Os and Hf isotopes in mantle xenoliths from Southern Patagonia: Evidence for Proterozoic SCLM fragments.

MUNDL, A.; NTAFLOS, TH.; ACKERMAN, L.; BIZIMIS, M.; BJERG, E. A.

Beni-Bousera

Conferencia; 6th Orogenic Lherzolite Conference; 2014

Geosciences Montpellier, France

Mantle xenoliths transported to the surface by alkali basalts from 6 different outcrops in Santa Cruz Province, Southern Patagonia were studied with focus on their petrography, whole rock and mineral chemistry, as well as their Re-Os and Lu-Hf isotopic compositions. The sample suite collected at Don Camilo, Gobernador Gregores, Tres Lagos and within the Pali Aike Volcanic Field (PAVF) ? Salsa, El Ruido and Potrok Aike - comprises sp-lherzolites, sp-harzburgites, one sp-dunite and exclusively within PAVF also sp-gt-lherzolites and sp-gt-harzburgites. Whole rock Al2O3 and CaO contents range from 0.63 to 3.54 wt.% and 0.24 to 3.44 wt.%, respectively and exhibit a linear correlation with MgO ranging from 39.2 to 49 wt.%. Mineral analyses reveal Fo and NiO contents in Ol between 89.4 and 92.2 and 0.38 and 0.44 wt.%, respectively. Cpx are mainly Cr-Diopsides with Mg#*100 between 89.7 and 94.4,compositions of En47-53Fs3-6Wo43-50 and Cr2O3 and TiO2 contents in the range 0.71 to 1.62 wt.% and 0.04 and 0.88 wt.%, respectively. Opx with composition En89-91Fs8-10Wo0.7-2.3 have Mg#*100, Cr2O3 and TiO2 contents between 90.1 and 92.6, 0.23 and 0.85 wt.% and 0.01 and 0.25 wt.%, respectively. Cr#*100 and Mg#*100 in sp range from 6.5 to 56.1 and 57.2 to 77.5, respectively. Gt in PAVF sp-gt-peridotites is pyrope with compositions Alm13-16Py71-74Spess0.6-0.7Gross11-13 and Cr2O3 contents between 1.18 and 1.64 wt.%. The Re-Os isotopic system provides information on the potential formation age of SCLM domains.