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Genesis of carbonate concretions in the Western Carpathian Keuper shale
Goldschmidt Conference Abstracts 2006
Himalayan evolutionary models: Constraints from Eocene–Miocene granitoid bodies 1
1,2
A.B. AIKMAN , T.M. HARRISON , D. LING
3
1
Research School of Earth Science, The Australian National University, Australia ([email protected]) 2 Department of Earth and Space Sciences, University of California, Los Angeles, USA ([email protected]) 3 Institute of Tibetan Plateau Research, Chinese Academy of Science, China ([email protected]) Orogenic reconstructions depend on adequate knowledge of the spatial and temporal associations between processes, structures and lithotectonic units. However, the present gamut of Himalayan evolutionary models may be biased by the paucity of data from the ca. 55 to 25 Ma period following the initiation of collision, the lack of constraints on the structural assembly of many parts of the orogenic zone, and traditional focus on the frontal parts of the High Himalaya. The record of granitoid magmatism preserved in the eastern North Himalaya and southern Tibetan plateau places important new constraints on the time-dependent structural architecture and locus of tectonic activity in the Himalaya since at least the mid-Eocene. Combined geochronological, geochemical and thermometric studies of undeformed Eocene granitoid plutons emplaced into Tethyan metasediments at 92 °E (the Dala granites) constrain the timing of deformation in the structurally highest (and inferred earliest accreted units of the Himalayan fold and thrust belt) to be older than 45 Ma. A similar study of nearby Miocene granites (the Yala-Xiangbo granites) provides further insight into subsequent reorganisation of the Himalayan thrust system and the formation of the north Himalayan gneiss domes (NHG). Petrogenesis of both suites, combined with documented evidence for essentially continuous arc-type magmatism along the southern margin of Eurasia, argue strongly against underthrusting of Indian lithosphere beneath southern Tibet, either as a means of thickening the crust or providing insulation to promote development of a weak mid-crustal layer. This study demonstrates the integrated application of geochemistry, geochronology and structural geology in probing the time-dependent structural evolution of an active orogenic zone. doi:10.1016/j.gca.2006.06.024
A5
Genesis of carbonate concretions in the Western Carpathian Keuper shale A.I. AL-JUBOURY Research Center for Dams and Water Resources, Mosul University, Iraq ([email protected]) Mineralogical and chemical investigations of carbonate concretions of the Upper Triassic Carpathian Keuper shale, Slovakia, were investigated to verify their genesis. These concretions are commonly distributed as red, violet calcite concretions in red hosted shale or as nodular yellowish brown dolomite concretions in red and green hosted shale. Generally, they are of spherical to ovate shapes and range 2–15 cm in size. Septarian calcite veins (0.1– 0.5 cm wide) are found in some of these concretions (see figure, left). The veins die out towards the margin of concretion; some concretions are enclosed by concentric shell along the margin.
Microscopic description of these concretions revealed that calcite is the main mineral and forming the micritic groundmass. Micrite recrystallization into microspar and pseudospar is also common. Sometimes scattered dolomite rhombs are also present. Other materials of the concretions include, fine quartz grains, feldspars mainly are sericitized, clayey materials, and some rubbish fragments of shale. Iron oxides and hydroxides are abundant and commonly they form rounded limonitic pebbles or finely disseminated grains. The surrounding rim is varied in thickness, the thicker part is of calcite enclosed cryptocrystalline silica (see figure, right). XRD analysis of the bulk samples of some concretions shows the presence of calcite and/or dolomite, quartz, chlorite illite and/or mica and kaolinite. The ratio of calcite and dolomite and the amount of insoluble residues (see table) revealed the dominance of calcite in the concretions of the Keuper shale from the Klippen belt, whereas dolomite is the main mineralogical component for those concretions from the High and Low Tatra Keuper. Sample location/No.
CaCO3 (%)
CaMg(CO3)2 (%)
Insoluble residues
Klippen belt/4 Klippen belt/8 High Tatra/39 Low Tatra/5
39.9 62.3 1.4 0.9
13.5 11.8 66.1 69.3
46.6 25.9 32.5 29.8
The studied concretions were most probably formed before the compaction of the hosted shale, that is, early diagenetic or penecontemporaneous in origin. doi:10.1016/j.gca.2006.06.025
Himalayan evolutionary models: Constraints from Eocene–Miocene granitoid bodies 1
1,2
A.B. AIKMAN , T.M. HARRISON , D. LING
3
1
Research School of Earth Science, The Australian National University, Australia ([email protected]) 2 Department of Earth and Space Sciences, University of California, Los Angeles, USA ([email protected]) 3 Institute of Tibetan Plateau Research, Chinese Academy of Science, China ([email protected]) Orogenic reconstructions depend on adequate knowledge of the spatial and temporal associations between processes, structures and lithotectonic units. However, the present gamut of Himalayan evolutionary models may be biased by the paucity of data from the ca. 55 to 25 Ma period following the initiation of collision, the lack of constraints on the structural assembly of many parts of the orogenic zone, and traditional focus on the frontal parts of the High Himalaya. The record of granitoid magmatism preserved in the eastern North Himalaya and southern Tibetan plateau places important new constraints on the time-dependent structural architecture and locus of tectonic activity in the Himalaya since at least the mid-Eocene. Combined geochronological, geochemical and thermometric studies of undeformed Eocene granitoid plutons emplaced into Tethyan metasediments at 92 °E (the Dala granites) constrain the timing of deformation in the structurally highest (and inferred earliest accreted units of the Himalayan fold and thrust belt) to be older than 45 Ma. A similar study of nearby Miocene granites (the Yala-Xiangbo granites) provides further insight into subsequent reorganisation of the Himalayan thrust system and the formation of the north Himalayan gneiss domes (NHG). Petrogenesis of both suites, combined with documented evidence for essentially continuous arc-type magmatism along the southern margin of Eurasia, argue strongly against underthrusting of Indian lithosphere beneath southern Tibet, either as a means of thickening the crust or providing insulation to promote development of a weak mid-crustal layer. This study demonstrates the integrated application of geochemistry, geochronology and structural geology in probing the time-dependent structural evolution of an active orogenic zone. doi:10.1016/j.gca.2006.06.024
A5
Genesis of carbonate concretions in the Western Carpathian Keuper shale A.I. AL-JUBOURY Research Center for Dams and Water Resources, Mosul University, Iraq ([email protected]) Mineralogical and chemical investigations of carbonate concretions of the Upper Triassic Carpathian Keuper shale, Slovakia, were investigated to verify their genesis. These concretions are commonly distributed as red, violet calcite concretions in red hosted shale or as nodular yellowish brown dolomite concretions in red and green hosted shale. Generally, they are of spherical to ovate shapes and range 2–15 cm in size. Septarian calcite veins (0.1– 0.5 cm wide) are found in some of these concretions (see figure, left). The veins die out towards the margin of concretion; some concretions are enclosed by concentric shell along the margin.
Microscopic description of these concretions revealed that calcite is the main mineral and forming the micritic groundmass. Micrite recrystallization into microspar and pseudospar is also common. Sometimes scattered dolomite rhombs are also present. Other materials of the concretions include, fine quartz grains, feldspars mainly are sericitized, clayey materials, and some rubbish fragments of shale. Iron oxides and hydroxides are abundant and commonly they form rounded limonitic pebbles or finely disseminated grains. The surrounding rim is varied in thickness, the thicker part is of calcite enclosed cryptocrystalline silica (see figure, right). XRD analysis of the bulk samples of some concretions shows the presence of calcite and/or dolomite, quartz, chlorite illite and/or mica and kaolinite. The ratio of calcite and dolomite and the amount of insoluble residues (see table) revealed the dominance of calcite in the concretions of the Keuper shale from the Klippen belt, whereas dolomite is the main mineralogical component for those concretions from the High and Low Tatra Keuper. Sample location/No.
CaCO3 (%)
CaMg(CO3)2 (%)
Insoluble residues
Klippen belt/4 Klippen belt/8 High Tatra/39 Low Tatra/5
39.9 62.3 1.4 0.9
13.5 11.8 66.1 69.3
46.6 25.9 32.5 29.8
The studied concretions were most probably formed before the compaction of the hosted shale, that is, early diagenetic or penecontemporaneous in origin. doi:10.1016/j.gca.2006.06.025