Low-Titanium Lamproites of the Ryabinoviy Massif (Aldan Shield): Crystallization Conditions and Lithospheric Source

2018 ◽  
Vol 481 (2) ◽  
pp. 1008-1012
Author(s):  
I. F. Chayka ◽  
A. E. Izokh ◽  
A. V. Sobolev ◽  
V. G. Batanova
Keyword(s):  
Aldan Shield ◽  
Crystallization Conditions

Low Titanium Lamproites of the Ashberry Massif (Aldan Shield): Crystallization Conditions and Lithospheric Source

2018 ◽  
Vol 481 (4) ◽  
pp. 426-429
Author(s):  
I. Chaika ◽  
◽  
A. Izokh ◽  
A. Sobolev ◽  
V. Batanova ◽  
...  
Keyword(s):  
Aldan Shield ◽  
Crystallization Conditions

Petrology and age determinations of the ultramafic (lamproitic) rocks from the Yakokut complex, Aldan Shield, Eastern Siberia

1995 ◽  
Vol 59 (396) ◽  
pp. 409-428 ◽  
Author(s):  
U. Mues-Schumacher ◽  
J. Keller ◽  
V. Konova ◽  
P. Suddaby
Keyword(s):  
Mantle Source ◽  
Aldan Shield ◽  
Eastern Siberia ◽  
Isotopic Data ◽  
Depleted Mantle ◽  
Heterogeneous Mantle ◽  
Crystallization Conditions ◽  
Alkaline Complexes ◽  
Subcontinental Lithosphere ◽  
Age Determinations

AbstractMineralogical, geochemical and isotopic data including K-Ar age determinations are presented for one of the largely unknown, Mesozoic ultramafic (lamproitic) occurrences of the Aldan Shield. Ultramafic, ultrapotassic rocks occur as isolated pipes or as dykes in alkaline complexes as the Yakokut complex. K-Ar dating of phlogopites from different ultramafic dyke rocks of Yakokut give cooling ages of 133.3 ± 1.3 Ma. These rocks generally contain olivine, clinopyroxene, phlogopite and spinel phenocrysts. Olivines are forsterite-rich (Fo86–94) and undeformed, suggesting that they are phenocrysts. The low Ti and Al contents of clinopyroxenes are close to those of lamproites. Phlogopite cores are rich in Al2O3 and TiO2 relative to the rims with two different zonation trends caused by distinct crystallization conditions after emplacement. Spinels are Ti-bearing magnetites and Ti-Al-magnesiochromites with high Cr/(Cr+Al) ratios (> 0.9), indicating their crystallization from a lamproitic melt.Geochemically, the rocks are ultrabasic — basic with high mg# values, low Ca, Al, Na and strong enrichments of Rb, Ba and K. Their CaO/Al2O3, Zr/Nb or Ba/Sr ratios indicate their lamproitic nature and origin in the subcontinental lithosphere of a depleted mantle source which had undergone metasomatic enrichment. As the rocks all show strong negative Nb anomalies and low Ti, Y and Yb contents, the enrichment is attributed to subduction zone fluids. The Sr-Nd-data (87Sr/86Sr0 0.70573−0.70605 ± 0.00003; ɛNd − 10.2 ± 0.7) indicate the origin by partial melting of a heterogeneous mantle source with relatively low Rb/Sr ratios and an early enrichment. The evolution model comprises a depletion of ‘basaltic elements’, leading to a harzburgitic source which was enriched by an early LREE contribution during the stabilization of the Archaean to Proterozoic Aldan Shield. It is further suggested that the Mesozoic northwesterly directed subduction of the Ochotsk-Chukotsk belt influenced the subcontinental lithosphere underneath the Aldan Shield, leading to the observed subduction-related signature of the Yakokut lamproites.

Purification and characterization of a nonpolymerizing long-pitch actin dimer

2006 ◽  
Vol 84 (5) ◽  
pp. 695-702 ◽  
Author(s):  
Braden Sweeting ◽  
John F. Dawson
Keyword(s):  
Critical Concentration ◽  
Dnase I ◽  
Actin Binding ◽  
Wild Type ◽  
Filamentous Actin ◽  
Rhodamine Phalloidin ◽  
Fold Reduction ◽  
Crystallization Conditions ◽  
Self Association ◽  
Pointed End

Atomic resolution structures of filamentous actin have not been obtained owing to the self-association of actin under crystallization conditions. Obtaining short filamentous actin complexes of defined lengths is therefore a highly desirable goal. Here we report the production and isolation of a long-pitch actin dimer employing chemical crosslinking between wild-type actin and Q41C/C374A mutant actin. The Q41C/C374A mutant actin possessed altered polymerization properties, with a 2-fold reduction in the rate of elongation and an increased critical concentration relative to wild-type actin. The Q41C/C374A mutant actin also displayed an increase in the IC50 for DNase I, a pointed-end actin-binding protein. The long-pitch dimer was bound by DNase I to prevent polymerization and purified. It was found that each actin dimer is bound by 2 DNase I molecules, 1 likely bound to each of the actin protomers. The long-pitch dimer bound by DNase I did not form short F actin structures, as assessed by the binding of rhodamine–phalloidin.

Chemical-physical constraints of the 2015 eruptive activity of Mt. Etna: new insights from thermo-barometry and geochemistry of olivine-hosted melt inclusions

2021 ◽  
Author(s):  
Pier Paolo Giacomoni ◽  
Federico Casetta ◽  
Virginia Valenti ◽  
Carmelo Ferlito ◽  
Gabriele Lanzafame ◽  
...  
Keyword(s):  
Melt Inclusions ◽  
New South ◽  
Basalt Magma ◽  
Feeding System ◽  
Physical Constraints ◽  
Eruptive Event ◽  
North East ◽  
Central Crater ◽  
Mt Etna ◽  
Crystallization Conditions

<p>The concomitant activation off all four summit craters of Mt. Etna during the December 2015 eruptive event allow us to investigate the chemical-physical crystallization conditions and magma dynamics in the shallower portion of the open-conduit feeding system. In this study, we discuss new petrological, geochemical and thermo-barometric data as well as the composition of major element and volatile content (H<sub>2</sub>O, CO<sub>2</sub>, F, Cl and S) of olivine-hosted melt inclusions from the explosive and effusive products emitted during the December 2015 eruptive event.</p><p>Results and rhyolite-MELTS thermodynamic modelling of mineral phase stability highlight the relatively shallow crystal equilibrium depth prior to the eruption ranging from 400-500 MPa for Central Crater and North East Crater, up to 200 MPa below the New South East Crater. The study of high-pressure and high-temperature homogenized olivine-hosted melt inclusions allowed us to identify the composition of the almost primary alkali-basalt magma (11.8 wt% MgO) containing up to 4.9 wt% and 8151 ppm of H<sub>2</sub>O and CO<sub>2 </sub>respectively. The results, together with those already reported for the previous paroxystic events of the 2011-2012 (Giacomoni et al., 2018), reinforce the model of a vertically extended feeding system and highlight that the activity at the New South East Crater was fed by a magma residing at significant shallower depth with respect to Central Craters and North East Crater, although all conduits are fed by a common deep (P = 530-440 MPa) basic magmatic refilling. Plagioclase stability model and dissolution and resorption textures confirm its dependence on H<sub>2</sub>O content, thus suggesting that further studies on the effect that flushing from fluids with different H<sub>2</sub>O/CO<sub>2</sub> ratio are needed in order to understand the eruption triggering mechanisms of paroxystic fountaining.</p><p> </p><p><strong>References</strong></p><p>Giacomoni P., Coltorti M., Mollo S., Ferlito C., Braiato M., Scarlato P. 2018. The 2011-2012 paroxysmal eruptions at Mt. Etna volcano: Insights on the vertically zoned plumbing system. JVGR 349, 370-391.</p>

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