (2)). For most metamorphosed objects, the peak metamorphic temperature can be estimated using a geothermometer calibrated with terrestrial metasediments [Beyssac O., Goffe B., Chopin C., and Rouzaud J. N. (2002) Raman spectrum of carbonaceous material in metasediments: a new geothermometer. J. Metamorph. Geol., 20, 859-871]. A value of 330 °C was obtained for Allende (CV chondrite), Warrenton and Isna, consistent with temperatures estimated from Fe diffusion [Weinbruch S., Armstrong J., and Palme H. (1994). Constraints on the thermal history of the Allende parent body as derive from olivine-spinel thermometry and Fe/Mg interdiffusion in olivine. Geochim. Cosmochim. Acta58(2), 1019-1030.], from the Ni content in sulfide-metal assemblages [Zanda B., Bourot-Denise M., and Hewins R. (1995) Condensate sulfide and its metamorphic transformations in primitive chondrites. Meteorit. Planet. Sci.30, A605.] and from the d002 interlayer spacing in poorly

  6. Lunar anorthosite 15415: texture, mineralogy, and metamorphic history.

    PubMed

    James, O B

    1972-01-28

    Lunar anorthosite 15415 consists almost entirely of anorthite (homogeneous anorthite 96.6 molecule percent), with accessory diopsidic augite and traces of hypersthene, ilmenite, and a silica mineral. The rock has had a complex metamorphic history. The texture reflects at least two episodes of shearing (followed by intense and partial recrystallization, respectively), one episode of cataclastic deformation, and one or more episodes of shattering and fragmentation. PMID:17731367

  7. Lunar anorthosite 15415 - Texture, mineralogy, and metamorphic history.

    NASA Technical Reports Server (NTRS)

    James, O. B.

    1972-01-01

    Lunar anorthosite 15415 consists almost entirely of anorthite (homogeneous anorthite 96.6 molecule percent), with accessory diopsidic augite and traces of hypersthene, ilmenite, and a silica mineral. The rock has had a complex metamorphic history. The texture reflects at least two episodes of shearing (followed by intense and partial recrystallization, respectively), one episode of cataclastic deformation, and one or more episodes of shattering and fragmentation.

  8. Lunar anorthosite 15415: Texture, mineralogy, and metamorphic history

    USGS Publications Warehouse

    James, O.B.

    1972-01-01

    Lunar anorthosite 15415 consists almost entirely of anorthite (homogeneous anorthite 96.6 molecule percent), with accessory diopsidic augite and traces of hypersthene, ilmenite, and a silica mineral. The rock has had a complex metamorphic history. The texture reflects at least two episodes of shearing (followed by intense and partial recrystallization, respectively), one episode of cataclastic deformation, and one or more episodes of shattering and fragmentation.

  9. Lunar anorthosite 15415: texture, mineralogy, and metamorphic history.

    PubMed

    James, O B

    1972-01-28

    Lunar anorthosite 15415 consists almost entirely of anorthite (homogeneous anorthite 96.6 molecule percent), with accessory diopsidic augite and traces of hypersthene, ilmenite, and a silica mineral. The rock has had a complex metamorphic history. The texture reflects at least two episodes of shearing (followed by intense and partial recrystallization, respectively), one episode of cataclastic deformation, and one or more episodes of shattering and fragmentation.

  10. Rb-Sr age of the Shergotty achondrite and implications for metamorphic resetting of isochron ages

    NASA Technical Reports Server (NTRS)

    Nyquist, L. E.; Bogard, D. D.; Wooden, J.; Bansal, B.; Wiesmann, H.; Mckay, G.

    1979-01-01

    The age of the Shergotty achondrite is determined by Rb-Sr isotope analysis and the metamorphic resetting of isochron ages, which is presumed to have occurred during a shock event in the history of the meteorite, is discussed. The isochron best fitting the Rb-Sr evolution diagram is found to correspond to an age of 165 million years, with an initial Sr-87/Sr-86 value of 0.72260. Different apparent ages obtained by the K-Ar and Sm-Nd methods are interpreted in terms of a model which quantifies the degree of resetting of internal isochron ages by low temperature solid state diffusion. On the basis of these considerations, it is concluded that Shergotty crystallized from a melt 650 million years ago, was shock heated to 300 to 400 C after its parent body was involved in a collision 165 million years ago, and was first exposed to cosmic rays two million years ago.

  11. Geospeedometry and the metamorphic history of the Late Cretaceous Chiwaukum Schist, west central Washington state

    SciTech Connect

    Evans, D.A. . Div. of Geological and Planetary Sciences); Lasaga, A.C.; Ague, J.J.; Brandon, M.T. . Dept. of Geology and Geophysics)

    1993-04-01

    The Chiwaukum Schist on the NE side of the Late Cretaceous Mount Stuart batholith (MSB) shows evidence of a low-P contact metamorphism, followed by a higher-P amphibolite-facies regional metamorphism (Evans and Berti, 1986). Samples were collected from this contact zone in order to quantify the time-temperature history of the schist using the geospeedometry method of Lasaga (1983). Pseudomorphic textures and garnet-aluminosilicate-plagioclase (GASP) geobarometry within some samples show an increase in pressure during crystal growth, consistent with the interpretation of Evans and Berti (1986), that regional metamorphism followed intrusion of the MSB. Geospeedometry exploits the kinetics of diffusion associated with the thermo-barometric exchange reactions in order to determine the retrograde cooling history of a metamorphic rock. This technique was applied using Fe-Mg diffusion between garnet and biotite as defined by that geothermometer. Modeling results indicate that the region was exhumed and cooled from about 22 km and 610 C to about 8 km and 525 C, in a period of about 2.5 Myr. The average exhumation rate is 5.6 km/Myr. These results are consistent with existing isotopic ages, which indicate that the northeast MSB was intruded at about 95 Ma (K/Ar hornblende and U/Pb zircon) and that the Chiwaukum Schist cooled through temperatures of about 350 C at 86 to 83 Ma (K/Ar muscovite). Rapid unroofing appears to follow shortly after the climax of crustal thickening within the Cascade metamorphic core and may be related to erosional and/or tectonic denudation within a mountainous collisional orogen.

  12. Proterozoic metamorphism and uplift history of the north-central Laramie Mountains, Wyoming, USA

    USGS Publications Warehouse

    Patel, S.C.; Frost, B.R.; Chamberlain, K.R.; Snyder, G.L.

    1999-01-01

    The Laramie Mountains of south-eastern Wyoming contain two metamorphic domains that are separated by the 1.76 Ga. Laramie Peak shear zone (LPSZ). South of the LPSZ lies the Palmer Canyon block, where apatite U-Pb ages are c. 1745 Ma and the rocks have undergone Proterozoic kyanite-grade Barrovian metamorphism. In contrast, in the Laramie Peak block, north of the shear zone, the U-Pb apatite ages are 2.4-2.1 Ga, the granitic rocks are unmetamorphosed and supracrustal rocks record only low-T amphibolite facies metamorphism that is Archean in age. Peak mineral assemblages in the Palmer Canyon block include (a) quartz-biotite-plagioclase-garnet-staurolite-kyanite in the pelitic schists; (b) quartz-biotite-plagioclase-low-Ca amphiboles-kyanite in Mg-Al-rich schists, and locally (c) hornblende-plagioclase-garnet in amphibolites. All rock types show abundant textural evidence of decompression and retrograde re-equilibration. Notable among the texturally late minerals are cordierite and sapphirine, which occur in coronas around kyanite in Mg-Al-rich schists. Thermobarometry from texturally early and late assemblages for samples from different areas within the Palmer Canyon block define decompression from > 7 kbar to < 3 kbar. The high-pressure regional metamorphism is interpreted to be a response to thrusting associated with the Medicine Bow orogeny at c. 1.78-1.76 Ga. At this time, the north-central Laramie Range was tectonically thickened by as much as 12 km. This crustal thickening extended for more than 60 km north of the Cheyenne belt in southern Wyoming. Late in the orogenic cycle, rocks of the Palmer Canyon block were uplifted and unroofed as the result of transpression along the Laramie Peak shear zone to produce the widespread decompression textures. The Proterozoic tectonic history of the central Laramie Range is similar to exhumation that accompanied late-orogenic oblique convergence in many Phanerozoic orogenic belts.

  13. Radiometric ages related to the timing of Paleozoic metamorphism and deformation in the Blue Ridge of northwestern North Carolina

    SciTech Connect

    Goldberg, S.A. . Dept. of Geology); Dallmeyer, R.D. . Dept. of Geology)

    1992-01-01

    Thrust sheets within the Blue Ridge (BR) of northwestern NC record different Paleozoic tectonic histories, recognized on the basis of detailed field and petrographic studies. Ar-40/Ar-39, Rb-Sr, Sm-Nd, and U-Pb data are reported on mineral separates, part of an ongoing study to define the ages of Paleozoic metamorphism and deformation within various segments of the Blue Ridge. East of the Gossan Lead fault in vicinity of the Grandfather Mountain window, the BR consists mainly of amphibolite and pelitic schist. These rocks record ordovician Sm-Nd ages, Devonian Rb-Sr ages, and Mississippian Ar-40/Ar-39 ages. A Sm-Nd mineral isochron based on hornblende, plagioclase, and sphene from an amphibolite defines an age of 465 [+-] 35 Ma. Rb-Sr data from an amphibolite of similar metamorphic grade yields Devonian mineral ages ranging from 365--408 Ma. Muscovite separates in associated pelitic schists record Ar-40/Ar-39 plateau ages of 324 [+-] 1 and 329 [+-] 1 Ma. The ages are interpreted to reflect extensive Paleozoic tectonothermal activity in eastern Blue Ridge sequences, commencing with high-grade Ordovician metamorphism, isotopic resetting in the Devonian associated with granitic intrusions, followed by further re-equilibration associated with Alleghanian thrusting. In contrast, thrust sheets from the westernmost BR exhibit low metamorphic grades and record mainly Taconic ages of metamorphism. Preliminary analysis suggests that only the easternmost thrust sheets of northwestern NC experienced thermal resetting during the Devonian.

  14. Mesoproterozoic syntectonic garnet within Belt Supergroup metamorphic tectonites: Evidence of Grenville-age metamorphism and deformation along northwest Laurentia

    USGS Publications Warehouse

    Nesheim, T.O.; Vervoort, J.D.; McClelland, W.C.; Gilotti, J.A.; Lang, H.M.

    2012-01-01

    Northern Idaho contains Belt-Purcell Supergroup equivalent metamorphic tectonites that underwent two regional deformational and metamorphic events during the Mesoproterozoic. Garnet-bearing pelitic schists from the Snow Peak area of northern Idaho yield Lu-Hf garnet-whole rock ages of 1085??2. Ma, 1198??79. Ma, 1207??8. Ma, 1255??28. Ma, and 1314??2. Ma. Garnet from one sample, collected from the Clarkia area, was micro-drilled to obtain separate core and rim material that produced ages of 1347??10. Ma and 1102??47. Ma. The core versus rim ages from the micro-drilled sample along with the textural and spatial evidence of the other Lu-Hf garnet ages indicate two metamorphic garnet growth events at ~. 1330. Ma (M1) and ~. 1080. Ma (M2) with the intermediate ages representing mixed ages. Some garnet likely nucleated and grew M1 garnet cores that were later overgrown by younger M2 garnet rims. Most garnet throughout the Clarkia and Snow Peak areas are syntectonic with a regional penetrative deformational fabric, preserved as a strong preferred orientation of metamorphic matrix minerals (e.g., muscovite and biotite). The syntectonic garnets are interpreted to represent one regional, coeval metamorphic and deformation event at ~. 1080. Ma, which overlaps in time with the Grenville Orogeny. The older ~. 1330. Ma ages may represent an extension of the East Kootenay Orogeny described in western Canada. These deformational and metamorphic events indicate that western Laurentia (North America) was tectonically active in the Mesoproterozoic and during the assembly of the supercontinent Rodinia. ?? 2011 Elsevier B.V.

  15. Mesoproterozoic syntectonic garnet within Belt Supergroup metamorphic tectonites: Evidence of Grenville-age metamorphism and deformation along northwest Laurentia

    NASA Astrophysics Data System (ADS)

    Nesheim, Timothy O.; Vervoort, Jeffrey D.; McClelland, William C.; Gilotti, Jane A.; Lang, Helen M.

    2012-03-01

    Northern Idaho contains Belt-Purcell Supergroup equivalent metamorphic tectonites that underwent two regional deformational and metamorphic events during the Mesoproterozoic. Garnet-bearing pelitic schists from the Snow Peak area of northern Idaho yield Lu-Hf garnet-whole rock ages of 1085 ± 2 Ma, 1198 ± 79 Ma, 1207 ± 8 Ma, 1255 ± 28 Ma, and 1314 ± 2 Ma. Garnet from one sample, collected from the Clarkia area, was micro-drilled to obtain separate core and rim material that produced ages of 1347 ± 10 Ma and 1102 ± 47 Ma. The core versus rim ages from the micro-drilled sample along with the textural and spatial evidence of the other Lu-Hf garnet ages indicate two metamorphic garnet growth events at ~ 1330 Ma (M1) and ~ 1080 Ma (M2) with the intermediate ages representing mixed ages. Some garnet likely nucleated and grew M1 garnet cores that were later overgrown by younger M2 garnet rims. Most garnet throughout the Clarkia and Snow Peak areas are syntectonic with a regional penetrative deformational fabric, preserved as a strong preferred orientation of metamorphic matrix minerals (e.g., muscovite and biotite). The syntectonic garnets are interpreted to represent one regional, coeval metamorphic and deformation event at ~ 1080 Ma, which overlaps in time with the Grenville Orogeny. The older ~ 1330 Ma ages may represent an extension of the East Kootenay Orogeny described in western Canada. These deformational and metamorphic events indicate that western Laurentia (North America) was tectonically active in the Mesoproterozoic and during the assembly of the supercontinent Rodinia.

  16. Deciphering the tectonometamorphis history of the Anarak Metamorphic Complex, Central Iran

    NASA Astrophysics Data System (ADS)

    Zanchetta, Stefano; Malaspina, Nadia; Zanchi, Andrea; Martin, Silvana; Benciolini, Luca; Berra, Fabrizio; Javadi, Hamid Reza; Koohpeyma, Meysam; Ghasemi, Mohammad R.; Sheikholeslami, Mohammad Reza

    2014-05-01

    The Cimmerian orogeny shaped the southern margin of Eurasia during the Late Permian and the Triassic. Several microplates, detached from Gondwana in the Early Permian, migrated northward to be accreted to the Eurasia margin. In the reconstruction of such orogenic event Iran is a key area. The occurrence of several "ophiolites" belt of various age, from Paleozoic to Cretaceous, poses several questions on the possibility that a single rather than multiple Paleotethys sutures occur between Eurasia and Iran. In this scenario the Anarak region in Central Iran still represents a conundrum. Contrasting geochronological, paleontological, paleomagnetic data and reported field evidence suggest different origins for the Anarak Metamorphic Complex (AMC). The AMC is either interpreted to be part of microplate of Gondwanan affinity, a relic of an accretionary wedge developed at the Eurasia margin during the Paleothetys subduction or part of the Cimmerian suture zone, occurring in NE Iran, displaced to central Iran by counterclockwise rotation of the central Iranian blocks from the Triassic. Our field structural data, petrographic and geochemical data, carried out in the frame of the DARIUS PROGRAMME, indicate that the AMC is not a single coherent block, but it consists of several units (Morghab, Chah Gorbeh, Patyar, Palhavand Gneiss, Lakh Marble, Doshak and dismembered "ophiolites") which display different tectonometamorphic evolutions. The Morghab and Chah Gorbeh units share a common history and they preserve, as a peculiar feature within metabasites, a prograde metamorphism with sin- to post-deformation growth of blueschists facies assemblages on pre-existing greenschist facies mineralogical associations. LT-HP metamorphism responsible for the growth of sodic amphibole has been recognized also within marble lenses at the southern limit of the Chah Gorbeh unit. Finally, evidence of LT-HP metamorphism also occur in the metabasites and possibly also in the serpentinites that form

  17. Linking monazite geochronology with fluid infiltration and metamorphic histories: Nature and experiment

    NASA Astrophysics Data System (ADS)

    Shazia, J. R.; Harlov, D. E.; Suzuki, K.; Kim, S. W.; Girish-Kumar, M.; Hayasaka, Y.; Ishwar-Kumar, C.; Windley, B. F.; Sajeev, K.

    2015-11-01

    Migmatised metapelites from the Kodaikanal region, central Madurai Block, southern India have undergone ultrahigh-temperature metamorphism (950-1000 °C; 7-8 kbar). In-situ electron microprobe Th-U-Pb isochron (CHIME) dating of monazites in a leucosome and surrounding silica-saturated and silica-poor restites from the same outcrop indicates three principal ages that can be linked to the evolutionary history of these rocks. Monazite grains from the silica-saturated restite have well-defined, inherited cores with thick rims that yield an age of ca. 1684 Ma. This either dates the metamorphism of the original metapelite or is a detrital age of inherited monazite. Monazite grains from the silica-poor restite, thick rims from the silica-saturated restite, and monazite cores from the leucosome have ages ranging from 520 to 540 Ma suggesting a mean age of 530 Ma within the error bars. In the leucosome the altered rim of the monazite gives an age of ca. 502 Ma. Alteration takes the form of Th-depleted lobes of monazite with sharp curvilinear boundaries extending from the monazite grain rim into the core. We have replicated experimentally these altered rims in a monazite-leucosome experiment at 800 °C and 2 kbar. This experiment, coupled with earlier published monazite-fluid experiments involving high pH alkali-bearing fluids at high P-T, helps to confirm the idea that alkali-bearing fluids, in the melt and along grain boundaries during crystallization, were responsible for the formation of the altered monazite grain rims via the process of coupled dissolution-reprecipitation.

  18. The age and petrography of two Luna 20 fragments and inferences for widespread lunar metamorphism.

    NASA Technical Reports Server (NTRS)

    Podosek, F. A.; Huneke, J. C.; Gancarz, A. J.; Wasserburg, G. J.

    1973-01-01

    Ages were determined by the Ar-40/Ar-39 method on two metaclastic rocks returned from the lunar highlands north of Mare Fecunditatis by the Luna 20 probe. Both samples gave very well-defined argon retention ages of 3.90 plus or minus 0.04 AE which are indistinguishable from each other within a resolution of 0.02 AE. Both fragments, 22006 and 22007, are highly recrystallized polymict breccias; there is no evidence of radiogenic Ar-40, and the age almost surely dates the time of recrystallization. The cosmic ray exposure ages of these fragments are similar and high: 900 million years for 22006, 1300 million years for 22007. 22007 also contains substantial trapped argon with a high Ar-40/Ar-36. The Luna 20 results greatly extend the area of the moon's surface exhibiting a well-defined record of metamorphism at 3.9 AE. So far, lunar history in the interval from 4.6 to 3.9 AE is not preserved in the ages of surface rocks. This obliteration suggests lunar-wide metamorphic conditions occurring or terminating at this time as a result of major impacts.

  19. Isotope and chemical age of the Greater Caucasus basement metamorphic rocks

    NASA Astrophysics Data System (ADS)

    Konilov, A. N.; Somin, M. L.; Mukhanova, A. A.

    2009-04-01

    complexes independently of baric type seem to be formed roughly synchronously during Variscan epoch. References: Gamkrelidze I.P., Shengelia D.M. ( 2005).The Precambrian-Paleozoic Regional Metamorphism, Granitoid Magmatism, and Geodynamics of the Caucasus. M: Nauchnyi Mir [in Russian]. Pyle J.M., Frank S. Spear F.S. et al. (2001). Monazite-Xenotime-Garnet Equilibrium in Metapelites and a New Monazite-Garnet Thermometer. Journal of Petrology, , 42, 2083-2107. Slagstad T. (2006).Chemical (U-Th-Pb) dating of monazite: Analytical protocol for a LEO 1450VP scanning electron microscope and examples from Rogaland and Finnmark, Norway. Norges geologiske undersøkelse Bulletin, 446, 11-18. Somin M.L. (2007a). Pre-Alpine basement of the Greater Caucasus: main features. In: Alpine history of the Greater Caucasus (Yu.G. Leonovб Ed.). GEOS. Moscow. P.15-38. Somin M.L., Lepekhina E.N., Konilov A.N. ( 2007b). Age of the High-Temperature Gneiss Core of the Central Caucasus. Doklady Earth Sciences, 415, 690-694. Somin M.L., Levchenkov O.A., Kotov A.B. et al. (2007c). The Paleozoic Age of High-Pressure Metamorphic Rocks in the Dakhov Salient, North-Western Caucasus: Results of U-Pb Geochronological Investigations. Doklady Earth Sciences, 416, 1018-1021. Suzuki K., Adachi M. (1991). Precambrian provenance and Silurian metamorphism of the Tsunosava paragneiss in South Kitakami terrane, northeast Japan, revealed by the chemical Th-U-total Pb isochron ages of monazite, zircon and xenotime. Journal of Geochemistry, 25, 357-376.

  20. Age and metamorphism of some massive sulflde deposits in Virginia, North Carolina and Tennessee

    USGS Publications Warehouse

    Kinkel, A.R., Jr.; Thomas, H.H.; Marvin, R.F.; Walthall, F.G.

    1965-01-01

    Isotopic ages of vein and wall-rock samples have been determined on five massive sulflde deposits of the southern Appalachians. Vein mineral ages of about 1100 m.y. indicate that some ore bodies formed at least as early as the Grenville metamorphism, and probably soon after the formation of the enclosing gneiss and schist. Present textures of the ore were formed during subsequent metamorphic periods at about 450 m.y. and 300 to 330 m.y. ago. ?? 1965.

  1. Peak metamorphic temperature and thermal history of the Southern Alps (New Zealand)

    NASA Astrophysics Data System (ADS)

    Beyssac, O.; Cox, S. C.; Vry, J.; Herman, F.

    2016-04-01

    The Southern Alps orogen of New Zealand results from late Cenozoic convergence between the Indo-Australian and Pacific plates and is one of the most active mountain belts in the world. Metamorphic rocks carrying a polymetamorphic legacy, ranging from low-greenschist to high-grade amphibolites, are exhumed in the hanging wall of the Alpine Fault. On a regional scale, the metamorphic grade has previously been described in terms of metamorphic zones and mineral isograds; application of quantitative petrology being severely limited owing to unfavorable quartzofeldspathic lithologies. This study quantifies peak metamorphic temperatures (T) in a 300 × 20 km area, based on samples forming 13 transects along-strike from Haast in the south to Hokitika in the north, using thermometry based on Raman spectroscopy of carbonaceous material (RSCM). Peak metamorphic T decreases across each transect from ≥ 640 °C locally in the direct vicinity of the Alpine Fault to less than 330 °C at the drainage divide 15-20 km southeast of the fault. Thermal field gradients exhibit a degree of similarity from the southernmost to the northernmost transects, are greater in low-grade semischist than high-grade schist, are affected by folding or discontinuous juxtaposition of metamorphic zones, and contain limited information on crustal-scale geothermal gradients. Temperatures derived by RSCM thermometry are slightly (≤ 50 °C) higher than those derived by traditional quantitative petrology using garnet-biotite thermometry and THERMOCALC modeling. The age of RSCM T appears to be mostly pre-Cenozoic over most of the area except in central Southern Alps (Franz Josef-Fox area), where the amphibolite facies schists have T of likely Cenozoic age. The RSCM T data place some constraints on the mode of exhumation along the Alpine Fault and have implications for models of Southern Alps tectonics.

  2. 40Ar/39Ar and K-Ar data bearing on the metamorphic and tectonic history of western New England.

    USGS Publications Warehouse

    Sutter, J.F.; Ratcliffe, N.M.; Mukasa, S.B.

    1985-01-01

    40Ar/39Ar ages of coexisting biotite and hornblende from Proterozoic Y gneisses of the Berkshire and Green Mt massifs, as well as 40Ar/39Ar and K/Ar mineral and whole-rock ages from Palaeozoic metamorphic rocks, suggest that the thermal peaks for the dominant metamorphic recrystallization in western New England occurred 465 + or - 5 m.y. (Taconian). 40Ar/39Ar age data from a poorly-defined terrain along the eastern strip of the area suggests that the area has been retrograded during a metamorphism that peaked at least 376 + or - 5 m.y. (Acadian). Available age and petrological data from western New England indicate the presence of at least three separate metamorphic-structure domains of Taconic age: 1) a small area of relict high-P and low-T metamorphism, 2) a broad area of normal Barrovian metamorphism from chlorite to garnet grade characterized by a gentle metamorphic gradient and, 3) a rather narrow belt of steep-gradient, Barrovian series metamorphic rocks. Areas of maximum metamorphic intensity within the last domain coincide with areas of maximum crustal thickening in the later stage of Taconic orogeny. -L.di H

  3. Larval history influences post-metamorphic condition in a coral-reef fish.

    PubMed

    Hamilton, Scott L

    2008-12-01

    Upon settlement, many fishes undergo an energetically costly metamorphic period that requires substantial nutritional reserves. Larval growth and the accumulation of lipids prior to metamorphosis are likely to influence growth and survival following this critical period. On the Caribbean island of St. Croix, I investigated relationships between larval growth, early life-history characteristics, and post-metamorphic lipid content in the bluehead wrasse Thalassoma bifasciatum. Lipid reserves remaining after metamorphosis were positively related (r2 = 0.62) to the width of the metamorphic band; thus, this otolith-derived trait may be used to estimate the condition at emergence of survivors collected at some later time. In contrast, pelagic larval duration, average larval growth, and otolith size at settlement were negatively related to post-metamorphic lipid content. Interestingly, the trend for slower growth among fish in good condition was not consistent over the entire pelagic larval duration. Analyses of daily larval growth histories indicated that fish with high lipid reserves grew rapidly in the last week prior to settlement, but relatively slowly during the early phases of larval life; those emerging with low lipid concentrations, however, displayed strikingly opposite patterns. These contrasting patterns of growth and energy storage were consistent at two sites and over three recruitment events. Otolith chemistry data suggested that differences in growth histories and body condition were consistent with the hypothesis of larval development in distinct oceanic environments (characterized by Pb concentration); but, within a water mass, differences reflected life-history trade-offs between growth and energy storage. The results have implications for understanding the processes driving juvenile survival, which may be condition dependent.

  4. Thermoluminescence constraints on the metamorphic, shock, and brecciation history of basaltic meteorites

    NASA Technical Reports Server (NTRS)

    Batchelor, J. D.; Sears, Derek W. G.

    1991-01-01

    The metamorphic, shock, and brecciation history of 18 eucrites, 13 howardites, 6 diogenites, and 15 mesosiderites is investigated via induced thermoluminescence measurements performed on them. The eucrites show a 15-fold range of TL sensitivities, which correlate with petrographic indicators of metamorphic intensity. The temperature of the dominant TL peak observed for basaltic meteorites, and experiments in which four eucrites with diverse petrographic properties were annealed at various temperatures in the laboratory, suggests that the metamorphic equilibration temperatures for most basaltic meteorites were not more than 800 C. Assuming this temperature was typical of conditions during metamorphism, then burial depths for type-above-5 eucrites were greater than 350 m and less than 50 m for type-2 eucrites. Since TL peak temperatures are related to the degree of disorder in the Al, Si chain in feldspar, the present data provide independent evidence for very slow cooling rates for mesosiderites and for the slower cooling rates for some cumulate eucrites relative to equilibrated noncumulate eucrites.

  5. Age and tectonic implications of some low-grade metamorphic rocks from the Yucatan Channel

    USGS Publications Warehouse

    Vedder, J.G.; MacLeod, N.S.; Lanphere, M.A.; Dillon, William P.

    1973-01-01

    Phyllite and marble dredged from the lower part of the continental slope between Cuba and the Yucatan Peninsula seem to support the contention that a pre-early Tertiary metamorphic belt extends from the western Greater Antilles into northern Central America. The minimum K-Ar ages derived from the samples suggest that the metamorphic event was pre-Late Cretaceous, and evaluation of the K-Ar data implies that this metamorphic event is not older than Late Jurassic. Greater antiquity, however, is inferred from structural and stratigraphic relations in British Honduras, where the latest regional metamorphic event was post-Early Permian and pre-Middle Jurassic.  Rifting and extension related to plate motions along the British Honduras Quintana Roo margin through Mesozoic and earliest Cenozoic time presumably would preclude extensive regional metamorphism, permitting only limited development of schistose rocks there during that interval. The timing of metamorphic events in western Cuba is uncertain, but a pre-Middle Jurassic episode possibly is reflected in the phyllite and marble terranes of Isla de Pinos and Sierra de Trinidad. Local incipient metamorphism of Early and Middle Jurassic strata in the Sierra de los Organos may have resulted from severe tectonism that began in Late Cretaceous time and diminished in the Eocene.

  6. Thermal and impact history of the H chondrite parent asteroid during metamorphism: Constraints from metallic Fe-Ni

    NASA Astrophysics Data System (ADS)

    Scott, Edward R. D.; Krot, Tatiana V.; Goldstein, Joseph I.; Wakita, Shigeru

    2014-07-01

    We have studied cloudy taenite, metallographic cooling rates, and shock effects in 30 H3-6 chondrites to elucidate the thermal and early impact history of the H chondrite parent body. We focused on H chondrites with old Ar-Ar ages (>4.4 Gyr) and unshocked and mildly shocked H chondrites, as strongly shocked chondrites with such old ages are very rare. Cooling rates for most H chondrites at 500 °C are 10-50 °C/Myr and do not decrease systematically with increasing petrologic type as predicted by the onion-shell model in which types 3-5 are arranged in concentric layers around a type 6 core. Some type 4 chondrites cooled slower than some type 6 chondrites and type 3 chondrites did not cool faster than other types, contrary to the onion-shell model. Cloudy taenite particle sizes, which range from 40 to 120 nm, are inversely correlated with metallographic cooling rates and show that the latter were not compromised by shock heating. The three H4 chondrites that were used to develop the onion-shell model, Ste. Marguerite, Beaver Creek, and Forest Vale, cooled through 500 °C at ⩾5000 °C/Myr. Our thermal modeling shows that these rates are 50× higher than could be achieved in a body that was heated by 26Al and cooled without disturbance by impact. Published Ar-Ar ages do not decrease systematically with increasing petrologic type but do correlate inversely with cloudy taenite particle size suggesting that impact mixing decreased during metamorphism. Metal and silicate compositions in regolith breccias show that impacts mixed material after metamorphism without causing significant heating. Impacts during metamorphism created Portales Valley and two other H6 chondrites with large metallic veins, excavated the fast-cooled H4 chondrites around 3-4 Myr after accretion, and mixed petrologic types. Metallographic data do not require catastrophic disruption by impact during cooling.

  7. Age and duration of eclogite-facies metamorphism, North Qaidam HP/UHP terrane, Western China

    USGS Publications Warehouse

    Mattinson, C.G.; Wooden, J.L.; Liou, J.G.; Bird, D.K.; Wu, C.L.

    2006-01-01

    Amphibolite-facies para-and orthogneisses near Dulan, at the southeast end of the North Qaidam terrane, enclose minor eclogite and peridotite which record ultra-high pressure (UHP) metamorphism associated with the Early Paleozoic continental collision of the Qilian and Qaidam microplates. Field relations and coesite inclusions in zircons from paragneiss suggest that felsic, mafic, and ultramafic rocks all experienced UHP metamorphism and a common amphibolite-facies retrogression. SHRIMP-RG U-Pb and REE analyses of zircons from four eclogites yield weighted mean ages of 449 to 422 Ma, and REE patterns (flat HREE, no Eu anomaly) and inclusions of garnet, omphacite, and rutile indicate these ages record eclogite-facies metamorphism. The coherent field relations of these samples, and the similar range of individual ages in each sample suggests that the ???25 m.y. age range reflects the duration of eclogite-facies conditions in the studied samples. Analyses from zircon cores in one sample yield scattered 433 to 474 Ma ages, reflecting partial overlap on rims, and constrain the minimum age of eclogite protolith crystallization. Inclusions of Th + REE-rich epidote, and zircon REE patterns are consistent with prograde metamorphic growth. In the Lu??liang Shan, approximately 350 km northwest in the North Qaidam terrane, ages interpreted to record eclogite-facies metamorphism of eclogite and garnet peridotite are as old as 495 Ma and as young as 414 Ma, which suggests that processes responsible for extended high-pressure residence are not restricted to the Dulan region. Evidence of prolonged eclogite-facies metamorphism in HP/UHP localities in the Northeast Greenland eclogite province, the Western Gneiss Region of Norway, and the western Alps suggests that long eclogite-facies residence may be globally significant in continental subduction/collision zones.

  8. Exotic metamorphic terranes in the Caledonides: Tectonic history of the Dalradian block, Scotland

    NASA Astrophysics Data System (ADS)

    Bluck, B. J.; Dempster, T. J.

    1991-11-01

    The Dalradian block, a part of the Precambrian metamorphic basement of Scotland, is thought to be exotic to Laurentia, having a provenance in Gondwana. In contrast to the rest of the Laurentian margin, which from ca. 700 to 530 Ma was undergoing extension, the Dalradian block was undergoing severe compression ca. 590 Ma. At the time of splitting of the Late Proterozoic supercontinent, both Gondwana and Laurentia shared a common history of extension; however, at ca. 670 Ma Gondwana converted to a destructive margin and underwent compression, whereas Laurentia remained in extension and passive to 500-510 Ma. The Dalradian block had two major phases of metamorphism and deformation, one in Gondwana, and the other in Laurentia. The second phase of classical Barrovian metamorphism may have been produced by thickening due to emplacement of ophiolitic and other nappes, rather than the earlier internal nappe structures. Late-stage ductile folding in the Moine basement to the north may be related to the final emplacement of the Dalradian block onto Laurentia.

  9. Annealing studies of the thermoluminescence of meteorites and implications for their metamorphic history

    SciTech Connect

    Guimon, R.K.

    1986-01-01

    The application of thermoluminescence to study metamorphism in the type 3 ordinary chondrites and five CAI from the Allende meteorite is explored. It has been found that the changes in the shape of the TL curve provide insight into the thermal history of the meteorites and meteoritic components. It is also shown that for ordinary chondrites, the TL sensitivity depends on the amount of feldspar present which, in turn, is governed by the intensity of metamorphism experienced. A type 3.4 ordinary chondrite shows changes in the peak temperature and width occurred upon annealing. These parameters showed a discontinuous increase after annealing at 800/sup 0/C; the peak temperature jumped from 130 to 200/sup 0/C and peak width increased from 90 to 150/sup 0/C. These changes in the TL emission characteristics suggest that type 3.3-3.5 ordinary chondrites have a low-feldspar as the dominant TL phosphor and > 3.5 have high feldspar as the phosphor. Thermoluminescence therefore provides a means of paleothermometry. In addition, experiments were performed aimed at causing the crystallization of feldspar in mesostasis glass in an attempt to reproduce the trends of increasing TL sensitivity with metamorphism. At high temperatures and longer annealing times, increases in TL sensitivity by factors of up to 40 were observed.

  10. Petrology and metamorphic history of metapelites in the Boehls Butte quadrangle, northern Idaho

    SciTech Connect

    Carey, J.W.; Rice, J.M.

    1985-01-01

    Metapelitic rocks in the Goat Mountain area record a pre-Beltian anatectic event and two later metamorphic events correlated to the M2 and M3 events observed by Lang and Rice. The co-occurrence of all three aluminosilicates is the result of M2 kyanite-sillimanite growth and M3 andalusite growth. The conditions of M2 metamorphism are estimated at 675 +/- 50/sup 0/C and 9.3 +/- 1.5 kb as determined from a variety of geothermo/barometers. M2 AFM mineral assemblages include Grt-Bt-Ky+/-Sil+/-Str and Crd-Bt-Ky+/-Sil. Partitioning of Mg and Fe in garnet and staurolite is normal (K/sub D/ > 1) for relict staurolite enclosed by aluminosilicate or muscovite and reversed (K/sub D/ < 1) for apparently stable staurolite and staurolite occurring as inclusions in garnet. Cordierite occurs as an overgrowth of kyanite; a texture which cannot be explained by reactions among the coexisting minerals. The texture may be explained by prograde consumption of chlorite or consumption of garnet upon decompression. The M3 event had limited effect on M2 mineral assemblages but resulted in crenulation and brittle deformation of M2 fabrics. The M3 event occurred during uplift and cooling following the M2 event. The M3 event is correlated to uplift of the Idaho batholith implying a Cretaceous age of M2 metamorphism.

  11. Resetting of RbSr ages of volcanic rocks by low-grade burial metamorphism

    USGS Publications Warehouse

    Asmeroma, Y.; Damon, P.; Shafiqullah, M.; Dickinson, W.R.; Zartman, R.E.

    1991-01-01

    We report a nine-point RbSr whole-rock isochron age of 70??3 Ma (MSWD 3.97) for Mid-Jurassic volcanic rocks. The same rocks have also been dated by the UThPb method on zircon, giving a crystallization age of 166 ?? 11 Ma, over twice as old as the RbSr age. The data demonstrate that whole-rock RbSr ages of volcanic rocks, even lava flows with SiO2 content as low as 57 wt.%, are susceptible to complete resetting. The rocks range in composition from rhyodacite tuffs to andesite lavas. The complete breakdown of all major minerals that contain Rb and Sr resulted in an alteration mineral assemblage consisting of phengite, albite, secondary quartz, and minor amounts of chlorite and epidote. Phengite is the K-bearing product of the breakdown of biotite and K-feldspar. Pressure during low-grade metamorphism of the volcanic rocks, estimated from phengite composition to have been in the range of 4 to 6 kbar, points to thrust-related burial as the main cause of resetting. Consequently, such reset isochrons may date large-scale events such as regional thrusting and metamorphism. The coherent resetting of the RbSr isochron suggests large-scale pervasive fluid movement during thrust-related burial metamorphism. ?? 1991.

  12. Ancient Protolith Ages and Scandian Metamorphism Across the Western Gneiss Region, Norway

    NASA Astrophysics Data System (ADS)

    Walsh, E. O.; Hacker, B. R.; Gans, P. B.; Grove, M.; Gehrels, G.

    2004-12-01

    Recent work shows the ultrahigh-pressure (UHP) eclogite-facies event in the Western Gneiss Region (WGR) occurred ˜415-400 Ma. However, other (U)HP eclogite-facies events in the Scandinavian Caledonides make it necessary to determine eclogite ages across the WGR before constructing tectonic models. Also, insufficient data exist to constrain the ages of two amphibolite-facies events (at 650-750° C, ˜11 kbar and at 6-7 kbar) characteristic to the WGR, which provide important pins on the exhumation process. To these ends, we dated zircon from eclogites, monazite and muscovite from pelites in a 220 x 100 km E-W band across the WGR. Zircon and monazite were dated by secondary ion mass spectrometry and laser-ablation inductively coupled plasma mass spectrometry to extract igneous core and metamorphic rim ages. Most eclogites record Gothian ( ˜1.7-1.5 Ga) or Sveconorwegian ( ˜1.2-0.9 Ga) igneous protolith ages similar to those of the Baltica orthogneiss. The easternmost eclogite records a Svecofennian ( ˜1.8-2.0 Ga) upper intercept age; zircon and monazite from the Trollstigen area record upper intercept and concordia ages > 2 Ga, not previously known in the WGR. While Upper Allochthon eclogites and pelitic gneisses retain the Early to Middle Ordovician and Early Silurian ages of their Iapetan protoliths, the age of the last metamorphism in all the eclogites is Scandian. Basement eclogites were least affected by this Scandian (re)crystallization, and the westernmost eclogites were most affected. Precambrian monazite ages occur only within basement gneisses; Upper Allochthon gneisses yield peak monazite ages of ˜424 Ma and ˜374 Ma. The most robust geochronological signature of the Scandian metamorphism is a steady westward decrease in muscovite 40Ar/39Ar ages from \\sim394 Ma to \\sim384 Ma. The entire WGR was involved in the Scandian phase of the Caledonian Orogeny, including the allochthons, which were emplaced onto the Baltica basement before subduction to UHP

  13. Thermal history of the H-chondrite parent body: Implications for metamorphic grade and accretionary time-scales

    NASA Astrophysics Data System (ADS)

    Monnereau, Marc; Toplis, Michael J.; Baratoux, David; Guignard, Jérémy

    2013-10-01

    Multiple temperature-age constraints for eight H-chondrite samples have been used to provide insight into the thermal history of their parent-body through combination with numerical models of thermal evolution assuming internal heating by 26Al and conductive cooling. The effect of spreading accretion out over time is the principal focus of this work. A wide range of body size and date of accretion is systematically tested for different values of accretion rate in order to quantify and illustrate the parameter space that is consistent with the available thermo-chronological data. We conclude that the H-chondrite samples considered have a thermal history consistent with a parent body that at some stage had a concentric 'onion-shell' internal structure. That body had a radius no larger than 130 km, and accretion most probably took place over a time interval on the order of 0.0-0.2 Myr, approximately 2 Myr after CAI condensation. In any case, the time interval of accretion is unlikely to have been more than 0.5 Myr supporting evidence in favour of rapid accretion, possibly through reassembly of the fragments of an earlier generation of bodies. Furthermore, the H-chondrites studied here are inferred to have come from a wide depth range within the body where they experienced metamorphism, indicating that preservation of the onion-shell structure is unlikely. The presence of an insulating regolith does not modify this conclusion, as appropriate thermal histories for the three H6 samples considered cannot be reproduced at depths near the surface. Asteroid 6-Hebe may be the parent body of the H-chondrites, but the high bulk density of the latter is difficult to reconcile with a 'rubble-pile' structure of pure H-chondrite material. Finally, optimized thermal histories are used to constrain the temperatures characterizing boundaries between petrological types (800, 1000, and 1140 K for the H3/4, H4/5, and H5/6 boundaries respectively). In detail, the type 6 samples studied

  14. New U-Pb Age and Trace Element Composition of Young Metamorphic Zircon Rims from the UHP Tso Morari Complex, NW Himalaya, Distinguishes Peak from Retrograde Metamorphism

    NASA Astrophysics Data System (ADS)

    Leech, M. L.; Coble, M. A.; Singh, S.; Guillot, S.; Jain, A. K.

    2014-12-01

    The ultrahigh-pressure (UHP) Tso Morari Complex (TMC) sits in the footwall of the Indus-Yarlung suture zone in the NW Himalaya. The timing of metamorphism during subduction and exhumation in the complex is critical to constraining the age of the India-Asia collision. de Sigoyer et al. (2000) and Leech et al. (2005) reported mean U-Pb ages for thin outer rims of sectioned zircon between 55 ± 6 Ma and 53.3 ± 0.7 Ma, respectively, for the age of peak UHP through retrograde metamorphism, and Leech et al. (2005) used these data to calculate the minimum age for the start of continental subduction at 57 ± 1 Ma. Recently published results for the TMC have reignited debate on the age of metamorphism and thus, the timing of India-Asia collision. We used the same TM38 sample analyzed for the results described in Leech et al. (2005) and performed new SIMS U-Pb depth-profiling analyses to target only the outermost ~1.5 micron rims of zircon. Our results yield a mean age of 44.9 ± 0.7 Ma; adjacent spots for REE analyses yielded positive, enriched HREE profiles with negative Eu anomalies and corresponding Ti-in-zircon temperatures of ~550° to 680° C. Sharp boundaries between zircon domains are clearly resolved with CL and BSE imaging of TM38 zircons, and there is a large age difference between rims and protolith core ages; any mixing during depth-profiling through rims is clear. The positive HREE profiles imply the period of zircon growth in the TMC at c. 45 Ma to be retrograde. We suggest that the 47-43 Ma peak ages and flat heavy REE profiles with no Eu anomaly recently reported by Donaldson et al. (2013) on sectioned zircons, and interpreted as the age of UHP metamorphism of the TMC, may actually represent mixing between zircon rims and cores. The Leech et al. (2005) collision age of 57 ± 1 Ma assumed the TMC represents the leading edge of India. However, numerical modeling of Warren et al. (2008) suggests all exhumed material is derived from the central part of the pro

  15. U-Pb ages for sphene in a contact metamorphic zone.

    NASA Technical Reports Server (NTRS)

    Hanson, G. N.; Catanzaro, E. J.; Anderson, D. H.

    1971-01-01

    U-Pb ages have been determined on sphene concentrates from the 2700 my old Giants Range Granite at varying distances from the contact with the 1100 my old Duluth gabbro. As the contact is approached the sphene ages become more discordant and plot along a chord between 1100 and 2700 my on a concordia diagram. The U-Pb ages for sphene in the contact aureole are more resistant to thermal metamorphism than are K-Ar ages for hornblende and biotite. The resistance relative to U-Pb ages for zircon is more difficult to interpret because the zircon U-Pb ages may have become discordant prior to or after 1100 my ago, whereas the U-Pb ages for sphene appear to have had episodic discordance only at 1100 my ago.

  16. Metamorphic conditions and CHIME monazite ages of Late Eocene to Late Oligocene high-temperature Mogok metamorphic rocks in central Myanmar

    NASA Astrophysics Data System (ADS)

    Maw Maw Win; Enami, Masaki; Kato, Takenori

    2016-03-01

    The high temperature (T)/pressure (P) regional Mogok metamorphic belt is situated in central Myanmar, and is mainly composed of pelitic gneisses, amphibolites, marbles, and calc-silicate rocks. The garnet-biotite-plagioclase-sillimanite-quartz assemblage and its partial system suggest equilibrium P/T conditions of 0.6-1.0 GPa/780-850 °C for the peak metamorphic stage, and 0.3-0.5 GPa/600-680 °C for the exhumation and hydration stage. Monazite grains show complex compositional zoning consisting of three segments-I, II, and III. Taking into consideration the monazite zoning and relative misfit curves, the calculated chemical Th-U-total Pb isochron method (CHIME) monazite age data (284 spot analyses) indicated four age components: 49.3 ± 2.6-49.9 ± 7.9, 37.8 ± 1.0-38.1 ± 1.7, 28.0 ± 0.8-28.8 ± 1.6, and 23.7 ± 1.3 Ma (2σ level). The ages of the Late Eocene and Late Oligocene epochs were interpreted as the peak metamorphic stage of upper-amphibolite and/or granulite facies and the postdated hydration stage, respectively.

  17. Over 400 m.y. metamorphic history of the Fennoscandian lithospheric segment in the Proterozoic (the East European Craton)

    NASA Astrophysics Data System (ADS)

    Skridlaite, G.; Bogdanova, S.; Taran, L.; Baginski, B.; Krzeminska, E.; Wiszniewska, J.; Whitehouse, M.

    2009-04-01

    Several Palaeoproterozoic terranes in the Fennoscandian lithospheric segment of the East European Craton (EEC) evolved differently prior to their final amalgamation at c. 1.8 Ga. South-westward younging of the major tectono-thermal events characterizes the Baltic -Belarus region between the Baltic and Ukrainian Shields of the EEC. While at c.1.89-1.87 Ga and 1.85-1.84 Ga rocks of some northern and eastern terranes (Estonia, Belarus and eastern Lithuania) experienced syncollisional, moderate P metamorphism, subduction-related volcanic island arc magmatism still dominated southwestern terranes in Lithuania and Poland. The available age determinations of metamorphic zircon (SIMS/NORDSIM and TIMS methods, Stockholm, SHRIMP method, RSES, ANU, Canberra) and metamorphic monazite (TIMS, Stockholm and EPMA method, Warsaw University) allow to distinguish several metamorphic events related to major orogenic processes: - 1.90-1.87 Ga amphibolite-facies H/MP metamorphism occurred along with emplacements of juvenile TTG-type granitoids in the North Estonian and Lithuanian-Belarus terranes. They are coeval with the main accretionary growth of the crust in the Svecofennian Domain in the Baltic Shield (e.g. Lahtinen et al., 2005). - 1.84-1.79 Ga high-grade metamorphism affected sedimentary and igneous rocks in almost all the terranes and is assumed to have been related to the major aggregation of the EEC (Bogdanova et al, 2006, 2008). In the metasedimentary granulites of western Lithuania, a prograde metamorphism commenced with monazite growth prior garnet at 1.84-1.83 Ga. The sediments and mafic igneous rocks in Lithuania, felsic igneous rocks in NE Poland underwent peak metamorphism and deformation at 1.81-1.79 Ga (zircon and monazite ages). The 1.83-1.79 Ga metamorphism has the same age as a metamorphic imprint and strong shearing of the crust in central Sweden (Andersson et al., 2004). The postcollisional granulite metamorphism of mafic intrusions at 1.80-1.79 Ga in Belarus

  18. Thermal histories of CO3 chondrites - Application of olivine diffusion modelling to parent body metamorphism

    NASA Technical Reports Server (NTRS)

    Jones, Rhian H.; Rubie, David C.

    1991-01-01

    The petrologic sequence observed in the CO3 chondrite group has been suggested to be the result of thermal metamorphism on a parent body. A model developed to examine the possibility that chondrule and matrix olivines equilibrated in situ, during parent body metamorphism is presented. The model considers Fe-Mg interdiffusion between chondrule and matrix olivines. Zoning profiles comparable to those observed in chondrule olivines from partially equilibrated members of the series are reproduced successfully. Metamorphism of CO3 chondrites on a parent body is therefore a viable model for the observed equilibration. Results indicate that peak metamorphic temperatures experienced by the CO3 chondrites were around 500 C, and that the range of peak temperatures between unequilibrated and equilibrated subtypes was relatively narrow, around 100 C.

  19. Tectono-metamorphic history of southern New Hampshire and southeastern Vermont

    SciTech Connect

    Chamberlain, C.P.; Lyons, J.B.; Thompson, J.B. Jr.; Rosenfeld, J.L.; Downie, E.

    1985-01-01

    A major boundary between two Acadian metamorphic terranes is marked by a band of low-grade rocks in the Connecticut River valley coinciding with the Monroe Line (ML) and separating higher-grade rocks in two distinct lithostratigraphic terranes. To the west, Cambro-Devonian rocks in the Vermont sequence overlie Grenvillian basement, whereas to the east a different Cambro-Dev. sequence rests upon Hadrynian basement. These terranes were assembled no later than the early Devonian. The eastern terrane, consisting of the Bronson Hill Anticlinorium(BHA) and Merrimack Synclinorium (MS), is bounded on the east by the older Massabesic Gneiss (650-480 my) and Ord (.) Merrimack Group. This southeastern terrane was in contact with the MS by the early Devonian because there is no break in metamorphism across the terrane boundary. Metamorphism in the western terrane (Vermont) is synkinematic and peaks in the Staur-Ky zone. The earliest metamorphism is believed to be Taconian and represents the thermal decay of relict blueschist metamorphism observed to the northwest and the accretion of an island-arc. The earliest metamorphism in the eastern terrane (BHA-MS) is Acadian and is associated with nappe formation and synkinematic plutons. Continued Acadian crustal shortening in the MS resulted in a pressure increase (from 3.8 to 7 kb), with rocks reaching peak metamorphism in the Sil-Mus up to Kspar-Cord zones. The authors suggest that this high-grade metamorphism was the result of a high transient heat flux initiated by crustal stretching in the MS during the Silurian and early Devonian when 8 km of clastics were deposited in a rapidly subsiding trough.

  20. Empirical Constraints on Extrusion Mechanisms Derived From Pressure-Temperature-Time Histories From the Himalayan Metamorphic Core (Sutlej Valley, NW India)

    NASA Astrophysics Data System (ADS)

    Chambers, J.; Caddick, M.; Argles, T.; Horstwood, M.; Harris, N.; Parrish, R.; Ahmad, T.

    2007-12-01

    The exhumed Himalayan core in the Sutlej Valley comprises the Greater Himalayan Sequence (GHS), bounded by the Main Central Thrust and the South Tibetan Detachment, and tectonically distinct metamorphosed units above (the Haimanta Group) and below (the Jutogh Group). While pressure-temperature-time (P-T-t) data from the GHS are broadly compatible with predictions of the channel flow model presented by Jamieson et al. (2004), corresponding data for the units bounding the putative channel are not: The underlying Jutogh Group experienced a tightly closed P-T path featuring upper-amphibolite prograde metamorphism at c. 11 Ma, followed by rapid cooling and exhumation. These data are consistent with a) prograde metamorphism during overthrusting (along the Main Central Thrust) and b) subsequent exhumation via accretion to the extruding GHS channel above. However, muscovite cooling ages from the GHS pre-date those from the Jutogh Group by at least 10 Ma, clearly indicating decoupled exhumation of the two crystalline units. Alongside evidence that motion on the Main Central Thrust had ceased by c. 16 Ma, concomitant extrusion of the Jutogh Group as part of a single widening GHS `channel' seems impossible. The Haimanta Group, considered uppermost in the GHS sequence and/or basal to the Tethyan Sedimentary Sequence, also reached upper-amphibolite grade during the Himalayan orogeny. As for the Jutogh Group, exhumation and cooling rapidly followed peak metamorphism. Coupled U-Pb monazite data and detailed textural and pseudosection analyses constrain prograde metamorphism at c. 35 to 30 Ma, the timing of which is compatible with channel flow model predictions. Importantly, however, P-T paths do not match numerical simulations, which imply shallower burial, lower peak temperatures and a distinct phase of isobaric heating. We conclude that the Sutlej Valley presents a tectonically complex metamorphic core for which a single, widening channel flow model does not accurately predict

  1. The Sutter's Mill meteorite: Thermoluminescence data on thermal and metamorphic history

    NASA Astrophysics Data System (ADS)

    Sears, Derek W.; Beauford, Robert

    2014-11-01

    A piece of the Sutter's Mill meteorite, fragment SM2-1d, has been examined using thermoluminescence techniques to better understand its thermal and metamorphic history. The sample had very weak but easily measureable natural and induced thermoluminescence (TL) signals; the signal-to-noise ratio was better than 10. The natural TL was restricted to the high-temperature regions of the glow curve suggesting that the meteorite had been heated to approximately 300 °C within the time it takes for the TL signal to recover from a heating event, probably within the last 105 years. It is possible that this reflects heating during release from the parent body, close passage by the Sun, or heating during atmospheric passage. Of these three options, the least likely is the first, but the other possibilities are equally likely. It seems that temperatures of approximately 300 °C reached 5 or 6 mm into the meteorite, so that all but one of the small Sutter's Mill stones have been heated. The Dhajala normalized induced TL signal for SM2-1d is comparable to that of type 3.0 chondrites and is unlike normal CM chondrites, the class it most closely resembles, which do not have detectable TL sensitivity. The shape of the induced TL curve is comparable to other low-type ordinary, CV, and CO chondrites, in that it has a broad hummocky structure, but does not resemble any of them in detail. This suggests that Sutter's Mill is a unique, low-petrographic-type (3.0) chondrite.

  2. Carboniferous U-Pb age of the Sebago batholith, southwestern Maine: metamorphic and tectonic implications.

    USGS Publications Warehouse

    Aleinikoff, J.H.; Moench, R.H.; Lyons, J.B.

    1985-01-01

    Two phases (pink and white granite) of the Sebago batholith have been dated by the U/Pb zircon method. The age of both phases is 325 m.y. Zircon in the pink phase has been reset in intrusion of the Pleasant Mountain stock approx 114 m.y. ago. Zircon in the white phase lost lead only recently. Metamorphic isograds in the vicinity of the batholith approximately parallel its shape, and may be at least partly Hercynian in age. Cooling and uplift of the Sebago batholith appear to have followed a complicated path involving little or no uplift in the Middle Carboniferous to Middle Permian, rapid cooling from 275 to 225 m.y. ago, and a slow cooling since Middle Triassic. Different rates of cooling may be related to changes in the tectonic regime.-L.C.H.

  3. K-Ar ages of allochthonous mafic and ultramafic complexes and their metamorphic aureoles, Western Brooks Range, Alaska

    SciTech Connect

    Boak, J.L.; Turner, D.L.; Wallace, W.K.; Moore, T.E.

    1985-04-01

    New K-Ar ages from allochthonous mafic and ultramafic complexes of the western Brooks Range (Brooks Range ophiolite) show that igneous rocks yielded ages nearly identical to those of underlying metamorphic aureole rocks. Dated rocks of the Misheguk igneous sequence from Tumit Creek consist of (1) hornblende gabbro with minor greenschist and lower grade alteration, hornblende age 147.2 +/- 4.4 Ma; and (2) hornblende-bearing diorite, also slightly altered, age 155.8 +/- 4.7 Ma. Both samples come from presumed higher levels of the Misheguk sequence. Dated samples of metamorphic aureole rocks come from outcrops near Kismilot Creek and lie structurally beneath the Iyikrok Mountain peridotite body. The rocks consist of amphibolite and garnet-bearing biotite-hornblende gneiss considered to be metamorphosed Copter igneous sequence and related sedimentary rocks. Hornblende ages are 154.2 +/- 4.6 Ma and 153.2 +/- 4.6 Ma. metamorphism is clearly related to the structurally overlying perioditite, as the degree of alteration decreases downward. The authors suggest that the K-Ar ages of these rocks represent the effects of thermal metamorphism post-dating igneous crystallization, and are related to tectonic emplacement of the complex. Earlier K-Ar data on igneous rocks give similar ages and have been interpreted as reflecting tectonothermal events. The age of igneous crystallization of the mafic and ultramafic rocks of the Misheguk igneous sequence remains uncertain.

  4. Metamorphic facies map of Southeastern Alaska; distribution, facies, and ages of regionally metamorphosed rocks

    USGS Publications Warehouse

    Dusel-Bacon, Cynthia; Brew, D.A.; Douglass, S.L.

    1996-01-01

    Nearly all of the bedrock in Southeastern Alaska has been metamorphosed, much of it under medium-grade conditions during metamorphic episodes that were associated with widespread plutonism. The oldest metamorphisms affected probable arc rocks near southern Prince of Wales Island and occurred during early and middle Paleozoic orogenies. The predominant period of metamorphism and associated plutonism occurred during Early Cretaceous to early Tertiary time and resulted in the development of the Coast plutonic-metamorphic complex that extends along the inboard half of Southeastern Alaska. Middle Tertiary regional thermal metamorphism affected a large part of Baranof Island.

  5. The West African Mauritanid metamorphic suite of Proterozoic age in the subsurface of peninsular Florida and environs

    SciTech Connect

    Winston, G.O.

    1993-03-01

    A high and low-grade Gondwanan metamorphic terrane is revealed by 14 wells in Florida and environs. Two high-grade metamorphics (gneiss and schist) are located in central Florida and are probably Early Proterozoic in age. The 12 other wells contain low-grade metamorphic suites, principally composed of inter-bedded argillites, acid volcanics and quartzites belonging to the Mauritanid sequence of West Africa. These suites are present in south Georgia, north Florida and offshore; a 3,975-foot section was penetrated in one well. These widespread metamorphic rocks are probably the terrane into which the Cambrian Osceola granite of central Florida was intruded. The two grades of metamorphics represent Early and Late Proterozoic episodes of sedimentation, each followed by metamorphism and erosion. Lower Ordovician to Devonian sediments were deposited on this terrane in southern Georgia and northern Florida. In the Early Jurassic, volcanics completely covered southern Florida, concealing the nature of the old underlying surface. Younger Mesozoic sediments eventually buried the entire Pre-Cambrian-Lower Jurassic terrane.

  6. Modelling of the thermal history of metamorphic zoning in the Connemara region (western Ireland)

    NASA Astrophysics Data System (ADS)

    Reverdatto, V. V.; Polyansky, O. P.

    2004-02-01

    The Connemara region of the Irish Caledonides is a classic example of regional-scale metamorphism of low pressure and high temperature. This terrane is considered as part of a fold belt comprising metasedimentary and metavolcanic rocks that are correlated with the Neoproterozoic-Lower Paleozoic Dalradian Supergroup of Scotland. In mid-Ordovician time, the extensive and high-temperature metamorphism was superimposed on the Dalradian rocks resulting in the Connemara zoning. The key feature of the zoning is elevated horizontal thermal gradient of ca. 14 °C/km. Geological data and geochronological evidence point to a causative link between metamorphism and associated magmatic intrusions, and a brief period of development for the metamorphic zoning. Magmatic intrusion into the middle part of continental crust is treated as a most plausible source of heat for metamorphism, and other conjectures as to the origin of the zoning (flow of hot fluid through the permeable rocks, fracture conduit flushed by flowing magma) are believed to be improbable. To examine in sufficient detail the problem of the nature of heat source, a series of appropriate calculations have been performed to reach the best agreement between the observed and simulated spatial distribution of maximum temperatures at different times. The mathematical modelling shows that the temperature-spatial structure of the Connemara zoning is best explained by the model version based on mid-crustal heating above the upper contact of magmatic intrusive body gently curved and tilted at an angle between 20° and 40°, with an initial temperature of the magma appropriate to a basaltic melt. The model estimate of total lifetime of the temperature anomaly in the crust is of the order of 5-6 Ma. In general, this is in rather good agreement with the currently available evidence of geochronological duration of metamorphism and magmatism in Connemara.

  7. Thermal history of the Maramureş area (Northern Romania) constrained by zircon fission track analysis: Cretaceous metamorphism and Late Cretaceous to Paleocene exhumation

    NASA Astrophysics Data System (ADS)

    Gröger, Heike R.; Tischler, Matthias; Fügenschuh, Bernhard; Schmid, Stefan M.

    2013-10-01

    This study presents zircon fission track data from the Bucovinian nappe stack (northern part of the Inner Eastern Carpathians, Rodna Mountains) and a neighbouring part of the Biharia nappe system (Preluca massif) in order to unravel the thermal history of the area and its structural evolution by integrating the fission track data with published data on the tectonic and sedimentary evolution of the area. The increase of metamorphic temperatures towards the SW detected by the zircon fission track data suggests SW-wards increasing tectonic overburden (up to at least 15 km) and hence top NE thrusting. Sub-greenschist facies conditions during the Alpine metamorphic overprint only caused partial annealing of fission tracks in zircon in the external main chain of the Central Eastern Carpathians. Full annealing of zircon points to at least 300 °C in the more internal elements (Rodna Mountains and Preluca massif). The zircon fission track central and single grain ages largely reflect Late Cretaceous cooling and exhumation. A combination of fission track data and stratigraphic constraints points to predominantly tectonic differential exhumation by some 7-11 km, connected to massive Late Cretaceous extension not yet detected in the area. Later events such as the latest Cretaceous ("Laramian") juxtaposition of the nappe pile with the internal Moldavides, causing exhumation by erosion, re-burial by sedimentation and tectonic loading during the Cenozoic had no impact on the zircon fission track data; unfortunately it prevented a study of the low temperature part of the Late Cretaceous exhumation history.

  8. Monazite Growth from the Eocene to the Miocene: New Interpretations of the Metamorphic History of Greater Himalayan Rocks in the Eastern Himalaya

    NASA Astrophysics Data System (ADS)

    Gordon, S. M.; Kauffman, R.; Gonzales-Clayton, B.; Long, S. P.; Kylander-Clark, A. R.

    2015-12-01

    Across the Himalaya, mid- to lower-crustal Greater-Himalayan (GH) rocks have been exhumed during active continent-continent collision. In the eastern Himalaya within Bhutan, GH rocks are divided into an upper and lower level by an intra-GH shear zone, the Kakthang thrust (KT). To decipher the metamorphic, melt-crystallization and exhumation history of the GH rocks exposed above and below the KT, monazite from metapelites and migmatites was dated and trace elements were analyzed by laser-ablation, split-stream ICPMS. The trace elements from the monazite were used to track when the rocks were at near-peak conditions (based on the depletion of HREE and the likely presence of garnet during monazite growth) versus likely undergoing initial exhumation and garnet breakdown (based on an increase in HREE). Samples were collected from two N-S transects that cross the KT in central and eastern Bhutan. The eastern transect reveals a progressive younging of near-peak metamorphism within the GH, with dates of ca. 23-20 Ma for the structurally-highest sample versus ca. 18-16 Ma in the structurally-lowest sample. The youngest dates from all structural levels of the eastern Bhutan metapelites are 13-15 Ma; the same analyses yield higher HREE abundances, suggesting garnet breakdown during their (re)crystallization. The migmatites yield ca. 14-16 Ma melt-crystallization ages, consistent with the GH having undergone cooling and initial exhumation to cause garnet breakdown by ca. 15 Ma. In comparison, the central Bhutan transect reveals older near-peak metamorphic ages, with garnet-stable monazite populations at ca. 48­-46 Ma within the KT zone, ca. 38-30 Ma for rocks in the middle of the upper-GH, and ca. 25-22 Ma for the structurally-highest sample. Youngest monazites from the central Bhutan transect that yield growth or recrystallization at garnet-unstable conditions range from ca. 17-26 Ma. These results suggest earlier metamorphism and exhumation of GH rocks in central Bhutan

  9. Metamorphic history of a high-grade blueschist exotic block from the Franciscan complex, California.

    USGS Publications Warehouse

    Moore, Diane E.

    1984-01-01

    A tectonic block (approx 6 m in diameter) in the NE Diablo Range shows evidence of three episodes of retrograde blueschist-facies metamorphism + or - deformation under progressively declining P-T conditions. Retrograde metamorphism began with the tectonic incorporation of fragments of the original metamorphic terrain into serpentinite, which provided Mg-bearing fluids for the reactions of both the first and second retrograde events. There is extensive CaCO3 veining which matches that of the associated metasediments. In the third retrograde event, aragonite crystallized, accompanied by lawsonite, chlorite, jadeitic pyroxene and crossite. Such tectonic blocks may have originally formed in a pre-Franciscan subduction zone setting; fragments of blueschist and eclogite from this metamorphic terrain were tectonically incorporated in a serpentinite diapir and developed alteration zones against the enclosing ultramafic rock. When the serpentinite reached the Earth's surface, such blocks were transferred to the Franciscan as detritus and were then re-subducted and metamorphosed along with their associated sedimentary sequences.-R.A.H.

  10. Geology and geochronology of granitoid and metamorphic rocks of late Archean age in northwestern Wisconsin

    USGS Publications Warehouse

    Sims, P.K.; Peterman, Z.E.; Zartman, R.E.; Benedict, F.C.

    1985-01-01

    Granitoid rocks of the Puritan Quartz Monzonite and associated biotite gneiss and amphibolite in northwestern Wisconsin compose the southwestern part of the Puritan batholith of Late Archean age. They differ from rocks in the Michigan segment of the batholith in having been deformed by brittle-ductile deformation and partly recrystallized during shearing accompanying development of the midcontinent rift system of Keweenawan (Middle Proterozoic) age. Granitoid rocks ranging in composition from granite to tonalite are dominant in the Wisconsin part of the batholith. To the north of the Mineral Lake fault zone, they are massive to weakly foliated and dominantly of granite composition, whereas south of the fault zone they are more strongly foliated and mainly of tonalite composition. Massive granite, leucogranite, and granite pegmatite cut the dominant granitoid rocks. Intercalated with the granitoid rocks in small to large conformable bodies are biotite gneiss, amphibolite, and local tonalite gneiss. Metagabbro dikes of probable Early Proterozoic age as much as 15 m thick cut the Archean rocks. Rubidium-strontium whole-rock data indicate a Late Archean age for the granitoids and gneisses, but data points are scattered and do not define a single isochron. Zircon from two samples of tonalitic gneiss for uranium-thorium-Iead dating define a single chord on a concordia diagram, establishing an age of 2,735?16 m.y. The lower intercept age of 1,052?70 m.y. is in close agreement with rubidium-strontium and potassium-argon biotite ages from the gneisses. Two episodes of deformation and metamorphism are recorded in the Archean rocks. Deformation during the Late Archean produced a steep west-northwest-oriented foliation and gently plunging fold axes and was accompanied by low amphibolite-facies metamorphism of the bedded rocks. A younger deformation resulting from largely brittle fracture was accompanied by retrogressive metamorphism; this deformation is most evident adjacent

  11. Chemical and physical studies of type 3 chondrites 12: The metamorphic history of CV chondrites and their components

    NASA Technical Reports Server (NTRS)

    Guimon, R. Kyle; Symes, Steven J. K.; Sears, Derek W. G.

    1995-01-01

    The induced thermoluminescence (TL) properties of 16 CV and CV-related chondrites, four CK chondrites and Renazzo (CR2) have been measured in order to investigate their metamorphic history. The petrographic, mineralogical and bulk compositional differences among the CV chondrites indicate that the TL sensitivity of the approximately 130 C TL peak is reflecting the abundance of ordered feldspar, especially in chondrule mesostasis, which in turn reflects parent-body metamorphism. The TL properties of 18 samples of homogenized Allende powder heated at a variety of times and temperatures, and cathodoluminescence mosaics of Axtell and Coolidge, showed results consistent with this conclusion. Five refractory inclusions from Allende, and separates from those inclusions, were also examined and yielded trends reflecting variations in mineralogy indicative of high peak temperatures (either metamorphic or igneous) and fairly rapid cooling. The CK chondrites are unique among metamorphosed chondrites in showing no detectable induced TL, which is consistent with literature data that suggests very unusual feldspar in these meteorites. Using TL sensitivity and several mineral systems and allowing for the differences in the oxidized and reduced subgroups, the CV and CV-related meteorites can be divided into petrologic types analogous to those of the ordinary and CO type 3 chondrites. Axtell, Kaba, Leoville, Bali, Arch and ALHA81003 are type 3.0-3.1, while ALH84018, Efremovka, Grosnaja, Allende and Vigarano are type 3.2-3.3 and Coolidge and Loongana 001 are type 3.8. Mokoia is probably a breccia with regions ranging in petrologic type from 3.0 to 3.2. Renazzo often plots at the end of the reduced and oxidized CV chondrite trends, even when those trends diverge, suggesting that in many respects it resembles the unmetamorphosed precursors of the CV chondrites. The low-petrographic types and low-TL peak temperatures of all samples, including the CV3.8 chondrites, indicates metamorphism

  12. Sr-isotopic composition of marbles from the Puerto Galera area (Mindoro, Philippines): additional evidence for a Paleozoic age of a metamorphic complex in the Philippine island arc

    SciTech Connect

    Knittel, U.; Daniels, U.

    1987-02-01

    The Sr-isotopic composition of marbles from the Puerto Galera area (Mindoro, Philippines) is compatible with either a Tertiary or a Paleozoic age. The former is considered as unlikely because nonmetamorphic sediments of that age overlie the metamorphic complex. This implies that the metamorphic complex does not represent the basement of the Philippine arc but is an accreted terrane.

  13. Metamorphic and age constraints on tectono-thermal reworking in the western H.U. Sverdrupfjella: A new crustal evolution model for Western Dronning Maud Land, Antarctica

    NASA Astrophysics Data System (ADS)

    Grosch, Eugene; Frimmel, Hartwig; Abu-Alam, Tamer; Košler, Jan

    2014-05-01

    Western Dronning Maud Land (WDML) of East Antarctica is argued to consist of two major crustal domains, namely the low-grade Archaean Kalahari-Grunehogna Craton and the high-grade Maud belt (e.g. Grantham et al., 1995; Jacobs et al. 2008). The geodynamic and tectono-thermal crustal evolution histories of these two proposed domains remain a debated topic in Rodinia and Gondwana reconstructions. In this study we conducted a petrological and metamorphic comparison of Mesoproterozoic metabasic rocks on the eastern margin of the Archaean Grunehogna Craton and the adjacent westernmost Maud Belt, across a major structural discontinuity known as the Pencksökket-Jutulstraumen Discontinuity (PJD). As such we evaluate to what extent the two domains of WDML represent independent crustal growth and metamorphic histories. Metamorphic constraints on low-grade rocks on the eastern Grunehogna craton record greenschist facies conditions of T = 340 ± 25oC and P = 2.9 ± 0.8 kbar. The high-grade PT-constraint of T =700 ± 30oC and P = 9.0 ± 2 kbar for the western extreme of the Maud Belt, derived from garnet-hornblende-plagioclase-quartz geothermobarometry and phase diagram modeling in PERPLEX, is very similar to that reported for the eastern Maud Belt and thus, does not support the concept of a westward decreasing metamorphic field gradient within the Maud Belt as previously proposed. Laser-ablation-ICP-MS U-Pb dating of titanite in a hornblende-plagioclase-quartz symplectite (after garnet breakdown), yielded a Pan-African age for high-grade metamorphism in the westernmost Maud belt, which overlaps with the age of tectonic decompression in the eastern Maud Belt. The new U-Pb age data argues against previous models that invoke only late-Mesoproterozoic high-grade metamorphism in the western Maud Belt. The new petrological data indicate that the inferred sub-glacial boundary (PJD) between the Grunehogna Craton and the Maud Belt, represents a major metamorphic hiatus as a Pan

  14. K-Ar ages of metamorphic rocks at the base of the Samail ophiolite, Oman

    SciTech Connect

    Lanphere, M.A.

    1981-04-10

    Hornblendes from amphiobolities in the sheet of metamorphic rocks beneath the peridotite member of the Samail ophiolite and phyllites farther from the peridotite contact have weighted mean /sup 40/Ar//sup 39/Ar total fusion ages of 90.0 +- 3.0 m.y. and 79.5 +- 3.0 m.y., respectively. The amphibolities represent the first tectonic slice welded to the base of the Samail ophiolite after it was detached from the Tethyan oceanic crust. Formation of the amphiobolities occurred no more than 3 to 7 m.y. after crystallization of plagiogranite in the ophiolite. The phyllites represent another tectonic slice of ocean floor sediments welded to the ophiolite as it was transported further from the Tethyan spreading axis. The K-Ar ages suggest, assuming a half-spreading rate of 2 to 5 cm/yr, that detachment of the Samail ophiolite and formation of amphibolite facies rocks occurred no more than 60 to 350 km from spreading center. Using the same spreading rate, one can calculate a minimum half width of 300 to 750 km for the Tethyan Ocean during the Late Cretaceous.

  15. Interpretation of ages of arc magmatism, metamorphism, and collisional tectonics in the taconian orogen of western New England

    USGS Publications Warehouse

    Ratcliffe, N.M.; Hames, W.E.; Stanley, R.S.

    1998-01-01

    Available geochronologic ages of volcanic and intrusive rocks of the Taconian arc complex of western New England suggest that the Shelburne Falls and Bronson Hill arcs are not temporally or spatially discrete. Arc activity ranges from earliest Ordovician to Silurian. Activity in the Early and Middle Ordovician coincided with outboard accretionary tectonics and metamorphism that was contemporaneous with the older igneous activity in the Shelburne Falls arc and Bronson Hill arcs. Activity at about 455 to 445 Ma coincides with the collisional stage of the Taconian orogeny that affected Caradocian and older rocks of the Laurentian margin. The 455 to 445 Ma range for the collisional stage of Taconian orogeny in western New England is bracketed by biostratigraphic ages of sedimentary rocks formed on the Laurentian margin and 40Ar/39Ar ages of prograde hornblende formed during Taconian metamorphism. The previous 40Ar/39Ar age estimate of 465 Ma for this collisional and metamorphic event is now known to be too old because this age violates the age of metasedimentary rocks involved in the collisional tectonics. Acceptance of the newer 40Ar/39Ar age estimates of 445 to 450 Ma for Taconian metamorphism during collision establishes the contemporaneity with arc activity in the Bronson Hill arc. Taken together these data support the concept of a long-lived volcanic arc terrane(s) that prograded oceanward. Collision with this time-composite arc terrane(s) in the Caradocian produced the Taconian orogeny rather than the collision of a separate and smaller arc called the "Shelburne Falls arc" by Karabinos and others (1998).

  16. Mesozoic thermal history and timing of structural events for the Yukon-Tanana Upland, east-central Alaska: 40Ar/39Ar data from metamorphic and plutonic rocks

    USGS Publications Warehouse

    Dusel-Bacon, C.; Lanphere, M.A.; Sharp, W.D.; Layer, P.W.; Hansen, V.L.

    2002-01-01

    We present new 40Ar/39Ar ages for hornblende, muscovite, and biotite from metamorphic and plutonic rocks from the Yukon-Tanana Upland, Alaska. Integration of our data with published 40Ar/39Ar, kinematic, and metamorphic pressure (P) and temperature (T) data confirms and refines the complex interaction of metamorphism and tectonism proposed for the region. The oldest metamorphic episode(s) postdates Middle Permian magmatism and predates the intrusion of Late Triassic (215-212 Ma) granitoids into the Fortymile River assemblage (Taylor Mountain assemblage of previous papers). In the eastern Eagle quadrangle, rapid and widespread Early Jurassic cooling is indicated by ???188-186 Ma 40Ar/39Ar plateau ages for hornblende from plutons that intrude the Fortymile River assemblage, and for metamorphic minerals from the Fortymile River assemblage and the structurally underlying Nasina assemblage. We interpret these Early Jurassic ages to represent cooling resulting from northwest-directed contraction that emplaced the Fortymile River assemblage onto the Nasina assemblage to the north as well as the Lake George assemblage to the south. This cooling was the final stage of a continuum of subduction-related contraction that produced crustal thickening, intermediate- to high-P metamorphism within both the Fortymile River assemblage and the structurally underlying Lake George assemblage, and Late Triassic and Early Jurassic plutonism in the Fortymile River and Nasina assemblages. Although a few metamorphic samples from the Lake George assemblage yield Jurassic 40Ar/39Ar cooling ages, most yield Early Cretaceous 40Ar/39Ar ages: hornblende ???135-115 Ma, and muscovite and biotite ???110-108 Ma. We interpret the Early Cretaceous metamorphic cooling, in most areas, to have resulted from regional extension and exhumation of the lower plate, previously tectonically thickened during Early Jurassic and older convergence.

  17. The kinematic and metamorphic history of the Sgurr Beag Thrust, Ross-shire, NW Scotland

    NASA Astrophysics Data System (ADS)

    Grant, Colin J.; Harris, Anthony L.

    2000-02-01

    This paper presents a field and microstructural study of a Caledonian amphibolite-facies shear zone within the Moine rocks of Northern Scotland. The shear zone, the Sgurr Beag thrust, is an important tectonic break within the Moine nappe of Ross-shire and is the structurally highest and oldest of the foreland-propagating thrust system the youngest and lowest of which marks the Caledonian front in Britain. Microstructures and quartz c-axis analysis show that fabrics formed during nappe emplacement were thoroughly recrystallised before or during peak Caledonian metamorphic conditions. One segment of the shear zone was reactivated as a north-directed thrust with retrograde reworking of annealed metamorphic textures. Quartz-rich mylonites from the reactivated zone display asymmetric or single-girdle quartz c-axis fabrics consistent with north-directed overthrust shear, except within and immediately beneath an allochthonous orthogneiss sheet of Archaean basement. Here, quartz c-axis fabrics have orthorhombic symmetry, implying that the orthogneiss unit and the thin smear of psammitic mylonites accreted to its base extended coaxially as a rigid sheet while the softer quartz-rich mylonites of the enclosing Moine accommodated the late non-coaxial strain. The thrust zone was probably reactivated within the old footwall and by ductile extension of the hanging wall along localised zones of intense non-coaxial strain. This conclusion emphasises the complexity and longevity of Caledonian ductile deformation.

  18. Metamorphic history of LP/HT migmatites from the Bavarian Unit (Bohemian Massif)

    NASA Astrophysics Data System (ADS)

    Sorger, Dominik; Hauzenberger, Christoph; Linner, Manfred; Iglseder, Christoph

    2016-04-01

    Granulite facies migmatites are commonly observed in the Bavarian Unit which were formed during a late Variscan (post 330 Ma) LP-HT overprint. This event is related to a delamination of mantle lithosphere and subsequent asthenospheric upwelling. Most of these rocks underwent high degrees of melting forming meta- and diatexites. Former work in the Sauwald area, Upper Austria, by Tropper et al. (2006) determined metamorphic conditions of 700-800°C and 0.4-0.5 Gpa. In this study samples were taken along the (1) Danube valley (west of Linz), from the (2) Lichtenberg area (north of Linz), the (3) Bad Leonfelden area (west of the Rodl Fault) and the (4) Sauwald area (south of the river Danube). Biotite and plagioclase bearing migmatite is very common and occurs all over the investigated area. These rocks are the product of intensive melting (anatexite) and formed at conditions of ~650-700°C and 0.25-0.45 Gpa. Scarce outcrops of garnet bearing Al-rich migmatitic metapelites occur along the Danube valley. The formation of the migmatitc texture with well-developed leucosomes (K-feldspar, plagioclase, quartz) and melanosomes (garnet, cordierite, sillimanite, spinel, ilmenite, ± biotite) indicate high temperature metamorphism. Most of the garnet grains show a homogenous iron-rich composition and form generally an almandine-pyrope (Xalm=0.78-0.80, Xprp=0.16-0.18) solid solution with minor contents of grossular and spessartine (Xgrs=0.028-0.032, Xsps=0.020-0.024). Large garnet porphyroblasts (up to 1cm in size) display a distinct chemical zoning, especially in grossular component. Elevated homogeneous grossular content in the core is followed discontinously by low grossular content at the rim indicating a two stage growth. Garnet core and rim also display different mineral inclusions. Thermobarometric calculations using garnet core compositions with inclusions and garnet rim compositions with matrix phases as well as pseudosection calculations allow the reconstruction of a P

  19. A Petrographic History of Martian Meteorite ALH84001: Two Shocks and an Ancient Age

    NASA Technical Reports Server (NTRS)

    Treiman, Allan H.

    1995-01-01

    ALH84001 is an igneous meteorite, an orthopyroxenite of martian origin. It contains petrographic evidence of two shock metamorphic events, separated by thermal and chemical events. The evidence for two shock events suggests that ALH84001 is ancient and perhaps a sample of the martian highlands. From petrography and mineral chemistry, the history of ALH84001 must include: crystallization from magma, a first shock (impact) metamorphism, thermal metamorphism, low-temperature chemical alteration, and a second shock (impact) metamorphism. Originally, ALH84001 was igneous, an orthopyroxene-chromite cumulate. In the first shock event, the igneous rock was cut by melt-breccia or cataclastic veinlets, now bands of equigranular fine-grained pyroxene and other minerals (crush zones). Intact fragments of the cumulate were fractured and strained (now converted to polygonized zones). The subsequent thermal metamorphism (possibly related to the first shock) annealed the melt-breccia or cataclastic veinlets to their present granoblastic texture and permitted chemical homogenization of all mineral species present. The temperature of metamorphism was at least 875 C, based on mineral thermometers. Next, Mg-Fe-Ca carbonates and pyrite replaced plagioclase in both clasts and granular bands, producing ellipsoidal carbonate globules with sub-micron scale compositional stratigraphy, repeated identically in all globules, The second shock event produced microfault offsets of carbonate stratigraphy and other mineral contacts, radial fractures around chromite and maskelynite, and strain birefringence in pyroxene. Maskelynite could not have been preserved from the first shock event, because it would have crystallized back to plagioclase. The martian source area for ALH84001 must permit this complex, multiple impact history. Very few craters on young igneous surfaces are on or near earlier impact features. It is more likely that ALH84001 was ejected from an old igneous unit (Hesperian or

  20. Protracted tectono-metamorphic history of the SE Superior Province : contribution of 40Ar/39Ar thermochronology in the Abitibi-Opatica contact zone, Québec, Canada

    NASA Astrophysics Data System (ADS)

    Daoudene, Yannick; Tremblay, Alain; Ruffet, Gilles; Leclerc, François; Goutier, Jean

    2015-04-01

    of an important sub-vertical shearing deformation as expected if it was a major upper plate-lower plate boundary. Furthermore, the contact does not present significant metamorphic break between the two domains, but a progressive increasing of metamorphism toward the OSP, from greenschist- to amphibolite-facies conditions. Based on these structural and metamorphic characteristics, we suggest that the OSP exposes the deepest rocks at outcrop of an ASP-OSP crust in the study area. Regionally, the 40Ar/39Ar ages acquired during this study indicate that the ASP-OSP contact records a protracted metamorphic history that started around 2685 Ma. The structural and isotopic age data suggest that, from ~2685 Ma to ~2632 Ma, the deepest level of the ASP and the underlying OSP reached amphibolite-facies metamorphic conditions and that regional deformation was accommodated by an overall horizontal shortening and sub-vertical transfers of crustal material. Subsequently, the cooling of these crustal rocks was accompanied by strain localisation, which led to the development of oblique strike-slip shear zones from ~2600 Ma, when the lateral flowing of crustal material became predominant. Our 40Ar/39Ar data compared with metamorphic ages documented in adjacent areas of the Superior Province suggests that the peak and duration of regional metamorphism might have been coeval over a large region. This rather favours a mode of pervasive deformation as expected in vertical tectonics.

  1. [sup 40]Ar/[sup 39]Ar mineral ages from southwestern Penobscot Bay, Maine: Evidence for Silurian metamorphism

    SciTech Connect

    West, D.P. Jr.; Guidotti, C.V.; Lux, D.R. . Dept. of Geological Sciences)

    1992-01-01

    The nature and timing of metamorphic events in the Coastal Lithotectonic Block of Maine remain poorly understood. Immediately west and southwest of Penobscot Bay the rocks are polymetamorphic showing evidence for at least two episodes of amphibolite facies metamorphism and later, perhaps regionally extensive, retrograde events. Hornblende mineral separates from two amphibolites din the Port Clyde area have identical Ar-40/Ar-39 plateau ages of 414.0 [+-] 3.3 and 414.0 [+-] 3.9 Ma. These ages are interpreted to reflect the time of cooling following the last significant thermal event in this area. Biotite from an amphibolite in the Port Clyde area gives a total gas age of 346.5 [+-] 3.2 Ma. Hornblende from an amphibolite 7 km to the west near Friendship gives a nearly concordant release spectrum with a plateau age of 369.0 [+-] 3.7 Ma. Coexisting biotite from this amphibolite gives a total gas age of 289.2 [+-] 2.7 Ma. Muscovite from the Waldoboro pluton has a nearly concordant release spectrum with a plateau age of 306.3 [+-] 2.2 Ma. Biotite from this sample gives a total gas age of 288.9 [+-] 2.2 Ma. The 414.0 Ma hornblende cooling ages from the Port Clyde area reflect cooling following a significant high grade Silurian thermal event. This Silurian metamorphism is the same age as tectonothermal events in the Nashoba Terrane in eastern Massachusetts, the Kingston Complex in southern New Brunswick, the Aspy Terrane in Cape Breton island, Nova Scotia, and the Hermitage Flexure in southern Newfoundland.d Thus a distinctive Silurian tectonothermal province located along the western edge of the Avalon Zone appears to extend discontinuously from Massachusetts to Newfoundland.

  2. Mineral inclusions in zircons of S-type granite: implications for high pressure metamorphism history of meta-sedimentary rocks in the Huai'an terrain, North China Craton

    NASA Astrophysics Data System (ADS)

    Wang, Haozheng; Zhang, Huafeng; Zhai, Mingguo; Cui, Xiahong

    2016-04-01

    The Paleoproterozoic evolution of North China Craton (NCC) arises many argument as geologists have different viewpoints on the distribution and metamorphic history of mafic granulites and granulite facies meta-sedimentary rocks. To provide more evidence of constraining the metamorphic history of granulite facies meta-sedimentary rocks, we select granulite facies meta-sedimentary rocks and co-existing S-type granite in the Huai'an terrain to make a deep research. Magmatic zircons derived from the S-type granite reveal the magmatic age of ˜1.95 Ga and metamorphic age of ˜1.85 Ga with ɛHf(t) value of -4.5 - -0.5. The ɛHf(t) value of S-type granite and relict of garnet-sillimanite gneiss suggest that the S-type granite is generated by melting of meta-sedimentary rocks. Zircons with ages of ˜1.95 Ga and ˜1.85 Ga have the mineral inclusions of Ky + Qz + Ru + Pl and these mineral inclusions are determined by method of Laser-Raman. The ˜1.95 Ga magmatic zircons with inclusions of Ky + Qz + Ru + Pl suggest that meta-sedimentary rocks have mineral assemblages Ky + Qz + Ru + Pl. However, previous studies in the Huai'an terrain showed that almost granulite facies metamorphic condition of meta-sedimentary rocks were regarded as medium pressure by considering the Sill + Grt + Bt + Pl + Qz + Ru + Kf. Presence of kyanite instructs that meta-sedimentary rocks may experience high pressure granulite facies metamorphism. According to pseudosection calculation by using effective bulk composition of garnet-sillimanite gneiss, mineral assemblage of Grt + Ky + Pl + Bt + Qz + Ru + Kf is regarded as the peak stage of high pressure metamorphism. This mineral assemblage is occurred at field of 1033 - 1123 K and 9 - 15 Kbar and the peak pressure is around 11 - 13 Kbar, determined by the XMg and XCa isopleths of garnet. This P-T result is consistent with peak condition of high pressure mafic granulite. Considering the ˜1.95 Ga magmatic age of S-type granite generated by decompression

  3. Different radiation and metamorphic history of the Kainsaz CO 3.2 chondrules

    NASA Technical Reports Server (NTRS)

    Kashkarov, L. L.; Kalinina, G. V.

    1993-01-01

    Track and thermoluminescence parameters in chondrules from the Kainsaz CO 3.2 chondrite have been studied. Obtained results elucidate their individual shock-thermal history and the early pre-accretion stage of the meteorite parent body formation.

  4. Age constraints on felsic intrusions, metamorphism and gold mineralisation in the Palaeoproterozoic Rio Itapicuru greenstone belt, NE Bahia State, Brazil

    USGS Publications Warehouse

    Mello, E.F.; Xavier, R.P.; McNaughton, N.J.; Hagemann, S.G.; Fletcher, I.; Snee, L.

    2006-01-01

    U-Pb sensitive high resolution ion microprobe mass spectrometer (SHRIMP) ages of zircon, monazite and xenotime crystals from felsic intrusive rocks from the Rio Itapicuru greenstone belt show two development stages between 2,152 and 2,130 Ma, and between 2,130 and 2,080 Ma. The older intrusions yielded ages of 2,152??6 Ma in monazite crystals and 2,155??9 Ma in zircon crystals derived from the Trilhado granodiorite, and ages of 2,130??7 Ma and 2,128??8 Ma in zircon crystals derived from the Teofila??ndia tonalite. The emplacement age of the syntectonic Ambro??sio dome as indicated by a 2,080??2-Ma xenotime age for a granite dyke probably marks the end of the felsic magmatism. This age shows good agreement with the Ar-Ar plateau age of 2,080??5 Ma obtained in hornblendes from an amphibolite and with a U-Pb SHRIMP age of 2,076??10 Ma in detrital zircon crystals from a quartzite, interpreted as the age of the peak of the metamorphism. The predominance of inherited zircons in the syntectonic Ambro??sio dome suggests that the basement of the supracrustal rocks was composed of Archaean continental crust with components of 2,937??16, 3,111??13 and 3,162??13 Ma. Ar-Ar plateau ages of 2,050??4 Ma and 2,054??2 Ma on hydrothermal muscovite samples from the Fazenda Brasileiro gold deposit are interpreted as minimum ages for gold mineralisation and close to the true age of gold deposition. The Ar-Ar data indicate that the mineralisation must have occurred less than 30 million years after the peak of the metamorphism, or episodically between 2,080 Ma and 2,050 Ma, during uplift and exhumation of the orogen. ?? Springer-Verlag 2006.

  5. Kibaran magmatism and Pan-African granulite metamorphism in northern Mozambique: single zircon ages and regional implications

    NASA Astrophysics Data System (ADS)

    Kroner, A.; Sacchi, R.; Jaeckel, P.; Costa, M.

    1997-10-01

    Single zircons from granitoid orthogneisses in the foreland of the Lurio Belt of northern' Mozambique were dated by the evaporation method and yielded 207Pb/ 206Pb magmatic emplacement ages between 1040.1 ±0.4 and 1148.2±0.4 Ma. These data confirm previous RbSr whole rock and SHRIMP zircon analyses and record a period of magmatic activity corresponding to the Kibaran event of east central Africa. A1300 Ma old zircon xenocryst in one sample suggests the presence of still older crust in the region. Metamorphic zircons from a granulite-facies psammopelitic gneiss of the Mugeba klippe, which is derived tectonically from the Lurio Belt, were dated by evaporation, conventional techniques and SHRIMP at ˜615 Ma. This us interpreted as reflecting the peak of high-grade metamorphism in this rock and, by implication, in the Lurio Belt. It is concluded from this that the main metamorphism in the basement of northern Mozambique occured in Pan-African times, as is the case in adjacent regions of Tanzania and Malawi, and that this may be the result of collision between East and West Gondwana

  6. Chondrite thermal histories from Low-CA pyroxene microstructures: Autometamorphism versus prograde metamorphism revisited

    NASA Technical Reports Server (NTRS)

    Brearley, Adrian J.; Jones, Rhian H.; Papike, J. J.

    1993-01-01

    In order to constrain the thermal histories of chondritic meteorites, a detailed study of the microstructures of low-Ca pyroxenes produced experimentally and in types 4 and 5 ordinary chondrites was carried out. Cooling experiments on synthetic MgSiO3 at cooling rates between 2 and 10000 C/hr from the protopyroxene stability field into that of orthopyroxene (OPX) were performed and the products of these experiments were annealed for a variety of annealing times. There are clear microstructural differences between samples which were cooled and those which were subsequently annealed. A comparison of the microstructures observed in the experimental samples with those in H4-5 ordinary chondrites shows that they cannot have experienced a single stage cooling history, as proposed for the autometamorphism model.

  7. Shock Metamorphism in Northwest Africa 8159, Tissint and Elephant Moraine A79001: Implications for Thermal Histories and Geochronology

    NASA Astrophysics Data System (ADS)

    Sharp, T. G.; Hu, J.; Walton, E. L.

    2016-08-01

    Shock metamorphic effects in martian meteorites provide a record of recent impact events on Mars. We examined the textures and mineralogy associated with shock melting in three highly shocked martian basalts: NWA 8159, Tissint and EET A79001.

  8. Metamorphic P-T conditions and CO2 influx history of medium-grade metapelites from Karakorum, Trans-Himalaya, India

    NASA Astrophysics Data System (ADS)

    Sachan, Himanshu K.; Santosh, M.; Prakash, Divya; Kharya, Aditya; Chandra Singh, P.; Rai, Santosh K.

    2016-07-01

    The medium grade metapelites of Pangong-Tso area in the trans-Himalayan region underwent sillimanite-grade metamorphism initiated during the Cretaceous, associated with the collision of the Kohistan arc and the Indian plate with Asia. This paper present results from a petrological and fluid inclusion study to understand the metamorphic P-T conditions and fluid history of these rocks. The calculated phase equilibria in the Na2O-CaO-K2O-FeO-MgO-MnO-Al2O3-SiO2-H2O-TiO2 (NCKFMMnASHT) system suggest P-T conditions of 8 kbar and 650 °C for the peak metamorphic event. Primary fluid inclusions occur in staurolite and garnet, whereas quartz carries mostly secondary fluid inclusions. The trapped fluids in primary inclusions show initial melting temperatures in the range of -56.9 to -56.6 °C, suggesting nearly pure CO2 composition. The secondary fluids are of mixed carbonic-aqueous nature. The re-equilibrated inclusions show annular morphology as well as necking phenomena. The CO2 isochores for the primary inclusions indicate pressures of 6.1-6.7 kbar, suggesting that the CO2-rich fluids were trapped during post-peak exhumation of the rocks, or that synmetamorphic carbonic fluids underwent density reversal during isothermal decompression. The secondary CO2-H2O fluids must have been trapped during the late exhumation stage, as their isochores define further lower pressures of 4.8 kbar. The morphology of re-equilibrated fluid inclusions and the rapid decrease in pressure are consistent with a near-isothermal decompression trajectory following the peak metamorphism. The carbonic fluids were probably derived locally from decarbonation reactions of the associated carbonate rocks during metamorphism or from a deep-seated reservoir through Karakorum fault.

  9. Contrast in stress-strain history during exhumation between high- and ultrahigh-pressure metamorphic units in the Western Alps: Microboudinage analysis of piemontite in metacherts

    NASA Astrophysics Data System (ADS)

    Omori, Yasutomo; Barresi, Antonello; Kimura, Nozomi; Okamoto, Atsushi; Masuda, Toshiaki

    2016-08-01

    Our analyses of microboudinage structures of piemontite grains embedded within six samples of metachert, one collected from an ultrahigh-pressure (UHP) metamorphic unit at Lago di Cignana in Italy of the Western Alps, and the other five from surrounding high-pressure (HP) metamorphic units in Italy and France, have revealed that the structures are all symmetrical in type, and were presumably produced in coaxial strain fields. Stress-strain analyses of the microboudinaged grains revealed significant contrasts in the stress and strain histories of the UHP and HP metamorphic units, with the differential stress recorded by the UHP sample being unequivocally lower than that recorded by the five HP samples. In addition, our analyses showed that the UHP sample underwent stress-relaxation during microboudinage, whereas the five HP samples did not. On the basis of these observations and analyses we discuss the mechanical decoupling of the UHP and HP units that led to different histories in differential stress between the units during exhumation of the Western Alps.

  10. The CO chondrites: Major recent Antarctic finds, their thermal and radiation history, and describing the metamorphic history of members of the class

    NASA Astrophysics Data System (ADS)

    Sears, Derek W. G.

    2016-09-01

    Thermoluminescence (TL) properties of 29 CO chondrites from the Miller Range (MIL) and five chondrites from the Dominion Range (DOM) have been measured. MIL has a relatively strong natural TL signal (19.6 ± 14.7 krad), while some of the DOM samples have a very weak natural TL signal (<1 krad) whereas others resemble the MIL meteorites. I argue that MIL and some of the DOM samples had a normal perihelion (∼1.0 AU) and terrestrial age of ∼450-700 ka, while some of the DOM samples have a terrestrial age of ∼100 ka but a perihelion of ∼0.8 AU. The DOM meteorites also show considerable heterogeneity in their induced TL properties, also suggesting that the DOM fragments represent more than one fall. The induced TL data for the MIL samples studied here are consistent with them all being from a single fragmented meteorite. Small (50 mg) chips have TL properties similar to 500 mg chips, so that the smaller chips are representative, although samples taken from original masses less than ∼2 g have low natural TL suggesting that they were heated during atmospheric fall. The properties of CO chondrites are reviewed in terms of their petrologic types. Correlations between TL sensitivity, the most quantitative technique for evaluating metamorphic alteration in CO chondrites, and data for olivine composition and heterogeneity, matrix composition, inert gas content, metal composition (Ni, Co, and Cr in the kamacite), bulk carbon, C and O isotopes, graphite ordering, spectral reflectance at 0.8 μm, and textural characteristics of the ameboid olivine and Ca-rich inclusions are examined. The petrographic types appear to be largely metamorphic in origin with perhaps a minor role for metasomatism. Contrary to recent proposals it is here argued that petrologic type definitions should (1) be specific enough to be meaningful, but broad enough to be simple in application and robust to new developments, (2) be descriptive and not interpretative, (3) should not oversimplify and

  11. Metamorphic fluids and uplift-erosion history of a portion of the Kapuskasing structural zone, Ontario, as deduced from fluid inclusions

    NASA Technical Reports Server (NTRS)

    Rudnick, R. L.; Ashwal, L. D.; Henry, D. J.

    1983-01-01

    Fluid inclusions can be used to determine the compositional evolution of fluids present in high grade metamorphic rocks (Touret, 1979) along with the general P-T path followed by the rocks during uplift and erosion (Hollister et al., 1979). In this context, samples of high grade gneisses from the Kapuskasing structural zone (KSZ, Fig. 1) of eastern Ontario were studied in an attempt to define the composition of syn- and post-metamorphic fluids and help constrain the uplift and erosion history of the KSZ. Recent work by Percival (1980), Percival and Card (1983) and Percival and Krogh (1983) shows that the KSZ represents lower crustal granulites that form the lower portion of an oblique cross section through the Archean crust, which was up faulted along a northeast striking thrust fault. The present fluid inclusion study places constraints upon the P-T path which the KSZ followed during uplift and erosion.

  12. Metamorphic facies map of Alaska

    SciTech Connect

    Dusel-Bacon, C.; O-Rourke, E.F.; Reading, K.E.; Fitch, M.R.; Klute, M.A.

    1985-04-01

    A metamorphic-facies of Alaska has been compiled, following the facies-determination scheme of the Working Group for the Cartography of the Metamorphic Belts of the World. Regionally metamorphosed rocks are divided into facies series where P/T gradients are known and into facies groups where only T is known. Metamorphic rock units also are defined by known or bracketed age(s) of metamorphism. Five regional maps have been prepared at a scale of 1:1,000,000; these maps will provide the basis for a final colored version of the map at a scale of 1:2,500,000. The maps are being prepared by the US Geological Survey in cooperation with the Alaska Division of Geological and Geophysical Surveys. Precambrian metamorphism has been documented on the Seward Peninsula, in the Baird Mountains and the northeastern Kuskokwim Mountains, and in southwestern Alaska. Pre-Ordovician metamorphism affected the rocks in central Alaska and on southern Prince of Wales Island. Mid-Paleozoic metamorphism probably affected the rocks in east-central Alaska. Most of the metamorphic belts in Alaska developed during Mesozoic or early Tertiary time in conjuction with accretion of many terranes. Examples are Jurassic metamorphism in east-central Alaska, Early Cretaceous metamorphism in the southern Brooks Range and along the rim of the Yukon-Kovyukuk basin, and late Cretaceous to early Tertiary metamorphism in the central Alaska Range. Regional thermal metamorphism was associated with multiple episodes of Cretaceous plutonism in southeastern Alaska and with early Tertiary plutonism in the Chugach Mountains. Where possible, metamorphism is related to tectonism. Meeting participants are encouraged to comment on the present version of the metamorphic facies map.

  13. New U-Pb ages from dykes cross-cutting the Demirci metamorphics, NW Turkey: Implications for multiple orogenic events

    NASA Astrophysics Data System (ADS)

    Sen, Fatih; Koral, Hayrettin; Peytcheva, Irena

    2016-04-01

    A high-grade metamorphic sequence in the Sünnice Mountains, Bolu, NW Turkey, is represented by migmatitic quartzo-feldspathic gneisses in amphibolite facies called the Demirci metamorphics/paragneisses, and a sequence of low-grade meta-volcanics containing meta-andesites with minor meta-rhyolites and meta-sedimentary rocks called the Yellice meta-volcanics. They are intruded by the Dirgine granite with an age of Upper Ediacaran (576-565 Ma) and are considered a part of the İstanbul-Zonguldak Tectonic Unit. The Demirci paragneisses are also intruded by a number of dykes in various directions, traditionally considered without radiometric dating to have been emplaced in a single magmatic phase in the Eocene related to post-collision regime of the Anatolide-Tauride platform. Mafic-intermediate-felsic dykes cross-cutting the Demirci paragneisses have been investigated in maps of 1/1000 scale, and their U-Pb zircon age, major-trace element and kinematic data have been obtained. The mafics dykes cross-cutting the Yellice meta-volcanics, equivalents of those in the Demirci paragneisses, occur in N400-500E orientations and have calc-alkaline basalt compositions with a subduction signature. The intermediate dykes occur in N650W, N800W orientations and have calc-alkaline basaltic andesite to andesitic compositions with a subduction signature. Some felsics occur in N150W and N800E orientations and have calc-alkaline dacitic compositions with a collisional tectonic setting. Other calc-alkaline granitic dykes occur in N750E orientation and calc-alkaline granitic compositions with a subduction signature. U-Pb LA-ICP-MS dating of zircons yield ages from 485.7±3.6 Ma (i.e. Cambro-Ordovician) for N800E trending dacite dykes; 443.0±5.4 Ma (i.e. Ordovician-Silurian) for N150W trending dacite dykes; 301.0±1.6 Ma (i.e. Upper Pennsylvanian-Carboniferous) for N650W trending basaltic andesite dykes; 268.2±2.4 Ma (i.e. Guadalupian-Permian) for N40-500E trending basalt dykes; 262.9±3

  14. High-pressure metamorphic age and significance of eclogite-facies continental fragments associated with oceanic lithosphere in the Western Alps (Etirol-Levaz Slice, Valtournenche, Italy)

    NASA Astrophysics Data System (ADS)

    Fassmer, Kathrin; Obermüller, Gerrit; Nagel, Thorsten J.; Kirst, Frederik; Froitzheim, Nikolaus; Sandmann, Sascha; Miladinova, Irena; Fonseca, Raúl O. C.; Münker, Carsten

    2016-05-01

    The Etirol-Levaz Slice in the Penninic Alps (Valtournenche, Italy) is a piece of eclogite-facies continental basement sandwiched between two oceanic units, the blueschist-facies Combin Zone in the hanging wall and the eclogite-facies Zermatt-Saas Zone in the footwall. It has been interpreted as an extensional allochthon from the continental margin of Adria, emplaced onto ultramafic and mafic basement of the future Zermatt-Saas Zone by Jurassic, rifting-related detachment faulting, and later subducted together with the future Zermatt-Saas Zone. Alternatively, the Etirol-Levaz Slice could be derived from a different paleogeographic domain and be separated from the Zermatt-Saas Zone by an Alpine shear zone. We present Lu-Hf whole rock-garnet ages of two eclogite samples, one from the center of the unit and one from the border to the Zermatt-Saas Zone below. These data are accompanied by a new geological map of the Etirol-Levaz Slice and the surrounding area, as well as detailed petrology of these two samples. Assemblages, mineral compositions and garnet zoning in both samples indicate a clockwise PT-path and peak-metamorphic conditions of about 550-600 °C/20-25 kbar, similar to conditions proposed for the underlying Zermatt-Saas Zone. Prograde garnet ages of the two samples are 61.8 ± 1.8 Ma and 52.4 ± 2.1 Ma and reflect different timing of subduction. One of these is significantly older than published ages of eclogite-facies metamorphism in the Zermatt-Saas Zone and thus contradicts the hypothesis of Mesozoic emplacement. The occurrence of serpentinite and metagabbro bodies possibly derived from the Zermatt-Saas Zone inside the Etirol-Levaz Slice suggests that the latter is a tectonic composite. The basement slivers forming the Etirol-Levaz Slice and other continental fragments were subducted earlier than the Zermatt-Saas Zone, but nonetheless experienced similar pressure-temperature histories. Our results support the hypothesis that the Zermatt-Saas Zone and the

  15. Thermal metamorphism

    NASA Astrophysics Data System (ADS)

    McSween, Harry Y., Jr.; Sears, Derek W. G.; Dodd, Robert T.

    Most chondrites have experienced thermal metamorphism, resulting in changes in texture, mineralogy and possibly chemical composition. The physical conditions for metamorphism range from approximately 400 to 1000 C at low lithostatic pressure. Metamorphism may have resulted from decay of short-lived radionuclides, electromagnetic induction or accretion of hot materials. Several thermal models for chondrite parent bodies have been proposed. The least metamorphosed type-3 chondrites probably carry the most information about the early solar system, but even these have been affected to some degree by thermal processing.

  16. The Age and Geodynamic Evolution of the Metamorphic sole rocks from Izmir-Ankara-Erzıncan suture zone (Northern-Turkey)

    NASA Astrophysics Data System (ADS)

    Melih Çörtük, Rahmi; Faruk Çelik, Ömer; Özkan, Mutlu; Sherlock, Sarah C.; Marzoli, Andrea; Altıntaş, İsmail Emir; Topuz, Gültekin

    2016-04-01

    The İzmir-Ankara-Erzincan suture zone in northern Turkey is one of the major tectonic zones separating the Pontides to the North from the Anatolide-Tauride block and Kı rşehir Massif to the South. The accretionary complex of the İzmir-Ankara-Erzincan suture zone, near Artova, is composed mainly of peridotites with varying degree serpentinization, metamorphic rocks, basalt, sandstones, pelagic and neritic limestones. The metamorphic rocks are represented by amphibolite, garnet micaschit, calc-schist and marble. The metamorphic rocks were interpreted as the metamorphic sole rocks. Because; (i) They are tectonically located beneath the serpentinized peridotites. (ii) Foliation planes of both the amphibolites and mantle tectonites are parallel to each other. (iii) The metamorphic rocks are crosscut by non-metamorphic dolerite dikes which exhibite Nb and Ta depletion relative to Th enrichment on the N-MORB normalized multi-element spider diagram. The dolerite dikes display flat REE patterns (LaN/YbN=0.85-1.24). These geochemical signatures of the dolerite dikes are indicative of subduction component during their occurrences. Geochemical observations of the amphibolites suggest E-MORB- and OIB-like signatures (LaN/SmN= 1.39-3.14) and their protoliths are represented by basalt and alkali basaltic rocks. Amphiboles from the amphibolites are represented by calcic amphiboles (magnesio-hornblende, tchermakite and tremolite) and they yielded 40Ar-39Ar ages between 157.8 ± 3.6 Ma and 139 ± 11 Ma. These cooling ages were interpreted to be the intra-oceanic subduction/thrusting time of the İzmir-Ankara-Erzincan oceanic domain. This study was funded by TÜBİTAK (Project no: 112Y123).

  17. World History in a Global Age.

    ERIC Educational Resources Information Center

    Geyer, Michael; Bright, Charles

    1995-01-01

    Argues that for years the emphasis on historical specialization relegated world history to the academic dustbin. Maintains that the globalization of culture, economics, and societies has created a reimagining of world history. Discusses issues and presents recommendations on research and curriculum development in world history. (CFR)

  18. Metamorphism of tectonic terranes in the eastern marginal zone of the Appalachian orogen, New England

    SciTech Connect

    Hepburn, J.C.; Olszewski, W.J.; Guidotti, C.V.

    1985-01-01

    Southeastern New England is subdivided into three major fault bounded tectonic terranes, each with a distinctive metamorphic history. The easternmost, the Avalon Terrane, has generally been metamorphosed no higher than the lower greenschist facies. Evidence for pre-Alleghanian metamorphism includes a Proterozoic Z(.) event, contact metamorphism adjacent to Ord.-Dev. alkaline plutons, and granulite facies crustal xenoliths in Mesozoic dikes. To the west the Nashoba Terrane has been deformed and polymetamorphosed to the sill. and 2nd sill. zones between approximately 415 and 450 m.y., based on ages of associated granitic and migmatitic rocks. 730 m.y. assumed basement gneisses (fish Brook) have likely experienced Late PC metamorphism. In the Merrimack Trough, here including the Massabesic Gneiss, the metamorphic grade ranges from the greenschist facies on the east to the 2nd sillimanite zones on the west toward the Massabesic. The two metamorphic events present here must predate the intrusion of the Exeter Diorite (473 m.y .), indicating one or both may be PC. To the east, the fault bounded Rye Formation has also experienced two pre- 470 m.y. metamorphisms (and -sill.) However, the terrane east of the Turtle Head Fault Zone (THFZ) has many similarities to the Boston Platform including general (Late PC.) lower greenschist metamorphism. Also, the area between the Norumbega FZ and the THFZ has experienced high grade metamorphism of probable Silurian age and thus may be similar to the Nashoba Terrane.

  19. Mesozoic and Cenozoic thermal history of the eastern Mojave Desert, California and western Arizona, with emphasis on the Old Woman Mountains area and the Chemehuevi metamorphic core complex

    SciTech Connect

    Foster, D.A.

    1989-01-01

    Mesozoic thickening and Cenozoic extension resulted in the juxtaposition of upper and middle crustal rocks in the eastern Mojave Desert, southeastern California and western Arizona. The application of {sup 40}Ar/{sup 39}Ar thermochronology and petrology/thermobarometry to rocks in this region provides information about the timing and nature of thrusting, plutonism, metamorphism, denudation, and detachment faulting. Orogenesis culminated during the Late Cretaceous when rocks exposed in the Old Woman-Piute, Chemehuevi, and Sacramento Mountains attained temperatures > 500C. High grade metamorphism of the Old Woman Mountains area was caused by the intrusion of the Old Woman-Piute batholith at 73 {plus minus} 1 Ma; Cretaceous mineral assemblages in Proterozoic pelites increase in grade from greenschist to upper amphibolite facies, and {sup 40}Ar/{sup 39}Ar hornblende ages from Proterozoic amphibolites decrease in age from {approximately} 1,600 Ma to 73 {plus minus} 1 Ma, in the direction of 73 Ma plutons. Pluton emplacement and metamorphism occurred at 3 to 3.5 kbars and 400 > 600C in the Piute Mountains, and 3.5 to 4.5 kbars and 530 to > 650C in the Old Woman Mountains. Following the Cretaceous, the eastern Mojave Desert underwent a period of cooling at a rate of 2 to 10C/Ma between 65 and 25 Ma. By 30 Ma rocks exposed in the Old Woman-Piute, Marble Ship, Clipper and Turtle Mountains were below {approximately} 100C. {sup 40}/{sup 39}Ar ages from the Sacramento Mountains suggest that mylonitization caused by the onset of regional extension occurred at 23 {plus minus} 1 Ma. When extension started in the Chemehuevi Mountains, rocks exposed in the southwestern and northeastern portions of footwall to the Chemehuevi detachment fault were at {approximately} 180C and {approximately} 350C, respectively which suggests that this fault initiated at a dip of 5 to 30{degree}.

  20. The genetic history of Ice Age Europe

    PubMed Central

    Fu, Qiaomei; Posth, Cosimo; Hajdinjak, Mateja; Petr, Martin; Mallick, Swapan; Fernandes, Daniel; Furtwängler, Anja; Haak, Wolfgang; Meyer, Matthias; Mittnik, Alissa; Nickel, Birgit; Peltzer, Alexander; Rohland, Nadin; Slon, Viviane; Talamo, Sahra; Lazaridis, Iosif; Lipson, Mark; Mathieson, Iain; Schiffels, Stephan; Skoglund, Pontus; Derevianko, Anatoly P.; Drozdov, Nikolai; Slavinsky, Vyacheslav; Tsybankov, Alexander; Cremonesi, Renata Grifoni; Mallegni, Francesco; Gély, Bernard; Vacca, Eligio; González Morales, Manuel R.; Straus, Lawrence G.; Neugebauer-Maresch, Christine; Teschler-Nicola, Maria; Constantin, Silviu; Moldovan, Oana Teodora; Benazzi, Stefano; Peresani, Marco; Coppola, Donato; Lari, Martina; Ricci, Stefano; Ronchitelli, Annamaria; Valentin, Frédérique; Thevenet, Corinne; Wehrberger, Kurt; Grigorescu, Dan; Rougier, Hélène; Crevecoeur, Isabelle; Flas, Damien; Semal, Patrick; Mannino, Marcello A.; Cupillard, Christophe; Bocherens, Hervé; Conard, Nicholas J.; Harvati, Katerina; Moiseyev, Vyacheslav; Drucker, Dorothée G.; Svoboda, Jiří; Richards, Michael P.; Caramelli, David; Pinhasi, Ron; Kelso, Janet; Patterson, Nick; Krause, Johannes; Pääbo, Svante; Reich, David

    2016-01-01

    Modern humans arrived in Europe ~45,000 years ago, but little is known about their genetic composition before the start of farming ~8,500 years ago. We analyze genome-wide data from 51 Eurasians from ~45,000-7,000 years ago. Over this time, the proportion of Neanderthal DNA decreased from 3–6% to around 2%, consistent with natural selection against Neanderthal variants in modern humans. Whereas the earliest modern humans in Europe did not contribute substantially to present-day Europeans, all individuals between ~37,000 and ~14,000 years ago descended from a single founder population which forms part of the ancestry of present-day Europeans. A ~35,000 year old individual from northwest Europe represents an early branch of this founder population which was then displaced across a broad region, before reappearing in southwest Europe during the Ice Age ~19,000 years ago. During the major warming period after ~14,000 years ago, a new genetic component related to present-day Near Easterners appears in Europe. These results document how population turnover and migration have been recurring themes of European pre-history. PMID:27135931

  1. Age and tectonic significance of metamorphic rocks along the axis of the Sierra Nevada batholith: A critical reappraisal

    SciTech Connect

    Schweickert, R.A.; Lahren, M.M. )

    1991-02-01

    Metamorphic rocks in many roof pendants along the axis of the Sierra Nevada batholith (SNB) between 36 and 38{degree}N lat. have been considered part of the Kings sequence, of probable Mesozoic age. However, most of the pendants are in fact undated by fossils and may contain Paleozoic or Precambrian strata. A critical reappraisal of new and existing data on these pendants has led to the following hypotheses: (1) A continental crustal silver referred to as the Snow Lake block, with the approximate dimensions of the Salinian block, and represented by metamorphosed Proterozoic and Cambrian miogeoclinal rocks, extends 120 mi (200 km) southeastward from northern YNP to the Kaweah River drainage, and includes rocks in the following pendants: Snow Lake, Piute Mountain, Glen Aulin, May Lake, Iron mountain, Shuteye Peak, Dinkey Creek, Patterson Mountain, Boyden Cave, and Sequoia Park. This silver was displaced about 400 km northward along an intrabatholithic dextral strike-slip fault during the Early Cretaceous time. (2) Based on reconnaissance studies, the authors propose that the Shoo Fly Complex, which lies west of the Snow Lake block, continues southeastward to 36{degree}N lat., and includes parts of the following pendants: Oakhurst, Lower Kings River, Kaweah River, Tule River, and Kern Canyon. The apparent juxtaposition of the Shoo Fly Complex with the Snow Lake block requires the presence of a major tectonic break between them. This structure, now largely obliterated by Cretaceous plutons of the SNB, may be the equivalent of the Golconda thrust in north-central Nevada.

  2. Integration of offshore seismic data, exploration wells, and onland outcrops as constraints on the tectonics and uplift age of metamorphic core complexes, eastern Papua New Guinea

    NASA Astrophysics Data System (ADS)

    Fitz, G. G.; Mann, P.; Campos Aguiniga, H.

    2009-12-01

    High-grade metamorphic domes of the D’Entrecasteaux Islands (DEI) of eastern Papua New Guinea are located within continental crust at the tip of the westward propagating Woodlark spreading ridge. Multi-channel seismic data collected by the RV Maurice Ewing in 1992 was integrated with seismic data from 1974 and two wells drilled by the oil industry in 1973 to understand pattern and age of faults and clastic wedges in offshore basins surrounding the 2-2.5-km high DEI. The WNW-trending line of the DEI demarcates two areas of contrasting deformational and depositional histories. In the area of the Kiribisi and Trobriand basins north of the DEI, normal faults occupy a WNW-striking basin that began to rift in the early Miocene and continued to rift sporadically until the early Pliocene when all normal faults were buried by ~650 m of undeformed Plio-Pleistocene sediments. We infer that these basins formed as sub-basins within a larger forearc basin bounded to the north by the forearc high of the Trobriand Islands and to the south by the DEI. Uplift of the forearc high and inversion of normal faults near the high during the Pleistocene and suggests the possibility of present-day, southward subduction along the Trobriand trench. To the south of the DEI in the Goodenough basin, the Pleistocene section is thicker and deformed by active, WNW-striking normal faults with seafloor scarps and high-angle dips. Wedging of the Pleistocene clastic fill in a half-graben geometry along the Owen-Stanley fault in the Southern part of the Goodenough basin along the southern coastline of the bay indicates that most normal motion has now shifted to this fault system. The shift in extension from north of the DEI to the Owen-Stanley fault zone in post-Pliocene time likely signals the arrival of the propagating rift tip of the Woodlark basin. The presence of conglomerate with high-grade metamorphic clasts in the Pliocene section north of the DEI supports the idea that the uplift and erosion

  3. Deformation and thermal histories of ordinary chondrites: Evidence for post-deformation annealing and syn-metamorphic shock

    NASA Astrophysics Data System (ADS)

    Ruzicka, Alex; Hugo, Richard; Hutson, Melinda

    2015-08-01

    We show that olivine microstructures in seven metamorphosed ordinary chondrites of different groups studied with optical and transmission electron microscopy can be used to evaluate the post-deformation cooling setting of the meteorites, and to discriminate between collisions affecting cold and warm parent bodies. The L6 chondrites Park (shock stage S1), Bruderheim (S4), Leedey (S4), and Morrow County (S5) were affected by variable shock deformation followed by relatively rapid cooling, and probably cooled as fragments liberated by impact in near-surface settings. In contrast, Kernouvé (H6 S1), Portales Valley (H6/7 S1), and MIL 99301 (LL6 S1) appear to have cooled slowly after shock, probably by deep burial in warm materials. In these chondrites, post-deformation annealing lowered apparent optical strain levels in olivine. Additionally, Kernouvé, Morrow County, Park, MIL 99301, and possibly Portales Valley, show evidence for having been deformed at an elevated temperature (⩾800-1000 °C). The high temperatures for Morrow County can be explained by dynamic heating during intense shock, but Kernouvé, Park, and MIL 99301 were probably shocked while the H, L and LL parent bodies were warm, during early, endogenically-driven thermal metamorphism. Thus, whereas the S4 and S5 chondrites experienced purely shock-induced heating and cooling, all the S1 chondrites examined show evidence for static heating consistent with either syn-metamorphic shock (Kernouvé, MIL 99301, Park), post-deformation burial in warm materials (Kernouvé, MIL 99301, Portales Valley), or both. The results show the pitfalls in relying on optical shock classification alone to infer an absence of shock and to construct cooling stratigraphy models for parent bodies. Moreover, they provide support for the idea that "secondary" metamorphic and "tertiary" shock processes overlapped in time shortly after the accretion of chondritic planetesimals, and that impacts into warm asteroidal bodies were

  4. Archean metamorphic sequence and surfaces, Kangerdlugssuaq Fjord, East Greenland

    NASA Technical Reports Server (NTRS)

    Kays, M. A.

    1986-01-01

    The characteristics of Archean metamorphic surfaces and fabrics of a mapped sequence of rocks older than about 3000 Ma provide information basic to an understanding of the structural evolution and metamorphic history in Kangerdlugssuaq Fjord, east Greenland. This information and the additional results of petrologic and geochemical studies have culminated in an extended chronology of Archean plutonic, metamorphic, and tectonic events. The basis for the chronology is considered, especially the nature of the metamorphic fabrics and surfaces in the Archean sequence. The surfaces, which are planar mineral parageneses, may prove to be mappable outside Kangerdlugssuaq Fjord, and if so, will be helpful in extending the events that they represent to other Archean sequences in east Greenland. The surfaces will become especially important reference planes if the absolute ages of their metamorphic assemblages can be determined in at least one location where strain was low subsequent to their recrystallization. Once an isochron is obtained, the dynamothermal age of the regionally identifiable metamorphic surface is determined everywhere it can be mapped.

  5. New insights into the history and origin of the southern Maya block, SE Mexico: U-Pb-SHRIMP zircon geochronology from metamorphic rocks of the Chiapas massif

    USGS Publications Warehouse

    Weber, Bodo; Iriondo, Alexander; Premo, Wayne R.; Hecht, Lutz; Schaaf, Peter

    2007-01-01

    The histories of the pre-Mesozoic landmasses in southern México and their connections with Laurentia, Gondwana, and among themselves are crucial for the understanding of the Late Paleozoic assembly of Pangea. The Permian igneous and metamorphic rocks from the Chiapas massif as part of the southern Maya block, México, were dated by U–Pb zircon geochronology employing the SHRIMP (sensitive high resolution ion microprobe) facility at Stanford University. The Chiapas massif is composed of deformed granitoids and orthogneisses with inliers of metasedimentary rocks. SHRIMP data from an anatectic orthogneiss demonstrate that the Chiapas massif was part of a Permian (∼ 272 Ma) active continental margin established on the Pacific margin of Gondwana after the Ouachita orogeny. Latest Permian (252–254 Ma) medium- to high-grade metamorphism and deformation affected the entire Chiapas massif, resulting in anatexis and intrusion of syntectonic granitoids. This unique orogenic event is interpreted as the result of compression due to flat subduction and accretionary tectonics. SHRIMP data of zircon cores from a metapelite from the NE Chiapas massif yielded a single Grenvillian source for sediments. The majority of the zircon cores from a para-amphibolite from the SE part of the massif yielded either 1.0–1.2 or 1.4–1.5 Ga sources, indicating provenance from South American Sunsás and Rondonian-San Ignacio provinces.

  6. The origin and age of the metamorphic sole from the Rogozna Mts., Western Vardar Belt: New evidence for the one-ocean model for the Balkan ophiolites

    NASA Astrophysics Data System (ADS)

    Borojević Šoštarić, S.; Palinkaš, A. L.; Neubauer, F.; Cvetković, V.; Bernroider, M.; Genser, J.

    2014-04-01

    This study brings new geochronological and petrochemical data from the metamorphic sole beneath the Rogozna Mts., Western Vardar ophiolite belt. The Rogozna metamorphic sole is located at the base of a serpentinite nappe and consists of amphibolites and talc-chlorite schists. The Rogozna amphibolites are medium- to fine-grained rocks with nematoblastic texture and pronounced foliation. They consist of green amphibole (~ 70 vol.%) with variable silica contents (6.4 to 7.8 Si apfu), as well as Mg# (molMg/[Mg + Fetot]; 0.53 to 0.77) and variably albitized plagioclase (~ 30 vol.%; Ab24-Ab98). Amphibolites are overprinted by a retrograde assemblage containing actinolite, epidote, clinoclore, sericite, chlorite, and magnetite. The amphibolites formed due to metamorphism of two basaltic suites: subalkaline/tholeiitic and alkaline. Subalkaline/tholeiitic amphibolites possess low Zr, Nb, Y, Th, Hf, TiO2, and P2O5 values and a LREE-depleted pattern, typical for the N-MORB (normal mid ocean ridge basalt) to BAB (back-arc basalt) origin. Alkaline amphibolites show elevated concentrations of Zr, Nb, Y, Th, Hf, TiO2, and P2O5 with a LREE-enriched pattern typically displayed by OIB (ocean island basalt). Amphibolites were crystallized during intra-oceanic thrusting at temperatures between 685 °C and 765 °C and at a depth of 12-17 km. 40Ar/39Ar cooling ages of amphibole, ranging from 165 to 170 Ma, slightly postdate the sole formation. Talc-chlorite schists are related to retrograde greenschist-facies metamorphism. They consist of Fe-rich talc and Cr-rich chlorite (peninite-diabantite) pseudomorphs after amphibole and MORB-type Cr-Al spinel, surrounded by Al- and Mg-poor ferrit chromite. The occurrence of ferrit chromite is related to earlier, amphibolite facies metamorphism. Chlorite pseudomorphs after amphibole were formed at 300-410 °C.

  7. Protolith and metamorphic ages of the Haiyangsuo Complex, eastern China: A non-UHP exotic tectonic slab in the Sulu ultrahigh-pressure terrane

    USGS Publications Warehouse

    Liou, J.G.; Tsujimori, T.; Chu, W.; Zhang, R.Y.; Wooden, J.L.

    2006-01-01

    The Haiyangsuo Complex in the NE Sulu ultrahigh-pressure (UHP) terrane has discontinuous, coastal exposures of Late Archean gneiss with amphibolitized granulite, amphibolite, Paleoproterozoic metagabbroic intrusives, and Cretaceous granitic dikes over an area of about 15 km2. The U-Pb SHRIMP dating of zircons indicates that theprotolith age of a garnet-biotite gneiss is >2500 Ma, whereas the granulite-facie metamorphism occurred at around 1800 Ma. A gabbroic intrusion was dated at ???1730 Ma, and the formation of amphibolite-facies assemblages in both metagabbro and granulite occurred at ???340-460 Ma. Petrologic and geochronological data indicate that these various rocks show no evidence of Triassic eclogite-facies metamorphism and Neoproterozoic protolith ages that are characteristics of Sulu-Dabie HP-UHP rocks, except Neoproterozoic inherited ages from post-collisional Jurassic granitic dikes. Haiyangsuo retrograde granulites with amphibolite-facies assemblages within the gneiss preserve relict garnet formed during granulite-facies metamorphism at ???1.85 Ga. The Paleoproterozoic metamorphic events are almost coeval with gabbroic intrusions. The granulite-bearing gneiss unit and gabbro-dominated unit of the Haiyangsuo Complex were intruded by thin granitic dikes at about 160 Ma, which is coeval with post-collisional granitic intrusions in the Sulu terrane. We suggest that the Haiyangsuo Complex may represent a fragment of the Jiao-Liao-Ji Paleoproterozoic terrane developed at the eastern margin of the Sino-Korean basement, which was juxtaposed with the Sulu terrane prior to Jurassic granitic activity and regional deformation. ?? Springer-Verlag 2006.

  8. The histories of ordinary chondrite parent bodies - U, Th-He age distributions

    SciTech Connect

    Wasson, J.T.; Wang, Sichao Purple Mountain Observatory, Nanjing )

    1991-06-01

    Age patterns observed in meteorite groups reflect the different thermal or impact histories experienced by their parent bodies. To assess the number of ordinary chondrite (OC) parent bodies, rare-gas data in the Schultz and Kruse (1989) data base were used to calculate U, Th-He gas-retention ages. Most H- and LL-chondrite ages are high; about 81 percent are greater than 2.2 Ga. In contrast, most L-chondrite ages are low; about 69 percent are not greater than 2.2 Ga, and about 35 percent are not greater than 0.9 Ga. The latter fraction is substantially lower than the value of 44 percent given by Heymann (1967). The difference is attributed to the preferential inclusion of shocked L chondrites in early studies. Broad age peaks in the H and LL groups near 3.4 Ga probably reflect thermal loss during metamorphism, but in the H distribution there is a hint of minor outgassing 'events' near 1 Ga. The L/LL chondrites have chemical properties intermediate between and unresolvable from L and LL chondrites. The high ages of most L/LL chondrites are evidence against these originating on the L parent body; the L/LL age distribution is consistent with an origin on the LL parent body or on an independent body. 22 refs.

  9. The histories of ordinary chondrite parent bodies - U, Th-He age distributions

    NASA Astrophysics Data System (ADS)

    Wasson, John T.; Wang, Sichao

    1991-06-01

    Age patterns observed in meteorite groups reflect the different thermal or impact histories experienced by their parent bodies. To assess the number of ordinary chondrite (OC) parent bodies, rare-gas data in the Schultz and Kruse (1989) data base were used to calculate U, Th-He gas-retention ages. Most H- and LL-chondrite ages are high; about 81 percent are greater than 2.2 Ga. In contrast, most L-chondrite ages are low; about 69 percent are not greater than 2.2 Ga, and about 35 percent are not greater than 0.9 Ga. The latter fraction is substantially lower than the value of 44 percent given by Heymann (1967). The difference is attributed to the preferential inclusion of shocked L chondrites in early studies. Broad age peaks in the H and LL groups near 3.4 Ga probably reflect thermal loss during metamorphism, but in the H distribution there is a hint of minor outgassing "events" near 1 Ga. The L/LL chondrites have chemical properties intermediate between and unresolvable from L and LL chondrites. The high ages of most L/LL chondrites are evidence against these originating on the L parent body; the L/LL age distribution is consistent with an origin on the LL parent body or on an independent body.

  10. Constraints on Age of India-Asia Collision and Pre-Collisional Subduction Metamorphism from the Sangsang Region, South Central Tibet

    NASA Astrophysics Data System (ADS)

    Borneman, N.; Hodges, K. V.; Van Soest, M. C.; Wartho, J. A.

    2014-12-01

    A common feature of continental collision zones is the entrainment of ophiolitic and subduction complex rock units. The crystallization and metamorphic ages of these units provide important constraints on both subduction zone evolution and the maximum age of ophiolite obduction. Ophiolites and subduction complexes have been well described in the Yarlung Tsangpo suture zone (YTSZ), but thus far relatively few high-pressure, low-temperature metamorphic assemblages from within the suture zone have been documented and successfully dated. Here we present structural, petrologic, and chronologic data from a recently discovered subduction complex occurrence of high-pressure (blueschist facies) rocks along the YTSZ in south central Tibet (29.31º N, 86.68º E). Mapping of the complex based on ASTER satellite image analysis as well as field work enabled the identification of four major lithostratigaphic units; from structurally highest to lowest, they are: 1) forarc affinity Chengdoi sandstones 2) a variably serpentinized ophiolitic fragment; 3) a structural mélange of blueschist-facies metabasic and metaclastic rocks; and 4) sandstones containing serpentinite and rutile detritus. The second and third of these tectonostratigraphic units are separated by thrust faults, whereas the Chengdoi sandstones unconformably overlie the ophiolitic fragment. We interpret the thrust separating the blueschists from the ophiolites as a paleo-subduction zone that dips northward when the entire section is rotated to restore the Chengdoi formation to horizontal. The subduction complex is further disrupted by oblique faults, including some with apparent normal sense offset that may be pre-collisional, intraoceanic normal faults. U/Pb zircon dating of the blueschist facies metavlocanic rocks implies a ca. 111 Ma protolith age, while a ca. 65 Ma 40Ar/39Ar amphibole date from one blueschist sample is interpreted as representing a close approximation of the timing of high-pressure metamorphism

  11. Thermal history of low metamorphic grade Paleoproterozoic sedimentary rocks of the Penokean orogen, Lake Superior region: Evidence for a widespread 1786 Ma overprint based on xenotime geochronology

    USGS Publications Warehouse

    Vallini, D.A.; Cannon, W.F.; Schulz, K.J.; McNaughton, N.J.

    2007-01-01

    Paleoproterozoic strata in northern Michigan, Wisconsin, and Minnesota were deposited between 2.3 and 1.75 Ga within the rifted margin and subsequent foreland basin of the Penokean orogen. These strata show evidence for multiple regional metamorphic events previously attributed entirely to the Penokean orogeny (1875-1835 Ma). Metasandstones from the Marquette Range Supergroup and the Animikie, Mille Lacs, and North Range Groups were sampled at multiple localities across Minnesota, Wisconsin and Michigan for metamorphic xenotime suitable for in situ SHRIMP U-Pb geochronology. All samples are from the northern Penokean foreland basin where the metamorphic grade is greenschist to sub-greenschist and the strata are virtually undeformed. Xenotime U-Pb ages in these samples have a bimodal population with means of 1786 ?? 4 Ma (n = 32) and 1861 ?? 10 Ma (n = 9). Xenotime of both ages are contained in metasandstones from the basal Chocolay Group in Michigan and Wisconsin and the Mille Lacs Group and North Range Groups in Minnesota. The older age records a regional low-temperature thermal event that is slightly older than the overlying Menominee Group in Michigan and the Animikie Group in Minnesota and Ontario. This 1861 Ma event coincides with regional uplift that led to the formation of the unconformity between the Menominee Group and the overlying Baraga Group in Michigan; hence xenotime growth must have occurred at shallow burial depths. Younger units from the Menominee and Baraga Groups in Michigan and the Animikie Group in Minnesota, record only the 1786 Ma event. A dominant 1800-1790 Ma metamorphic monazite population that overprints Penokean-interval monazite has been documented within amphibolite- to granulite-facies rocks immediately north of the Niagara Fault Zone within the vicinity of gneiss domes and granitic plutons. In contrast, the 1786 Ma xenotime ages are from low-grade, virtually undeformed rocks 50-150 km from the high-grade zones and thus do not appear

  12. The Pacific Age in World History.

    ERIC Educational Resources Information Center

    Korhonen, Pekka

    1996-01-01

    Tracks the intermittent appearances and variations of the historical concept of a "Pacific Age" from the 1890s to the present. Discusses the social, economic, and historical conditions that resulted in the term's heralding of either economic optimism or racist peril. Suggests these interpretations come in cycles. (MJP)

  13. History of the Calendar : In Different Countries Through the Ages

    NASA Astrophysics Data System (ADS)

    Saha, M. N.; Lahiri, N. C.

    This volume contains Part of the Report of the Calendar Reform Committee appointed by the Council of Scientific and Industrial Research (CSIR) on history of the Calendar in different countries through the Ages.

  14. Paleoproterozoic layered PGE-bearing Monchetundra pluton, Kola Peninsula: Sm-Nd age of metamorphic alteration of mafic rocks

    NASA Astrophysics Data System (ADS)

    Kunakkuzin, E. L.; Serov, P. A.; Bayanova, T. B.; Nerovich, L. I.; Borisenko, E. S.

    2015-09-01

    The aim of this work is Sm-Nd study of metamorphic alteration of massive gabbronorites from the Monchetundra pluton. The mafic rocks of the pluton are unevenly metamorphosed up to amphibolite facies with the formation of garnet, hornblende, and other minerals. The presence of garnet is a distinctive feature of this pluton in comparison with other Paleoproterozoic PGE-bearing plutons of the eastern part of the Baltic shield: Mt. General'skaya, Fedorovo-Pana, Imandra lopolith, and Monchepluton [9]. The degree of metamorphic alteration of rocks increases near the faults, the largest of which is Monchetundra fault separating the studied pluton from the Monchepluton. This fault was formed about 1.9-2.0 Ga ago according to Sm-Nd and Rb-Sr mineral isochrons for minerals from metagabbro-anorthosites of the M1 well.

  15. Late Cretaceous Localized Crustal Thickening as a Primary Control on the 3-D Architecture and Exhumation Histories of Cordilleran Metamorphic Core Complexes

    NASA Astrophysics Data System (ADS)

    Gans, P. B.; Wong, M.

    2014-12-01

    The juxtaposition of mylonitic mid-crustal rocks and faulted supracrustal rocks in metamorphic core complexes (MMCs) is usually portrayed in 2 dimensions and attributed to a single event of large-scale slip ± isostatic doming along a low-angle "detachment fault"/ shear zone. This paradigm does not explain dramatic along strike (3-D) variations in slip magnitude, footwall architecture, and burial / exhumation histories of most MMCs. A fundamental question posed by MMCs is how did their earlier thickening and exhumation histories influence the geometric evolution and 3-D slip distribution on the subsequent detachment faults? New geologic mapping and 40Ar/39Ar thermochronology from the Snake Range-Kern Mts-Deep Creek Mts (SKDC) complex in eastern Nevada offer important insights into this question. Crustal shortening and thickening by large-scale non-cylindrical recumbent folds and associated thrust faults during the late Cretaceous (90-80 Ma) resulted in deep burial (650°C, 20-25 km) of the central part of the footwall, but metamorphic grade decreases dramatically to the N and S in concert with decreasing amplitude on the shortening structures. Subsequent Paleogene extensional exhumation by normal faulting and ESE-directed mylonitic shearing is greatest in areas of maximum earlier thickening and brought highest grade rocks back to depths of~10-12 km. After ≥15 Ma of quiescence, rapid E-directed slip initiated along the brittle Miocene Snake Range detachment at 20 Ma and reactivated the Eocene shear zone. The ≥200°C gradient across the footwall at this time implies that the Miocene slip surface originated as a moderately E-dipping normal fault. This Miocene slip surface can be tracked for more than 100 km along strike, but the greatest amount of Miocene slip also coincides with parts of the footwall that were most deeply buried in the Cretaceous. These relations indicate that not only is the SKDC MMC a composite feature, but that the crustal welt created by

  16. Passive absolute age and temperature history sensor

    SciTech Connect

    Robinson, Alex; Vianco, Paul T.

    2015-11-10

    A passive sensor for historic age and temperature sensing, including a first member formed of a first material, the first material being either a metal or a semiconductor material and a second member formed of a second material, the second material being either a metal or a semiconductor material. A surface of the second member is in contact with a surface of the first member such that, over time, the second material of the second member diffuses into the first material of the first member. The rate of diffusion for the second material to diffuse into the first material depends on a temperature of the passive sensor. One of the electrical conductance, the electrical capacitance, the electrical inductance, the optical transmission, the optical reflectance, or the crystalline structure of the passive sensor depends on the amount of the second material that has diffused into the first member.

  17. Zircon ages of metamorphic and magmatic rocks within peridotite-bearing mélanges: Crucial time constraints on early Carboniferous extensional tectonics in the Chinese Tianshan

    NASA Astrophysics Data System (ADS)

    Jian, Ping; Kröner, Alfred; Jahn, Bor-ming; Liu, Dunyi; Zhang, Wei; Shi, Yuruo; Ma, Huadong

    2013-07-01

    We dated and geochemically characterized peridotite-bearing mélanges in the Chinese South Tianshan and within the Main Tianshan Shear Zone. The Yushugou-Tonghuashan mélange in the Chinese South Tianshan exposes a tectonic juxtaposition of a diapirically emplaced metaperidotite (predominantly lherzolite) massif with a high-grade metamorphic terrane (ca. 10 km long; protolith age ≥ ca. 445-466 Ma). Metamorphic zircons of a mafic granulite (εNd(t) = 5.0) yielded a weighted mean 206Pb/238U age of 341 ± 8 Ma that we interpret as the time of granulite-facies metamorphism. The youngest zircon rims of an intermediate granulite (εNd(t) = - 4.3) have a mean age of 332 ± 13 Ma that records a retrogressive metamorphic event. These ages determine the timing (ca. 341-332 Ma) of mantle diapirism through continental crust. A dolerite dike (εNd(t) = 2.3) emplaced into metaperidote has a crystallization age of 335 ± 5 Ma, that, on the basis of geochemistry, we interpret as representing E-MORB-OIB magmatism that accompanied mantle diapirism. An undeformed pink granite (εNd(t) = - 3.6) intrudes the mélange matrix and has an emplacement age of 324 ± 5 Ma, thus providing an upper time limit for a tectonic movement that led to mélange formation. The older time limit of deformation (ca. 362-352 Ma) is constrained by the youngest ages of thermo-tectonically modified zircons in a mylonitized metagabbro and a foliated meta-andesite. Magmatic zircons in the meta-andesite (εNd(t) = - 3.3) and a dacite (εNd(t) = - 5.6) have eruption ages of 433 ± 4 Ma and 435 ± 3 Ma that date formation of the mélange matrix. A microgabbro dike (εNd(t) = 10.0) cutting metasediments (i.e. mélange matrix) has an emplacement age of 279 ± 3 Ma and contains abundant zircon xenocrysts ranging in age from Archean to late Paleozoic. Similarly, a dolerite dike, a meta-andesite, an intermediate granulite, and a metagabbro all contain inherited Precambrian to Paleozoic zircons. We accordingly conclude

  18. The genetic history of Ice Age Europe.

    PubMed

    Fu, Qiaomei; Posth, Cosimo; Hajdinjak, Mateja; Petr, Martin; Mallick, Swapan; Fernandes, Daniel; Furtwängler, Anja; Haak, Wolfgang; Meyer, Matthias; Mittnik, Alissa; Nickel, Birgit; Peltzer, Alexander; Rohland, Nadin; Slon, Viviane; Talamo, Sahra; Lazaridis, Iosif; Lipson, Mark; Mathieson, Iain; Schiffels, Stephan; Skoglund, Pontus; Derevianko, Anatoly P; Drozdov, Nikolai; Slavinsky, Vyacheslav; Tsybankov, Alexander; Cremonesi, Renata Grifoni; Mallegni, Francesco; Gély, Bernard; Vacca, Eligio; Morales, Manuel R González; Straus, Lawrence G; Neugebauer-Maresch, Christine; Teschler-Nicola, Maria; Constantin, Silviu; Moldovan, Oana Teodora; Benazzi, Stefano; Peresani, Marco; Coppola, Donato; Lari, Martina; Ricci, Stefano; Ronchitelli, Annamaria; Valentin, Frédérique; Thevenet, Corinne; Wehrberger, Kurt; Grigorescu, Dan; Rougier, Hélène; Crevecoeur, Isabelle; Flas, Damien; Semal, Patrick; Mannino, Marcello A; Cupillard, Christophe; Bocherens, Hervé; Conard, Nicholas J; Harvati, Katerina; Moiseyev, Vyacheslav; Drucker, Dorothée G; Svoboda, Jiří; Richards, Michael P; Caramelli, David; Pinhasi, Ron; Kelso, Janet; Patterson, Nick; Krause, Johannes; Pääbo, Svante; Reich, David

    2016-05-01

    Modern humans arrived in Europe ~45,000 years ago, but little is known about their genetic composition before the start of farming ~8,500 years ago. Here we analyse genome-wide data from 51 Eurasians from ~45,000-7,000 years ago. Over this time, the proportion of Neanderthal DNA decreased from 3-6% to around 2%, consistent with natural selection against Neanderthal variants in modern humans. Whereas there is no evidence of the earliest modern humans in Europe contributing to the genetic composition of present-day Europeans, all individuals between ~37,000 and ~14,000 years ago descended from a single founder population which forms part of the ancestry of present-day Europeans. An ~35,000-year-old individual from northwest Europe represents an early branch of this founder population which was then displaced across a broad region, before reappearing in southwest Europe at the height of the last Ice Age ~19,000 years ago. During the major warming period after ~14,000 years ago, a genetic component related to present-day Near Easterners became widespread in Europe. These results document how population turnover and migration have been recurring themes of European prehistory.

  19. The genetic history of Ice Age Europe.

    PubMed

    Fu, Qiaomei; Posth, Cosimo; Hajdinjak, Mateja; Petr, Martin; Mallick, Swapan; Fernandes, Daniel; Furtwängler, Anja; Haak, Wolfgang; Meyer, Matthias; Mittnik, Alissa; Nickel, Birgit; Peltzer, Alexander; Rohland, Nadin; Slon, Viviane; Talamo, Sahra; Lazaridis, Iosif; Lipson, Mark; Mathieson, Iain; Schiffels, Stephan; Skoglund, Pontus; Derevianko, Anatoly P; Drozdov, Nikolai; Slavinsky, Vyacheslav; Tsybankov, Alexander; Cremonesi, Renata Grifoni; Mallegni, Francesco; Gély, Bernard; Vacca, Eligio; Morales, Manuel R González; Straus, Lawrence G; Neugebauer-Maresch, Christine; Teschler-Nicola, Maria; Constantin, Silviu; Moldovan, Oana Teodora; Benazzi, Stefano; Peresani, Marco; Coppola, Donato; Lari, Martina; Ricci, Stefano; Ronchitelli, Annamaria; Valentin, Frédérique; Thevenet, Corinne; Wehrberger, Kurt; Grigorescu, Dan; Rougier, Hélène; Crevecoeur, Isabelle; Flas, Damien; Semal, Patrick; Mannino, Marcello A; Cupillard, Christophe; Bocherens, Hervé; Conard, Nicholas J; Harvati, Katerina; Moiseyev, Vyacheslav; Drucker, Dorothée G; Svoboda, Jiří; Richards, Michael P; Caramelli, David; Pinhasi, Ron; Kelso, Janet; Patterson, Nick; Krause, Johannes; Pääbo, Svante; Reich, David

    2016-06-01

    Modern humans arrived in Europe ~45,000 years ago, but little is known about their genetic composition before the start of farming ~8,500 years ago. Here we analyse genome-wide data from 51 Eurasians from ~45,000-7,000 years ago. Over this time, the proportion of Neanderthal DNA decreased from 3-6% to around 2%, consistent with natural selection against Neanderthal variants in modern humans. Whereas there is no evidence of the earliest modern humans in Europe contributing to the genetic composition of present-day Europeans, all individuals between ~37,000 and ~14,000 years ago descended from a single founder population which forms part of the ancestry of present-day Europeans. An ~35,000-year-old individual from northwest Europe represents an early branch of this founder population which was then displaced across a broad region, before reappearing in southwest Europe at the height of the last Ice Age ~19,000 years ago. During the major warming period after ~14,000 years ago, a genetic component related to present-day Near Easterners became widespread in Europe. These results document how population turnover and migration have been recurring themes of European prehistory. PMID:27135931

  20. Re-Os ages for Archean molybdenite and pyrite, Kuittila-Kivisuo, Finland and Proterozoic molybdenite, Kabeliai, Lithuania: Testing the chronometer in a metamorphic and metasomatic setting

    USGS Publications Warehouse

    Stein, H.J.; Sundblad, K.; Markey, R.J.; Morgan, J.W.; Motuza, G.

    1998-01-01

    Seven 187Re-187Os ages were determined for molybdenite and pyrite samples from two well-dated Precambrian intrusions in Fennoscandia to examine the sustainability of the Re-Os chronometer in a metamorphic and metasomatic setting. Using a new 187Re decay constant (1.666 x 10-11y-1) with a much improved uncertainty (??0.31%), we determined replicate Re-Os ages for molybdenite and pyrite from the Kuittila and Kivisuo prospects in easternmost Finland and for molybdenite from the Kabeliai prospect in southernmost Lithuania. These two localities contain some of the oldest and youngest plutonic activity in Fennoscandia and are associated with newly discovered economic Au mineralization (Ilomantsi, Finland) and a Cu-Mo prospect (Kabeliai, Lithuania). Two Re-Os ages for veinhosted Kabeliai molybdenite average 1486 ?? 5 Ma, in excellent agreement with a 1505 ?? 11 Ma U-Pb zircon age for the hosting Kabeliai granite pluton. The slightly younger age suggests the introduction of Cu-Mo mineralization by a later phase of the Kabeliai magmatic system. Mean Re-Os ages of 2778 ?? 8 Ma and 2781 ?? 8 Ma for Kuittila and Kivisuo molybdenites, respectively, are in reasonable agreement with a 2753 ?? 5 Ma weighted mean U-Pb zircon age for hosting Kuittila tonalite. These Re-Os ages agree well with less precise ages of 2789 ?? 290 Ma for a Rb-Sr whole-rock isochron and 2771 ?? 75 Ma for the average of six Sm-Nd T(DM) model ages for Kuittila tonalite. Three Re-Os analyses of a single pyrite mineral separate, from the same sample of Kuittila pluton that yielded a molybdenite separate, provide individual model ages of 2710 ?? 27, 2777 ?? 28, and 2830 ?? 28 Ma (Re = 17.4, 12.1, and 8.4 ppb, respectively), with a mean value of 2770 ?? 120 Ma in agreement with the Kuittila molybdenite age. The Re and 187Os abundances in these three pyrite splits are highly correlated (r = 0.9994), and provide a 187Re-187Os isochron age of 2607 ?? 47 Ma with an intercept of 21 ppt 187Os (MSWD = 1.1). It appears

  1. Preliminary fission track ages for samples from western Maine: Implications for the low temperature thermal history of the region

    SciTech Connect

    Lux, D.R. . Dept. of Geological Sciences); Johnson, K. )

    1992-01-01

    In order to elucidate the low temperature cooling history of the region, 12 preliminary samples from a N-S traverse from the central Sebago batholith to the Chain of Ponds pluton were selected for fission track dating. The range of Ar-40/Ar-39 ages from the selected samples is 140 Ma (371--231 Ma) for biotites, 63 Ma (304--241 Ma) for muscovites and 61 Ma (375--304 Ma) for hornblendes. Twelve samples were dated by the external detector method and yield ages between 114 and 79 Ma. The southern most samples from the Sebago batholith and Songo pluton, within the highest metamorphic zones, are the youngest and range from 101 to 79 Ma. Those from the Mooselookmeguntic and Chain of Ponds plutons, within lower metamorphic zones, vary between 114 and 92 Ma. This general discordance trend is similar but of much smaller magnitude than the regional pattern of Ar-40/Ar-39 cooling ages. The much smaller range of apatite ages than biotite ages suggests that large differences in the thermal regime across of the region during Late Paleozoic time had largely been erased by the Early Cretaceous. The new fission track ages are interpreted to represent regional cooling through the apatite closure temperature, assumed to be ca 100 C. Young apatite ages may be the result of a regional thermal disturbance related to the intrusion of magmas of the White Mountains Plutonic Suite, as the youngest plutons are similar in age to the apatites. Alternatively, they could be the result of regional exhumation of the Acadian orogen. The authors conclude that the latter interpretation is more consistent with their data and attribute the ages to time of regional exhumation and uplift through the apatite closure temperature.

  2. Metamorphic belts of Anatolia

    NASA Astrophysics Data System (ADS)

    Oberhänsli, Roland; Prouteau, Amaury; Candan, Osman; Bousquet, Romain

    2015-04-01

    Investigating metamorphic rocks from high-pressure/low-temperature (HP/LT) belts that formed during the closure of several oceanic branches, building up the present Anatolia continental micro-plate gives insight to the palaeogeography of the Neotethys Ocean in Anatolia. Two coherent HP/LT metamorphic belts, the Tavşanlı Zone (distal Gondwana margin) and the Ören-Afyon-Bolkardağ Zone (proximal Gondwana margin), parallel their non-metamorphosed equivalent (the Tauride Carbonate Platform) from the Aegean coast in NW Anatolia to southern Central Anatolia. P-T conditions and timing of metamorphism in the Ören-Afyon-Bolkardağ Zone (>70?-65 Ma; 0.8-1.2 GPa/330-420°C) contrast those published for the overlying Tavşanlı Zone (88-78 Ma; 2.4 GPa/500 °C). These belts trace the southern Neotethys suture connecting the Vardar suture in the Hellenides to the Inner Tauride suture along the southern border of the Kirşehir Complex in Central Anatolia. Eastwards, these belts are capped by the Oligo-Miocene Sivas Basin. Another HP/LT metamorphic belt, in the Alanya and Bitlis regions, outlines the southern flank of the Tauride Carbonate Platform. In the Alanya Nappes, south of the Taurides, eclogites and blueschists yielded metamorphic ages around 82-80 Ma (zircon U-Pb and phengite Ar-Ar data). The Alanya-Bitlis HP belt testifies an additional suture not comparable to the northerly Tavşanlı and Ören-Afyon belts, thus implying an additional oceanic branch of the Neotethys. The most likely eastern lateral continuation of this HP belt is the Bitlis Massif, in SE Turkey. There, eclogites (1.9-2.4 GPa/480-540°C) occur within calc-arenitic meta-sediments and in gneisses of the metamorphic (Barrovian-type) basement. Zircon U-Pb ages revealed 84.4-82.4 Ma for peak metamorphism. Carpholite-bearing HP/LT metasediments representing the stratigraphic cover of the Bitlis Massif underwent 0.8-1.2 GPa/340-400°C at 79-74 Ma (Ar-Ar on white mica). These conditions compares to the Tav

  3. Rock relationships in the Mogok metamorphic belt, Tatkon to Mandalay, central Myanmar

    NASA Astrophysics Data System (ADS)

    Mitchell, A. H. G.; Htay, Myint Thein; Htun, Kyaw Min; Win, Myint Naing; Oo, Thura; Hlaing, Tin

    2007-03-01

    The Mogok metamorphic belt (MMB), over 1450 km long and up to 40 km wide, consists of regionally metamorphosed rocks including kyanite and sillimanite schists and granites lying along the Western margin of the Shan Plateau in central Myanmar and continuing northwards to the eastern Himalayan syntaxis. Exposures in quarries allow correlation of Palaeozoic meta-sedimentary, early Mesozoic meta-igneous and late Mesozoic intrusive rocks within a 230 km long northerly-trending segment of the MMB, from Tatkon to Kyanigan north of Mandalay, and with the Mogok gemstone district 100 km to the northeast. Relationships among the metamorphic and intrusive rocks, with sparse published radiometric age controls, indicate at least two metamorphic events, one before and one after the intrusion of Late Jurassic to early Cretaceous calc-alkaline rocks. These relationships can be explained by either of two possible tectonic histories. One, constrained by correlation of mid-Permian limestones across Myanmar, requires early Permian and early Jurassic regional metamorphic events, prior to an early Tertiary metamorphism, in the western part of but within a Shan-Thai - western Myanmar block. The second, not compatible with a single laterally continuous Permian limestone, requires pre-Upper Jurassic regional metamorphism and orogenic gold mineralization in the Mergui Group and western Myanmar, early Cretaceous collision of an east-facing Mergui-western Myanmar island arc with the Shan Plateau, and early Tertiary metamorphism in the MMB related to reversal in tectonic polarity following the arc-Plateau collision.

  4. The Inextricable Link between Age and Criminal History in Sentencing

    ERIC Educational Resources Information Center

    Bushway, Shawn D.; Piehl, Anne Morrison

    2007-01-01

    In sentencing research, significant negative coefficients on age research have been interpreted as evidence that actors in the criminal justice system discriminate against younger people. This interpretation is incomplete. Criminal sentencing laws generally specify punishment in terms of the number of past events in a defendant's criminal history.…

  5. Integrating field, microstructures, magnetic fabrics, metamorphic studies to establish Yavapai-Mazatazal-aged syntectonic pluton emplacement and strain localization in the Tusas Mountains, New Mexico

    NASA Astrophysics Data System (ADS)

    Davis, P.; Kruckenberg, S. C.

    2012-12-01

    Paleoproterozoic metamorphic rocks in the northern Tusas Mountains of New Mexico record the conditions of deposition, deformation and tectonic processes during assembly and stabilization of these rocks to the southern margin of the Laurentian craton. Metasedimentary and metavolcanic supracrustal rocks of the Vadito and Hondo groups comprise the majority of exposures, detrital zircon from within these units constrain the age of deposition ca. 1.70 Ga. - the Yavapai-Mazatazal temporal orogenic boundary. P-T conditions are ~425-600 C and 4-6 kbars. Two pervasive fold and fabric events are regionally displayed that have been locally modified by a third deformation event. Regional constraints on tectonism timing are mixed, with recent work showing that tectonism occurred ca. 1.4 Ga. Two orthogneiss bodies, the Tres Piedras (TP) and Tusas Mountain (TM) granites, were emplaced into supracrustal host rocks at ca. 1.69 Ga. Several datasets that include mapping and characterization of metamorphic assemblages, EBSD microstructural analysis, and anisotropy of magnetic susceptibility analyses suggest that emplacement was syntectonic. Metamorphic assemblages show a field-gradient that is roughly concentric to the TP and TM plutons from greenschist facies (ca. 400-425 C) in the distant country rock, to upper amphibolite facies (ca. 650 C) near the pluton contacts. This is a new discovery for the region, as most of northern New Mexico displays a regional amphibolite facies signature. Quartz and feldspar microstructures suggest that the body of both plutons record non-coaxial deformation from near solidus to high-T conditions (>600 C). Muscovite inclusions in cm-scale euhedral microcline grains are aligned with S1, and isoclinal folds in the TP lack an axial planar fabric. Measurement of the anisotropy of magnetic susceptibility (AMS) suggest that the orientation of magmatic fabrics within these plutons are consistent with principal regional fabrics (D1) recorded in the

  6. Constraints on the metamorphic history of a mélange complex within the easternmost Himalayan orogen, northern Indo-Burma Range, based on P-T pseudosection and thermobarometric studies.

    NASA Astrophysics Data System (ADS)

    Haproff, P. J.; Yin, A.

    2015-12-01

    Despite many petrologic and structural studies surrounding the eastern Himalayan syntaxis, P-T histories of metamorphic rocks within the northern Indo-Burman mélange of the easternmost Himalayas remain largely unknown. We present metamorphic P-T conditions of three schists from successive thrust sheets related to generation of the Himalayan orogen, based on mineral assemblage thermobarometry and pseudosection phase diagrams. Use of the garnet-muscovite-biotite-plagioclase thermobarometer and Ti-in-biotite thermometer yield peak conditions of 676 ± 78°C and 10.6 ± 1.3 kbar for schist (PH-1-8-13-26) thrust atop metavolcanics, mafic schist, and ultramafics of the Indus-Ysangpo suture zone (IYSZ). Within this sample, quartz is recrystallized along grain boundaries and garnets contain no significant compositional zoning. Pseudosections constructed from bulk-rock composition and equilibrium mineral assemblages yield a clockwise P-T path with similar peak garnet amphibolite conditions. At structurally lower levels, garnet chlorite schist (PH-1-8-13-8) from a thrust klippe of the IYSZ record peak temperatures below 650°C. Garnets display growth zoning, with increasing Mn and decreasing Fe and Mg from rim to core. Application of the Ti-in-biotite thermometer to a mafic schist (PH-1-3-13-1B) within the klippe near a southwestward-directed thrust yields a peak temperature of 679 ± 24°C. Our study reveals a complex metamorphic history throughout the northern Indo-Burman mélange zone that likely records metamorphism at deep crustal levels during thrust motion and growth of the Himalayan orogen around the northeastern corner of India.

  7. Distinguishing among major controls on the apparent thermal and barometric structure of metamorphic belts

    SciTech Connect

    Day, H.W.

    1985-01-01

    The apparent thermal and barometric structures of metamorphosed terrains are expressed in the map patterns of isograds and bathograds. Geographic variation in the apparent P,T of peak metamorphism may be the result of: (1) differences in the amount of tectonic thickening (2) variation in the thermal properties of the lithosphere or (3) differential uplift across the mountain belt. Oversimplified tectonic models of a burial and uplift event, combined with simple physical models for the conductive transfer of heat, have normally been used. The results suggest that the relative roles of the three large scale controls on metamorphism may be distinguished. In mountain belts having variable tectonic thickening, apparent isotherms and isobars of peak metamorphism are parallel. Geographic variation in either thermal properties or uplift history, by contrast, leads to patterns of intersecting apparent isobars and isotherms (e.g.. the New England Appalachians). In terrains that experienced rapid and differential uplift, the most rapidly uplifted portions show the shortest cooling times, the least discordance between apparent mineral ages, and the lowest pressures at peak metamorphism and no necessary correlation between metamorphic grade and cooling time (e.g.. the Alps). In contrast, in terrains with large variations in either thermal parameters or tectonic thickening, long cooling times are directly associated with the highest metamorphic temperatures and the least discordance between apparent mineral ages (e.g.. the Scottish Highlands).

  8. Thermal metamorphism of mantle chromites and the stability of noble-metal nanoparticles

    NASA Astrophysics Data System (ADS)

    González-Jiménez, José M.; Reich, Martin; Camprubí, Antoni; Gervilla, Fernando; Griffin, William L.; Colás, Vanessa; O'Reilly, Suzanne Y.; Proenza, Joaquín A.; Pearson, Norman J.; Centeno-García, Elena

    2015-08-01

    The Loma Baya complex in south-western Mexico is a volume of chromitite-bearing oceanic mantle that records a complex metamorphic history, defined by a first stage of hydrous metamorphism overprinted by a short-lived thermal event associated with an Eocene granite intrusion. During the hydrous metamorphism, the primary magmatic chromite-olivine assemblage was replaced by a secondary, porous intergrowth of Fe2+-rich chromite and chlorite. The heat supplied by an Eocene-age granite intrusion reversed the hydration reaction, producing chromite rims with perfectly developed crystal faces. This third-generation chromite is in equilibrium with highly magnesian (neoformed) olivine and defines a chemical trend analogous to the original magmatic one. The preservation of both reactions in the Loma Baya chromitite provides compelling evidence that the hydration of chromite can be reversed by either prograde metamorphism or any heating event, confirming previous thermodynamic predictions. Understanding these complex features is of particular interest due to the fact that changes in temperature and variable degrees of fluid/rock interaction during metamorphism and intrusion have also significantly affected the chromite-hosted IPGE carrier phases. Here, we propose that the metamorphic fluids involved in the hydrous metamorphism have caused the desulphurization of laurite RuS2, releasing minute particles of Ru-Os-Ir alloys <50 nm in diameter. The following short-lived thermal event that promoted dehydration in the chromitite had the opposite effect on nanoparticle stability, producing a significant coarsening of metal nanoparticles to dimensions larger than a micron. Based on such observations, we argue that IPGE nanoparticles can be exsolved and grown (or coarsen) from sulphide matrices during prograde metamorphism or heating and not exclusively upon cooling under magmatic conditions as it has been previously suggested. These results provide new insights on the relevant role of

  9. History of the Pasamonte achondrite: Relative susceptibility of the SmNd, RbSr, and UPb systems to metamorphic events

    USGS Publications Warehouse

    Unruh, D.M.; Nakamura, N.; Tatsumoto, M.

    1977-01-01

    The RbSr, SmNd, and UPb systematics of the eucrite Pasamonte have been studied in order to investigate the relative susceptibility of the different systems to post-crystallization events and to determine the age and history of the meteorite. The RbSr and 238U-206Pb data of mineral separates do not define an isochron but the SmNd data define an internal isochron which corresponds to the formation age of 4.58 ?? 0.12 b.y. (109 years). The 207Pb-206Pb data of mineral separates define an apparent age of 4.53 ?? 0.03 b.y., however we conclude that this age, while in agreement with the SmNd age, is not strictly valid since the UPb data indicate at least three stages of evolution. The UPb data indicate that the parent body of the meteorite experienced brecciation shortly after the formation of the parent body surface (???4.2-4.45 b.y. ago) and a recent disturbance (collision?) 6 ?? 30 m.y. ago. The latter age is within the range of cosmic ray exposure ages for achondrites. ?? 1977.

  10. Magmatic and metamorphic belts and plutonic-metamorphic complexes of southeastern Alaska

    SciTech Connect

    Brew, D.A.; Himmelberg, G.R.; Ford, A.B.; Loney, R.A. . Branch of Alaskan Geology Univ. of Missouri, Columbia, MO . Dept. of Geology)

    1993-04-01

    The Cordilleran orogen in southeastern Alaska includes 24 distinct magmatic belts, ranging in age from Cambrian to Holocene, that are defined by map relations, lithology, age, and chemical composition. The youngest magmatic features are Quaternary-age pre- and post-glacial volcanic rocks that occur in three major fields in the region, as well as in isolated locations. Cenozoic magmatic features consist of four major and three minor belts. The major Tkope-Portland Peninsula belt of Oligocene age includes both volcanic and plutonic rocks. The major calcalkalic Coast Mountains belt of early and middle Eocene age is the single largest magmatic feature of the region. Early Tertiary and latest Cretaceous magmatism is represented by the major calcalkalic great tonalite sill belt, a remarkable long and narrow feature along the west side of the Coast Mountains. Cretaceous and Jurassic intrusive rocks occur in five major belts and two minor belts in the region and Paleozoic intrusive rocks occur in four major and two minor belts. The three major plutonic-metamorphic complexes (PMC), from east to west, are: the Coast PMC in the Coast Mountains; the Glacier Bay-Chichag of plutonic complex (Chugach MC) in the northern outer islands. The Coast PMC records dynamothermal and regional contact metamorphic events related to regional plutonism within several juxtaposed terranes; its lengthy and complicated history is related to the Late Cretaceous collision of the Alexander and Wrangellia terranes and the Gravina overlap assemblage to the west against the Yukon prong and Stikine terrane to the east. The relatively simple Glacier Bay PC history is recorded as the roots of a Late Jurassic through late Early Cretaceous island arc that probably developed during the early stages of the above tectonic event. The complicated Chugach MC history developed during and after the Late Cretaceous collision of the Chugach terrane with the Wrangellia and Alexander terranes.

  11. SHRIMP U-Pb age and high temperature conditions of the collisional metamorphism in the Várzea do Capivarita Complex: Implications for the origin of Pelotas Batholith, Dom Feliciano Belt, southern Brazil

    NASA Astrophysics Data System (ADS)

    Philipp, Ruy Paulo; Bom, Francisco Molina; Pimentel, Márcio Martins; Junges, Sérgio Luiz; Zvirtes, Gustavo

    2016-03-01

    The Várzea do Capivarita Complex is composed of pelitic gneisses with subordinate calc-silicate rock, marble and rare quartzite. It is part of the neoproterozoic Dom Feliciano Belt, in southern Brazil. The gneisses are associated to veins and tabular leucogranite bodies, which are the product of anatexis of the pelitic gneiss. The paragneisses of the Várzea do Capivarita Complex are tectonically juxtaposed to orthogneisses of the Arroio dos Ratos Complex. This complex is exposed as megaxenoliths in granites of the Encruzilhada do Sul Suite and as smaller fragments in the Quitéria and Cordilheira Granites, all part of the Pelotas Batholith. The metamorphic foliation is oriented to N30°W, with dips between 35 and 55° to the SW and mineral lineation is suborizontal with rake ranging from 15° to 30° and down dip to NW and SE, suggesting deformation associated with a transpressive system. Based on the paragenesis garnet-cordierite-sillimanite-biotite, metamorphism occurred at 720-820° C and pressure of 8-9 kbar, characterizing it as of intermediate pressure and high temperature series. Zircon grains of one sample of garnet-cordierite-sillimanite-biotite gneiss and one of peraluminous leucogranite was dated by the U-Pb SHRIMP method. The paragneiss metamorphic zircon yielded an age of 619 ± 4.3 Ma interpreted as an age of the main metamorphic event, whereas igneous zircon grains from the leucogranite indicates that magma crystallization took place at 620 ± 6.3 Ma. The main metamorphic foliation (S2) of the paragneiss and the leucogranite magmatic foliation (S0) are parallel to each other, indicating that they were formed during the same event. This suggests that anatexis of the paragneisses of the Várzea do Capivarite Complex generated the peraluminous leucogranites right after the climax of the collisional metamorphism.

  12. Rare Earth Element Abundances and Pb-Pb Ages of Merrillite in Jinju H5 Chondrite: Implications to Shock Metamorphism

    NASA Astrophysics Data System (ADS)

    Goh, S.; Choi, B.-G.

    2016-08-01

    Jinju merrillite shows homogeneous REE abundances and relatively young Pb-Pb ages. Jinju H5 chondrite was probably neither equilibrated nor compacted prior to the impact and the shock made trace elements including REEs and U-Pb equilibrated.

  13. Ar-39-Ar-40 Ages of Euerites and the Thermal History of Asteroid 4-Vesta

    NASA Technical Reports Server (NTRS)

    Bogard, Donald D.; Garrison, Daniel H.

    2002-01-01

    Eucrite meteorites are igneous rocks that derive from a large asteroid, probably 4 Vesta. Prior studies have shown that after eucrites formed, most were subsequently metamorphosed to temperatures up to equal to or greater than 800 C, and much later many were brecciated and heated by large impacts into the parent body surface. The uncommon basaltic, unbrecciated eucrites also formed near the surface but presumably escaped later brecciation, whereas the cumulate eucrites formed at depth where metamorphism may have persisted for a considerable period. To further understand the complex HED parent body thermal history, we determined new Ar-39-Ar-40 ages for nine eucrites classified as basaltic but unbrecciated, six eucrites classified as cumulate, and several basaltic-brecciated eucrites. Relatively precise Ar-Ar ages of two cumulate eucrites (Moama and EET87520) and four unbrecciated eucrites give a tight cluster at 4.48 +/1 0.01 Gyr. Ar-Ar ages of six additional unbrecciated eucrites are consistent with this age, within their larger age uncertainties. In contrast, available literature data on Pb-Pb isochron ages of four cumulate eucrites and one unbrecciated eucrite vary over 4.4-4.515 Gyr, and Sm-147 - Nd-143 isochron ages of four cumulate and three unbrecciated eucrites vary over 4.41-4.55 Gyr. Similar Ar-Ar ages for cumulate and unbrecciated eucrites imply that cumulate eucrites do not have a younger formation age than basaltic eucrites, as previously proposed. Rather, we suggest that these cumulate and unbrecciated eucrites resided at depth where parent body temperatures were sufficiently high to cause the K-Ar and some other chronometers to remain open diffusion systems. From the strong clustering of Ar-Ar ages at approximately 4.48 Gyr, we propose that these meteorites were excavated from depth in a single large impact event approximately 4.48 Gyr ago, which quickly cooled the samples and started the K-Ar chronometer. A large (approximately 460 km) crater

  14. Ar-Ar ages and thermal histories of enstatite meteorites

    NASA Astrophysics Data System (ADS)

    Bogard, Donald D.; Dixon, Eleanor T.; Garrison, Daniel H.

    2010-05-01

    Compared with ordinary chondrites, there is a relative paucity of chronological and other data to define the early thermal histories of enstatite parent bodies. In this study, we report 39Ar-40Ar dating results for five EL chondrites: Khairpur, Pillistfer, Hvittis, Blithfield, and Forrest; five EH chondrites: Parsa, Saint Marks, Indarch, Bethune, and Reckling Peak 80259; three igneous-textured enstatite meteorites that represent impact melts on enstatite chondrite parent bodies: Zaklodzie, Queen Alexandra Range 97348, and Queen Alexandra Range 97289; and three aubrites, Norton County, Bishopville, and Cumberland Falls Several Ar-Ar age spectra show unusual 39Ar recoil effects, possibly the result of some of the K residing in unusual sulfide minerals, such as djerfisherite and rodderite, and other age spectra show 40Ar diffusion loss. Few additional Ar-Ar ages for enstatite meteorites are available in the literature. When all available Ar-Ar data on enstatite meteorites are considered, preferred ages of nine chondrites and one aubrite show a range of 4.50-4.54Ga, whereas five other meteorites show only lower age limits over 4.35-4.46Ga. Ar-Ar ages of several enstatite chondrites are as old or older as the oldest Ar-Ar ages of ordinary chondrites, which suggests that enstatite chondrites may have derived from somewhat smaller parent bodies, or were metamorphosed to lower temperatures compared to other chondrite types. Many enstatite meteorites are brecciated and/or shocked, and some of the younger Ar-Ar ages may record these impact events. Although impact heating of ordinary chondrites within the last 1Ga is relatively common for ordinary chondrites, only Bethune gives any significant evidence for such a young event.

  15. Ar-Ar and I-Xe Ages and the Thermal History of IAB Meteorites

    NASA Technical Reports Server (NTRS)

    Bogard, Donald D.; Garrison, Daniel H.; Takeda, Hiroshi

    2004-01-01

    Studies of several samples of the large Caddo County IAB iron meteorite reveal andesitic material, enriched in Si, Na, Al and Ca, which is essentially unique among meteorites. This material is believed to have formed from a chondritic source by partial melting and to have further segregated by grain coarsening. Such an origin implies extended metamorphism of the IAB parent body. New Ar-39-Ar-40 ages for silicate from three different Caddo samples are consistent with a common age of 4.50-4.51 Gyr ago. Less well defined Ar-Ar degassing ages for inclusions from two other IABs, EET8333 and Udei Station, are approx.4.32 Gyr, whereas the age for Campo del Cielo varies considerably over approx.3.23-4.56 Gyr. New I-129-Xe-129 ages for Caddo County and EET8333 are 4561.9+/-0.1 Myr and 4560- 4563 Myr, respectively, relative to an age of 4566 Myr for Shallowater. Considering all reported Ar-Ar ages for IABs and related winonaites, the range is approx.4.32-4.53 Gyr, but several IABs give similar Ar ages of 4.50-4.52 Gyr. We interpret these older ages to represent cooling after the time of last significant metamorphism on the parent body, and the younger ages to represent later Ar-40 diffusion loss. These older Ar-Ar ages are similar to Sm-Nd and Rb-Sr isochron ages reported in the literature for Caddo County. Considering the possibility that IAB parent body formation was followed by impact disruption, reassembly, and metamorphism (e.g., Benedix et al. 2000), the time of the post-assembly metamorphism may have been as late as approx.4.53 Gyr ago. However, precise I-Xe ages reported for some IABs define a range of ages of approx.4560 to approx.4576 Myr. The older I-Xe ages exceed the oldest precise radiometric ages of meteorites, appear unrealistic, and s,uggest a bias in the calibration of all I-Xe ages. But even with such a bias, the I-Xe ages of IABs cannot easily be reconciled with the much younger Ar-Ar and Sm-Nd ages and with cooling rates deduced from Ni concentration

  16. Ar-Ar and I-Xe Ages and the Thermal History of IAB Meteorites

    NASA Technical Reports Server (NTRS)

    Bogard, Donald D.; Garrison, Daniel H.; Takeda, Hiroshi

    2004-01-01

    Studies of several samples of the large Caddo County IAB iron meteorite reveal andesitic material, enriched in Si, Nay Al and Ca, which is essentially unique among meteorites. This material is believed to have formed from a chondritic source by partial melting and to have further segregated by grain coarsening. Such an origin implies extended metamorphism of the IAB parent body. New Ar-39-Ar-40 ages for silicate from three different Caddo samples are consistent with a common age of 4.50- 4.51 Gyr ago. Less well defined Ar-Ar degassing ages for inclusions from two other IABs, EET8333 and Udei Station, are approx.4.32 Gyr, whereas the age for Campo del Cielo varies considerably over approx.3.23-4.56 Gyr. New I-129-Xe-129 ages for Caddo County and EET8333 are 4561.9 +/-0.1 Myr and 4560-4563 Myr, respectively, relative to an age of 4566 Myr for Shallowater. Considering all reported Ar-Ar ages for IABs and related winonaites, the range is approx.4.32-4.53 Gyr, but several IABs give similar Ar ages of 4.50-4.52 Gyr. We interpret these older ages to represent cooling after the time of last significant metamorphism on the parent body, and the younger ages to represent later Ar-40 diffusion loss. These older Ar-Ar ages are similar to Sm-Nd and Rb-Sr isochron ages reported in the literature for Caddo County. Considering the possibility that IAB parent body formation was followed by impact disruption, reassembly, and metamorphism (e.g., Benedix et al. 2000), the time of the post-assembly metamorphism may have been as late as approx.4.53 Gyr ago. However, precise I-Xe ages reported for some IABs define a range of ages of approx.4560 to approx.4576 My. The older I-Xe ages exceed the oldest precise radiometric ages of meteorites, appear unrealistic, and suggest a bias in the calibration of all I-Xe ages. But even with such a bias, the I-Xe ages of IABs cannot easily be reconciled with the much younger Ar-Ar and Sm-Nd ages and with cooling rates deduced from Ni concentration

  17. Ar-Ar and I-Xe Ages and the Thermal History of IAB Meteorites

    NASA Technical Reports Server (NTRS)

    Bogard, Donald D.; Garrison, Daniel H.; Takeda, Hiroshi

    2005-01-01

    Studies of several samples of the large Caddo County IAB iron meteorite reveal andesitic material, enriched in Si, Na, Al and Ca, which is essentially unique among meteorites. This material is believed to have formed from a chondritic source by partial melting and to have further segregated by grain coarsening. Such an origin implies extended metamorphism of the IAB parent body. New Ar-39- Ar-40 ages for silicate from three different Caddo samples are consistent with a common age of 4.50-4.51 Gyr ago. Less well defined Ar-Ar degassing ages for inclusions from two other IABs, EET8333 and Udei Station, are approx.4.32 Gyr, whereas the age for Campo del Cielo varies considerably over approx.3.23-4.56 Gyr. New I-129-Xe-129 ages for Caddo County and EET8333 are 4557.9+/-0.1 Myr and 4557-4560 Myr, respectively, relative to an age of 4562.3 Myr for Shallowater. Considering all reported Ar-Ar degassing ages for IABs and related winonaites, the range is approx.4.32-4.53 Gyr, but several IABs give similar Ar ages of 4.50-4.52 Gyr. We interpret these older Ar ages to represent cooling after the time of last significant metamorphism on the parent body, and the younger ages to represent later 40Ar diffusion loss. The older Ar-Ar ages for IABs are similar to Sm-Nd and Rb-Sr isochron ages reported in the literature for Caddo County. Considering the possibility that IAB parent body formation was followed by impact disruption, reassembly, and metamorphism (e.g., Benedix et al. 2000), the Ar-Ar ages and IAB cooling rates deduced from Ni concentration profiles in IAB metal (Herpfer et al., 1994) are consistent if the time of the post-assembly metamorphism was as late as approx.4.53 Gyr ago. However, I-Xe ages reported for some IABs define much older ages of approx.4558-4566 Myr, which cannot easily be reconciled with the much younger Ar-Ar and Sm-Nd ages. An explanation for the difference in radiometric ages of IABs may reside in combinations of the following: a) I-Xe ages have very

  18. Ar-Ar and I-XE Ages and the Thermal History of IAB Meteorites

    NASA Technical Reports Server (NTRS)

    Bogard, Donald D.; Garrison, Daniel H.; Takeda, Hiroshi

    2006-01-01

    Studies of several samples of the large Caddo County IAB iron meteorite reveal andesitic material, enriched in Si, Na, Al and Ca which is essentially unique among meteorites. This material is believed to have formed from a chondritic source by partial melting and to have further segregated by grain coarsening. Such an origin implies extended metamorphism of the IAB parent body. New Ar-39- Ar-40 ages for silicate from three different Caddo samples are consistent with a common age of 4.50- 4.51 Gyr ago. Less well defined Ar-Ar degassing ages for inclusions from two other IABs, EET8333 and Udei Station, are approx. 4.32 Gyr, whereas the age for Campo del Cielo varies considerably over approx. 3.23-4.56 Gyr. New I-129-Xe-129 ges for Caddo County and EET8333 are 4561.9 plus or minus 0.1 Myr and 4560-4563 Myr, respectively, relative to an age of 4566 Myr for Shallowater. Considering all reported Ar-Ar ages for IABs and related winonaites, the range is approx. 4.32-4.53 Gyr, but several IABs give similar Ar ages of 4.50-4.52 Gyr. We interpret these older ages to represent cooling after the time of last significant metamorphism on the parent body, and the younger ages to represent later 40Ar diffusion loss. These older Ar-Ar ages are similar to Sm-Nd and Rb-Sr isochron ages reported in the literature for Caddo County. Considering the possibility that IAB parent body formation was followed by impact disruption, reassembly, and metamorphism (e.g., Benedix et al. 2000), the time of the postassembly metamorphism may have been as late as approx. 4.53 Gyr ago. However, precise I-Xe ages reported for some IABs define a range of ages of approx. 4560 to approx. 4576 Myr. The older I-Xe ages exceed the oldest precise radiometric ages of meteorites, appear unrealistic, and suggest a bias in the calibration of all I-Xe ages. But even with such a bias, the I-Xe ages of IABs cannot easily be reconciled with the much younger Ar-Ar and Sm-Nd ages and with cooling rates deduced from Ni

  19. Timing and duration of garnet granulite metamorphism in magmatic arc crust, Fiordland, New Zealand

    USGS Publications Warehouse

    Stowell, H.; Tulloch, A.; Zuluaga, C.; Koenig, A.

    2010-01-01

    Pembroke Granulite from Fiordland, New Zealand provides a window into the mid- to lower crust of magmatic arcs. Garnet Sm-Nd and zircon U-Pb ages constrain the timing and duration of high-P partial melting that produced trondhjemitic high Sr/Y magma. Trace element zoning in large, euhedral garnet is compatible with little post growth modification and supports the interpretation that garnet Sm-Nd ages of 126.1??2.0 and 122.6??2.0. Ma date crystal growth. Integration of the garnet ages with U-Pb zircon ages elucidates a history of intrusion(?) and a protracted period of high-temperature metamorphism and partial melting. The oldest zircon ages of 163 to 150. Ma reflect inheritance or intrusion and a cluster of zircon ages ca. 134. Ma date orthopyroxene-bearing mineral assemblages that may be magmatic or metamorphic in origin. Zircon and garnet ages from unmelted gneiss and garnet reaction zones record garnet granulite facies metamorphism at 128 to 126. Ma. Peritectic garnet and additional zircon ages from trondhjemite veins and garnet reaction zones indicate that garnet growth and partial melting lasted until ca. 123. Ma. Two single fraction garnet ages and young zircon ages suggest continued high-temperature re-equilibration until ca. 95. Ma. Phase diagram sections constrain orthopyroxene assemblages to <0.6 GPa @ 650??C, peak garnet granulite facies metamorphic conditions to 680-815??C @ 1.1-1.4. GPa, and a P-T path with a P increase of???0.5. GPa. These sections are compatible with water contents???0.28wt.%, local dehydration during garnet granulite metamorphism, and <0.3. GPa P increases during garnet growth. Results demonstrate the utility of integrated U-Pb zircon and Sm-Nd garnet ages, and phase diagram sections for understanding the nature, duration, and conditions of deep crustal metamorphism and melting. Geochronologic and thermobarometric data for garnet granulite indicate that thickening of arc crust, which caused high-pressure metamorphism in northern

  20. Zircon U-Pb ages, Hf isotope data, and tectonic implications of Early-Middle Triassic granitoids in the Ailaoshan high-grade metamorphic belt of Southeast Tibet

    NASA Astrophysics Data System (ADS)

    Wu, Wenbin; Liu, Junlai; Chen, Xiaoyu; Zhang, Lisheng

    2016-05-01

    The Ailaoshan tectonic belt, where the effects of the Paleo-Tethyan ocean evolution and Indian-Eurasian plate collision are superimposed, is one of the most significant geological discontinuities in western Yunnan province of southeast Tibet. An Ailaoshan micro-block within the belt is bounded by the Ailaoshan suture zone to the west and the Red River Fault to the east, and consists of low- and high-grade metamorphic belts. Late Permian-Middle Triassic granitoids that are widely distributed to the west of the Ailaoshan suture zone and within the Ailaoshan micro-block may yield significant information on the Tethyan tectonic evolution of the Ailaoshan tectonic belt. This study reports new LA-ICP-MS zircon U-Pb geochronology and Hf isotope data of four granitoids from the Ailaoshan high-grade metamorphic belt. Zircon grains from the Yinjie granitoid do not have inherited cores and yield a weighted mean U-Pb age of 247.1 ± 2.0 Ma. The zircon ɛ Hf(t) values range from 7.8 to 12.1, and Hf model ages from 775 to 546 Ma, indicating that the granitoid was derived from juvenile crust. The rims of zircons from the Majie and Yuanjiang granitoids yield weighted mean U-Pb ages of 239.5 ± 1.8 and 237.9 ± 2.6 Ma, respectively, whereas the cores yield ages of 1608-352 Ma. The ɛ Hf(t) values of zircon rims range from -20.4 to -5.3, yielding Hf model ages from 2557 to 1606 Ma and suggesting that the source magma of the Majie and Yuanjiang granitoids was derived from ancient crust. An additional granitoid located near the Majie Village yields a zircon U-Pb age of 241.2 ± 1.0 Ma. Based on our geochronological and geochemical data, combined with geological observations, we propose that the Ailaoshan micro-block was derived from the western margin of the Yangtze block, and is comparable to the Zhongzan and Nam Co micro-blocks. The presence of late Permian mafic rocks with rift-related geochemical characteristics within the Ailaoshan micro-block, together with granitoids derived

  1. Acting Out History from the Ice Age to the Modern Age.

    ERIC Educational Resources Information Center

    Mattioli, Denee J.; Drake, Frederick

    1999-01-01

    Addresses the teaching methods of Michael Welch, a seventh grade teacher, who incorporates the humanities, such as drama and literature, into his history classroom in order to help students learn to question, think analytically, solve problems, and make decisions. Summarizes a particular unit on the Ice Age. (CMK)

  2. LIFE HISTORY. Age-related mortality explains life history strategies of tropical and temperate songbirds.

    PubMed

    Martin, Thomas E

    2015-08-28

    Life history theory attempts to explain why species differ in offspring number and quality, growth rate, and parental effort. I show that unappreciated interactions of these traits in response to age-related mortality risk challenge traditional perspectives and explain life history evolution in songbirds. Counter to a long-standing paradigm, tropical songbirds grow at similar overall rates to temperate species but grow wings relatively faster. These growth tactics are favored by predation risk, both in and after leaving the nest, and are facilitated by greater provisioning of individual offspring by parents. Increased provisioning of individual offspring depends on partitioning effort among fewer young because of constraints on effort from adult and nest mortality. These growth and provisioning responses to mortality risk finally explain the conundrum of small clutch sizes of tropical birds.

  3. Upper Cretaceous exhumation of the western Rhodope Metamorphic Province (Chalkidiki Peninsula, northern Greece)

    NASA Astrophysics Data System (ADS)

    Kydonakis, Konstantinos; Gallagher, Kerry; Brun, Jean-Pierre; Jolivet, Marc; Gueydan, Frédéric; Kostopoulos, Dimitrios

    2014-06-01

    The Vertiskos Unit of northern Greece is an elongated basement belt with a complex poly-metamorphic history. It extends from Greece (Chalkidiki peninsula), to the south, up to Serbia, in the north, and arguably represents the westernmost part of the Rhodope Metamorphic Province (northern Greece to southern Bulgaria). The Vertiskos Unit experienced a medium pressure lower amphibolite-facies metamorphic overprint during the Alpine Orogeny. The available medium-temperature geochronology implies that it remained at temperature of approximately 300°C (or slightly higher) during Lower Cretaceous. In order to constrain its post-Lower Cretaceous thermal history, until near-surface exposure, we applied apatite fission track analysis. The central ages obtained range from 68.5 ± 3.8 to 46.6 ± 3.6 Ma (uppermost Cretaceous to Middle Eocene) and mean track lengths between 13 and 13.5 µm. We applied two inverse thermal modeling approaches using either each sample independently (high degree of freedom in the thermal history, better data fit) or all samples together interpreting them as a vertical profile (simpler thermal history, worse data fit). Irrespective of the modeling approach, we conclude that the bulk thermal history of the Vertiskos Unit crosses the high-temperature limit of the apatite partial annealing zone by the uppermost Cretaceous and reaches near-surface conditions as early as lower/middle Eocene. These results contrast with the thermal history of the other domains of the Rhodope Metamorphic Province further east (namely the Southern Rhodope Core Complex and the Northern Rhodope Complex) and establish the Vertiskos basement complex as the oldest exhumed coherent basement fragment of the Rhodope Metamorphic Province and Greece.

  4. New U-Pb and Sm-Nd isotope data of the age of formation and metamorphic alteration of the Kandalaksha-Kolvitsa gabbro-anorthosite complex (Baltic Shield)

    NASA Astrophysics Data System (ADS)

    Steshenko, Ekaterina; Bayanova, Tamara; Serov, Pavel; Chashchin, Viktor

    2016-04-01

    The aim of this research was to study the isotope U-Pb age of zircon and rutile and Sm-Nd (rock forming and sulphide minerals) in Kandalaksha-Kolvitsa gabbro-anorthosite complex. Kandalaksha-Kolvitsa gabbro-anorthosite complex is located in the N-E part of Baltic shield and consists of three parts. Marginal zone (mesocratic metanorite) lies at the base of the massif. Main zone is composed of leucocratic metagabbro. The upper zone is alteration of mataanorthosite and leucocratic metagabbro. All rocks were subjected to granulate metamorphism. New U-Pb and Sm-Nd isotopic and geochronological data for the rocks of the Kandalaksha-Kolvitsa Paleoproterozoic gabbro-anorthosite complex is presented. For the first time single zircon grains from metagabbros of Kolvitsa massif were dated 2448±5 Ma, using U-Pb method with an artificial 205Pb tracer. Sm-Nd isotopic age of the metamorphic minerals apatite, garnet and sulphide WR Kolvitsa array is 1985 ± 17 Ma, which is interpreted granulite metamorphism. Two fractions of single zircons from anorthosite of the Kandalaksha massif gave U-Pb age 2450± 3 Ma. Leucocratic gabbro-norite (Kandalaksha massif) were dated by U-Pb on single zircon, with age up to 2230±10 Ma. This age reflects the time of granulite metamorphism according to data of [1]. Two fractions of rutile from anorthosite of the Kandalaksha massif have been analyzed by U-Pb method and reflect age of 1700 ± 10 Ma. It is known that the closure temperature of U-Pb system rutile 400-450 ° C [2], thus cooling of the massif to these temperatures was about 1.7 Ga. These data suggested two stages of metamorphic transformations of the massif. Sm-Nd research Kandalaksha massif reflected the age of the high-temperature metasomatic transformations -1887 ± 37 Ma. Time of regional fluid processing - 1692 ± 71 Ma. A model Sm-Nd age metagabbros Kolvitsa massif is 3.3 Ga with a negative value ɛNd = -4.6, which corresponds to the most likely primary enriched mantle reservoir of

  5. The history and illustration of anatomy in the Middle Ages.

    PubMed

    Gurunluoglu, Raffi; Gurunluoglu, Aslin; Williams, Susan A; Cavdar, Safiye

    2013-11-01

    This article reviews the influence of key figures on the pictorial representation of anatomy and the evolution of anatomical illustration during the Middle Ages until the time of the Renaissance, based on medical history books, journals and ancient medical books. During the early period in the Middle Ages, most illustrations were traditional drawings of emblematic nature, oftentimes unrealistic, not only because the precise knowledge of anatomy was lacking but also because the objective was to elucidate certain principles for teaching purposes. Five figure-series that came down to us through ancient manuscripts and textbooks represent the best examples of such traditional illustrations. With the advent of human dissection in the 13th and 14th centuries, a significant transformation in the depiction of anatomy began to project the practice of human dissection, as we see in the works of Mondino de Luzzi, Henri de Mondeville and Guido de Vigevano. After the invention of book printing in the second half of the 15th century, the reproduction of books was commonly practised and the woodcut made multiplication of pictures easier. Peter of Abano, Hieronymous Brunschwig, Johannes de Ketham, Johannes Peyligk, Gregory Reisch, Magnus Hundt, Laurentius Phryesen and many more included several anatomical illustrations in their treatises that demonstrated the development of anatomical illustration during the later Middle Ages.

  6. The history and illustration of anatomy in the Middle Ages.

    PubMed

    Gurunluoglu, Raffi; Gurunluoglu, Aslin; Williams, Susan A; Cavdar, Safiye

    2013-11-01

    This article reviews the influence of key figures on the pictorial representation of anatomy and the evolution of anatomical illustration during the Middle Ages until the time of the Renaissance, based on medical history books, journals and ancient medical books. During the early period in the Middle Ages, most illustrations were traditional drawings of emblematic nature, oftentimes unrealistic, not only because the precise knowledge of anatomy was lacking but also because the objective was to elucidate certain principles for teaching purposes. Five figure-series that came down to us through ancient manuscripts and textbooks represent the best examples of such traditional illustrations. With the advent of human dissection in the 13th and 14th centuries, a significant transformation in the depiction of anatomy began to project the practice of human dissection, as we see in the works of Mondino de Luzzi, Henri de Mondeville and Guido de Vigevano. After the invention of book printing in the second half of the 15th century, the reproduction of books was commonly practised and the woodcut made multiplication of pictures easier. Peter of Abano, Hieronymous Brunschwig, Johannes de Ketham, Johannes Peyligk, Gregory Reisch, Magnus Hundt, Laurentius Phryesen and many more included several anatomical illustrations in their treatises that demonstrated the development of anatomical illustration during the later Middle Ages. PMID:24585828

  7. {sup 40}Ar/{sup 39}Ar thermochronology and thermobarometry of metamorphism, plutonism, and tectonic denudation in the Old Woman Mountains area, California

    SciTech Connect

    Foster, D.A.; Miller, C.F.; Harrison, T.M.; Hoisch, T.D.

    1992-02-01

    Discrimination of individual tectonometamorphic events in polymetamorphosed terranes requires a comprehensive understanding of the relative timing and conditions of metamorphism and plutonism. We have applied a combination of {sup 40}Ar/{sup 39} Ar thermochronology, petrology, and thermobarometry to reconstruct the complex Early Proterozoic through early Cenozoic tectonic and metamorphic evolution of continental crust in the Old Woman Mountains area, southeastern California. Strong Mesozoic thermal events obscure the earlier history in much of the Old Woman Mountains area. In those areas where Early Proterozoic rocks underwent only lower-greenschist-facies metamorphism during the Mesozoic, thermobarometry of pelitic schists indicates that Proterozoic metamorphism occurred at 9 to 11 kbar and {approximately}700 {degrees}C. {sup 40}Ar/{sup 39}Ar ages of hornblende from samples of interbedded Proterozoic amphibolite indicate that this high-grade metamorphism took place before 1600 Ma. The relatively high-pressure conditions of Early Proterozoic metamorphism in the Old Woman Mountains area contrast with the low-pressure granulite-facies metamorphism that occurred elsewhere in the Mojave Desert at this time. {sup 40}Ar/{sup 39}Ar analyses of hornblende from Proterozoic rocks within Mesozoic shear zones and hornblende barometry from Jurassic intrusive rocks suggest that tectonism and burial of Paleozoic strata to >10 km began between 170 and 150 Ma. This tectonism resulted in regional greenschist-facies metamorphism. Late-stage mineral assemblages in Proterozoic and Paleozoic pelitic rocks in the Old Woman Mountains area indicate an increase in metamorphic grade from greenschist to upper amphibolite facies toward Later Cretaceous Plutons of the 73 Ma Old Woman-Piute batholith. Barometric calculations from garnet-bearing metamorphic rocks suggest that this Cretaceous metamorphism took place at 3.5 to 5.0 kbar in the Old Woman Mountains. 68 refs., 11 figs., 3 tabs.

  8. History of allergy in the middle ages and renaissance.

    PubMed

    Ring, Johannes

    2014-01-01

    In the Middle Ages little innovative medical literature came from Western Europe. The Greek-Roman tradition with the scriptures of Hippocrates and Galenos was preserved in Byzantium and then in the Middle East by Arabic medicine; it then returned to Europe in Latin translations mostly made in Italy and Spain. There were innovative developments in Arabic medicine also with regard to the history of allergy, especially with the first description of 'rose fever', which is described as very similar in symptomatology to hay fever. Under Arabic influence, the first medical university in Salerno was famous for its well-known text Tacuinum sanitatis in which a description of asthma can be found. With the beginning of renaissance new developments were also registered in Europe, with new observations and a new way of thinking.

  9. History of allergy in the middle ages and renaissance.

    PubMed

    Ring, Johannes

    2014-01-01

    In the Middle Ages little innovative medical literature came from Western Europe. The Greek-Roman tradition with the scriptures of Hippocrates and Galenos was preserved in Byzantium and then in the Middle East by Arabic medicine; it then returned to Europe in Latin translations mostly made in Italy and Spain. There were innovative developments in Arabic medicine also with regard to the history of allergy, especially with the first description of 'rose fever', which is described as very similar in symptomatology to hay fever. Under Arabic influence, the first medical university in Salerno was famous for its well-known text Tacuinum sanitatis in which a description of asthma can be found. With the beginning of renaissance new developments were also registered in Europe, with new observations and a new way of thinking. PMID:24925380

  10. Shock Metamorphism of the Dhofar 378 Basaltic Shergottite

    NASA Technical Reports Server (NTRS)

    Mikouchi, T.; McKay, G.

    2006-01-01

    Shock metamorphism is one of the most fundamental processes in the history of Martian meteorites, especially shergottites, which affect their mineralogy and chronology. The formation of "maskelynite" from plagioclase and shock melts is such major mineralogical effects. Dhofar 378 is one of the recently found desert shergottites that is mainly composed of plagioclase and pyroxene. This shergottite is important because of its highly shocked nature and unique plagioclase texture, and thus has a great potential for assessing a "shock" age of shergottites. We have been working on a combined study of mineralogy and chronology of the same rock chip of Dhofar 378. This abstract reports its mineralogical part.

  11. Class Struggles: Teaching History in the Postmodern Age.

    ERIC Educational Resources Information Center

    Wilton, Shirley

    1999-01-01

    Describes Generation X students. Believes that teaching history to Generation X requires rebuilding the connections between community college teachers and four year schools that invent the "new history." Discusses how teachers can use the new history, "reflexive methodology," pictures from art history, and storytelling in the postmodern classroom.…

  12. New Ar/Ar single grain mineral ages from Korean orogenic belts with implications for the Triassic cooling and exhumation history

    NASA Astrophysics Data System (ADS)

    de Jong, Koenraad; Ruffet, Gilles; Han, Seokyoung

    2013-04-01

    The Korean peninsula is located in the eastern margin of the Eurasian continent where major late Palaeozoic to early Mesozoic continental collision zones, like the Central Asian Orogenic Belt and the Qinling-Dabie-Sulu Belt, merge with circum-Pacific subduction-accretion systems. Deciphering the tectonic evolution of Korea is thus crucial for the understanding of the amalgamation of East Asia. Classically, research in Korea has focused on the search for (ultra)high-pressure metamorphic rocks and their isotopic dating, most recently applying SHRIMP on Th- and U-bearing accessory minerals, in order to substantiate links with the Qinling-Dabie-Sulu Belt across the Yellow Sea in China. Instead of trying to date peak pressure conditions we focused on 40Ar/39Ar laser-probe step-heating dating of single grains of the fabric-forming minerals muscovite, biotite and amphibole, formed during retrograde recrystallisation and exhumation. This is a big advantage as their growth can be straightforwardly correlated to major phases of the tectono-metamorphic evolution of rocks. This approach helps to meet the major geochronological challenge of obtaining age estimates for the timing of specific tectono-metamorphic events in the Korean orogenic belts. The Korean peninsula comprises a number of Palaeoproterozoic high-grade gneiss terranes; only one of which has been affected by Permo-Triassic metamorphism: the Gyeonggi Massif. We concentrated on the uppermost Gyeonggi Massif and the overlying Imjingang Belt, to the North, and the ill-defined Hongseong zone to the West, both constituted by younger metamorphic rocks. Both belts contain rare lenses of mafic rocks with relics of high-pressure metamorphism. Hornblende from a corona-textured amphibolite from the lowermost part of the Imjingang Belt yielded a U-shaped age spectrum, the base of which is formed by four concordant steps with a weighted mean age of 242.8 ± 2.4 Ma (15% 39Ar release). Muscovites from strongly retrogressed and

  13. Late Carboniferous high-pressure metamorphism of the Kassan Metamorphic Complex (Kyrgyz Tianshan) and assembly of the SW Central Asian Orogenic Belt

    NASA Astrophysics Data System (ADS)

    Mühlberg, M.; Hegner, E.; Klemd, R.; Pfänder, J. A.; Kaliwoda, M.; Biske, Y. S.

    2016-11-01

    High-pressure (HP) metamorphism of the Kassan Metamorphic Complex (KMC) in the western Kyrgyz Tianshan has been related to either late Ordovician or late Carboniferous-Permian subduction processes. We report Sm-Nd ages for retrogressed eclogite samples and 40Ar/39Ar cooling ages for enclosing garnet-muscovite samples from the KMC as new age constraints on HP metamorphism and rock exhumation. These data will be used for an upgraded paleogeographic model for late Paleozoic crustal consolidation in the southwestern Central Asian Orogenic Belt. The retrogressed eclogite samples have transitional alkaline to tholeiitic affinity and trace-element patterns consistent with protoliths derived from garnet-bearing mantle sources at rifting plate margins. Geothermobarometric data for a retrogressed eclogite sample indicate peak-metamorphic conditions of 540 ± 30 °C at 1.6 ± 0.1 GPa. Samples from different lithotectonic units of the KMC provide coherent Sm-Nd garnet-whole rock ages of 317 ± 4 Ma and 316 ± 3 Ma (2σ). The prograde major-element zoning in the mm-sized garnets in combination with the moderate peak-metamorphic temperature, support our interpretation of the Sm-Nd garnet ages as unambiguous evidence for late Carboniferous HP metamorphism. The Sm-Nd garnet growth ages overlap within-error with the 40Ar/39Ar mica cooling ages of 314 ± 2 Ma and 313 ± 2 Ma (2σ) indicating rapid uplift of the subduction complex after peak metamorphism. The ca. 317-313 Ma HP-exhumation event of the KMC is contemporaneous with those of the Atbashi and Akeyazi (ca. 500 km east in NW China) HP complexes and implies similar collision histories at the South Tianshan Suture to the east and west of the Talas-Fergana Fault (TFF). The exhumation of the KMC and Atbashi HP complexes overlaps with the initiation of the TFF (Rolland et al., 2013) suggesting incipient separation of the Chatkal and Atbashi complexes during rock exhumation and early plate collision.

  14. Timing and conditions of regional metamorphism and crustal shearing in the granulite facies basement of south Namibia: Implications for the crustal evolution of the Namaqualand metamorphic basement in the Mesoproterozoic

    NASA Astrophysics Data System (ADS)

    Bial, Julia; Büttner, Steffen; Appel, Peter

    2016-11-01

    Granulite facies basement gneisses from the Grünau area in the Kakamas Domain of the Namaqua-Natal Metamorphic Province in south Namibia show high-grade mineral assemblages, most commonly consisting of garnet, cordierite, sillimanite, alkali feldspar and quartz. Cordierite + hercynitic spinel, and in some places quartz + hercynitic spinel, indicate granulite facies P-T conditions. The peak assemblage equilibrated at 800-850 °C at 4.0-4.5 kbar. Sillimanite pseudomorphs after kyanite1 and late-stage staurolite and kyanite2 indicate that the metamorphic record started and ended within the stability field of kyanite. Monazite in the metamorphic basement gneisses shows a single-phase growth history dated as 1210-1180 Ma, which we interpret as the most likely age of the regional metamorphic peak. This time coincides with the emplacement of granitic plutons in the Grünau region. The ∼10 km wide, NW-SE striking Grünau shear zone crosscuts the metamorphic basement and overprints high-temperature fabrics. In sheared metapelites, the regional metamorphic peak assemblage is largely obliterated, and is replaced by synkinematic biotite2, quartz, alkali feldspar, sillimanite and cordierite or muscovite. In places, gedrite, staurolite, sillimanite and green biotite3 may have formed late- or post-kinematically. The mylonitic mineral assemblage equilibrated at 590-650 °C at 3.5-5.0 kbar, which is similar to a retrograde metamorphic stage in the basement away from the shear zone. Monazite cores in two mylonite samples are similar in texture and age (∼1200 Ma) to monazite in metapelites away from the shear zone. Chemically distinct monazite rims indicate a second growth episode at ∼1130-1120 Ma. This age is interpreted to date the main deformation episode along the Grünau shear zone and the retrograde metamorphic stage seen in the basement. The main episode of ductile shearing along the Grünau shear zone took place 70-80 million years after the thermal peak metamorphism

  15. Pressure-temperature evolution of Neoproterozoic metamorphism in the Welayati Formation (Kabul Block), Afghanistan

    NASA Astrophysics Data System (ADS)

    Collett, Stephen; Faryad, Shah Wali

    2015-11-01

    The Welayati Formation, consisting of alternating layers of mica-schist and quartzite with lenses of amphibolite, unconformably overlies the Neoarchean Sherdarwaza Formation of the Kabul Block that underwent Paleoproterozoic granulite-facies and Neoproterozoic amphibolite-facies metamorphic events. To analyze metamorphic history of the Welayati Formation and its relations to the underlying Sherdarwaza Formation, petrographic study and pressure-temperature (P-T) pseudosection modeling were applied to staurolite- and kyanite-bearing mica-schists, which crop out to the south of Kabul City. Prograde metamorphism, identified by inclusion trails and chemical zonation in garnet from the micaschists indicates that the rocks underwent burial from around 6.2 kbar at 525 °C to maximum pressure conditions of around 9.5 kbar at temperatures of around 650 °C. Decompression from peak pressures under isothermal or moderate heating conditions are indicated by formation of biotite and plagioclase porphyroblasts which cross-cut and overgrow the dominant foliation. The lack of sillimanite and/or andalusite suggests that cooling and further decompression occurred in the kyanite stability field. The results of this study indicate a single amphibolite-facies metamorphism that based on P-T conditions and age dating correlates well with the Neoproterozoic metamorphism in the underlying Sherdarwaza Formation. The rocks lack any paragenetic evidence for a preceding granulite-facies overprint or subsequent Paleozoic metamorphism. Owing to the position of the Kabul Block, within the India-Eurasia collision zone, partial replacement of the amphibolite-facies minerals in the micaschist could, in addition to retrogression of the Neoproterozoic metamorphism, relate to deformation associated with the Alpine orogeny.

  16. Timing of Proterozoic deformation, plutonism, and metamorphism in the Los Pinos Mountains, Central New Mexico

    SciTech Connect

    Shastri, L.L. . Dept. of Geology); Bowring, S.A. )

    1992-01-01

    Geochronologic, structural, and metamorphic studies within the Los Pinos Mountains (LPM), central NM provide new insights into the Proterozoic geologic history of this area. The LPM consist of a NE-trending, NW-dipping sequence of complexly deformed amphibolites and felsic schists. These have been intruded by a pervasively deformed granitic pluton. Two predominant deformational fabrics exist in the LPM. S1 is an early northwest-trending foliation, commonly parallel to compositional layering, which is folded about S2. S2 is axial planar foliation to tight to isoclinal folds and is the regional NE-trending fabric. Other fabrics and complex fold interference patterns may be related to localized strain partitioning around granitic bodies. A network of granitic dikes associated with the pluton crosscuts S2 but contains a weak foliation parallel to S2, suggesting synkinematic intrusion of the dikes. Regional metamorphism in the LPM took place at upper greenschist to lower amphibolite facies. Electron microprobe traverses of garnets show compositional variation indicative of growth zoning. No abrupt changes in composition representative of multiple metamorphic events are observed. Garnet-biotite geothermometry yields average rim temperatures of 454 [+-] 50 C. U-Pb geochronology of zircons from amphibolite, granite, and a granite dike indicates essentially the same age for all three units (1.66 Ga). The amphibolite contains abundant zircons which have complex morphologies typical of metamorphic growth; however, an igneous origin cannot yet be precluded. Spheres from the same amphibolite yield a near concordant age of 1.62 Ga. Thus, deformation, plutonism, and possibly the peak of metamorphism, were coeval at ca. 1.66 Ga, with metamorphism cooling through the blocking temperature of sphene at 1.62 Ga. The LPM are similar to other mountain ranges in south-central New Mexico where 1.66 Ga ages have been reported.

  17. Canada basin: age and history of its continental margin

    SciTech Connect

    Sweeney, J.F.

    1985-02-01

    Presently available age controls suggest that the Canada basin formed during the Cretaceous Period between about 131 and 79 Ma. The opening process began with continental breakup that may have involved all parts of the North American polar margin at about the same time. The opening was completed by the formation of oceanic crust during the extended Cretaceous interval of normal geomagnetic polarity. Features characteristics of continental breakup, insofar as they are known, show systematic regional differences. From Brock to Axel Heiberg Island, continental breakup was associated with an extended (100 + Ma) stratigraphic hiatus and, northeastward from Ellef Ringnes Island, with extensive tholeiitic igneous activity. From Banks Island to northeastern Alaska, the breakup interval was abbreviated (20-30 Ma), and sparse igneous activity occurred. These differences can be produced by changes in the rate and/or amount of crustal stretching during margin formation and would imply relatively faster or more stretching northeast of Brock island. A continental margin of fixed age, exhibiting the indicated pattern of crustal stretching, could be produced along the trailing edge of a rotating block (Arctic Alaska terrane AA) with its pivot near the Mackenzie delta. When the rotation is restored, however, geological discrepancies are evident between Devonian and older rocks across the conjugate margins, suggesting an earlier history of drifting for the AA. Early Paleozoic correlations appear improved if the AA is placed, polar margin to polar margin, against northern Ellesmere Island and Greenland, where in the middle Paleozoic, it was sheared sinistrally along the Canadian margin to its pre-rotated position opposite Banks Island.

  18. Wastewater management through the ages: a history of mankind.

    PubMed

    Lofrano, Giusy; Brown, Jeanette

    2010-10-15

    Although much has been written about the history of water supply systems, there is a lack of corresponding information on wastewater management. This is surprising since the lack of sanitation affects human development to the same or even greater extent as the lack of clean water. While there may be an added stigma to discussing waste treatment, sanitation is widely perceived as meriting a significant claim on financial and political resources as well on the evolution of mankind. A literature review is presented on the evolution of wastewater management through the ages and its concurrent impact on human health and environment. Hopefully this information will improve the awareness of the past with a view to impacting future policies and technical developments. The review highlights the connection of environmental contamination with the ability to measure it, as well as the ways pollution control has been changed by advances in scientific knowledge. Attention is also drawn to the effects of political and societal events on wastewater management. A sanitation timeline has been constructed pointing out significant developments in the treatment of wastewater and improvements in analytical environmental chemistry. This review has been written in the belief that historical research showing the collective experience and "philosophy of sanitation" can provide inspiration to face future challenges.

  19. The timing of metamorphism in the Odenwald-Spessart basement, Mid-German Crystalline Zone

    NASA Astrophysics Data System (ADS)

    Will, T. M.; Schulz, B.; Schmädicke, E.

    2016-07-01

    New in situ electron microprobe monazite and white mica 40Ar/39Ar step heating ages support the proposition that the Odenwald-Spessart basement, Mid-German Crystalline Zone, consists of at least two distinct crustal terranes that experienced different geological histories prior to their juxtaposition. The monazite ages constrain tectonothermal events at 430 ± 43 Ma, 349 ± 14 Ma, 331 ± 16 Ma and 317 ± 12 Ma/316 ± 4 Ma, and the 40Ar/39Ar analyses provide white mica ages of 322 ± 3 Ma and 324 ± 3 Ma. Granulite-facies metamorphism occurred in the western Odenwald at c. 430 and 349 Ma, and amphibolite-facies metamorphism affected the eastern Odenwald and the central Spessart basements between c. 324 and 316 Ma. We interpret these data to indicate that the Otzberg-Michelbach Fault Zone, which separates the eastern Odenwald-Spessart basement from the Western Odenwald basement, is part of the Rheic Suture, which marks the position of a major Variscan plate boundary separating Gondwana- and Avalonia-derived crustal terranes. The age of the Carboniferous granulite-facies event in the western Odenwald overlaps with the minimum age of eclogite-facies metamorphism in the adjacent eastern Odenwald. The granulite- and eclogite-facies rocks experienced contrasting pressure-temperature paths but occur in close spatial proximity, being separated by the Rheic Suture. As high-pressure and high-temperature metamorphisms are of similar age, we interpret the Odenwald-Spessart basement as a paired metamorphic belt and propose that the adjacent high-pressure and high-temperature rocks were metamorphosed in the same subduction zone system. Juxtaposition of these rocks occurred during the final stages of the Variscan orogeny along the Rheic Suture.

  20. Metamorphism in mesosiderites

    NASA Technical Reports Server (NTRS)

    Delaney, J. S.; Prinz, M.; Harlow, G. E.; Nehru, C. E.

    1982-01-01

    Previous studies of mesosiderites have identified a metamorphic overprint in these meteorites. However, the effects and implications of this overprint have not yet been explored in detail. The present study documents several important textural and chemical features of the mesosiderites. The components of mesosiderites are examined, taking into account orthopyroxenites, olivine in clasts, mesosiderite mafic clasts, and metal. The characteristics of the silicate matrix of the mesosiderites is explored, and textural and chemical evidence of metamorphism is discussed, giving attention to coronas on olivine clasts, overgrowths on Mg-pyroxene clasts, rims on iron rich pyroxene grains, poikiloblasts of plagioclase, and resorption of clasts. Aspects of redox formation of merrillite are considered along with the causes and the implications of metamorphism. It is found that metamorphism has radically changed the texture of the silicate fraction of the mesosiderites.

  1. Color Me Metamorphic.

    ERIC Educational Resources Information Center

    Birdd, Donald L.

    1990-01-01

    Described are five activities using crayons to demonstrate the rock cycle including weathering, erosion and sedimentation, and sedimentary, metamorphic, and igneous rock formation. Discussed are materials, procedures, and probable results. (CW)

  2. Plate tectonics: Metamorphic myth

    NASA Astrophysics Data System (ADS)

    Korenaga, Jun

    2016-01-01

    Clear evidence for subduction-induced metamorphism, and thus the operation of plate tectonics on the ancient Earth has been lacking. Theoretical calculations indicate that we may have been looking for something that cannot exist.

  3. Post-metamorphic brecciation in type 3 ordinary chondrites

    NASA Astrophysics Data System (ADS)

    Scott, E. R. D.; McCoy, T. J.; Keil, K.

    1993-03-01

    Type 3.1-3.9 ordinary chondrites can be divided into two kinds: those in which the compositions of chondrule silicates are entirely consistent with metamorphism of type 3.0 material, and those in which the computational heterogeneity appears to be too extreme for in situ metamorphism. We present petrologic data for three LL3 chondrites of the second kind--Ngawi, ALH A77278 (both type 3.6), and Hamlet (type 3.9)--and compare these data with results for the first kind of LL3-4 chondrites. Given that chondrules form in the nebula and that metamorphic equilibration occurs in asteroids, our new data imply that Ngawi, A77278, Hamlet, and many other type 3 ordinary chondrites are post-metamorphic breccias containing materials with diverse metamorphic histories; they are not metamorphic rocks or special kinds of 'primitive breccias.' We infer also that metamorphism to type 3.1-3.9 levels produces very friable material that is easily remixed into breccias and lithified by mild shock. Thus, petrologic types and subtypes of chondrites indicate the mean metamorphic history of the ingredients, not the thermal history of the rock. The metamorphic history of individual type 1 or 2 porphyritic chondrules in type 3 breccias is best derived from olivine and pyroxene analyses and the data of McCoy et al. for unbrecciated chondrites. The new chondrule classification schemes of Sears, DeHart et al., appears to provide less information about the original state and metamorphic history of individual porphyritic chondrules and should not replace existing classification schemes.

  4. Post-metamorphic brecciation in type 3 ordinary chondrites

    NASA Technical Reports Server (NTRS)

    Scott, E. R. D.; Mccoy, T. J.; Keil, K.

    1993-01-01

    Type 3.1-3.9 ordinary chondrites can be divided into two kinds: those in which the compositions of chondrule silicates are entirely consistent with metamorphism of type 3.0 material, and those in which the computational heterogeneity appears to be too extreme for in situ metamorphism. We present petrologic data for three LL3 chondrites of the second kind--Ngawi, ALH A77278 (both type 3.6), and Hamlet (type 3.9)--and compare these data with results for the first kind of LL3-4 chondrites. Given that chondrules form in the nebula and that metamorphic equilibration occurs in asteroids, our new data imply that Ngawi, A77278, Hamlet, and many other type 3 ordinary chondrites are post-metamorphic breccias containing materials with diverse metamorphic histories; they are not metamorphic rocks or special kinds of 'primitive breccias.' We infer also that metamorphism to type 3.1-3.9 levels produces very friable material that is easily remixed into breccias and lithified by mild shock. Thus, petrologic types and subtypes of chondrites indicate the mean metamorphic history of the ingredients, not the thermal history of the rock. The metamorphic history of individual type 1 or 2 porphyritic chondrules in type 3 breccias is best derived from olivine and pyroxene analyses and the data of McCoy et al. for unbrecciated chondrites. The new chondrule classification schemes of Sears, DeHart et al., appears to provide less information about the original state and metamorphic history of individual porphyritic chondrules and should not replace existing classification schemes.

  5. Metamorphic geodesic regression.

    PubMed

    Hong, Yi; Joshi, Sarang; Sanchez, Mar; Styner, Martin; Niethammer, Marc

    2012-01-01

    We propose a metamorphic geodesic regression approach approximating spatial transformations for image time-series while simultaneously accounting for intensity changes. Such changes occur for example in magnetic resonance imaging (MRI) studies of the developing brain due to myelination. To simplify computations we propose an approximate metamorphic geodesic regression formulation that only requires pairwise computations of image metamorphoses. The approximated solution is an appropriately weighted average of initial momenta. To obtain initial momenta reliably, we develop a shooting method for image metamorphosis.

  6. Petrology of metamorphic rocks

    SciTech Connect

    Suk, M.

    1983-01-01

    ''Petrology of Metamorphic Rocks'' reviews Central European opinions about the origin and formation of metamorphic rocks and their genetic systems, confronting the works of such distinguished European scientists as Rosenbusch, Becke, Niggli, Sander, Eskola, Barth and others with present-day knowledge and the results of Soviet and American investigations. The initial chapters discuss the processes that give rise to metamorphic rocks, and the main differences between regional metamorphism and other types of alterations, the emphasis being laid on the material characteristic of the processes of metamorphism, metasomatism and ultrametamorphism. Further chapters give a brief characterization of research methods, together with a detailed genetic classification based on the division of primary rocks into igneous rocks, sediments and ore materials. The effects of metamorphic alterations and those of the properties of the primary rocks are analyzed on the basis of examples taken chiefly from the Bohemian Massif, the West Carpathians, other parts of the European Variscides, from the crystalline Scandinavian Shelf in Norway and Finland, and from the Alps. Typical examples are documented by a number of charts, photographs and petrographical - particularly petrochemical - data.

  7. The history of a continent from U-Pb ages of zircons from Orinoco River sand and Sm-Nd isotopes in Orinoco basin river sediments

    USGS Publications Warehouse

    Goldstein, S.L.; Arndt, N.T.; Stallard, R.F.

    1997-01-01

    We report SHRIMP U-Pb ages of 49 zircons from a sand sample from the lower Orinoco River, Venezuela, and Nd model ages of the fine sediment load from the main river and tributaries. The U-Pb ages reflect individual magmatic or metamorphic events, the Sm-Nd model ages reflect average crustal-residence ages of the sediment sources. Together they allow delineation of the crust-formation history of the basement precursors of the sediments. The U-Pb ages range from 2.83 to 0.15 Ga, and most are concordant or nearly so. Discrete age groupings occur at ??? 2.8, ??? 2.1, and ??? 1.1 Ga. The oldest group contains only three samples but is isolated from its closest neighbors by a ??? 600 Ma age gap. Larger age groupings at ??? 2.1 and ??? 1.1 Ga make up about a third and a quarter of the total number of analyses, respectively. The remaining analyses scatter along concordia, and most are younger than 1.6 Ga. The ??? 2.8 and ??? 2.1 Ga ages correspond to periods of crust formation of the Imataca and Trans-Amazonian provinces of the Guyana Shield, respectively, and record intervals of short but intensive continental growth. These ages coincide with ??? 2.9 and ??? 2.1 Ga Nd model ages of sediments from tributaries draining the Archean and Proterozoic provinces of the Guyana Shield, respectively, indicating that the U-Pb ages record the geological history of the crystalline basement of the Orinoco basin. Zircons with ages corresponding to the major orogenies of the North Atlantic continents (the Superior at ??? 2.7 Ga and Hudsonian at 1.7-1.9 Ga) were not found in the Orinoco sample. The age distribution may indicate that South and North America were separated throughout their history. Nd model ages of sediments from the lower Orinoco River and Andean tributaries are ??? 1.9 Ga, broadly within the range displayed by major rivers and dusts. This age does not coincide with known thermal events in the region and reflects mixing of sources with different crust-formation ages. The

  8. Maternal Chronological Age, Prenatal and Perinatal History, Social Support, and Parenting of Infants

    ERIC Educational Resources Information Center

    Bornstein, Marc H.; Putnick, Diane L.; Suwalsky, Joan T. D.; Gini, Motti

    2006-01-01

    The role of maternal chronological age in prenatal and perinatal history, social support, and parenting practices of new mothers (N=335) was examined. Primiparas of 5-month-old infants ranged in age from 13 to 42 years. Age effects were zero, linear, and nonlinear. Nonlinear age effects were significantly associated up to a certain age with little…

  9. Teaching History in a Post-Industrial Age

    ERIC Educational Resources Information Center

    Bianchetti, Ann

    2004-01-01

    As a social studies teacher, the author emphasizes the story of history (sticking to the facts as much as they are known) and the human qualities of the players. Middle school kids are in the throes of exploring self-identity and attempting to define their worlds. They love drama, and history provides plenty of it. The author finds that teaching…

  10. Late Cretaceous to Paleocene metamorphism and magmatism in the Funeral Mountains metamorphic core complex, Death Valley, California

    USGS Publications Warehouse

    Mattinson, C.G.; Colgan, J.P.; Metcalf, J.R.; Miller, E.L.; Wooden, J.L.

    2007-01-01

    Amphibolite-facies Proterozoic metasedimentary rocks below the low-angle Ceno-zoic Boundary Canyon Detachment record deep crustal processes related to Meso-zoic crustal thickening and subsequent extension. A 91.5 ?? 1.4 Ma Th-Pb SHRIMP-RG (sensitive high-resolution ion microprobe-reverse geometry) monazite age from garnet-kyanite-staurolite schist constrains the age of prograde metamorphism in the lower plate. Between the Boundary Canyon Detachment and the structurally deeper, subparallel Monarch Spring fault, prograde metamorphic fabrics are overprinted by a pervasive greenschist-facies retrogression, high-strain subhorizontal mylonitic foliation, and a prominent WNW-ESE stretching lineation parallel to corrugations on the Boundary Canyon Detachment. Granitic pegmatite dikes are deformed, rotated into parallelism, and boudinaged within the mylonitic foliation. High-U zircons from one muscovite granite dike yield an 85.8 ?? 1.4 Ma age. Below the Monarch Spring fault, retrogression is minor, and amphibolite-facies mineral elongation lineations plunge gently north to northeast. Multiple generations of variably deformed dikes, sills, and leucosomal segregations indicate a more complex history of partial melting and intrusion compared to that above the Monarch Spring fault, but thermobarometry on garnet amphibolites above and below the Monarch Spring fault record similar peak conditions of 620-680 ??C and 7-9 kbar, indicating minor (<3-5 km) structural omission across the Monarch Spring fault. Discordant SHRIMP-RG U-Pb zircon ages and 75-88 Ma Th-Pb monazite ages from leucosomal segregations in paragneisses suggest that partial melting of Proterozoic sedimentary protoliths was a source for the structurally higher 86 Ma pegmatites. Two weakly deformed two-mica leucogranite dikes that cut the high-grademetamorphic fabrics below the Monarch Spring fault yield 62.3 ?? 2.6 and 61.7 ?? 4.7 Ma U-Pb zircon ages, and contain 1.5-1.7 Ga cores. The similarity of metamorphic

  11. Martian Meteorite Ages and Implications for Martian Cratering History

    NASA Technical Reports Server (NTRS)

    Nyquist, Laurence E.

    2006-01-01

    New radiometrically determined ages of Martian meteorites add to the growing number with crystallization ages < 1.4 Ga. The observation of mainly geologically young ages for the Martian meteorites, the only exception being the 4.5 Ga ALH84001 [1], is paradoxical when viewed in context of a Martian surface thought to be mostly much older as inferred from the surface density of meteorite craters [2]. There appears to be at least a twofold difference between the observed ages of Martian meteorites and their expected ages as inferred from the ages of Martian surfaces obtained from crater densities.

  12. Re-equilibration history and P- T path of eclogites from Variscan Sardinia, Italy: a case study from the medium-grade metamorphic complex

    NASA Astrophysics Data System (ADS)

    Cruciani, Gabriele; Franceschelli, Marcello; Groppo, Chiara; Oggiano, Giacomo; Spano, Maria Elena

    2015-04-01

    Retrogressed eclogites are hosted within the Variscan low- to medium-grade metamorphic complex near Giuncana, north-central Sardinia. These rocks are medium to fine grained with garnet and amphibole as the most abundant mineral phases along with clinopyroxene, plagioclase, quartz, biotite, chlorite, epidote, ilmenite, rutile and titanite. Four stages of mineralogical re-equilibration have been distinguished. The stage I is characterized by the occurrence of omphacite, epidote, quartz, amphibole, rutile and ilmenite in garnet poikiloblasts. The stage II is characterized by two types of symplectitic microstructures: (1) amphibole + quartz symplectite and (2) clinopyroxene + plagioclase ± amphibole symplectite. The first symplectite type replaces omphacite included in garnet, whereas the second one is widespread in the matrix. Biotite droplets and/or lamellae intimately growing with fine-grained plagioclase resemble biotite + plagioclase symplectite after phengite. The stage III is characterized by the widespread formation of amphibole: (1) as zoned porphyroblasts in the matrix, (2) as corona-type microstructure replacing garnet. Subordinate plagioclase (oligoclase) is also present in the amphibole corona. The stage IV is characterized by the local formation of biotite replacing garnet, actinolite, chlorite, albite and titanite. P- T pseudosections calculated with Perple_X give P- T conditions 580 < T < 660 °C, 1.3 < P < 1.8 GPa for the stage I. After the stage I, pressure decrease and temperature increase led to the breakdown of omphacite with the formation of clinopyroxene + plagioclase ± amphibole symplectite at ~1.25-1.40 GPa and 650-710 °C (stage II). P- T conditions of the amphibolite-facies stage III have been defined at 600-670 °C, P = 0.65-0.95 GPa. P- T conditions of the latest stage IV are in the range of greenschist facies. The P- T path of the retrogressed eclogite hosted in the medium-grade micaschist and paragneiss of Giuncana recalls the P- T

  13. No Paleozoic metamorphics in Palawan (the Philippines)? Evidence from single grain U-Pb dating of detrital zircons

    NASA Astrophysics Data System (ADS)

    Walia, Monika; Knittel, Ulrich; Suzuki, Shigeyuki; Chung, Sun-Lin; Pena, Rolando E.; Yang, Tsanyao Frank

    2012-06-01

    The Palawan Continental Terrane (PCT) is a fragment of the margin of SE China that drifted south as a result of the Cenozoic opening of the South China Sea. This fragment is of great interest as it may contain a record of the early history of the continental margin of SE China that is not exposed on the mainland. The age and potential correlations of meta-sediments exposed on Palawan Island, Philippines, with those exposed on the other islands of Philippine Archipelago and Asia are a long standing problem of the geology of this island. Given the presence of non-metamorphic sedimentary sequences of Permian and Triassic age in the northern part of the island, a Paleozoic age was inferred for the metamorphics but recently also a younger age for these rocks was considered possible. U/Pb dating of detrital zircons by the laser-ablation ICP-MS method reveals the presence of 80-98 Ma old zircons in all of the usually distinguished units, hence despite significant differences in degree of metamorphism and tectonic deformation, all meta-sediments appear to be of late Cretaceous or younger age. Thus, in principle, these clastic rocks could be overly derived from the older sequences. However, the relatively higher degree of metamorphism of the younger rocks suggests a tectonic contact with the older sequences.

  14. Evolution of a Neoproterozoic suture in the Iberian Massif, Central Portugal: New U-Pb ages of igneous and metamorphic events at the contact between the Ossa Morena Zone and Central Iberian Zone

    NASA Astrophysics Data System (ADS)

    Henriques, S. B. A.; Neiva, A. M. R.; Ribeiro, M. L.; Dunning, G. R.; Tajčmanová, L.

    2015-04-01

    A Neoproterozoic suture is exposed at the contact between the Ossa Morena Zone and the Central Iberian Zone, in the Iberian Massif (Central Portugal), the westernmost segment of the European Variscides. Although, the Cadomian magmatic and tectonometamorphic events have been previously documented, their timing is still poorly constrained, particularly in the inner zones of the suture. We used geochronological (ID-TIMS U-Pb) data to establish the sequence of events, isotopic (Rb-Sr, Sm-Nd) data to characterize the magmatic sources and thermodynamic modelling to determine the maximum P-T conditions attained during the Cadomian metamorphism. The first event, in the future Ossa Morena Zone, is the onset of island arc magmatism represented mainly by tholeiites with a MORB signature. Their igneous crystallization age is unknown, but they are older than ca. 539 Ma. This magmatic activity was accompanied by deposition of fine-grained sediments in a Neoproterozoic basin. The second event is the evolution of the Cadomian magmatic arc in different stages. The earliest magmatic stage occurs at ca. 692 Ma, which is the oldest igneous age known in the Ossa Morena Zone. It is followed by the generation of subalkaline and peraluminous protoliths at ca. 569 Ma, with the isotopic signature of old crustal sources. The final phase of the arc magmatism (ca. 548-544 Ma) involved mainly partial melting of continental crust. The range of the main magmatic activity must have been between ca. 569 Ma and ca. 544 Ma as mentioned for other areas in the Ossa Morena Zone. A major metamorphic event, recorded in metamorphic monazite, zircon and titanite at ca. 540 Ma, attained upper amphibolite facies conditions close to the transition to granulite facies (7-8 kbar and 640-660 °C). It represents the continental arc accretion of the Ossa Morena Zone with the Iberian Autochthon passive margin (future Central Iberian Zone). The Early Ordovician rocks (ca. 483-477 Ma) were generated from depleted and

  15. Meta-Analysis at Middle Age: A Personal History

    ERIC Educational Resources Information Center

    Glass, Gene V.

    2015-01-01

    The 40-year history of meta-analysis is traced from the vantage point of one of its originators. Research syntheses leading to the first examples of meta-analysis are identified. Early meta-analyses of the literature on psychotherapy outcomes and school class size are recounted. The influence on the development of meta-analysis of several…

  16. American Memory--History Meets the Age of Technology.

    ERIC Educational Resources Information Center

    Hagenbruch, Harriet

    1994-01-01

    Describes American Memory, a multimedia computer system that incorporates CD-ROM and videodisk to provide access in electronic format to some of the Library of Congress archival materials on American history. Highlights include participating libraries; contents of the collections; searching; evaluation; and examples of the system's use at Barnard…

  17. Geologic and Geochronologic Studies of the Early Proterozoic Kanektok Metamorphic Complex of Southwestern Alaska

    USGS Publications Warehouse

    Turner, Donald L.; Forbes, Robert B.; Aleinikoff, John N.; McDougall, Ian; Hedge, Carl E.; Preface by: Wilson, Frederic H.; Layer, Paul W.; Hults, Chad P.

    2009-01-01

    having been partially reset during the late Mesozoic thermal event. 40Ar/39Ar incremental heating experiments suggest metamorphism occurred at least 1.2 b.y. ago but do not exhibit high temperature plateau ages significantly older than the 40Ar/39Ar total fusion ages of these samples. The age spectra are much more uniform than expected from a terrane with such a complex thermal history, perhaps caused by the small grain size of the samples which may possibly be less than the effective Ar diffusion radii of the analyzed hornblendes.

  18. One-dimensional thermal modelling of Acadian metamorphism in southern Vermont, USA

    USGS Publications Warehouse

    Armstrong, T.R.; Tracy, R.J.

    2000-01-01

    One-dimensional thermal (1DT) modelling of an Acadian (Devonian) tectonothermal regime in southern Vermont, USA, used measured metamorphic pressures and temperatures and estimated metamorphic cooling ages based on published thermobarometric and geochronological studies to constrain thermal and tectonic input parameters. The area modelled lies within the Vermont Sequence of the Acadian orogen and includes: (i) a western domain containing garnet-grade pre-Silurian metasedimentary and metavolcanic rocks from the eastern flank of an Acadian composite dome structure (Rayponda-Sadawga Dome); and (ii) an eastern domain containing similar, but staurolite- or kyanite-grade, rocks from the western flank of a second dome structure (Athens Dome), approximately 10 km farther east. Using reasonable input parameters based on regional geological, petrological and geochronological constraints, the thermal modelling produced plausible P-T paths, and temperature-time (T-t) and pressure-time (P-t) curves. Information extracted from P-T-t modelling includes values of maximum temperature and pressure on the P-T paths, pressure at maximum temperature, predicted Ar closure ages for hornblende, muscovite and K-feldspar, and integrated exhumation and cooling rates for segments of the cooling history. The results from thermal modelling are consistent with independently obtained pressure, temperature and Ar cooling age data on regional metamorphism in southern Vermont. Modelling results provide some important bounding limits on the physical conditions during regional metamorphism, and indicate that the pressure contemporaneous with the attainment of peak temperature was probably as much as 2.5 kbar lower than the actual maximum pressure experienced by rocks along various particle paths. In addition, differences in peak metamorphic grade (garnet-grade versus staurolite-grade or kyanite-grade) and peak temperature for rocks initially loaded to similar crustal depths, differences in calculated

  19. U-Pb zircon and CHIME monazite dating of granitoids and high-grade metamorphic rocks from the Eastern and Peninsular Thailand - A new report of Early Paleozoic granite

    NASA Astrophysics Data System (ADS)

    Kawakami, T.; Nakano, N.; Higashino, F.; Hokada, T.; Osanai, Y.; Yuhara, M.; Charusiri, P.; Kamikubo, H.; Yonemura, K.; Hirata, T.

    2014-07-01

    also share the similar plutono-metamorphic history with the Khanom and the Hub-Kapong to Pran Buri areas. This suggests that these three areas belong to the Sibumasu block, and the Sibumasu block records similar plutono-metamorphic history from Northern to Peninsular Thailand. Relative abundance of oceanic components in the Khao Chao gneiss, their Late Triassic magmatic ages, and the Early Jurassic metamorphic ages prefer the interpretation that the Khao Chao gneiss belongs to the Sukhothai Arc.

  20. 40Ar/39Ar age-spectrum data for hornblende, biotite, white mica, and K-feldspar samples from metamorphic rocks in the Great Smoky Mountains of North Carolina and Tennessee

    USGS Publications Warehouse

    Kunk, Michael J.; McAleer, Ryan

    2011-01-01

    This report contains reduced 40Ar/39Ar data of hornblende, biotite, white mica and (or) sericite, and potassium-feldspar mineral separates and phyllite groundmass samples from metamorphic rocks of the Great Smoky Mountains in North Carolina and Tennessee. Included in this report are information on the location of the samples and a brief description of the samples. The data contained herein are not interpreted in a geological context, and care should be taken by users unfamiliar with argon isotopic data in the use of these results. No geological meaning is implied for any of the apparent ages presented below, and many of the individual apparent ages are not geologically meaningful. This report is primarily a detailed source document for subsequent publications that will integrate these data into a geological context. All the samples in this report were collected in and around the Great Smoky Mountain National Park in western North Carolina and eastern Tennessee.

  1. Thrust involvement of metamorphic rocks, southwestern Brooks Range, Alaska

    SciTech Connect

    Till, A.B.; Schmidt, J.M.; Nelson, S.W. )

    1988-10-01

    Most models for the tectonic history of the western Brooks Range treat Proterozoic and lower Paleozoic metamorphic rocks exposed in the southern part of the range as passive structural basement vertically uplifted late in the Mesozoic orogenic episode. Mapping in the metamorphic rocks shows that they can de divided into two structurally and metamorphically distinct belts, both of which were folded and thrust during the orogeny. Recognition of these belts and the nature of the contact separating them is critical to construction of accurate tectonic models of the Brooks Range fold and thrust belt.

  2. Politics as Social History: Political Cartoons in the Gilded Age.

    ERIC Educational Resources Information Center

    Edwards, Rebecca

    1999-01-01

    Provides analyses of four political cartoons in order to suggest approaches to Gilded Age politics that reveal key issues, such as gender, religion, and ethnicity, as well as the struggles over material resources in a stratified economy. Maintains that political cartoons assist students in understanding the ideology of a past era. (CMK)

  3. Bombardment History of the Galilean Satellites and Derived Ages

    NASA Astrophysics Data System (ADS)

    Neukum, G.; Wagner, R.; Wolf, U.; Head, J. W., III; Pappalardo, R.; Chapman, C. R.; Merline, W.; Belton, M. S.

    1997-07-01

    During the first seven Galileo flybys, high resolution imagery of the three Galilean moons, Europa, Ganymede and Callisto have been obtained. The new imaging data allow to measure crater diameters as small as ~ 100 m. In combination with Voyager data, size-frequency distribution characteristics in the size range of ~ 100 m to ~ 100 km have been determined. Crater distributions show steep slopes (cumulative index about -3) at smaller diameters on each satellite and are shallower at larger diameters, similar to what is seen on the Moon and the asteroids Gaspra and Ida. % % At D = 1 km, crater densities differ by about a factor of 10 between % average dark terrain of Galileo Regio and youngest bright resurfaced areas % on Ganymede. % Crater densities on the most heavily cratered regions on both Ganymede and Callisto are fairly comparable. On Europa, crater densities have turned out to be about a factor of 10 lower than on the youngest bright terrain in the Uruk Sulcus region of Ganymede. The similarity to crater size-frequency distributions found in the inner solar system suggests a similar origin of the projectiles, probably mainly stemming from the asteroid belt, and the impact rate on the Galilean satellites may have had a lunar-like decay with time. Under this assumption, absolute ages may be derived making use of the idea of the ''marker horizon'', i. e. formation of the youngest basins, such as Gilgamesh on Ganymede, about 3.8 b.y. ago. Thus, the most densely cratered dark terrains on both Ganymede and Callisto have likely ages of 4.1 - 4.3 b.y. Basins such as Neith (on Ganymede) or Adlinda (on Callisto) yield likely ages of about 3.9 b.y. Some areas on Europa may be as old as 3 - 3.3 b.y. Other scenarios based on values proposed for the present-day comet impact rate in the Jovian system with non-lunar-like flux time dependences are conceivable and would result in generally younger ages, possibly as young as 10 m.y. These young ages and impact rates for Europa

  4. Ubiquitous brecciation after metamorphism in equilibrated ordinary chondrites

    NASA Technical Reports Server (NTRS)

    Scott, E. R. D.; Lusby, D.; Keil, K.

    1985-01-01

    Ten objects with aberrant Fe/(Fe + Mg) ratios have been found in apparently unbrecciated types 4-6 H and L chondrites. Since the Fe/(Fe + Mg) ratios of these objects are incompatible with the metamorphic history of the host chondrites, it is concluded that a high proportion of ordinary chondrites are breccias that were lithified after peak metamorphism. This is consistent with the results of Scott (1984), who concluded that most type three ordinary chondrites are breccias of materials with diverse thermal histories, even though they do not show prominent brecciation. It is found that the classification scheme of Van Schmus and Wood (1967) does not identify chondrites with similar thermal histories; the petrologic type of a chondrite is only a measure of the average thermal history of its ingredients. Chondrite and achondrite breccias are also compared in order to understand how brecciation of chondrites after metamorphism is so well camouflaged.

  5. History of a Bronze Age tell and its environment

    NASA Astrophysics Data System (ADS)

    Kovács, Gabriella; Füleky, György; Vicze, Magdolna

    2016-04-01

    Százhalombatta-Földvár is the most excessively researched Bronze Age tell site in Hungary. Parallel to the investigation of the settlement structure and activity patterns the changes of the landscape and the effect of human alteration is also studied. Significant changes of the landscape can be detected from the Bronze Age until the recent natural and cultural heritage protection of the area. Archaeological, soil analytical and thin section soil micromorphological methods are used to reconstruct the past 4000 years of the tell and its immediate surroundings. Prior to the Bronze Age the area was covered by forest vegetation, so the initial settling could only be realised after deforestation (2000 BC). The result of the soil corings and the prepared soil thin sections are solid proves of this action. It also became evident that at some areas - so far it seems that at locales where house floors were laid for the very first time - even the topsoil was removed so intensively that only the B horizon of the relict forest soil can be found. This observation needs to be further tested outside the habitation area to define the horizontal extension of the forest clearance and the topsoil removal. The northern side of the settlement is bordered by a natural erosion gully. At 2000 BC it was just a natural depression, but by 1500 BC it was deepened to serve as a fortification ditch. Around 1200 BC the ditch started to be filled in and by 1000 BC it was refilled to such an extent that its surface was utilised again. At about 600 BC (Late Iron Age) a smaller inner rampart was erected on the southern side of the ditch for inner separation. Not much is known about the Roman period of this area (200 AD) but the remnants of a watchtower indicate their presence. During the 18th century AD the area was used for grape cultivation and later for hobby gardens up until the protection of the area in the late 20th century. Since then species of the original vegetation started to grow back

  6. A history of the future: the emergence of contemporary anti-ageing medicine.

    PubMed

    Everts Mykytyn, Courtney

    2010-02-01

    The emergence of anti-ageing medicine over the past 20 years has posed tremendous challenges for the understanding of ageing and the concomitant responsibilities of biomedicine. Though highly contentious and loosely organised at best, anti-ageing targets ageing for biomedical intervention. This article examines a history of anti-ageing in the United States from 1993 to 2008, outlining its evolution from a scientific 'backwater' to a field with such promise that many within and outside the field believe efficacious therapies are an inevitability. In large part, the language of anti-ageing has shifted from predictions to expectations; it has become less a question of 'if' and more a question of 'when' and 'how' this rhetorical shift is directly linked with increasing legitimacy constructed upon a complex web of factors including mounting practitioner involvement, research interest, media attention, and popular desire. In this article I briefly review this history alongside the strategic histories marshalled by the various proponents and opponents to support their claims of legitimacy. The history of anti-ageing medicine is one of an emerging scientific and clinical practice as well as a history of an idea that has very recently made its way out of science fiction and into science future.

  7. Maternal chronological age, prenatal and perinatal history, social support, and parenting of infants.

    PubMed

    Bornstein, Marc H; Putnick, Diane L; Suwalsky, Joan T D; Gini, Motti

    2006-01-01

    The role of maternal chronological age in prenatal and perinatal history, social support, and parenting practices of new mothers (N=335) was examined. Primiparas of 5-month-old infants ranged in age from 13 to 42 years. Age effects were zero, linear, and nonlinear. Nonlinear age effects were significantly associated up to a certain age with little or no association afterward; by spline regression, estimated points at which the slope of the regression line changed were 25 years for prenatal and perinatal history, 31 years for social supports, and 27 years for parenting practices. Given the expanding age range of first-time parents, these findings underscore the importance of incorporating maternal age as a factor in studies of parenting and child development. PMID:16942495

  8. First evidence of the Ellesmerian metamorphism on Svalbard

    NASA Astrophysics Data System (ADS)

    Kośmińska, Karolina; Majka, Jarosław; Manecki, Maciej; Schneider, David A.

    2016-04-01

    The Ellesmerian fold-and-thrust belt is exposed in the High Arctic from Ellesmere Island in the east, through North Greenland, to Svalbard in the west (e.g. Piepjohn et al., 2015). It developed during Late Devonian - Early Carboniferous, and overprinted older (mainly Caledonian) structures. It is thought that this fold-and-thrust belt was formed due to collision of the Pearya Terrane and Svalbard with the Franklinian Basin of Laurentia. Traditionally, the Ellesmerian fold-and-thrust belt comprises a passive continental margin affected by foreland deformation processes, but the exact larger scale tectonic context of this belt is disputable. It is partly because the Eocene Eurekan deformation superimposed significantly the Ellesmerian structures, thus making the reconstruction of the pre-Eurekan history very difficult. Here we present for the first time evidence for Ellesmerian metamorphism within the crystalline basement of Svalbard. These rocks are exposed in the Pinkie unit on Prins Karls Forland (W-Svalbard), which exhibits tectonic contacts with the overlying sequences. The Pinkie unit is mainly composed of strongly deformed lithologies such as laminated quartzites, siliciclastic rocks and garnet-bearing mica schists. Detrital zircon dating yielded ages as young as Neoproterozoic (0.95-1.05 Ga), thus the Pinkie unit is considered to be Neoproterozoic (Kośmińska et al., 2015a). The M1 assemblages and D1 structures are affected by D2 mylonitization (cf. Faehnrich et al., 2016, this meeting). Petrological characterization and Th-U-total Pb chemical monazite dating have been performed on the Pinkie metapelites. These rocks exhibit an apparent inverted Barrovian metamorphic sequence, within which three metamorphic zones have been distinguished: garnet+staurolite+muscovite+biotite, garnet+staurolite+kyanite+muscovite+biotite, garnet+kyanite+muscovite+biotite. The P-T estimates using the QuiG barometry coupled with thermodynamic modelling revealed that the

  9. From the Axial Age to the New Age: Religion as a Dynamic of World History.

    ERIC Educational Resources Information Center

    Tucker, Carlton H.

    In order to broaden student understanding of past and contemporary situations, the world history survey course needs to consider religion as a vehicle through which history moves. The course proposal includes prehistory and paleolithic times to contemporary Islamic culture. The course is thematic and comparative in orientation, but moves through…

  10. Coincidence of gabbro and granulite formation and their implication for Variscan HT metamorphism in the Moldanubian Zone (Bohemian Massif), example from the Kutná Hora Complex

    NASA Astrophysics Data System (ADS)

    Faryad, Shah Wali; Kachlík, Václav; Sláma, Jiří; Jedlicka, Radim

    2016-11-01

    Leucocratic metagabbro and amphibolite from a mafic-ultramafic body within migmatite and granulite in the Kutná Hora Complex were investigated. The mafic-ultramafic rocks show amphibolite facies metamorphism, but in the central part of the body some metagabbro preserves cumulus and intercumulus plagioclase, clinopyroxene and spinel. Spinel forms inclusions in both clinopyroxene and plagioclase and shows various degree of embayment structure, that was probably a result of reaction with melt during magmatic crystallization. In the metagabbro, garnet forms coronae around clinopyroxene at the contacts with plagioclase. Amphibolite contains garnet with prograde zoning and plagioclase. Phase relations of igneous and metamorphic minerals indicate that magmatic crystallization and subsequent metamorphism occurred as a result of isobaric cooling at a depth of 30-35 km. U-Pb dating on zircon from leucogabbro yielded a Variscan age (337.7 ± 2 Ma) that is similar or close to the age of granulite facies metamorphism (ca 340 Ma) in the Moldanubian Zone. Based on the calculated PT conditions and age data, both the mafic-ultramafic body and surrounding granulite shared the same exhumation path from their middle-lower crustal position at the end of Variscan orogeny. The coincidence of mafic-ultramafic intrusives and granulite-amphibolite facies metamorphism is explained by lithospheric upwelling beneath the Moldanubian Zone that occurred due to slab break-off during the final stages of subduction of the Moldanubian plate beneath the Teplá Barrandian Block. The model also addresses questions about the preservation of minerals and/or their compositions from the early metamorphic history of the rocks subjected to ultradeep subduction and subsequent granulite facies metamorphism.

  11. Baking, ageing, diabetes: a short history of the Maillard reaction.

    PubMed

    Hellwig, Michael; Henle, Thomas

    2014-09-22

    The reaction of reducing carbohydrates with amino compounds described in 1912 by Louis-Camille Maillard is responsible for the aroma, taste, and appearance of thermally processed food. The discovery that non-enzymatic conversions also occur in organisms led to intensive investigation of the pathophysiological significance of the Maillard reaction in diabetes and ageing processes. Dietary Maillard products are discussed as "glycotoxins" and thus as a nutritional risk, but also increasingly with regard to positive effects in the human body. In this Review we give an overview of the most important discoveries in Maillard research since it was first described and show that the complex reaction, even after over one hundred years, has lost none of its interdisciplinary actuality. PMID:25044982

  12. Association between history of abortion and metabolic syndrome in middle-aged and elderly Chinese women.

    PubMed

    Xu, Baihui; Zhang, Jie; Xu, Yu; Lu, Jieli; Xu, Min; Chen, Yuhong; Bi, Yufang; Ning, Guang

    2013-03-01

    Epidemiologic studies have suggested that abortion may cause long term health consequences such as cardiovascular disease. Until recently, studies focusing on the association between history of abortion and metabolic diseases were limited. In the present study, we aimed to investigate the association between history of abortion and metabolic syndrome (MetS) in middle-aged and elderly Chinese women. A cross-sectional survey was performed in 6302 women (age ≥ 40 years) in Shanghai. Standardized questionnaire was used to obtain the information about reproductive histories. Overall, we observed a positive association between history of induced abortion and the prevalence of MetS, independent of potential confounding factors. A multivariable-adjusted logistic regression analysis revealed that compared to those without a history of induced abortion, women with a history of induced abortion remained at 1.25 times more likely to have MetS (OR = 1.25, 95% CI = 1.06-1.47, P < 0.05), and the association was number-dependent. However, no significant association between history of spontaneous abortion and the prevalence of MetS was observed. Compared to those without a history of spontaneous abortion, the multivariate-adjusted odds ratio associated with a history of spontaneous abortion for MetS was 0.88 (95% CI = 0.65-1.19, P > 0.05).

  13. Rubidium-strontium whole-rock ages of Kataragama and Pottuvil charnockites and East Vijayan gneiss: Indication of a 2 Ga metamorphism in the highlands of southeast Sri Lanka

    SciTech Connect

    De Maesschalck, A.A.; Oen, I.S. ); Hebeda, E.H.; Verschure, R.H. ); Arps, C.E.S. )

    1990-09-01

    Highland Group granulite-facies rocks of the Kataragama klippe in southeast Sri Lanka yield a Rb-Sr whole-rock apparent age of 1,930 {plus minus} 130 Ma, MSWD = 39, and a {sup 87}Sr/{sup 86}Sr intercept of 0.715 {plus minus} 0.005, indicating a Highlandian metamorphism about 2.0 Ga ago. A charnockitic gneiss at Komari near Pottuvil, east Sri Lanka, gives a Rb-Sr whole-rock isochron age of 820 {plus minus} 70 Ma, MSWD = 0.78, initial {sup 87}Sr/{sup 86}Sr = 0.725 {plus minus} 0.007, suggesting a metamorphic resetting at about 0.8 Ga. The Rb-Sr whole-rock data of an East Vijayan biotite-hornblende gneiss fit a reference isochron of 800 Ma with a {sup 87}Sr/{sup 86}Sr intercept of 0.705; the low {sup 87}Sr/{sup 86}Sr intercept may be explained by a juvenile addition to the older crust. A review of available data from various isotopic dating methods suggests that the Highland Group supracrustals were deposited 2.5-2.0 Ga ago, metamorphosed in the granulite-facies about 2.0 Ga (M1) ago, and disturbed by resetting events about 1.1 Ga (M2), 0.8 Ga (M3), and 0.55 Ga (M4) ago. The East Vijayan supracrustals were deposited 2.0-1.1 Ga ago, invaded by granites and metamorphosed in the amphibolite-facies about 1.1 Ga (M2) ago, and disturbed by resetting events about 0.8 (M3) and 0.55 Ga (M4) ago. Overthrusting of the Kataragama granulites over the East Vijayan gneisses occurred post-M3.

  14. Searching for the Kinkeepers: Historian Gender, Age, and Type 2 Diabetes Family History

    ERIC Educational Resources Information Center

    Giordimaina, Alicia M.; Sheldon, Jane P.; Kiedrowski, Lesli A.; Jayaratne, Toby Epstein

    2015-01-01

    Kinkeepers facilitate family communication and may be key to family medical history collection and dissemination. Middle-aged women are frequently kinkeepers. Using type 2 diabetes (T2DM) as a model, we explored whether the predicted gender and age effects of kinkeeping can be extended to family medical historians. Through a U.S. telephone survey,…

  15. Chronology of paleozoic metamorphism and deformation in the Blue Ridge thrust complex, North Carolina and Tennessee

    SciTech Connect

    Goldberg, S.A.; Dallmeyer, R.D.

    1997-05-01

    The Blue Ridge province in northwestern North Carolina and northeastern Tennessee records a multiphase collisional and accretionary history from the Mesoproterozoic through the Paleozoic. To constrain the tectonothermal evolution in this region, radiometric ages have been determined for 23 regionally metamorphosed amphibolites, granitic gneisses, and pelitic schists and from mylonites along shear zones that bound thrust sheets and within an internal shear zone. The garnet ages from the Pumpkin Patch a thrust sheet (458, 455, and 451 Ma) are similar to those from the structurally overlying Spruce Pine thrust sheet (460, 456, 455, and 450 Ma). Both thrust sheets exhibit similar upper amphibolite-facies conditions. Because of the high closure temperature for garnet, the garnet ages are interpreted to date growth at or near the peak of Taconic metamorphism. Devonian metamorphic ages are recognized in the Spruce Pine thrust sheet, where Sm-Nd and Rb-Sr garnet ages of 386 and 393 Ma and mineral isochron ages of 397 {+-} 14 and 375 {+-} 27 Ma are preserved. Hornblendes record similar {sup 40}Ar/{sup 39}Ar, Sm-Nd, and Rb-Sr ages of 398 to 379 Ma. Devonian {sup 40}Ar/{sup 39}Ar hornblende ages are also recorded in the structurally lower Pumpkin Patch thrust sheet. The Devonian mineral ages are interpreted to date a discrete tectonothermal event, as opposed to uplift and slow cooling from an Ordovician metamorphic event. The Mississippian mylonitization is interpreted to represent thrusting and initial assembly of crystalline sheets associated with the Alleghanian orogeny. The composite thrust stack of the Blue Ridge complex was subsequently thrust northwestward along the Linville Falls fault during middle Alleghanian orogeny (about 300 Ma).

  16. Modelling Metamorphism by Abstract Interpretation

    NASA Astrophysics Data System (ADS)

    Dalla Preda, Mila; Giacobazzi, Roberto; Debray, Saumya; Coogan, Kevin; Townsend, Gregg M.

    Metamorphic malware apply semantics-preserving transformations to their own code in order to foil detection systems based on signature matching. In this paper we consider the problem of automatically extract metamorphic signatures from these malware. We introduce a semantics for self-modifying code, later called phase semantics, and prove its correctness by showing that it is an abstract interpretation of the standard trace semantics. Phase semantics precisely models the metamorphic code behavior by providing a set of traces of programs which correspond to the possible evolutions of the metamorphic code during execution. We show that metamorphic signatures can be automatically extracted by abstract interpretation of the phase semantics, and that regular metamorphism can be modelled as finite state automata abstraction of the phase semantics.

  17. Energetics of metamorphic climax in the southern toad (Bufo terrestris).

    PubMed

    Beck, Christopher W; Congdon, Justin D

    2003-11-01

    During metamorphic climax, anuran larvae must rely on stored energy because changes in oral and digestive morphology prevent foraging and efficient assimilation. Thus, the time required to store adequate energy for metamorphic climax may set a lower limit on age at which it can occur. Therefore, the amount and type of energy used during metamorphic climax must be determined. To quantify the energetic costs of metamorphic climax in Bufo terrestris, oxygen consumption during climax was measured. Wet mass, dry mass, and lipid mass for a group of individuals at the initiation of climax (forelimb emergence, FL) and for another group at the end of climax (complete tail resorption, TR) were also measured to determine whether lipids were used to fuel metamorphic climax. The total amount of energy used, maintenance costs, and development costs during metamorphic climax varied considerably among individuals. Variation in energy metabolism during climax was not related to differences in energy metabolism during larval development or body mass at initiation of climax. TR individuals were significantly lighter in terms of wet mass and had less body water than FL individuals. However, the two groups did not differ in dry mass or lipid mass. Therefore, lipid catabolism is not a major source of energy during metamorphic climax in B. terrestris. As a result, decreases in age at metamorphosis may not be constrained by the need to store energy in the form of lipids.

  18. Metamorphic Testing for Cybersecurity

    PubMed Central

    Chen, Tsong Yueh; Kuo, Fei-Ching; Ma, Wenjuan; Susilo, Willy; Towey, Dave; Voas, Jeffrey

    2016-01-01

    Testing is a major approach for the detection of software defects, including vulnerabilities in security features. This article introduces metamorphic testing (MT), a relatively new testing method, and discusses how the new perspective of MT can help to conduct negative testing as well as to alleviate the oracle problem in the testing of security-related functionality and behavior. As demonstrated by the effectiveness of MT in detecting previously unknown bugs in real-world critical applications such as compilers and code obfuscators, we conclude that software testing of security-related features should be conducted from diverse perspectives in order to achieve greater cybersecurity. PMID:27559196

  19. Bushveld-aged fluid flow, peak metamorphism, and gold mobilization in the Witwatersrand basin, South Africa: Constraints from in situ SHRIMP U-Pb dating of monazite and xenotime

    NASA Astrophysics Data System (ADS)

    Rasmussen, Birger; Fletcher, Ian R.; Muhling, Janet R.; Mueller, Andreas G.; Hall, Greg C.

    2007-10-01

    In situ U-Pb dating of monazite and xenotime in gold reefs and unmineralized greenschist facies sedimentary rocks from the Witwatersrand basin, South Africa, reveals two episodes of tectonothermal activity. A major event between 2.06 and 2.03 Ga is recorded in the Wit-watersrand and Transvaal Supergroups in the northwestern and central basin, and broadly coincides with the ca. 2.06 Ga Bushveld event. In the central and southern basin, a previously unrecognized event has been dated between 2.14 and 2.12 Ga. The widespread geographic and stratigraphic occurrence of Bushveld-aged monazite and xenotime, including both auriferous reefs and unmineralized strata, indicates that metamorphism and fluid flow associated with magmatism was pervasive, affecting most of the succession (>10 km thick) in the central and northern parts of the basin. The metamorphic phosphate dates, which are younger away from the complex, indicate a lag of 20-30 m.y. between emplacement and phosphate growth in the central basin (˜100 km south), suggesting that heat related to magmatism was transferred southward at an average rate of 3-5 mm yr-1. The absence of 2.06-2.03 Ga phosphates in the Welkom goldfield at the southern end of the basin implies that Bushveld-related heating and fluid flow did not affect this part of the basin. The intergrowth of ca. 2.045 Ga monazite with gold in quartz-pebble conglomerate from the West Rand goldfield indicates that fluid flow related to the Bushveld event caused mobilization of gold in the Witwatersrand basin.

  20. The baboon model (Papio hamadryas) of fetal loss: Maternal weight, age, reproductive history and pregnancy outcome

    PubMed Central

    Schlabritz-Loutsevitch, Natalia; Moore, Charleen M.; Lopez-Alvarenga, Juan Carlos; Dunn, Betty G.; Dudley, Donald; Hubbard, Gene B.

    2010-01-01

    Background Several risk factors are associated with the incidence of human stillbirths. The prevention of stillbirths in women is a pressing clinical problem. Methods We reviewed 402 pathology records of fetal loss occurring in a large baboon (Papio spp.) colony during a 15-year period. Clinical histories of 565 female baboons with one or more fetal losses during a 20-year period were analyzed for weight, age, and reproductive history. Results Fetal loss was most common at term (35.57%) and preterm (28.61%) and less common in the first half of gestation (11.20%) and post-term (5.22%). Greater maternal weight, older age, history of stillbirth and higher parity were independent predictors for stillbirth. An exponential increase in the incidence of fetal loss was observed beginning at age 14 years in baboons. Conclusion Fetal loss and maternal risk factors associated with stillbirths in baboons were similar to those documented in women. PMID:19017195

  1. Cosmic Ray Exposure Ages, Ar-Ar Ages, and the Origin and History of Eucrites

    NASA Technical Reports Server (NTRS)

    Wakefield, Kelli; Bogard, Donald; Garrison, Daniel

    2004-01-01

    HED meteorites likely formed at different depths on the large asteroid 4-Vesta, but passed through Vesta-derived, km-sized intermediary bodies (Vestoids), before arriving at Earth. Most eucrites and diogenites (and all howardites) are brecciated, and impact heating disturbed or reset the K-Ar ages (and some Rb-Sr ages) of most eucrites in the time period of approx. 3.4 - 4.1 Gyr ago. Some basaltic eucrites and most cumulate eucrites, however, are not brecciated. We recently showed that the Ar-39 - Ar-40 ages for several of these eucrites tightly cluster about a value of 4.48 +/- 0.02 Gyr, and we argue that this time likely represents a single large impact event on Vesta, which ejected these objects from depth and quenched their temperatures. A different parent body has been suggested for cumulate eucrites, although the Ar-Ar ages argue for a common parent. Similarities in the cosmic-ray (space) exposure ages for basaltic eucrites and diogenites also have been used to infer a common parent body for some HEDs. Here we present CRE ages of several cumulate and unbrecciated basaltic (UB) eucrites and compare these with CRE ages of other HEDs. This comparison also has some interesting implications for the relative locations of various HED types on Vesta and/or the Vestoids.

  2. Crystal Histories and Crustal Magmas: Insights into Magma Storage from U-Series Crystal Ages

    NASA Astrophysics Data System (ADS)

    Cooper, K. M.

    2014-12-01

    The dynamic processes operating within crustal magma reservoirs control many aspects of the chemical composition of erupted magmas, and crystals in volcanic rocks can provide a temporally-constrained archive of these changing environments. A new compilation of 238U-230Th ages of accessory phases and 238U-230Th-226Ra ages of bulk mineral separates of major phases documents that crystals in individual samples often have ages spanning most of the history of a volcanic center. Somewhat surprisingly, this observation holds for surface analyses as well as interior analyses, indicating that the latest stages of growth took place at different times for different grains. Nevertheless, average ages of surfaces are younger than interiors (as expected), and the dominant surface age population is often within error of eruption age. In contrast to accessory phase ages, less than half of the bulk separate 238U-230Th-226Ra ages for major phases are more than 10 kyr older than eruption. This suggests that major phases may in general reflect a later stage of development of an eruptible magma body than do accessory phases, or that the extent of discordance between ages of major and accessory phases reflects the extent to which a crystal mush was remobilized during processes leading to eruption. Crystal ages are most useful for illuminating magmatic processes when combined with crystal-scale trace-element or isotopic data, and I will present several case studies where such combined data sets exist. For example, at Yellowstone and at Okataina Caldera Complex, New Zealand, the combination zircon surface and interior analyses (of age, Hf isotopic, and trace-element data) with bulk dating and in-situ trace-element and isotopic compositions of feldspar allows a comparison of the early history of storage in a crystal mush with the later history of melt extraction and further crystallization prior to eruption, thus tracking development of erupted magma bodies from storage through eruption.

  3. Shock metamorphism of ordinary chondrites

    NASA Technical Reports Server (NTRS)

    Stoeffler, Dieter; Keil, Klaus; Scott, Edward R. D.

    1991-01-01

    This study proposes a revised petrographic classification of progressive stages of shock metamorphism of 26 ordinary chondrites. Six stages of shock (S1 to S6) are defined on the basis of shock effects in olivine and plagioclase as recognized by thin section microscopy, and the characteristic shock effects of each shock stage are described. It is concluded that shock effects and the sequence of progressively increasing degrees of shock metamorphosis are very similar in H, L, and LL groups. Differences in the frequency distribution of shock stages are relatively minor. It is suggested that the collisional histories of the H, L, and LL parent bodies were similar. Petrologic type-3 chondrites are deficient in stages S4 and S6 and, with increasing petrologic type, the frequency of stages S4 to S6 increases. It is suggested that the more porous and volatile-rich Type-3 chondrites are subject to melting at a lower shock pressure than the nonporous chondrites of higher petrologic type. Stage S3 is the most abundant in nearly all petrologic types.

  4. Shock metamorphism of ordinary chondrites

    NASA Astrophysics Data System (ADS)

    Stoeffler, Dieter; Keil, Klaus; Scott, Edward R. D.

    1991-12-01

    This study proposes a revised petrographic classification of progressive stages of shock metamorphism of 26 ordinary chondrites. Six stages of shock (S1 to S6) are defined on the basis of shock effects in olivine and plagioclase as recognized by thin section microscopy, and the characteristic shock effects of each shock stage are described. It is concluded that shock effects and the sequence of progressively increasing degrees of shock metamorphosis are very similar in H, L, and LL groups. Differences in the frequency distribution of shock stages are relatively minor. It is suggested that the collisional histories of the H, L, and LL parent bodies were similar. Petrologic type-3 chondrites are deficient in stages S4 and S6 and, with increasing petrologic type, the frequency of stages S4 to S6 increases. It is suggested that the more porous and volatile-rich Type-3 chondrites are subject to melting at a lower shock pressure than the nonporous chondrites of higher petrologic type. Stage S3 is the most abundant in nearly all petrologic types.

  5. Life histories and the evolution of aging in bacteria and other single-celled organisms.

    PubMed

    Johnson, Leah R; Mangel, Marc

    2006-10-01

    The disposable soma theory of aging was developed to explore how differences in lifespans and aging rates could be linked to life history trade-offs. Although generally applied for multicellular organisms, it is also useful for exploring life history strategies of single-celled organisms such as bacteria. Motivated by recent research of aging in E. coli, we explore the effects of aging on the fitness of simple single-celled organisms. Starting from the Euler-Lotka equation, we propose a mathematical model to explore how a finite reproductive lifespan affects fitness and resource allocation in simple organisms. This model provides quantitative predictions that have the potential for direct comparison with experiment, providing an opportunity to test the disposable soma theory more directly.

  6. Exploring opportunities for healthy aging among older persons with a history of homelessness in Toronto, Canada.

    PubMed

    Waldbrook, Natalie

    2015-03-01

    Within the areas of literature on both population aging and health and homelessness, little attention has been given to the opportunities and barriers to healthy aging among older persons with a history of homelessness. Set in the context of inner-city Toronto, Canada, this article reports on the findings from qualitative interviews with 29 formerly homeless older persons. The findings illustrate participants' experiences of positive health change since moving into a stable housing environment and the aspects of housing they perceive to have improved their health and wellbeing. The qualitative findings also draw attention to the ongoing barriers to healthy aging that can be experienced among older persons with a history of homelessness. Overall, this study draws on the lived experiences of formerly homeless older persons to offer a better understanding of the long-term effects of homelessness on health, wellbeing, and aging.

  7. Evolvability of an avian life history trait declines with father's age.

    PubMed

    Kim, S-Y; Drummond, H; Torres, R; Velando, A

    2011-02-01

    Studies of laboratory organisms have suggested that parental age affects the genetic variance of offspring traits. This effect can engender age-specific variance in genetic contributions to evolutionary change in heritable traits under directional selection, particularly in age-structured populations. Using long-term population data of the blue-footed booby (Sula nebouxii), we tested whether genetic variance of recruiting age varies with parental age. Using robust quantitative genetic models fitted to pedigree, we found a significant genotype-by-paternal age interaction for recruiting age. Genetic potential for adaptive change in recruiting age was greater in progeny of young (age 1-6 years) fathers (males: CV(A)=6.68; females: CV(A)=7.59) than those of middle age (7-9 years) fathers (males: CV(A) = 4.64; females: CV(A)=5.08) and old (10-14 years) fathers (CV(A)=0 for both sexes). Therefore, parental age dependence of heritable variance, in addition to age-related variation in survival and fecundity, should affect the strength of natural selection for evolutionary changes. Our results provide rare evidence for the influence of parental age on the evolutionary potential of a life history trait in a wild population.

  8. Evolvability of an avian life history trait declines with father's age.

    PubMed

    Kim, S-Y; Drummond, H; Torres, R; Velando, A

    2011-02-01

    Studies of laboratory organisms have suggested that parental age affects the genetic variance of offspring traits. This effect can engender age-specific variance in genetic contributions to evolutionary change in heritable traits under directional selection, particularly in age-structured populations. Using long-term population data of the blue-footed booby (Sula nebouxii), we tested whether genetic variance of recruiting age varies with parental age. Using robust quantitative genetic models fitted to pedigree, we found a significant genotype-by-paternal age interaction for recruiting age. Genetic potential for adaptive change in recruiting age was greater in progeny of young (age 1-6 years) fathers (males: CV(A)=6.68; females: CV(A)=7.59) than those of middle age (7-9 years) fathers (males: CV(A) = 4.64; females: CV(A)=5.08) and old (10-14 years) fathers (CV(A)=0 for both sexes). Therefore, parental age dependence of heritable variance, in addition to age-related variation in survival and fecundity, should affect the strength of natural selection for evolutionary changes. Our results provide rare evidence for the influence of parental age on the evolutionary potential of a life history trait in a wild population. PMID:21044208

  9. Thermobarometric constraints on mid-Cretaceous to late Cretaceous metamorphic events in the western metamorphic belt of the Coast Mountains complex near Petersburg, southeastern Alaska

    USGS Publications Warehouse

    Himmelberg, Glen R.; Brew, David A.

    2005-01-01

    The western metamorphic belt is part of the Coast Mountains Complex of southeastern Alaska and western Canada. This complex formed as a result of mid-Cretaceous through middle Eocene crustal shortening between the previously amalgamated Wrangellia and Alexander terranes (Insular superterrane) and previously accreted terranes of the North American continental margin (Intermontane superterrane). The western metamorphic belt, which ranges from a few kilometers to several tens of kilometers in width, records a complex sequence of contact-metamorphic and regional metamorphic events, the most significant of which are designated M1R, M2C-R, and M3R. The M1R regional metamorphic event ranged in grade from subgreenschist to greenschist facies and was overprinted by the M2C-R and M3R metamorphic events. The M2C-R metamorphic event is recorded in discrete contact-metamorphic aureoles and regional metamorphic-mineral assemblages related to tonalite-granodiorite plutons of the Admiralty-Revillagigedo plutonic belt. The M3R metamorphic belt, which is adjacent to the M2C-R belt, is characterized by regional Barrovian isograds of garnet, staurolite, kyanite, and sillimanite. Using the THERMOCALC program, pressure-temperature (P-T) conditions for the M2C-R metamorphic event are estimated to be in the ranges 5.3-7.5 kbars and 525-640 deg.C and for the M3R metamorphic event in the ranges 9.4-12.6 kbars and 730-895 deg.C. The M2C-R metamorphic event occurred at approximately 90 Ma, but the timing of the M3R metamorphic event is poorly documented and uncertain. On the basis of an 40Ar/39Ar age on actinolitic amphibole and a Sm-Nd age on garnet core, the timing of metamorphism might be constrained between 90+/-1 and 80+/-9 Ma, although the Sm-Nd age of 80+/-9 m.y. possibly reflects postpeak growth. Thermobarometric data suggest that the two events occurred at different crustal levels and followed different P-T paths. No evidence exists that M2C-R metamorphic-mineral assemblages were

  10. Mesozoic age of the Gilyui Metamorphic Complex in the junction zone of the Selenga-Stanovoi and Dzhugdzhur-Stanovoi superterranes, Central Asian fold belt

    NASA Astrophysics Data System (ADS)

    Velikoslavinskii, S. D.; Kotov, A. B.; Kovach, V. P.; Larin, A. M.; Sorokin, A. A.; Sorokin, A. P.; Tolmacheva, E. V.; Salnikova, E. B.; Wang, K. L.; Jahn, B. M.; Cung, S. L.

    2016-06-01

    The Gilyui Complex includes sedimentary and volcanic rocks metamorphosed to amphibolite and epidote-amphibolite facies, which constitute blocks confined to the main structural sutures of the Dzhugdzhur-Stanovoi superterrane in the Central Asian fold belt. In recent stratigraphic scales, they are considered as being Neoarchean in age with Nd model age values of 1.5-3.0 Ga. The youngest detrital zircons from metamorphosed mudstone of the Gilyui Complex yield a date of 285 ± 4 Ma, which determines the lower age limit for the formation of its protolith. The age of crystallization of rhyolites from the Gilyui Complex is determined to be 231 ± 4 Ma. If the rhyolites form volcanic flow units or sills, the Gilyui Complex is approximately 230 Ma or 231 ± 4 to 285 ± 4 Ma old, respectively.

  11. Meeting Report: International Symposium on the Genetics of Aging and Life History II.

    PubMed

    Artan, Murat; Hwang, Ara B; Lee, Seung V; Nam, Hong Gil

    2015-06-01

    The second International Symposium on the Genetics of Aging and Life History was held at the campus of Daegu Gyeongbuk Institute of Science and Technology (DGIST), Daegu, South Korea, from May 14 to 16, 2014. Many leading scientists in the field of aging research from all over the world contributed to the symposium by attending and presenting their recent work and thoughts. The aim of the symposium was to stimulate international collaborations and interactions among scientists who work on the biology of aging. In the symposium, the most recent and exciting work on aging research was presented, covering a wide range of topics, including the genetics of aging, age-associated diseases, and cellular senescence. The work was conducted in various organisms, includingC. elegans, mice, plants, and humans. Topics covered in the symposium stimulated discussion of novel directions for future research on aging. The meeting ended with a commitment for the third International Symposium on the Genetics of Aging and Life History, which will be held in 2016.

  12. Ostwald ripening of clays and metamorphic minerals

    USGS Publications Warehouse

    Eberl, D.D.; Srodon, J.; Kralik, M.; Taylor, B.E.; Peterman, Z.E.

    1990-01-01

    Analyses of particle size distributions indicate that clay minerals and other diagenetic and metamorphic minerals commonly undergo recrystallization by Ostwald ripening. The shapes of their particle size distributions can yield the rate law for this process. One consequence of Ostwald ripening is that a record of the recrystallization process is preserved in the various particle sizes. Therefore, one can determine the detailed geologic history of clays and other recrystallized minerals by separating, from a single sample, the various particle sizes for independent chemical, structural, and isotopic analyses.

  13. Stratigraphic and structural implications of conodont and detrital zircon U-Pb ages from metamorphic rocks of the Coldfoot terrane, Brooks Range, Alaska

    USGS Publications Warehouse

    Moore, T.E.; Aleinikoff, J.N.; Harris, A.G.

    1997-01-01

    New paleontologic and isotopic data from the Emma Creek and Marion Creek schists of the Coldfoot terrane, Arctic Alaska superterrane, central Brooks Range, suggest Devonian and possibly younger ages of deposition for their sedimentary protoliths. Conodonts from marble of the Emma Creek schist, intruded by a roughly 392 Ma orthogneiss, are late Lochkovian (early Early Devonian, between about 408 and 396 Ma) and Silurian to Devonian at two other locations. Spherical to oblong detrital zircons from quartz-mica schist of the overlying Marion Creek schist yield mostly discordant U-Pb data suggestive of provenance ages of 3.0, 2.0-1.8, and 1.5-1.4 Ga; however, several euhedral grains of zircon from Marion Creek quartz-mica schist have concordant U-Pb ages from 370 to 360 Ma. The Marion Creek schist in our study area therefore is at least 26 m.y. younger than the Emma Creek schist. The age data imply that the protolith of the Emma Creek schist is age correlative with Devonian carbonate rocks in the Hammond and North Slope terranes, whereas the Marion Creek schist is age correlative with Upper Devonian and Lower Mississippian clastic sedimentary rocks of the Endicott Group in the Endicott Mountains terrane and shale and carbonate units in the De Long Mountains and Sheenjek River terranes. Consequently, tectonic models restoring the entire Coldfoot terrane beneath partly or wholly coeval rocks of the Hammond, Endicott Mountains, De Long Mountains, and Sheenjek River terranes of the Arctic Alaska superterrane require revision. Alternative reconstructions, including restoration of the Coldfoot terrane inboard of the Endicott Mountains terrane or outboard of the De Long Mountains and Sheenjek River terranes are plausible but require either larger amounts of shortening than previously suggested or indicate problematic facies relations. copyright. Published in 1997 by the American Geophysical Union.

  14. Equilibrium and kinetics in metamorphism

    NASA Astrophysics Data System (ADS)

    Pattison, D. R.

    2012-12-01

    The equilibrium model for metamorphism is founded on the metamorphic facies principle, the repeated association of the same mineral assemblages in rocks of different bulk composition that have been metamorphosed together. Yet, for any metamorphic process to occur, there must be some degree of reaction overstepping (disequilibrium) to initiate reaction. The magnitude and variability of overstepping, and the degree to which it is either a relatively minor wrinkle or a more substantive challenge to the interpretation of metamorphic rocks using the equilibrium model, is an active area of current research. Kinetic barriers to reaction generally diminish with rising temperature due to the Arrhenius relation. In contrast, the rate of build-up of the macroscopic energetic driving force needed to overcome kinetic barriers to reaction, reaction affinity, does not vary uniformly with temperature, instead varying from reaction to reaction. High-entropy reactions that release large quantities of H2O build up reaction affinity more rapidly than low-entropy reactions that release little or no H2O, such that the former are expected to be overstepped less than the latter. Some consequences include: (1) metamorphic reaction intervals may be discrete rather than continuous, initiating at the point that sufficient reaction affinity has built up to overcome kinetic barriers; (2) metamorphic reaction intervals may not correspond in a simple way to reaction boundaries in an equilibrium phase diagram; (3) metamorphic reactions may involve metastable reactions; (4) metamorphic 'cascades' are possible, in which stable and metastable reactions involving the same reactant phases may proceed simultaneously; and (5) fluid generation, and possibly fluid presence in general, may be episodic rather than continuous, corresponding to discrete intervals of reaction. These considerations bear on the interpretation of P-T-t paths from metamorphic mineral assemblages and textures. The success of the

  15. Constraining the Star Forming History in Monoceros: A Study of Embedded Cluster Ages and Spatial Structure

    NASA Astrophysics Data System (ADS)

    Lada, Elizabeth A.; Marinas, Naibi; Levine, Joanna L.; Ferreira, Bruno

    2009-08-01

    We propose to use FLAMINGOS multi-object spectrometer on the KPNO 4 meter telescope to complete a spectroscopic survey of 7 clusters in the Monoceros GMC. The data will be combined with existing FLAMINGOS photometry to determine the ages and masses of the stars in the clusters using the HR Diagram and PMS evolutionary models. This information, combined with the spatial distribution of clusters in the cloud, determined from previous observations, will allow us to investigate the ages and age spreads of the embedded clusters and the star forming histories of the clusters and the molecular cloud.

  16. Constraining the Star Forming History in Monoceros: A Study of Embedded Cluster Ages and Spatial Structure

    NASA Astrophysics Data System (ADS)

    Marinas, Naibi; Lada, Elizabeth; Ybarra, Jason; Fleming, Scott

    2010-08-01

    We propose to use FLAMINGOS multi-object spectrometer on the KPNO 4 meter telescope to complete a spectroscopic survey of 5 clusters in the Monoceros GMC. The data will be combined with existing FLAMINGOS photometry to determine the ages and masses of the stars in the clusters using the HR Diagram and PMS evolutionary models. This information, combined with the spatial distribution of clusters in the cloud, determined from previous observations, will allow us to investigate the ages and age spreads of the embedded clusters and the star forming histories of the clusters and the molecular cloud.

  17. Formation Ages of the Apollo 16 Regolith Breccias: Implications for Accessing the Bombardment History of the Moon

    NASA Technical Reports Server (NTRS)

    Joy, K. H.; Kring, D. A.; Bogard, D. D.; Zolensky, M. E.; McKay, D. S.

    2010-01-01

    Regolith breccias are lithified samples of the regolith that have been fused together by impact shock and thermal metamorphism. In lunar regolith samples, the ratio of trapped 40Ar/36Ar is a useful indicator of antiquity and can be used to model the closure age/lifithication event of the regolith (i.e. the apparent time when Ar became trapped [1]), thus providing an important insight into specific times when that regolith was interacting with the the dynamic inner solar system space environment [2-4].

  18. History vs. snapshot: how slab morphology relates to slab age evolution

    NASA Astrophysics Data System (ADS)

    Garel, Fanny; Goes, Saskia; Davies, Rhodri; Davies, Huw; Lallemand, Serge; Kramer, Stephan; Wilson, Cian

    2016-04-01

    The age of the subducting plate at the trench ("slab age") spans a wide range, from less than 10 Myr in Central and South America to 150 Myr in the Marianas. The morphology of subducting slab in the upper mantle is also very variable, from slabs stagnating at the top of the lower mantle to slabs penetrating well beyond 1000 km depth. People have looked rather unsucessfully for correlations between slab morphology and subduction parameters, including age at the trench, on the basic assumption that old (thick) plates are likely to generate a large slab pull force that would influence slab dip. Thermo-mechanical models reveal complex feedbacks between temperature, strain rate and rheology, and are able to reproduce the evolution of plate ages as a function of time, subducting plate velocity and trench velocity. In particular, we show how initially young subducting plates can rapidly age at the surface because of a slow sinking velocity. As a consequence, different slab morphologies can exhibit similar ages at the trench provided that subduction history is different. We illustrate how models provide insights into Earth subduction zones for which we have to consider their history (evolution of trench velocity, relative plate ages at time of initiation) in order to unravel their present-day geometry.

  19. Meeting Report: International Symposium on the Genetics of Aging and Life History II

    PubMed Central

    Lee, Seung‐Jae V.; Nam, Hong Gil

    2015-01-01

    The second International Symposium on the Genetics of Aging and Life History was held at the campus of Daegu Gyeongbuk Institute of Science and Technology (DGIST), Daegu, South Korea, from May 14 to 16, 2014. Many leading scientists in the field of aging research from all over the world contributed to the symposium by attending and presenting their recent work and thoughts. The aim of the symposium was to stimulate international collaborations and interactions among scientists who work on the biology of aging. In the symposium, the most recent and exciting work on aging research was presented, covering a wide range of topics, including the genetics of aging, age‐associated diseases, and cellular senescence. The work was conducted in various organisms, including C. elegans, mice, plants, and humans. Topics covered in the symposium stimulated discussion of novel directions for future research on aging. The meeting ended with a commitment for the third International Symposium on the Genetics of Aging and Life History, which will be held in 2016. PMID:26115541

  20. Paternal age effect on age of onset in bipolar I disorder is mediated by sex and family history.

    PubMed

    Grigoroiu-Serbanescu, Maria; Wickramaratne, Priya J; Mihailescu, Radu; Prelipceanu, Dan; Sima, Dorina; Codreanu, Marina; Grimberg, Mihaela; Elston, Robert C

    2012-07-01

    This study investigated for the first time in the psychiatric literature the effect of parental age on age-of-onset (AO) in bipolar I disorder (BPI) in relation to proband sex and family history (FH) for major psychoses in a sample of 564 BPI probands. All probands, 72.68% of their first-degree and 12.13% of their second-degree relatives were directly interviewed. The FH-method was used for all unavailable relatives. The diagnoses were made according to DSM-IV(TR) . The impact of parental age on proband early/late AO was evaluated through logistic regression with the cut-off for early AO determined through commingling analysis. We found evidence for a significant influence of increasing paternal age, and especially age ≥ 35 years, on AO of BPI disorder in the total sample (OR = 0.54, CI: 0.35-0.80), in the female subsample (OR = 0.44, CI: 0.25-0.78), in the sporadic subsample (OR = 0.64, CI: 0.38-0.95), and in the subsample with FH of recurrent unipolar major depression (Mdd-RUP) (OR = 0.55, CI: 0.34-0.87). No significant effect of paternal age on disease AO was found in patients with FH of bipolar (BP), schizoaffective disorders (SA), or schizophrenia (SCZ), nor in males. Mean age was significantly higher in fathers of sporadic cases and of cases with FH of Mdd-RUP than in fathers of cases with FH of BP/SA/SCZ (P = 0.011). Maternal age had no significant effect either in the total sample or in subsamples defined by proband sex or FH. In conclusion, in our sample increasing paternal age lowered the onset of BPI selectively, the effect being related to the female sex and FH-type.

  1. Natural history of obesity in 6,946 women between 50 and 59 years of age.

    PubMed Central

    Hartz, A J; Rimm, A A

    1980-01-01

    A health survey of 6946 50-to-59 year-old women of TOPS, an organization for weight reduction, was used to study the natural history of obesity. Weight history was compared for four groups of women divided on the basis of their per cent above ideal body weight (IBW) in their 50s (less than 20%, 20-49%, 50-99% and 100+%). In each of the four groups, the majority of women were not obese by age 20. Sixteen per cent of the women who were 100+% overweight in their 50s were not obese at anytime during their first 30 years of life. Thirty-six per cent of the women who were 50-99% about IBW were not overweight at anytime prior to their 30th birthday. The history of obesity prior to age 30 was not associated with weight gain between the ages of 30 and 50. These data suggest: 1) than there is no critical time for the development of obesity, and 2) that previous weight history is not a dominant factor in determining subsequent weight gain. PMID:7361956

  2. Metamorphic and stratigraphic constraints on the evolution of the Santa Catalina Mountains metamorphic core complex, Arizona

    SciTech Connect

    Palais, D.G.; Peacock, S.M. )

    1990-01-10

    Contact metamorphic mineral assemblages in the Santa Catalina Mountains metamorphic core complex constrain the emplacement depth of the metaluminous Late Cretaceous Leatherwood quartz diorite to between 7.5 and 14 km (2-3.8 kbar). The peraluminous Eocene Wilderness granite is constrained to have been emplaced at depths of less than 14 km. Stratigraphic and tectonic considerations are consistent with emplacement of both the Leatherwood quartz diorite and Wilderness granite at upper crustal levels. Published igneous thermobarometry (Anderson et al., 1988), although in approximate agreement with the metamorphic and tectonostratigraphic estimates for the depth of emplacement of the Wilderness granite, suggests that the Leatherwood quartz diorite was emplaced at depths of {approximately} 21 km (5.6 kbar) or greater. The discrepancy between the different emplacement estimates may reflect ambiguities associated with interpretations of the results from each technique. Igneous barometric assemblages may reflect conditions experienced during a period of crystallization during ascent of the magma through the crust (i.e., ponding of the magma). Alternatively, emplacement of the voluminous Wilderness granite and associated plutons may have entirely overprinted earlier Leatherwood-related contact metamorphism. The proposed upper crustal emplacement of the Leatherwood quartz diorite is consistent with the observation that Laramide-age crustal thickening in southeast Arizona probably did not exceed 8 km.

  3. Evolution of Himalayan Metamorphism and the Genesis of Inverted Metamorphic Gradients: Evidence From the Sutlej Valley, NW India

    NASA Astrophysics Data System (ADS)

    Caddick, M.; Bickle, M.; Holland, T.; Harris, N.

    2002-12-01

    An inverted metamorphic gradient is commonly preserved where the high-grade Greater Himalayan Crystalline Sequence (GHCS) overthrusts the Lesser Himalayan foreland. This structural break (the Main Central Thrust, or MCT) is a key feature of Himalayan tectonics, generally considered to have taken up at least 200-300 km of shortening since the Early Miocene. The timing of displacement along the MCT and its relationship with inverted metamorphism is debated, with existing temperature inversion models requiring either (a) post-metamorphic faulting along young shear zones; (b) continual or episodic syn-metamorphic thrust development; or (c) single phase pre- to syn-metamorphic thrusting and subsequent thermal relaxation. Here, we use the P-T-t evolution of individual rock samples to study the contrasting histories of the GHCS and LHS units and deduce the relationship between metamorphism and thrusting. The Sutlej River Valley exposes an inverted metamorphic succession consisting of a 9-km thick amphibolite-facies core (the GHCS), structurally underlain by greenschist and amphibolite-facies Lesser Himalayan Sequence (LHS) metapelites which preserve garnet-in, staurolite-in and kyanite/sillimanite-in isograds. The GHCS displays kyanite-in and sillimanite-in isograds, with migmatisation at the top of the sequence. A major thrust-zone (interpreted as the MCT) separates the LHS from the GHCS. The application of rim-thermobarometry to Sutlej samples identifies both the inverted metamorphic gradient in the LHS and GHCS units, and the inherent frailty of cation-exchange thermobarometers when studying high-grade rocks that have been subjected to subsequent retrograde diffusion. The construction of pseudosections and contouring of mineral composition isopleths, however, identifies the PT-paths that both units have taken, allowing a detailed reconstruction of the burial and uplift histories of the units that constitute the MCT-zone. Pseudosections in the systems KFMASH and Mn

  4. Signaling mechanisms underlying metamorphic transitions in animals.

    PubMed

    Heyland, Andreas; Moroz, Leonid L

    2006-12-01

    orchestrating life history transitions. Alternatively, these regulatory modules may have been used by the RCA for other purposes and have been independently co-opted to regulate metamorphic transitions in a variety of distantly related animals. We propose that such instances of independent origin or homoplasy in the evolution of metamorphosis might have resulted from specific constraints in signal transduction pathways. Modern genomic tools can help to further explore homoplastic signaling modules when used in a comparative context.

  5. Monazite geochronology of the Bodonch metamorphic complex, southwestern Mongolia

    NASA Astrophysics Data System (ADS)

    Cina, S. E.; Yin, A.; Dash, B.; Manning, C.

    2007-12-01

    The Bodonch metamorphic complex in southwestern Mongolia is a steeply dipping assemblage of low to high grade metamorphic rocks exposed along a ~30 km stretch of the Bodonch River which has been variably regarded as either a microcontinental block, due to presence of gneissic foliation; a metamorphic core complex; or an accretionary complex in the Central Asian Orogenic System. Metamorphic grade generally increases from subgreenschist facies at the southern margin of the complex to amphibolite facies in the central section, and decreases again to subgreenschist facies further to the north. Foliation is approximately E-W striking and predominately dips northward, although isoclinal folding is pervasive at all scales. Lithologically, the complex consists primarily of metapelites, with minor interbedded metavolcanics and metacherts. Carbonates and quartzites are generally absent and are observed only in thin depositional lenses. The entire complex is intruded by granitic dikes ranging from ~1 m in thickness to several tens of meters which postdate the metamorphism. The most striking feature of the Bodonch metamorphic complex is the occurrence of garnet bearing schist in the central section which contains zones of almost pure garnet mineralization. Along its southern margin, the assemblage is thrust over a sequence of unmetamorphosed to low grade Devonian-Carboniferous volcanics and sediments which are classified as belonging to an oceanic island arc terrane. Based on the observed lithologies, lack of crystalline basement, and style of deformation we favor the accretionary complex model for the tectonic origin of the Bodonch metamorphic complex. We present new Th-Pb ages of monazite inclusions in garnets obtained using in situ ion-microprobe techniques, which are interpreted to correspond to the timing of accretion related metamorphism.

  6. The Western Sierras Pampeanas: Protracted Grenville-age history (1330-1030 Ma) of intra-oceanic arcs, subduction-accretion at continental-edge and AMCG intraplate magmatism

    NASA Astrophysics Data System (ADS)

    Rapela, C. W.; Pankhurst, R. J.; Casquet, C.; Baldo, E.; Galindo, C.; Fanning, C. M.; Dahlquist, J. M.

    2010-01-01

    New U-Pb SHRIMP zircon ages combined with geochemical and isotope investigation in the Sierra de Maz and Sierra de Pie de Palo and a xenolith of the Precordillera basement (Ullún), provides insight into the identification of major Grenville-age tectonomagmatic events and their timing in the Western Sierras Pampeanas. The study reveals two contrasting scenarios that evolved separately during the 300 Ma long history: Sierra de Maz, which was always part of a continental crust, and the juvenile oceanic arc and back-arc sector of Sierra de Pie de Palo and Ullún. The oldest rocks are the Andino-type granitic orthogneisses of Sierra de Maz (1330-1260 Ma) and associated subalkaline basic rocks, that were part of an active continental margin developed in a Paleoproterozoic crust. Amphibolite facies metamorphism affected the orthogneisses at ca. 1175 Ma, while granulite facies was attained in neighbouring meta-sediments and basic granulites. Interruption of continental-edge magmatism and high-grade metamorphism is interpreted as related to an arc-continental collision dated by zircon overgrowths at 1170-1230 Ma. The next event consisted of massif-type anorthosites and related meta-jotunites, meta-mangerites (1092 ± 6 Ma) and meta-granites (1086 ± 10 Ma) that define an AMCG complex in Sierra de Maz. The emplacement of these mantle-derived magmas during an extensional episode produced a widespread thermal overprint at ca. 1095 Ma in neighbouring country rocks. In constrast, juvenile oceanic arc and back-arc complexes dominated the Sierra de Pie de Palo-Ullún sector, that was fully developed ca. 1200 Ma (1196 ± 8 Ma metagabbro). A new episode of oceanic arc magmatism at ˜1165 Ma was roughly coeval with the amphibolite high-grade metamorphism of Sierra de Maz, indicating that these two sectors underwent independent geodynamic scenarios at this age. Two more episodes of arc subduction are registered in the Pie de Palo-Ullún sector: (i) 1110 ± 10 Ma orthogneisses and

  7. Role of Family Resources and Paternal History of Substance Use Problems in Psychosocial Adjustment among School-Aged Children

    ERIC Educational Resources Information Center

    Peleg-Oren, Neta; Rahav, Giora; Teichman, Meir

    2009-01-01

    The present study examines the role of family resources (parenting style and family cohesion) and paternal history of substance abuse on the psychosocial adjustment of their school-aged children. Data were collected from 148 children aged 8-11 (72 of fathers with history of substance use disorder, 76 children of fathers with no substance use…

  8. Iron Age and Anglo-Saxon genomes from East England reveal British migration history

    PubMed Central

    Schiffels, Stephan; Haak, Wolfgang; Paajanen, Pirita; Llamas, Bastien; Popescu, Elizabeth; Loe, Louise; Clarke, Rachel; Lyons, Alice; Mortimer, Richard; Sayer, Duncan; Tyler-Smith, Chris; Cooper, Alan; Durbin, Richard

    2016-01-01

    British population history has been shaped by a series of immigrations, including the early Anglo-Saxon migrations after 400 CE. It remains an open question how these events affected the genetic composition of the current British population. Here, we present whole-genome sequences from 10 individuals excavated close to Cambridge in the East of England, ranging from the late Iron Age to the middle Anglo-Saxon period. By analysing shared rare variants with hundreds of modern samples from Britain and Europe, we estimate that on average the contemporary East English population derives 38% of its ancestry from Anglo-Saxon migrations. We gain further insight with a new method, rarecoal, which infers population history and identifies fine-scale genetic ancestry from rare variants. Using rarecoal we find that the Anglo-Saxon samples are closely related to modern Dutch and Danish populations, while the Iron Age samples share ancestors with multiple Northern European populations including Britain. PMID:26783965

  9. Iron Age and Anglo-Saxon genomes from East England reveal British migration history.

    PubMed

    Schiffels, Stephan; Haak, Wolfgang; Paajanen, Pirita; Llamas, Bastien; Popescu, Elizabeth; Loe, Louise; Clarke, Rachel; Lyons, Alice; Mortimer, Richard; Sayer, Duncan; Tyler-Smith, Chris; Cooper, Alan; Durbin, Richard

    2016-01-01

    British population history has been shaped by a series of immigrations, including the early Anglo-Saxon migrations after 400 CE. It remains an open question how these events affected the genetic composition of the current British population. Here, we present whole-genome sequences from 10 individuals excavated close to Cambridge in the East of England, ranging from the late Iron Age to the middle Anglo-Saxon period. By analysing shared rare variants with hundreds of modern samples from Britain and Europe, we estimate that on average the contemporary East English population derives 38% of its ancestry from Anglo-Saxon migrations. We gain further insight with a new method, rarecoal, which infers population history and identifies fine-scale genetic ancestry from rare variants. Using rarecoal we find that the Anglo-Saxon samples are closely related to modern Dutch and Danish populations, while the Iron Age samples share ancestors with multiple Northern European populations including Britain. PMID:26783965

  10. [Beyond the asylum -An other view on the history of psychiatry in the modern age].

    PubMed

    Fauvel, Aude

    2015-07-01

    If one thinks medicine, madness and the past, one image immediately pops into mind: that of the mental asylum. Following the famous work by Michel Foucault, Madness and Civilization: A History of Insanity in the Age of Reason, many historians have thus considered that the medicalization of insanity in the modern age had mostly led to a "great confinement" and a greater segregation of all individuals deemed mentally unfit during the "asylum era': However, new research demonstrates that this classic narrative of the psychiatric past needs to be revised. It discloses that, ever since the 191h century, a whole other medical culture existed as a challenge to asylums, a culture that advocated the integration of the mad and fought to disassociate psychiatry from the dominant model of confinement all throughout the occidental world. This article aims at presenting the results of these historical works that depict another aspect of the psychiatric history, exploring "boarding out" practices, instead of asylum ones.

  11. [Beyond the asylum -An other view on the history of psychiatry in the modern age].

    PubMed

    Fauvel, Aude

    2015-07-01

    If one thinks medicine, madness and the past, one image immediately pops into mind: that of the mental asylum. Following the famous work by Michel Foucault, Madness and Civilization: A History of Insanity in the Age of Reason, many historians have thus considered that the medicalization of insanity in the modern age had mostly led to a "great confinement" and a greater segregation of all individuals deemed mentally unfit during the "asylum era': However, new research demonstrates that this classic narrative of the psychiatric past needs to be revised. It discloses that, ever since the 191h century, a whole other medical culture existed as a challenge to asylums, a culture that advocated the integration of the mad and fought to disassociate psychiatry from the dominant model of confinement all throughout the occidental world. This article aims at presenting the results of these historical works that depict another aspect of the psychiatric history, exploring "boarding out" practices, instead of asylum ones. PMID:26111838

  12. Association of Family History of Epilepsy with Earlier Age Onset of Juvenile Myoclonic Epilepsy

    PubMed Central

    NAJAFI, Mohammad Reza; NAJAFI, Mohammad Amin; SAFAEI, Ali

    2016-01-01

    Objective Juvenile myoclonic epilepsy (JME) is supposedly the most frequent subtype of idiopathic generalized epilepsies (IGE). The aim of this study was to determine the prevalence of JME and comparison of patients’ demographics as well as timeline of the disease between positive family history epileptic patients (PFHE) and negative family history epileptic patients (NFHE) among sample of Iranian epileptic patients. Materials & Methods From Feb. 2006 to Oct. 2009, 1915 definite epileptic patients (873 females) referred to epilepsy clinics in Isfahan, central Iran, were surveyed and among them, 194 JME patients were diagnosed. JME was diagnosed by its specific clinical and EEG criteria. Patients were divided into two groups as PFHE and NFHE and data were compared between them. Results JME was responsible for 10% (194 patients) of all types of epilepsies. Of JME patients, 53% were female. In terms of family history of epilepsy, 40% were positive. No significant differences was found between PFHE and NFHE groups as for gender (P>0.05). Age of epilepsy onset was significantly earlier in PFHE patients (15 vs. 22 yr, P<0.001). Occurrence of JME before 18 yr old among PFHE patients was significantly higher (OR=2.356, P=0.007). Conclusion A family history of epilepsy might be associated with an earlier age of onset in patients with JME. PMID:27247579

  13. The history of bronchial asthma from the ancient times till the Middle Ages.

    PubMed

    Cserháti, E

    2004-01-01

    The aim of the paper is to give an overview of the knowledge on asthma through the history of mankind. The text begins with ancient China and it is finished with the medicine of Middle Age. During this time, a lot of theories came and this appeared about the etiology and therapy of the disease. The paper is giving a short description of the changing medical views during this very long period including China, Egypt Greco-roman period, Mesopotamia, the Hebrews, the physicians of India, the pre-Columbian medicine in the America and the Arabic world, and partly the European medicine of the Middle Ages.

  14. The history of bronchial asthma from the ancient times till the Middle Ages.

    PubMed

    Cserháti, E

    2004-01-01

    The aim of the paper is to give an overview of the knowledge on asthma through the history of mankind. The text begins with ancient China and it is finished with the medicine of Middle Age. During this time, a lot of theories came and this appeared about the etiology and therapy of the disease. The paper is giving a short description of the changing medical views during this very long period including China, Egypt Greco-roman period, Mesopotamia, the Hebrews, the physicians of India, the pre-Columbian medicine in the America and the Arabic world, and partly the European medicine of the Middle Ages. PMID:16438118

  15. Fission track studies of xenolithic chondrites - Implications regarding brecciation and metamorphism

    NASA Technical Reports Server (NTRS)

    Kothari, B. K.; Rajan, R. S.

    1982-01-01

    Fission tracks in phosphates from one gas-poor chondrite and three gas-rich ones are studied to determine their thermal history and brecciation time scales. Model fission track ages are calculated for given track densities due to Pu-244 and U-238; track densities and uranium measurements for whitlockite are shown, and possible sources of the tracks are mentioned. Details of track density and uranium measurements are discussed for each meteorite separately. Whitlockites from all the meteorites give model fission track ages of 4.4 Gyr assuming a Pu/U ratio at 4.55 Gyr of 0.045. The final brecciation event definitely did not reset the track clock in phosphates of one meteor and probably not in another two. It is concluded that the observed fission track ages date the end of metamorphic cooling in the meteorite parent bodies and support the planetesimal model for the formation of xenolithic chondrites.

  16. GENOMIC BASIS OF AGING AND LIFE HISTORY EVOLUTION IN DROSOPHILA MELANOGASTER

    PubMed Central

    Remolina, Silvia C.; Chang, Peter L.; Leips, Jeff; Nuzhdin, Sergey V.; Hughes, Kimberly A.

    2015-01-01

    Natural diversity in aging and other life history patterns is a hallmark of organismal variation. Related species, populations, and individuals within populations show genetically based variation in life span and other aspects of age-related performance. Population differences are especially informative because these differences can be large relative to within-population variation and because they occur in organisms with otherwise similar genomes. We used experimental evolution to produce populations divergent for life span and late-age fertility and then used deep genome sequencing to detect sequence variants with nucleotide-level resolution. Several genes and genome regions showed strong signatures of selection, and the same regions were implicated in independent comparisons, suggesting that the same alleles were selected in replicate lines. Genes related to oogenesis, immunity, and protein degradation were implicated as important modifiers of late-life performance. Expression profiling and functional annotation narrowed the list of strong candidate genes to 38, most of which are novel candidates for regulating aging. Life span and early-age fecundity were negatively correlated among populations; therefore the alleles we identified also are candidate regulators of a major life-history trade-off. More generally, we argue that hitchhiking mapping can be a powerful tool for uncovering the molecular bases of quantitative genetic variation. PMID:23106705

  17. Zircon Messengers Reveal the Age and History of Great Basin Crust, Kern Mountains, Nevada

    NASA Astrophysics Data System (ADS)

    Gottlieb, E. S.; Miller, E. L.; Wooden, J. L.

    2011-12-01

    Results of SHRIMP-RG analyses of complexly zoned zircons from muscovite-bearing granitic rocks exposed in the Kerns Mountains of East-Central Nevada constrain the timing, duration, and loci of zircon growth within the interior of the U.S. Cordillera during Late Cretaceous through Eocene time. The Kern Mountains are an exhumed block of greenschist to amphibolite facies metamorphosed miogeoclinal rocks that were pervasively intruded by the Late Cretaceous Tungstonia granite pluton and the Eocene Skinner Canyon and Uvada plutons (Best et al., 1974). Euhedral zircons separated from a coarse-grained (2-3 cm) muscovite-bearing phase of the Tungstonia pluton exhibit complex cathodeluminescence (CL) zonation. Sub-angular to sub-rounded cores with highly variable CL are overgrown by oscillatory-zoned zircon which in turn is rimmed by dark CL zircon (U>5000 ppm). A weighted mean Pb/U age of 70.2±0.9 Ma (n=20, MSWD=2.5) obtained from the oscillatory-zoned zircon coincides with the end of Cretaceous peak metamorphism at shallow crustal levels. Pb/U ages from core zones (n=18) predominantly are 0.9-1.4 Ga (n=11; 7 of which <15% discordant) or 2.4-2.7 Ga (n=5; 1 of which <15% discordant), consistent with ages of detrital zircons within the Late Proterozoic McCoy Creek Group exposed in adjacent ranges. A previously undated muscovite-bearing dike in Skinner Canyon yielded a texturally complex population of subhedral zircon grains. CL imaging of these grains reveals fragmental, ghost-like cores surrounded by irregularly shaped overgrowth zones with diffuse boundaries which are rimmed by oscillatory-zoned zircon. Both oscillatory zoned and gradational rim areas (n=32) yielded Late Cretaceous to Eocene ages. Twelve spots define the age of intrusion at 41.7±0.3 Ma (MSWD=1.8), consistent with the local onset of Eocene magmatism. An older period of zircon growth from ~75-45 Ma, coincident with the proposed duration of the Laramide shallow slab, is defined by zircon with flat to

  18. Age at menopause, reproductive history and venous thromboembolism risk among postmenopausal women

    PubMed Central

    Canonico, Marianne; Plu-Bureau, Geneviève; O’Sullivan, Mary Jo; Stefanick, Marcia L.; Cochrane, Barbara; Scarabin, Pierre-Yves; Manson, JoAnn E.

    2013-01-01

    Objectives To investigate VTE risk in relation to age at menopause, age at menarche, parity, bilateral oophorectomy and time since menopause, as well as any interaction with randomized HT assignment among postmenopausal women. Methods Using pooled data from the Women’s Health Initiative HT clinical trials including 27,035 postmenopausal women ages 50 to 79 years with no history of VTE, we assessed the risk of VTE in relation to age at menopause, age at menarche, parity, bilateral oophorectomy and time since menopause by Cox proportional hazard models. Linear trends, quadratic relationships and interactions of reproductive life characteristics with HT on VTE risk were systematically tested. Results During the follow-up, 426 women reported a first VTE, including 294 nonprocedure-related events. No apparent interaction of reproductive life characteristics with HT assignment on VTE risk was detected and there was any significant association of VTE with age at menarche, age at menopause, parity, oophorectomy or time since menopause. However, analyses restricted to nonprocedure-related VTE showed a U-shaped relationship between age at menopause and thrombotic risk that persisted after multivariable analysis (p<0.01). Compared to women aged 40 to 49 years at menopause, those with early menopause (age<40 years) or with late menopause (age>55 years) had a significant increased VTE risk (HR=1.8;95%CI:1.2–2.7 and HR=1.5;95%CI:1.0–2.4, respectively). Conclusion Reproductive life characteristics have little association with VTE and do not seem to influence the effect of HT on thrombotic risk among postmenopausal women. Nevertheless, early and late onset of menopause might be newly identified risk factors for nonprocedure-related VTE. PMID:23760439

  19. Age and zircon inheritance of eastern Blue Ridge plutons, southwestern North Carolina and northeastern Georgia, with implications for magma history and evolution of the southern Appalachian origin

    SciTech Connect

    Miller, C.F.; Hatcher, R.D. Jr.; Ayers, J.C.; Coath, C.D.; Harrison, T.M.

    2000-02-01

    High-resolution ion microprobe analysis of zircon has provided ages for previously undated plutons of the high-grade eastern Blue Ridge of northeastern Georgia and southwestern North Carolina. These data, together with backscattered electron imaging, reveal the presence of nearly ubiquitous inherited cores of highly variable age and magmatic rims that have experienced variable Pb loss, thus making interpretation of conventional U-Pb analyses very difficult. Ion probe rim analyses indicate that the plutons were emplaced during both the mod-Ordovician and mid-Devonian. Zircons from all intrusions have predominantly 1.0 to 1.25 Ga cores (Grenvillian). In addition, both Devonian and Ordovician plutons have smaller populations of Late Proterozoic-early Paleozoic (0.5--0.75 Ga), Middle Proterozoic (1.4 Ga), and Late Archean (2.6--2.9 Ga) cores. The ubiquitous, round cores and thick magmatic rims suggest significant resorption and then protracted growth within the melts. Zircon saturation temperatures based on whole-rock ({approximately}melt) Zr concentrations are lower than expected for magma generation (710--760 C). Zirconium concentrations may not reflect saturation at maximum temperature, if melting was very rapid (<{approximately}10{sup 5} yrs), or if zircon cores represent grains that were shielded from melt inside host grains for much of the magmatic history. Ages of magmatic and inherited zones of zircon from the plutons demonstrate that similar crust underlay the eastern Blue Ridge during both Taconian and Acadian orogenies, that there was no single episode of voluminous magmatism, and that metamorphism and deformation began before 470 Ma and continued after 370 Ma. These plutons do not constitute a significant convergence-related arc, though it is possible that they represent a displaced part of an arc that lies primarily to the east (in the Inner Piedmont?).

  20. New [sup 40]Ar/[sup 39]Ar mica ages from eastern New Hampshire and southern Maine: Implications for the exhumation history of the region

    SciTech Connect

    Lux, D.R.; West, D.P. Jr. . Dept. of Geological Science)

    1993-03-01

    It has long been recognized that micas from the high-grade metamorphic terrane of Maine and New Hampshire have anomalously young K-Ar ages. Furthermore, ages show systematic spatial patterns. Samples from western New Hampshire are youngest and become progressively older towards the east. In the Kearsarge-Central Maine Synclinorium (KCMS) of western Maine, ages are oldest along the northern terminus of high grade metamorphism and become progressively younger towards the southwest. In order to understand this peculiar relationship, micas from 20 sites in eastern New Hampshire and southern Maine were dated by the [sup 40]Ar/[sup 39]Ar method. The following relationships are observed: (1) Micas from the KCMS of southern New Hampshire have Permo-Carboniferous ages and coexisting micas are highly discordant, (2) micas from within or very near the Massabesic Gneiss Complex have young ages ([approximately]240--250 Ma) and show little to no discordance, (3) with one exception, micas from south of the Sebago batholith in Maine are also young ([approximately]240--250 Ma) and show little to no discordance. North of the Sebago batholith the transition to older micas is gradual. Mica ages from the Massabesic Gneiss Complex are younger than in surrounding regions and the transition to older ages roughly coincides with the Campbell Hill and Flint Hill faults. Outside the zone of young micas, cooling curves are concave upward for the same temperature interval. The young micas are concordant indicating rapid cooling but they are [approximately]40 Ma younger than the time of Late Paleozoic metamorphism. Therefore the young ages cannot be explained by rapid post-metamorphic cooling. The authors believe the accelerated cooling is the result of regional tectonic exhumation related to the earliest stages of rifting associated with opening of the Atlantic.

  1. Growth of mica porphyroblasts under low-grade metamorphism - A Taiwanese case using in-situ40Ar/39Ar laser microprobe dating

    NASA Astrophysics Data System (ADS)

    Chen, Chih-Tung; Chan, Yu-Chang; Lo, Ching-Hua; Lu, Chia-Yu

    2016-11-01

    Mica porphyroblasts, a common metamorphic microstructure, are analyzed in the slate belt of northern Taiwan where large fish-like growths are found within a meta-pyroclastics. With constraints on the time-temperature history from deposition through peak metamorphic state to exhumation, in-situ40Ar/39Ar laser microprobe dating was carried out on muscovite and corrensite fibers of mm-scale mica porphyroblasts grown on a pressure-solution seam. Because the peak metamorphic temperature and the porphyroblast formation condition (∼250 °C) remained far below the closure temperature of the K-Ar radioisotope system in muscovite, and the absence of muscovite in the mafic protolith, the dating results likely document the growth of the mica porphyroblast fabrics. The syn-kinematic nature of the analyzed porphyroblasts is confirmed by the ∼6 to ∼2.5 Ma growth ages, suggesting that the host rock was continuously deformed during the earlier two-thirds of the Taiwan Orogeny. The pattern of fiber growth, in contrast to outward-decreasing ages normally observed in peripheral recrystallization, appears random and resembles void fills in boudin openings. We postulate that syntaxial crack-seal following tensile micro-boudinage, along with slips on sub-grain boundaries, as a viable mechanism for the development of mica porphyroblasts and fish especially in lower-grade metamorphic rocks.

  2. The Utilization of Local History in Teaching American Religious History: A Gilded Age and Progressive Era North Dakota Case Study

    ERIC Educational Resources Information Center

    Price, Christopher Neal

    2013-01-01

    Teachers of college-level courses on American religious history generally leave out the importance of local and regional histories when telling the story of religion in America. The study of local history provides a fertile ground for understanding broad national trends in a local context. This dissertation focuses upon a little-studied religious…

  3. Application of Lu-Hf garnet dating to unravel the relationships between deformation, metamorphism and plutonism: An example from the Prince Rupert area, British Columbia

    NASA Astrophysics Data System (ADS)

    Wolf, David E.; Andronicos, Christopher L.; Vervoort, Jeffery D.; Mansfield, Michael R.; Chardon, Dominique

    2010-04-01

    The tectonic history of the Prince Rupert area is marked by profound crustal thickening from thrusting that produced inverted metamorphic field gradients and transpression in crustal-scale shear zones. Syn-tectonic garnet in the Prince Rupert area has Lu-Hf ages of 102.6 ± 3.7 Ma and 108.3 ± 4.1 Ma (2 σ). Porphyroblast-matrix relationships in these samples, and samples from the same outcrops, indicate syn-tectonic garnet growth. These relationships imply that the garnet ages directly date the development of the metamorphic foliations. A third sample of migmatitic garnet amphibolite from the contact aureole of the 94-90 Ma Ecstall pluton had complex isotope systematics interpreted to indicate a garnet growth episode ˜ 105 Ma, similar to the ages obtained from the other samples and a growth or equilibration event at ˜ 94 Ma during pluton emplacement. The data show that the older Lu-Hf garnet ages date prograde metamorphism during foliation development and modification during pluton emplacement. The Ecstall pluton was emplaced 10 to 15 m.y. after regional metamorphism and thrust stacking in the Prince Rupert area. In order to place our samples in a regional tectonic context we compare our results to patterns of regional deformation, metamorphism and plutonism throughout the North American Cordillera in the time period between 110 and 85 Ma. Contractional and transpressional deformation occurred throughout much of the North American Cordillera at this time, from southeastern Alaska to the Baja Peninsula in Mexico. Left-lateral transpression dominated the Canadian Cordillera, whereas, right-lateral transpression affected areas south of the Idaho-Salmon River suture zone, including the Sierra Nevada batholith. This reversal in kinematics in the northern and southern cordillera within coeval magmatic belts appears to be a first-order feature of the geology of the North American Cordillera during the Cretaceous.

  4. Interactive effects of working memory and trial history on Stroop interference in cognitively healthy aging.

    PubMed

    Aschenbrenner, Andrew J; Balota, David A

    2015-03-01

    Past studies have suggested that Stroop interference increases with age; however the robustness of this effect after controlling for processing speed has been questioned. Both working memory (WM) and the congruency of the immediately preceding trial have also been shown to moderate the magnitude of Stroop interference. Specifically, interference is smaller both for individuals with higher working memory capacity and following an incongruent trial. At present, it is unclear whether and how these 3 variables (age, WM and previous congruency) interact to predict interference effects in the standard Stroop color-naming task. We present analyses of Stroop interference in a large database of Stroop color-naming trials from a lifespan sample of well-screened, cognitively healthy, older adults. Our results indicated age-related increases in interference (after controlling for processing speed) that were exaggerated for individuals with low WM. This relationship between age and WM occurred primarily when the immediately preceding trial was congruent. Following an incongruent trial, interference increased consistently with age, regardless of WM. Taken together, these results support previous accounts of multiple mechanisms underlying control in the Stroop task and provide insight into how each component is jointly affected by age, WM, and trial history.

  5. The eastern limit of Acadian high grade metamorphism in northern New England: Implications for the location of the Acadian Suture''

    SciTech Connect

    West, D.P. Jr. . Dept. of Geological Sciences)

    1993-03-01

    Identifying the eastern limit of Acadian high grade metamorphism in New England is complicated by the presence of pre-Devonian high grade relics, locally intense Late Paleozoic thermal overprints, and post-metamorphic faults. New [sup 40]Ar/[sup 39]Ar mineral ages from along the eastern margin of high grade metamorphism in Maine and New Hampshire help delineate the eastern limit of Devonian amphibolite facies metamorphism thereby placing constraints on the location of the Acadian suture. In New Hampshire, Acadian high grade metamorphism extends southeast at least as far as the Campbell Hill fault and perhaps as far as the Flint Hill fault. New [sup 40]Ar/[sup 39]Ar hornblende ages and previously published U-Pb monazite ages from the Massabesic Gneiss Complex are Permian indicating high grade Alleghanian metamorphism. New [sup 40]Ar/[sup 39]Ar hornblende ages from the Rye Formation, although complicated by excess argon, are considerably older, indicating an earlier Pre-Silurian amphibolite facies metamorphism affected these rocks. North of Portland, [sup 40]Ar/[sup 39]Ar hornblende ages east of the Norumbega Fault Zone from high grade rocks of the Casco Bay Group have ages that range from Middle Devonian to Early Carboniferous, consistent with diachronous cooling following Acadian metamorphism. Further northeast, in upper amphibolite facies rocks of the Passagassawakeag Gneiss, new [sup 40]Ar/[sup 39]Ar hornblende ages range from 385--395 Ma suggesting that these rocks were also affected by high grade Acadian metamorphism.

  6. Contrasting metamorphism across cauvery shear zone, south India

    NASA Astrophysics Data System (ADS)

    John, Manish M.; Balakrishnan, S.; Bhadra, B. K.

    2005-04-01

    The Palghat Cauvery Shear Zone (CSZ) is a major shear zone that possibly extends into different fragments of Gondwanaland. In the present study mafic granulites occurring on either side of the CSZ in Namakkal area, southern India are examined. Textural features recorded in the mafic granulites are crucial in elucidating the metamorphic history of the southern granulite terrane (SGT). In the mafic granulites occurring to the south of CSZ, evidence of garnet breaking down during near isothermal decompression (ITD) is indicated by the development of orthopyroxene + plagioclase moats in between quartz and garnet. The presence of comparatively small elongated second generation garnet embedded in pyroxenes from the mafic granulites occurring to the north of CSZ is indicative of the garnet formation via reaction between pyroxenes and plagioclase, which occurred during isobaric cooling (IBC). Rocks occurring to the south of CSZ have recorded comparatively higher temperature and pressure (849‡C and 9.6kbar) than those occurring to the north of the CSZ (731‡C and 8.6kbar) using conventional geothermobarometry. The rocks occurring to the north of CSZ have suffered more complex metamorphic histories in comparison to the southern part. Integrating the results of the present field and metamorphic studies with the earlier investigations and available geochronological data we suggest that the CSZ could represent a suture zone between two different continental blocks that underwent distinct metamorphic evolution.

  7. Health maintenance in school-aged children: Part I. History, physical examination, screening, and immunizations.

    PubMed

    Riley, Margaret; Locke, Amy B; Skye, Eric P

    2011-03-15

    The goals of the well-child examination in school-aged children (kindergarten through early adolescence) are promoting health, detecting disease, and counseling to prevent injury and future health problems. A complete history should address any concerns from the patient and family and screen for lifestyle habits, including diet, physical activity, daily screen time (e.g., television, computer, video games), hours of sleep per night, dental care, and safety habits. School performance can be used for developmental surveillance. A full physical examination should be performed; however, the U.S. Preventive Services Task Force recommends against routine scoliosis screening and testicular examination. Children should be screened for obesity, which is defined as a body mass index at or above the 95th percentile for age and sex, and resources for comprehensive, intensive behavioral interventions should be provided to children with obesity. Although the evidence is mixed regarding screening for hypertension before 18 years of age, many experts recommend checking blood pressure annually beginning at three years of age. The American Academy of Pediatrics recommends vision and hearing screening annually or every two years in school-aged children. There is insufficient evidence to recommend screening for dyslipidemia in children of any age, or screening for depression before 12 years of age. All children should receive at least 400 IU of vitamin D daily, with higher doses indicated in children with vitamin D deficiency. Children who live in areas with inadequate fluoride in the water (less than 0.6 ppm) should receive a daily fluoride supplement. Age-appropriate immunizations should be given, as well as any missed immunizations. PMID:21404978

  8. Health maintenance in school-aged children: Part I. History, physical examination, screening, and immunizations.

    PubMed

    Riley, Margaret; Locke, Amy B; Skye, Eric P

    2011-03-15

    The goals of the well-child examination in school-aged children (kindergarten through early adolescence) are promoting health, detecting disease, and counseling to prevent injury and future health problems. A complete history should address any concerns from the patient and family and screen for lifestyle habits, including diet, physical activity, daily screen time (e.g., television, computer, video games), hours of sleep per night, dental care, and safety habits. School performance can be used for developmental surveillance. A full physical examination should be performed; however, the U.S. Preventive Services Task Force recommends against routine scoliosis screening and testicular examination. Children should be screened for obesity, which is defined as a body mass index at or above the 95th percentile for age and sex, and resources for comprehensive, intensive behavioral interventions should be provided to children with obesity. Although the evidence is mixed regarding screening for hypertension before 18 years of age, many experts recommend checking blood pressure annually beginning at three years of age. The American Academy of Pediatrics recommends vision and hearing screening annually or every two years in school-aged children. There is insufficient evidence to recommend screening for dyslipidemia in children of any age, or screening for depression before 12 years of age. All children should receive at least 400 IU of vitamin D daily, with higher doses indicated in children with vitamin D deficiency. Children who live in areas with inadequate fluoride in the water (less than 0.6 ppm) should receive a daily fluoride supplement. Age-appropriate immunizations should be given, as well as any missed immunizations.

  9. Microsurgical varicocelectomy for infertile couples with advanced female age: natural history in the era of ART.

    PubMed

    O'Brien, Jeanne H; Bowles, Ben; Kamal, Khaled M; Jarvi, Keith; Zini, Armand

    2004-01-01

    Varicocele represents the most common cause of male infertility, and most reports indicate that varicocelectomy has a beneficial effect on male fertility and pregnancy outcome. Assisted reproductive technologies (ARTs) are an alternative to varicocelectomy for the management of couples with a varicocele. The age of the female partner is important in the decision-making process; however, the true influence of female age on pregnancy outcome following varicocelectomy or ART in these couples is unknown. We evaluated the outcomes of 2 cohorts of infertile men with a varicocele and a female partner 35 years of age or older; one group selected varicocelectomy and the other a nonsurgical approach. We reviewed a group of consecutive infertile men who underwent microsurgical varicocelectomy and whose partners are 35 years of age or older (n = 110). We also reviewed a consecutive group of men with varicoceles who elected not to have surgery and whose partners are 35 years of age or older (n = 94). The outcome measures included changes in semen parameters, pregnancy rates (assisted and unassisted), and use of ART. The surgical and nonsurgical groups had comparable semen parameters and female ages. Mean sperm concentration and motility increased significantly after varicocelectomy (P < .05). At a mean of 30 months follow-up, 35% of couples in the surgical group achieved a spontaneous pregnancy and an additional 6% achieved a pregnancy via ART (20% of this group attempted ART). In the nonsurgical group, 25% achieved a spontaneous pregnancy and an additional 16% achieved a pregnancy with ART (40% of this group attempted ART). This study on the natural history of infertile men with varicocele and advanced female age suggests that the surgical and nonsurgical approaches offer comparable pregnancy outcome (combined assisted and unassisted pregnancy rates are about 40%). Overall, these data suggest that varicocelectomy is an acceptable option for couples with advanced female age

  10. Age-velocity dispersion relations and heating histories in disc galaxies

    NASA Astrophysics Data System (ADS)

    Aumer, Michael; Binney, James; Schönrich, Ralph

    2016-10-01

    We analyse the heating of stellar discs by non-axisymmetric structures and giant molecular clouds (GMCs) in N-body simulations of growing disc galaxies. The analysis resolves long-standing discrepancies between models and data by demonstrating the importance of distinguishing between measured age-velocity dispersion relations (AVRs) and the heating histories of the stars that make up the AVR. We fit both AVRs and heating histories with formulae ∝tβ and determine the exponents βR and βz derived from in-plane and vertical AVRs and tilde{β }_R and tilde{β }_z from heating histories. Values of βz are in almost all simulations larger than values of tilde{β }_z, whereas values of βR are similar to or mildly larger than values of tilde{β }_R. Moreover, values of βz (tilde{β }_z) are generally larger than values of βR (tilde{β }_R). The dominant cause of these relations is the decline over the life of the disc in importance of GMCs as heating agents relative to spiral structure and the bar. We examine how age errors and biases in solar neighbourhood surveys influence the measured AVR: they tend to decrease β values by smearing out ages and thus measured dispersions. We compare AVRs and velocity ellipsoid shapes σz/σR from simulations to solar neighbourhood data. We conclude that for the expected disc mass and dark halo structure, combined GMC and spiral/bar heating can explain the AVR of the Galactic thin disc. Strong departures of the disc mass or the dark halo structure from expectation spoil fits to the data.

  11. Settlement and landscape history of the Northern Franconian Jura during the Bronze and Iron Ages

    NASA Astrophysics Data System (ADS)

    Kothieringer, Katja; Lambers, Karsten; Seregély, Timo; Schäfer, Andreas

    2014-05-01

    This paper describes the results of initial archaeological and geoarchaeological fieldwork in the Northern Franconian Jura between the cities of Bayreuth and Bamberg. Our research aims at the reconstruction of settlement patterns and strategies of land use during the Metal Ages (Bronze Age and Iron Age) in the catchment area of the river Weismain. The project is designed as a case study for research into the settlement and landscape history of a rural region of the Central German Uplands during the last two millennia before our era. During the Bronze Age and Iron Age (about 2.100 BC to 30 BC), the Northern Franconian Jura must have been densely populated, as evidenced by numerous burial monuments, prominent hillforts like the Staffelberg, and ritual places on the Jurassic plateau. However, little is known about small rural settlements and hamlets which would have accounted for most of the settlement activity in the region. Thus, we lack the most important element for understanding the cultural history and development of the region as well as the consequences of human impact on the landscape. This impact must have induced changes in vegetation and subsequent erosion processes, leading to the formation of geoarchives like colluvial layers. During our initial fieldwork we identified such colluvial layers in depressions on the Jurassic plateau or at footslope positions. As radiocarbon datings of charcoal fragments showed, some of them date from the Metal Ages. The type is wood of these charcoal fragments is oak, which recently only occurs sporadically in mixed forests with beeches. The quantification of the shift of sediments from the plateau to the valleys will be the next important step of geoarchaeological research. Thus, investigations both on the plateau and in the river valleys will accompany archaeological survey. Apart from landscape reconstruction, they will also provide information on the state of preservation and the conditions for identifying archaeological

  12. Coupling of Oceanic and Continental Crust During Eocene Eclogite-Facies Metamorphism: Evidence From the Monte Rosa Nappe, Western Alps, Italy

    NASA Astrophysics Data System (ADS)

    Lapen, T. J.; Johnson, C. M.; Baumgartner, L. P.; Skora, S.; Mahlen, N. J.; Beard, B. L.

    2006-12-01

    Subduction of continental crust to HP-UHP metamorphic conditions requires overcoming density contrasts that are unfavorable to deep burial, whereas exhumation of these rocks can be reasonably explained through buoyancy-assisted transport in the subduction channel to more shallow depths. In the western Alps, both continental and oceanic lithosphere has been subducted to eclogite-facies metamorphic conditions. The burial and exhumation histories of these sections of lithosphere bear directly on the dynamics of subduction and the stacking of units within the subduction channel. We address the burial history of the continental crust with high precision U-Pb rutile and Lu-Hf garnet geochronology of the eclogite-facies Monte Rosa nappe (MR), western Alps, Italy. U-Pb rutile ages from quartz-carbonate-white mica-rutile veins that are hosted within eclogite and schist of the MR, Gressoney Valley, Italy, indicate that it was at eclogite-facies metamorphic conditions at 42.6 +/- 0.6 Ma. The sample area (Indren glacier, Furgg zone; Dal Piaz, 2001) consists of eclogite boudins that are surrounded by micaceous schist. Associated with the eclogite and schist are quartz-carbonate-white mica-rutile veins that formed in tension cracks in the eclogite and along the contact between eclogite and surrounding schist. Intrusion of the veins occurred at eclogite-facies metamorphic conditions (480-570°C, >1.3-1.4 GPa) based on textural relations, oxygen isotope thermometry, and geothermobarometry. Lu-Hf geochronology of garnet from a chloritoid-talc-garnet-phengite-quartz-calcite-pyrite - chalcopyrite bearing boudin within talc-chloritoid whiteschists of the MR, Val d'Ayas, Italy (Chopin and Monie, 1984; Pawlig, 2001) yields an age of 40.54 +/- 0.36 Ma. The talc-chloritoid whiteschists from the area record pressures and temperatures of 1.6-2.4 GPa and 500-530°C (Chopin and Monie, 1984; Le Bayon et al., 2006) indicating near UHP metamorphic conditions. Based on the age, P-T, and textural

  13. Geochemical, geochronological characterization and tectonic setting of the metamorphic rocks from the Biga Peninsula, NW Turkey

    NASA Astrophysics Data System (ADS)

    Şengün, F.; Tunç, Ä.°. O.; Yiǧitbaş, E.

    2012-04-01

    The Biga Peninsula in the northwest Turkey is one of the world's important natural laboratories to study geochronology due to having complex geology. The Biga Peninsula has different metamorphic basements including Kazdağ Massif, Çamlıca metamorphics, Kemer metamorphics and Karadağ Massif under cover of the Cenozoic volcano-sedimentary association. The Çamlıca metamorphic assemblage are one of the most critical regions for understanding of the geology of northwestern Turkey. The Çamlıca metamorphic association located on the westernmost part of Turkey is mainly composed of the Andıktası formation, the Dedetepe formation and the Salihler formation, from bottom to top. Metasedimentary rocks of the Çamlıca metamorphics have high SiO2 and medium Al2O3 and TiO2 values. The protolith of these metasediments is arkose-subarkose and greywacke. However, whole-rock geochemistry for the HP eclogite/blueschist within the Çamlıca metamorphics suggests that their protolith was basalt with high TiO2 and K2O-Na2O content and Nb/Y ratios. REE pattern and trace element contents of the HP eclogite/blueschist similar to typical MORB based on tectonic discrimination diagrams. The metavolcanic rocks occurring on the lowest part of the Çamlıca metamorphicassociation has andesitic composition with calc-alkaline character. All metavolcanic rocks in this unit cluster within the volcanic arc field. Zircon grains from metavolcanic rocks and HP eclogite/blueschists were dated by LA-ICPMS. Zircon ages of two metavolcanic samples yielded 328.6 ± 3.5 Ma and 343.2 ± 2.6 Ma, respectively. These ages are interpreted as the time of protolith crystallization of metavolcanic rocks. Moreover, zircon ages from HP eclogite/blueschist yielded 338 ± 1.8 Ma (Early Carboniferous) which is interpreted as the age of protolith crystallization of HP eclogite/blueschist. Geochemical and isotopic data indicate that Early Carboniferous Variscan ages within the Sakarya Zone may form the eastern

  14. Exposure age and erosional history of an upland planation surface in the US Atlantic Piedmont

    USGS Publications Warehouse

    Stanford, S.D.; Seidl, M.A.; Ashley, G.M.

    2000-01-01

    The upland planation surface in the Piedmont of central New Jersey consists of summit flats, as much as 130 km2 in area, that truncate bedding and structure in diabase, basalt, sandstone, mudstone and gneiss. These flats define a low-relief regional surface that corresponds in elevation to residual hills in the adjacent Coastal Plain capped by a fluvial gravel of late Miocene age. A Pliocene fluvial sand is inset 50 m below the upland features. These associations suggest a late Miocene or early Pliocene age for the surface. To assess exposure age and erosional history, a 4??4 m core of clayey diabase saprolite on a 3 km2 remnant of the surface was sampled at six depths for atmospherically produced cosmogenic 10Be. The measured inventory, assuming a deposition rate of 1??3 x 106 atoms cm-2 a-1, yields a minimum exposure age of 227 000 years, or, assuming continuous surface erosion, a constant erosion rate of 10 m Ma-1. Because the sample site lies about 60 m above the aggradation surface of the Pliocene fluvial deposit, and itself supports a pre-Pliocene fluvial gravel lag, this erosion rate is too high. Rather, episodic surface erosion and runoff bypassing probably have produced an inventory deficit. Reasonable estimates of surface erosion (up to 10 m) and bypassing (up to 50 per cent of total precipitation) yield exposure ages of as much as 6??4 Ma. These results indicate that (1) the surface is probably of pre-Pleistocene age and has been modified by Pleistocene erosion, and (2) exposure ages based on 10Be inventories are highly sensitive to surface erosion and runoff bypassing. Copyright (C) 2000 John Wiley and Sons, Ltd.

  15. MEAN AGE GRADIENT AND ASYMMETRY IN THE STAR FORMATION HISTORY OF THE SMALL MAGELLANIC CLOUD

    SciTech Connect

    Cignoni, M.; Cole, A. A.; Tosi, M.; Gallagher, J. S.; Sabbi, E.; Anderson, J.; Nota, A.; Grebel, E. K.

    2013-10-01

    We derive the star formation history (SFH) in four regions of the Small Magellanic Cloud (SMC) using the deepest VI color-magnitude diagrams (CMDs) ever obtained for this galaxy. The images were obtained with the Advanced Camera for Surveys on board the Hubble Space Telescope (HST) and are located at projected distances of 0.°5-2° from the SMC center, probing the main body and the wing of the galaxy. We derived the SFHs of the four fields using two independent procedures to fit synthetic CMDs to the data. We compare the SFHs derived here with our earlier results for the SMC bar to create a deep pencil-beam survey of the global history of the central SMC. We find in all the six fields observed with HST a slow star formation (SF) pace from 13 to 5-7 Gyr ago, followed by a ≈2-3 times higher activity. This is remarkable because dynamical models do not predict a strong influence of either the Large Magellanic Cloud (LMC) or the Milky Way at that time. The level of the intermediate-age SF rate enhancement systematically increases toward the center, resulting in a gradient in the mean age of the population, with the bar fields being systematically younger than the outer ones. SF over the most recent 500 Myr is strongly concentrated in the bar, the only exception being the area of the SMC wing. The strong current activity of the latter is likely driven by interaction with the LMC. At a given age, there is no significant difference in metallicity between the inner and outer fields, implying that metals are well mixed throughout the SMC. The age-metallicity relations we infer from our best-fitting models are monotonically increasing with time, with no evidence of dips. This may argue against the major merger scenario proposed by Tsujimoto and Bekki in 2009, although a minor merger cannot be ruled out.

  16. Large impact crater histories of Mars: The effect of different model crater age techniques

    NASA Astrophysics Data System (ADS)

    Robbins, Stuart J.; Hynek, Brian M.; Lillis, Robert J.; Bottke, William F.

    2013-07-01

    Impact events that produce large craters primarily occurred early in the Solar System's history because the largest bolides were remnants from planetary formation. Determining when large impacts occurred on a planetary surface such as Mars can yield clues to the flux of material in the early inner Solar System which, in turn, can constrain other planetary processes such as the timing and magnitude of resurfacing and the history of the martian core dynamo. We have used a large, global planetary database in conjunction with geomorphologic mapping to identify craters superposed on the rims of 78 larger craters with diameters D ⩾ 150 km on Mars, ≈78% of which have not been previously dated in this manner. The densities of superposed craters with diameters larger than 10, 16, 25, and 50 km, as well as isochron fits were used to derive model crater ages of these larger craters and basins from which we derived an impact flux. In discussing these ages, we point out several internal inconsistencies of crater-age modeling techniques and chronology systems and, all told, we explain why we think isochron-fitting is the most reliable indicator of an age. Our results point to a mostly obliterated crater record prior to ˜4.0 Ga with the oldest preserved mappable craters on Mars dating to ˜4.3-4.35 Ga. We have used our results to constrain the cessation time of the martian core dynamo which we found to have occurred between the formation of Ladon and Prometheus basins, approximately 4.06-4.09 Ga. We also show that, overall, surfaces on Mars older than ˜4.0-4.1 Ga have experienced >1 km of resurfacing, while those younger than ˜3.8-3.9 Ga have experienced significantly less.

  17. Women in American History: A Series. Book Two, Women in the Ages of Expansion and Reform 1820-1860.

    ERIC Educational Resources Information Center

    Sanders, Beverly

    The document, one in a series of four on women in American history, discusses women in the ages of expansion and reform (1820-1860). Designed to supplement U.S. history textbooks, the book is presented in six chapters. Chapter I describes the "true woman," an ideal cultivated by women writers, educators, and magazine editors. The four virtues were…

  18. Natural history of age-related lobular involution and impact on breast cancer risk.

    PubMed

    Radisky, Derek C; Visscher, Daniel W; Frank, Ryan D; Vierkant, Robert A; Winham, Stacey; Stallings-Mann, Melody; Hoskin, Tanya L; Nassar, Aziza; Vachon, Celine M; Denison, Lori A; Hartmann, Lynn C; Frost, Marlene H; Degnim, Amy C

    2016-02-01

    Age-related lobular involution (LI) is a physiological process in which the terminal duct lobular units of the breast regress as a woman ages. Analyses of breast biopsies from women with benign breast disease (BBD) have found that extent of LI is negatively associated with subsequent breast cancer development. Here we assess the natural course of LI within individual women, and the impact of progressive LI on breast cancer risk. The Mayo Clinic BBD cohort consists of 13,455 women with BBD from 1967 to 2001. The BBD cohort includes 1115 women who had multiple benign biopsies, 106 of whom had developed breast cancer. Within this multiple biopsy cohort, the progression of the LI process was examined by age at initial biopsy and time between biopsies. The relationship between LI progression and breast cancer risk was assessed using standardized incidence ratios and by Cox proportional hazards analysis. Women who had multiple biopsies were younger age and had a slightly higher family history of breast cancer as compared with the overall BBD cohort. Extent of LI at subsequent biopsy was greater with increasing time between biopsies and for women age 55 + at initial biopsy. Among women with multiple biopsies, there was a significant association of higher breast cancer risk among those with involution stasis (lack of progression, HR 1.63) as compared with those with involution progression, p = 0.036. The multiple biopsy BBD cohort allows for a longitudinal study of the natural progression of LI. The majority of women in the multiple biopsy cohort showed progression of LI status between benign biopsies, and extent of progression was highest for women who were in the perimenopausal age range at initial biopsy. Progression of LI status between initial and subsequent biopsy was associated with decreased breast cancer risk. PMID:26846985

  19. Psychosocial Adjustment in School-age Girls With a Family History of Breast Cancer

    PubMed Central

    Bradbury, Angela R.; Patrick-Miller, Linda; Schwartz, Lisa; Egleston, Brian; Sands, Colleen Burke; Chung, Wendy K.; Glendon, Gord; McDonald, Jasmine A.; Moore, Cynthia; Rauch, Paula; Tuchman, Lisa; Andrulis, Irene L.; Buys, Saundra S.; Frost, Caren J.; Keegan, Theresa H.M.; Knight, Julia A.; Terry, Mary Beth; John, Esther M.; Daly, Mary B.

    2016-01-01

    OBJECTIVE Understanding how young girls respond to growing up with breast cancer family histories is critical given expansion of genetic testing and breast cancer messaging. We examined the impact of breast cancer family history on psychosocial adjustment and health behaviors among >800 girls in the multicenter LEGACY Girls Study. METHODS Girls aged 6 to 13 years with a family history of breast cancer or familial BRCA1/2 mutation (BCFH+), peers without a family history (BCFH−), and their biological mothers completed assessments of psychosocial adjustment (maternal report for 6- to 13-year-olds, self-report for 10- to 13-year-olds), breast cancer–specific distress, perceived risk of breast cancer, and health behaviors (10- to 13-year-olds). RESULTS BCFH+ girls had better general psychosocial adjustment than BCFH− peers by maternal report. Psychosocial adjustment and health behaviors did not differ significantly by self-report among 10- to 13-year-old girls. BCFH+ girls reported higher breast cancer–specific distress (P = .001) and were more likely to report themselves at increased breast cancer risk than BCFH− peers (38.4% vs 13.7%, P < .001), although many girls were unsure of their risk. In multivariable analyses, higher daughter anxiety was associated with higher maternal anxiety and poorer family communication. Higher daughter breast cancer–specific distress was associated with higher maternal breast cancer-specific distress. CONCLUSIONS Although growing up in a family at risk for breast cancer does not negatively affect general psychosocial adjustment among preadolescent girls, those from breast cancer risk families experience greater breast cancer–specific distress. Interventions to address daughter and mother breast cancer concerns and responses to genetic or familial risk might improve psychosocial outcomes of teen daughters. PMID:26482668

  20. Penecontemporaneous metamorphism, fragmentation, and reassembly of ordinary chondrite parent bodies

    NASA Technical Reports Server (NTRS)

    Grimm, R. E.

    1985-01-01

    The thermal histories of ordinary chondrites and the canonical internal heating or onion shell models, which predict an inverse relation between the petrologic type of chondrites and the metallographic cooling rate, are reviewed. The thermal and accretional requirements of the 'metamorphosed planetesimal' model proposed by Scott and Rajan (1981) are analyzed, and an alternative model consistent with the metallographic cooling rate constraints is suggested in which ordinary chondrite parent bodies are collisionally fragmented and then rapidly reassembled before metamorphic heat has been dissipated.

  1. A strontium, neodymium and oxygen isotope study of hydrothermal metamorphism and crustal anatexis in the Trois Seigneurs Massif, Pyrenees, France

    NASA Astrophysics Data System (ADS)

    Bickle, M. J.; Wickham, S. M.; Chapman, H. J.; Taylor, H. P.

    1988-12-01

    within the Hercynian crust, both at Trois Seigneurs ( ɛ Nd=-3 to -7) and elsewhere in the Pyrenees; almost all igneous lithologies have depleted-mantle, mid-Proterozoic model ages, consistent with efficient recycling of crustal material following original crustal accretion in this area at about 1600 Ma or earlier. Rb-Sr mineral ages exhibit a complex cooling history reflecting late Hercynian and Mesozoic thermal events. Our results show that profound homogenization of the 87Sr/86Sr and 18O/16O ratios of large volumes of the crust can occur during regional metamorphism and crustal anatexis, particularly in regions undergoing extensional tectonics. Such processes can significantly modify the isotopic compositions of the protoliths of granitic magmas; this may explain why many peraluminous Hercynian granitoids of Western Europe have anomalously low (87Sr/86Sr) initial values compared to their probable sedimentary parent rocks.

  2. Demographic patterns of Ferocactus cylindraceus in relation to substrate age and grazing history

    USGS Publications Warehouse

    Bowers, Janice E.

    1997-01-01

    Three subpopulations of Ferocactus cylindraceus, a short-columnar cactus of the Sonoran and Mojave deserts, were sampled in Grand Canyon, Arizona, USA, at sites representing a range of substrate ages and different grazing histories. Age-height relations were determined from annual growth, then used to estimate probable year of establishment for each cohort. Eight years between 1944 and 1992 were especially favorable for establishment. Six of these 8 years coincided with El Nino-Southern Oscillation conditions, indicating that as for many woody plants in arid regions, somewhat unusual climatic conditions are necessary if populations are to replace themselves. Comparison of age structures showed that established and developing populations have somewhat different dynamics in that the rate of population increase was slowest on the youngest terrace. On the ancient terraces, about half the plants were less than 25 years old. Plants older than 40 years were few; however the oldest plants in the study (about 49 years) grew on the ancient terraces. On the recent terrace, 76% of the subpopulation was 25 years or younger, and the oldest living plant was about 36 years of age. The age structures of subpopulations on grazed and ungrazed sites also differed markedly. On ungrazed sites, subpopulations were more or less at equilibrium, with enough young plants to replace old ones as they died. In contrast, the subpopulation on the grazed site was in a state of marked disequilibrium. Grazing before 1981 largely extirpated a palatable subshrub that was probably an important nurse plant. Until the shrub population at Indian Canyon recovers from decades of burro grazing, a rebound in E cylindraceus establishment is not to be expected.

  3. Accessing probable thermal histories through dispersed, partially-reset zircon (U-Th)/He ages

    NASA Astrophysics Data System (ADS)

    Powell, Jeremy; Schneider, David

    2016-04-01

    exhibited by the datasets. We do not recommend selecting only the youngest dates from samples or averaging (U-Th)/He dates, as these methods do not acknowledge the complexity of the (U-Th)/He system and potentially exclude non-obvious, but equally probable, geologic scenarios. To this extent, using the vertical profile approach to assess exhumation rates from cooling age data may also provide an inaccurate result if the strata have not been buried to sufficient temperatures to completely reset any prior thermal history. As an alternative, we analyzed more grains from individual samples and combine data from similar structural regions to assess regional trends in thermal history. We believe that this approach does an appropriate job of acknowledging the errors and assumptions involved in the technique while providing meaningful information on thermal history of a region. Thermal modeling of the Mackenzie Mountains data reveals that (1) a substantial sedimentary package was deposited following the Devonian and removed during Permo-Triassic cooling, and (2) the Cordilleran deformation front propagated through the study area from the Albian to the Paleocene, with a moderate increase in cooling rates between 75-67 Ma in the southwest, and 60-55 Ma at the deformation front.

  4. Controlling for Landform Age When Determining the Settlement History of the Kuril Islands

    PubMed Central

    MacInnes, Breanyn; Fitzhugh, Ben; Holman, Darryl

    2014-01-01

    Archaeological investigations of settlement patterns in dynamic landscapes can be strongly biased by the evolution of the Earth’s surface. The Kuril Island volcanic arc exemplifies such a dynamic landscape, where landscape-modifying geological forces were active during settlement, including sea-level changes, tectonic emergence, volcanic eruptive processes, coastal aggradation, and dune formation. With all these ongoing processes, in this paper we seek to understand how new landscape formation in the Holocene might bias archaeological interpretations of human settlement in the Kurils. Resolving this issue is fundamental to any interpretation of human settlement history derived from the distribution and age of archaeological sites from the region. On the basis of a comparison of landform ages and earliest archaeological occupation ages on those landforms, we conclude that landform creation did not significantly bias our aggregate archaeological evidence for earliest settlement. Some sections of the archipelago have larger proportions of landform creation dates closer to archaeological evidence of settlement and undoubtedly some archaeological sites have been lost to geomorphic processes. However, comparisons between regions reveal comparable archaeological establishment patterns irrespective of geomorphic antiquity. PMID:25684855

  5. Permo-Triassic and Paleoproterozoic metamorphism related to continental collision in Yangpyeong, South Korea

    NASA Astrophysics Data System (ADS)

    Oh, Chang Whan; Imayama, Takeshi; Lee, Seung Yeol; Yi, Sang-Bong; Yi, Keewook; Lee, Byung Choon

    2015-02-01

    Gneisses and migmatites exposed in the Yangpyeong area in the northern Gyeonggi Massif provide insight into the Paleoproterozoic and Triassic metamorphic events in South Korea. Garnet-biotite gneiss and sillimanite-garnet-biotite gneiss in the western part of the area reveal Paleoproterozoic metamorphism (1888-1871 Ma) at P-T conditions of 760-820 °C and 8-10 kbar and 710-750 °C and 5-7 kbar, respectively. These rocks were overprinted by low-P/T type metamorphism (590-650 °C, 3-4 kbar) during the Triassic (ca. 237 Ma). In contrast, a cordierite-rich migmatite near the post-collisional Triassic igneous complex in the eastern part of the area was strongly metamorphosed during the Triassic (ca. 235 Ma) at 750-790 °C and 7-8 kbar. The similar Triassic ages in the western and eastern areas suggest that low-P/T type metamorphism occurred as a second stage of regional metamorphism, which is characterized by the production of cordierite with an irregularly shaped garnet. The metamorphic grade of the Triassic metamorphism decreases spatially towards the west from granulite facies to amphibolite facies metamorphic conditions, and the Paleoproterozoic metamorphism is well preserved in the western part with low grade Triassic metamorphism. The new discovery of the Triassic metamorphic event in the Yangpyeong area, in addition to the previously reported Triassic post-collision igneous event, supports the idea that the continental collision belt between the North and South China blocks extends from the Hongseong area into the Odesan area through the Yangpyeong area in South Korea.

  6. Three Dimensional Petrography of Kernouve: A Story of Vein Formation, Compaction, and Metamorphism

    SciTech Connect

    Friedrich, J.M.; Ruzicka, A.; Ebel, D.S.; Thostenson, J.; Rudolph, R.A.; Rivers, M.L.; Macke, R.J.; Britt, D.T.

    2012-03-26

    Metallic veins in ordinary chondrites, like those found in Kernouve (H5, S1), have been attributed to impact or shock processes on the parent body. However, Kernouve is widely known to exhibit few traditional signs of shock loading and has a very old {sup 39}Ar-{sup 40}Ar age (4.46 Ga), making the significance of vein formation in Kernouve unclear. One possibility is early vein formation followed by partial obliteration due to thermal metamorphism. We examine this scenario here. The metal vein in Kernouve can be explained as a pre-metamorphic shock-induced structure, given the evidence for current weak compaction and low shock stage. However, it is not clear how one explains high porosity and low shock stage if the meteorite experienced early shock sufficiently strong to mobilize metal into a vein-like structure. Some combination of unusual conditions during shock (e.g. high temperatures) or mobility of metal during metamorphism may be needed. One possible mechanism occurring early on the H chondrite parent body follows: blocks of slightly indurated but porous material were disturbed by an impact which caused a physical concentration of metallic phases akin to slickensides. Shearing of these materials caused the warm, ductile metal grains to be concentrated on rock surfaces. This process would have imparted the rocks with indicators cited by as shock induced. This event happened early in the history of the chondrite otherwise shearing forces would have imparted a preferred orientation upon the metal grains. Subsequent annealing due to radiogenic heating erased any preferential orientation and further coalesced the vein metal. The final compaction of the material occurred yielding the porosity seen in the samples today. The material escaped other major shock episodes.

  7. Metamorphic evolution of pelitic-semipelitic granulites in the Kon Tum massif (south-central Vietnam)

    NASA Astrophysics Data System (ADS)

    Tích, Vu Van; Leyreloup, Andrey; Maluski, Henry; Lepvrier, Claude; Lo, Chinh-hua; Vượng, Nguyễn V.

    2013-09-01

    Pelitic and semipelitic anatectic granulites form one of the major lithological units in Kan Nack complex of the Kon Tum massif (in south-central Vietnam), which comprises HT metamorphic and magmatic rocks including granulites and charnockites is classically regarded as the older part of the Gondwana-derived Indosinia terrain. Metamorphic evolution study of pelitic granulite, the most abundant among granulites exposed in this massif, facilitates to understand that tectonic setting take place during the Indosinian time. The paragenetic assemblages, mineral chemistry, thermobarometry and P-T evolution path of pelitic-semipelitic granulites from Kon Tum massif has been studied in detail. Petrographic feature demonstrates that the pelitic granulite experienced prograde history, from pregranulitic conditions in the amphibolite facies up to the peak granulitic assemblages. Successive prograde reactions led to the temperature-climax giving rise to assemblages with cordierite-hercynite and cordierite-hercynite-K-feldspar. Then, as attested by the mineralogic association occurring in cordieritic coronas, these rocks have been affected by retrograde conditions coeval with a decrease of the pressure. Thermobarometic results show that the highest temperature obtained by ksp/pl thermometry is 850 °C and the highest pressure obtained by GASP (Garnet Alumino-Silicate Plagioclase) is 7.8 kbar. The obtained clockwise P-T evolution path involving heating decompression, then nearly isothermal decompression and nearly isobar cooling conditions shows that high temperature-low pressure metamorphism of the studied pelitic anatectic granulites of Kan Nack complex occurred possibly in extensional setting during the Indosinian orogeny of 260-240 Ma in age.

  8. Testosterone related to age and life-history stages in male baboons and geladas

    PubMed Central

    Beehner, Jacinta C.; Gesquiere, Laurence; Seyfarth, Robert M.; Cheney, Dorothy L.; Alberts, Susan C.; Altmann, Jeanne

    2013-01-01

    Despite significant advances in our knowledge of how testosterone mediates life-history trade-offs, this research has primarily focused on seasonal species. We know comparatively little about the relationship between testosterone and life-history stages for non-seasonally breeding species. Here we examine testosterone profiles across the lifespan of males from three non-seasonally breeding primates: yellow baboons (Papio cynocephalus or P. hamadryas cynocephalus), chacma baboons (Papio ursinus or P. h. ursinus), and geladas (Theropithecus gelada). First, we predict that testosterone profiles will track the reproductive profiles of each taxon across their respective breeding years. Second, we evaluate age-related changes in testosterone to determine whether several life-history transitions are associated with these changes. Subjects include males (>2.5 years) from wild populations of each taxon from whom we had fecal samples for hormone determination. Although testosterone profiles across species were broadly similar, considerable variability was found in the timing of two major changes: (1) the attainment of adult levels of testosterone, and (2) the decline in testosterone after the period of maximum production. Attainment of adult testosterone levels was delayed by one year in chacmas compared with yellows and geladas. With respect to the decline in testosterone, geladas and chacmas exhibited a significant drop after three years of maximum production, while yellows declined so gradually that no significant annual drop was ever detected. For both yellows and chacmas, increases in testosterone production preceded elevations in social dominance rank. We discuss these differences in the context of ecological and behavioral differences exhibited by these taxa. PMID:19712676

  9. Validity of self-reported history of endodontic treatment in the Baltimore Longitudinal Study of Aging

    PubMed Central

    Gomes, Maximiliano Schünke; Hugo, Fernando Neves; Hilgert, Juliana Balbinot; Padilha, Dalva Maria Pereira; Simonsick, Eleanor Marie; Ferrucci, Luigi; Reynolds, Mark Allan

    2012-01-01

    Introduction Self-reported history of endodontic treatment (SRHET) has been used as a simplified method to estimate history of endodontic disease and treatment. This study aimed to quantify the validity of SRHET, as reported in the Baltimore Longitudinal Study of Aging (BLSA), as a method to: 1- identify individuals who experienced endodontic treatment (ET); and 2- identify individuals who present with apical periodontitis (AP). Methods SRHET was collected through the BLSA questionnaire in 247 participants. Data on ET and AP were determined from panoramic radiographs. The total number of ET, AP and missing teeth were recorded for each individual. Validity of SRHET was determined based on ET and AP, separately. Accuracy, efficiency, sensitivity, specificity, positive and negative predictive values (+PV, −PV) and positive and negative likelihood ratios (+LR, −LR) were calculated according to standard methods. Results After exclusions, 229 participants were available for ET analysis and 129 for AP analysis. The SRHET validity values were: sensitivity (ET=0.915; AP=0.782), specificity (ET=0.891; AP=0.689), +PV (ET=0.824; AP=0.353), −PV (ET=0.949; AP=0.936), +LR (ET=8.394; AP=2.514) and −LR (ET=0.095; AP=0.316). Conclusions SRHET was found to be a highly accurate method to predict ET but a weak predictor of the presence of AP among participants in the BLSA. PMID:22515884

  10. Ar-Ar and I-Xe Ages of Caddo County and Thermal History of IAB Iron Meteorites

    NASA Technical Reports Server (NTRS)

    Bogard, Donald D.; Garrison, Daniel H.; Takeda, Hiroshi

    2005-01-01

    Inclusions in IAB iron meteorites include non-chondritic silicate and those with more primitive chondritic silicate composition. Coarse-grained gabbroic material rich in plagioclase and diopside occurs in the Caddo County IAB iron meteorite and represents a new type of chemically differentiated, extra-terrestrial, andesitic silicate. Other parts of Caddo contain mostly andesitic material. Caddo thus exhibits petrologic characteristics of parent body metamorphism of a chondrite-like parent and inhomogeneous segregation of melts. Proposed IAB formation models include parent body partial melting and fractional crystallization or incomplete differentiation due to internal heat sources, and impact/induced melting and mixing. Benedix et al. prefer a hybrid model whereby the IAB parent body largely melted, then underwent collisional breakup, partial mixing of phases, and reassembly. Most reported 129I- Xe-129 ages of IABs are greater than 4.56 Gyr and a few are greater than or = 4.567 Gyr. These oldest ages exceed the 4.567 Gyr Pb-Pb age of Ca, Al-rich inclusions in primitive meteorites,

  11. Apoptosis: its origin, history, maintenance and the medical implications for cancer and aging

    NASA Astrophysics Data System (ADS)

    Kaczanowski, Szymon

    2016-06-01

    Programmed cell death is a basic cellular mechanism. Apoptotic-like programmed cell death (called apoptosis in animals) occurs in both unicellular and multicellular eukaryotes, and some apoptotic mechanisms are observed in bacteria. Endosymbiosis between mitochondria and eukaryotic cells took place early in the eukaryotic evolution, and some of the apoptotic-like mechanisms of mitochondria that were retained after this event now serve as parts of the eukaryotic apoptotic machinery. Apoptotic mechanisms have several functions in unicellular organisms: they include kin-selected altruistic suicide that controls population size, sharing common goods, and responding to viral infection. Apoptotic factors also have non-apoptotic functions. Apoptosis is involved in the cellular aging of eukaryotes, including humans. In addition, apoptosis is a key part of the innate tumor-suppression mechanism. Several anticancer drugs induce apoptosis, because apoptotic mechanisms are inactivated during oncogenesis. Because of the ancient history of apoptosis, I hypothesize that there is a deep relationship between mitochondrial metabolism, its role in aerobic versus anaerobic respiration, and the connection between apoptosis and cancer. Whereas normal cells rely primarily on oxidative mitochondrial respiration, most cancer cells use anaerobic metabolism. According to the Warburg hypothesis, the remodeling of the metabolism is one of the processes that leads to cancer. Recent studies indicate that anaerobic, non-mitochondrial respiration is particularly active in embryonic cells, stem cells, and aggressive stem-like cancer cells. Mitochondrial respiration is particularly active during the pathological aging of human cells in neurodegenerative diseases. According to the reversed Warburg hypothesis formulated by Demetrius, pathological aging is induced by mitochondrial respiration. Here, I advance the hypothesis that the stimulation of mitochondrial metabolism leads to pathological aging.

  12. Apoptosis: its origin, history, maintenance and the medical implications for cancer and aging.

    PubMed

    Kaczanowski, Szymon

    2016-01-01

    Programmed cell death is a basic cellular mechanism. Apoptotic-like programmed cell death (called apoptosis in animals) occurs in both unicellular and multicellular eukaryotes, and some apoptotic mechanisms are observed in bacteria. Endosymbiosis between mitochondria and eukaryotic cells took place early in the eukaryotic evolution, and some of the apoptotic-like mechanisms of mitochondria that were retained after this event now serve as parts of the eukaryotic apoptotic machinery. Apoptotic mechanisms have several functions in unicellular organisms: they include kin-selected altruistic suicide that controls population size, sharing common goods, and responding to viral infection. Apoptotic factors also have non-apoptotic functions. Apoptosis is involved in the cellular aging of eukaryotes, including humans. In addition, apoptosis is a key part of the innate tumor-suppression mechanism. Several anticancer drugs induce apoptosis, because apoptotic mechanisms are inactivated during oncogenesis. Because of the ancient history of apoptosis, I hypothesize that there is a deep relationship between mitochondrial metabolism, its role in aerobic versus anaerobic respiration, and the connection between apoptosis and cancer. Whereas normal cells rely primarily on oxidative mitochondrial respiration, most cancer cells use anaerobic metabolism. According to the Warburg hypothesis, the remodeling of the metabolism is one of the processes that leads to cancer. Recent studies indicate that anaerobic, non-mitochondrial respiration is particularly active in embryonic cells, stem cells, and aggressive stem-like cancer cells. Mitochondrial respiration is particularly active during the pathological aging of human cells in neurodegenerative diseases. According to the reversed Warburg hypothesis formulated by Demetrius, pathological aging is induced by mitochondrial respiration. Here, I advance the hypothesis that the stimulation of mitochondrial metabolism leads to pathological aging

  13. Apoptosis: its origin, history, maintenance and the medical implications for cancer and aging.

    PubMed

    Kaczanowski, Szymon

    2016-05-11

    Programmed cell death is a basic cellular mechanism. Apoptotic-like programmed cell death (called apoptosis in animals) occurs in both unicellular and multicellular eukaryotes, and some apoptotic mechanisms are observed in bacteria. Endosymbiosis between mitochondria and eukaryotic cells took place early in the eukaryotic evolution, and some of the apoptotic-like mechanisms of mitochondria that were retained after this event now serve as parts of the eukaryotic apoptotic machinery. Apoptotic mechanisms have several functions in unicellular organisms: they include kin-selected altruistic suicide that controls population size, sharing common goods, and responding to viral infection. Apoptotic factors also have non-apoptotic functions. Apoptosis is involved in the cellular aging of eukaryotes, including humans. In addition, apoptosis is a key part of the innate tumor-suppression mechanism. Several anticancer drugs induce apoptosis, because apoptotic mechanisms are inactivated during oncogenesis. Because of the ancient history of apoptosis, I hypothesize that there is a deep relationship between mitochondrial metabolism, its role in aerobic versus anaerobic respiration, and the connection between apoptosis and cancer. Whereas normal cells rely primarily on oxidative mitochondrial respiration, most cancer cells use anaerobic metabolism. According to the Warburg hypothesis, the remodeling of the metabolism is one of the processes that leads to cancer. Recent studies indicate that anaerobic, non-mitochondrial respiration is particularly active in embryonic cells, stem cells, and aggressive stem-like cancer cells. Mitochondrial respiration is particularly active during the pathological aging of human cells in neurodegenerative diseases. According to the reversed Warburg hypothesis formulated by Demetrius, pathological aging is induced by mitochondrial respiration. Here, I advance the hypothesis that the stimulation of mitochondrial metabolism leads to pathological aging.

  14. Zircon and monazite response to prograde metamorphism in the Reynolds Range, central Australia

    NASA Astrophysics Data System (ADS)

    Rubatto, Daniela; Williams, Ian S.; Buick, Ian S.

    2001-01-01

    We report an extensive field-based study of zircon and monazite in the metamorphic sequence of the Reynolds Range (central Australia), where greenschist- to granulite-facies metamorphism is recorded over a continuous crustal section. Detailed cathodoluminescence and back-scattered electron imaging, supported by SHRIMP U-Pb dating, has revealed the different behaviours of zircon and monazite during metamorphism. Monazite first recorded regional metamorphic ages (1576 ± 5 Ma), at amphibolite-facies grade, at ˜600 °C. Abundant monazite yielding similar ages (1557 ± 2 to 1585 ± 3 Ma) is found at granulite-facies conditions in both partial melt segregations and restites. New zircon growth occurred between 1562 ± 4 and 1587 ± 4 Ma, but, in contrast to monazite, is only recorded in granulite-facies rocks where melt was present (≥700 °C). New zircon appears to form at the expense of pre-existing detrital and inherited cores, which are partly resorbed. The amount of metamorphic growth in both accessory minerals increases with temperature and metamorphic grade. However, new zircon growth is influenced by rock composition and driven by partial melting, factors that appear to have little effect on the formation of metamorphic monazite. The growth of these accessory phases in response to metamorphism extends over the 30 Ma period of melt crystallisation (1557-1587 Ma) in a stable high geothermal regime. Rare earth element patterns of zircon overgrowths in leucosome and restite indicate that, during the protracted metamorphism, melt-restite equilibrium was reached. Even in the extreme conditions of long-lasting high temperature (750-800 °C) metamorphism, Pb inheritance is widely preserved in the detrital zircon cores. A trace of inheritance is found in monazite, indicating that the closure temperature of the U-Pb system in relatively large monazite crystals can exceed 750-800 °C.

  15. Exposure history and terrestrial ages of ordinary chondrites from the Dar al Gani region, Libya

    NASA Astrophysics Data System (ADS)

    Welten, K. C.; Nishiizumi, K.; Finkel, R. C.; Hillegonds, D. J.; Jull, A. J. T.; Franke, L.; Schultz, L.

    2004-03-01

    We measured the concentrations of noble gases in 32 ordinary chondrites from the Dar al Gani (DaG) region, Libya, as well as concentrations of the cosmogenic radionuclides 14C, 10Be, 26Al, 36Cl, and 41Ca in 18 of these samples. Although the trapped noble gases in five DaG samples show ratios typical of solar or planetary gases, in all other DaG samples, they are dominated by atmospheric contamination, which increases with the degree of weathering. Cosmic ray exposure (CRE) ages of DaG chondrites range from ~1 Myr to 53 Myr. The CRE age distribution of 10 DaG L chondrites shows a cluster around 40 Myr due to four members of a large L6 chondrite shower. The CRE age distribution of 19 DaG H chondrites shows only three ages coinciding with the main H chondrite peak at ~7 Myr, while seven ages are <5 Myr. Two of these H chondrites with short CRE ages (DaG 904 and 908) show evidence of a complex exposure history. Five of the H chondrites show evidence of high shielding conditions, including low 22Ne/21Ne ratios and large contributions of neutron-capture 36Cl and 41Ca. These samples represent fragments of two or more large pre-atmospheric objects, which supports the hypothesis that the high H/L chondrite ratio at DaG is due to one or more large unrecognized showers. The 14C concentrations correspond to terrestrial ages <35 kyr, similar to terrestrial ages of chondrites from other regions in the Sahara but younger than two DaG achondrites. Despite the loss of cosmogenic 36Cl and 41Ca during oxidation of metal and troilite, concentrations of 36Cl and 41Ca in the silicates are also consistent with 14C ages <35 kyr. The only exception is DaG 343 (H4), which has a 41Ca terrestrial age of 150 ± 40 kyr. This old age shows that not only iron meteorites and achondrites but also chondrites can survive the hot desert environment for more than 50 kyr. A possible explanation is that older meteorites were covered by soils during wetter periods and were recently exhumed by removal of

  16. Resource allocation as a driver of senescence: life history tradeoffs produce age patterns of mortality.

    PubMed

    Davison, Raziel; Boggs, Carol L; Baudisch, Annette

    2014-11-01

    We investigate the effects of optimal time and resource allocation on age patterns of fertility and mortality for a model organism with (1) fixed maximum lifespan, (2) distinct juvenile and adult diets, and (3) reliance on nonrenewable resources for reproduction. We ask when it is optimal to tolerate starvation vs. conserve resources and then examine the effects of these decisions on adult mortality rates. We find that (1) age-related changes in tradeoffs partition the life cycle into as many as four discrete phases with different optimal behavior and mortality patterns, and (2) given a cost of reproduction, terminal investment can produce a signal of actuarial senescence. Also, given limitations imposed by non-replenishable resources, individuals beginning adult life with more replenishable resources do not necessarily live longer, since they can engage in capital breeding and need not defer reproduction to forage; low reproductive overheads and low costs of starvation also encourage capital breeding and may lead to earlier terminal investment and earlier senescence. We conclude that, even for species with qualitatively similar life histories, differences in physiological, behavioral and environmental tradeoffs or constraints may strongly influence optimal allocation schedules and produce variation in mortality patterns and life expectancy. PMID:25051533

  17. COPD prevalence is increased in lung cancer, independent of age, sex and smoking history.

    PubMed

    Young, R P; Hopkins, R J; Christmas, T; Black, P N; Metcalf, P; Gamble, G D

    2009-08-01

    Chronic obstructive pulmonary disease (COPD) is a common comorbid disease in lung cancer, estimated to affect 40-70% of lung cancer patients, depending on diagnostic criteria. As smoking exposure is found in 85-90% of those diagnosed with either COPD or lung cancer, coexisting disease could merely reflect a shared smoking exposure. Potential confounding by age, sex and pack-yr smoking history, and/or by the possible effects of lung cancer on spirometry, may result in over-diagnosis of COPD prevalence. In the present study, the prevalence of COPD (pre-bronchodilator Global Initiative for Chronic Obstructive Lung Disease 2+ criteria) in patients diagnosed with lung cancer was 50% compared with 8% in a randomly recruited community control group, matched for age, sex and pack-yr smoking exposure (n = 602, odds ratio 11.6; p<0.0001). In a subgroup analysis of those with lung cancer and lung function measured prior to the diagnosis of lung cancer (n = 127), we found a nonsignificant increase in COPD prevalence following diagnosis (56-61%; p = 0.45). After controlling for important variables, the prevalence of COPD in newly diagnosed lung cancer cases was six-fold greater than in matched smokers; this is much greater than previously reported. We conclude that COPD is both a common and important independent risk factor for lung cancer.

  18. Exhumation history of the NW Indian Himalaya revealed by fission track and 40Ar/39Ar ages

    USGS Publications Warehouse

    Schlup, M.; Steck, A.; Carter, A.; Cosca, M.; Epard, J.-L.; Hunziker, J.

    2011-01-01

    New fission track and Ar/Ar geochronological data provide time constraints on the exhumation history of the Himalayan nappes in the Mandi (Beas valley) - Tso Morari transect of the NW Indian Himalaya. Results from this and previous studies suggest that the SW-directed North Himalayan nappes were emplaced by detachment from the underthrusted upper Indian crust by 55. Ma and metamorphosed by ca. 48-40. Ma. The nappe stack was subsequently exhumed to shallow upper crustal depths (<10. km) by 40-30. Ma in the Tso Morari dome (northern section of the transect) and by 30-20. Ma close to frontal thrusts in the Baralacha La region. From the Oligocene to the present, exhumation continued slowly.Metamorphism started in the High Himalayan nappe prior to the Late Oligocene. High temperatures and anatexis of the subducting upper Indian crust engendered the buoyancy-driven ductile detachment and extrusion of the High Himalayan nappe in the zone of continental collision. Late extrusion of the High Himalayan nappe started about 26. Ma ago, accompanied by ductile extensional shearing in the Zanskar shear zone in its roof between 22 and 19. Ma concomitant with thrusting along the basal Main Central Thrust to the south. The northern part of the nappe was then rapidly exhumed to shallow depth (<10. km) between 20 and 6. Ma, while its southern front reached this depth at 10-5. Ma. ?? 2010 Elsevier Ltd.

  19. Oxidation during metamorphism of the ordinary chondrites

    NASA Technical Reports Server (NTRS)

    Mcsween, Harry Y., Jr.; Labotka, Theodore C.

    1993-01-01

    It is suggested that some current concepts about the conditions of metamorphism in ordinary chondrites may be flawed. These meteorites display small systematic variations in the oxidation state of Fe. Evidence is presented that oxidation of Fe is linked to metamorphic grade in types 4-6 ordinary chondrites. This conclusion is at variance with a commonly accepted model for chondrite metamorphism that assumes Fe reduction by graphite.

  20. Organic nitrogen chemistry during low-grade metamorphism

    USGS Publications Warehouse

    Boudou, J.-P.; Schimmelmann, A.; Ader, M.; Mastalerz, Maria; Sebilo, M.; Gengembre, L.

    2008-01-01

    Most of the organic nitrogen (Norg) on Earth is disseminated in crustal sediments and rocks in the form of fossil nitrogen-containing organic matter. The chemical speciation of fossil Norg within the overall molecular structure of organic matter changes with time and heating during burial. Progressive thermal evolution of organic matter involves phases of enhanced elimination of Norg and ultimately produces graphite containing only traces of nitrogen. Long-term chemical and thermal instability makes the chemical speciation of Norg a valuable tracer to constrain the history of sub-surface metamorphism and to shed light on the subsurface biogeochemical nitrogen cycle and its participating organic and inorganic nitrogen pools. This study documents the evolutionary path of Norg speciation, transformation and elimination before and during metamorphism and advocates the use of X-ray photoelectron spectroscopy (XPS) to monitor changes in Norg speciation as a diagnostic tool for organic metamorphism. Our multidisciplinary evidence from XPS, stable isotopes, traditional quantitative coal analyses, and other analytical approaches shows that at the metamorphic onset Norg is dominantly present as pyrrolic and pyridinic nitrogen. The relative abundance of nitrogen substituting for carbon in condensed, partially aromatic systems (where N is covalently bonded to three C atoms) increases exponentially with increasing metamorphic grade, at the expense of pyridinic and pyrrolic nitrogen. At the same time, much Norg is eliminated without significant nitrogen isotope fractionation. The apparent absence of Rayleigh-type nitrogen isotopic fractionation suggests that direct thermal loss of nitrogen from an organic matrix does not serve as a major pathway for Norg elimination. Instead, we propose that hot H, O-containing fluids or some of their components gradually penetrate into the carbonaceous matrix and eliminate Norg along a progressing reaction front, without causing nitrogen

  1. Verification of phylogenetic inference programs using metamorphic testing.

    PubMed

    Sadi, Md Shaik; Kuo, Fei-Ching; Ho, Joshua W K; Charleston, Michael A; Chen, T Y

    2011-12-01

    Many phylogenetic inference programs are available to infer evolutionary relationships among taxa using aligned sequences of characters, typically DNA or amino acids. These programs are often used to infer the evolutionary history of species. However, in most cases it is impossible to systematically verify the correctness of the tree returned by these programs, as the correct evolutionary history is generally unknown and unknowable. In addition, it is nearly impossible to verify whether any non-trivial tree is correct in accordance to the specification of the often complicated search and scoring algorithms. This difficulty is known as the oracle problem of software testing: there is no oracle that we can use to verify the correctness of the returned tree. This makes it very challenging to test the correctness of any phylogenetic inference programs. Here, we demonstrate how to apply a simple software testing technique, called Metamorphic Testing, to alleviate the oracle problem in testing phylogenetic inference programs. We have used both real and randomly generated test inputs to evaluate the effectiveness of metamorphic testing, and found that metamorphic testing can detect failures effectively in faulty phylogenetic inference programs with both types of test inputs.

  2. Metamorphism, alteration, and timing of mineralization at Hemlo, Ontario

    SciTech Connect

    Ferreira, M.C.; Fyfe, W.S.

    1985-01-01

    Relative age discrimination between metamorphic and mineralizing processes related to Archean gold deposits is often equivocal. The mineralogy and/or stability range of hydrothermal alteration assemblages in and around the deposits are, in most cases, similar to the low grade metamorphic assemblages characteristic of their host sequences. At Hemlo, the distinction is made easier by the relatively high metamorphic rank recorded in the host rocks. From a regional perspective, the mineralization at Hemlo sits in a highly deformed zone flanked by intermediate to mafic volcanic rocks in the footwall, and clastic to volcaniclastic (sensu lato) rocks in the hanging wall. Amphibolite facies assemblages in both hanging wall and footwall are progressively altered, via hydrolysis and hydration, to greenschist facies assemblages. The extent and intensity of alteration increase towards the mineralization. Accordingly, alteration and mineralization at Hemlo postdate peak metamorphic conditions. Whereas structurally enhanced permeability may have played an important role in facilitating access to mineralizing solutions, gold deposition was probably controlled by host rock composition and reactivity. Gold precipitation may have been triggered by an increase in hydrogen ion activity of mineralizing solutions related to white mica replacement of aluminosilicates.

  3. Shock metamorphism in lunar samples.

    PubMed

    von Engelhardt, W; Arndt, J; Müller, W F; Stöffler, D

    1970-01-30

    Indications of shock metamorphism produced by pressures up to the megabar region have been observed in the fine material and the breccias, but very rarely in the coarser fragments of crystalline rocks. These indications are deformation structures in plagioclase and pyroxene, diaplectic plagioclase glasses, and glasses formed by shock-induced melting of lunar rocks. Two sources of shock waves have been distinguished: primary impact of meteorites and secondary impact of crater ejecta. There are two major chemical types of shock-induced melts. The differences in chemistry may be related to impact sites in mare and highland areas.

  4. In the Age of the Web: Strategies for Building a Collection of Primary Sources for European History from the Middle Ages to the Eighteenth Century.

    ERIC Educational Resources Information Center

    Saenger, Paul

    2003-01-01

    Describes efforts by the Newberry Library (Chicago) to obtain original source materials for studying the literature and history of western Europe from the Middle Ages to the eighteenth century. Discusses joint acquisitions with higher education institutions; acquisition of rare book collections from religious colleges and seminaries; and…

  5. Archean gold mineralization and metamorphism: timing constraints from precise U-Pb dating

    SciTech Connect

    Colvine, A.C.; Corfu, F.; Davis, D.W.; Stott, G.M.

    1985-01-01

    Gold mineralization is tightly constrained to an event closely following establishment of peak metamorphic condition, in all areas of the Superior Province of Canada where precise dating has been applied to defined field relationships. In the Abitibi and Wabigoon Subprovinces of the Southern Superior Domain, peak metamorphism caused by major batholith emplacement is consistently >2685 Ma and affects Archean supracrustal units of all ages (mainly >2700 Ma). Gold is commonly hosted by felsic stocks, dated at a specific age in the Abitibi Belt (2688-2684 Ma), and is therefore close to or younger than peak metamorphism. Dateable units crosscutting mineralization are extremely rare, but at Shebandowan and Mine Centre dated field relationships bracket the maximum and minimum age of mineralization between 2689 - 2684 and 2692 - 2686 Ma, respectively. While the metamorphic event in the Northern Superior Domain is approximately 20 my older, relative timing of gold mineralization is identical. At Red Lake, gold is hosted by units ranging in age from 2990-2718 Ma, all metamorphosed at >2704 Ma. Peak metamorphic minerals are retrograded by alteration during gold localization and mineralization is cut by a 2704 Ma dyke. These data show that gold mineralization was the product of a tectonic event during the latest Archean which involved major plutonism, deformation and metamorphism.

  6. The Natural History of Insomnia in the Ibadan Study of Ageing

    PubMed Central

    Gureje, Oye; Oladeji, Bibilola Damilola; Abiona, Taiwo; Makanjuola, Victor; Esan, Oluyomi

    2011-01-01

    Study Objectives: To determine the incidence and risk factors for insomnia among an under-studied population of elderly persons in Sub-Saharan Africa. Setting: Eight contiguous predominantly Yoruba-speaking states in south-west and north-central Nigeria representing about 22% of the national population. Participants: 1307 elderly community-dwelling persons, aged 65 years and older. Measurements: Face-to-face assessment with the Composite International Diagnostic Interview, version 3 (CIDI.3) in 2007 and 12 months later in 2008 to determine the occurrence and risk factors of incident and persistent insomnia, defined as syndrome or symptom. Results: The incidence of insomnia syndrome in 2008 at 12 months was 7.97% (95% CI, 6.60–9.60), while that of insomnia symptom was 25.68% (22.68–28.66). Females were at elevated risk for both syndrome and symptom. Among persons with insomnia symptom or syndrome at the baseline, 47.36% (95% CI 43.07–51.68) continued to have it one year later. Decreasing economic status was associated with increasing incidence of insomnia. Persons with chronic medical conditions at baseline were at increased risk for new onset of insomnia. Compared to persons with the lowest body mass index (BMI) (< 18.5), those with higher BMI were at elevated risk for persistence of their insomnia, with those in the obese range (≥ 30) having a 4-fold risk. Conclusions: There is a high incidence and chronicity of insomnia in this elderly population. Persons with chronic health conditions are particularly at risk of new onset as well as persistence of insomnia. Citation: Gureje O; Oladeji BD; Abiona T; Makanjuola V; Esan O. The natural history of insomnia in the Ibadan Study of Ageing. SLEEP 2011;34(7):965-973. PMID:21731147

  7. Progressive low pressure metamorphism of metapelitic rocks from the Casco Bay area, southwestern Maine

    SciTech Connect

    Grover, T.W. . Dept. of Geology and Geophysics); Lang, H.M. . Dept. of Geology and Geography); Gordon, T.M. . Dept. of Geology and Geophysics)

    1993-03-01

    A prograde sequence of metapelitic rocks occurs in the Casco Bay area, southwestern Maine. Excellent exposure along the coast of Orrs Island, Harpswell Neck, and Small Point have allowed for the delineation of several metamorphic zones which show an increase in metamorphic grade from west to east across the area. These zones are, in order of increasing metamorphic grade, a garnet zone, a staurolite zone, a staurolite + andalusite zone and a sillimanite [plus minus] andalusite [plus minus] staurolite zone. The widespread occurrence of coexisting andalusite + sillimanite in the highest grade portion of the area, along with the presence of andalusite [plus minus] sillimanite veins on Hermit Island suggest peak metamorphism was near the andalusite-sillimanite transition. Staurolite is also found in apparent textural equilibrium in many of the sillimanite-bearing samples. Metamorphic pressures and temperatures were determined using the approach of Gordon. Peak temperatures range from [approx] 440C in garnet zone rocks to [approx] 510C in sillimanite [plus minus] andalusite zone rocks. Metamorphic pressures are [approx] 3-3.5 kbars. These P-T estimates are consistent with those determined using GeO-Calc. In contrast with the static style of metamorphism reported in central and western Maine, metamorphism in the Casco Bay area, located east of the Norumbega Fault, was synchronous with deformation. The same sequence of porphyroblast growth reported for the Orrs Island-Harpswell Neck area is also found in the Small Point area, suggesting the same metamorphic event affected the entire region. However, coarse grained muscovite pseudomorphs after andalusite or staurolite in rocks with stable andalusite and staurolite are found in the Small Point area suggesting these rocks have a polymetamorphic history. Evidence for polymetamorphism is not found elsewhere in the area.

  8. A brief history of cancer: age-old milestones underlying our current knowledge database.

    PubMed

    Faguet, Guy B

    2015-05-01

    This mini-review chronicles the history of cancer ranging from cancerous growths discovered in dinosaur fossils, suggestions of cancer in Ancient Egyptian papyri written in 1500-1600 BC, and the first documented case of human cancer 2,700 years ago, to contributions by pioneers beginning with Hippocrates and ending with the originators of radiation and medical oncology. Fanciful notions that soon fell into oblivion are mentioned such as Paracelsus and van Helmont substituting Galen's black bile by mysterious ens or archeus systems. Likewise, unfortunate episodes such as Virchow claiming Remak's hypotheses as his own remind us that human shortcomings can affect otherwise excellent scientists. However, age-old benchmark observations, hypotheses, and practices of historic and scientific interest are underscored, excerpts included, as precursors of recent discoveries that shaped modern medicine. Examples include: Petit's total mastectomy with excision of axillary glands for breast cancer; a now routine practice, Peyrilhe's ichorous matter a cancer-causing factor he tested for transmissibility one century before Rous confirmed the virus-cancer link, Hill's warning of the dangers of tobacco snuff; heralding today's cancer pandemic caused by smoking, Pott reporting scrotum cancer in chimney sweepers; the first proven occupational cancer, Velpeau's remarkable foresight that a yet unknown subcellular element would have to be discovered in order to define the nature of cancer; a view confirmed by cancer genetics two centuries later, ending with Röntgen and the Curies, and Gilman et al. ushering radiation (1896, 1919) and medical oncology (1942), respectively.

  9. A brief history of cancer: age-old milestones underlying our current knowledge database.

    PubMed

    Faguet, Guy B

    2015-05-01

    This mini-review chronicles the history of cancer ranging from cancerous growths discovered in dinosaur fossils, suggestions of cancer in Ancient Egyptian papyri written in 1500-1600 BC, and the first documented case of human cancer 2,700 years ago, to contributions by pioneers beginning with Hippocrates and ending with the originators of radiation and medical oncology. Fanciful notions that soon fell into oblivion are mentioned such as Paracelsus and van Helmont substituting Galen's black bile by mysterious ens or archeus systems. Likewise, unfortunate episodes such as Virchow claiming Remak's hypotheses as his own remind us that human shortcomings can affect otherwise excellent scientists. However, age-old benchmark observations, hypotheses, and practices of historic and scientific interest are underscored, excerpts included, as precursors of recent discoveries that shaped modern medicine. Examples include: Petit's total mastectomy with excision of axillary glands for breast cancer; a now routine practice, Peyrilhe's ichorous matter a cancer-causing factor he tested for transmissibility one century before Rous confirmed the virus-cancer link, Hill's warning of the dangers of tobacco snuff; heralding today's cancer pandemic caused by smoking, Pott reporting scrotum cancer in chimney sweepers; the first proven occupational cancer, Velpeau's remarkable foresight that a yet unknown subcellular element would have to be discovered in order to define the nature of cancer; a view confirmed by cancer genetics two centuries later, ending with Röntgen and the Curies, and Gilman et al. ushering radiation (1896, 1919) and medical oncology (1942), respectively. PMID:25113657

  10. The history of mare volcanism in the Orientale Basin: Mare deposit ages, compositions and morphologies

    NASA Technical Reports Server (NTRS)

    Kadel, S. D.; Greeley, R.; Neukum, G.; Wagner, R.

    1993-01-01

    The eruptive history of mare basalts in the Orientale Basin has been studied, using Lunar Orbiter 4 high-resolution photographs, Zond 8 photographs, and recently acquired Galileo EM-1 multispectral images. This work represents a refined set of compositional data incorporating the use of a linear mixing model for mare compositions, crater count data, and a comprehensive morphologic analysis of Orientale Basin mare deposits. Evidence for multiple eruptive episodes has been found, with compositions ranging from medium- to high-Ti basalt (less than 4 to greater than 6 wt. percent TiO2). Eruptive styles included flood, rille-forming, and shield-forming eruptions. Impact crater densities of mare units in the Orientale Basin enable determination of the ages of these deposits, using the method of Neukum et al. Earliest eruptions of mare basalt in the basin occurred at greater than or equal to 3.80 Ga and the latest eruptions occurred at about 2.3-2.5 Ga. Hence, mare volcanism occurred over a period of nearly 1.5 Ga.

  11. Highlights in IBD Epidemiology and Its Natural History in the Paediatric Age

    PubMed Central

    2013-01-01

    Background. The number of patients of all age brackets diagnosed with Inflammatory Bowel Disease (IBD) has risen dramatically worldwide over the past 50 years. IBD's changing epidemiology suggests that environmental factors play a major role in modifying disease expression. Aim. To review studies carried out worldwide analyzing IBD epidemiology. Methods. A Medline search indicating as keywords “Inflammatory Bowel Disease,” “epidemiology,” “natural history,” “Crohn's Disease,” “Ulcerative Colitis,” and “IBD Unclassified” was performed. A selection of clinical cohort and systematic review studies that were carried out between 2002 and 2013 was reviewed. Studies referring to an earlier date were also considered whenever the data were relevant to our review. Results. The current mean prevalence of IBD in the total population of Western countries is estimated at 1/1,000. The highest prevalence and incidence rates of IBD worldwide are reported from Canada. Just as urbanization and socioeconomic development, the incidence of IBD is rising in China. Conclusions. Multicenter national registers and international networks can provide information on IBD epidemiology and lead to hypotheses about its causes and possible management strategies. The rising trend in the disease's incidence in developing nations suggests that its epidemiological evolution is linked to industrialization and modern Westernized lifestyles. PMID:24454343

  12. A ˜ 700 Ma Sm Nd garnet whole rock age from the granulite facies Central Kaoko Zone (Namibia): Evidence for a cryptic high-grade polymetamorphic history?

    NASA Astrophysics Data System (ADS)

    Jung, S.; Kröner, A.; Kröner, S.

    2007-09-01

    Continental collision of the Kalahari and the Congo craton in Africa and the Rio de la Plata Craton in South America resulted in a structurally complex Neoproterozoic belt system, the Kaoko-Dom Feliciano-Ribeira belt. It is uncertain whether these three cratons collided more or less simultaneously during one single orogenic event at ˜ 580-550 Ma or whether the belt owe its structural and metamorphic features to several so far poorly constrained events. The Kaoko Belt (NW Nambia), representing the belt system between the southern Congo Craton and the Rio de la Plata Craton, is an ideal object to study these complexities. Within this belt, high-grade meta-igneous and metasedimentary rocks of the sillimanite-K-feldspar zone contain large garnet porphyroblasts that grew at ca. 730 ± 10 °C at 6.7 ± 1.2 kbar during peak metamorphic granulite-facies conditions. A Sm-Nd garnet-whole rock errorchron ( n = 7, MSWD = 6.0) obtained on a siliceous metasediment yielded an unexpected old age of 692 ±14 Ma which is interpreted as an inherited metamorphic age of an older granulite facies event. It is evident that the dated garnets survived the younger high-grade granulite facies metamorphism that occurred between ca. 570 and 520 Ma and preserved their old Sm-Nd isotope systematics implying that the closure temperature for Sm-Nd in garnet is higher than ca. 730 °C in this case. These results imply fast cooling rates at different times during the Pan-African orogeny that prevent isotopic homogenization at sample scale. Moreover, it is suggestive that trace element (REE) diffusion in garnet is considerably slower than major element diffusion. From a regional point of view, it is possible that these specific siliceous metasedimentary rocks may be unrelated to the Pan-African metamorphic evolution of the Kaoko Belt between 570 and 520 Ma and may represent lithological units that belong to so far unrecognized terranes in the Kaoko Belt.

  13. Oman metamorphic sole formation reveals early subduction dynamics

    NASA Astrophysics Data System (ADS)

    Soret, Mathieu; Agard, Philippe; Dubacq, Benoît; Plunder, Alexis; Ildefonse, Benoît; Yamato, Philippe; Prigent, Cécile

    2016-04-01

    Metamorphic soles correspond to m to ~500m thick tectonic slices welded beneath most of the large-scale ophiolites. They typically show a steep inverted metamorphic structure where the pressure and temperature conditions of crystallization increase upward (from 500±100°C at 0.5±0.2 GPa to 800±100°C at 1.0±0.2 GPa), with isograds subparallel to the contact with the overlying ophiolitic peridotite. The proportion of mafic rocks in metamorphic soles also increases from the bottom (meta-sediments rich) to the top (approaching the ophiolite peridotites). These soles are interpreted as the result of heat transfer from the incipient mantle wedge toward the nascent slab (associated with large-scale fluid transfer and possible shear heating) during the first My of intra-oceanic subduction (as indicated by radiometric ages). Metamorphic soles provide therefore major constraints on early subduction dynamics (i.e., thermal structure, fluid migration and rheology along the nascent slab interface). We present a detailed structural and petrological study of the metamorphic sole from 4 major cross-sections along the Oman ophiolite. We show precise pressure-temperature estimates obtained by pseudosection modelling and EBSD measurements performed on both the garnet-bearing and garnet-free high-grade sole. Results allow quantification of the micro-scale deformation and highlight differences in pressure-temperature-deformation conditions between the 4 different locations, showing that the inverted metamorphic gradient through the sole is not continuous in all locations. Based on these new constraints, we suggest a new tectonic-petrological model for the formation of metamorphic soles below ophiolites. This model involves the stacking of several homogeneous slivers of oceanic crust leading to the present-day structure of the sole. In this view, these thrusts are the result of rheological contrasts between the sole and the peridotite as the plate interface progressively cools down

  14. Resolving the Youngest Episode of Zircon Rim Growth with High-Spatial Resolution SIMS: U-Pb Ages and Trace Element Analyses from <1 um Thick Metamorphic Zircon Rims from the Zanskar Shear Zone and Tso Morari UHP Complex, NW Himalaya

    NASA Astrophysics Data System (ADS)

    Coble, M. A.; Leech, M. L.

    2014-12-01

    Dating the youngest phase of metamorphic or magmatic zircon growth by in-situ techniques on sectioned zircons can be challenging when rims are only a few microns thick; in the worst case, geologically meaningless measurements result from mixing between different age and/or compositional growth domains. This is especially true for zircons from the Zanskar Shear Zone and Tso Morari UHP Complex, NW Himalaya, which contain Eocene to Miocene rims that grew over Paleozoic and Proterozoic protolith cores during peak and retrograde metamorphism. These metamorphic rims are typically only 0.5 to 3.0 microns thick and require high-spatial resolution to resolve. We used the SHRIMP-RG ion-microprobe to perform new U-Pb depth-profiling analyses on zircon surfaces (non-polished) pressed into indium metal. Zircons from a leucogranite dike from Malung Tokpo along the Zanskar Shear Zone, which have 2000-5000 ppm U rims, were selected for detailed depth-profiling to evaluate the depth-resolution by SIMS for U-Pb and trace element analyses. Due to the high U concentration, we were able to decrease the primary beam intensity (sputter rate) and the count times for U and Pb isotopes, and increase the number of cycles through the run-table (45 peak-hopping scans). As a result, each cycle yielded a 0.04 micron depth-resolved zircon age and trace element composition. The youngest 13 scans yielded a U-Pb age of 21.3 ± 0.5 Ma, representing a 0.6 micron rim with uniform U, Th, and Hf concentrations. At 1.15 microns, the primary beam sputtered into a ~600 Ma core; this older age is complicated by the fact that it reflects mixing between the bottom of the sputter volume and the Miocene ages of the pit margins and rim, because the diameter of the spot tends to increase with time. Trace element analyses on zircon surfaces from the Tso Morari UHP Complex are highly reproducible, showing enriched HREE profiles with negative Eu anomalies - a result that is difficult to reproduce by analyses of

  15. Metamorphic geology: Why should we care?

    NASA Astrophysics Data System (ADS)

    Tajcmanova, Lucie; Moulas, Evangelos; Vrijmoed, Johannes

    2016-04-01

    Estimation of pressure-temperature (P-T) from petrographic observations in metamorphic rocks has become a common practice in petrology studies during the last 50 years. This data then often serves as a key input in geodynamic reconstructions and thus directly influences our understanding of lithospheric processes. Such an approach might have led the metamorphic geology field to a certain level of quiescence. Obtaining high-quality analytical data from metamorphic rocks has become a standard part of geology studies. The numerical tools for geodynamic reconstructions have evolved to a great extend as well. Furthermore, the increasing demand on using the Earth's interior for sustainable energy or nuclear waste disposal requires a better understanding of the physical processes involved in fluid-rock interaction. However, nowadays, metamorphic data have apparently lost their importance in the "bigger picture" of the Earth sciences. Interestingly, the suppression of the metamorphic geology discipline limits the potential for understanding the aforementioned physical processes that could have been exploited. In fact, those phenomena must be considered in the development of new generations of fully coupled numerical codes that involve reacting materials with changing porosity while obeying conservation of mass, momentum and energy. In our contribution, we would like to discuss the current role of metamorphic geology. We will bring food for thoughts and specifically touch upon the following questions: How can we revitalize metamorphic geology? How can we increase the importance of it? How can metamorphic geology contribute to societal issues?

  16. Why do women stop reproducing before menopause? A life-history approach to age at last birth.

    PubMed

    Towner, Mary C; Nenko, Ilona; Walton, Savannah E

    2016-04-19

    Evolutionary biologists have long considered menopause to be a fundamental puzzle in understanding human fertility behaviour, as post-menopausal women are no longer physiologically capable of direct reproduction. Menopause typically occurs between 45 and 55 years of age, but across cultures and history, women often stop reproducing many years before menopause. Unlike age at first reproduction or even birth spacing, a woman nearing the end of her reproductive cycle is able to reflect upon the offspring she already has--their numbers and phenotypic qualities, including sexes. This paper reviews demographic data on age at last birth both across and within societies, and also presents a case study of age at last birth in rural Bangladeshi women. In this Bangladeshi sample, age at last birth preceded age at menopause by an average of 11 years, with marked variation around that mean, even during a period of high fertility. Moreover, age at last birth was not strongly related to age at menopause. Our literature review and case study provide evidence that stopping behaviour needs to be more closely examined as an important part of human reproductive strategies and life-history theory. Menopause may be a final marker of permanent reproductive cessation, but it is only one piece of the evolutionary puzzle. PMID:27022074

  17. New terrace ages better constrain the uplift history for the Mejillones Peninsula, northern Chile

    NASA Astrophysics Data System (ADS)

    Liermann, Ariane; Dunai, Tibor; Binnie, Steven; Heinze, Stefan; Dewald, Alfred; Victor, Pia; González, Gabriel

    2013-04-01

    The Mejillones Peninsula is a promontory extending spectacularly from the northern Chilean coastline. The peninsula is marked by well preserved marine terraces extending from just above sea-level to greater than 400 m. These staircased planar expressions result from a combination of glacioeustatic sea-level fluctuation and tectonic uplift. It has been shown by several studies that such terraces are formed during interglacial marine high-stands and are preserved because of abandonment in intervening sea-level low-stands. Post Mid Pleistocene transition high-stands (MIS 1 to 19) were within 10 m of the current sea-level (Siddall et al. 2006). We present cosmogenic 10Be exposure ages from marine pebbles deposited on the surface of the terraces when they were at sea-level in order to constrain the uplift history of the northwestern highland part of the peninsula. Based on the mean age (n=10) of the oldest terrace measured (~140 m) we obtain an average uplift rate of ~0.3 m/ka for the last ~465 ka. This average uplift rate can be subdivided into a recent slower and an older, more rapid rate. The average uplift rate between ~465 and ~280 ka was ~0.6 m/ka, and based on the observed linear increase in age with altitude the uplift was steady throughout this period. However, for the last ~280 ka we calculate a slower uplift rate of ~0.1 m/ka. Tracing the surface expressions of the marine terraces northwards we observe an anomalous increase of >100 m elevation over length-scales of ~2 km. This suggests different amounts of tectonic uplift for adjacent regions within the northern part of the peninsula. From a single terrace surface (288m) in the more elevated region we measured an exposure age of ~405 ka, compatible with the temporal framework of uplift defined by the lower elevation ages. However, the higher altitude of this terrace, in comparison to the adjacent, lower region suggests a more rapid rate of uplift (~0.7 m/ka) and thus differential uplift within the northern

  18. Fi Investigations On Hp-Rocks From The Lower Engadine Window New Insights On Its Late Tectono-Metamorphic Evolution

    NASA Astrophysics Data System (ADS)

    Bertle, R. J.; Götzinger, M. A.; Koller, F.

    2003-04-01

    acknowledged. References: BERTLE, R. J. 2000: Zur Geologie und Geochronologie um Alp Trida (Samnaun/Schweiz) einschließlich ingenieurgeologischer Fragen der Gebirgsauflösung und des Permafrosts. - Unpubl. Msc-Thesis. Univ. Wien, 395 S. BOUSQUET, R., GOFFÉ, B., VIDAL, O., OBERHÄNSLI, R. & PATRIAT, M. 2002: The tectono-metamorphic history of the Valaisan domain from the Western to the Central Alps: new constraints on the evolution of the Alps. - Geol. Soc. America Bull., 114/2, S. 207-225. KÜSTER, M. &STÖCKHERT, B. 1997: Density changes of fluid inclusions in high-pressure low-temperature metamorphic rocks from Crete: A thermobarometric approach based on the creep strength of the host minerals. Lithos, 41, S. 151-167. MATTMÜLLER, C. R. 1996: Geometrische Untersuchung des Inntalgewölbes. - Jahrb. Geol. B.-A., 139/1, S. 45-69, Wien 1996. RING, U. 1989: Tectonogenesis of the Penninic/Austroalpine Boundary Zone: The Arosa Zone (Grisons Rätikon area, Swiss-Austrian Alps). - Unpubl. Phd.-Thesis., 177 p., Tübingen. STOECKHERT, B., RÖSSNER, G., KÜSTER, M., HEIDER, M., GUNDLACH, K. &RICHTER, D.K. 1990: High-Pressure Metamorphism of the Mesozoic Sediments in the Lower Engadine Window, Eastern Alps. - Terra Abstracts, 2, S. 34, 1990. THÖNI, M. 1981: Degree and Evolution of the Alpine Metamorphism in the Austroalpine Unit W of the Hohe Tauern in the light of K/Ar and Rb/Sr Age Determinations on Micas. - Jahrb. Geol. B.-A., 124/1, S. 111-174, Wien 1981.

  19. The Kokchetav Massif, Kazakhstan: "Type locality" of diamond-bearing UHP metamorphic rocks

    NASA Astrophysics Data System (ADS)

    Schertl, H.; Sobolev, N. V.

    2012-12-01

    Since the first discovery of in situ metamorphic diamond in the Kokchetav Massif in 1990, numerous scientists from different disciplines paid special attention to petrological and geochemical features, geodynamics and the mechanism of deep subduction and exhumation of UHP rocks. This discovery was a trigger for an intense search of further possible diamondiferous UHP terranes worldwide, successfully documented by numerous new findings. Thus far, more than 350 papers have been published on various aspects of the Kokchetav UHP rocks. A compilation of the most important and far-reaching implications are outlined here. PT-estimates yield peak metamorphic conditions of at least 43 kbar at temperatures of about 950-1000°C. Zircon separates show inherited Proterozoic cores and mantle with the peak of UHP metamorphism at about 537-530 Ma. Several Ar-Ar-ages on micas scatter around 529-528 and 521-517 Ma and reflect different stages of the exhumation history. Migmatization occurred during exhumation at about 526-520 Ma. Microdiamonds which reach a grain size of 300 micrometers, contain highly potassic fluid inclusions as well as solid inclusions like carbonates, different silicates and metal sulfides, which favours the idea of a diamond formation from a C-O-H bearing fluid. Nitrogen isotope data and negative δ13C values of Kokchetav diamonds indicate a metasedimentary origin. δ18O studies on garnet and clinopyroxene of a layered calcsilicate are ruling out a primitive mantle protolith; similar studies on eclogite indicate their basaltic protolith to have experienced water-rock interaction prior to UHP metamorphism. A number of unique mineralogical findings have been made. K-feldspar exsolutions in clinopyroxene demonstrate that potassium can be incorporated into the clinopyroxene structure under upper mantle pressures. Other significant observations are coesite exsolutions in titanite, quartz-rods in clinopyroxene, the discovery of K-tourmaline as well as new minerals

  20. Effects of magmatic and metamorphic volatiles on the evolution of fluid-rock interactions and fluid pressure during contact metamorphism

    SciTech Connect

    Hanson, R.B. )

    1992-01-01

    Finite difference models of hydrothermal flow around a cooling intrusion that include fluid production from the magma during crystallization and from wall rocks during heating are used to investigate the evolution of fluid pressure and fluid-rock interactions during the contact metamorphism. For a granodiorite intrusion with a width of 9 km and releasing just 1: H[sub 2]O linearly during crystallization, fluid production elevates fluid pressures to lithostatic values above and adjacent to the intrusion when permeabilities are less than 1 [mu]D (10[sup [minus]18] m[sup 2]). Alternatively, hydrofracturing resulting from fluid production would be sufficient to create and maintain a time-averaged permeability of 1 [mu]D for 50,000 years: permeability decreases gradually with time afterward until the magma crystallizes (350,000 years). In detail, the history depends strongly on how fluids are released from the crystallizing magma. The effect is comparable to that obtained for devolatilization of 5% H[sub 2]O by weight over heating of 400 C in adjacent wall rocks. Fluid production dominates other mechanisms for elevating fluid pressures such as thermal expansion of pore fluids or ductile strain. In models with both magmatic and metamorphic fluids, fluid flow is outward from the inner aureole for much of the cooling history at wall-rock permeabilities of [le]100 [mu]D. Extensive up-temperature flow is not predicted. The evolution of flow is such that magmatic fluids can initially dominate fluid-rock interactions in a plume above the intrusion, although the timing of interaction of magmatic and metamorphic waters is sensitive to the detailed devolatilization histories. Initial pore fluids rapidly become insignificant in the overall fluid budget. Surface or external fluids infiltrate only late in the cooling history, as rocks within a few kilometers of the intrusion are cooling.

  1. Lu-Hf Garnet Geochronology Reveals the Tectonic History of Precambrian Rocks in the Southern Rocky Mountains

    NASA Astrophysics Data System (ADS)

    Aronoff, R.; Andronicos, C.; Vervoort, J. D.; Hunter, R. A.

    2014-12-01

    Lu-Hf garnet dating of Proterozoic rocks of the southwestern United States provides constraints on the timing and geographic extent of metamorphism associated with the Yavapai, Mazatzal, and newly recognized Picuris orogenies. Prior work focusing on U-Pb dating of plutons and Ar geochronology has left the timing of prograde metamorphism ambiguous, particularly in northern New Mexico and southern Colorado. Because the Lu-Hf system dates the onset of garnet growth, it can constrain the timing of the prograde P-T path. Garnet schist samples from central and northern New Mexico exhibit garnet growth restricted to the time period between ~1460 and 1400 Ma. In the Picuris and Manzano mountains, the oldest Lu-Hf garnet ages predate the U-Pb ages of ~1.4 Ga plutons located near the dated samples. This implies that garnet growth, and therefore the onset of amphibolite facies metamorphism, cannot be driven by contact metamorphism, as has been previously inferred. Garnet-bearing samples from the Needle and Wet Mountains in southern Colorado display a range of garnet ages between ~1750 and 1470 Ma. A garnet gneiss from the Needle Mountains in southwestern Colorado yields an age of 1748 Ma, which is consistent with the Yavapai orogeny. This Lu-Hf garnet age has not been reset by contact metamorphism associated with the emplacement of the ~1.4 Ga Eolus batholith. Anatectic garnet in an orthogneiss from the northern Wet Mountains yields an age of 1601 Ma and is interpreted to date partial melting at the close of the Mazatzal orogeny. A 1476 Ma garnet age from the aureole of the 1440 Ma Oak Creek pluton is interpreted to date upper amphibolite facies metamorphism. The age distribution of these samples shows that rocks in Colorado underwent a complex, poly-metamorphic history, while rocks in New Mexico underwent a single progressive metamorphic event. This contrast implies that the boundary between rocks deformed and metamorphosed during the ~1800-1600 Ma Yavapai and Mazatzal

  2. Shock metamorphism of carbonaceous chondrites

    NASA Technical Reports Server (NTRS)

    Scott, Edward R. D.; Keil, Klaus; Stoeffler, Dieter

    1992-01-01

    Shock effects were studied in 69 carbonaceous chondrites, including CM2, CO3, CV3, ungrouped C2-C4, and CK4-6 chondrites, using optical microscopy of thin sections. It is shown that the classification scheme of Stoeffler et al. (1991) for the progressive stages of shock metamorphism in ordinary chondrites is also applicable to carbonaceous chondrites. On the basis of shock effects in olivine, the 69 carbonaceous chondrites could be assigned to four shock stage, S1 to S4. The CM2 and CO3 groups were found to be the least shocked chondrite groups, whereas the CK4-6 and CV3 were the most strongly shocked groups.

  3. Combustion metamorphism in southern california.

    PubMed

    Bentor, Y K; Kastner, M

    1976-08-01

    In several places in Southern California bituminous sediments of the Monterey Formation-siliceous shales, phosphatic rocks, dolomites, and arkoses-were affected during the Pleistocene and as late as the l9th century by spontaneous subsurface combustion of organic matter, during which temperatures up to 1600 degrees C were reached. This oxidative heating (combustion metamorphism) affected rock complexes over areas of tens of square kilometers that tend to occur in clusters. As a result of these processes, the rocks recrystallized and partially melted to form pseudomagmas which intruded the country rocks. The chemical compositions of these melts differ from those of igneous magmas. Acid and intermediate siliceous melts as well as phosphatic melts have formed. These two types are generally immiscible. The following high-temperature minerals were determined: alpha- and beta-cristobalite, quartz, calcic plagioclase, diopsidic pyroxene, wollastonite, cordierite, graphite, fluorapatite, and fluorite; at lower temperature pyrite, gypsum, aragonite, calcite, jarosite, and hexahydrite crystallized.

  4. Metamorphism and partial melting of ordinary chondrites: Calculated phase equilibria

    NASA Astrophysics Data System (ADS)

    Johnson, T. E.; Benedix, G. K.; Bland, P. A.

    2016-01-01

    Constraining the metamorphic pressures (P) and temperatures (T) recorded by meteorites is key to understanding the size and thermal history of their asteroid parent bodies. New thermodynamic models calibrated to very low P for minerals and melt in terrestrial mantle peridotite permit quantitative investigation of high-T metamorphism in ordinary chondrites using phase equilibria modelling. Isochemical P-T phase diagrams based on the average composition of H, L and LL chondrite falls and contoured for the composition and abundance of olivine, ortho- and clinopyroxene, plagioclase and chromite provide a good match with values measured in so-called equilibrated (petrologic type 4-6) samples. Some compositional variables, in particular Al in orthopyroxene and Na in clinopyroxene, exhibit a strong pressure dependence when considered over a range of several kilobars, providing a means of recognising meteorites derived from the cores of asteroids with radii of several hundred kilometres, if such bodies existed at that time. At the low pressures (<1 kbar) that typify thermal metamorphism, several compositional variables are good thermometers. Although those based on Fe-Mg exchange are likely to have been reset during slow cooling, those based on coupled substitution, in particular Ca and Al in orthopyroxene and Na in clinopyroxene, are less susceptible to retrograde diffusion and are potentially more faithful recorders of peak conditions. The intersection of isopleths of these variables may allow pressures to be quantified, even at low P, permitting constraints on the minimum size of parent asteroid bodies. The phase diagrams predict the onset of partial melting at 1050-1100 °C by incongruent reactions consuming plagioclase, clinopyroxene and orthopyroxene, whose compositions change abruptly as melting proceeds. These predictions match natural observations well and support the view that type 7 chondrites represent a suprasolidus continuation of the established petrologic

  5. Koolen metamorphic complex, NE Russia: Implications for the tectonic evolution of the Bering Strait region

    NASA Astrophysics Data System (ADS)

    Akinin, Vyacheslav V.; Gelman, Mikhail L.; Sedov, Boris M.; Amato, Jeffrey M.; Millwer, Elizabeth L.; Toro, Jaime; Calvert, Andrew T.; Fantini, Riccardo M.; Wright, James E.; Natal'in, Boris A.

    Structural culminations of midcrustal metamorphic rocks are found on both sides of the Bering Strait in Alaska and Russia and occur within a magmatic belt of Cretaceous age. Geologic mapping in the Koolen Lake-Lavrentia Bay region of the Chukchi Peninsula, Russia, outlines the basic relations between deformation, metamorphism, and magmatism in one of these structural culminations, the Koolen metamorphic complex. Here, a 10-15 km-thick, southwest dipping structural succession of gneisses and high-grade metamorphic rocks is exposed. The succession consists of a lower sequence of granitic gneisses and an upper sequence of biotite-rich gneisses, quartzofeldspathic gneisses, lesser amphibolite and marble, and gneisses and schists with an increasing abundance of intercalated marble and calc-silicate units toward the top. All rocks are strongly foliated and exhibit north-south trending stretching lineations. Deformation occurred during sillimanite-grade metamorphism concurrent with partial melting of the crust. Metamorphic conditions varied from 7 to 3 kbar and from 700°C-500°C. Three fractions of monazite from a deformed pegmatite yielded ages of 104 Ma. Igneous monazite from undeformed biotite granite yielded a U-Pb age of 94 Ma, indicating peak metamorphism and deformation is Cretaceous. Relations in the Koolen complex are similar to those in the Kigluaik gneiss dome, Seward Peninsula, Alaska, where upper amphibolite to granulite facies metamorphism and deformation occurred between ~105 and 90 Ma. Our findings,together with regional relations, suggest that wholesale crustal extension or extensional collapse of the crust affected this region, perhaps during Pacific-ward migration of subduction. The results do not support large amounts of east-west shortening between North America and Russia predicted by poles of rotation related to opening of the North Atlantic in the Late Cretaceous and Tertiary.

  6. An outline of tectonic, igneous, and metamorphic events in the Goshute-Toano Range between Silver Zone Pass and White Horse Pass, Elko County, Nevada; a history of superposed contractional and extensional deformation

    USGS Publications Warehouse

    Ketner, Keith Brindley; Day, Warren C.; Elrick, Maya; Vaag, Myra K.; Zimmerman, Robert A.; Snee, Lawrence W.; Saltus, Richard W.; Repetski, John E.; Wardlaw, Bruce R.; Taylor, Michael E.; Harris, Anita G.

    1998-01-01

    Seven kinds of fault-bounded tracts are described. One of the tracts provides a good example of Mesozoic contractional folding and faulting; six exemplify various aspects of Miocene extensional faulting. Massive landslide deposits resulting from Tertiary faulting are described. Mesozoic intrusive rocks and extensive exposures of Miocene volcanic rocks are described and dated. The age ranges of stratigraphic units were based on numerous conodont collections, and ages of igneous rocks were determined by argon/argon and fission-track methods. The geologic complexity of the Goshute-Toano Range provides opportunities for many additional productive structural studies.

  7. Using Age-Based Life History Data to Investigate the Life Cycle and Vulnerability of Octopus cyanea

    PubMed Central

    Herwig, Jade N.; Depczynski, Martial; Roberts, John D.; Semmens, Jayson M.; Gagliano, Monica; Heyward, Andrew J.

    2012-01-01

    Octopus cyanea is taken as an unregulated, recreationally fished species from the intertidal reefs of Ningaloo, Western Australia. Yet despite its exploitation and importance in many artisanal fisheries throughout the world, little is known about its life history, ecology and vulnerability. We used stylet increment analysis to age a wild O. cyanea population for the first time and gonad histology to examine their reproductive characteristics. O. cyanea conforms to many cephalopod life history generalisations having rapid, non-asymptotic growth, a short life-span and high levels of mortality. Males were found to mature at much younger ages and sizes than females with reproductive activity concentrated in the spring and summer months. The female dominated sex-ratios in association with female brooding behaviours also suggest that larger conspicuous females may be more prone to capture and suggests that this intertidal octopus population has the potential to be negatively impacted in an unregulated fishery. Size at age and maturity comparisons between our temperate bordering population and lower latitude Tanzanian and Hawaiian populations indicated stark differences in growth rates that correlate with water temperatures. The variability in life history traits between global populations suggests that management of O. cyanea populations should be tailored to each unique set of life history characteristics and that stylet increment analysis may provide the integrity needed to accurately assess this. PMID:22912898

  8. 81Kr-Kr age and multiple cosmic-ray exposure history of the Vaca Muerta mesosiderite

    NASA Astrophysics Data System (ADS)

    Bajo, Ken-Ichi; Nagao, Keisuke

    2011-04-01

    Noble gas isotopic compositions were measured for a eucritic pebble and bulk material of a silicate-metal mixture from the Vaca Muerta mesosiderite as well as pyroxene and plagioclase separated from the eucritic pebble by total melting and stepwise heating methods. Trapped noble gases were degassed completely by a high-temperature thermal event, probably at the formation of the Vaca Muerta parent body (VMPB). The presence of fissiogenic Xe isotopes from extinct 244Pu in the bulk samples might be a result of rapid cooling from an early high-temperature metamorphism. High concentrations of cosmogenic noble gases enabled us to determine precise isotopic ratios of cosmogenic Kr and Xe. Spallogenic Ne from Na and unique Ar isotopic compositions were observed. The 81Kr-Kr exposure age of 168 ± 8 Myr for the silicate pebble is distinctly longer than the age of 139 ± 8 Myr for the bulk samples. The precursor of the pebble had been irradiated on the surface of the VMPB for more than 60 Myr (first stage irradiation), with subsequent incorporation into bulk materials approximately 4 Gyr ago. The Vaca Muerta meteorite was excavated from the VMPB 140 Myr ago (second stage irradiation). Relative diffusion rates among the cosmogenic Ar, Kr, and Xe based on data obtained by stepwise heating indicate that Kr and Xe can be partially retained in pyroxene and plagioclase under the condition that resets the K-Ar system. This result supports the presence of fission Xe and of excess concentration of cosmogenic Kr, which could have survived the thermal event approximately 3.8 Gyr ago.

  9. The timing of tertiary metamorphism and deformation in the Albion-Raft River-Grouse Creek metamorphic core complex, Utah and Idaho

    USGS Publications Warehouse

    Strickland, A.; Miller, E.L.; Wooden, J.L.

    2011-01-01

    The Albion-Raft River-Grouse Creek metamorphic core complex of southern Idaho and northern Utah exposes 2.56-Ga orthogneisses and Neoproterozoic metasedimentary rocks that were intruded by 32-25-Ma granitic plutons. Pluton emplacement was contemporaneous with peak metamorphism, ductile thinning of the country rocks, and top-to-thewest, normal-sense shear along the Middle Mountain shear zone. Monazite and zircon from an attenuated stratigraphic section in the Middle Mountain were dated with U-Pb, using a SHRIMP-RG (reverse geometry) ion microprobe. Zircons from the deformed Archean gneiss preserve a crystallization age of 2532 ?? 33 Ma, while monazites range from 32.6 ?? 0.6 to 27.1 ?? 0.6 Ma. In the schist of the Upper Narrows, detrital zircons lack metamorphic overgrowths, and monazites produced discordant U-Pb ages that range from 52.8 ?? 0.6 to 37.5 ?? 0.3 Ma. From the structurally and stratigraphically highest unit sampled, the schist of Stevens Spring, narrow metamorphic rims on detrital zircons yield ages from 140-110 Ma, and monazite grains contained cores that yield an age of 141 ??2 Ma, whereas rims and some whole grains ranged from 35.5 ?? 0.5 to 30.0 ?? 0.4 Ma. A boudinaged pegmatite exposed in Basin Creek is deformed by the Middle Mountains shear zone and yields a monazite age of 27.6 ?? 0.2 Ma. We interpret these data to indicate two periods of monazite and metamorphic zircon growth: a poorly preserved Early Cretaceous period (???140 Ma) that is strongly overprinted by Oligocene metamorphism (???32-27 Ma) related to regional plutonism and extension. ?? 2011 by The University of Chicago.

  10. Jurassic to Miocene magmatism and metamorphism in the Mogok metamorphic belt and the India-Eurasia collision in Myanmar

    NASA Astrophysics Data System (ADS)

    Barley, M. E.; Pickard, A. L.; Zaw, Khin; Rak, P.; Doyle, M. G.

    2003-06-01

    Situated south of the eastern Himalayan syntaxis at the western margin of the Shan-Thai terrane the high-grade Mogok metamorphic belt (MMB) in Myanmar occupies a key position in the tectonic evolution of Southeast Asia. The first sensitive high-resolution ion microprobe U-Pb in zircon geochronology for the MMB shows that strongly deformed granitic orthogneisses near Mandalay contain Jurassic (˜170 Ma) zircons that have partly recrystallized during ˜43 Ma high-grade metamorphism. A hornblende syenite from Mandalay Hill also contains Jurassic zircons with evidence of Eocene metamorphic recrystallization rimmed by thin zones of 30.9 ± 0.7 Ma magmatic zircon. The relative abundance of Jurassic zircons in these rocks is consistent with suggestions that southern Eurasia had an Andean-type margin at that time. Mid-Cretaceous to earliest Eocene (120 to 50 Ma) I-type granitoids in the MMB, Myeik Archipelago, and Western Myanmar confirm that prior to the collision of India, an up to 200 km wide magmatic belt extended along the Eurasian margin from Pakistan to Sumatra. Metamorphic overgrowths to zircons in the orthogneiss near Mandalay date a period of Eocene (˜43 Ma) high-grade metamorphism possibly during crustal thickening related to the initial collision between India and Eurasia (at 65 to 55 Ma). This was followed by emplacement of syntectonic hornblende syenites and leucogranites between 35 and 23 Ma. Similar syntectonic syenites and leucogranites intruded the Ailao Shan-Red River shear belt in southern China and Vietnam during the Eocene-Oligocene to Miocene, and the Wang Chao and Three Pagodas faults in northern Thailand (that most likely link with the MMB) were also active at this time. The complex history of Eocene to early Miocene metamorphism, deformation, and magmatism in the MMB provides evidence that it may have played a key role in the network of deformation zones that accommodated strain during the northwards movement of India and resulting extrusion or

  11. Contrasting Metamorphic Record of Heat Production Anomalies in the Penokean Orogen of Northern Michigan.

    PubMed

    Attoh

    2000-05-01

    It is proposed that the contrasting metamorphic mineral assemblages of the isolated amphibolite facies metamorphic highs in the Penokean orogen of northern Michigan may be caused by different heat production rates in the Archean basement. This hypothesis is based on concentrations of K, U, and Th in the Archean basement gneisses and Paleoproterozoic metasediments that indicate significant contribution of radiogenic heating during Penokean metamorphism. Heat production was anomalously high ( approximately 10.6 µWm-3) where andalusite-bearing mineral assemblages indicate that high temperatures were attained at shallow crustal levels ( approximately 550 degrees -600 degrees C at approximately 3 kbar). In contrast, where exposed metamorphic rocks indicate peak temperatures of 600 degrees -650 degrees C at 6-7 kbar, heat production in the Archean basement was lower ( approximately 3.7 µWm-3). The effect of heat production rates on the metamorphic pressure-temperature paths was tested with numerical thermal models. The calculations show (1) that if the heat production rate, where andalusite-bearing assemblages formed, was significantly <6.0 µWm-3, the estimated pressure at peak temperatures (PTmax) would be much higher and lie in the sillimanite or kyanite stability fields; and (2) differences between PTmax estimates for the metamorphic highs based on thermobarometry can be reproduced if thermal history involved significant crustal thickening as well as moderate unroofing rates. PMID:10769161

  12. Contrasting Metamorphic Record of Heat Production Anomalies in the Penokean Orogen of Northern Michigan.

    PubMed

    Attoh

    2000-05-01

    It is proposed that the contrasting metamorphic mineral assemblages of the isolated amphibolite facies metamorphic highs in the Penokean orogen of northern Michigan may be caused by different heat production rates in the Archean basement. This hypothesis is based on concentrations of K, U, and Th in the Archean basement gneisses and Paleoproterozoic metasediments that indicate significant contribution of radiogenic heating during Penokean metamorphism. Heat production was anomalously high ( approximately 10.6 µWm-3) where andalusite-bearing mineral assemblages indicate that high temperatures were attained at shallow crustal levels ( approximately 550 degrees -600 degrees C at approximately 3 kbar). In contrast, where exposed metamorphic rocks indicate peak temperatures of 600 degrees -650 degrees C at 6-7 kbar, heat production in the Archean basement was lower ( approximately 3.7 µWm-3). The effect of heat production rates on the metamorphic pressure-temperature paths was tested with numerical thermal models. The calculations show (1) that if the heat production rate, where andalusite-bearing assemblages formed, was significantly <6.0 µWm-3, the estimated pressure at peak temperatures (PTmax) would be much higher and lie in the sillimanite or kyanite stability fields; and (2) differences between PTmax estimates for the metamorphic highs based on thermobarometry can be reproduced if thermal history involved significant crustal thickening as well as moderate unroofing rates.

  13. 40Ar/39Ar thermochronology of mesoproterozoic metamorphism in the Colorado Front Range

    USGS Publications Warehouse

    Shaw, C.A.; Snee, L.W.; Selverstone, J.; Reed, J.C.

    1999-01-01

    A low-pressure metamorphic episode in the Colorado Front Range has been identified by the presence of staurolite, andalusite, cordierite, and garnet porphyroblasts overprinting earlier assemblages. The overprinting assemblages and reaction textures are most consistent with porphyroblast growth on a prograde metamorphic path with peak temperatures exceeding ~525??C. Twenty-eight 40Ar/39Ar dates on hornblende, muscovite, biotite, and microcline were used to infer the age and thermal conditions of metamorphism. Muscovite and biotite 40Ar/39Ar ages fall mainly in the interval 1400-1340 Ma, consistent with cooling through the closure temperature interval of micas (~400??-300??C) after about 1400 Ma. In contrast, hornblende apparent ages (T(c)~500??-550??C) between 1600 and 1390 Ma reflect variable retention of radiogenic argon. Forward modeling of argon diffusion shows that the distribution of hornblende and mica ages is consistent with the partial resetting of argon systematics ca. 1400 Ma by a thermal pulse reaching maximum temperatures around 550??C and decaying within <20 m.yr. These temperatures match the conditions inferred from the overprinting assemblage; thus, muscovite and biotite ages are interpreted to date the cooling phase of this metamorphic event. This late metamorphism is broadly coeval with the intrusion of ca. 1400-Ma granitic plutons in the study area and throughout the southwestern United States. However, thermal effects are observed far from pluton margins, suggesting pervasive, regional crustal heating rather than restricted contact metamorphism. Our results suggest that ca. 1400-Ma metamorphism and plutonism are manifestations of a regional thermal episode that both partially melted the lower crust and pervasively metamorphosed middle crustal rocks.

  14. Granulite Facies Metamorphism in the Kabul Block, Afghanistan

    NASA Astrophysics Data System (ADS)

    Collett, S.; Faryad, S. W.

    2012-04-01

    The Proterozoic Kabul Block is part of the Afghan Central Massif and occurs between the Hindu Kush and Sulaiman Mountain ranges. It consists of amphibolite to granulite facies rocks of Paleo-Neoproterzoic age. The Kabul block has a lens-like shape and is encircled by the Chaman fault from NW and the Altimoor faults from SE. The basement rocks of the Kabul Block are predominantly represented by schists, gneisses and migmatites with lenses of amphibolites and locally also marble. They are mostly unconformably overlain by low-grade early to late Paleozoic sequences. As the Kabul block occurs between the magmatic arc and accretionary wedge which formed during subduction and subsequent collision of the Indian Plate beneath the Laurasian continent, it was subjected to compression and a metamorphic overprint during Alpine orogeny to various degrees. The granulite facies rocks are exposed only locally within amphibolite facies gneisses and migmatites, exposed in the hills that surround Kabul city. They are represented by quartz-feldspathic lithology, which contains lenses of marble and amphibolite. Granulite facies conditions are confirmed by the presence of orthopyroxene both in the gneiss and amphibolite. In addition to orthopyroxene (XMg = 0.4, Al2O3 = 1.3 wt %), the gneiss contains quartz, plagioclase (An27-36), orthoclase and biotite with XMg = 0.36 and TiO2 = 3.5 wt %. The rocks are overprinted by amphibolite facies metamorphism, which is represented by the formation of garnet overgrowing biotite and orthopyroxene. The mafic rocks consist of plagioclase (An87), hornblende (XMg = 0.81), biotite and orthopyroxene (XMg = 0.57, Al2O3 = 1.1 wt %) with inclusions of ilmenite, cummingtonite (XMg = 0.6) and biotite. Hornblende forms as a rim around cummingtonite and overgrows orthopyroxene. Biotite present in this sample has XMg = 0.63 with almost 4 wt % TiO2. Marble adjacent to the granulites are mostly pure calcite, but at contact with surrounding rocks may contain also

  15. A History of Alcohol Dependence Augments HIV-associated Neurocognitive Deficits in Persons Aged 60 and Older

    PubMed Central

    Gongvatana, Assawin; Morgan, Erin E.; Iudicello, Jennifer E.; Letendre, Scott L.; Grant, Igor; Woods, Steven Paul

    2014-01-01

    Background Excessive alcohol use is common among people living with HIV. Given the growing prevalence of older HIV+ adults, and observations indicating higher risk for neurocognitive impairment in older adults with either HIV infection or alcoholism, an increased understanding of their combined impact in the context of this increasingly aged population is crucial. Methods We conducted comprehensive neurocognitive assessment in 112 older HIV+ individuals aged 50 to 69 years. Regression analyses were conducted to examine the interaction between age and the presence of lifetime alcohol dependence on neurocognitive measures, controlling for years of education, hepatitis C serostatus, and lifetime non-alcohol substance use disorder. Results Significant interactions of age and alcohol dependence history were found for global neurocognitive function, which was driven by the domains of executive function, processing speed, and semantic memory. Follow-up analyses indicated adverse effects of alcohol use history on neurocognitive measures that were evident only in HIV+ individuals 60 years and older. Conclusions While mounting evidence in younger cohorts indicates adverse synergistic HIV/alcohol effects on neurocognitive function, our novel preliminary findings in this elderly HIV+ cohort demonstrated the importance of even a relatively distant alcohol use history on the expression of HIV-associated neurocognitive disorders that may not become apparent until much later in life. PMID:25201556

  16. Perspectives on elasmobranch life-history studies: a focus on age validation and relevance to fishery management.

    PubMed

    Cailliet, G M

    2015-12-01

    Life-history (age, growth, age validation, reproduction and demography) studies of elasmobranchs date back to the middle of the last century with major early contributions made by British fishery scientists. As predicted by Holden in the early 1970s, many sharks and rays can be vulnerable to fishery mortality because they grow slowly, mature late in life, reproduce infrequently, have relatively low fecundities and can have relatively long life spans. As has now been found, however, not all species exhibit these traits. Also, ageing structures (neural arches and caudal thorns), other than vertebrae and spines, have since been evaluated. Various methods for validating age and growth estimates have been developed and tested on numerous species of elasmobranchs. These include tag-recapture analyses, oxytetracycline injections, centrum or spine edge and marginal increment analyses, and bomb radiocarbon dating of calcified structures. Application of these techniques has sometimes not only validated relatively slow growth and long life span estimates, but also has produced other results. A brief historical perspective on the applications and limitations of these techniques for elasmobranchs is provided, along with a discussion of selected species for which these techniques worked well, did not work at all or have produced variable and conflicting results. Because many fishery management techniques utilize age or stage-specific information, often through demographic analyses, accurate information on the life histories of fished populations, especially age validation, is extremely important for the fishery management of these cartilaginous fishes.

  17. Perspectives on elasmobranch life-history studies: a focus on age validation and relevance to fishery management.

    PubMed

    Cailliet, G M

    2015-12-01

    Life-history (age, growth, age validation, reproduction and demography) studies of elasmobranchs date back to the middle of the last century with major early contributions made by British fishery scientists. As predicted by Holden in the early 1970s, many sharks and rays can be vulnerable to fishery mortality because they grow slowly, mature late in life, reproduce infrequently, have relatively low fecundities and can have relatively long life spans. As has now been found, however, not all species exhibit these traits. Also, ageing structures (neural arches and caudal thorns), other than vertebrae and spines, have since been evaluated. Various methods for validating age and growth estimates have been developed and tested on numerous species of elasmobranchs. These include tag-recapture analyses, oxytetracycline injections, centrum or spine edge and marginal increment analyses, and bomb radiocarbon dating of calcified structures. Application of these techniques has sometimes not only validated relatively slow growth and long life span estimates, but also has produced other results. A brief historical perspective on the applications and limitations of these techniques for elasmobranchs is provided, along with a discussion of selected species for which these techniques worked well, did not work at all or have produced variable and conflicting results. Because many fishery management techniques utilize age or stage-specific information, often through demographic analyses, accurate information on the life histories of fished populations, especially age validation, is extremely important for the fishery management of these cartilaginous fishes. PMID:26709208

  18. White matter microstructure in late middle-age: Effects of apolipoprotein E4 and parental family history of Alzheimer's disease

    PubMed Central

    Adluru, Nagesh; Destiche, Daniel J.; Lu, Sharon Yuan-Fu; Doran, Samuel T.; Birdsill, Alex C.; Melah, Kelsey E.; Okonkwo, Ozioma C.; Alexander, Andrew L.; Dowling, N. Maritza; Johnson, Sterling C.; Sager, Mark A.; Bendlin, Barbara B.

    2014-01-01

    Introduction Little is still known about the effects of risk factors for Alzheimer's disease (AD) on white matter microstructure in cognitively healthy adults. The purpose of this cross-sectional study was to assess the effect of two well-known risk factors for AD, parental family history and APOE4 genotype. Methods This study included 343 participants from the Wisconsin Registry for Alzheimer's Prevention, who underwent diffusion tensor imaging (DTI). A region of interest analysis was performed on fractional anisotropy maps, in addition to mean, radial, and axial diffusivity maps, aligned to a common template space using a diffeomorphic, tensor-based registration method. The analysis focused on brain regions known to be affected in AD including the corpus callosum, superior longitudinal fasciculus, fornix, cingulum, and uncinate fasciculus. Analyses assessed the impact of APOE4, parental family history of AD, age, and sex on white matter microstructure in late middle-aged participants (aged 47–76 years). Results Both APOE4 and parental family history were associated with microstructural white matter differences. Participants with parental family history of AD had higher FA in the genu of the corpus callosum and the superior longitudinal fasciculus. We observed an interaction between family history and APOE4, where participants who were family history positive but APOE4 negative had lower axial diffusivity in the uncinate fasciculus, and participants who were both family history positive and APOE4 positive had higher axial diffusivity in this region. We also observed an interaction between APOE4 and age, whereby older participants (=65 years of age) who were APOE4 carriers, had higher MD in the superior longitudinal fasciculus and in the portion of the cingulum bundle running adjacent to the cingulate cortex, compared to non-carriers. Older participants who were APOE4 carriers also showed higher radial diffusivity in the genu compared to non-carriers. Across

  19. Potential contributions of metamorphic petrology studies in an ultra-deep drillhole in the southern Appalachians

    SciTech Connect

    Speer, J.A.

    1985-01-01

    The proposed, ultra-deep hole in the southeast U.S. will penetrate allochthonous, medium- to high-grade metamorphic rocks of the Inner Piedmont and Blue Ridge thrust sheets. It is anticipated that the hole will then encounter autochthonous low-grade, metasedimentary cover rocks before bottoming out in crystalline Precambrian basement rocks. Metamorphic petrology in the recent past has concentrated on unraveling the physical and chemical history (P, T, X/sub fluid/, etc.) of metamorphic rocks. The techniques that have been developed are ideally suited to the study of relatively limited samples from drill core. Detailed studies of the allochthonous and autochthonous rocks from the drillhole, combined with comparable studies of the surface rocks, by metamorphic petrologists experimented with these approaches, would give a 3-dimensional picture of the PTX evolution in the region of the ultra-deep hole, and thus an idea of the geometrical, chemical, and physical changes the rocks experienced. This would place constraints on conditions of the rocks before and after thrusting and thus any tectonic models of thrusting in the southern Appalachians. With limited sampling this could be a problem, with more complete sampling it will be an advantage. The metamorphic petrology of the rocks will provide basic support for the other studies of the drill core and drillhole, most notably geochronology and stable isotopes. It should not be forgotten that in addition to the historical metamorphism, the expected, present-day conditions in the drillhole are those of burial metamorphism. The hole will present an excellent opportunity to study such active metamorphic conditions.

  20. Carry-over effects of the larval environment on post-metamorphic performance in two hylid frogs.

    PubMed

    Van Allen, Benjamin G; Briggs, Venetia S; McCoy, Michael W; Vonesh, James R

    2010-12-01

    Life history theory and empirical studies suggest that large size or earlier metamorphosis are suitable proxies for increased lifetime fitness. Thus, across a gradient of larval habitat quality, individuals with similar phenotypes for these traits should exhibit similar post-metamorphic performance. Here we examine this paradigm by testing for differences in post-metamorphic growth and survival independent of metamorphic size in a temperate (spring peeper, Pseudacris crucifer) and tropical (red-eyed treefrog, Agalychnis callidryas) anuran reared under differing larval conditions. For spring peepers, increased food in the larval environment increased post-metamorphic growth efficiency more than predicted by metamorphic phenotype and led to increased mass. Similarly, red-eyed treefrogs reared at low larval density ended the experiment at a higher mass than predicted by metamorphic phenotype. These results show that larval environments can have delayed effects not captured by examining only metamorphic phenotype. These delayed effects for the larval environment link larval and juvenile life history stages and could be important in the population dynamics of organisms with complex life cycles.

  1. Neoarchean metamorphism recorded in high-precision Sm-Nd isotope systematics of garnets from the Jack Hills (Western Australia)

    NASA Astrophysics Data System (ADS)

    Eccles, K. A.; Baxter, E. F.; Mojzsis, S. J.; Marschall, H.; Williams, M. L.; Jercinovic, M. J.

    2013-12-01

    Studies of metasedimentary rocks from the Jack Hills, which host Earth's oldest known detrital minerals, have focused on zircon and occasionally monazite or xenotime, but no attention has been directed toward one of the most common mineral markers of metamorphism: garnet. Garnet can provide a record of the post-depositional, prograde metamorphic history of Archean metasedimentary rocks. Additionally, the use of a newly developed detrital garnet dating technique [1,2] may reveal information about pre-depositional metamorphism that could address lingering questions about the nature and timing of Earth's earliest tectonometamorphic events. Here we investigate garnet from the Jack Hills metasedimentary rocks to test whether they record in situ metamorphism or are a detrital relict of even older metamorphic events. We identified garnet in two bulk quartz-pebble conglomerate samples collected from the 'discovery' outcrop at Eranondoo Hill in the Jack Hills of Western Australia. Electron microprobe analyses of polished grains and SEM measurements of unpolished grain surfaces are consistent, revealing garnet composition indicative of a single generation/population of predominantly almandine-spessartine solid solution (~10-35% mole fraction spessartine). Compositional maps of garnet grains reveal little zoning and no discontinuities, most consistent with a single growth event. Dating Jack Hills' garnet via the Sm-Nd system is possible due to continued development of small sample analysis techniques, including running NdO+ TIMS analyses with Ta2O5 activator [3] permitting <50 ppm 2 sigma analytical precision on a 400pg in-house standard and continued improvement in blanks (<15pg full procedural blanks). Additionally, employing a nondestructive chemical prescreening technique (tabletop SEM) allows for grouping of multiple grains based on chemical similarity. Final Nd loads in the 450-750pg range routinely yield dates with precisions <×10Ma for two point isochrons between

  2. Thermal metamorphism. [of chondrite parent bodies

    NASA Technical Reports Server (NTRS)

    Mcsween, Harry Y., Jr.; Sears, Derek W. G.; Dodd, Robert T.

    1988-01-01

    Most chondrites have experienced thermal metamorphism, resulting in changes in texture, mineralogy and possibly chemical composition. The physical conditions for metamorphism range from approximately 400 to 1000 C at low lithostatic pressure. Metamorphism may have resulted from decay of short-lived radionuclides, electromagnetic induction or accretion of hot materials. Several thermal models for chondrite parent bodies have been proposed. The least metamorphosed type-3 chondrites probably carry the most information about the early solar system, but even these have been affected to some degree by thermal processing.

  3. Quantitative estimates of metamorphic equilibria: Tallassee synform, Dadeville belt, Alabama's Inner Piedmont

    SciTech Connect

    Drummond, M.S.; Neilson, M.J. . Dept. of Geology)

    1993-03-01

    The Tallassee synform is the major structural feature in the western part of the Dadeville belt. This megascopic F2 structure folds amphibolite (Ropes Creek Amphibolite) and metasedimentary units (Agricola Schist, AS), as well as tonalitic (Camp Hill Gneiss, CHG), granitic (Chattasofka Creek Gneiss, CCG), and mafic-ultramafic plutons (Doss Mt. and Slaughters suites). Acadian-age prograde regional metamorphism preceded the F2 folding event, producing the pervasive S1 foliation and metamorphic recrystallization. Prograde mineralogy in the metapelites and metagraywackes of the AS includes garnet, biotite, muscovite, plagioclase, kyanite, sillimanite, and epidote. The intrusive rocks, both felsic and mafic-ultramafic, are occasionally garnetiferous and provide suitable mineral assemblages for P-T evaluation. The AS yields a range of T-P from 512--635C and 5.1--5.5 kb. Muscovite from the AS exhibits an increase in Ti content from 0.07 to 0.15 Ti/22 O formula unit with progressively increasing T's from 512 to 635C. This observation is consistent with other studies that show increasing Ti content with increasing grade. A CHG sample records an average metamorphic T-P of 604C and 5.79 kb. Hornblende-garnet pairs from a Doss Mt. amphibolite sample provides an average metamorphic T of 607C. These data are consistent with regional Barrovian-type middle to upper amphibolite facies metamorphism for the Tallassee synform. Peak metamorphism is represented by kyanite-sillimanite zone conditions and localized migmatization of the AS. The lithotectonic belts bounding the Dadeville belt to the NW and SE are the eastern Blue Ridge and Opelika belts. Studies have shown that these belts have also experienced Acadian-age amphibolite facies metamorphism with comparable P-T estimates to those presented here. These data suggest that the eastern Blue Ridge and Inner Piedmont of AL experienced the same pervasive dynamothermal Barrovian-type metamorphic episode during Acadian orogenesis.

  4. Tectonometamorphic evolution of the Bohemian Massif: evidence from high pressure metamorphic rocks

    NASA Astrophysics Data System (ADS)

    O'Brien, P. J.; Carswell, D. A.

    1993-09-01

    The Variscan orogenic belt, of which the Bohemian Massif is a part, is typically recognized for its characteristic low pressure, high temperature metamorphism and a large volume of granites. However, there are also bodies of high pressure rocks (eclogites, garnet peridotites and high pressure granulites) which are small in size but widely distributed throughtout the Massif. Initially the high pressure rocks were considered to be relicts of a much older orogenic event, but the increasing data derived from isotopic and geochronological investigations show that many of these rocks have Palaeozoic protoliths. Metamorphic ages from the high pressure rocks define no single event. Instead, a number of discrete clusters of ages are found between about 430 Ma and the time of the dominant low pressure event at around 320 330 Ma. Most of the eclogite and granulite facies rocks are assigned to allochthonous nappes that arrived close to the end of the low pressure event, but before final granite intrusion. The nappes contain a mixture of different units and the relationship between rocks with high pressure relicts and host gneisses with no apparent signs of deep burial is still problematic. Some of the high pressure rocks retain evidence of multiple stages of partial re-equilibration during uplift. Moreover, it can be shown in certain instances that host gneisses also endured a multistage metamorphic development but with a peak event convergent with one of the breakdown stages in the enclosed rocks with high pressure relicts. It thus appears that the nappe units are composite bodies probably formed during episodic intracrustal thrusting. Fluids derived from prograde dehydration reactions in the newly under thrusting slab are taken to be the catalysts that drove the partial re-equilibrations. On the scale of the whole Massif it can be seen within the units with high pressure relicts that the temperature at the peak recorded pressure and that during the breakdown are variable in

  5. What shall I do now? State-dependent variations of life-history traits with aging in Wandering Albatrosses

    PubMed Central

    Pardo, Deborah; Barbraud, Christophe; Weimerskirch, Henri

    2014-01-01

    Allocation decisions depend on an organism's condition which can change with age. Two opposite changes in life-history traits are predicted in the presence of senescence: either an increase in breeding performance in late age associated with terminal investment or a decrease due to either life-history trade-offs between current breeding and future survival or decreased efficiency at old age. Age variation in several life-history traits has been detected in a number of species, and demographic performances of individuals in a given year are influenced by their reproductive state the previous year. Few studies have, however, examined state-dependent variation in life-history traits with aging, and they focused mainly on a dichotomy of successful versus failed breeding and non-breeding birds. Using a 50-year dataset on the long-lived quasi-biennial breeding wandering albatross, we investigated variations in life-history traits with aging according to a gradient of states corresponding to potential costs of reproduction the previous year (in ascending order): non-breeding birds staying at sea or present at breeding grounds, breeding birds that failed early, late or were successful. We used multistate models to study survival and decompose reproduction into four components (probabilities of return, breeding, hatching, and fledging), while accounting for imperfect detection. Our results suggest the possible existence of two strategies in the population: strict biennial breeders that exhibited almost no reproductive senescence and quasi-biennial breeders that showed an increased breeding frequency with a strong and moderate senescence on hatching and fledging probabilities, respectively. The patterns observed on survival were contrary to our predictions, suggesting an influence of individual quality rather than trade-offs between reproduction and survival at late ages. This work represents a step further into understanding the evolutionary ecology of senescence and its

  6. Reconstructing the history of major Greenland glaciers since the Little Ice Age

    NASA Astrophysics Data System (ADS)

    Csatho, B. M.; Schenk, A. F.; van der Veen, C. J.; Stearns, L.; Babonis, G. S.

    2008-12-01

    The Greenland Ice Sheet may have been responsible for rapid sea level rise during the last interglacial period and recent studies indicate that it is likely to make a faster contribution to sea-level rise than previously believed. Rapid thinning and velocity increase has been observed on most major outlet glaciers with terminus retreat that might lead to increased discharge from the interior and consequent further thinning and retreat. Potentially, such behavior could have serious implications for global sea level. However, the current thinning may simply be a manifestation of longer-term behavior of the ice sheet as it responds to the general warming following the Little Ice Age (LIA). Although Greenland outlet glaciers have been comprehensively monitored since the 1980s, studies of long-term changes mostly rely on records of the calving front position. Such records can be misleading because the glacier terminus, particularly if it is afloat, can either advance or retreat as ice further upstream thins and accelerates. To assess whether recent trends deviate from longer-term behavior, we examined three rapidly thinning and retreating outlet glaciers, Jakobshavn Isbrae in west, Kangerdlussuaq Glacier in east and Petermann Glacier in northwest Greenland. Glacier surface and trimline elevations, as well as terminus positions were measured using historical photographs and declassified satellite imagery acquired between the 1940s and 1985. These results were combined with data from historical records, ground surveys, airborne laser altimetry, satellite observations and field mapping of lateral moraines and trimlines, to reconstruct the history of changes since the (LIA) up to the present. We identified several episodes of rapid thinning and ice shelf break-up, including thinning episodes that occurred when the calving front was stationary. Coastal weather station data are used to assess the influence of air temperatures and intensity of surface melting, and to isolate

  7. Birth history, age structure, and post World War II fertility in ten developed countries: an exploratory empirical analysis.

    PubMed

    Artzrouni, M A; Easterlin, R A

    1982-01-01

    A post World War 2 swing in fertility occurred in many industrialized countries. Research focusing chiefly on the US has suggested that a country's prior birth history has, through its effects on age structure, been an important cause of this fertility swing. The reasoning is that the pre-World War 2 depression in fertility and post World War 2 baby boom produced after 1945 1st a scarcity and then an abundance of those in family-forming ages relative to older adults. The relative scarcity of young adults, in turn, created favorable economic and psychological conditions among those in child bearing ages and promoted marriage and child bearing; the relative abundance had the opposite effect. This paper examines the relation between birth history and fertility from 1951-76 in England, Wales, France, Netherlands, Sweden, Finland, Denmark, Switzerland, Spain, Italy, and the US and explores the implications of the analysis for experience in the remainder of this century. The analysis builds on the well-known proposition that age structure is primarily determined by a country's birth history. Birth data can be thought of as yielding an imputed age ratio, that which would prevail in the absence of mortality and migration. Analysis of data indicates that the pattern of change in the imputed ratio usually approximates fairly closely that in the actual ratio. A ratio of old to young can be thought of as consisting of an upper age limit, lower age limit, and an intermediate age that divides the population into young and old. With all 3 of these ages free to vary, a computer program then determines within certain constraints which of all possible imputed ratios of old to young has the highest (positive or negative) correlation with the total fertility rate from 1951-76. In all countries except Italy the results support the hypothesis that a scarcity of adults in the younger adult ages relative to those in older ages leads to a relatively high total fertility rate; a relative

  8. Histamine is a modulator of metamorphic competence in Strongylocentrotus purpuratus (Echinodermata: Echinoidea)

    PubMed Central

    2012-01-01

    Background A metamorphic life-history is present in the majority of animal phyla. This developmental mode is particularly prominent among marine invertebrates with a bentho-planktonic life cycle, where a pelagic larval form transforms into a benthic adult. Metamorphic competence (the stage at which a larva is capable to undergo the metamorphic transformation and settlement) is an important adaptation both ecologically and physiologically. The competence period maintains the larval state until suitable settlement sites are encountered, at which point the larvae settle in response to settlement cues. The mechanistic basis for metamorphosis (the morphogenetic transition from a larva to a juvenile including settlement), i.e. the molecular and cellular processes underlying metamorphosis in marine invertebrate species, is poorly understood. Histamine (HA), a neurotransmitter used for various physiological and developmental functions among animals, has a critical role in sea urchin fertilization and in the induction of metamorphosis. Here we test the premise that HA functions as a developmental modulator of metamorphic competence in the sea urchin Strongylocentrotus purpuratus. Results Our results provide strong evidence that HA leads to the acquisition of metamorphic competence in S. purpuratus larvae. Pharmacological analysis of several HA receptor antagonists and an inhibitor of HA synthesis indicates a function of HA in metamorphic competence as well as programmed cell death (PCD) during arm retraction. Furthermore we identified an extensive network of histaminergic neurons in pre-metamorphic and metamorphically competent larvae. Analysis of this network throughout larval development indicates that the maturation of specific neuronal clusters correlates with the acquisition of metamorphic competence. Moreover, histamine receptor antagonist treatment leads to the induction of caspase mediated apoptosis in competent larvae. Conclusions We conclude that HA is a modulator

  9. Life-History Related Differences in Possible Selves in Very Old Age

    ERIC Educational Resources Information Center

    Hoppmann, Christiane; Smith, Jacqui

    2007-01-01

    The impact of early life events that take place under specific historical and societal circumstances on adult development have rarely been investigated in old age. We examined whether having started a family in young adulthood was related to the contents of possible selves generated by women aged 85 to 100+ in the Berlin Aging Study (N = 129; M…

  10. Complex Histories of Two Lunar Zircons as Evidenced by their Internal Structures and U-Pb Ages

    NASA Technical Reports Server (NTRS)

    Pidgeon, R. T.; Nemchin, A. A.; Meyer, Charles

    2006-01-01

    The U-Pb dating of lunar zircon by ion-microprobe provides a robust technique for investigating the timing of lunar events [1,2]. However, we have now identified two cases where the U-Pb systems in a single zircon show more than one age. These complex zircons provide new opportunities for extending our knowledge on the timing of events in the early history of the Moon.

  11. Long-term tectonothermal history of Laramide basement from zircon-He age-eU correlations

    NASA Astrophysics Data System (ADS)

    Orme, Devon A.; Guenthner, William R.; Laskowski, Andrew K.; Reiners, Peter W.

    2016-11-01

    The long-term (>1 Ga) thermal histories of cratons are enigmatic, with geologic data providing only limited snapshots of their evolution. We use zircon (U-Th)/He (zircon He) thermochronology and age-composition correlations to understand the Proterozoic-Phanerozoic thermal history of Archean Wyoming province rocks exposed in the northern Laramide ranges of western North America. Zircon He ages from the Wind River Range (54 dates) and Bighorn Mountains (32 dates) show negative correlations with effective uranium (eU), a proxy for radiation damage. Zircon dates from the Bighorns are between 960 Ma (low-eU) and 20 Ma (high-eU) whereas samples from the Wind Rivers are between 582 Ma (low-eU) and 33 Ma (high-eU). We applied forward modeling using the zircon radiation damage and annealing model ZrDAAM to understand this highly variable dataset. A long-term t-T path that is consistent with the available geologic constraints successfully reproduced age-eU correlations. The best fit to the Wind Rivers data involves two phases of rapid cooling at 1800-1600 Ma and 900-700 Ma followed by slower cooling until 525 Ma. During the Phanerozoic, these samples were heated to maximum temperatures between 160 and 125 °C prior to Laramide cooling to 50 °C between 60 and 40 Ma. Data from the Bighorn Mountains were successfully reproduced with a similar thermal history involving cooler Phanerozoic temperatures of ∼115 °C and earlier Laramide cooling between 85 and 60 Ma. Our results indicate that age-eU correlations in zircon He datasets can be applied to extract long-term thermal histories that extend beyond the most recent cooling event. In addition, our results constrain the timing, magnitude and rates of cooling experienced by Archean Wyoming Province rocks between recognized deformation events, including the >1 Ga period represented by the regionally-extensive Great Unconformity.

  12. Fluid-absent metamorphism in the Adirondacks

    NASA Technical Reports Server (NTRS)

    Valley, J. W.

    1986-01-01

    Results on late Proterozoic metamorphism of granulite in the Adirondacks are presented. There more than 20,000 sq km of rock are at granulite facies. Low water fugacites are implied by orthopyroxene bearing assemblages and by stability of k'spar-plag-quartz assemblages. After mentioning the popular concept of infiltration of carbon dioxide into Precambrian rocks and attendent generation of granulite facies assemblages, several features of Adirondack rocks pertinent to carbon dioxide and water during their metamorphism are summarized: wollastonite occurs in the western lowlands; contact metamorphism by anorthosite preceeding granulite metamorphism is indicated by oxygen isotopes. Oxygen fugacity lies below that of the QFM buffer; total P sub water + P sub carbon dioxide determined from monticellite bearing assemblages are much less than P sub total (7 to 7.6 kb). These and other features indicate close spatial association of high- and low-P sub carbon dioxide assemblages and that a vapor phase was not present during metamorphism. Thus Adirondack rocks were not infiltrated by carbon dioxide vapor. Their metamorphism, at 625 to 775 C, occurred either when the protoliths were relatively dry or after dessication occurred by removal of a partial melt phase.

  13. Early Tertiary Anaconda metamorphic core complex, southwestern Montana

    USGS Publications Warehouse

    O'Neill, J. M.; Lonn, J.D.; Lageson, D.R.; Kunk, M.J.

    2004-01-01

    A sinuous zone of gently southeast-dipping low-angle Tertiary normal faults is exposed for 100 km along the eastern margins of the Anaconda and Flint Creek ranges in southwest Montana. Faults in the zone variously place Mesoproterozoic through Paleozoic sedimentary rocks on younger Tertiary granitic rocks or on sedimentary rocks older than the overlying detached rocks. Lower plate rocks are lineated and mylonitic at the main fault and, below the mylonitic front, are cut by mylonitic mesoscopic to microscopic shear zones. The upper plate consists of an imbricate stack of younger-on-older sedimentary rocks that are locally mylonitic at the main, lowermost detachment fault but are characteristically strongly brecciated or broken. Kinematic indicators in the lineated mylonite indicate tectonic transport to the east-southeast. Syntectonic sedimentary breccia and coarse conglomerate derived solely from upper plate rocks were deposited locally on top of hanging-wall rocks in low-lying areas between fault blocks and breccia zones. Muscovite occurs locally as mica fish in mylonitic quartzites at or near the main detachment. The 40Ar/39Ar age spectrum obtained from muscovite in one mylonitic quartzite yielded an age of 47.2 + 0.14 Ma, interpreted to be the age of mylonitization. The fault zone is interpreted as a detachment fault that bounds a metamorphic core complex, here termed the Anaconda metamorphic core complex, similar in age and character to the Bitterroot mylonite that bounds the Bitterroot metamorphic core complex along the Idaho-Montana state line 100 km to the west. The Bitterroot and Anaconda core complexes are likely components of a continuous, tectonically integrated system. Recognition of this core complex expands the region of known early Tertiary brittle-ductile crustal extension eastward into areas of profound Late Cretaceous contractile deformation characterized by complex structural interactions between the overthrust belt and Laramide basement uplifts

  14. A rift-related origin for regional medium-pressure, high-temperature metamorphism

    NASA Astrophysics Data System (ADS)

    Tucker, Naomi M.; Hand, Martin; Payne, Justin L.

    2015-07-01

    Crustal-scale exhumation during the Alice Springs Orogeny (c. 450-320 Ma) in central Australia has exposed a region of medium-pressure, high-temperature metasedimentary and metabasic rocks that comprise the Harts Range Group (HRG). Similarities in the detrital zircon age spectra between the HRG and surrounding unmetamorphosed, intraplate late Neoproterozoic-Cambrian basin sequences suggest that the HRG is a highly metamorphosed equivalent of these successions. Calculated phase equilibria modelling and thermobarometry constrain peak metamorphic conditions to ˜ 880 °C and 10.5 kbar, and ˜ 680 °C and 5.5-8.0 kbar, in the structurally lowest and highest parts of the HRG, respectively. Metamorphic conditions also indicate that burial occurred along a near-linear moderately-high apparent thermal gradient, recorded by the prograde development of andalusite-bearing mineral assemblages at shallower structural levels. Prograde and peak metamorphism was associated with voluminous intrusive and extrusive mafic magmatism, the development of a coarse layer-parallel fabric and north-directed normal shear-sense kinematics. Collectively, these point to an extensional regime. Furthermore, burial and metamorphism at c. 480-460 Ma was concurrent with a shallow epicontinental marine environment and ongoing sedimentation in central Australia. Accordingly, the deep burial, metamorphism and deformation of the HRG to mid-lower crustal depths (˜ 20- 35 km) must be justified in the context of the broader intraplate basin evolution at this time. It is difficult to reconcile medium-pressure, high-temperature metamorphism of the HRG with deep burial by tectonic overthickening which is commonly assumed to be the case. In contrast, metamorphism of the HRG seems more compatible with burial within a deep rift-style basin driven by high heat flow and mafic magmatism, suggesting that regional medium-pressure metamorphic terranes are not necessarily reflective of compressional thickening of the

  15. Sexual interest, attitudes, knowledge, and sexual history in relation to sexual behavior in the institutionalized aged.

    PubMed

    White, C B

    1982-02-01

    Although the idea that sexuality is a lifelong need is gaining greater research support and greater acceptability to the general public, few consider the institutionalized aged as having sexual needs or being able to benefit from sexual intimacy. The research presented here indicates that sexual activity in the institutionalized aged is related to their attitudes and behavior toward sexuality and to their sexual interest level and prior frequency of sexual activity. Institutionalized aged persons evidence sexual needs and do engage in sexual behavior.

  16. Differential effects of age and history of hypertension on regional brain volumes and iron

    PubMed Central

    Rodrigue, Karen M.; Haacke, E. Mark; Raz, Naftali

    2010-01-01

    Aging affects various structural and metabolic properties of the brain. However, associations among various aspects of brain aging are unclear. Moreover, those properties and associations among them may be modified by age-associated increase in vascular risk. In this study, we measured volume of brain regions that vary in their vulnerability to aging and estimated local iron content via T2* relaxometry. In 113 healthy adults (19–83 years old), we examined prefrontal cortex (PFC), primary visual cortex (VC), hippocampus (HC), entorhinal cortex (EC), caudate nucleus (Cd), and putamen (Pt). In some regions (PFC, VC, Cd, Pt) age-related differences in iron and volume followed similar patterns. However, in the medial temporal structures, volume and iron content exhibited different age trajectories. Whereas age-related volume reduction was mild in HC and absent in EC, iron content evidenced significant age-related declines. In hypertensive participants significantly greater iron content was noted in all examined regions. Thus, iron content as measured by T2* may be a sensitive index of regional brain aging and may reveal declines that are more prominent than gross anatomical shrinkage. PMID:20923707

  17. Ortigalita Peak gabbro, Franciscan complex: U-Pb dates of intrusion and high-pressure low-temperature metamorphism

    NASA Astrophysics Data System (ADS)

    Mattinson, James M.; Echeverria, Lina M.

    1980-12-01

    Paleontological and isotopic age data from the Franciscan complex in the Ortigalita Peak quadrangle, Diablo Range, California, provide new insight into the tectonic evolution of at least part of the Franciscan complex. Graywacke, shale, pillowed greenstone, and chert in the quadrangle were deposited in Late Jurassic (Tithonian) time, about 135 to 150 m.y. ago, on the basis of radiolaria. These rocks then were incorporated in an accretionary wedge prior to the intrusion of gabbroic magma 95 m.y. ago (U-Pb dating on zircons). Subduction (metamorphism of gabbro and surrounding sedimentary rocks to blueschist grade) closely followed intrusion at about 92 m.y. ago (U-Pb dating on metamorphic titanite and “plagioclase” = albite + pumpellyite ± quartz). The brief interval between intrusion and subduction confirms the idea that the gabbro was intruded into the accretionary wedge, essentially at the site of plate convergence. The much longer interval (about 40 to 55 m.y.) between deposition and subduction reveals that the Franciscan had a long presubduction history and provides a time frame within which more speculative concepts such as extensive northward translation of the Franciscan must be constrained.

  18. Magmatism and metamorphism linked to the accretion of continental blocks south of the Hindu Kush, Afghanistan

    NASA Astrophysics Data System (ADS)

    Faryad, Shah Wali; Collett, Stephen; Petterson, Mike; Sergeev, Sergey A.

    2013-08-01

    Metamorphic basement rocks in the southern part of the Western Hindu Kush at contact with the Kabul and Helmand crustal blocks were investigated to elucidate pressure-temperature variation and relative time relations among different metamorphic rocks. The rocks are represented by Proterozoic amphibolite facies para-/orthogneisses and migmatites with low-grade Paleozoic volcano-sedimentary sequences. Major- and trace-element geochemistry from two orthogneiss bodies and geochronological data, including new SHRIMP analyses on zircon from one of these bodies shows that they are derived from granitic rocks that related to two different magmatic arcs of Triassic and Cretaceous ages. The Triassic granites are common in the Western Hindu Kush where they intrude basement units; the Cretaceous granitic belt crosses the Afghan Central blocks south of the Hindu Kush Mountains. Three different metamorphic events have been distinguished in the southern part of Western Hindu Kush. Based on an unconformity between basement units and Carboniferous cover sequences, the first two amphibolite and greenschist facies metamorphic events are Proterozoic and Pre-Carboniferous in age respectively. The third metamorphism was recognized in Triassic and Cretaceous granitic rocks near to contact with the Kabul Block. It is of Eocene age and reached medium pressure amphibolite facies conditions. This event is genetically linked to the collision of India and Eurasia which produced a series of trans-Afghan Central block magmatic arcs and crustal scale deformation.

  19. Learning US History in an Age of Globalization and Transnational Migration

    ERIC Educational Resources Information Center

    An, Sohyun

    2009-01-01

    This paper examines US Korean youth's perspectives on US history and the impact of their sociocultural backgrounds, particularly their migration status, on their historical interpretations. Based on in-depth interviews with 42 US Korean high school students, the study opens up the question of diversity within an ethnic group, while it also begins…

  20. Studying Local History in the Digital Age: The Story of Asaph Perry

    ERIC Educational Resources Information Center

    Lee, John K.; Clarke, W. Guy

    2004-01-01

    In this article, the authors speak of an encounter they had in which they discovered some forgotten and unused historical resources hidden in a storage closet at the Cherokee County Georgia Historical Society. From these resources, they were able to weave an intriguing narrative encompassing people and events in history. They hope their story will…

  1. Sleep Problems in Chinese School-Aged Children with a Parent-Reported History of ADHD

    ERIC Educational Resources Information Center

    Li, Shenghui; Jin, Xinming; Yan, Chonghuai; Wu, Shenghu; Jiang, Fan; Shen, Xiaoming

    2009-01-01

    Objective: The objective was to survey the prevalence of parent-reported ADHD diagnosis and to assess its associations with sleep problems among urban school-aged children in China. Method: A random sample of 20,152 school-aged children participated in a cross-sectional survey in eight cities of China. A parent-administered questionnaire and the…

  2. Syn-extensional plutonism and peak metamorphism in the albion-raft river-grouse creek metamorphic core complex

    USGS Publications Warehouse

    Strickland, A.; Miller, E.L.; Wooden, J.L.; Kozdon, R.; Valley, J.W.

    2011-01-01

    The Cassia plutonic complex (CPC) is a group of variably deformed, Oligocene granitic plutons exposed in the lower plate of the Albion-Raft River- Grouse Creek (ARG) metamorphic core complex of Idaho and Utah. The plutons range from granodiorite to garnet-bearing, leucogranite, and during intrusion, sillimanite- grade peak metamorphism and ductile attenuation occurred in the country rocks and normal-sense, amphibolite-grade deformation took place along the Middle Mountain shear zone. U-Pb zircon geochronology from three variably deformed plutons exposed in the lower plate of the ARG metamorphic core complex revealed that each zircon is comprised of inherited cores (dominantly late Archean) and Oligocene igneous overgrowths. Within each pluton, a spread of concordant ages from the Oligocene zircon overgrowths is interpreted as zircon recycling within a long-lived magmatic system. The plutons of the CPC have very low negative whole rock ??Nd values of -26 to -35, and initial Sr values of 0.714 to 0.718, consistent with an ancient, crustal source. Oxygen isotope ratios of the Oligocene zircon overgrowths from the CPC have an average ??18O value of 5.40 ?? 0.63 permil (2SD, n = 65) with a slight trend towards higher ??18O values through time. The ??18O values of the inherited cores of the zircons are more variable at 5.93 ?? 1.51 permil (2SD, n = 29). Therefore, we interpret the plutons of the CPC as derived, at least in part, from melting Archean crust based on the isotope geochemistry. In situ partial melting of the exposed Archean basement that was intruded by the Oligocene plutons of the CPC is excluded as the source for the CPC based on field relationships, age and geochemistry. Correlations between Ti and Hf concentrations in zircons from the CPC suggest that the magmatic system may have become hotter (higher Ti concentration in zircon) and less evolved (lower Hf in zircon concentration) through time. Therefore, the CPC represents prolonged or episodic magmatism

  3. In search of early life: Carbonate veins in Archean metamorphic rocks as potential hosts of biomarkers

    NASA Astrophysics Data System (ADS)

    Peters, Carl A.; Piazolo, Sandra; Webb, Gregory E.; Dutkiewicz, Adriana; George, Simon C.

    2016-11-01

    to - 4 ‰ and δ18OVPDB ranging from - 18 ‰ to - 12 ‰. Evidently, the migration and entrapment of hydrocarbons occurred after peak metamorphism under temperatures congruous with late catagenesis and from fluids of different compositions. The relatively high temperatures of vein formation and the known geotectonic history of the rocks analysed suggest a probable minimum age of 1.8 billion yrs (Paleoproterozoic). Our results demonstrate that post peak-metamorphic veins provide an exciting opportunity in the search for evidence of early life. The integration of petrological and organic geochemical techniques is crucial for any future studies that use biomarkers to reconstruct the early biosphere.

  4. Low-grade, M1 metamorphism of the western metamorphic belt near Juneau, Alaska

    SciTech Connect

    Himmelberg, G.R. . Dept. of Geology); Brew, D.A.; Ford, A.B. )

    1993-04-01

    The western metamorphic belt is part of the Coast plutonic-metamorphic complex of western Canada and southeastern Alaska that developed as a result of tectonic overlap and/or compressional thickening of crustal rocks during collision of the Alexander terrane and Gravina assemblage on the west against the Yukon Prong and Stikine terranes to the east. Sub-greenschist to lower greenschist facies metabasalts exposed along the west end of the western metamorphic belt near Juneau, Alaska record the earliest metamorphic event (M1). These low-grade rocks are gradational with younger, higher-grade assemblages that define an inverted metamorphic gradient (metamorphic event M5). The most common metamorphic mineral assemblages are chlorite-epidote-actinolite with or without pumpellyite and stilpnomelane. There is no systematic distribution of metamorphic mineral assemblages in the study area, and all assemblages are in the pumpellyite-actinolite facies near the transition to the lower greenschist facies. Different low-variance assemblages can be attributed to minor differences in pressure, temperature, or X[sub CO[sub 2

  5. Cosmic-Ray-Exposure Ages of Diogenites and the Collisional History of the HED Parent Body or Bodies

    NASA Technical Reports Server (NTRS)

    Welten, K. C.; Lindner, L.; vanderBorg, K.; Loeken, T.; Scherer, P.; Schultz, L.

    1996-01-01

    Cosmic-ray-exposure ages of meteorites provide information on the collisional history of their parent bodies and the delivery mechanism of meteorites to Earth. The exposure-age distributions of ordinary chondrites show distinct patterns for H, L, and LL types, consistent with their origin on different parent bodies. The exposure-age distributions of howardites, eucrites. and diogenites (HEDS) show a common pattern with major peaks at 22 Ma and 38 Ma This provides additional evidence for a common origin of the HED meteorites, possibly 4 Vesta, although orbital dynamics calculations showed that the delivery of meteorites from Vesta to Earth is difficult. However, the discovery of several kilometer-sized Vesta-like asteroids in the region between Vesta and the 3:1 resonance suggested that these seem more likely parent bodies of the HEDs than Vesta itself. This implies that the exposure-age clusters may represent samples of several parent bodies. Therefore, the near-absence of diogenites with ages <20 Ma might be of interest for the composition of these kilometer-sized fragments of Vesta. Here we present cosmic-ray-exposure ages of 20 diogenites, including 9 new meteorites. In addition, we calculate the probability for each peak to occur by chance, assuming a constant production rate of HED fragments.

  6. From papyrus to the electronic tablet: a brief history of the clinical medical record with lessons for the digital age.

    PubMed

    Gillum, Richard F

    2013-10-01

    A major transition is underway in documentation of patient-related data in clinical settings with rapidly accelerating adoption of the electronic health record and electronic medical record. This article examines the history of the development of medical records in the West in order to suggest lessons applicable to the current transition. The first documented major transition in the evolution of the clinical medical record occurred in antiquity, with the development of written case history reports for didactic purposes. Benefiting from Classical and Hellenistic models earlier than physicians in the West, medieval Islamic physicians continued the development of case histories for didactic use. A forerunner of modern medical records first appeared in Paris and Berlin by the early 19th century. Development of the clinical record in America was pioneered in the 19th century in major teaching hospitals. However, a clinical medical record useful for direct patient care in hospital and ambulatory settings was not developed until the 20th century. Several lessons are drawn from the 4000-year history of the medical record that may help physicians improve patient care in the digital age. PMID:24054954

  7. Inflammatory nociception responses do not vary with age, but diminish with the pain history

    PubMed Central

    Simón-Arceo, Karina; Contreras, Bernardo; León-Olea, Martha; Coffeen, Ulises; Jaimes, Orlando; Pellicer, Francisco

    2014-01-01

    Some of the relevant factors that must be considered when dealing with old age include its growing numbers in the general population and pain contention in this age group. In this sense, it is important to study whether antinociceptive responses change with age. To elucidate this point, persistent pain in animals is the preferred model. In addition, the response to inflammatory pain in the same individual must be explored along its lifetime. Male Wistar rats were infiltrated with carrageenan (50 μl intraplantar) and tested 3 h and 24 h after injection using thermal (plantar test) and mechanociceptive tests (von Frey). The rats were divided into the following groups: (a) young rats infiltrated for the first time at 12 weeks of age and re-infiltrated at 15 and 17 weeks; (b) adult rats infiltrated for the first time at 28 weeks of age and re-infiltrated at 44 and 56 weeks; and (c) old rats infiltrated for the first time at 56 weeks of age and re-infiltrated at 72 weeks. The rats tested for the first time at 12 and 56 weeks of age showed hyperalgesia due to carrageenan infiltration at 3 h and 24 h after injection. This result showed that old rats maintain the same antialgesic response due to inflammation. However, when the injection was repeated in the three age groups, the latency to the thermal and mechanociceptive responses at 3 h is increased when compared to animals exposed for the first time to inflammation. The response to thermal and mechanociception in old rats is the same as in young animals as long as the nociceptive stimulus is not repeated. The repetition of the stimulus produces changes compatible with desensitization of the response and evidences the significance of algesic stimulus repetition in the same individual rather than the age of the individual. PMID:25120479

  8. Metamorphism and aqueous alteration in low petrographic type ordinary chondrites

    NASA Astrophysics Data System (ADS)

    Sears, D. W. G.; Morse, A. D.; Hutchison, R.; Guimon, R. K.; Jie, Lu; Alexander, C. M. O'd.; Benoit, P. H.; Wright, I.; Pillinger, C.; Xie, Tian; Lipschutz, M. E.

    1995-03-01

    In order to investigate the relative importance of dry metamorphism and aqueous alteration in the history of chondrules, chondrules were hand-picked from the Semarkona (petrographic type 3.0), Bishunpur (3.1), Chainpur (3.4), Dhajala (3.8) and Allegan (5) chondrites, and matrix samples were extracted from the first three ordinary chondrites. The thermoluminescence (TL) properties of all the samples were measured, and appropriate subsets of the samples were analyzed by electron-microprobe and radiochemical neutron activation and the water and H-isotopic composition determined. The Th data for chondrules from Semarkona and Bishunpur scatter widely showing no unambiguous trends, although group B 1 chondrules tend to have lower sensitivities and lower peak temperatures compared with group AS chondrules. It is argued that these data reflect the variety of processes accompanying chondrule formation. The chondrules show remarkably uniform contents of the highly labile elements, indicating mineralogical control on abundance and volatile loss from silicates and loss and recondensation of mobile chalcophiles and siderophiles in some cases. Very high D/H values (up to ˜8000‰ SMOW) are observed in certain Semarkona chondrules, a confirmation of earlier work. With increasing petrographic type, mean TL sensitivities of the chondrules increase, the spread of values within an individual meteorite decreases, and peak temperatures and peak widths show trends indicating that the Th is mainly produced by feldspar and that dry, thermal metamorphism is the dominant secondary process experienced by the chondrules. The TL sensitivities of matrix samples also increase with petrographic type. Chainpur matrix samples show the same spread of peak temperatures and peak widths as Chainpur chondrules, indicating metamorphism-related changes in the feldspar are responsible for the Th of the matrix. The Th data for the Semarkona and Bishunpur matrix samples provide, at best, only weak evidence

  9. Metamorphism and aqueous alteration in low petrographic type ordinary chondrites

    NASA Technical Reports Server (NTRS)

    Xie, T.; Lipschutz, M. E.; Sears, D. W. G.; Guimon, R. K.; Jie, Lu; Benoit, P. H.; O'D. Alexander, C. M.; Wright, Ian; Pillinger, C.; Morse, A. D.; Hutchison, Robert

    1995-01-01

    In order to investigate the relative importance of dry metamorphism and aqueous alteration in the history of chondruies, chondruies were hand-picked from the Semarkona (petrographic type 3.0), Bishunpur (3. 1), Chainpur (3.4), Dhajala (3.8) and Allegan (5) chondrites, and matrix samples were extracted from the first three ordinary chondrites. The thermoluminescence (TL) properties of all the samples were measured, and appropriate subsets of the samples were analyzed by electron-microprobe and radiochemical neutron activation and the water and H-isotopic composition determined. The TL data for chondrules from Semarkona and Bishunpur scatter widely showing no unambiguous trends, although group B1 chondrules tend to have lower sensitivities and lower peak temperatures compared with group A5 chondrules. It is argued that these data reflect the variety of processes accompanying chondrule formation. The chondrules show remarkably uniform contents of the highly labile elements, indicating mineralogical control on abundance and volatile loss from silicates and loss and recondensation of mobile chalcophiles and siderophiles in some cases. Very high D/H values (up to approx. 8000% SMOW) are observed in certain Semarkona chondrules, a confirmation of earlier work. With increasing petrographic type, mean TL sensitivities of the chondrules increase, the spread of values within an individual meteorite decreases, and peak temperatures and peak widths show trends indicating that the TL is mainly produced by feldspar and that dry, thermal metamorphism is the dominant secondary process experienced by the chondrules. The TL sensitivities of matrix samples also increase with petrographic type. Chainpur matrix samples show the same spread of peak temperatures and peak widths as Chainpur chondruies, indicating metamorphism-related changes in the feldspar are responsible for the TL of the matrix. The TL data for the Semarkona and Bishunpur matrix samples provide, at best, only weak

  10. Teaching Igneous and Metamorphic Petrology Through Guided Inquiry Projects

    NASA Astrophysics Data System (ADS)

    McMillan, N. J.

    2003-12-01

    Undergraduate Petrology at New Mexico State University (GEOL 399) has been taught using three, 5-6 week long projects in place of lectures, lab, and exams for the last six years. Reasons for changing from the traditional format include: 1) to move the focus from identification and memorization to petrologic thinking; 2) the need for undergraduate students to apply basic chemical, structural, and field concepts to igneous and metamorphic rocks; 3) student boredom in the traditional mode by the topic that has captivated my professional life, in spite of my best efforts to offer thrilling lectures, problems, and labs. The course has three guided inquiry projects: volcanic, plutonic, and pelitic dynamothermal. Two of the rock suites are investigated during field trips. Each project provides hand samples and thin sections; the igneous projects also include whole-rock major and trace element data. Students write a scientific paper that classifies and describes the rocks, describes the data (mineralogical and geochemical), and uses data to interpret parameters such as tectonic setting, igneous processes, relationship to phase diagrams, geologic history, metamorphic grade, metamorphic facies, and polymetamorphic history. Students use the text as a major resource for self-learning; mini-lectures on pertinent topics are presented when needed by the majority of students. Project scores include evaluation of small parts of the paper due each Friday and participation in peer review as well as the final report. I have found that petrology is much more fun, although more difficult, to teach using this method. It is challenging to be totally prepared for class because students are working at different speeds on different levels on different aspects of the project. Students enjoy the course, especially the opportunity to engage in scientific investigation and debate. A significant flaw in this course is that students see fewer rocks and have less experience in rock classification

  11. Permo-Carboniferous granitoids with Jurassic high temperature metamorphism in Central Pontides, Northern Turkey

    NASA Astrophysics Data System (ADS)

    Gücer, Mehmet Ali; Arslan, Mehmet; Sherlock, Sarah; Heaman, Larry M.

    2016-04-01

    likely that peak metamorphism took place during the Jurassic as reflected by the U-Pb zircon ages (199-158 Ma) and also 40Ar/39Ar from hornblende/biotite (163-152 Ma). The four biotite 40Ar/39Ar average ages from the rock samples are ca. 156 Ma, suggesting that the metamorphic rocks cooled to 350-400 °C at ca. 156 Ma. Conclusively, the Devrekani metamorphic rocks can be ascribed as products of Permo-Carboniferous continental arc magmatism overprinted by Jurassic metamorphism in the northern Central Pontides.

  12. Chemical and physical studies of type 3 chondrites. VIII - Thermoluminescence and metamorphism in the CO chondrites

    NASA Technical Reports Server (NTRS)

    Keck, Bradly D.; Sears, Derek W. G.

    1987-01-01

    A possible relationship between the thermoluminescence (TL) properties of CO chondrites and their metamorphic history was investigated by measuring the TL properties of seven normal CO chondrites and of the Colony and the Allan Hills A77307 (ALHA 77307) CO-related chondrites. With the exception of Colony and ALHA 77307, whose maximum induced TL emission is at approximately 350 C, the CO chondrites were found to exhibit two TL peaks: a 130 C and a 250 C peaks. Among the CO chondrites, the 130 C peak showed a 100-fold range in TL sensitivity and was found to correlate with various metamorphism-related phenomena, such as silicate heterogeneity, metal composition, and McSween's metamorphic subtypes. The peak at 250 did not show these correlations and, with exception of Colony, showed little variation.

  13. UHP metamorphism in the Western Mediterranean : A tale of a Tethys fragment (Edough Massif, NE Algeria) and its geodynamic consequences

    NASA Astrophysics Data System (ADS)

    Bruguier, Olivier; Bosch, Delphine; Caby, Renaud; Fernandez, Laure; Abdallah, Nachida; Arnaud, Nicolas; Hammor, Dalila; Laouar, Rabah; Mechati, Medhi; Monié, Patrick; Ouabadi, Aziouz; Toubal, Abder

    2016-04-01

    The Edough Massif of NE Algeria is part of the Maghrebides, a peri-Mediterranean Alpine belt that extends from Morocco to Tunisia. The belt resulted mainly from the eastward retreat of the Tethyan slab and from the drift of continental fragments, some of which finally collided with the north African margin. In this study we report the recent discovery of metamorphic diamonds (5-30 μm in size) included in a garnet megacryst and identified by Raman spectroscopy and the characteristic sharp band at 1332 cm‑1 for crystalline diamond. The studied megacryst was taken from a weathered actinolitite horizon inserted within a major mylonite-ultramylonite band, which outcrops at the base of an allochtonous oceanic unit thrust onto the African paleomargin. The host garnet is almandine-dominant with a sharp increase in grossular component in the rim and is rich in exsolution of small acicular rutile needles. Major and trace elements show a gradual but significant zonation from core to rim characterized by a decrease in HREE, Y and Mn, typical of a prograde growth in a closed system. Trace element analyses of large prismatic rutile (up to 300 μm) indicate that the host metamorphic rock was a mafic protolith of MORB affinity and the Zr-in-rutile thermometry indicates a temperature range of 724-778°C for rutile growth. U-Pb analyses of these large rutile crystals provide an age of 32.4 ± 3.3 Ma interpreted as dating the prograde subduction stage of the mafic protolith. Minute zircons (≤ 30μm), disseminated in the garnet, display a multifaceted appearance and low Th/U ratios consistent with a metamorphic origin. The lack of HREE depletion in these zircons indicates that their metamorphic growth was not coeval with garnet. U-Pb analyses and Ti-in-zircon thermometry indicate they nucleated at 20.9 ± 2.2 Ma during near isothermal decompression related to exhumation of the UHP units. This study allows bracketing the age of UHP metamorphism in the Western Mediterranean to the

  14. UHP metamorphism in the Western Mediterranean : A tale of a Tethys fragment (Edough Massif, NE Algeria) and its geodynamic consequences

    NASA Astrophysics Data System (ADS)

    Bruguier, Olivier; Bosch, Delphine; Caby, Renaud; Fernandez, Laure; Abdallah, Nachida; Arnaud, Nicolas; Hammor, Dalila; Laouar, Rabah; Mechati, Medhi; Monié, Patrick; Ouabadi, Aziouz; Toubal, Abder

    2016-04-01

    The Edough Massif of NE Algeria is part of the Maghrebides, a peri-Mediterranean Alpine belt that extends from Morocco to Tunisia. The belt resulted mainly from the eastward retreat of the Tethyan slab and from the drift of continental fragments, some of which finally collided with the north African margin. In this study we report the recent discovery of metamorphic diamonds (5-30 μm in size) included in a garnet megacryst and identified by Raman spectroscopy and the characteristic sharp band at 1332 cm-1 for crystalline diamond. The studied megacryst was taken from a weathered actinolitite horizon inserted within a major mylonite-ultramylonite band, which outcrops at the base of an allochtonous oceanic unit thrust onto the African paleomargin. The host garnet is almandine-dominant with a sharp increase in grossular component in the rim and is rich in exsolution of small acicular rutile needles. Major and trace elements show a gradual but significant zonation from core to rim characterized by a decrease in HREE, Y and Mn, typical of a prograde growth in a closed system. Trace element analyses of large prismatic rutile (up to 300 μm) indicate that the host metamorphic rock was a mafic protolith of MORB affinity and the Zr-in-rutile thermometry indicates a temperature range of 724-778°C for rutile growth. U-Pb analyses of these large rutile crystals provide an age of 32.4 ± 3.3 Ma interpreted as dating the prograde subduction stage of the mafic protolith. Minute zircons (≤ 30μm), disseminated in the garnet, display a multifaceted appearance and low Th/U ratios consistent with a metamorphic origin. The lack of HREE depletion in these zircons indicates that their metamorphic growth was not coeval with garnet. U-Pb analyses and Ti-in-zircon thermometry indicate they nucleated at 20.9 ± 2.2 Ma during near isothermal decompression related to exhumation of the UHP units. This study allows bracketing the age of UHP metamorphism in the Western Mediterranean to the

  15. Metamorphic fluid flow - a question of scale, crustal depth and bulk rock composition

    SciTech Connect

    Tracy, R.J.; Rye, D.M.

    1985-01-01

    Recent studies have indicated that certain metamorphic rocks interacted with significant volumes of aqueous fluid during their time-integrated mineral reaction history. Rather than demonstrating that pervasive fluid flow is general in metamorphic rocks, these documented cases instead suggest the likelihood of pronounced to extreme channelization of through-going in fluids in deep-seated metamorphic terranes (P>3 kbar). In rocks more shallowly buried, and therefore under low lithostatic stress, pervasive flow along grain boundaries and open microfractures probably occurred, as at Skye and the Skaergaard Complex. In higher pressure metamorphic environments, documented cases of high fluid/rock ratio make a strong case for flow channelized in veins or in impure marble aquifers where pore space and permeability were created by decarbonation reactions driven by infiltration of aqueous fluid. The source of this fluid may commonly be traced to a nearby wet granitic intrusion or quartz vein. As long as the pressurized source of aqueous fluid continued, outward flow was possible as fluid held open the intergranular pore space which was created only at the infiltration/reaction front where a reduction in solid volume accompanied reaction. Cessation or interruption of fluid flow would allow the pore space to close due to porous-rock strength being exceeded by lithostatic stress. Pervasive flow or aqueous fluid in deepseated metamorphic terranes is therefore probably limited to carbonate-bearing lithologies adjacent to sources of major volumes of fluid; otherwise, fluid flow is likely to be localized in fractures or veins.

  16. Plant induced defenses depend more on plant age than previous history of damage: implications for plant-herbivore interactions.

    PubMed

    Quintero, Carolina; Bowers, M Deane

    2011-09-01

    Herbivore-induced plant responses can significantly change as a function of plant developmental stage and previous history of damage. Yet, empirical tests that assess the combined role of multiple damage events and age-dependent constraints on the ability of plants to induce defenses within and among tissues are scarce. This question is of particular interest for annual and/or short-lived perennial plant species, whose responses to single or multiple damage events over a growing season are likely to interact with ontogenetic constraints in affecting a plant's ability to respond to herbivory. Using Plantago lanceolata and one of its specialist herbivores, Junonia coenia, we examined the effect of plant ontogeny (juvenile vs. mature developmental stages) and history of damage (single and multiple damage events early and/or late in the season) on plant responses to leaf damage. Plant responses to herbivory were assessed as induced chemical defenses (iridoid glycosides) and compensatory regrowth, in both above- and below-ground tissues. We found that constitutive concentration of iridoid glycosides markedly increased as plants matured, but plant ability to induce chemical defenses was limited to juvenile, but not mature, plant stages. In addition, induced defenses observed 7 d following herbivory in juvenile plants disappeared 5 wk after the first herbivory event, and mature plants that varied considerably in the frequency and intensity of damage received over 5 wk, did not differ significantly in their levels of chemical defenses. Also, only small changes in compensatory regrowth were detected. Finally, we did not observe changes in below-ground tissues' defenses or biomass a week following 50% removal of leaf tissues at either age class or history of damage. Together, these results suggest that in P. lanceolata and perhaps other systems, ontogenetic trajectories in plant growth and defenses leading to strong age-dependent induced responses may prevail over

  17. Evidence for multiple metamorphic events in the Adirondack Mountains, N. Y

    SciTech Connect

    McLelland, J.; Lochhead, A.; Vyhnal, C.

    1988-05-01

    Field evidence consisting of: (1) rotated, foliated xenoliths, (2) country rock foliation truncated by isoclinally folded igneous intrusions bearing granulite facies assemblages document one, or more, early dynamothermal event(s) of regional scale and high grade. Early metamorphism resulted in pronounced linear and planar fabric throughout the Adirondacks and preceded the emplacement of the anorthosite-mangerite-charnockite-granite-alaskite (AMCA) suite which contains xenoliths of the metamorphosed rocks. Olivine metagabbros, believed to be approximately contemporaneous with the AMCA-suite, also crosscut and contain xenoliths of, strongly foliated metasediments. These intrusive rocks caused contact metamorphism in the metasediments which locally exhibit both anatectite and restite assemblages. Subsequently, this already complex framework underwent three phases of folding, including an early recumbent isoclinical event, and was metamorphosed to granulite facies P,T conditions. The age of the early metamorphism cannot yet be narrowly constrained, but isotopic results suggest that it may be as young as approx. 1200 Ma or older than approx. 1420 Ma. U-Pb zircon ages indicate emplacement of the AMCA-(metagabbro)-suite in the interval 1160-1130 Ma and place the peak of granulite facies metamorphism between 1070-1025 Ma. The anorogenic character of the AMCA-suite, and the occurrence of metadiabase dike swarms within it, are further evidence of the separate nature of the metamorphic events that precede and postdate AMCA emplacement.

  18. Ages of flow units in the far eastern maria and implications for basin-filling history

    NASA Technical Reports Server (NTRS)

    Boyce, J. M.; Jonnson, D. A.

    1978-01-01

    The spatial distribution of major units of uniform relative age exposed in the far eastern maria and Mare Humorum was determined using a crater density mapping technique. Correlation of crater densities and radiometric ages of Apollo and Luna landing sites provided estimates of the absolute ages for the units. The combination of such data with relative age data from previous crater morphology studies produced a complete map of the distribution of major age units in the lunar near-side maria. The map shows that there are young (2.5 + or - 0.5 billion years old) mare basalts in the eastern maria, although most young flows occur in the western maria. The vents for the young flows generally are found along the edges of basins. Because old mare units (greater than 3.5 billion years old) are also commonly found around the edges of the basins, it is suggested that the basins were subsiding during filling, probably as a result of isostatic compensation due to the weight of the lava.

  19. Zircon SHRIMP U-Pb dating of metamorphic complexes in the conjunction of the Greater and Lesser Xing'an ranges, NE China: Timing of formation and metamorphism and tectonic implications

    NASA Astrophysics Data System (ADS)

    Miao, Laicheng; Zhang, Fuqin; Zhu, Mingshuai; Liu, Dunyi

    2015-12-01

    Metamorphic complexes, including the Luomahu, Xinkailing and Fengshuigouhe groups, are scattered in the conjunction of the Greater and the Lesser Xing'an ranges, NE China, and have long been interpreted to represent the Precambrian basement of the so-called "Xing'an" and "Songnen" blocks although reliable evidence is lacking. Thin-section examination and mineral assemblage indicate that the protoliths of these metamorphic rocks are mainly meta-sedimentary and meta-volcanic rocks and have experienced greenschist- to amphibolite-facies metamorphism and strong deformation. Zircon SHRIMP U-Pb dating results of the metamorphic complexes and associated pre- or syn-kinematic veins constrained the formation and metamorphic ages of the Luomahuo Group at 175 ± 3 Ma and 159 ± 3 Ma, the Xingkailing Group at 200 ± 2 Ma and 158 ± 3 Ma, and the Fengshuigouhe Group at between 230-310 Ma and 170 ± 3 Ma, respectively. Additionally, all these rocks contain some Late Paleozoic detrital or inherited zircons with ages between 290-390 Ma, but no Precambrian, even if Early Paleozoic, age information was detected from these metamorphic rocks. These new data suggest that the metamorphic complexes were formed during Mesozoic-Late Paleozoic period, rather than in Precambrian as previously inferred, and that all of them underwent metamorphism and deformation during Middle Jurassic between 170-160 Ma. Consequently, these metamorphic complexes are not basement rocks of the so-called Precambrian continental blocks. Instead, there are likely metamorphosed Late Paleozoic-Mesozoic accretionary complexes and/or arc terranes. These results, in combination with published data, illustrate an overall young trend from north to south in the tectonic evolution of the northern Xing'an region. Significantly, the Jurassic (170-160 Ma) metamorphism and deformation event firstly identified by this study from the metamorphic complexes likely recorded the coinstantaneous Mongol-Okhotsk collisional and

  20. Social life histories: jackdaw dominance increases with age, terminally declines and shortens lifespan.

    PubMed

    Verhulst, Simon; Geerdink, Moniek; Salomons, H Martijn; Boonekamp, Jelle J

    2014-09-22

    Behaviour may contribute to changes in fitness prospects with age, for example through effects of age-dependent social dominance on resource access. Older individuals often have higher dominance rank, which may reflect a longer lifespan of dominants and/or an increase in social dominance with age. In the latter case, increasing dominance could mitigate physiological senescence. We studied the social careers of free-living jackdaws over a 12 year period, and found that: (i) larger males attained higher ranks, (ii) social rank increased with age within individuals, and (iii) high-ranked individuals had shorter lifespan suggesting that maintaining or achieving high rank and associated benefits comes at a cost. Lastly, (iv) social rank declined substantially in the last year an individual was observed in the colony, and through its effect on resource access this may accelerate senescence. We suggest that behaviour affecting the ability to secure resources is integral to the senescence process via resource effects on somatic state, where behaviour may include not only social dominance, but also learning, memory, perception and (sexual) signalling. Studying behavioural effects on senescence via somatic state may be most effective in the wild, where there is competition for resources, which is usually avoided in laboratory conditions.

  1. Integrating Teaching about the Little Ice Age with History, Art, and Literature.

    ERIC Educational Resources Information Center

    Glenn, William Harold

    1996-01-01

    Discusses climate change during the Little Ice Age as experienced during several historical events, including the settlement and demise of the Norse Greenland colonies, the landing of the Pilgrims at Plymouth, and both the Battle of Trenton and Washington's encampment at Valley Forge during the American Revolution. Associated artistic and literary…

  2. Teaching the Nuclear Age: A History Institute for Teachers. Footnotes. Volume 14, Number 5

    ERIC Educational Resources Information Center

    Kuehner, Trudy

    2009-01-01

    On March 28-29, 2009, FPRI's Wachman Center hosted 43 teachers from across the country for a weekend of discussion on teaching the nuclear age. In his opening remarks, Walter A. McDougall observed that although students today are not made to crawl under their desks in air raid drills, that atomic power remains, and it is still necessary to raise a…

  3. Diffuse white matter tract abnormalities in clinically normal ageing retired athletes with a history of sports-related concussions.

    PubMed

    Tremblay, Sebastien; Henry, Luke C; Bedetti, Christophe; Larson-Dupuis, Camille; Gagnon, Jean-François; Evans, Alan C; Théoret, Hugo; Lassonde, Maryse; De Beaumont, Louis

    2014-11-01

    Sports-related concussions have been shown to lead to persistent subclinical anomalies of the motor and cognitive systems in young asymptomatic athletes. In advancing age, these latent alterations correlate with detectable motor and cognitive function decline. Until now, the interacting effects of concussions and the normal ageing process on white matter tract integrity remain unknown. Here we used a tract-based spatial statistical method to uncover potential white matter tissue damage in 15 retired athletes with a history of concussions, free of comorbid medical conditions. We also investigated potential associations between white matter integrity and declines in cognitive and motor functions. Compared to an age- and education-matched control group of 15 retired athletes without concussions, former athletes with concussions exhibited widespread white matter anomalies along many major association, interhemispheric, and projection tracts. Group contrasts revealed decreases in fractional anisotropy, as well as increases in mean and radial diffusivity measures in the concussed group. These differences were primarily apparent in fronto-parietal networks as well as in the frontal aspect of the corpus callosum. The white matter anomalies uncovered in concussed athletes were significantly associated with a decline in episodic memory and lateral ventricle expansion. Finally, the expected association between frontal white matter integrity and motor learning found in former non-concussed athletes was absent in concussed participants. Together, these results show that advancing age in retired athletes presenting with a history of sports-related concussions is linked to diffuse white matter abnormalities that are consistent with the effects of traumatic axonal injury and exacerbated demyelination. These changes in white matter integrity might explain the cognitive and motor function declines documented in this population.

  4. Diffuse white matter tract abnormalities in clinically normal ageing retired athletes with a history of sports-related concussions

    PubMed Central

    Tremblay, Sebastien; Henry, Luke C.; Bedetti, Christophe; Larson-Dupuis, Camille; Gagnon, Jean-François; Evans, Alan C.; Théoret, Hugo; Lassonde, Maryse

    2014-01-01

    Sports-related concussions have been shown to lead to persistent subclinical anomalies of the motor and cognitive systems in young asymptomatic athletes. In advancing age, these latent alterations correlate with detectable motor and cognitive function decline. Until now, the interacting effects of concussions and the normal ageing process on white matter tract integrity remain unknown. Here we used a tract-based spatial statistical method to uncover potential white matter tissue damage in 15 retired athletes with a history of concussions, free of comorbid medical conditions. We also investigated potential associations between white matter integrity and declines in cognitive and motor functions. Compared to an age- and education-matched control group of 15 retired athletes without concussions, former athletes with concussions exhibited widespread white matter anomalies along many major association, interhemispheric, and projection tracts. Group contrasts revealed decreases in fractional anisotropy, as well as increases in mean and radial diffusivity measures in the concussed group. These differences were primarily apparent in fronto-parietal networks as well as in the frontal aspect of the corpus callosum. The white matter anomalies uncovered in concussed athletes were significantly associated with a decline in episodic memory and lateral ventricle expansion. Finally, the expected association between frontal white matter integrity and motor learning found in former non-concussed athletes was absent in concussed participants. Together, these results show that advancing age in retired athletes presenting with a history of sports-related concussions is linked to diffuse white matter abnormalities that are consistent with the effects of traumatic axonal injury and exacerbated demyelination. These changes in white matter integrity might explain the cognitive and motor function declines documented in this population. PMID:25186429

  5. Tectono-metamorphic evolution of the Jomolhari massif: Variations in timing of syn-collisional metamorphism across western Bhutan

    NASA Astrophysics Data System (ADS)

    Regis, Daniele; Warren, Clare J.; Young, David; Roberts, Nick M. W.

    2014-03-01

    Our current understanding of the rates and timescales of mountain-building processes is largely based on information recorded in U-bearing accessory minerals such as monazite, which is found in low abundance but which hosts the majority of the trace element budget. Monazite petrochronology was used to investigate the timing of crustal melting in migmatitic metasedimentary rocks from the Jomolhari massif (NW Bhutan). The samples were metamorphosed at upper amphibolite to granulite facies conditions (~ 0.85 GPa, ~ 800 °C), after an earlier High-Pressure stage (P > 1.4 GPa), and underwent partial melting through dehydration melting reactions involving muscovite and biotite. In order to link the timing of monazite growth/dissolution to the pressure-temperature (P-T) evolution of the samples, we identified 'chemical fingerprints' in major and accessory phases that were used to back-trace specific metamorphic reactions. Variations in Eu anomaly and Ti in garnet were linked to the growth and dissolution of major phases (e.g. growth of K-feldspar and dehydration melting of muscovite/biotite). Differences in M/HREE and Y from garnet core to rim were instead related to apatite breakdown and monazite-forming reactions. Chemically zoned monazite crystals reacted multiple times during the metamorphic evolution suggesting that the Jomolhari massif experienced a prolonged high-temperature metamorphic evolution from 36 Ma to 18 Ma, significantly different from the P-T-time path recorded in other portions of the Greater Himalayan Sequence (GHS) in Bhutan. Our data demonstrate unequivocally that the GHS in Bhutan consists of units that experienced independent high-grade histories and that were juxtaposed across different tectonic structures during exhumation. The GHS may have been exhumed in response to (pulsed) mid-crustal flow but cannot be considered a coherent block.

  6. Detrital zircon geochronology of the Tananao Metamorphic Complex, Taiwan

    NASA Astrophysics Data System (ADS)

    Huang, Y. C.; Chen, W. S.; Feng, H. T.; Liu, C. H.; Chung, S. L.; Lee, Y. H.

    2014-12-01

    The oldest rock of the Tananao Metamorphic Complex exposed at the Backbone Range which consists of marble, schist, and gneiss. According to the stratigraphy and structural analysis, the Complex in the ascending order can be divided into Chiuchu Marble, Paiyang Schist with Kuyuan Schist, and Pilu Formation. Based on Sr isotope dating, it is speculated that the formation age of Chiuchu Marble is closed to 250±20 Ma. Using the zircon U-Pb dating, the magnetic age of gneiss (I-type granite) yields 105- 86 Ma. The stratigraphic age of schist is difficult to define because of fossils are poorly-preserved. In our study, we use the detrital zircon U-Pb dating, by LA-ICPMS, to yield the maximum depositional age of the schist formation. We analyze fifteen samples in this study. The depositional age of the Kuyuan and Paiyang Schists would be not older than late Cretaceous, and the depositional age of the Pilu Formation may have formed in late Cretaceous and younger than Kuyuan and Paiyang Schists. Results from the above mentioned, we are interpreted as the tectonic setting of the Tananao Metamorpic Complex. The region was located on a passive continental margin that formed carbonate platform deposits during the late Permian period. The clastic sediments were unconformably deposited on Chiuchu Marble during the early Cretaceous. Then the paleo-Pacific plate subducted to the Cathaysia Block forming the granite at about 105-86 Ma. Afterwards, the clastic sediments were deeply buried caused by continuing subduction formed as schist rock. The metamorphic event is known as the Nanao orogeny.

  7. The Combined Effects of Bacterial Symbionts and Aging on Life History Traits in the Pea Aphid, Acyrthosiphon pisum

    PubMed Central

    Fan, Maretta H.; Gerardo, Nicole M.

    2014-01-01

    While many endosymbionts have beneficial effects on hosts under specific ecological conditions, there can also be associated costs. In order to maximize their own fitness, hosts must facilitate symbiont persistence while preventing symbiont exploitation of resources, which may require tight regulation of symbiont populations. As a host ages, the ability to invest in such mechanisms may lessen or be traded off with demands of other life history traits, such as survival and reproduction. Using the pea aphid, Acyrthosiphon pisum, we measured survival, lifetime fecundity, and immune cell counts (hemocytes, a measure of immune capacity) in the presence of facultative secondary symbionts. Additionally, we quantified the densities of the obligate primary bacterial symbiont, Buchnera aphidicola, and secondary symbionts across the host's lifetime. We found life history costs to harboring some secondary symbiont species. Secondary symbiont populations were found to increase with host age, while Buchnera populations exhibited a more complicated pattern. Immune cell counts peaked at the midreproductive stage before declining in the oldest aphids. The combined effects of immunosenescence and symbiont population growth may have important consequences for symbiont transmission and maintenance within a host population. PMID:24185857

  8. Revealing the significance and polyphase tectonothermal evolution of a major metamorphic unit in an orogen: the central Sanandaj-Sirjan zone, Zagros Mts., Iran

    NASA Astrophysics Data System (ADS)

    Shakerardakani, Farzaneh; Neubauer, Franz; Genser, Johann; Liu, Xiaoming; Dong, Yunpeng; Monfaredi, Behzad; Benroider, Manfred; Finger, Fritz; Waitzinger, Michael

    2016-04-01

    environment. The Darijune gabbro with the mean U-Pb zircon age of 170.2 ± 3.1 Ma postdates greenschist facies-grade metamorphism. This age marks the beginning of the initial subduction of Neotethyan oceanic in a continental arc setting. The best average P-T estimates for the metamorphic mineral assemblages of the Galeh-Doz orthogneiss range between 600 ± 50 °C at 2 ± 0.8 kbar. The subsequent cooling history after an amphibolite facies-grade metamorphism has been constrained with 40Ar-39Ar amphibole ages of plateau ages between 240-260 Ma. The estimate P-T conditions for the Carboniferous metagabbro from core (580 ± 50 °C, 4.0 ± 0.8 kbar) to rim (700 ± 20 °C, 7.5 ± 0.7 kbar) are in favor of a prograde P-T path. The new 40Ar-39Ar mineral ages integrated with structural field and microfabric studies reveals that the amphibolite-grade Carboniferous metagabbro indicate a Late Carboniferous age of amphibolite-grade metamorphism associated with ductile deformation of the new-detected Galeh-Doz nappe (Galeh-Doz orthogneiss and Amphibolite-Metagabbro unit). In the same unit, two lenses of metapelite including a garnet-muscovite-biotite schist give a P-T estimate of garnet cores from 640 ± 20 °C at 6.2 ± 0.8 kbar and garnet rims from 680 ± 20 °C at 7.2 ± 1.0 kbar, as well as garnet-biotite schist that yield lower P-T conditions, which vary from 620 °C at 5.5 ± 0.5 kbar in garnet cores to 600 ± 30 °C at 4.0 ± 1.0 kbar in garnet rims. Chemical monazite ages from garnet micaschists are at 322 ± 28 Ma. 40Ar-39Ar experiments on white mica in the first and second types yield staircase patterns from ca. 36 to 170 Ma and a plateau age of 137.84 ± 0.65 Ma, respectively. Taking all data together, we suggest that amphibolite-grade metamorphism is Carboniferous and is overprinted by two events: (1) during Late Jurassic- Cretaceous during ductile dextral transpressive nappe emplacement of the Galeh-Doz nappe over the June complex (peak conditions of greenschist facies

  9. Removing the effects of metamorphism from the Neoproterozoic carbon isotope record: a case study on Islay, western Scotland

    NASA Astrophysics Data System (ADS)

    Skelton, Alasdair

    2016-04-01

    The Port Askaig Formation on Islay, western Scotland is the first discovered tillite (glacial sediment) of Neoproterozoic age. This formation is sandwiched between carbonate rocks which preserve an extreme negative carbon isotope excursion. This so called "Islay anomaly" has been correlated with other such anomalies worldwide and together with the tillites has been cited as evidence of major (worldwide) glaciation events. During subsequent mountain building, this carbonate-tillite- carbonate sequence has been folded, producing a major en-echelon anticlinal fold system. Folding was accompanied by metamorphism at greenschist facies conditions which was, in turn, accompanied by metamorphic fluid flow. Mapping of the δ18O and δ13C values of these carbonate rocks reveals that metamorphic fluids were channelled through the axial region of the anticlinal fold. The metamorphic fluid was found to have a highly negative δ13C value, which was found to be in equilibrium with metamorphosed graphitic mudstones beneath the carbonate-tillite-carbonate sequence. Devolatilisation of these mudstones is therefore a likely source of this metamorphic fluid. Removal of the effects of metamorphic fluid flow on δ13C values recorded by metamorphosed carbonate rocks on Islay allows us to re-evaluate the isotopic evidence used to reconstruct Neoproterozoic climate. We are able to show that extreme negative δ13C values can partly be attributed to metamorphic fluid flow.

  10. Ultrahigh-Temperature Metamorphism in Madurai Granulites, Southern India: Evidence from Carbon Isotope Thermometry.

    PubMed

    Satish-Kumar

    2000-07-01

    Ultrahigh-temperature (UHT) metamorphism in the Madurai Block of the southern Indian granulite terrain has been verified using the calcite-graphite isotope exchange thermometer. Carbon isotope thermometry has been applied to marbles from a locality near the reported occurrence of sapphirine granulites that have yielded temperature estimates of around 1000 degrees C. The delta(13)C and delta(18)O values of calcite are homogenous, implying equilibration of the isotopes during metamorphism. However, the delta(13)C values of single graphite crystals show variations in the order of 1 per thousand within a hand specimen. Detailed isotopic zonation studies indicate that graphite preserves either the time-integrated crystal growth history or reequilibrium fractionation during its cooling history. The graphite cores preserve higher delta(13)C values than the rims. The fractionation between calcite and graphite cores gives the highest metamorphic temperature of about 1060 degrees C, which matches the petrologically inferred temperature estimates in the high-magnesian pelites. The fractionation between graphite rims and calcite suggests a temperature of around 750 degrees C, which is interpreted to reflect retrograde cooling. This event is also observed in the sapphirine granulites. Calcite-graphite thermometry thus provides a useful tool to define UHT metamorphism in granulite terrains.

  11. ERBB4 Polymorphism and Family History of Psychiatric Disorders on Age-Related Cortical Changes in Healthy Children

    PubMed Central

    Douet, Vanessa; Chang, Linda; Lee, Kristin; Ernst, Thomas

    2015-01-01

    Background Genetic variations in ERBB4 were associated with increased susceptibility for schizophrenia (SCZ) and bipolar disorders (BPD). Structural imaging studies showed cortical abnormalities in adolescents and adults with SCZ or BPD. However, less is known about subclinical cortical changes or the influence of ERBB4 on cortical development. Methods 971 healthy children (ages 3–20 years old; 462 girls and 509 boys) were genotyped for the ERBB4-rs7598440 variants, had structural MRI, and cognitive evaluation (NIH Toolbox ®). We investigated the effects of ERBB4 variants and family history of SCZ and/or BPD (FH) on cortical measures and cognitive performances across ages 3–20 years using a general additive model. Results Variations in ERBB4 and FH impact differentially the age-related cortical changes in regions often affected by SCZ and BPD. The ERBB4-TT-risk genotype children with no FH had subtle cortical changes across the age span, primarily located in the left temporal lobe and superior parietal cortex. In contrast, the TT-risk genotype children with FH had more pronounced age-related changes, mainly in the frontal lobes compared to the non-risk genotype children. Interactive effects of age, FH and ERBB4 variations were also found on episodic memory and working memory, which are often impaired in SCZ and BPD. Conclusions Healthy children carrying the risk-genotype in ERBB4 and/or with FH had cortical measures resembling those reported in SCZ or BPD. These subclinical cortical variations may provide early indicators for increased risk of psychiatric disorders and improve our understanding of the effect of the NRG1–ERBB4 pathway on brain development. PMID:25744101

  12. Implications of IODP Expedition 349 Age Results for the Spreading History of the South China Sea

    NASA Astrophysics Data System (ADS)

    Briais, Anne

    2016-04-01

    The International Ocean Discovery Program (IODP) Expedition 349 in the South China Sea drilled three sites (U1431, U1433, and U1434) into the basaltic crustal basement near the fossil spreading center in the East and Southwest Subbasins. These results provided age constraints on the termination of seafloor spreading in the South China Sea (SCS) basin. Shipboard biostratigraphic analysis of microfossils from the sediment immediately above or between flows in the basaltic basement indicates early Miocene ages: 16.7-17.6 Ma for Site U1431 in the East Subbasin, ~18-21 Ma for Site U1433 in the Southwest Subbasin. Since Expedition 349, Ar/Ar dating of basalt samples from these two sites have confirmed these ages in the east, and have provided an age of 17 Ma in the Southwest. The similarity in crustal age between sites suggests that the last stages of spreading have been coeaval in both the East and Southwest Subbasins, forming a single mid-ocean ridge system with a series of transform faults and discontinuities between the two subbasins. Expedition 349 also drilled Site U1435 on a bathymetric high along the northwestern continent-ocean boundary. Onboard core description, biostratigraphy and magnetostratigraphy revealed that sediment at this site shows a sharp discontinuity at about 33 Ma, interpreted to represent the breakup unconformity and date the beginning of seafloor spreading in the East Subbasin. The results of IODP Exp. 349, as well as results from deep-towed magnetic surveys, thus imply that oceanic seafloor spreading in the SCS, from 33 to ~16-18 Ma, is coeval with a large part of the left-lateral motion along the Ailao Shan-Red River Fault Zone (dated 34 to 17 Ma). This episode of the extension of the South China Sea basin is therefore more likely driven by the extrusion of the Indochina tectonic block resulting from the collision of India with Eurasia than by the subduction of a proto-South China Sea to the south.

  13. Proterozoic metamorphism in the Neoarchean Kabul Block, Afghanistan

    NASA Astrophysics Data System (ADS)

    Collett, Stephen; Wali Faryad, Shah

    2015-04-01

    The Kabul Block is an elongate crustal fragment that is situated within a tectonic zone known as the Afghan Central Blocks, which form at the triple junction between the Indian, Eurasian, and Arabian plates. Unique amongst the Afghan Central Blocks, the Kabul Block contains quantifiably Precambrian basement rocks. Recent U/Pb SHRIMP analysis of zircons from the lowermost basement formations (the Sherdarwaza and Khair Khana) indicated the presence of a small Neoarchean component (~2700 Ma), while the majority of zircon cores yielded ages of 2200-2500 Ma. The Sherdarwaza and Khair Khana Formations consist predominantly of migmatites and orthogneisses that reached granulite-facies conditions. Conventional geothermobarometry and phase equilibria modelling on well preserved granulite-facies assemblages indicate that the rocks reached peak conditions in excess of 850°C and up to 7 kbar. U/Pb SHRIMP dating of zircon rims in addition to Th/U dating of monazite inclusions in garnet suggest that this event occurred in the late Paleoproterozoic (1800-1900 Ma). The granulite-facies assemblages are overprinted by a younger amphibolite-facies metamorphism, and are unconformably overlain by amphibolite-facies rocks belonging to younger formations (the Kharog and Welayati) that lack paragenetic evidence for a preceding high-grade metamorphism. The Welayati formation crops-out extensively in the south of Kabul City and consists of a variety of mica-schists and garnet-amphibolites, which contain textural relations suitable for the construction of a pressure-temperature (P-T) path. Inclusion assemblages in porphyroblastic garnet yield P-T conditions of around 525°C and 6 kbar. Chemical zonation in the garnet and phase equilibria modelling indicates that from this point garnet grew during a pressure increase of ~3.5 kbar over a temperature increase of ~125°C. A subsequent period of near isothermal decompression over ~2 kbar is confirmed by the growth of plagioclase, kyanite, and

  14. 40Ar/39Ar impact ages and time-temperature argon diffusion history of the Bunburra Rockhole anomalous basaltic achondrite

    NASA Astrophysics Data System (ADS)

    Jourdan, Fred; Benedix, Gretchen; Eroglu, Ela.; Bland, Phil. A.; Bouvier, Audrey.

    2014-09-01

    The Bunburra Rockhole meteorite is a brecciated anomalous basaltic achondrite containing coarse-, medium- and fine-grained lithologies. Petrographic observations constrain the limited shock pressure to between ca. 10 GPa and 20 GPa. In this study, we carried out nine 40Ar/39Ar step-heating experiments on distinct single-grain fragments extracted from the coarse and fine lithologies. We obtained six plateau ages and three mini-plateau ages. These ages fall into two internally concordant populations with mean ages of 3640 ± 21 Ma (n = 7; P = 0.53) and 3544 ± 26 Ma (n = 2; P = 0.54), respectively. Based on these results, additional 40Ar/39Ar data of fusion crust fragments, argon diffusion modelling, and petrographic observations, we conclude that the principal components of the Bunburra Rockhole basaltic achondrite are from a melt rock formed at ∼3.64 Ga by a medium to large impact event. The data imply that this impact generated high enough energy to completely melt the basaltic target rock and reset the Ar systematics, but only partially reset the Pb-Pb age. We also conclude that a complete 40Ar∗ resetting of pyroxene and plagioclase at this time could not have been achieved at solid-state conditions. Comparison with a terrestrial analog (Lonar crater) shows that the time-temperature conditions required to melt basaltic target rocks upon impact are relatively easy to achieve. Ar data also suggest that a second medium-size impact event occurred on a neighbouring part of the same target rock at ∼3.54 Ga. Concordant low-temperature step ages of the nine aliquots suggest that, at ∼3.42 Ga, a third smaller impact excavated parts of the ∼3.64 Ga and ∼3.54 Ga melt rocks and brought the fragments together. The lack of significant impact activity after 3.5 Ga, as recorded by the Bunburra Rockhole suggests that (1) either the meteorite was ejected in a small secondary parent body where it resided untouched by large impacts, or (2) it was covered by a porous heat

  15. Age, body mass index, current smoking history, and serum insulin-like growth factor-I levels associated with bone mineral density in middle-aged Korean men.

    PubMed

    Rhee, Eun-Jung; Oh, Ki-Won; Lee, Won-Young; Kim, Sun-Woo; Oh, Eun-Sook; Baek, Ki-Hyun; Kang, Moo-Il; Park, Cheol-Young; Choi, Moon-Gi; Yoo, Hyung-Joon; Park, Sung-Woo

    2004-01-01

    Osteoporosis is a growing health problem in women and in men. This cross-sectional study examined the association of anthropometric, lifestyle, and hormonal factors with bone mineral density (BMD) in 152 healthy Korean middle-aged men. Smoking habits and alcohol consumption were assessed by interview. Serum testosterone and insulin-like growth factor-I (IGF-I) levels were measured by radioimmunoassay, and serum growth hormone (GH) levels were measured by immunoradiometric assay. GH stimulation tests were performed after the ingestion of 500 mg of L-dopa. BMD was measured at the lumbar spine and at the femoral neck by dual-energy X-ray absorptiometry. Of the middle-aged men, 3.9% were osteoporotic and 28.3% were osteopenic at the lumbar spine site, and 5.9% were osteoporotic and 45.4% were osteopenic at the femoral neck site. Lumbar spine BMD correlated significantly with body mass index (BMI), and femoral neck BMD correlated significantly with age, BMI, and serum IGF-I levels. The lowest quartile group for serum IGF-I levels showed the lowest femoral neck BMD. Osteoporotic men by lumbar spine BMD showed significant differences from the normal BMD group in terms of BMI and smoking habits. Also, osteoporotic men by femoral neck BMD were significantly different for mean age, BMI, and serum IGF-I levels compared with the normal BMD group. On multiple regression analysis, BMI was found to be the only independent predictor of lumbar spine BMD, whereas both BMI and serum IGF-I levels were found to be the independent predictors of femoral neck BMD. Overall, 28.3%-45.4% of middle-aged Korean men were osteopenic. We suggest that higher age, a lower BMI, current smoking history, and lower serum IGF-I levels are risk factors for lower BMD in middle-aged Korean men; however, serum testosterone levels and GH secretory capacity were not found to be correlated with BMD.

  16. Mississippian fossils from southern appalachian metamorphic rocks and their implications for late paleozoic tectonic evolution.

    PubMed

    Gastaldo, R A; Guthrie, G M; Steltenpohl, M G; Gastaldo, R A; Steltenpohl, M G

    1993-10-29

    Fossils of Periastron reticulatum Unger emended. Beck recovered from the Erin Slate of the Talladega slate belt of Alabama establish that these rocks have a Mississippian (Kinderhookian-Tournaisian) age. The Talladega slate belt, the southwestern extension of the western Blue Ridge belt, was interpreted to have been affected by regional dynamothermal metamorphism and coeval deformation as a result of the Acadian orogeny. This fossil find indicates that metamorphism and deformation of the Talladega belt occurred after the Early Carboniferous (Alleghanian), requiring a reevaluation of tectonic interpretations of the southernmost Appalachians.

  17. Lessons from history: Surviving old age during The Great Depression in the United States.

    PubMed

    Matthews, Sarah H; Dunkle, Ruth E

    2013-12-01

    This paper focuses on 30 couples who received a pension and other services from two private trusts in Detroit, Michigan beginning in 1929 or 1930. Results of the qualitative analysis of case files, which contain notes recorded chronologically for 17 of the couples and then surviving spouses, provide a portrait of older couples' lives prior to a partner's death, circumstances surrounding the death, and changes in the social support systems of widows and widowers until their deaths. Close examination of the experiences of these couples is a reminder of how old age and widowhood were experienced prior to the enactment of public pensions and health insurance in the United States.

  18. Platy Hematite and Metamorphism on Mars

    NASA Technical Reports Server (NTRS)

    Lane, M. D.; Morris, R. V.; Hartmann, W. K.; Christensen, P. R.; Mertzman, S. A.

    2002-01-01

    Emissivity spectra of Sinus Meridiani, Mars suggest that the hematite consists of platy particles that occur as consolidated, schistose lenses or loose, platy particles. This platy hematite may have originated as a result of burial metamorphism. Additional information is contained in the original extended abstract.

  19. Metamorphic quantum dots: Quite different nanostructures

    SciTech Connect

    Seravalli, L.; Frigeri, P.; Nasi, L.; Trevisi, G.; Bocchi, C.

    2010-09-15

    In this work, we present a study of InAs quantum dots deposited on InGaAs metamorphic buffers by molecular beam epitaxy. By comparing morphological, structural, and optical properties of such nanostructures with those of InAs/GaAs quantum dot ones, we were able to evidence characteristics that are typical of metamorphic InAs/InGaAs structures. The more relevant are: the cross-hatched InGaAs surface overgrown by dots, the change in critical coverages for island nucleation and ripening, the nucleation of new defects in the capping layers, and the redshift in the emission energy. The discussion on experimental results allowed us to conclude that metamorphic InAs/InGaAs quantum dots are rather different nanostructures, where attention must be put to some issues not present in InAs/GaAs structures, namely, buffer-related defects, surface morphology, different dislocation mobility, and stacking fault energies. On the other hand, we show that metamorphic quantum dot nanostructures can provide new possibilities of tailoring various properties, such as dot positioning and emission energy, that could be very useful for innovative dot-based devices.

  20. Chemical demineralization of different metamorphic grade coals

    SciTech Connect

    Yusupov, T.S.; Shumskaya, L.G.; Burdukov, A.P.

    2009-07-15

    The paper analyzes a process of deep mineralization of various metamorphic grade coals pre-ground in different destructive units, namely, in centrifugal-planetary mill and disintegrator. Coal dispergation in higher energy intensive mills greatly enhances inorganic component extraction to acidic solutions. This is explained by distortion of crystal structure and amorphization of minerals under various kinds and different intensity mechanical actions.

  1. The progenitors of quiescent galaxies at z~2: precision ages and star-formation histories from WFC3/IR spectroscopy

    NASA Astrophysics Data System (ADS)

    Barro, Guillermo

    2013-10-01

    The important "adolescent" epoch at redshifts z 1 to 2 bridges a universe of "adult" galaxies at z<1 to an earlier "childhood" period z>2 when galaxies were dramatically different. During this transition, the early quenching of star formation and later enlargement of compact quiescent galaxies since z 2 remain key unsolved mysteries. We have identified a population of compact star-forming galaxies at 2.5 whose structural properties and number densities suggest an evolutionary connection with the first quiescent galaxies. But demonstrating full consistency between progenitor to descendant populations requires high-precision redshifts, ages, and star formation histories to make reliable links in time. We thus propose adding a 56 orbit G102 survey to GOODS-North. The G102 grism meets the required spectral resolution to resolve stellar population ages and connect progenitors to quiescent galaxies, and perfectly bridges the gap for galaxies at 1ages and star formation histories between their cores and outskirts during the transition era. Given its high value for legacy science, the new data will have no proprietary period.

  2. Metamorphic conditions in the Ashe Metamorphic Suite, North Carolina Blue Ridge

    SciTech Connect

    McSween, H.Y. Jr. ); Abbott, R.N.; Raymond, L.A. )

    1989-12-01

    Taconian metamorphism of mafic rocks in the Ashe Metamorphic Suite can be characterized by reference to an isograd corresponding to the reaction bio + epi = hbl + gar, which separates rocks into two zones of low-variance assemblages. Temperatures and pressures estimated from mineral exchange geothermometers and a barometer suggest that this reaction occurred at approximately 600-650C and 7.5 kbar. Phase equilibria between biotite and hornblende, as well as the sharpness of the mapped isograd, indicate that the reaction is discontinuous. Inferred differences in metamorphic grade between Ashe amphibolites and mafic dikes in the underlying basement suggest that these units are in faulted contact. Isograd patterns in pelitic rocks suggest an elongated domal uplift that developed after metamorphism and thrusting, the core of which is exposed in the adjacent Grandfather Mountain window.

  3. The insanities of the third age: a conceptual history of paraphrenia.

    PubMed

    Berrios, G E

    2003-01-01

    In 1863, Kahlbaum used the term 'paraphrenia' to refer to insanities related to transitional periods life (there were adolescent and senile forms); Kraepelin used paraphrenia to refer to a form of paranoid psychosis with attenuated hallucinatory disturbances; and Leonhard named with it at least seven types of insanities. Since the turn of the 20th century the population hit by 'old age' has grown larger and cases of 'late-onset' insanity seem to be on the increase. Some of these insanities have different clinical features and respond differently to treatment and it is unclear whether this is due to pathoplastic effects, organic factors or social expectation. In the 1950s, the Newcastle school introduced 'late-paraphrenia'. The problem of how to classify the insanities of old age remains parasitical upon beliefs about the insanities affecting people. Historians see science and medicine as examples of social narrative and practice; clinicians see science and medicine as purveyors of absolute truth and as the only way to understand the insanities. This lack of convergence is hampering the understanding and management of elderly people suffering from insanity and must be resolved.

  4. Geochronology and geochemistry of zircon from the northern Western Gneiss Region: Insights into the Caledonian tectonic history of western Norway

    NASA Astrophysics Data System (ADS)

    Gordon, Stacia M.; Whitney, Donna L.; Teyssier, Christian; Fossen, Haakon; Kylander-Clark, Andrew

    2016-03-01

    The Western Gneiss Region (WGR) of Norway is divided by the Møre-Trøndelag shear zone (MTSZ) into a southern region that contains domains of Caledonian ultrahigh-pressure (UHP) metamorphic rocks (> 2.5 GPa) and a northern area of similar Caledonian-aged rocks that record a maximum pressure reported thus far of ~1.5 GPa. Although both regions contain similar lithologies (primarily migmatitic quartzofeldspathic gneiss containing mafic lenses) and structural relationship of basement rocks to infolded nappes, this difference in maximum pressure implies a difference in tectonic history (continental subduction south of the shear zone, none to the north) and raises questions about the role of the MTSZ in the metamorphic history (including exhumation) of the WGR. Previous geochronology results indicated a difference in timing of peak metamorphism (older in north, younger in south). In order to better understand the tectonic history of the northern WGR and the MTSZ, and in particular the late- to post-Caledonian tectonic history, U-Pb zircon geochronology and trace-element abundances were obtained using the split-stream, laser-ablation ICPMS technique from metabasaltic lenses and migmatitic quartzofeldspathic host rocks from the structurally lowest exposed region of the northern WGR (Roan Peninsula basement), as well as leucosomes from an intercalated portion of the Seve Nappe Complex and a pegmatite in the MTSZ. Zircon from Roan gneiss and metabasite yield metamorphic ages of ca. 410-406 Ma, and zircon from a variety of migmatite samples (foliation-parallel leucosome to dikes) indicate melt crystallization at ca. 410 to 405 Ma. The Seve Nappe leucosomes yield only early Caledonian dates that cluster at ca. 437 Ma and ca. 465 Ma, suggesting that the allochthons in this region did not experience (or record) the same Scandian tectonic history as the basement rocks. Zircon from a weakly deformed pegmatite dike within the MTSZ crystallized at ca. 404 Ma, indicating that this

  5. Age-Related Changes in Segmental Body Composition by Ethnicity and History of Weight Change across the Adult Lifespan

    PubMed Central

    Tian, Simiao; Morio, Béatrice; Denis, Jean-Baptiste; Mioche, Laurence

    2016-01-01

    This study assessed age-related changes in body composition (specifically in trunk fat and appendicular lean masses), with consideration of body mass index (BMI) at age 20 years (BMI reference age, “BMIref”), ethnicity and lifetime weight change history. A cross-sectional dual-energy X-ray absorptiometry-based dataset was extracted from the U.S. National Health and Nutrition Examination Survey (NHANES) 1999–2004. Only European-American and African-American subjects were used (2705 men, 2527 women). For each gender and ethnicity, 6 analytic cases were considered, based on three BMIref categories (normal, overweight and obese, being 22, 27 and 30 kg/m2, respectively) and two weight contexts (stable weight or weight gain across the lifespan). A nonparametric model was developed to investigate age-related changes in body composition. Then, parametric modelling was developed for assessing BMIref- and ethnicity-specific effects during aging. In the stable weight, both genders’ and ethnicities’ trunk fat (TF) increased gradually; body fat (BF) remained stable until 40 years and increased thereafter; trunk lean (TL) remained stable, but appendicular lean (APL) and body lean (BL) declined from 20 years. In the weight gain context, TF and BF increased at a constant rate, while APL, TL and BL increased until 40–50 years, and then declined slightly. Compared with European-American subjects of both genders, African-American subjects had lower TF and BF masses. Ethnic differences in body composition were quantified and found to remain constant across the lifespan. PMID:27529269

  6. Age-Related Changes in Segmental Body Composition by Ethnicity and History of Weight Change across the Adult Lifespan.

    PubMed

    Tian, Simiao; Morio, Béatrice; Denis, Jean-Baptiste; Mioche, Laurence

    2016-01-01

    This study assessed age-related changes in body composition (specifically in trunk fat and appendicular lean masses), with consideration of body mass index (BMI) at age 20 years (BMI reference age, "BMIref"), ethnicity and lifetime weight change history. A cross-sectional dual-energy X-ray absorptiometry-based dataset was extracted from the U.S. National Health and Nutrition Examination Survey (NHANES) 1999-2004. Only European-American and African-American subjects were used (2705 men, 2527 women). For each gender and ethnicity, 6 analytic cases were considered, based on three BMIref categories (normal, overweight and obese, being 22, 27 and 30 kg/m², respectively) and two weight contexts (stable weight or weight gain across the lifespan). A nonparametric model was developed to investigate age-related changes in body composition. Then, parametric modelling was developed for assessing BMIref- and ethnicity-specific effects during aging. In the stable weight, both genders' and ethnicities' trunk fat (TF) increased gradually; body fat (BF) remained stable until 40 years and increased thereafter; trunk lean (TL) remained stable, but appendicular lean (APL) and body lean (BL) declined from 20 years. In the weight gain context, TF and BF increased at a constant rate, while APL, TL and BL increased until 40-50 years, and then declined slightly. Compared with European-American subjects of both genders, African-American subjects had lower TF and BF masses. Ethnic differences in body composition were quantified and found to remain constant across the lifespan. PMID:27529269

  7. Nucleosynthetic history of elements in the Galactic disk. [X/Fe]-age relations from high-precision spectroscopy

    NASA Astrophysics Data System (ADS)

    Spina, L.; Meléndez, J.; Karakas, A. I.; Ramírez, I.; Monroe, T. R.; Asplund, M.; Yong, D.

    2016-10-01

    Context. The chemical composition of stars is intimately linked to the formation and evolution of the Galaxy. Aims: We aim to trace the chemical evolution of the Galactic disk through the inspection of the [X/Fe]-age relations of 24 species from C to Eu. Methods: Using high-resolution and high signal-to-noise UVES spectra of nine solar twins, we obtained precise estimates of stellar ages and chemical abundances. These determinations have been integrated with additional accurate age and abundance determinations from recent spectroscopic studies of solar twins existing in the literature, comprising superb abundances with 0.01 dex precision. Based on this data set, we outlined the [X/Fe]-age relations over a time interval of 10 Gyr. Results: We present the [X/Fe] - age relations for 24 elements (C, O, Na, Mg, Al, Si, S, K, Ca, Sc, Ti, V, Cr, Mn, Co, Ni, Cu, Zn, Y, Ba, La, Ce, Nd, and Eu). Each different class of elements showed a distinct evolution with time that relies on the different characteristics, rates, and timescales of the nucleosynthesis sites from which they are produced. The α-elements are characterized by a [X/Fe] decrease with time. Strikingly, the opposite behavior is observed for Ca. The iron-peak elements show an early [X/Fe] increase followed by a decrease towards the youngest stars. The [X/Fe] for the n-capture elements decrease with age. We also found that both [Mg/Y] and [Al/Y] are precise stellar clocks, with [Al/Y] showing the steepest dependence on age. Conclusions: Knowledge of the [X/Fe]-age relations is a gold mine from which we can achieve a great understanding of the processes that governed the formation and evolution of the Milky Way. Through the reverse engineering of these relations we will be able to put strong constraints on the nature of the stellar formation history, the SNe rates, the stellar yields, and the variety of the SNe progenitors. Based on observations obtained at the ESO VLT at Paranal Observatory (Observing program 083

  8. The age of the martian meteorite Northwest Africa 1195 and the differentiation history of the shergottites

    NASA Astrophysics Data System (ADS)

    Symes, Steven J. K.; Borg, Lars E.; Shearer, Charles K.; Irving, Anthony J.

    2008-03-01

    Samarium-neodymium isotopic analyses of unleached and acid-leached mineral fractions from the recently identified olivine-bearing shergottite Northwest Africa 1195 yield a crystallization age of 347 ± 13 Ma and an ɛNd143 value of +40.1 ± 0.9. Maskelynite fractions do not lie on the Sm-Nd isochron and appear to contain a martian surface component with low 147Sm/ 144Nd and 143Nd/ 144Nd ratios that was added during shock. The Rb-Sr system is disturbed and does not yield an isochron. Terrestrial Sr appears to have affected all of the mineral fractions, although a maximum initial 87Sr/ 86Sr ratio of 0.7016 is estimated by passing a 347 Ma reference line through the maskelynite fraction that is least affected by contamination. The high initial ɛNd143 value and the low initial 87Sr/ 86Sr ratio, combined with the geologically young crystallization age, indicate that Northwest Africa 1195 is derived from a source region characterized by a long-term incompatible-element depletion. The age and initial Sr and Nd isotopic compositions of Northwest Africa 1195 are very similar to those of Queen Alexandra Range 94201, indicating these samples were derived from source regions with similar Sr-Nd isotopic systematics. These similarities suggest that these two meteorites share a close petrogenetic relationship and might have been erupted from a common volcano. The meteorites Yamato 980459, Dar al Gani 476, Sayh al Uhaymir 005/008, and Dhofar 019 also have relatively old ages between 474 and 575 Ma and trace element and/or isotopic systematics that are indicative of derivation from incompatible-element-depleted sources. This suggests that the oldest group of meteorites is more closely related to one another than they are to the younger meteorites that are derived from less incompatible-element-depleted sources. Closed-system fractional crystallization of this suite of meteorites is modeled with the MELTS algorithm using the bulk composition of Yamato 980459 as a parent. These

  9. The age of the martian meteorite Northwest Africa 1195 and the differentiation history of the shergottites

    SciTech Connect

    Symes, S; Borg, L; Shearer, C; Irving, A

    2007-04-05

    Samarium-neodymium isotopic analyses of unleached and acid-leached mineral fractions from the recently identified olivine-bearing shergottite Northwest Africa 1195 yield a crystallization age of 348 {+-} 19 Ma and an {var_epsilon}{sub Nd}{sup 143} value of +40.1 {+-} 1.3. Maskelynite fractions do not lie on the Sm-Nd isochron and appear to contain a martian surface component with low {sup 147}Sm/{sup 144}Nd and {sup 143}Nd/{sup 144}Nd ratios that was added during shock. The Rb-Sr system is disturbed and does not yield an isochron. Terrestrial Sr appears to have affected all of the mineral fractions, although a maximum initial {sup 87}Sr/{sup 86}Sr ratio of 0.701614 {+-} 16 is estimated by passing a 348 Ma reference isochron through the maskelynite fraction that is least affected by contamination. The high initial {var_epsilon}{sub Nd}{sup 143} value and the low initial {sup 87}Sr/{sup 86}Sr ratio, combined with the geologically young crystallization age, indicate that Northwest Africa 1195 is derived from a source region characterized by a long-term incompatible element depletion. The age and initial Sr and Nd isotopic compositions of Northwest Africa 1195 are very similar to those of Queen Alexandra Range 94201, indicating these samples were derived from source regions with nearly identical Sr-Nd isotopic systematics. These similarities suggest that these two meteorites share a close petrogenetic relationship and might have been erupted from a common volcano. The meteorites Yamato 980459, Dar al Gani 476, Sayh al Uhaymir 005/008, and Dhofar 019 also have relatively old ages between 474-575 Ma and trace element and/or isotopic systematics that are indicative of derivation from incompatible-element-depleted sources. This suggests that the oldest group of meteorites is more closely related to one another than they are to the younger meteorites that are derived from less incompatible-element-depleted sources. Closed-system fractional crystallization of this suite of

  10. Is the onset of the 6th century 'dark age' in Maya history related to explosive volcanism?

    NASA Astrophysics Data System (ADS)

    Nooren, Kees; Hoek, Wim Z.; Van der Plicht, Hans; Sigl, Michael; Galop, Didier; Torrescano-Valle, Nuria; Islebe, Gerald; Huizinga, Annika; Winkels, Tim; Middelkoop, Hans; Van Bergen, Manfred

    2016-04-01

    Maya societies in Southern Mexico, Guatemala and Belize experienced a 'dark age' during the second half of the 6th century. This period, also known as the 'Maya Hiatus', is characterized by cultural downturn, political instability and abandonment of many sites in the Central Maya Lowlands. Many theories have been postulated to explain the occurrence of this 'dark age' in Maya history. A possible key role of a large volcanic eruption in the onset of this 'dark age' will be discussed. Volcanic deposits recovered from the sedimentary archive of lake Tuspán and the Usumacinta-Grijalva delta were studied in detail and the combination of multiple dating techniques allowed the reconstruction of the timing of a large 6th century eruption. Volcanic glass shards were fingerprinted to indicate the source volcano and high resolution pollen records were constructed to indicate the environmental impact of the eruption. Results are compared with available archaeological data and causality with the disruption of Maya civilization will be evaluated.

  11. Geospeedometry in the inverted metamorphic gradient of the Nestos Thrust Zone in central Rhodope (Northern Greece)

    NASA Astrophysics Data System (ADS)

    Cioldi, Stefania; Moulas, Evangelos; Burg, Jean-Pierre

    2015-04-01

    Thrust tectonics and inverted metamorphic gradients are major consequences of large and likely fast movements of crustal segments in compressional environments. The purpose of this study is to investigate the tectonic setting and the timescale of inverted metamorphic zonations related to crustal-scale thrusting. The aim is to contribute understanding the link between mechanical and thermal evolution of major thrust zones and to clarify the nature and the origin of orogenic heat. The Rhodope metamorphic complex (Northern Greece) is interpreted as a part of the Alpine-Himalaya orogenic belt and represents a collisional system with an association of both large-scale thrusting and pervasive exhumation tectonics. The Nestos Shear Zone overprints the suture boundary with a NNE-dipping pile of schists displaying inverted isograds. The inverted metamorphic zones start from chlorite-muscovite grade at the bottom and reach kyanite-sillimanite grades with migmatites in the upper structural levels. In order to reconstruct the thermo-tectonic evolution of inverted metamorphic zonation, reliable geochronological data are essential. 40Ar/39Ar geochronology with step-heating technique on white mica from micaschists provided a temporal resolution with the potential to characterize shearing. 40Ar/39Ar dating across the Nestos Shear Zone yields Late Eocene-Early Oligocene (40-30 Ma) cooling (~400-350° C) ages, which correspond to local thermo-deformation episodes linked to late and post-orogenic intrusions. U-Pb Sensitive High Resolution Ion Microprobe (SHRIMP) zircon geochronology on leucosomes from migmatitic orthogneisses were considered to estimate the age of peak metamorphic conditions, contemporaneous with anatexis. U-Pb ages of zircon rims specify regional partial melting during the Early Cretaceous (160-120 Ma). This is in disagreement with previous assertions, which argued that the formation of leucosomes in this region is Late Eocene (42-35 Ma) and implied multiple

  12. New geochemical and geochronological data constraining metamorphism of the Tavşanlı Zone, NW Turkey

    NASA Astrophysics Data System (ADS)

    Aydın, Halil Can; Özdamar, Şenel

    2016-04-01

    The Tavşanlı Zone is a high-grade metamorphic belt, representing subduction and exhumation between the Sakarya Zone and the Afyon-Bolkardaǧ Zone in Western Anatolia. The Sivrihisar area of the Tavşanlı Zone comprises Paleozoic metamorphic rocks including sedimentary and magmatic origanated; Eocene granites; Neogene sedimentary rocks and alluvium. Metasedimantary rocks are composed of marble, schist and quartzite. Metamagmatics are gneiss and metabazites. This study presents new and precise, whole-rock chemistry; phengite-40Ar/39Ar age data from this area to constrain the high pressure (HP)-low temperature (LT) metamorphism of the Tavşanlı Zone. 40Ar/39Ar dating of two phengite samples from schists gave plateau ages between 82,5 ± 0,14 and 83,29 ± 0,22 Ma, which are interpreted as the metamorphic age of these schists, and as the age of metamorphism affected the Tavşanlı Zone. Also these ages constrain the timing of the closure of the Neo-Tethys.

  13. THE STAR FORMATION AND NUCLEAR ACCRETION HISTORIES OF NORMAL GALAXIES IN THE AGES SURVEY

    SciTech Connect

    Watson, Casey R.; Kochanek, Christopher S.; Forman, William R.; Hickox, Ryan C.; Jones, Christine J.; Kenter, Almus T.; Murray, Steve S.; Vikhlinin, Alexey; Fazio, Giovani G.; Green, Paul J.; Brown, Michael J. I.; Brand, Kate; Dey, Arjun; Jannuzi, Buell T.; Rieke, Marcia; Eisenstein, Daniel J.; McNamara, Brian R.; Shields, Joseph C.

    2009-05-10

    We combine IR, optical, and X-ray data from the overlapping, 9.3 deg{sup 2} NOAO Deep Wide-Field Survey, AGN and Galaxy Evolution Survey (AGES), and XBooetes Survey to measure the X-ray evolution of 6146 normal galaxies as a function of absolute optical luminosity, redshift, and spectral type over the largely unexplored redshift range 0.1 {approx}< z {approx}< 0.5. Because only the closest or brightest of the galaxies are individually detected in X-rays, we use a stacking analysis to determine the mean properties of the sample. Our results suggest that X-ray emission from spectroscopically late-type galaxies is dominated by star formation, while that from early-type galaxies is dominated by a combination of hot gas and active galactic nucleus (AGN) emission. We find that the mean star formation and supermassive black hole accretion rate densities evolve like {approx}(1 + z){sup 3{+-}}{sup 1}, in agreement with the trends found for samples of bright, individually detectable starburst galaxies and AGN. Our work also corroborates the results of many previous stacking analyses of faint source populations, with improved statistics.

  14. Maximum-limiting ages of Lake Michigan coastal dunes: Their correlation with Holocene lake level history

    USGS Publications Warehouse

    Arbogast, Alan F.; Loope, Walter L.

    1999-01-01

    At each site, thick deposits of eolian sand overlie late-Pleistocene lacustrine sands. Moderately developed Spodosols (Entic Haplorthods) formed in the uppermost part of the lake sediments are buried by thick dune sand at three sites. At the fourth locality, a similar soil occurs in a very thin (1.3 m) unit of eolian sand buried deep within a dune. These soils indicate long-term (∼ 4,000 years) stability of the lake deposits following subaerial exposure. Radiocarbon dating of charcoal in the buried sola indicates massive dune construction began between 4,900 and 4,500 cal. yr B.P. at the Nordhouse Dunes site, between 4,300 and 3,900 cal. yr B.P. at the Jackson and Nugent Quarries, and between 3,300 to 2,900 cal. yr B.P. at Rosy Mound. Given these ages, it can be concluded that dune building at one site occurred during the Nipissing high stand but that the other dunes developed later. Although lake levels generally fell after the Nipissing, it appears that dune construction may have resulted from small increases in lake level and destabilization of lake-terrace bluffs.

  15. Women healers of the middle ages: selected aspects of their history.

    PubMed Central

    Minkowski, W L

    1992-01-01

    The stellar role of women as healers during the Middle Ages has received some attention from medical historians but remains little known or appreciated. In the three centuries preceding the Renaissance, this role was heightened by two roughly parallel developments. The first was the evolution of European universities and their professional schools that, for the most part, systematically excluded women as students, thereby creating a legal male monopoly of the practice of medicine. Ineligible as healers, women waged a lengthy battle to maintain their right to care for the sick and injured. The 1322 case of Jacqueline Felicie, one of many healers charged with illegally practicing medicine, raises serious questions about the motives of male physicians in discrediting these women as incompetent and dangerous. The second development was the campaign--promoted by the church and supported by both clerical and civil authorities--to brand women healers as witches. Perhaps the church perceived these women, with their special, often esoteric, healing skills, as a threat to its supremacy in the lives of its parishioners. The result was the brutal persecution of unknown numbers of mostly peasant women. Images p290-a p291-a PMID:1739168

  16. A combined diffusion and thermal modeling approach to determine peak temperatures of thermal metamorphism experienced by meteorites

    NASA Astrophysics Data System (ADS)

    Schwinger, Sabrina; Dohmen, Ralf; Schertl, Hans-Peter

    2016-10-01

    Carbonaceous chondrites are affected to different degrees by thermal and aqueous metamorphism on their parent bodies. However, the degree of alteration has been categorized mainly by relative scales and achieving quantitative information about metamorphic temperature by conventional mineral thermometry is problematic for low petrologic types. We have developed a general approach to estimate the metamorphic peak temperature experienced by type 3 chondrites from diffusion zoning in minerals, and have applied this approach to olivine in type I and type II chondrules of CO3 chondrites. To obtain metamorphic temperatures from diffusion zoning, we have combined diffusion modeling with thermal modeling of the meteorite parent body. The integrated diffusion coefficient over time (Γ) was identified as a useful parameter to quantify the extent of chemical change by diffusion occurring in a mineral during a given thermal history. Knowing the temperature dependence of the diffusion coefficient, Γ values can be calculated for each thermal history and be compared to the Γ values obtained from diffusion modeling. For thermal histories realistic for the parent body, Γ depends primarily on the metamorphic peak temperature, so that Γ values determined from diffusion profiles in meteorite minerals can be directly related to the metamorphic peak temperature. This general approach is relatively insensitive to uncertainties in the input parameters for the thermal model. We found that chemical zoning in type I and type II chondrule olivine of the CO chondrites Kainsaz and Lancé was largely influenced by solid state diffusion, which is evident from the observed correlation of zoning anisotropy with the crystallographic orientation. Chemical zoning in type II chondrule olivine is mainly igneous for CO chondrites of petrologic types up to at least 3.2 (Kainsaz) and was influenced only minor by diffusion during parent body metamorphism. Fe-Mg zoning in type II chondrule olivine and

  17. Degree of equilibration of eucritic pyroxenes and thermal metamorphism of the earliest planetary crust

    SciTech Connect

    Takeda, Hiroshi; Graham, A.L. Natural History Museum, London )

    1991-06-01

    The pyroxenes in two new monomict eucrites from Antarctica, Yamato 791186 and Yamato 792510, have been studied and compared with those of other Antarctic and non-Antarctic eucrites. The purpose of this study is to identify compositional and textural relationship shown by these pyroxenes which may be used as indicators of the thermal history of the meteorite. An attempt is made, using petrographic and compositional criteria, to distinguish between the initial cooling history and subsequent thermal events. It is suggested that it is possible to identify stages of thermal 'metamorphism' which may be used to indicate the conditions on the surface and crust of the parent body. A picture of the geological setting of the HED (Howardites, Eucrites, Diogenites) parent body is proposed, for which thermal metamorphism by impact heating is an important process. 22 refs.

  18. Blueschist-facies metamorphism related to regional thrust faulting

    USGS Publications Warehouse

    Blake, M.C.; Irwin, W.P.; Coleman, R.G.

    1969-01-01

    Rocks of the blueschist (glaucophane schist) facies occur throughout the world in narrow tectonic belts associated with ultramafic rocks. In the Coast Range province of California, blueschist rocks are devloped in the eugeosynclinal Franciscan Formation of Late Mesozoic age. The blueschist rocks form a narrow belt for more than 800 km along the eastern margin of this province and commonly are separated from rocks of an overlying thrust plate by serpentinite. Increasing metamorphism upward toward the thrust fault is indicated mineralogically by a transition from pumpellyite to lawsonite and texturally by a transition from metagraywacke to schist. The blueschist metamorphism probably occurred during thrusting in a zone of anomalously high water pressure in the lower plate along the sole of the thrust fault. This tectonic mode of origin for blueschist differs from the generally accepted hypothesis involving extreme depth of burial. Other belts of blueschist-facies rocks, including the Sanbagawa belt of Japan, the marginal synclinal belt of New Zealand, and the blueschist-ultramafic belts of Venezuela, Kamchatka, Ural mountains, and New Caledonia have similar geologic relations and might be explained in the same manner. ?? 1969.

  19. A prospective study of cognitive health in the elderly (Oregon Brain Aging Study): effects of family history and apolipoprotein E genotype.

    PubMed Central

    Payami, H; Grimslid, H; Oken, B; Camicioli, R; Sexton, G; Dame, A; Howieson, D; Kaye, J

    1997-01-01

    The oldest old are the fastest-growing segment of our population and have the highest prevalence of dementia. Little is known about the genetics of cognitive health in the very old. The aim of this study was to determine whether the genetic risk factors for Alzheimer disease (AD)--namely, apolipoprotein E (APOE) epsilon4 allele and a family history of dementia-continue to be important factors in the cognitive health of the very old. Case-control studies suggest that the effect of genetic factors diminishes at age >75 years. The present prospective study provided evidence to the contrary. We studied 114 Caucasian subjects who were physically healthy and cognitively intact at age 75 years and who were followed, for an average of 4 years, with neurological, psychometric, and neuroimaging examinations. Excellent health at entry did not protect against cognitive decline. Incidence of cognitive decline rose sharply with age. epsilon4 and a family history of dementia (independent of epsilon4) were associated with an earlier age at onset of dementia. Subjects who had epsilon4 or a family history of dementia had a ninefold-higher age-specific risk for dementia than did those who had neither epsilon4 nor a family history of dementia. These observations suggest that the rate of cognitive decline increases with age and that APOE and other familial/genetic factors influence the onset age throughout life. PMID:9106542

  20. Thermal metamorphism of the Arunachal Himalaya, India: Raman thermometry and thermochronological constraints on the tectono-thermal evolution

    NASA Astrophysics Data System (ADS)

    Mathew, George; De Sarkar, Sharmistha; Pande, Kanchan; Dutta, Suryendu; Ali, Shakir; Rai, Apritam; Netrawali, Shilpa

    2013-05-01

    Determination of the peak thermal condition is vital in order to understand tectono-thermal evolution of the Himalayan belt. The Lesser Himalayan Sequence (LHS) in the Western Arunachal Pradesh, being rich in carbonaceous material (CM), facilitates the determination of peak metamorphic temperature based on Raman spectroscopy of carbonaceous material (RSCM). In this study, we have used RSCM method of Beyssac et al. (J Metamorph Geol 20:859-871, 2002a) and Rahl et al. (Earth Planet Sci Lett 240:339-354, 2005) to estimate the thermal history of LHS and Siwalik foreland from the western Arunachal Pradesh. The study indicates that the temperature of 700-800 °C in the Greater Himalayan Sequence (GHS) decreases to 650-700 °C in the main central thrust zone (MCTZ) and decreases further to <200 °C in the Mio-Pliocene sequence of Siwaliks. The work demonstrates greater reliability of Rahl et al.'s (Earth Planet Sci Lett 240:339-354, 2005) RSCM method for temperatures >600 and <340 °C. We show that the higher and lower zones of Bomdila Gneiss (BG) experienced temperature of ~600 °C and exhumed at different stages along the Bomdila Thrust (BT) and Upper Main Boundary Thrust (U.MBT). Pyrolysis analysis of the CM together with the Fission Track ages from upper Siwaliks corroborates the RSCM thermometry estimate of ~240 °C. The results indicate that the Permian sequence north of Lower MBT was deposited at greater depths (>12 km) than the upper Siwalik sediments to its south at depths <8 km before they were exhumed. The 40Ar/39Ar ages suggest that the upper zones of Se La evolved ~13-15 Ma. The middle zone exhumed at ~11 Ma and lower zone close to ~8 Ma indicating erosional unroofing of the MCT sheet. The footwall of MCTZ cooled between 6 and 8 Ma. Analyses of P-T path imply that LHS between MCT and U.MBT zone falls within the kyanite stability field with near isobaric condition. At higher structural level, the temperatures increase gradually with P-T conditions in the

  1. SOCIAL CONSEQUENCES OF ETHANOL: IMPACT OF AGE, STRESS AND PRIOR HISTORY OF ETHANOL EXPOSURE

    PubMed Central

    Varlinskaya, Elena I.; Spear, Linda P.

    2014-01-01

    The adolescent period is associated with high significance of interactions with peers, high frequency of stressful situations, and high rates of alcohol use. At least two desired effects of alcohol that may contribute to heavy and problematic drinking during adolescence are its abilities to both facilitate interactions with peers and to alleviate anxiety, perhaps especially anxiety seen in social contexts. Ethanol-induced social facilitation can be seen using a simple model of adolescence in the rat, with normal adolescents, but not their more mature counterparts, demonstrating this ethanol-related social facilitation. Prior repeated stress induces expression of ethanol-induced social facilitation in adults and further enhances socially facilitating effects of ethanol among adolescent rats. In contrast, under normal circumstances, adolescent rats are less sensitive than adults to the social inhibition induced by higher ethanol doses and are insensitive to the socially anxiolytic effects of ethanol. Sensitivity to the socially anxiolytic effects of ethanol can be modified by prior stress or ethanol exposure at both ages. Shortly following repeated restraint or ethanol exposure, adolescents exhibit social anxiety-like behavior, indexed by reduced social preference, and enhanced sensitivity to the socially anxiolytic effects of ethanol, indexed through ethanol-associated reinstatement of social preference in these adolescents. Repeated restraint, but not repeated ethanol, induces similar effects in adults as well, eliciting social anxiety-like behavior and increasing their sensitivity to the socially anxiolytic effects of acute ethanol; the stressor also decreases sensitivity of adults to ethanol-induced social inhibition. The persisting consequences of early adolescent ethanol exposure differ from its immediate consequences, with males exposed early in adolescence, but not females or those exposed later in adolescence, showing social anxiety-like behavior when tested

  2. Social consequences of ethanol: Impact of age, stress, and prior history of ethanol exposure.

    PubMed

    Varlinskaya, Elena I; Spear, Linda P

    2015-09-01

    The adolescent period is associated with high significance of interactions with peers, high frequency of stressful situations, and high rates of alcohol use. At least two desired effects of alcohol that may contribute to heavy and problematic drinking during adolescence are its abilities to both facilitate interactions with peers and to alleviate anxiety, perhaps especially anxiety seen in social contexts. Ethanol-induced social facilitation can be seen using a simple model of adolescence in the rat, with normal adolescents, but not their more mature counterparts, demonstrating this ethanol-related social facilitation. Prior repeated stress induces expression of ethanol-induced social facilitation in adults and further enhances socially facilitating effects of ethanol among adolescent rats. In contrast, under normal circumstances, adolescent rats are less sensitive than adults to the social inhibition induced by higher ethanol doses and are insensitive to the socially anxiolytic effects of ethanol. Sensitivity to the socially anxiolytic effects of ethanol can be modified by prior stress or ethanol exposure at both ages. Shortly following repeated restraint or ethanol exposure, adolescents exhibit social anxiety-like behavior, indexed by reduced social preference, and enhanced sensitivity to the socially anxiolytic effects of ethanol, indexed through ethanol-associated reinstatement of social preference in these adolescents. Repeated restraint, but not repeated ethanol, induces similar effects in adults as well, eliciting social anxiety-like behavior and increasing their sensitivity to the socially anxiolytic effects of acute ethanol; the stressor also decreases sensitivity of adults to ethanol-induced social inhibition. The persisting consequences of early adolescent ethanol exposure differ from its immediate consequences, with males exposed early in adolescence, but not females or those exposed later in adolescence, showing social anxiety-like behavior when tested

  3. Raman spectroscopy of carbon and solid bitumens in sedimentary and metamorphic rocks.

    PubMed

    Jehlicka, Jan; Urban, Ondrej; Pokorný, Jan

    2003-08-01

    Different types of carbonaceous matter from rocks display Raman spectral features which knowledge permits to obtain structural information of these materials. Application of Raman microspectroscopy to investigate kerogen, bitumen, fossils, highly carbonified amorphous carbon as well as graphite from different environments is reviewed. Differences in Raman spectra and structural differences between carbonaceous samples differing in their metamorphic history are discussed on the basis of new data.

  4. Impact Metamorphism of Subsurface Organic Matter on Mars: A Potential Source for Methane and Surface Alteration

    NASA Technical Reports Server (NTRS)

    Oehler, D. Z.; Allen, C. C.; McKay, D. S.

    2005-01-01

    Reports of methane in the Martian atmosphere have spurred speculation about sources for that methane [1-3]. Discussion has centered on cometary/ meteoritic delivery, magmatic/mantle processes, UV-breakdown of organics, serpentinization of basalts, and generation of methane by living organisms. This paper describes an additional possibility: that buried organic remains from past life on Mars may have been generating methane throughout Martian history as a result of heating associated with impact metamorphism.

  5. Meteoric water in metamorphic core complexes

    NASA Astrophysics Data System (ADS)

    Teyssier, Christian; Mulch, Andreas

    2015-04-01

    The trace of surface water has been found in all detachment shear zones that bound the Cordilleran metamorphic core complexes of North America. DeltaD values of mica fish in detachment mylonites demonstrate that these synkinematic minerals grew in the presence of meteoric water. Typically deltaD values are very negative (-120 to -160 per mil) corresponding to deltaD values of water that are < -100 per mil given the temperature of water-mica isotopic equilibration (300-500C). From British Columbia (Canada) to Nevada (USA) detachment systems bound a series of core complexes: the Thor-Odin, Valhalla, Kettle-Okanogan, Bitterroot -Anaconda, Pioneer, Raft River, Ruby Mountain, and Snake Range. The bounding shear zones range in thickness from ~100 m to ~1 km, and within the shear zones, meteoric water signature is recognized over 10s to 100s of meters beneath the detachment fault. The age of shearing ranges generally from Eocene in the N (~50-45 Ma) to Oligo-Miocene in the S (25-15 Ma). DeltaD water values derived from mica fish in shear zones are consistent with supradetachment basin records of the same age brackets and can be used for paleoaltimetry if coeval isotopic records from near sea level are available. Results show that a wave of topography (typically 4000-5000 m) developed from N to S along the Cordillera belt from Eocene to Miocene, accompanied by the propagation of extensional deformation and volcanic activity. In addition, each detachment system informs a particular extensional detachment process. For example, the thick Thor-Odin detachment shear zone provides sufficient age resolution to indicate the downward propagation of shearing and the progressive incorporation of footwall rocks into the hanging wall. The Kettle detachment provides a clear illustration of the dependence of fluid circulation on dynamic recrystallization processes. The Raft River system consists of a thick Eocene shear zone that was overprinted by Miocene shearing; channels of meteoric

  6. Carbonic metamorphism, granulites and crustal growth

    NASA Technical Reports Server (NTRS)

    Newton, R. C.; Smith, J. V.; Windley, B. F.

    1980-01-01

    Stabilization of early crust against melting by high radioactivity and against resorption into the mantle by fast convective overturn requires that water and heat producers were flushed upwards within 50 Myr of accretion. Creation of a refractory base of granulite by metamorphism associated with CO2 vapour explains CO2-rich fluid inclusions in ancient high-grade rocks, minor-element depletions and local phenomena of arrested development of charnockite in Precambrian terrains. The hot-spot and plate-tectonic models of Precambrian crustal evolution lead to different schemes for CO2 delivery to continental roots. New tectonic concepts may be needed to explain carbonic metamorphism and other features of early crustal evolution.

  7. Heat transfer by fluids in granulite metamorphism

    NASA Technical Reports Server (NTRS)

    Morgan, Paul; Ashwal, Lewis D.

    1988-01-01

    The thermal role of fluids in granulite metamorphism was presented. It was shown that for granulites to be formed in the middle crust, heat must be advected by either magma or by volatile fluids, such as water or CO2. Models of channelized fluid flow indicate that there is little thermal difference between channelized and pervasive fluid flow, for the same total fluid flux, unless the channel spacing is of the same order or greater than the thickness of the layer through which the fluids flow. The volumes of volatile fluids required are very large and are only likely to be found associated with dehydration of a subducting slab, if volatile fluids are the sole heat source for granulite metamorphism.

  8. Shape Metamorphism Using p-Laplacian Equation

    SciTech Connect

    Cong, Ge; Esser, Mehmet; Parvin, Bahram; Bebis, George

    2004-05-19

    We present a new approach for shape metamorphism, which is a process of gradually changing a source shape (known) through intermediate shapes (unknown) into a target shape (known). The problem, when represented with implicit scalar function, is under-constrained, and regularization is needed. Using the p-Laplacian equation (PLE), we generalize a series of regularization terms based on the gradient of the implicit function, and we show that the present methods lack additional constraints for a more stable solution. The novelty of our approach is in the deployment of a new regularization term when p --> infinity which leads to the infinite Laplacian equation (ILE). We show that ILE minimizes the supremum of the gradient and prove that it is optimal for metamorphism since intermediate solutions are equally distributed along their normal direction. Applications of the proposed algorithm for 2D and 3D objects are demonstrated.

  9. Metamorphic reactions in the Chaunskij mesosiderite

    NASA Astrophysics Data System (ADS)

    Petaev, M. I.

    1994-07-01

    The Chaunskij meteorite, found in 1985, recently has been found to be the most highly metamorphosed, shock-modified, and metal-rich mesosiderite. It contains approximately 10 vol% mono- and polymineralic troilite-phosphate-silicate inclusions, micrometers to centimeters in size. Two dominant silicate lithologies have been found in the inclusions. The primary 'igneous' lithology, making up the largest inclusion studied, is generally a microophitic fine-grained aggregate of pyroxene, plagioclase, and minor silica, with scattered coarser-grained granoblastic spots enriched in silica and troilite. The secondary 'metamorphic' lithology occurs as separate small inclusions and as larger areas in intimate contact with the 'igneous' lithology, separated by highly irregular boundaries from each other, in the largest inclusion. In small inclusions the metamorphic lithology consists of a fine-grained hornfelsic to granoblastic aggregate of cordierite, orthopyroxene, quartz, and whitlockite with variable amounts of opaque minerals. In the largest inclusion the metamorphic lithology is a generally granoblastic to poikiloblastic aggregate of cordierite and quartz with minor amounts of other minerals. The Opx-Chr mineral thermometer and the Cord-Sp barometer have been applied to estimate the conditions of Chaunskij metamorphism. The data for 16 Opx-Chr pairs from different inclusions and lithologies correspond to a temperature of 590 +/- 30 C. The data for 9 Cord-Chr pairs from different inclusions correspond to a pressure of 6.0 +/- 0.2 kbar. While the composition of spinel in Chaunskij much richer in Cr than were the spinels used to calibrate Cord-Sp barometer the estimated pressure is consistent with the occurrence in the igneous lithology of two small pyroxene grains enriched in the CaAl2SiO6 molecule, coexisting with quartz and plagioclase. This mineral assemblage is unstable below approximately 5 kbar at 600 C.

  10. Metamorphic sole formation, emplacement and blueschist overprint: early obduction dynamics witnessed by W. Turkey ophiolites

    NASA Astrophysics Data System (ADS)

    Plunder, Alexis; Agard, Philippe; Chopin, Christian; Soret, Mathieu; Okay, Aral; Whitechurch, Hubert

    2016-04-01

    Western Turkey, with a >200 km long-belt of unmetamorphosed ophiolite overlying continental lithosphere is one or even the largest obducted ophiolite on Earth and therefore a key example to study obduction and early subduction dynamics. All Western Turkish ophiolite fragments are considered as part of the same Neotethyan branch resulting of a long-lived continental subduction (or underthrusting). Synchronous (ca. ~ 93 Ma) metamorphic sole formation and preservation at the base of most of the Turkish ophiolite fragments support this single event and place a strong constraint on the age of subduction initiation. Metamorphic soles are indeed generally considered to have formed during the early and hot subduction zone at 25 ± 10 km depths and welded to the overriding oceanic lithosphere. In Western Turkey however (as for most places worldwide) a systematic study of the pressure-temperature conditions with modern thermobarometric tools is generally lacking, and fundamental mechanisms of formation or accretion to the upper plate are poorly (if at all) constrained. We herein reappraise Western Turkish metamorphic soles focusing on the following points and issues: (i) detailed structures of metamorphic sole and other subduction derived units, petrological evolution and refined pressure-temperature conditions; peak pressure-temperature conditions of metamorphic sole were estimated using garnet, clinopyroxene, amphibole and plagioclase as the peak paragenesis at 10.5 ± 2 kbar and 800 ± 50°C based on pseudosections using the Theriak/Domino package (ii) the rather unique (and enigmatic) blueschist facies overprint found in places was investigated in terms of structural position and pressure-temperature conditions. Conditions of overprint were estimated around 12 kbar and 425 °C from the presence of glaucophane, lawsonite, jadeite and garnet overgrowing the amphibolite-facies assemblage. This field-based study provides clues to mechanisms of metamorphic sole underplating

  11. Thermal history and extensional exhumation of a high-temperature crystalline complex (Hırkadağ Massif, Central Anatolia)

    NASA Astrophysics Data System (ADS)

    Lefebvre, Côme; Kalijn Peters, M.; Wehrens, Philip C.; Brouwer, Fraukje M.; van Roermund, Herman L. M.

    2015-12-01

    The Central Anatolian Crystalline Complex (CACC) is a large continental domain exposed in central Turkey that was affected by high temperature metamorphism during the Late Cretaceous. As a result of this event, Paleozoic sediments became metamorphosed, initially under Barrovian conditions, then overprinted locally by high temperature-low pressure metamorphism, and intruded by widespread batholiths. In this study we focus on the crystalline Hırkadağ Massif located in the central part of the CACC, where we applied an integrated approach involving metamorphic, structural and geochronological analysis in order to elucidate its tectonic history from burial to exhumation. Our metamorphic study reveals that conditions of metamorphism reached ~ 7-8 kbar/700 °C and were relatively homogeneous at the scale of the Hırkadağ Massif. Coeval with the regional metamorphism, the rocks were intensely deformed as reflected by isoclinal folding, the development of a pervasive foliation and top-to-the-SE shearing. This was followed by decompression to pressures of ~ 3-4 kbar at 800 °C, which may be linked to the emplacement of local granodioritic intrusions at ~ 77 Ma. Subsequent cooling of the Hırkadağ high-grade metamorphic and intrusive rocks is indicated by 40Ar/39Ar cooling ages of 68.8 ± 0.9 Ma (biotite) and 67.0 ± 1.2 Ma (potassium feldspar). Evidence for tectonic exhumation has been identified within the marbles at the NE margin of the Hırkadağ Massif, in the form of discrete protomylonitic and mylonitic shear bands showing a consistent N40-60 top-to-NE sense of shear. Further east, the contact between brecciated mylonitic marbles and non-metamorphic conglomerates preserves the typical structural features of an upper-crustal detachment fault. Restoration of the Hırkadağ Massif and the CACC to their late Cretaceous configuration suggests that the LP-HT metamorphism, magmatism and extensional structures evolved as a result of the development and exhumation of a ~ N

  12. Metamorphic proteins mediate evolutionary transitions of structure.

    PubMed

    Yadid, Itamar; Kirshenbaum, Noam; Sharon, Michal; Dym, Orly; Tawfik, Dan S

    2010-04-20

    The primary sequence of proteins usually dictates a single tertiary and quaternary structure. However, certain proteins undergo reversible backbone rearrangements. Such metamorphic proteins provide a means of facilitating the evolution of new folds and architectures. However, because natural folds emerged at the early stages of evolution, the potential role of metamorphic intermediates in mediating evolutionary transitions of structure remains largely unexplored. We evolved a set of new proteins based on approximately 100 amino acid fragments derived from tachylectin-2--a monomeric, 236 amino acids, five-bladed beta-propeller. Their structures reveal a unique pentameric assembly and novel beta-propeller structures. Although identical in sequence, the oligomeric subunits adopt two, or even three, different structures that together enable the pentameric assembly of two propellers connected via a small linker. Most of the subunits adopt a wild-type-like structure within individual five-bladed propellers. However, the bridging subunits exhibit domain swaps and asymmetric strand exchanges that allow them to complete the two propellers and connect them. Thus, the modular and metamorphic nature of these subunits enabled dramatic changes in tertiary and quaternary structure, while maintaining the lectin function. These oligomers therefore comprise putative intermediates via which beta-propellers can evolve from smaller elements. Our data also suggest that the ability of one sequence to equilibrate between different structures can be evolutionary optimized, thus facilitating the emergence of new structures.

  13. Magmas, Mushes and Mobility: Thermal Histories of Magma Reservoirs from Combined U-Series and Diffusion Ages

    NASA Astrophysics Data System (ADS)

    Cooper, K. M.; Rubin, A. E.; Schrecengost, K.; Kent, A. J.; Huber, C.

    2014-12-01

    The thermal conditions of magma storage control many aspects of the dynamics of a magma reservoir system. For example, the temperature of magma storage directly relates to the crystallinity, and magmas stored at relatively low temperatures in a crystal mush (more than 40-50% crystalline) must be remobilized (e.g., by heating) before they can be erupted. A better understanding of the duration of magma storage at largely-liquid vs. largely-solid conditions is thus critical to understanding crustal magmatic processes such as magma mixing and for quantifying the hazard potential of a given volcano. Although mineral thermometry reflects the conditions of crystal growth or equilibration, these may not correspond to the thermal conditions of crystal storage. The duration of crystal storage at high temperatures can be quantified by comparing U-series crystal ages with the time scales over which disequilibrium trace-element profiles in the same crystals would be erased by diffusion. In the case of Mount Hood, OR, such a comparison for the two most recent eruptions shows that <12% of the total lifetime of plagioclase crystals (minimum 21 kyr) was spent at temperatures high enough that the magma would be easily mobilized. Partial data sets for other systems suggest such behavior is common, although the diffusion and U-series ages in these cases are from different samples and may not be directly comparable. We will present preliminary data combining U-series dating and diffusion timescales on the same samples for other volcanic systems (e.g., Lassen Volcanic Center, Mount St. Helens, Okataina Volcanic Center, New Zealand). Combining these data with numerical models offers additional insights into the controls on the conditions of storage. In addition, extension of this approach to combining U-Th ages with time scales of Li diffusion in zircon offers a promising new method to quantify thermal histories of silicic reservoir systems.

  14. Ultrahigh-temperature metamorphism under isobaric heating: New evidence from the North China Craton

    NASA Astrophysics Data System (ADS)

    Yang, Qiong-Yan; Santosh, M.; Tsunogae, Toshiaki

    2014-12-01

    The Khondalite Belt within Inner Mongolia Suture Zone (IMSZ) in the North China Craton (NCC) preserves evidence for extreme crustal metamorphism under ultra-high temperature (UHT) conditions at ca. 1.92 Ga, associated with the subduction-collision tectonics between the Yinshan and Ordos Blocks. Here we report a new locality in Hongsigou where cordierite- and spinel-bearing granulites record UHT metamorphism. The prograde, peak, and retrograde mineral assemblages in these pelitic granulites have been identified based on petrography and mineral chemistry as: Bt1 + Grt1 + Sil1 + Kfs1 + Pl1 + Ilm + Qtz1, Grt1 + Sil2 + Kfs2 + Pl2 + Spl + Ilm + Qtz2 + Liq, and Crd + Grt2 + Sil3 + Kfs2 + Pl2 + Ilm + Qtz2 respectively. The peak metamorphic conditions of the pelitic granulite were estimated as 930-1050 °C and 6.5-7.5 kbar based on pseudosection analysis in the system NCKFMASHTO, suggesting extreme thermal metamorphism. We report LA-ICPMS zircon U-Pb data from the granulite which show weighted mean 207Pb/206Pb age of 1881 ± 6.6 Ma, marking the timing of UHT metamorphism. Lu-Hf analyses of the zircons show εHf(t) values within a restricted range of -4.2 to 0.3 and together with Hf model ages, a Paleoproterozoic arc magmatic source is inferred for the detrital zircons. The estimated P-T path for the UHT granulite suggests isobaric heating followed by cooling and decompression along a clockwise trajectory, different from the anti-clockwise P-T paths defined in earlier studies for the 1.92 Ga UHT rocks from the IMSZ. The younger age and the isobaric heating trajectory suggest that the Hongsigou UHT rocks are related to heat input from underplated mafic magmas following continental collision.

  15. The analysis of chemical zoning in a garnet population: Determination of the P-T-t path of Grenvillian metamorphism in southeastern Ontario

    NASA Astrophysics Data System (ADS)

    McCarron, T.; Gaidies, F.

    2013-12-01

    Growth zoning developed in a population of garnet porphyroblasts of a metapelite from the Grenville Province of southeastern Ontario has been used to infer the metamorphic P-T-t history of the garnet-bearing rock. The sample is a garnet-biotite-staurolite bearing schist of the Flinton Group, a package of metasediments in southeastern Ontario metamorphosed during the Grenville Orogeny between ca. 1080-980 Ma. Characterization of the garnet population with high-resolution X-ray micro-computed tomography revealed a unimodal, slightly positively skewed crystal size distribution (CSD). A representative set of garnet porphyroblasts ranging from 4000 to 200 μm in diameter from the different size classes of the CSD were centrally sectioned. Electron probe micro analyses across the centrally sectioned garnet porphyroblasts revealed decreasing Xsps and Xgrs and increasing Xalm and Xpyp from core to rim consistent with growth zoning. Garnet growth simulations with THERIA_G (Gaidies et al., 2008) successfully reproduced the observed growth zoning in the differently sized grains allowing to derive a significant part of the rock's metamorphic P-T-t history. Large porphyroblasts of the population were used to determine a clockwise P-T path over the interval 3.7 to 5.9 kbar and 512 to 615°C whereas modification of growth zoning via intracrystalline diffusion in relatively small porphyroblasts was used to infer an average heating rate of 2°C Ma-1. This suggests a timescale of ca. 53 Ma for garnet growth and an average growth rate of 30 μm Ma-1. Using LA-ICP-MS U-Pb geochronology, a major age population at 977×4 Ma was identified for metamorphic monazite commonly included in the outer 200 μm of the garnet grains. That age is interpreted to represent monazite growth at the expense of allanite and apatite late in garnet's growth history providing an absolute calibration for the relative timescales predicted through THERIA_G modeling. Gaidies, F., de Capitani, C. & Abart, R

  16. Dramatic effects of stress on metamorphic reactions

    NASA Astrophysics Data System (ADS)

    Wheeler, John

    2014-05-01

    Temperature and pressure are primary controls on mineralogy in the Earth; calculations may predict mineralogy from temperature and pressure and vice versa. Such calculations assume that stress is isotropic despite the fact that differential stresses prevail in the Earth, resulting from large scale tectonics and/or differences between fluid and rock pressures in porous rocks. For more than 25 years I have explored how stress may interact with chemical effects through theory (Sheldon & Wheeler 2003, Wheeler 1987, 1992) and more recently experiments (Llana-Funez et al. 2012). New calculations (Wheeler submitted) show that differential stress can have very significant effects on thresholds for metamorphic reactions, depending on the grain-scale reaction pathways. A differential stress may, depending on the reaction pathway, have an effect equivalent to a pressure difference of the order of (assemblage volume)/(reaction volume change) times (differential stress). The multiplying factor is typically 10 or more. For example the onset of a garnet + clinopyroxene breakdown reaction may be offset by the equivalent of +500 MPa in pressure for a 50 MPa differential stress. The effect is equivalent to a temperature difference of the order of (assemblage volume)/(reaction entropy change) times (differential stress). For example the onset of muscovite + quartz breakdown may be offset by the equivalent of +130 degrees C for a 50 MPa differential stress. Much of the Earth is under differential stress, so the new calculations invite a reappraisal of metamorphic mineralogy and microstructure. This is relevant for exploring possible deviations from lithostatic pressure in the Earth. Diagnosing the effect of pressure on mineralogy should be coupled to diagnosing the effects of differential stress - one effect may cloak the other but the scientific rewards for distinguishing them could be significant. Llana-Funez, S., Wheeler, J. & Faulkner, D. R. 2012. Metamorphic reaction rate

  17. Prograde Metamorphism recorded in Antarctic Granulite

    NASA Astrophysics Data System (ADS)

    Marschall, H.; Pauly, J.; Chatterjee, N.; Monteleone, B.; Meyer, H. P.

    2015-12-01

    High-grade metamorphic rocks provide an archive of tectonic processes and record conditions in the deep roots of orogenic belts. Granulites typically preserve chemical and mineralogical evidence of the peak temperature to which crustal rocks may be subjected, and they commonly preserve a multitude of textural and chemical features that allow a rather detailed reconstruction of their cooling and exhumation. More rarely, however, is it possible to reconstruct parts of the prograde path, which would allow a reconstruction of the loading and heating of the rocks. Access to the prograde P-T path and the rates and durations involved in granulite formation would provide important constraints on the convergence part of orogenic processes. Here we investigated a sample of felsic granulite from the H.U. Sverdrupfjella, which is part of the high-grade Maud Belt (East Antarctica). Peak-metamorphic conditions of approximately 925 °C and 1.45 GPa persisted for a maximum of circa 14 million years and were attained shortly after 570 Ma. In addition to the short-lived temperature peak, zircon preserved evidence for protracted granulite facies conditions with temperatures above 800 °C persisting for approximately 40 million years. Constraints on prograde metamorphism are recorded by garnet that preserved pre-peak metamorphic growth zones, by Ti zonation in zircon and by rutile inclusions in garnet. Zr-in-rutile thermometry using rutile included in different generations of garnet is used to reconstruct the prograde P-T path documenting burial followed by heating to ultra-high temperatures at peak pressures. Complementary, Ti zonation in prograde cores of zircon grains document and date heating, whereas younger zircon rims show again lower Ti-in-zircon temperatures and date the retrograde stages of metamorphism. The highest T is recorded in rutile, but not in zircon, consistent with the dissolution rather than growth of zircon at ultra-high temperatures. The clockwise loading

  18. Inheritance, Variscan tectonometamorphic evolution and Permian to Mesozoic rejuvenations in the metamorphic basement complexes of the Romanian Carpathians revealed by monazite microprobe geochronology

    NASA Astrophysics Data System (ADS)

    Săbău, Gavril; Negulescu, Elena

    2014-05-01

    Monazite U-Th-Pb chemical dating reaches an acceptable compromise between precision and accuracy on one side, and spatial resolution and textural constraints on the other side. Thus it has a powerful potential in testing the coherence of individual metamorphic basement units, and enabling correlations among them. Yet, sensitivity and specificity issues in monazite response to thermotectonic events, especially in the case of superposed effects, remain still unclear. Monazite dating at informative to detailed scale in the main metamorphic basement units of the Carpathians resulted in complex age spectra. In the main, the spectra are dominated by the most pervasive thermal and structural overprint, as checked against independent geochronological data. Post-peak age resetting is mostly present, but statistically subordinate. Resetting in case of superposed events is correlated with the degree of textural and paragenetic overprinting, inheritances being always indicated by more or less well-defined age clusters. The lack of relict ages correlating with prograde structural and porphyroblast zonation patterns is indicative for juvenile formations. Age data distribution in the Carpathians allowed distinction of pre-Variscan events, syn-metamorphic Variscan tectonic stacking of juvenile and reworked basement, post-Variscan differential tectonic uplift, as well as prograde metamorphic units ranging down to Upper Cretaceous ages. In the South Carpathians, the Alpine Danubian domain consists of several Variscan and Alpine thrust sheets containing a metamorphic complex dominated by Upper Proterozoic to Lower Cambrian metamorphic and magmatic ages (Lainici-Păiuş), and several complexes with metamorphic overprints ranging from Carboniferous to Lower Permian. Any correlation among these units, as well as geotectonic models placing a Lower Paleozoic oceanic domain between pre-existing Lainici-Păiuş and Drăgşan terranes are precluded by the age data. Other basement of the

  19. PTt path in metamorphic rocks of the Khoy region (northwest Iran) and their tectonic significance for Cretaceous Tertiary continental collision

    NASA Astrophysics Data System (ADS)

    Azizi, H.; Moinevaziri, H.; Mohajjel, M.; Yagobpoor, A.

    2006-06-01

    Metamorphic rocks in the Khoy region are exposed between obducted ophiolites to the southwest and sedimentary rocks of Precambrian-Paleozoic age to the northeast. The Qom formation (Oligocene-Miocene) with a basal conglomerate transgressively overlies all of these rocks. The metamorphic rocks consist of both metasediments and metabasites. The metasediments are micaschist, garnet-staurolite schist and garnet-staurolite sillimanite schist with some meta-arkose, marble and quartzite. The metabasites are metamorphosed to greenschist and amphibolite facies from a basaltic and gabbroic protolith of tholeiitic and calc-alkaline rocks. Geothermobarometry based on the equivalence of minerals stability and their paragenesis in these rocks and microprobe analyses by several different methods indicate that metamorphism occurred in a temperature range between 450 and 680 °C at 5.5 and 7.5 kb pressure. Rims of minerals reveal a considerable decrease of pressure (<2 kb) and insignificant decrease of temperature. The PTt path of this metamorphism is normal. The MFG line passes above the triple junction of Al 2SiO 5 polymorphs, and the average geothermal gradient during metamorphism was from 27 to 37 °C/km, which is more concordant with the temperature regime of collision zones. We infer that crustal thickening during post-Cretaceous (possibly Eocene) collision of the Arabian plate and the Azerbaijan-Albourz block was the main factor that caused the metamorphism in the studied area.

  20. Differentiating Detrital and Metamorphic Monazite in Greenschist-Facies Sandstones From the Witwatersrand Supergroup

    NASA Astrophysics Data System (ADS)

    Muhling, J. R.; Rasmussen, B.

    2009-05-01

    Monazite is a robust and reliable geochronometer of low-temperature metamorphic and hydrothermal events. It is a widespread accessory phase in sedimentary rocks metamorphosed at prehnite-pumpellyite to lower greenschist facies grade, and also in a range of hydrothermal ore deposits. Its ability to date multiple fluid-flow events in low-grade metasedimentary belts has been largely neglected, possibly because of a misconception that it is rare in these rocks and possibly because of misidentification of metamorphic monazite grains as detrital. Both detrital and metamorphic monazites are present in sandstone and conglomerate from the Witwatersrand Supergroup but can be distinguished by their occurrence, chemistry and age. Detrital grains were unstable during regional greenschist-facies metamorphism, and show evidence for a number of destructive reactions dependent on bulk rock composition and the original composition of the monazite. In quartz sandstone and conglomerate, detrital grains were present in heavy mineral bands with pyrite, zircon and chromite. The monazite grains have been pseudomorphed by intergrowths of apatite, florencite and Th-silicate, as well as matrix muscovite and chlorite. In some samples, Th-silicate forms only minute specks but in others it forms larger prismatic crystals that comprise up to 2% of some pseudomorphs. These variations may reflect differences in the original compositions of the detrital grains. In other samples detrital monazite cores, dated at 2.8-3.0 Ga, are enclosed within 2.04 Ga metamorphic rims. These composite grains formed by dissolution and reprecipitation of monazite during metamorphism. The cores and rims have distinctly different compositions, and the metamorphic rims show pronounced zoning of REE. In more calcic sandstone monazite occurs in heavy mineral bands with chromite, zircon, rutile, pyrite, apatite, Th-silicate, allanite and baddeleyite. These sandstones are notably rich in Ca-bearing minerals such as epidote

  1. Fluid heterogeneity during granulite facies metamorphism in the Adirondacks: stable isotope evidence

    USGS Publications Warehouse

    Valley, J.W.; O'Neil, J.R.

    1984-01-01

    The preservation of premetamorphic, whole-rock oxygen isotope ratios in Adirondack metasediments shows that neither these rocks nor adjacent anorthosites and gneisses have been penetrated by large amounts of externally derived, hot CO2-H2O fluids during granulite facies metamorphism. This conclusion is supported by calculations of the effect of fluid volatilization and exchange and is also independently supported by petrologic and phase equilibria considerations. The data suggest that these rocks were not an open system during metamorphism; that fluid/rock ratios were in many instances between 0.0 and 0.1; that externally derived fluids, as well as fluids derived by metamorphic volatilization, rose along localized channels and were not pervasive; and thus that no single generalization can be applied to metamorphic fluid conditions in the Adirondacks. Analyses of 3 to 4 coexisting minerals from Adirondack marbles show that isotopic equilibrium was attained at the peak of granulite and upper amphibolite facies metamorphism. Thus the isotopic compositions of metamorphic fluids can be inferred from analyses of carbonates and fluid budgets can be constructed. Carbonates from the granulite facies are on average, isotopically similar to those from lower grade or unmetamorphosed limestones of the same age showing that no large isotopic shifts accompanied high grade metamorphism. Equilibrium calculations indicate that small decreases in ??18O, averaging 1 permil, result from volatilization reactions for Adirondack rock compositions. Additional small differences between amphibolite and granulite facies marbles are due to systematic lithologie differences. The range of Adirondack carbonate ??18O values (12.3 to 27.2) can be explained by the highly variable isotopic compositions of unmetamorphosed limestones in conjunction with minor 18O and 13C depletions caused by metamorphic volatilization suggesting that many (and possibly most) marbles have closely preserved their

  2. Telemagmatic metamorphism superimposed on regional metamorphism: Evidence from coals in central China

    SciTech Connect

    Tang, Y. . Dept. of Geological Sciences)

    1993-02-01

    Coal (Lower Permian No. 1) in north-central Henan province, central China, exhibits a zoned rank distribution. The rank varies between high-volatile bituminous and anthracite. Highest rank coal occurs in a northwest-southeast trending zone that cuts across the center of the study area. Coal rank decreases from this central zone towards both the northeast and southwest. Core data indicate that the anthracite is currently overlain by over 4,600 m of sedimentary cover, which represents more or less continuous sedimentation during the Permian and Triassic. In the lower rank area to the southwest, erosion has removed all but approximately 1,000 m of strata. The rank distribution in this area has been attributed to regional metamorphism by previous workers as the higher coal rank coincides with the thicker strata. However, this study reveals that anthracite in the area has a much higher vitrinite reflectance, between 3--6% (Ro max, in oil), with some locations exhibiting reflectances greater than 6%. Petrographically, the anthracite is characterized by well developed pores (5--10 [mu]m in diameter) and mosaic structure. It is suggested that the higher heat flow is due to the presence of deep-seated plutons. It is proposed that coal metamorphism in this area involved three stages: (1) Pre-orogenic (early Permian-late Triassic). Regional metamorphism produced coals of subbituminous to high-volatile bituminous rank; (2) Orogenic (early Jurassic-late Cretaceous). Telemagmatic metamorphism resulted in zones of higher rank coal (medium volatile through anthracite rank); (3) Post-orogenic (Tertiary-Quaternary). Shallow burial depth due to the tectonic uplift followed by erosion had a negligible effect on coal rank. It is suggested, therefore, that coalification in this area is the result of regional metamorphism overprinted by telemagmatic metamorphism.

  3. Strontium and neodymium isotopic variations in early Archean gneisses affected by middle to late Archean high-grade metamorphic processes: West Greenland and Labrador

    NASA Technical Reports Server (NTRS)

    Collerson, K. D.; Mcculloch, M. T.; Bridgwater, D.; Mcgregor, V. R.; Nutman, A. P.

    1986-01-01

    Relicts of continental crust formed more than 3400 Ma ago are preserved fortuitously in most cratons. The cratons provide the most direct information about crust and mantle evolutionary processes during the first billion years of Earth history. In view of their polymetamorphic character, these terrains are commonly affected by subsequent tectonothermal events. Hence, their isotope systematics may be severely disturbed as a result of bulk chemical change or local isotopic homogenization. This leads to equivocal age and source information for different components within these terrains. The Sr and Nd isotopic data are presented for early Archean gneisses from the North Atlantic Craton in west Greenland and northern Labrador which were affected by younger metamorphic events.

  4. Disturbance of isotope systematics in meteorites during shock and thermal metamorphism and implications for shergottite chronology

    SciTech Connect

    Gaffney, A M; Borg, L E; Asmerom, Y

    2008-12-10

    Shock and thermal metamorphism of meteorites from differentiated bodies such as the Moon and Mars have the potential to disturb chronometric information contained in these meteorites. In order to understand the impact-related mechanisms and extent of disturbance to isochrons, we undertook experiments to shock and heat samples of 10017, a 3.6 billion year old lunar basalt. One sub-sample was shocked to 55 GPa, a second subsample was heated to 1000 C for one week, and a third sub-sample was maintained as a control sample. Of the isotope systems analyzed, the Sm-Nd system was the least disturbed by shock or heat, followed by the Rb-Sr system. Ages represented by the {sup 238}U-{sup 206}Pb isotope system were degraded by shock and destroyed with heating. In no case did either shock or heating alone result in rotated or reset isochrons that represent a spurious age. In some cases the true crystallization age of the sample was preserved, and in other cases age information was degraded or destroyed. Although our results show that neither shock nor thermal metamorphism alone can account for the discordant ages represented by different isotope systems in martian meteorites, we postulate that shock metamorphism may render a meteorite more susceptible than unshocked material to subsequent disturbance during impact-related heating or aqueous alteration on Mars or Earth. The combination of these processes may result in the disparate chronometric information preserved in some meteorites.

  5. Regional metamorphism in the Condrey Mountain Quadrangle, north-central Klamath Mountains, California

    USGS Publications Warehouse

    Hotz, Preston Enslow

    1979-01-01

    A subcircular area of about 650 km 2 in northern California and southwestern Oregon is occupied by rocks of the greenschist metamorphic facies called the Condrey Mountain Schist. This greenschist terrane is bordered on the east and west by rocks belonging to the amphibolite metamorphic facies that structurally overlie and are thrust over the Condrey Mountain Schist. The amphibolite facies is succeeded upward by metavolcanic and metasedimentary rocks belonging to the greenschist metamorphic facies. The Condrey Mountain Schist is composed predominantly of quartz-muscovite schist and lesser amounts of actinolite-chlorite schist formed by the metamorphism of graywacke and spilitic volcanic rocks that may have belonged to the Galice Formation of Late Jurassic age. Potassium-argon age determinations of 141?4 m.y. and 155?5 m.y. obtained on these metamorphic rocks seem to be incompatible with the Late Jurassic age usually assigned the Galice. The rocks that border the amphibolite facies are part of an extensive terrane of metavolcanic and metasedimentary rocks belonging to the western Paleozoic and Triassic belt. The metavolcanic rocks include some unmetamorphosed spilite but are mostly of the greenschist metamorphic facies composed of oligoclase (An15-20) and actinolite with subordinate amounts of chlorite and clinozoisiteepidote. The interbedded sedimentary rocks are predominantly argillite and slaty argillite, less commonly siliceous argillite and chert, and a few lenticular beds of marble. On the south, high-angle faults and a tabular granitic pluton separate the greenschist metavolcanic terrane from the amphibolite facies rocks; on the east, nonfoliated amphibolite is succeeded upward, apparently conformably, by metasedimentary rocks belonging to the greenschist metavolcanic terrane. In the southern part of Condrey Mountain quadrangle, an outlier of a thrust plate composed of the Stuart Fork Formation overlies the metavolcanic and metasedimentary rocks. The Stuart

  6. Age and genesis of precious metals deposits, Buffalo Hump district, central Idaho: implications for depth of emplacement of quartz veins.

    USGS Publications Warehouse

    Lund, K.; Snee, L.W.; Evans, K.V.

    1986-01-01

    Three samples (metamorphic country rock, Idaho batholith granite, and auriferous quartz vein) were dated by the 40Ar/39Ar age spectrum technique. The lode deposits are Cretaceous (71 m.y.); their cooling histories and depths of emplacement, inferred from the age spectra, are evidence for the granite plutons and the lode deposits having been emplaced at the same 40-9 km depth and being genetically related. Thus, the Idaho batholith is not barren, and at least two precious-metal mineralizing events, Cretaceous and Eocene in age, occur in central Idaho. Class differences between the two ages of deposits, of style, alteration and mineralogy, are suggested. -G.J.N.

  7. An Influence of Birth Weight, Gestational Age, and Apgar Score on Pattern Visual Evoked Potentials in Children with History of Prematurity

    PubMed Central

    Michalczuk, Marta; Urban, Beata; Chrzanowska-Grenda, Beata; Oziębło-Kupczyk, Monika; Bakunowicz-Łazarczyk, Alina

    2015-01-01

    Purpose. The objective of our study was to examine a possible influence of gestational age, birth weight, and Apgar score on amplitudes and latencies of P100 wave in preterm born school-age children. Materials and Methods. We examined the following group of school-age children: 28 with history of prematurity (mean age 10.56 ± 1.66 years) and 25 born at term (mean age 11.2 ± 1.94 years). The monocular PVEP was performed in all children. Results. The P100 wave amplitudes and latencies significantly differ between preterm born school-age children and those born at term. There was an essential positive linear correlation of the P100 wave amplitudes with birth weight, gestational age, and Apgar score. There were the negative linear correlations of P100 latencies in 15-minute stimulation from O1 and Oz electrode with Apgar score and O1 and O2 electrode with gestational age. Conclusions. PVEP responses vary in preterm born children in comparison to term. Low birth weight, early gestational age, and poor baseline output seem to be the predicting factors for the developmental rate of a brain function in children with history of prematurity. Further investigations are necessary to determine perinatal factors that can affect the modified visual system function in preterm born children. PMID:26417461

  8. Fitness consequences of larval traits persist across the metamorphic boundary.

    PubMed

    Crean, Angela J; Monro, Keyne; Marshall, Dustin J

    2011-11-01

    Metamorphosis is thought to provide an adaptive decoupling between traits specialized for each life-history stage in species with complex life cycles. However, an increasing number of studies are finding that larval traits can carry-over to influence postmetamorphic performance, suggesting that these life-history stages may not be free to evolve independently of each other. We used a phenotypic selection framework to compare the relative and interactive effects of larval size, time to hatching, and time to settlement on postmetamorphic survival and growth in a marine invertebrate, Styela plicata. Time to hatching was the only larval trait found to be under directional selection, individuals that took more time to hatch into larvae survived better after metamorphosis but grew more slowly. Nonlinear selection was found to act on multivariate trait combinations, once again acting in opposite directions for selection acting via survival and growth. Individuals with above average values of larval traits were most likely to survive, but surviving individuals with intermediate larval traits grew to the largest size. These results demonstrate that larval traits can have multiple, complex fitness consequences that persist across the metamorphic boundary; and thus postmetamorphic selection pressures may constrain the evolution of larval traits.

  9. Age of the Dawson Arkose, southwestern Air Force Academy, Colorado, and implications for the uplift history of the Front Range

    SciTech Connect

    Kluth, C.F.; Nelson, S.N. )

    1988-01-01

    An angular unconformity within the synorogenic Dawson Arkose (Late Cretaceous-Eocene) is preserved and exposed in areas south of Denver, Colorado, along the eastern side of the Front Range uplift. In the southwestern part of the Air Force Academy, the basal Dawson is concordant with the underlying Laramie and Fox Hills formations and dips 72-84{degree} eastward. Above an intraformational angular unconformity, younger units of the Dawson dip 24{degree}-46{degree} eastward. Smaller angular unconformities (10{degree}{plus minus}), and beds with gradually decreasing dip occur higher in the Dawson section. Rocks above the largest unconformity contain a rich palynomorph assemblage of Late Maestrichtain age. These data indicate that approximately 30{degree}-40{degree}, and possibly as much as approximately 70{degree}, of tilting of the underlying rocks occurred during the Late Maestrichtian (66-70 Ma). It is also possible that approximately 30{degree}-40{degree} of the tilting of the Late Cretaceous rocks occurred between latest Maestrichtian and Eocene (approximately 45 Ma). These results suggest that the transition from a tectonically quiet marine environment to a non-marine, tectonically active condition took place rapidly, probably within a few million years. When combined with published data, the authors study indicates that the Front Range has different tectonic histories on its eastern and its western side, and that the deformation is diachronous along the strike of the eastern side of the Front Range.

  10. Cerebral blood flow is diminished in asymptomatic middle-aged adults with maternal history of Alzheimer's disease.

    PubMed

    Okonkwo, Ozioma C; Xu, Guofan; Oh, Jennifer M; Dowling, N Maritza; Carlsson, Cynthia M; Gallagher, Catherine L; Birdsill, Alex C; Palotti, Matthew; Wharton, Whitney; Hermann, Bruce P; LaRue, Asenath; Bendlin, Barbara B; Rowley, Howard A; Asthana, Sanjay; Sager, Mark A; Johnson, Sterling C

    2014-04-01

    Cerebral blood flow (CBF) provides an indication of the metabolic status of the cortex and may have utility in elucidating preclinical brain changes in persons at risk for Alzheimer's disease (AD) and related diseases. In this study, we investigated CBF in 327 well-characterized adults including patients with AD (n = 28), patients with amnestic mild cognitive impairment (aMCI, n = 23), older cognitively normal (OCN, n = 24) adults, and asymptomatic middle-aged adults (n = 252) with and without a family history (FH) of AD. Compared with the asymptomatic cohort, AD patients displayed significant hypoperfusion in the precuneus, posterior cingulate, lateral parietal cortex, and the hippocampal region. Patients with aMCI exhibited a similar but less marked pattern of hypoperfusion. Perfusion deficits within the OCN adults were primarily localized to the inferior parietal lobules. Asymptomatic participants with a maternal FH of AD showed hypoperfusion in hippocampal and parietofrontal regions compared with those without a FH of AD or those with only a paternal FH of AD. These observations persisted when gray matter volume was included as a voxel-wise covariate. Our findings suggest that having a mother with AD might confer a particular risk for AD-related cerebral hypoperfusion in midlife. In addition, they provide further support for the potential utility of arterial spin labeling for the measurement of AD-related neurometabolic dysfunction, particularly in situations where [18F]fluorodeoxyglucose imaging is infeasible or clinically contraindicated.

  11. Windows on Martian dynamo history: electron reflection (ER) magnetic signatures and crater retention ages of basins and volcanoes

    NASA Astrophysics Data System (ADS)

    Lillis, R. J.; Frey, H. V.; Manga, M.; Halekas, J. S.; Mitchell, D. L.; Lin, R. P.

    2006-12-01

    A picture continues to emerge of a Martian dynamo that began extremely early in the planet's history. After reversing polarity at least once and possibly varying significantly in strength, it permanently ceased operating prior to 4 billion years ago (using the Hartmann-Neukum chronology), when the core could no longer sustain the required convective motion. By combining ER magnetometry and MOLA topography, we use the derived magnetic signatures and crater retention ages (CRAs) of large basins and volcanoes to constrain the ambient magnetic conditions present during their formation. Here we present results that support the above picture; in particular case studies involving several large visible and buried basins and highland volcanoes, implying that Mars' last dynamo activity likely ceased prior to 4.07 ± 0.04 Gyr ago and later than 4.15 ± 0.05 Gyr ago and that this cessation was, within uncertainties, coincident with the formation of the 3 giant northern lowland basins Acidalia, Chryse and Utopia. We also present a statistical study of the magnetic signatures and CRAs of the ~500 largest basins on Mars which tentatively suggests that the dynamo may have weakened considerably for a period during its active lifetime.

  12. A new approach to quantification of metamorphism using ultra-small and small angle neutron scattering.

    SciTech Connect

    Anovitz, Lawrence {Larry} M; Lynn, Gary W; Cole, David R

    2009-12-01

    In this paper we report the results of a study using small angle and ultra-small angle neutron scattering techniques (SANS and USANS) to examine the evolution of carbonates during contact metamorphism. Data were obtained from samples collected along two transects in the metamorphosed Hueco limestone at the Marble Canyon, Texas, contact aureole. These samples were collected from the igneous contact out to {approx}1700 m. Scattering curves obtained from these samples show mass fractal behavior at low scattering vectors, and surface fractal behavior at high scattering vectors. Significant changes are observed in the surface and mass fractal dimensions as well as the correlation lengths (pore and grain sizes), surface area to volume ratio and surface Gibbs Free energy as a function of distance, including regions of the aureole outside the range of classic metamorphic petrology. A change from mass-fractal to non-fractal behavior is observed at larger scales near the outer boundary of the aureole that implies significant reorganization of pore distributions early in the metamorphic history. Surface fractal results suggest significant smoothing of grain boundaries, coupled with changes in pore sizes. A section of the scattering curve with a slope less than -4 appears at low-Q in metamorphosed samples, which is not present in unmetamorphosed samples. A strong spike in the surface area to volume ratio is observed in rocks near the mapped metamorphic limit, which is associated with reaction of small amounts of organic material to graphite. It may also represent an increase in pore volume or permeability, suggesting that a high permeability zone forms at the boundary of the aureole and moves outwards as metamorphism progresses. Neutron scattering data also correlate well with transmission electron microscopic (TEM) observations, which show formation of micro- and nanopores and microfractures during metamorphism. The scattering data are, however, quantifiable for a bulk rock

  13. A new approach to quantification of metamorphism using ultra-small and small angle neutron scattering

    NASA Astrophysics Data System (ADS)

    Anovitz, Lawrence M.; Lynn, Gary W.; Cole, David R.; Rother, Gernot; Allard, Lawrence F.; Hamilton, William A.; Porcar, Lionel; Kim, Man-Ho

    2009-12-01

    In this paper we report the results of a study using small angle and ultra-small angle neutron scattering techniques (SANS and USANS) to examine the evolution of carbonates during contact metamorphism. Data were obtained from samples collected along two transects in the metamorphosed Hueco limestone at the Marble Canyon, Texas, contact aureole. These samples were collected from the igneous contact out to ˜1700 m. Scattering curves obtained from these samples show mass fractal behavior at low scattering vectors, and surface fractal behavior at high scattering vectors. Significant changes are observed in the surface and mass fractal dimensions as well as the correlation lengths (pore and grain sizes), surface area to volume ratio and surface Gibbs Free energy as a function of distance, including regions of the aureole outside the range of classic metamorphic petrology. A change from mass-fractal to non-fractal behavior is observed at larger scales near the outer boundary of the aureole that implies significant reorganization of pore distributions early in the metamorphic history. Surface fractal results suggest significant smoothing of grain boundaries, coupled with changes in pore sizes. A section of the scattering curve with a slope less than -4 appears at low- Q in metamorphosed samples, which is not present in unmetamorphosed samples. A strong spike in the surface area to volume ratio is observed in rocks near the mapped metamorphic limit, which is associated with reaction of small amounts of organic material to graphite. It may also represent an increase in pore volume or permeability, suggesting that a high permeability zone forms at the boundary of the aureole and moves outwards as metamorphism progresses. Neutron scattering data also correlate well with transmission electron microscopic (TEM) observations, which show formation of micro- and nanopores and microfractures during metamorphism. The scattering data are, however, quantifiable for a bulk rock in a

  14. Opposite shifts in size at metamorphosis in response to larval and metamorph predators.

    PubMed

    Vonesh, James R; Warkentin, Karen M

    2006-03-01

    Predation risk can cause organisms to alter the timing of life history switch points. Theory suggests that increased risk in an early life stage should select for switching earlier and smaller, while increased risk in the subsequent stage should select for switching later and larger. This framework has frequently been applied to metamorphosis in amphibians, with mixed results. Few studies examining the effect of larval predation risk on metamorphosis have observed the predicted pattern, and no studies, to our knowledge, have examined the effect of increased risk during and after metamorphosis on the timing of this switch point. Here we examine the effect of larval and post-metamorphic predation risk on metamorphosis in the red-eyed treefrog, Agalychnis callidryas. We raised tadpoles in the presence or absence of cues from caged water bugs fed larvae and cues from spiders fed emerging metamorphs. Water bugs are effective larval predators, while spiders are poor larval predators but prey on metamorphs. Furthermore, since spiders forage on the water surface it is possible that tadpoles could assess future risk from this predator. Predators induced opposite shifts in life history. Tadpoles emerged smaller and less developed in response to water bugs, but later and larger in response to spiders. Interestingly, predator effects on larval duration were not independent; tadpoles delayed emerging in response to spiders, but only in the absence of water bugs.

  15. Strain-collapsed metamorphic isograds in a sillimanite gneiss dome, Seward Peninsula, Alaska

    SciTech Connect

    Miller, E.L.; Calvert, A.T.; Little, T.A. )

    1992-06-01

    Unusually closely spaced Barrovian series isograds have been described along the flanks of the Kigluaik Mountains, Seward Peninsula, Alaska, where they separate a high-grade gneiss complex intruded by granites of Cretaceous age from surrounding, regionally developed, blueschist to greenschist facies rocks. Structural mapping of the transition zone between the two metamorphic types indicates that their juxtaposition was aided by significant syn- to late-metamorphic solid-state flow that served to attenuate the overlying rock column and thus collapse the field metamorphic gradient. On the basis of field relations, structural data, petrography, and geochronologic data, strain appears to have accompanied the rapid (adiabatic) rise of high-temperature rocks from several tens of kilometers to less than 10 km depth during the Cretaceous, in an event younger than the unrelated to high-P metamorphism. Granite-cored gneiss domes on the Seward Peninsula may have formed during extension of previously thickened continental crust, resulting in the {approximately}35-km-thick crust and near-sea-level elevations of the region today.

  16. New evidence for polyphase metamorphism of glaucophane schist and eclogite exotic blocks in the Franciscan Complex, California and Oregon

    USGS Publications Warehouse

    Moore, Diane E.; Blake, M.C., Jr.

    1989-01-01

    The early metamorphic history of high-grade exotic blocks in the Franciscan Complex may be more complicated than previously supposed. The different assemblages of high-grade glaucophane schists, eclogite, amphibolite and hornblende schist are commonly considered to have formed at the same time from essentially unmetamorphosed oceanic crust. However, new textural and mineralogical data presented here suggest that high-grade glaucophane schist and eclogite have replaced an earlier epidote-amphibolite facies assemblage that is identical to the primary assemblages in many of the hornblende-rich blocks. At least some of the hornblende-rich blocks may therefore be well-preserved remnants of the earlier metamorphism. Comparison of the mineral assemblages and element partititioning in the mixed-assemblage blocks suggests that the glaucophane schist and eclogite metamorphism took place at slightly lower temperatures but at the same or higher pressures than the earlier, hornblende-forming stage. -Authors

  17. Heat generation during metamorphic processes in snow

    NASA Astrophysics Data System (ADS)

    Tyagunin, A. V.; Koposov, G. D.

    2016-09-01

    The research analyzes known metamorphic processes in the snow from the point of view of energy approach. A list of these processes is complemented with the processes associated with runoff of a quasi-liquid layer from snow granules. The experimental results of studying the heat generation from the snow cover and the temperature gradient at the depth of the snow cover are presented. It is emphasized that snow cover is not merely a passive conductor of heat but also it is a heat generating medium.

  18. Plate tectonics. Seismological detection of slab metamorphism.

    PubMed

    Julian, Bruce

    2002-05-31

    The occurrence of more or less continuous ground vibrations ("volcanic tremor") is an important indicator of volcanic activity. But results from the "Hi-net" seismic network in Japan reported by Obara show that continuous ground vibrations can occur far away from any volcanic activity. In his Perspective, Julian discusses the idea that this tremor is excited by flow of metamorphic fluids. He also identifies other possible locations where such a tremor may be detected and explains what may be learnt from measuring it.

  19. Metamorphism of the ca. 3800 Ma supracrustal rocks at Isua, West Greenland: implications for early Archaean crustal evolution

    NASA Astrophysics Data System (ADS)

    Boak, Jeremy L.; Dymek, Robert F.

    1982-06-01

    A detailed mineralogical and petrological study has been carried out on samples from two clastic metasedimentary lithologies from the ˜ 3800 Ma Isua Supracrustal Belt, West Greenland. Semipelitic to pelitic "garnet-biotite schist" contains the limiting AKFM assemblage: muscovite-biotite-garnet-staurolite (+ quartz + plagioclase + ilmenite), whereas "muscovite-biotite gneiss", derived from felsic volcanogenic graywacke, locally contains kyanite (+ quartz+ plagioclase + Ca-, Mn-rich garnet). Temperatures calculated from Fe-Mg partitioning between coexisting garnet- biotite indicate equilibration for garnet coresat T ˜550°C, and ˜460°C for garnet rims. We interpret the higher T as a minimum estimate for prograde regional metamorphism which we argue occurred before 3600 Ma, whereas the lower T reflects later retrogression as indicated by the development of chlorite ± sericite in many samples. The presence of kyanite as the stable aluminosilicate polymorph, combined with phase assemblage data, indicate P ˜5 kbar during prograde metamorphism, and a depthof burial of at least 15 km. The Isua supracrustals are the oldest comprehensively dated rocks on Earth, and the metamorphic mineral assemblages reported here constitute the earliest direct record of thermal regimes in Archaean crust. Therefore, characterization of the metamorphic history of the Isua region places an important constraint on models of early Earth history. Our data and observations indicate that prograde regional metamorphism at Isua occurred at conditions which are considered "normal" for an orogenic system, with a metamorphic thermal gradient ˜35°C/km. Moreover, our results contraindicate the universal occurrence of "thin" Archaean crust and excessively "steep" crustal thermal gradients as proposed by some investigators. Such conclusion appears at odds with estimates for higher terrestrial heat production during the early Archaean, but can be resolved by appealing to more rapid convection and

  20. Reconstruction of the metamorphic evolution of the Hamadan high-grade metapelites, Sanandaj-Sirjan Zone, western Iran

    NASA Astrophysics Data System (ADS)

    Monfaredi, Behzad; Hauzenberger, Christoph; Neubauer, Franz; Schulz, Bernhard; Shakerardakani, Farzaneh; Genser, Johann; Halama, Ralf

    2016-04-01

    C, suggesting that garnet growth is the result of two growth cycles. Despite textural differences, U-Th-Pb monazite geochronology revealed similar ages between 168 ± 11 Ma and 149 ± 19 Ma for schistose/hornfels rocks, which is within the same timeframe of the Alvand pluton intrusion. 40Ar-39Ar white mica age patterns yielded total gas ages ranging from 80 to 70 Ma over the entire transect. Microfabrics indicate formation of the foliation during garnet growth, which is followed subsequently by a retrogression to chlorite. Consequently, the Ar-Ar ages most likely indicate the final stage of foliation formation and accompanying cooling of the Hamadan complex to less than ca. 425 ± 25 °C (argon retention temperature in white mica). Temperature-time paths from all accessible mineral ages suggest, therefore, slow cooling and exhumation within two episodes toward the contact. Since absence or lack of plutonic rocks in the higher-grade sillimanite-bearing rocks and irregular metamorphic zones, we postulate that the Alvand batholith extends at shallow levels below the entire basement or is disturbed by shearing or a large number of smaller granitoid intrusions are hidden below the surface at mid- to upper-crustal depths. References Mahmoudi, S., Corfu, F., Masoudi, F., Mehrabi, B., Mohajjel, M., 2011. U-Pb dating and emplacement history of granitoid plutons in the northern Sanandaj-Sirjan Zone, Iran. J. Asian Earth Sci. 41, 238-249. Moynihan, D. P., Pattison, D. R. M., 2013. An automated method for the calculation of P-T paths from garnet zoning, with application to metapelitic schist from the Kootenay Arc, British Columbia, Canada. J. Metamorphic Geol. 31, 525-548. Shahbazi, H., Siebel,W., Pourmoafee, M., Ghorbani, M., Sepahi, A.A., Shang, C.K., Vosoughi Abedini, M., 2010. Geochemistry and U-Pb zircon geochronology of the Alvand plutonic complex in Sanandaj-Sirjan Zone (Iran): new evidence for Jurassic magmatism. J. Asian Earth Sci. 9, 668-683.

  1. U-Th age distribution of coral fragments from multiple rubble ridges within the Frankland Islands, Great Barrier Reef: Implications for past storminess history

    NASA Astrophysics Data System (ADS)

    Liu, Entao; Zhao, Jian-xin; Feng, Yue-xing; Leonard, Nicole D.; Clark, Tara R.; Roff, George

    2016-07-01

    Prograded coral rubble ridges have been widely used as archives for reconstructing long-term storm or storminess history. Chronologies of ridge systems in previous studies are often based on a limited number of low-resolution radiocarbon or optically-stimulated luminescence (OSL) ages per ridge (usually only one age per ridge), which carry intrinsic age uncertainties and make interpretation of storm histories problematic. To test the fidelity of storm ridges as palaeo-storm archives, we used high-precision U-Th dating to examine whether different samples from a single ridge are temporally constrained. We surveyed three transects of ridge systems from two continental islands (Normanby Island and High Island) within the Frankland Islands, Great Barrier Reef (GBR), and obtained 96 U-Th dates from coral rubble samples collected from within and between different ridges. Our results revealed significant differences in age ranges between the two islands. The steeper and more defined rubble ridges present on Normanby Island revealed that the majority of U-Th ages (over 60%) from a single ridge clustered within a narrow age range (∼100 years). By contrast, the lower and less defined ridges on High Island, which were more likely formed during both storm and non-storm high-energy events, revealed significant scatter in age distribution (>>200 years) with no notable clustering. The narrower age ranges obtained from the steeper and more defined rubble ridges suggest that previous approaches of using either limited samples from a single ridge or low-precision dating methods to establish chronologies are generally valid at centennial to millennial timescales, although caution must be taken to use such approaches for storm history reconstruction on shorter timescales (e.g. decadal). The correlation between U-Th mortality ages of coral rubble and historical stormy periods highlights the possibility of using coral rubble age distribution from rubble ridges to reconstruct the long

  2. The digital global geologic map of Mars: chronostratigraphic ages, topographic and crater morphologic characteristics, and updated resurfacing history

    USGS Publications Warehouse

    Tanaka, K.L.; Robbins, S.J.; Fortezzo, C.M.; Skinner, J.A.; Hare, T.M.

    2014-01-01

    A new global geologic map of Mars has been completed in a digital, geographic information system (GIS) format using geospatially controlled altimetry and image data sets. The map reconstructs the geologic history of Mars, which includes many new findings collated in the quarter century since the previous, Viking-based global maps were published, as well as other discoveries that were made during the course of the mapping using new data sets. The technical approach enabled consistent and regulated mapping that is appropriate not only for the map's 1:20,000,000 scale but also for its widespread use by diverse audiences. Each geologic unit outcrop includes basic attributes regarding identity, location, area, crater densities, and chronostratigraphic age. In turn, units are grouped by geographic and lithologic types, which provide synoptic global views of material ages and resurfacing character for the Noachian, Hesperian, and Amazonian periods. As a consequence of more precise and better quality topographic and morphologic data and more complete crater-density dating, our statistical comparisons identify significant refinements for how Martian geologic terrains are characterized. Unit groups show trends in mean elevation and slope that relate to geographic occurrence and geologic origin. In comparison with the previous global geologic map series based on Viking data, the new mapping consists of half the number of units due to simpler, more conservative and globally based approaches to discriminating units. In particular, Noachian highland surfaces overall have high percentages of their areas now dated as an epoch older than in the Viking mapping. Minimally eroded (i.e., pristine) impact craters ≥3 km in diameter occur in greater proportion on Hesperian surfaces. This observation contrasts with a deficit of similarly sized craters on heavily cratered and otherwise degraded Noachian terrain as well as on young Amazonian surfaces. We interpret these as reflecting the

  3. The Relative Importance of Family History, Gender, Mode of Onset, and Age at Onset in Predicting Clinical Features of First-Episode Psychotic Disorders.

    PubMed

    Compton, Michael T; Berez, Chantal; Walker, Elaine F

    2014-11-01

    Objective: Family history of psychosis, gender, mode of onset, and age at onset are considered prognostic factors important to clinicians evaluating first-episode psychosis; yet, clinicians have little guidance as to how these four factors differentially predict early-course substance abuse, symptomatology, and functioning. We conducted a "head-to-head comparison" of these four factors regarding their associations with key clinical features at initial hospitalization. We also assessed potential interactions between gender and family history with regard to age at onset of psychosis and symptom severity.Methods: Consecutively admitted first-episode patients (n=334) were evaluated in two studies that rigorously assessed a number of early-course variables. Associations among variables of interest were examined using Pearson correlations, ÷2 tests, Student's t-tests, and 2x2 factorial analyses of variance.Results: Substance (nicotine, alcohol, and cannabis) abuse and positive symptom severity were predicted only by male gender. Negative symptom severity and global functioning impairments were predicted by earlier age at onset of psychosis. General psychopathology symptom severity was predicted by both mode of onset and age at onset. Interaction effects were not observed with regard to gender and family history in predicting age at onset or symptom severity.Conclusions: The four prognostic features have differential associations with substance abuse, domains of symptom severity, and global functioning. Gender and age at onset of psychosis appear to be more predictive of clinical features at the time of initial evaluation (and thus presumably longer-term outcomes) than the presence of a family history of psychosis and a more gradual mode of onset. PMID:25367167

  4. The Relative Importance of Family History, Gender, Mode of Onset, and Age at Onset in Predicting Clinical Features of First-Episode Psychotic Disorders.

    PubMed

    Compton, Michael T; Berez, Chantal; Walker, Elaine F

    2014-11-01

    Objective: Family history of psychosis, gender, mode of onset, and age at onset are considered prognostic factors important to clinicians evaluating first-episode psychosis; yet, clinicians have little guidance as to how these four factors differentially predict early-course substance abuse, symptomatology, and functioning. We conducted a "head-to-head comparison" of these four factors regarding their associations with key clinical features at initial hospitalization. We also assessed potential interactions between gender and family history with regard to age at onset of psychosis and symptom severity.Methods: Consecutively admitted first-episode patients (n=334) were evaluated in two studies that rigorously assessed a number of early-course variables. Associations among variables of interest were examined using Pearson correlations, ÷2 tests, Student's t-tests, and 2x2 factorial analyses of variance.Results: Substance (nicotine, alcohol, and cannabis) abuse and positive symptom severity were predicted only by male gender. Negative symptom severity and global functioning impairments were predicted by earlier age at onset of psychosis. General psychopathology symptom severity was predicted by both mode of onset and age at onset. Interaction effects were not observed with regard to gender and family history in predicting age at onset or symptom severity.Conclusions: The four prognostic features have differential associations with substance abuse, domains of symptom severity, and global functioning. Gender and age at onset of psychosis appear to be more predictive of clinical features at the time of initial evaluation (and thus presumably longer-term outcomes) than the presence of a family history of psychosis and a more gradual mode of onset.

  5. New chronometers for the metamorphism of ophiolitic rocks: 40Ar/39Ar neptunite and 232Th/208Pb joaquinite

    NASA Astrophysics Data System (ADS)

    Borneman, N.; Hodges, K. V.; Van Soest, M. C.

    2015-12-01

    Both primary magmatism and metamorphism of ophiolite sequences are difficult to date, due in large part to the fact that the majority of lithologies present tend to contain very low concentrations of radioactive elements. As a result, researchers are often forced to process large amounts of material to search for accessory phases like zircons in gabbro, or to employ geochronometers that often yield multiply interpretable results (e.g., 40Ar/39Ar glaucophane or phengite), or to rely on indirect evidence for inferring ages. Here, we introduce two new options for chronometery of metamorphosed ophiolites: 40Ar/39Ar neptunite and 232Th/208Pb joaquinite. The best known locality for these rare minerals is the New Idria serpentinite diapir, found within the southern Diablo Range of the Coast Range Province of California. Here, both the joaquinite and neptunite chronometers record indistinguishable dates that we interpret to be the crystallization age of the phases during diapir ascent, based on the demonstrated low temperature history of the diapir as whole and the agreement of dates from chromonometers that almost certainly have different closure temperatures. This age is generally inferred to be coincident with the timing of the passage of the Mendocino Triple Junction and associated initiation of the San Andreas fault in this area. We propose that the mean40Ar/39Ar neptunite plateau date of 12.375 ± 0.082 Ma and corroborating 232Th/208Pb joaquinite date (12.08 ± 0.59 Ma) may represent a high-precision constraint on the timing of this event. We also report a second application of these chronometers to samples from the Yarlung suture, which formed at the time of initial India-Eurasia collision in southern Tibet. Here, both chronometers record indistinguishable dates of ca. 52 Ma, which we also interpret as the crystallization age. This age is consistent with most previously published estimates for the timing of the India-Eurasia collision.

  6. Accessories after the facts: Constraining the timing, duration and conditions of high-temperature metamorphic processes

    NASA Astrophysics Data System (ADS)

    Taylor, Richard J. M.; Kirkland, Christopher L.; Clark, Chris

    2016-11-01

    High-temperature metamorphic rocks are the result of numerous chemical and physical processes that occur during a potentially long-lived thermal evolution. These rocks chart the sequence of events during an orogenic episode including heating, cooling, exhumation and melt interaction, all of which may be interpreted through the elemental and isotopic characteristics of accessory minerals such as zircon, monazite and rutile. Developments in imaging and in situ chemical analysis have resulted in an increasing amount of information being extracted from these accessory phases. The refractory nature of these minerals, combined with both their use as geochronometers and tracers of metamorphic mineral reactions, has made them the focus of many studies of granulite-facies terrains. In such studies the primary aim is often to determine the timing and conditions of the peak of metamorphism, and high-temperature metasedimentary rocks may seem ideal for this purpose. For example pelites typically contain an abundance of accessory minerals in a variety of bulk compositions, are melt-bearing, and may have endured extreme conditions that facilitate diffusion and chemical equilibrium. However complexities arise due to the heterogeneous nature of these rocks on all scales, driven by both the composition of the protolith and metamorphic differentiation. In additional to lithological heterogeneity, the closure temperatures for both radiogenic isotopes and chemical thermometers vary between different accessory minerals. This apparent complexity can be useful as it permits a wide range of temperature and time (T-t) information to be recovered from a single rock sample. In this review we cover: 1) characteristic internal textures of accessory minerals in high temperature rocks; 2) the interpretation of zircon and monazite age data in relation to high temperature processes; 3) rare earth element partitioning; 4) trace element thermometry; 5) the incorporation of accessory mineral growth

  7. Crustal channel flows: 2. Numerical models with implications for metamorphism in the Himalayan-Tibetan orogen

    NASA Astrophysics Data System (ADS)

    Jamieson, Rebecca A.; Beaumont, Christopher; Medvedev, Sergei; Nguyen, Mai H.

    2004-06-01

    Results from a thermal-mechanical model (HT1) that includes midcrustal channel flow are compatible with many features of the Himalayan-Tibetan system. Radioactive self-heating and rheological weakening of thickened model orogenic crust lead to the formation of a hot, low-viscosity midcrustal channel and a broad plateau. Channel material, corresponding to the Greater Himalayan Sequence (GHS), flows outward from beneath the plateau in response to topographically induced differential pressure. At the plateau flank it is exhumed by focused surface denudation and juxtaposed with cooler, newly accreted material corresponding to the Lesser Himalayan Sequence (LHS). The model channel is bounded by coeval thrust and normal sense ductile shear zones, interpreted to represent the Main Central Thrust (MCT) zone and South Tibetan Detachment system, respectively. Inverted metamorphism associated with the model MCT zone results from distributed ductile shear along the MCT and extrusion of the hot channel. A variety of model P-T-t path styles, resembling those observed in the GHS and LHS, are produced for points traveling through contrasting tectonic regimes that coexist in different parts of the model. Predicted times of peak metamorphism, cooling, and erosion of metamorphic facies are generally compatible with observations, although model GHS cooling ages are too young. The times of M1 and M2 metamorphic "events" observed in the GHS correspond to model times of maximum burial and maximum heating, respectively. The results highlight the need to integrate tectonics and metamorphism in continental collision models and demonstrate the importance of lateral transport of both heat and material in large hot orogens.

  8. A key extensional metamorphic complex reviewed and restored: The Menderes Massif of western Turkey

    NASA Astrophysics Data System (ADS)

    van Hinsbergen, Douwe J. J.

    2010-09-01

    This paper provides a review of the structure and metamorphism of the Menderes Massif in western Turkey, and subsequently a map-view restoration of its Neogene unroofing history. Exhumation of this massif — among the largest continental extensional provinces in the world — is generally considered to have occurred along extensional detachments with a NE-SW stretching direction. Restoration of the early Miocene history, however, shows that these extensional detachments can only explain part of the exhumation history of the Menderes Massif, and that NE-SW stretching can only be held accountable for half, or less, of the exhumation. Restoration back to ˜ 15 Ma is relatively straightforward, and is mainly characterised by a previously reported 25-30° vertical axis rotation difference between the northern Menderes Massif, and the Southern Menderes Massif and overlying HP nappes, Lycian Nappes and Bey Dağları about a pivot point close to Denizli. To the west of this pole, the rotation was accommodated by exhumation of the Central Menderes core complex since middle Miocene times, and to the east probably by shortening. At the end of the early Miocene, the Menderes Massif formed a rectangular, NE-SW trending tectonic window of ˜ 150 × 100 km. Geochronology suggests unroofing between ˜ 25 and 15 Ma. The north-eastern Menderes Massif was exhumed along the early Miocene Simav detachment, over a distance of ≤ 50 km. The accommodation of the remainder of the exhumation is enigmatic, but penetrative NE-SW stretching lineations throughout the Menderes Massif suggest a prominent role of NE-SW extension. This, however, requires that the eastern margin of the Menderes Massif, bordering a region without significant extension, is a transform fault with an offset of ˜ 150 km, cutting through the Lycian Nappes. For this, there is no evidence. The Lycian Nappes — a non-metamorphic stack of sedimentary thrust slices and an overlying ophiolite and ophiolitic mélange

  9. Using Family Health History for Chronic Disease Prevention in the Age of Genomics: Translation to Health Education Practice

    ERIC Educational Resources Information Center

    Hanson, Carl; Novilla, Lelinneth; Barnes, Michael; De La Cruz, Natalie; Meacham, Aaron

    2007-01-01

    Advances in the field of human genomics have important implications for the prevention of chronic disease. In response to these advancements, public health professionals--including health educators--must become competent in the principles underlying the interface between genomics and the use of family health history. Family health history captures…

  10. Metamorphism of eucrite meteorites studied quantitatively using induced thermoluminescence

    NASA Technical Reports Server (NTRS)

    Batchelor, J. David; Sears, Derek W. G.

    1991-01-01

    Induced thermoluminescence studies provide a new and quantitative means of determining relative metamorphic intensities for eucrite meteorites, the simplest and most ancient products of basaltic volcanism. Using this technique, it is shown that the eucrites constitute a continuous metamorphic series and not, as commonly assumed, two groups of metamorphosed and nonmetamorphosed meteorites. It is suggested that the method may have applications to other basalts.

  11. A Simulated Research Problem for Undergraduate Metamorphic Petrology.

    ERIC Educational Resources Information Center

    Amenta, Roddy V.

    1984-01-01

    Presents a laboratory problem in metamorphic petrology designed to simulate a research experience. The problem deals with data on scales ranging from a geologic map to hand specimens to thin sections. Student analysis includes identifying metamorphic index minerals, locating their isograds on the map, and determining the folding sequence. (BC)

  12. Isothermal densification and metamorphism of new snow

    NASA Astrophysics Data System (ADS)

    Schleef, S.; Loewe, H.; Schneebeli, M.

    2012-12-01

    The interplay between overburden stress and surface energy induced growth and coarsening is relevant for the densification of snow and porous ice at all densities. The densification of new snow is amenable to high precision experiments on short time scales. To this end we investigate the coupling of densification and metamorphism of new snow via time-lapse tomography experiments in the laboratory. We compare the evolution of density, strain, and specific surface area to previous long-time metamorphism experiments of snow and creep of polycrystalline ice. Experimental conditions are tailored to the requirements of time-lapse tomography and the measurements are conducted under nearly isothermal conditions at -20°C with a duration of two days. Images were taken with temporal resolution of a few hours which reveal precise details of the microstructure evolution due to sintering and compaction. We used different crystal shapes of natural new snow and snow samples obtained by sieving crystals grown in a snowmaker in the laboratory. To simulate the effect of overburden stress due to an overlying snowpack additional weights were applied to the sample. As expected we find an influence of the densification rate on initial density and overburden stress. We calculated strain rates and identified a transient creep behavior with a similar power law for all crystal types which substantially differs from the Andrade creep of polycrystalline ice. As a main result we found that the evolution of the specific surface area is independent of the density and follows a unique decay form for all measurements of each crystal type. The accuracy of the measurements allows to obtain a decay exponent for the SSA which is the same as previously obtained from the long-time regime during isothermal metamorphism after several months. Our preliminary results for all available types of new snow suggest a correlation between the initial density and SSA. We also find snow samples which coincide in

  13. Fluid flow and chemical reaction kinetics in metamorphic systems

    SciTech Connect

    Lasaga, A.C.; Rye, D.M. )

    1993-05-01

    The treatment and effects of chemical reaction kinetics during metamorphism are developed along with the incorporation of fluid flow, diffusion, and thermal evolution. The interplay of fluid flow and surface reaction rates, the distinction between steady state and equilibrium, and the possible overstepping of metamorphic reactions are discussed using a simple analytic model. This model serves as an introduction to the second part of the paper, which develops a reaction model that solves the coupled temperature-fluid flow-chemical composition differential equations relevant to metamorphic processes. Consideration of stable isotopic evidence requires that such a kinetic model be considered for the chemical evolution of a metamorphic aureole. A general numerical scheme is discussed to handle the solution of the model. The results of this kinetic model allow us to reach several important conclusions regarding the factors controlling the chemical evolution of mineral assemblages during a metamorphic event. 41 refs., 19 figs., 5 tabs.

  14. Pseudotachylyte in the Tananao Metamorphic Complex, Taiwan: Occurrence and dynamic phase changes of fossil earthquakes

    NASA Astrophysics Data System (ADS)

    Chu, Hao-Tsu; Hwang, Shyh-Lung; Shen, Pouyan; Yui, Tzen-Fu

    2012-12-01

    Pseudotachylyte veins and cataclasites were studied in the mylonitized granitic gneiss of the Tananao Metamorphic Complex at Hoping, Eastern Taiwan. The aphanitic pseudotachylyte veins vary in thickness, ranging from millimeters to about 1 cm. Field and optical microscopic observations show that such pseudotachylyte veins cut across cataclasites, which, in turn, transect the mylonitized granitic gneiss. Scanning electron microscopic images also show that both the pseudotachylyte veins and the cataclasites have been metasomatized by a K-rich fluid, resulting in the replacement of Na-plagioclase by K-feldspar (veins). Analytical electron microscopic observations reveal further details of physical and chemical changes (mainly fragmentation, dislocations, cleaving-healing with inclusions and relic voids, and retention of high-temperature albite) of quartz and feldspar in crushed grains. Pseudotachylytes occur as dark veins having a higher content of chlorite-biotite, clinozoisite-epidote and titanite fragments than cataclasites. These veins, coupled with hematite/jarosite-Fe-rich amorphous shell/carbonaceous material, indicate that crushing, healing/sintering, and inhomogeneous melt/fluid infiltration involving incipient and intermediate/high temperature melt patches, before and/or contemporaneous with the metasomatic K-rich fluid, prevailed in a coupled or sequential manner in the faulting event to form nonequilibrium phase assemblage. The chlorite-biotite, carbonaceous material and other nanoscale minerals could be vulnerable in future earthquakes under the influence of water. The timing of the formation of these pseudotachylyte veins should be later than the area's age of mylonitization of granitic gneiss of approximately 4.1-3.0 Ma (Wang et al., 1998). The formation of pseudotachylytes registers the fossil earthquakes during early stages in the exhumation history of the uplifting Taiwan Mountain belt since the Plio-Pleistocene Arc-Continent collision.

  15. Timing of middle Paleozoic (Acadian) metamorphism in the southern Appalachians: K-Ar studies in the Talladega belt, Alabama

    SciTech Connect

    Kish, S.A. )

    1990-07-01

    The Talladega belt of Alabama and Georgia is located at the southernmost exposed part of the southern Appalachian orogen and is one of the westernmost metamorphic terranes in this part of the orogen. The presence of the Lower Devonian Jemison Chert of the Talladega Group provides a maximum age for the timing of greenschist facies metamorphism and penetrative slaty cleavage formation in this terrane. Six slate collected form upper Precambrian( )-Lower Cambrian, and Silurian( )-Devonian rocks of the Talladega belt have an average K-Ar age of 399 {plus minus} 17 Ma. This age is interpreted to be the approximate time of regional greenschist facies metamorphism. The timing of metamorphism in the Talladega belt is similar to the age of the Acadian orogeny in the Maritime and northern Appalachians. Unlike the accreted nature of the Acadian terranes in the northern Appalachians, the Talladega belt appears to have been part of the early to middle Paleozoic cratonic margin of North America. The results of this study indicate that Acadian dynamothermal events extended into parts of the Laurentian margin in the southern Appalachians. Paleozoic igneous activity in the southern Appalachians was less extensive compared with the voluminous Acadian plutonism of the northern Appalachians; however, synkinematic to postkinematic Devonian plutons are present in the central and western parts of the orogen.

  16. A review of the plate convergence history of the East Anatolia-Transcaucasus region during the Variscan: Insights from the Georgian basement and its connection to the Eastern Pontides

    NASA Astrophysics Data System (ADS)

    Rolland, Y.; Hässig, M.; Bosch, D.; Meijers, M. J. M.; Sosson, M.; Bruguier, O.; Adamia, Sh.; Sadradze, N.

    2016-05-01

    This article summarizes the geodynamic evolution of the Variscan to Mesozoic Tethyan subduction history, based on a review of geochronological data from Eastern Anatolia and the Lesser Caucasus, and new isotopic ages for the Georgian crystalline basements. The geological history of the basements of Georgia (Transcaucasus) and NE Turkey (eastern Pontides) appears to be similar and provides evidence for a continuously active continental margin above a north-dipping subduction since at least the Lower Jurassic. New La-ICPMS U-Pb ages from the Georgian basement provide further evidence for the derivation of the Transcaucasus and its western continuation (the eastern Pontides) from Gondwana. A migmatized granodiorite provides preserved magmatic zircon cores with an age of 474 ± 3 Ma, while the age of migmatization is constrained by its 343 ± 2 Ma metamorphic rims. Metamorphism is synchronous with widespread I-type granites that were emplaced at 335 ± 8 Ma in the neighbouring Dzirula massif, and in the eastern Pontides. These U-Pb ages are in close agreement with recently obtained Ar/Ar ages from biotites and muscovites from metamorphic schists and U-Pb ages ranging from 340 to 330 Ma in the Georgian basement. The narrow range of ages suggests that the Variscan LP-HT metamorphic event in the eastern Pontides and Georgia was of short duration and likely related to mantle-derived intrusives. Furthermore, we suggest that (1) rifting of the Pontides-Transcaucasus block (PTB) from Gondwana at 450-350 Ma could have been driven by roll-back of the south-dipping Rheic slab, (2) that the main metamorphic and coeval magmatic events are related to the accretion of the PTB to the Eurasian margin at c. 350 Ma, while the source of magmatism is ascribed to slab detachment of the south-dipping slab at 340 Ma and that (3) three subduction zones may have been contemporaneously active in the Tethyan domain during the Jurassic: (i) the Lesser Caucasus South Armenian Block (SAB) shares a

  17. Shock metamorphism of lunar and terrestrial basalts

    NASA Technical Reports Server (NTRS)

    Schaal, R. B.; Hoerz, F.

    1977-01-01

    Lonar Crater (India) basalt and lunar basalt 75035 were shock loaded under controlled laboratory conditions up to 1000 kbar, generally in a CO/CO2 (1:1) environment evacuated to 10 to the minus seventh power torr. The Kieffer et al. (1976) classification scheme of progressive shock metamorphism is found to apply to lunar basalts. The major shock features of the five classes that span the range 0 to 1000 kbar are described. Only three out of 152 basalt specimens show shock effects in their natural state as severe as Class 2 features. The scarcity of shocked basalt hand samples in contrast to the abundance of shock-produced agglutinates and homogeneous glass spheres in the lunar regolith indicates the dominant role of micrometeorite impact in the evolution of the lunar regolith. The overall glass content in asteroidal and Mercurian regoliths is considered.

  18. Redistribution of volatiles during lunar metamorphism

    NASA Technical Reports Server (NTRS)

    Cirlin, E. H.; Housley, R. M.

    1980-01-01

    Thermal release profiles of Pb, Zn, and Cd in sample 66095 (highly shocked breccia with melt rock matrix) showed that these volatiles were mostly present on the surface of the grains. Zn in rusty grains from 66095 was also mostly surface Zn, probably from sphalerite in grain boundaries and cracks. Simulation experiments of volatile transfer showed that Fe, FeCl2, iron phosphide, and troilite (FeS) can be produced and transported during subsolidus reactions. These results suggest that volatiles, rust, schreibersite, and possible siderophiles which are observed in lunar highland samples might have been redistributed during disequilibrium thermal metamorphism in hot ejecta blankets, and were not necessarily introduced by volcanic activity or meteoritic addition.

  19. Metamorphic Perspectives of Subduction Zone Volatiles Cycling

    NASA Astrophysics Data System (ADS)

    Bebout, G. E.

    2008-12-01

    Field study of HP/UHP metamorphic rocks provides "ground-truthing" for experimental and theoretical petrologic studies estimating extents of deep volatiles subduction, and provides information regarding devolatilization and deep subduction-zone fluid flow that can be used to reconcile estimates of subduction inputs and arc volcanic outputs for volatiles such as H2O, N, and C. Considerable attention has been paid to H2O subduction in various bulk compositions, and, based on calculated phase assemblages, it is thought that a large fraction of the initially structurally bound H2O is subducted to, and beyond, subarc regions in most modern subduction zones (Hacker, 2008, G-cubed). Field studies of HP/UHP mafic and sedimentary rocks demonstrate the impressive retention of volatiles (and fluid-mobile elements) to depths approaching those beneath arcs. At the slab-mantle interface, high-variance lithologies containing hydrous phases such as mica, amphibole, talc, and chlorite could further stabilize H2O to great depth. Trench hydration in sub-crustal parts of oceanic lithosphere could profoundly increase subduction inputs of particularly H2O, and massive flux of H2O-rich fluids from these regions into the slab-mantle interface could lead to extensive metasomatism. Consideration of sedimentary N concentrations and δ15N at ODP Site 1039 (Li and Bebout, 2005, JGR), together with estimates of the N concentration of subducting altered oceanic crust (AOC), indicates that ~42% of the N subducting beneath Nicaragua is returned in the corresponding volcanic arc (Elkins et al., 2006, GCA). Study of N in HP/UHP sedimentary and basaltic rocks indicates that much of the N initially subducted in these lithologies would be retained to depths approaching 100 km and thus available for addition to arcs. The more altered upper part of subducting oceanic crust most likely to contribute to arcs has sediment-like δ15NAir (0 to +10 per mil; Li et al., 2007, GCA), and study of HP/UHP eclogites

  20. Shock metamorphic effects in lunar microcraters

    NASA Technical Reports Server (NTRS)

    Schaal, R. B.; Hoerz, F.; Gibbons, R. V.

    1976-01-01

    Detailed petrographic descriptions and results of electron microprobe analyses are presented for impact glasses as well as shocked and unshocked minerals associated with individual lunar microcraters (diameters of 0.4 to 4.4 mm). Rocks of four typical lunar lithologies are studied: anorthosite, anorthositic norite, ophitic basalt, and polymict breccia. Textures, mineralogies, and chemical compositions are examined along a radial traverse through each microcrater; i.e., across the impact glasses lining the crater wall, the shock-metamorphosed zone immediately underlying the glass liner, and the unshocked host rock. The microcraters are discussed in a sequence of increasing mineralogical complexity of the host rock (from anorthosite to polymict breccia) in order to distinguish shock effects among mineral types. The shock metamorphic features observed are found to be comparable to those reported in shocked basalt from Lonar Crater, India, and are categorized into five shock-intensity classes with pressures experimentally calibrated.

  1. Maximum sedimentation ages and provenance of metasedimentary rocks from Tinos Island, Cycladic blueschist belt, Greece

    NASA Astrophysics Data System (ADS)

    Hinsken, Tim; Bröcker, Michael; Berndt, Jasper; Gärtner, Claudia

    2016-10-01

    U-Pb zircon ages of five metasedimentary rocks from the Lower Unit on Tinos Island (Cycladic blueschist belt, Greece) document supply of detritus from various Proterozoic, Paleozoic and Mesozoic source rocks as well as post-depositional metamorphic zircon formation. Essential features of the studied zircon populations are Late Cretaceous (70-80 Ma) maximum sedimentation ages for the lithostratigraphic succession above the lowermost dolomite marble, significant contributions from Triassic to Neoproterozoic source rocks, minor influx of detritus recording Paleoproterozoic and older provenance (1.9-2.1, 2.4-2.5 and 2.7-2.8 Ga) and a lack or paucity of zircons with Mesoproterozoic ages (1.1-1.8 Ga). In combination with biostratigraphic evidence, the new dataset indicates that Late Cretaceous or younger rocks occur on top of or very close to the basal Triassic metacarbonates, suggesting a gap in the stratigraphic record near the base of the metamorphic succession. The time frame for sediment deposition is bracketed by the youngest detrital zircon ages (70-80 Ma) and metamorphic overgrowths that are related to high-pressure/low-temperature overprinting in the Eocene. This time interval possibly indicates a significant difference to the sedimentation history of the southern Cyclades, where Late Cretaceous detrital zircons have not yet been detected.

  2. Maximum sedimentation ages and provenance of metasedimentary rocks from Tinos Island, Cycladic blueschist belt, Greece

    NASA Astrophysics Data System (ADS)

    Hinsken, Tim; Bröcker, Michael; Berndt, Jasper; Gärtner, Claudia

    2015-10-01

    U-Pb zircon ages of five metasedimentary rocks from the Lower Unit on Tinos Island (Cycladic blueschist belt, Greece) document supply of detritus from various Proterozoic, Paleozoic and Mesozoic source rocks as well as post-depositional metamorphic zircon formation. Essential features of the studied zircon populations are Late Cretaceous (70-80 Ma) maximum sedimentation ages for the lithostratigraphic succession above the lowermost dolomite marble, significant contributions from Triassic to Neoproterozoic source rocks, minor influx of detritus recording Paleoproterozoic and older provenance (1.9-2.1, 2.4-2.5 and 2.7-2.8 Ga) and a lack or paucity of zircons with Mesoproterozoic ages (1.1-1.8 Ga). In combination with biostratigraphic evidence, the new dataset indicates that Late Cretaceous or younger rocks occur on top of or very close to the basal Triassic metacarbonates, suggesting a gap in the stratigraphic record near the base of the metamorphic succession. The time frame for sediment deposition is bracketed by the youngest detrital zircon ages (70-80 Ma) and metamorphic overgrowths that are related to high-pressure/low-temperature overprinting in the Eocene. This time interval possibly indicates a significant difference to the sedimentation history of the southern Cyclades, where Late Cretaceous detrital zircons have not yet been detected.

  3. The eruptive history of the Tequila volcanic field, western Mexico: ages, volumes, and relative proportions of lava types

    NASA Astrophysics Data System (ADS)

    Lewis-Kenedi, Catherine B.; Lange, Rebecca A.; Hall, Chris M.; Delgado-Granados, Hugo

    2005-06-01

    The eruptive history of the Tequila volcanic field (1600 km2) in the western Trans-Mexican Volcanic Belt is based on 40Ar/39Ar chronology and volume estimates for eruptive units younger than 1 Ma. Ages are reported for 49 volcanic units, including Volcán Tequila (an andesitic stratovolcano) and peripheral domes, flows, and scoria cones. Volumes of volcanic units ≤1 Ma were obtained with the aid of field mapping, ortho aerial photographs, digital elevation models (DEMs), and ArcGIS software. Between 1120 and 200 kyrs ago, a bimodal distribution of rhyolite (~35 km3) and high-Ti basalt (~39 km3) dominated the volcanic field. Between 685 and 225 kyrs ago, less than 3 km3 of andesite and dacite erupted from more than 15 isolated vents; these lavas are crystal-poor and show little evidence of storage in an upper crustal chamber. Approximately 200 kyr ago, ~31 km3 of andesite erupted to form the stratocone of Volcán Tequila. The phenocryst assemblage of these lavas suggests storage within a chamber at ~2 3 km depth. After a hiatus of ~110 kyrs, ~15 km3 of andesite erupted along the W and SE flanks of Volcán Tequila at ~90 ka, most likely from a second, discrete magma chamber located at ~5 6 km depth. The youngest volcanic feature (~60 ka) is the small andesitic volcano Cerro Tomasillo (~2 km3). Over the last 1 Myr, a total of 128±22 km3 of lava erupted in the Tequila volcanic field, leading to an average eruption rate of ~0.13 km3/kyr. This volume erupted over ~1600 km2, leading to an average lava accumulation rate of ~8 cm/kyr. The relative proportions of lava types are ~22 43% basalt, ~0.4 1% basaltic andesite, ~29 54% andesite, ~2 3% dacite, and ~18 40% rhyolite. On the basis of eruptive sequence, proportions of lava types, phenocryst assemblages, textures, and chemical composition, the lavas do not reflect the differentiation of a single (or only a few) parental liquids in a long-lived magma chamber. The rhyolites are geochemically diverse and were likely

  4. UHT granulite-facies metamorphism in Rogaland, S Norway, is polyphase in nature

    NASA Astrophysics Data System (ADS)

    Laurent, Antonin; Duchene, Stéphanie; Bingen, Bernard; Seydoux-Guillaume, Anne-Magali; Bosse, Valérie

    2016-04-01

    Propensity of metamorphic assemblages to remain metastable after melt extraction complicates singularly the petrologist's task to discriminate between a single granulite-facies P-T path and a polyphase one. Using an integrated petrological and in-situ geochronological approach in key rock-samples, we reconstruct the pressure-temperature-time path of Sveconorwegian metamorphism across a 30 km-wide metamorphic gradient ranging from upper amphibolite facies to ultra-high temperature (UHT) granulite-facies in Rogaland, S. Norway. Thermodynamic modelling of phase equilibria in the Na2O-CaO-K2O-FeO-MgO-Al2O3-SiO2-H2O-Ti2O-O2 chemical system (PerpleX code) are carried out with an emphasis on moderately oxidized, spinel-bearing assemblages resulting from either garnet or sapphirine breakdown. Geochronological U-(Th)-Pb data acquired on both monazite (LA-ICP-MS) and zircon (SIMS) are complemented by minor- and trace-elements signatures of both minerals, to monitor REE distribution through time and to evaluate garnet apparition or demise. Coupling field, petrological and geochronological data lead to a polyphase metamorphic history, lasting about 100 My. The onset of regional granulite facies metamorphism at 1035 Ma is associated with the emplacement of large volumes of granitic magmas in the amphibolite to granulite facies transition zone. In the deeper part of the crustal section, localized sapphirine-bearing restitic lithologies testify to UHT temperatures (900‑920 °C). These conditions were reached at ca. 1010 Ma following a tight clockwise P-T path associated with minor exhumation (7 to 5.5 kbar) and subsequent cooling to 700 °C. A distinct thermal episode, initiated at ca. 950 Ma, reached UHT granulite-facies conditions with the intrusion of massif-type anorthosite plutons at ca. 930 Ma producing a 5-km wide aureole. The aureole is delimited by the presence of osumilite in high Fe-Al rocks yielding quantitative estimates of 900-950 °C at a maximum pressure of 5

  5. UHT granulite-facies metamorphism in Rogaland, S Norway, is polyphase in nature

    NASA Astrophysics Data System (ADS)

    Laurent, Antonin; Duchene, Stéphanie; Bingen, Bernard; Seydoux-Guillaume, Anne-Magali; Bosse, Valérie

    2016-04-01

    Propensity of metamorphic assemblages to remain metastable after melt extraction complicates singularly the petrologist's task to discriminate between a single granulite-facies P-T path and a polyphase one. Using an integrated petrological and in-situ geochronological approach in key rock-samples, we reconstruct the pressure-temperature-time path of Sveconorwegian metamorphism across a 30 km-wide metamorphic gradient ranging from upper amphibolite facies to ultra-high temperature (UHT) granulite-facies in Rogaland, S. Norway. Thermodynamic modelling of phase equilibria in the Na2O-CaO-K2O-FeO-MgO-Al2O3-SiO2-H2O-Ti2O-O2 chemical system (PerpleX code) are carried out with an emphasis on moderately oxidized, spinel-bearing assemblages resulting from either garnet or sapphirine breakdown. Geochronological U-(Th)-Pb data acquired on both monazite (LA-ICP-MS) and zircon (SIMS) are complemented by minor- and trace-elements signatures of both minerals, to monitor REE distribution through time and to evaluate garnet apparition or demise. Coupling field, petrological and geochronological data lead to a polyphase metamorphic history, lasting about 100 My. The onset of regional granulite facies metamorphism at 1035 Ma is associated with the emplacement of large volumes of granitic magmas in the amphibolite to granulite facies transition zone. In the deeper part of the crustal section, localized sapphirine-bearing restitic lithologies testify to UHT temperatures (900-920 °C). These conditions were reached at ca. 1010 Ma following a tight clockwise P-T path associated with minor exhumation (7 to 5.5 kbar) and subsequent cooling to 700 °C. A distinct thermal episode, initiated at ca. 950 Ma, reached UHT granulite-facies conditions with the intrusion of massif-type anorthosite plutons at ca. 930 Ma producing a 5-km wide aureole. The aureole is delimited by the presence of osumilite in high Fe-Al rocks yielding quantitative estimates of 900-950 °C at a maximum pressure of 5 kbar

  6. Conodont color and textural alteration: an index to regional metamorphism, contact metamorphism, and hydrothermal alteration.

    USGS Publications Warehouse

    Rejebian, V.A.; Harris, A.G.; Huebner, J.S.

    1987-01-01

    Experimental and field data are used to extend the utility of conodonts as semi-quantitative thermal indices into the regimes of regional and contact metamorphism, as well as hydrothermal alteration. These experiments approximate the type of Colour Alteration Indices mixture characteristically found in conodonts recovered from hydrothermally altered rocks. These data indicate that CAI values of 6 to 8 cannot be used to assess precise temperatures of hydrothermally altered rocks but may serve as useful indicators of potential mineralization. - from Authors

  7. High-pressure amphibolite facies dynamic metamorphism and the Mesozoic tectonic evolution of an ancient continental margin, east- central Alaska

    USGS Publications Warehouse

    Dusel-Bacon, C.; Hansen, V.L.; Scala, J.A.

    1995-01-01

    Ductilely deformed amphibolite facies tectonites comprise two adjacent terranes in east-central Alaska: the northern, structurally higher Taylor Mountain terrane and the southern, structurally lower Lake George subterrane of the Yukon-Tanana terrane. The pressure, temperature, kinematic and age data are interpreted to indicate that the metamorphism of the Taylor Mountain terrane and Lake George subterrane took place during different phases of a latest Palaeozoic through early Mesozoic shortening episode resulting from closure of an ocean basin now represented by klippen of the Seventymile-Slide Mountain terrane. High- to intermediate-pressure metamorphism of the Taylor Mountain terrane took place within a SW-dipping (present-day coordinates) subduction system. High- to intermediate-pressure metamorphism of the Lake George subterrane and the structural contact zone occurred during NW-directed overthrusting of the Taylor Mountain, Seventymile-Slide Mountain and Nisutlin terranes, and imbrication of the continental margin in Jurassic time. -from Authors

  8. The grand tour of the Ruby-East Humboldt metamorphic core complex, northeastern Nevada: Part 1 - Introduction & road log

    USGS Publications Warehouse

    Snoke, A.W.; Howard, K.A.; McGrew, A.J.; Burton, B.R.; Barnes, C.G.; Peters, M.T.; Wright, J.E.

    1997-01-01

    The purpose of this geological excursion is to provide an overview of the multiphase developmental history of the Ruby Mountains and East Humboldt Range, northeastern Nevada. Although these mountain ranges are commonly cited as a classic example of a Cordilleran metamorphic core complex developed through large-magnitude, mid-Tertiary crustal extension, a preceding polyphase Mesozoic contractional history is also well preserved in the ranges. An early phase of this history involved Late Jurassic two-mica granitic magmatism, high-temperature but relatively low-pressure metamorphism, and polyphase deformation in the central Ruby Mountains. In the northern Ruby Mountains and East Humboldt Range, a Late Cretaceous history of crustal shortening, metamorphism, and magmatism is manifested by fold-nappes (involving Archean basement rocks in the northern East Humboldt Range), widespread migmatization, injection of monzogranitic and leucogranitic magmas, all coupled with sillimanite-grade metamorphism. Following Late Cretaceous contraction, a protracted extensional deformation partially overprinted these areas during the Cenozoic. This extensional history may have begun as early as the Late Cretaceous or as late as the mid-Eocene. Late Eocene and Oligocene magmatism occurred at various levels in the crust yielding mafic to felsic orthogneisses in the deep crust, a composite granitic pluton in the upper crust, and volcanic rocks at the surface. Movement along a west-rooted, extensional shear zone in the Oligocene and early Miocene led to core-complex exhumation. The shear zone produced mylonitic rocks about 1 km thick at deep crustal levels, and an overprint of brittle detachment faulting at shallower levels as unroofing proceeded. Megabreccias and other synextensional sedimentary deposits are locally preserved in a tilted, upper Eocene through Miocene stratigraphic sequence. Neogene magmatism included the emplacement of basalt dikes and eruption of rhyolitic rocks. Subsequent

  9. Thermoluminescence of Antarctic meteorites: A rapid screening technique for terrestrial age estimation, pairing stud