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Meteoritic debris from the Transantarctic Mountains: evidence for a regional distribution
No full textAggregates 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 [1]. 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 [1] 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: [1] van Ginneken M. et al. 2010. Earth &
Planetary Science Letters 293:104–113. [2] Rochette P. et al.
2008. Proceedings of the National Academy of Sciences
105:18206–18211. [3] Folco L. et al. 2008. Geology 36:291–294.
[4] Folco L. et al. 2011. Geochimica et Cosmochimica Acta
75:2356-2360. [5] van Ginneken M. et al. 2011. Meteoritcs &
Planetary Science 46(Suppl.):A63. [6] Narcisi B. et al. 2007.
Geophysical Research Letters 34:L15502.1–L15502.5. [7]
Misawa K. et al. 2010. Earth & Planetary Science Letters
289:287–297.
Acknowledgements. Work supported by PNRA
(PEA2009/A2.08 project, P.I.: LF)
124 new meteorite finds from the blue ice fields in the Rennick Glacier and David Glacier regions and the discovery of a new type of micrometeorite trap on top of Frontier Mountain
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Chondritic micrometeorites from the Transantarctic Mountains
No full textOn the basis of morphological and petrographic characteristics, eight "giant" unmelted micrometeorites in the 300-1100μm size range were selected from the Transantarctic Mountain micrometeorite collection, Victoria Land, Antarctica. Mineralogical and geochemical data obtained by means of scanning electron microscopy, electron probe microanalyses, and synchrotron X-ray diffraction allow their classification as chondritic micrometeorites. The large size of the micrometeorites increases considerably the amount of mineralogical and geochemical information compared to micrometeorites in smaller size fractions, therefore allowing a better definition of their parent material. A large variety of material is observed: five micrometeorites are related to unequilibrated and equilibrated ordinary chondrite, one to CV chondrite, one to CM chondrite, and one to CI chondrite parent materials. Besides reporting the first occurrence of a CV-like micrometeorite, our study shows that the abundance of chondritic material supports observations from recent studies on cosmic spherules that a large part of the micrometeorite flux in this size range is of asteroidal origin
Sahara 03505 sulfide-rich iron meteorite: evidence for efficient segregation of sulfide-rich metallic melt during high-degree impact melting of an ordinary chondrite
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