TY  - JOUR
A1  - Tubiana, C.
A1  - Rinaldi, G.
A1  - Guettler, C.
A1  - Snodgrass, C.
A1  - Shi, X.
A1  - Hu, X.
A1  - Marschall, R.
A1  - Fulle, M.
A1  - Bockeele-Morvan, D.
A1  - Naletto, G.
A1  - Capaccioni, F.
A1  - Sierks, H.
A1  - Arnold, G.
A1  - Barucci, M. A.
A1  - Bertaux, J-L
A1  - Bertini, I
A1  - Bodewits, D.
A1  - Capria, M. T.
A1  - Ciarniello, M.
A1  - Cremonese, G.
A1  - Crovisier, J.
A1  - Da Deppo, V
A1  - Debei, S.
A1  - De Cecco, M.
A1  - Deller, J.
A1  - De Sanctis, M. C.
A1  - Davidsson, B.
A1  - Doose, L.
A1  - Erard, S.
A1  - Filacchione, G.
A1  - Fink, U.
A1  - Formisano, M.
A1  - Fornasier, S.
A1  - Gutierrez, P. J.
A1  - Ip, W-H
A1  - Ivanovski, S.
A1  - Kappel, David
A1  - Keller, H. U.
A1  - Kolokolova, L.
A1  - Koschny, D.
A1  - Krueger, H.
A1  - La Forgia, F.
A1  - Lamy, P. L.
A1  - Lara, L. M.
A1  - Lazzarin, M.
A1  - Levasseur-Regourd, A. C.
A1  - Lin, Z-Y
A1  - Longobardo, A.
A1  - Lopez-Moreno, J. J.
A1  - Marzari, F.
A1  - Migliorini, A.
A1  - Mottola, S.
A1  - Rodrigo, R.
A1  - Taylor, F.
A1  - Toth, I
A1  - Zakharov, V
T1  - Diurnal variation of dust and gas production in comet 67P/Churyumov-Gerasimenko at the inbound equinox as seen by OSIRIS and VIRTIS-M on board Rosetta
JF  - Astronomy and astrophysics : an international weekly journal
N2  - Context. On 27 April 2015, when comet 67P/Churyumov-Gerasimenko was at 1.76 au from the Sun and moving toward perihelion, the OSIRIS and VIRTIS-M instruments on board the Rosetta spacecraft simultaneously observed the evolving dust and gas coma during a complete rotation of the comet. Aims. We aim to characterize the spatial distribution of dust, H2O, and CO2 gas in the inner coma. To do this, we performed a quantitative analysis of the release of dust and gas and compared the observed H2O production rate with the rate we calculated using a thermophysical model. Methods. For this study we selected OSIRIS WAC images at 612 nm (dust) and VIRTIS-M image cubes at 612 nm, 2700 nm (H2O emission band), and 4200 nm (CO2 emission band). We measured the average signal in a circular annulus to study the spatial variation around the comet, and in a sector of the annulus to study temporal variation in the sunward direction with comet rotation, both at a fixed distance of 3.1 km from the comet center. Results. The spatial correlation between dust and water, both coming from the sunlit side of the comet, shows that water is the main driver of dust activity in this time period. The spatial distribution of CO2 is not correlated with water and dust. There is no strong temporal correlation between the dust brightness and water production rate as the comet rotates. The dust brightness shows a peak at 0 degrees subsolar longitude, which is not pronounced in the water production. At the same epoch, there is also a maximum in CO2 production. An excess of measured water production with respect to the value calculated using a simple thermophysical model is observed when the head lobe and regions of the southern hemisphere with strong seasonal variations are illuminated (subsolar longitude 270 degrees-50 degrees). A drastic decrease in dust production when the water production (both measured and from the model) displays a maximum occurs when typical northern consolidated regions are illuminated and the southern hemisphere regions with strong seasonal variations are instead in shadow (subsolar longitude 50 degrees-90 degrees). Possible explanations of these observations are presented and discussed.
KW  - comets: general
KW  - comets: individual: 67P/Churyumov-Gerasimenko
KW  - methods: data analysis
Y1  - 2019
U6  - https://doi.org/10.1051/0004-6361/201834869
SN  - 1432-0746
VL  - 630
PB  - EDP Sciences
CY  - Les Ulis
ER  - 
TY  - JOUR
A1  - Halama, Ralf
A1  - Konrad-Schmolke, Matthias
A1  - Sudo, Masafumi
A1  - Marschall, Horst R.
A1  - Wiedenbeck, Michael
T1  - Effects of fluid-rock interaction on Ar-40/Ar-39 geochronology in high-pressure rocks (Sesia-Lanzo Zone, Western Alps)
JF  - Geochimica et cosmochimica acta : journal of the Geochemical Society and the Meteoritical Society
N2  - In situ UV laser spot Ar-40/Ar-39 analyses of distinct phengite types in eclogite-facies rocks from the Sesia-Lanzo Zone (Western Alps, Italy) were combined with SIMS boron isotope analyses as well as boron (B) and lithium (Li) concentration data to link geochronological information with constraints on fluid-rock interaction. In weakly deformed samples, apparent Ar-40/Ar-39 ages of phengite cores span a range of similar to 20 Ma, but inverse isochrons define two distinct main high-pressure (HP) phengite core crystallization periods of 88-82 and 77-74 Ma, respectively. The younger cores have on average lower B contents (similar to 36 mu g/g) than the older ones (similar to 43-48 mu g/g), suggesting that loss of B and resetting of the Ar isotopic system were related. Phengite cores have variable delta B-11 values (-18 parts per thousand to -10 parts per thousand), indicating the lack of km scale B homogenization during HP crystallization.
 Overprinted phengite rims in the weakly deformed samples generally yield younger apparent Ar-40/Ar-39 ages than the respective cores. They also show variable effects of heterogeneous excess 40 Ar incorporation and Ar loss. One acceptable inverse isochron age of 77.1 +/- 1.1 Ma for rims surrounding older cores (82.6 +/- 0.6 Ma) overlaps with the second period of core crystallization. Compared to the phengite cores, all rims have lower B and Li abundances but similar delta B-11 values (-15 parts per thousand to -9 parts per thousand), reflecting internal redistribution of B and Li and internal fluid buffering of the B isotopic composition during rim growth. The combined observation of younger Ar-40/Ar-39 ages and boron loss, yielding comparable values of both parameters only in cores and rims of different samples, is best explained by a selective metasomatic overprint. In low permeability samples, this overprint caused recrystallization of phengite rims, whereas higher permeability in other samples led to complete recrystallization of phengite grains.
 Strongly deformed samples from a several km long, blueschist-facies shear zone contain mylonitic phengite that forms a tightly clustered group of relatively young apparent Ar-40/Ar-39 ages (64.7-68.8 Ma), yielding an inverse isochron age of 65.0 +/- 3.0 Ma. Almost complete B and Li removal in mylonitic phengite is due to leaching into a fluid. The B isotopic composition is significantly heavier than in phengites from the weakly deformed samples, indicating an external control by a high-delta B-11 fluid (delta B-11 = + 7 +/- 4 parts per thousand). We interpret this result as reflecting phengite recrystallization related to deformation and associated fluid flow in the shear zone. This event also caused partial resetting of the Ar isotope system and further B loss in more permeable rocks of the adjacent unit. We conclude that geochemical evidence for pervasive or limited fluid flow is crucial for the interpretation of Ar-40/Ar-39 data in partially metasomatized rocks.
Y1  - 2014
U6  - https://doi.org/10.1016/j.gca.2013.10.023
SN  - 0016-7037
SN  - 1872-9533
VL  - 126
SP  - 475
EP  - 494
PB  - Elsevier
CY  - Oxford
ER  -