@article{ReimoldFischerMuelleretal.2015,
  author    = {Reimold, Wolf Uwe and Fischer, Luise and M{\"u}ller, Jan and Kenkmann, Thomas and Schmitt, Ralf-Thomas and Altenberger, Uwe and Kowitz, Astrid},
  title     = {Impact-generated pseudotachylitic breccia in drill core BH-5 Hattberg, Siljan impact structure, Sweden},
  series = {GFF},
  volume    = {137},
  journal   = {GFF},
  number    = {2},
  publisher = {Routledge, Taylor \& Francis Group},
  address   = {Abingdon},
  issn      = {1103-5897},
  doi       = {10.1080/11035897.2015.1015264},
  pages     = {141 -- 162},
  year      = {2015},
  abstract  = {Pseudotachylitic breccia (PTB) in the form of cm-wide melt breccia veinlets locally occurs on the exposed central uplift of the 380Ma Siljan impact structure. The host rock to the PTBs is the so-called Jarna granite of quartz monzonitic to syenodioritic composition. The nearly 603m long BH-5 drill core from Hattberg, near the centre of the Siljan central uplift, contains numerous veins and pods of PTB. In particular, two major zones of 60m combined width contain extensive PTB network breccias (30\% actual melt breccia component), with individual melt breccia occurrences up to >1m in length. Core logging and petrographic and geochemical analysis of the core have been performed, and the data are interpreted to suggest the following. (1) The impact event caused low to moderate (at essentially <20GPa) shock deformation in the host rock and in clasts of this lithology within the PTB. (2) Macroscopic deformation of the basement mainly comprises fracturing, with only localised cataclasis. (3) No evidence for shock melting (i.e. compression/decompression melting early in the cratering process) could be observed. (4) Optical and scanning electron microscopy showed that dark PTB contains a definite melt component. (5) Shearing has significantly affected this part of the central uplift, but its effects are limited to very short displacements and likely did not result in extensive melting. (6) A frictional heating component upon melt generation can, however, not be excluded, as many PTB samples contain clasts of a mafic (gabbroic) component, although only in one place along the entire core, a 1.2cm-wide section through such material in direct contact to host rock was observed. Consequently, we suggest that, upon uplift in the central part of the impact structure, considerable melt volumes were generated locally, especially in areas that had been affected by extensive cataclasis and where grain size comminution favoured melt formation. Rapid decompression related to central uplift formation is the preferred process for the generation of the PTB melt breccias.},
  language  = {en}
}
@article{FritzTagleAshworthetal.2016,
  author    = {Fritz, Joerg and Tagle, Roald and Ashworth, Luisa and Schmitt, Ralf Thomas and Hofmann, Axel and Luais, Beatrice and Harris, Phillip D. and Hoehnel, Desiree and {\"O}zdemir, Seda and Mohr-Westheide, Tanja and Koeberl, Christian},
  title     = {Nondestructive spectroscopic and petrochemical investigations of Paleoarchean spherule layers from the ICDP drill core BARB5, Barberton Mountain Land, South Africa},
  series = {Quaestiones geographicae},
  volume    = {51},
  journal   = {Quaestiones geographicae},
  publisher = {Wiley-Blackwell},
  address   = {Hoboken},
  issn      = {1086-9379},
  doi       = {10.1111/maps.12736},
  pages     = {2441 -- 2458},
  year      = {2016},
  abstract  = {A Paleoarchean impact spherule-bearing interval of the 763 m long International Continental Scientific Drilling Program (ICDP) drill core BARB5 from the lower Mapepe Formation of the Fig Tree Group, Barberton Mountain Land (South Africa) was investigated using nondestructive analytical techniques. The results of visual observation, infrared (IR) spectroscopic imaging, and micro-X-ray fluorescence (lXRF) of drill cores are presented. Petrographic and sedimentary features, as well as major and trace element compositions of lithologies from the micrometer to kilometer-scale, assisted in the localization and characterization of eight spherule-bearing intervals between 512.6 and 510.5 m depth. The spherule layers occur in a strongly deformed section between 517 and 503 m, and the rocks in the core above and below are clearly less disturbed. The lXRF element maps show that spherule layers have similar petrographic and geochemical characteristics but differences in (1) sorting of two types of spherules and (2) occurrence of primary minerals (Ni-Cr spinel and zircon). We favor a single impact scenario followed by postimpact reworking, and subsequent alteration. The spherule layers are Al2O3-rich and can be distinguished from the Al2O3-poor marine sediments by distinct Al-OH absorption features in the short wave infrared (SWIR) region of the electromagnetic spectrum. Infrared images can cover tens to hundreds of square meters of lithologies and, thus, may be used to search for Al-OH-rich spherule layers in Al2O3-poor sediments, such as Eoarchean metasediments, where the textural characteristics of the spherule layers are obscured by metamorphism.},
  language  = {en}
}