24 research outputs found

    Physical Conditions and Star Formation Activity in the Intragroup Medium of Stephan's Quintet

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    New multi-band observations of the famous compact group of galaxies Stephan's Quintet (SQ) are presented and analyzed. These include far infrared (FIR) images at 60Ī¼m\mu m and 100Ī¼m\mu m (ISOPHOT C-100 camera), radio continuum images at 1.4 GHz (VLA B-array) and 4.86 GHz (VLA C-array), and long-slit optical spectrographs (Palomar 200"200" telescope). With these new data, we aim to learn more about the X-ray/radio ridge in the middle of the intragroup medium (IGM) and the IGM starburst SQ-A, both are likely to be caused by the high speed collision (āˆ¼900\sim 900 km sāˆ’1^{-1}) between the intruder galaxy NGC 7318b (v=5700v = 5700 km sāˆ’1^{-1}) and the IGM (v=6600v = 6600 km sāˆ’1^{-1}).Comment: 31 pages text, 17 figures. Accepted by ApJ. A PS file including all figures can be found in http://spider.ipac.caltech.edu/staff/cxu/preprints/sq/apj_sq.ps.g

    Oxygen and hydrogen isotopes at DSDP Leg 65 Holes

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    In order to provide information on the degree of alteration of the very young basaltic basement drilled on Leg 65 in the mouth of the Gulf of California, we have measured the oxygen isotopic composition of whole rocks and mineral separates. Considerable data already exist for older ocean crust, in particular for the deep holes drilled in the Atlantic Ocean on Deep Sea Drilling Project (DSDP) Legs 37, 45, 46, and 51-53. These data indicate that in all of these holes, which include crust as young as 3.5 m.y. old, a significant amount of alteration has taken place as the result of low-temperature interaction between basalt and seawater (cf. Muehlenbachs, 1977, 1980; Hoernes et al., 1978; Friedrichsen and Hoernes, 1980). It is therefore of interest to determine whether Leg 65 crust, which is only 0.5 to 1.5 m.y. old, has experienced a similar degree of alteration

    Trace element and isotopic (Sr, Nd, Pb, O) arguments for a mid-crustal origin of Pan-African garnet-bearing S-type granites from the Damara orogen (Namibia)

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    Geochronological data, major and trace element abundances, Nd and Sr isotope ratios, Ī“18O whole rock values and Pb isotope ratios from leached feldspars are presented for garnet-bearing granites (locality at Oetmoed and outcrop 10 km north of Omaruru) from the Damara Belt (Namibia). For the granites from outcrop 10 km Nā€² Omaruru, reversely discordant Uā€“Pb monazite data give 207Pb/235U ages of 511Ā±2 Ma and 517Ā±2 Ma, similar to previously published estimates for the time of regional high grade metamorphism in the Central Zone. Based on textural and compositional variations, garnets from these granites are inferred to be refractory residues from partial melting in the deep crust. Because Pā€“T estimates from these xenocrystic garnets are significantly higher (800Ā°C/9ā€“10 kbar) than regional estimates (700Ā°C/5 kbar), the monazite ages are interpreted to date the peak of regional metamorphism in the source of the granites. Smā€“Nd garnetā€“whole rock ages are between āˆ¼500 and āˆ¼490 Ma indicating the age of extraction of the granites from their deep crustal sources. For the granites from Oetmoed, both Smā€“Nd and Pbā€“Pb ages obtained on igneous garnets range from āˆ¼500 to āˆ¼490 Ma. These ages are interpreted as emplacement ages and are significantly younger than the previously proposed age of āˆ¼520 Ma for these granites based on Rb/Sr whole rock age determinations. Major and trace element compositions indicate that the granites are moderately to strongly peraluminous S-type granites. High initial 87Sr/86Sr ratios (>0.716), high Ī“18O values of >13.8ā€°, negative initial ĪµNd values between āˆ’4 and āˆ’7 and evolved Pb isotope ratios indicate formation of the granites by anatexis of mid-crustal rocks similar to the exposed metapelites into which they intruded. The large range of Pb isotope ratios and the lack of correlation between Pb isotope ratios and Nd and Sr isotope ratios indicate heterogeneity of the involved crustal rocks. Evidence for the involvement of isotopically highly evolved lower crust is scarce and the influence of a depleted mantle component is unlikely. The crustal heating events that produced these granites might have been caused by crustal thickening and thrusting of crustal sheets enriched in heat-producing elements. Very limited fluxing of volatiles from underthrust low- to medium-grade metasedimentary rocks may have also been a factor in promoting partial melting. Furthermore, delamination of the lithospheric mantle and uprise of hot mantle could have caused localized high-T regions. The presence of coeval A-type granites at Oetmoed that have been derived at least in part from a mantle source supports this model
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