Composition and provenance of the Lilljeborgfjellet Conglomerate Haakon VII Land, Spitsbergen
AbstractThe Siktefjellet Group of late Silurian or early Devonian age, consisting of the Lilljeborgfjellet Conglomerate and the overlying Siktefjellet Sandstone, is generally accepted as the oldest part of the Old Red Sandstone in Spitsbergen. Most of the clasts of the conglomerate are only slightly rounded and consist of lithologies typical for the underlying basement. A minor component of quartz porphyry clasts is present; these are well-rounded, indicating a longer transport. The provenance of the quartz porphyry clasts is discussed in relation to the known outcrops of quartz porphyry in Svalbard, one occurring in the neighbourhood of the conglomerate, the other ones far away. The quartz porphyry in close proximity is younger than the Lilljeborgfjellet Conglomerate and therefore not a possible source rock. A close petrographic and geochemical comparison with the quartz porphyries at three localities in Nordaustlandet (150-200 km in easterly direction and of probable Grenvillian age) is presented showing many similarities, but enough differences to question their interrelationship. The porphyries of the Hornsund area (300 km in southerly direction and also of probable Grenvillian age) are found to be chemically and pctrographically distinctly different from the Lilljeborgfjellet clast porphyry. Metarhyolite reported from the Planclfjella and Har-kerbreen Groups in Ny Fricsland are not comparable with the clast porphyry. As no unquestionable source rock among the quartz porphyries is known in outcrop, the possibility of a hidden or completely eroded parent rock is considered.
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