Aggregates of microscopic meteoritic ablation spheres were discovered in the micrometeorite traps on top of Miller Butte, Victoria Land Transantarctic Mountains, during the 2006 Programma Nazionale di Ricerche in Antartide (PNRA) expedition . These traps consisting of joints and fractures on glacially eroded granitic surfaces filled by local detritus have been collecting micrometeorites by direct fall over the last ~1Ma [2, 3, 4]. Based on a homogeneous chondritic composition, [1, 5] proposed that the Transantarctic Mountain meteoritic ablation spheres resulted from a single major meteoritic event of carbonaceous chondrite parentage. Furthermore, [1, 5] provided petrographic and geochemical evidence for pairing the Transantarctic Mountain aggregates with the ~480 ka old extraterrestrial dust L2 and DF2691 layers found in the EPICA - Dome C and Dome Fuji ice cores, respectively [6, 7], and concluded that they document a continental-scale, Tunguska-like meteorite impact (aerial burst) over Antarctica ~480 ka ago of a 108 kg (or larger) fragment of a stony, primitive asteroid. During the 2009 PNRA expedition we extended the search for these microscopic meteoritic ablation spheres towards the Daniles Range, inland catchment of the middle Rennick Glacier, in order to verify their regional distribution. Several particles consisting of aggregates of microscopic spherules were found together with 100s of micrometeorites and Australasian microtektites in the fine-grained detritus (<800 μm) accumulated within a micrometeorite trap on top of Schroeder Spur (71°39′S, 160°19′E; 1800 m a.s.l.) ca. 130 km due north of Miller Butte. The spherulitic aggregates were studied under the SEM-EDS and by means of XRD. They consist of a porous aggregates of a myriad of quench-textured spherules, with individual spherules ranging from less than 1 μm to 50 μm in diameter. Dominant spherule types include dendritic magnesioferrite spherules plus microporphyritic olivine (Fa17) and magnesioferrite spherules. Aggregate cavities are encrusted by jarosite. Overall, the spherulitic aggregates from Schroeder Spur are identical to those from Miller Butte and represent the same meteoritic event. The Schroeder Spur finding documents the consistent occurrence of these meteoritc ablation spheres in the Victoria Land Transantarctic Mountains and supports the argument  of a continental-scale distribution of meteoritc debris associated with the airburst of a cosmic body several tens of meters in size which impacted the Earth’s atmosphere over Antarctica ~480 ka ago. References:  van Ginneken M. et al. 2010. Earth & Planetary Science Letters 293:104–113.  Rochette P. et al. 2008. Proceedings of the National Academy of Sciences 105:18206–18211.  Folco L. et al. 2008. Geology 36:291–294.  Folco L. et al. 2011. Geochimica et Cosmochimica Acta 75:2356-2360.  van Ginneken M. et al. 2011. Meteoritcs & Planetary Science 46(Suppl.):A63.  Narcisi B. et al. 2007. Geophysical Research Letters 34:L15502.1–L15502.5.  Misawa K. et al. 2010. Earth & Planetary Science Letters 289:287–297. Acknowledgements. Work supported by PNRA (PEA2009/A2.08 project, P.I.: LF).
|Titolo:||Meteoritic debris from the Transantarctic Mountains: evidence for a regional distribution|
|Anno del prodotto:||2012|
|Appare nelle tipologie:||1.5 Abstract in rivista|