Abstract
The Himalia Ridge Formation (Fossil Bluff Group), Alexander Island is a 2.2-km-thick sequence of Upper Jurassic-Lower Cretaceous conglomerates, sandstones and mudstones, derived from an andesitic volcanic arc and deposited in a fore-arc basin. The metamorphic and thermal history of the formation has been determined using authigenic mineral assemblages and vitrinite reflectance measurements. Metamorphic effects include compaction, pore-space reduction, cementation and dissolution and replacement of detrital grains by clay minerals (smectite, illite/smectite, corrensite and kaolinite), calcite, chlorite, laumontite, prehnite, pumpellyite, albite and mica, with less common quartz, haematite, pyrite and epidote. The authigenic mineral assemblages exhibit a depth-dependence, and laumontite and calcite exhibit a strong antipathetic relationship. Detrital organic matter in the argillaceous layers has vitrinite reflectance values (R-o) ranging from 2.3 to 3.7%. This indicates considerable thermal maturation, with a systematic increase in reflectivity with increasing depth. There is good correlation of metamorphic mineral assemblages with chlorite crystallinity and vitrinite reflectance values-all indicating temperatures in the range of 140 +/- 20degreesC at the top of the sequence to 250 +/- 10degreesC at the base of the sequence. The temperatures suggest a geothermal gradient of 36-64degreesC/km and a most likely gradient of 50degreesC/km. It is suggested that this higher-than-average gradient for a fore-arc basin resulted either from rifting during basin formation or from a late-stage arc migration event.
Original language | English |
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Pages (from-to) | 1453-1465 |
Number of pages | 12 |
Journal | Journal of Petrology |
Volume | 45 |
Issue number | 7 |
DOIs | |
Publication status | Published - Feb 2004 |
Keywords
- Antarctica
- diagenesis
- fore-arc basin
- low-temperature metamorphism
- vitrinite reflectance
- ILLITE CRYSTALLINITY
- GEOTHERMAL GRADIENTS
- FACIES METAMORPHISM
- FISSION-TRACK
- PENINSULA
- SUBDUCTION
- EXPLORATION
- REFLECTANCE
- MODEL
- PLATE