2,236 research outputs found
Algebras of operations in K-theory
We describe explicitly the algebras of degree zero operations in connective
and periodic p-local complex K-theory. Operations are written uniquely in terms
of certain infinite linear combinations of Adams operations, and we give
formulas for the product and coproduct structure maps. It is shown that these
rings of operations are not Noetherian. Versions of the results are provided
for the Adams summand and for real K-theory.Comment: 25 page
The discrete module category for the ring of K-theory operations
We study the category of discrete modules over the ring of degree zero stable
operations in p-local complex K-theory. We show that the p-local K-homology of
any space or spectrum is such a module, and that this category is isomorphic to
a category defined by Bousfield and used in his work on the K-local stable
homotopy category (Amer. J. Math., 1985). We also provide an alternative
characterisation of discrete modules as locally finitely generated modules.Comment: 19 page
TRACKING THE P–T PATH OF PRECAMBRIAN ECLOGITE USING PSEUDOSECTION, Ti-IN-QUARTZ AND Zr-IN-RUTILE THERMOBAROMETRY
International audienceSveconorwegian eclogite occur as a nappe within the high-grade metamorphic region in southernSweden, which constitutes a window into the deepest part of this Precambrian mountain belt. Distinctmicrostructural domains (i.e., garnet core, garnet rim, and matrix) in a Fe-Ti-rich eclogite variety containabundant quartz, rutile and zircon.A pseudosection approach was first applied and compared to results from a combination of Zr-in-rutileand Ti-in-quartz. The pressure input used for both thermometers was first deduced for each microstructuraldomain from the pseudosection. For the garnet core, Zr-in-rutile yields temperatures of 700-715°C and Ti-inquartz~ 635°C at 7 kbar. For the garnet rim, temperatures of 760-790°C (Zr-in-rutile) and 740-890°C (Ti-inquartz)at 12-18 kbar were calculated. Matrix rutile recorded temperatures of ~ 810°C, while quartz recordedtemperatures up to ~ 890°C. Additionally, direct combination of Ti content in quartz and Zr content in rutileisopleths (i.e., independent from the pseudosection) yield a prograde path in nearly perfect agreement withthe one deduced from the pseudosection.The pseudosection shows that rutile was produced by continuous breakdown of ilmenite during the earlystages of prograde metamorphism, a reaction that ran to completion at ~ 730°C. Most rutile grains in garnetrim and matrix are interpreted to subsequently form by recrystallization of smaller matrix grains. However,they generally do not record the peak-P temperatures and instead range mostly between 775 and 815°C,interpreted as a result of more efficient recrystallization during a dehydration reaction (progressivereplacement of hornblende by clinopyroxene).This study illustrates that both Zr-in-rutile and Ti-in-quartz thermometry cannot only robustly constrain aprograde evolution, but when combined with a pseudosection model can also yield information onrecrystallization processes. In fact, the combination of these three methods provides an unrivalled tool forpetrologic interpretation.The variation in Ti concentration in quartz is small regardless of crystal size. This P–T path reach veryhigh temperatures (up to 875°C) with a high dP/dT ratio, both during prograde and retrograde histories. Thesteep P–T path, together with preservation of garnet growth zoning, symplectitic textures and the lack ofsignificant Ti diffusion in quartz is consistent with a short residence time at high-temperature, implyingunusual fast burial and exhumation of the eclogite-bearing nappe
Timing and Petrogenesis of the Permo-Carboniferous Larvik Plutonic Complex, Oslo Rift, Norway : New Insights from U-Pb, Lu-Hf, and O Isotopes in Zircon
The Permo-Carboniferous Oslo Rift is a narrow, aborted continental rift with comparatively little extension but voluminous magmatism, developed at a Proterozoic lithospheric discontinuity. On the southern flank of the onshore part of the rift, the multiple intrusive phase Larvik plutonic complex (LPC) encompasses almost the width of the rift with a conspicuous over- to undersaturated assemblage of monzonite (larvikite, tonsbergite) and nepheline syenite (lardalite, foyaite). We present new single-crystal U-Pb-, Lu-Hf-, and O-in-zircon isotope data for the intrusive centers of the complex. U-Pb ages of slightly over- to undersaturated monzonites show a shift in igneous activity from 299 Ma on the eastern edge of the complex to 289 Ma in the west. The western part of the complex is built of two consanguineous magmatic systems with a northward shift in the locus of magmatism, from 296 to 289 Ma (undersaturated monzonite) and 296 to similar to 288 Ma (nepheline syenite). Moreover, an early oversaturated monzonite was emplaced in the eastern part of the complex at similar to 302 Ma. The Hf and O isotope composition of the monzonites and nepheline syenites shows little variation with zircon epsilon(Hf) (295 Ma) values of +5.5 to +8 and delta(18)Omicron values of +4.79 parts per thousand to +5.49 parts per thousand. No change in isotope values is observed with varying alkalinity and the Hf and O isotope compositions are interpreted as mantle source values. The source of the precursors of the monzonitic and nepheline syenitic magmas was probably a mildly depleted, sublithospheric peridotite in the lithosphere-asthenosphere boundary zone (at 3-4 GPa). Rhyolite-MELTS modeling implies polybaric fractionation of weakly alkaline basaltic melts from the source having led to an oversaturated/saturated liquid line of descent at similar to 0.5 GPa and an undersaturated one at similar to 1 GPa. Magmatism had an imperative role in the evolution of the rift by localizing strain and weakening the lithosphere along the discontinuity. A fractionating crustal melt column was tapped at varying depths in the course of advancing rupturing with no significant mixing of the over- and undersaturated melts, and magma batches were emplaced as sequential nested plutons in response to differential opening of the rift. Among continental saturated-undersaturated alkaline complexes, the LPC may be unique in the emplacement of successive magma batches across a continental rift in the direction of opening, tapping of increasingly deeper parts of the melt column with advancing rifting, and intrusion of two contemporaneous, contrasting magmatic lineages at the end of igneous activity. The marked lithospheric step at the rift locus in the Precambrian basement of southeastern Norway was probably the driving force for the inception and evolution of the Larvik magmatic system.Peer reviewe
Biogenic processes in crystalline bedrock fractures indicated by carbon isotope signatures of secondary calcite
Peer reviewe
Geochronology and Stable Isotope Analysis of Fracture-Fill and Karst Mineralization Reveal Sub-Surface Paleo-Fluid Flow and Microbial Activity of the COSC-1 Borehole, Scandinavian Caledonides
The deep biosphere hosted in fractured rocks within the upper continental crust is one of the least understood and studied ecological realms on Earth. Scarce knowledge of ancient life and paleo-fluid flow within this realm is owing to the lack of deep drilling into the crust. Here we apply microscale high spatial-resolution analytical techniques to fine-grained secondary minerals in a deep borehole (COSC-1) drilled into the Silurian-Devonian Scandinavian Caledonide mountain range in central Sweden. The aim is to detect and date signs of ancient microbial activity and low-temperature fluid circulation in micro-karsts (foliation-parallel dissolution cavities in the rock) and fractures at depth in the nappe system. Vein carbonates sampled at 684 to 2210 m show a decreased C isotope variability at depths below 1050 m; likely due to decreased influence of organic-C at great depth. Micro-karsts at 122–178 m depth feature at least two generations of secondary calcite and pyrite growth in the voids as shown by secondary ion mass spectrometry analytical transects within individual grains. The younger of these two precipitation phases shows 34S-depleted δ34Spyrite values (−19.8 ± 1.6‰ vs. Vienna-Canyon Diablo Troilite (V-CDT)) suggesting microbial sulfate reduction in situ. The calcite of this late phase can be distinguished from the older calcite by higher δ18Ocalcite values that correspond to precipitation from ambient meteoric water. The late stage calcite gave two separate laser ablation inductively coupled mass spectrometry-derived U-Pb ages (9.6 ± 1.3 Ma and 2.5 ± 0.2 Ma), marking a minimum age for widespread micro-karst formation within the nappe. Several stages of fluid flow and mineral precipitation followed karst formation; with related bacterial activity as late as the Neogene-Quaternary; in structures presently water conducting. The results show that our combined high spatial-resolution stable isotope and geochronology approach is suitable for characterizing paleo-fluid flow in micro-karst; in this case, of the crystalline crust comprising orogenic nappe units
A revised Ordovician age for the Sisargas orthogneiss, Galicia (Spain). Zircon U-Pb ion-microprobe and LA-ICPMS dating
The Sisargas orthogneiss is located in the Schistose Domain of the Galicia Trás-Os-Montes Zone. It has previously been dated by Allegret and Iglesias (1987) who reported an U-Pb upper intercept at 570 ± 14 Ma, considered to be the crystallization age. For this reason, the Sisargas orthogneiss has traditionally been considered one of the oldest magmatic rocks of the Central Iberian Zone. However, new SIMS and LA-ICPMS data reveal that it crystallized at 479 ± 7 Ma and contains zircons with abundant pre-magmatic cores with ages clustering at 585 ± 15 Ma. This suggests that the Sisargas orthogneiss derives from the melting of a Pan-African protolith
Boning up on autophagy: the role of autophagy in skeletal biology.
From an evolutionary perspective, the major function of bone is to provide stable sites for muscle attachment and affording protection of vital organs, especially the heart and lungs (ribs) and spinal cord (vertebrae and intervertebral discs). However, bone has a considerable number of other functions: serving as a store for mineral ions, providing a site for blood cell synthesis and participating in a complex system-wide endocrine system. Not surprisingly, bone and cartilage cell homeostasis is tightly controlled, as is the maintenance of tissue structure and mass. While a great deal of new information is accruing concerning skeletal cell homeostasis, one relatively new observation is that the cells of bone (osteoclasts osteoblasts and osteocytes) and cartilage (chondrocytes) exhibit autophagy. The focus of this review is to examine the significance of this process in terms of the functional demands of the skeleton in health and during growth and to provide evidence that dysregulation of the autophagic response is involved in the pathogenesis of diseases of bone (Paget disease of bone) and cartilage (osteoarthritis and the mucopolysaccharidoses). Delineation of molecular changes in the autophagic process is uncovering new approaches for the treatment of diseases that affect the axial and appendicular skeleton
Isotopic signatures of precent-day calcite and pyrite in low-temperature crystalline bedrock, Olkiluoto, SW Finland
Geochemical characteristics of precipitated fracture filling calcite and pyrite can provide much useful information about the deep bedrock environment at the time of their deposition. However, it has been difficult to identify fracture coatings precipitated from the present-day groundwater system. The aim of this study was to evaluate the relationship between the coexisting calcite and pyrite, and the groundwater present at the time of precipitation. Here we investigated fine-grained mineral precipitate deposited over a four-year period on the surface of groundwater monitoring equipment inserted into a drillhole at 530 m below sea level, at Olkiluoto, which is the planned site for a final repository of spent nuclear fuel. The experimental setting is also artificial in the sense that the drillholes have possibly affected groundwater circulation and a foreign object has been inserted into the drillhole. Combining the elemental and isotope geochemical composition of the precipitated calcite and pyrite with previously published compositional data on groundwater and evidence for microbial communities on this site, offered a possibility to get new insight of the precipitation and isotope fractionation processes taking place in deep crystalline bedrock. The concentration of the redox sensitive manganese in the precipitate gives supporting evidence for the influx of groundwater from overlying groundwater units. The delta C-13 (n = 13) and delta O-18 (n = 15) values of calcite vary from-13.2 to-9.7 parts per thousand and from-9.1 to-7.4 parts per thousand respectively. Comparison to the respective values in the local groundwater indicated that the precipitated calcite is in near isotopic equilibrium with its environment with respect to carbon and oxygen. The potential ultimate source of the carbon in the DIC and in the precipitate is likely in old fracture calcite coatings. The 834S values of pyrite (n = 9) show relatively small variation from-5.7 to 8.3 parts per thousand. This differs greatly from the huge span of 834S values from-50 to 80%o in fracture pyrites reported for the latest calcite fillings at Olkiluoto. The restricted range of 834S values is interpreted to result from open system conditions during precipitation, with new dissolved sulfate entering from the large brackish SO4-type groundwater unit above. The isotopic fractionation of sulfur between dissolved sulfate and sulfide is estimated to be 25 & PLUSMN; 10%o, which is in agreement with the results reported in laboratory experiments for bacterial sulfate reduction.Peer reviewe
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