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| 2. |
- Breitfeld, H. T., et al.
(författare)
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The onshore West Baram Delta deposits: Provenance and drainage in the Middle Miocene to Pliocene in NW Borneo and comparison to the Champion Delta
- 2023
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Ingår i: Marine and Petroleum Geology. - 0264-8172. ; 158
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Tidskriftsartikel (refereegranskat)abstract
- The Baram Delta province in NW Borneo forms a major hydrocarbon reservoir offshore northern Sarawak and Brunei. The delta sequence is thereby subdivided into the West Baram delta to the south and the Champion delta to the north. Onshore are the remains of the Neogene delta deposits exposed and provide the possibility to study the equivalent offshore successions in outcrop. This study focuses on the Neogene West Baram delta successions which were studied for sedimentological facies and provenance characteristics. The successions consist of the Lambir, Miri, Tukau, and the enigmatic southern Lambir/Belait-Sarawak formations. Deposition took place in various mixed-energy delta environments between the Langhian and early Pliocene. The sediments are all quartzrich and heavy minerals are dominated by ultra-stable zircon, rutile and tourmaline. Dominant detrital zircon age clusters are in the Early Cretaceous and Permian-Triassic. Based on light mineral petrography, heavy mineral assemblages, and detrital zircon U-Pb geochronology, all formations are interpreted as derived from multirecycled sources, likely the underlying Paleogene Rajang Group turbidites and the Oligocene to Lower Miocene Nyalau-Tatau delta deposits. Additionally, literature data of the Champion Delta and one sample from Labuan analysed for provenance in this study are used to demonstrate that the Champion Delta can be distinguished from the West Baram Delta by having higher chrome spinel and garnet contents and slightly different detrital zircon age populations. The Champion Delta deposits are interpreted as sourced by recycling of the Crocker Formation and older turbidites (e.g., Sapulut Formation) with potentially input from ultra-mafic basement rocks of Sabah.
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| 3. |
- Decree, S., et al.
(författare)
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In-situ trace element and Sr isotope signature of apatite: A new key to unravelling the genesis of polymetallic mineralisation in black shales of the Early Cambrian Niutitang Formation, Southern China
- 2022
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Ingår i: Ore Geology Reviews. - : Elsevier BV. - 0169-1368. ; 150
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Tidskriftsartikel (refereegranskat)abstract
- The Early Cambrian Mo-Ni-PGE sulphidic black shale in the Niutitang Formation on the margin of the Yangtze Craton (Southern China) is known for its extremely high metal concentrations. It is also very rich in phosphate that formed contemporaneously with the sulphides. Detailed petrological as well as in-situ trace element and Sr isotope analyses of authigenic apatite revealed new information on the metallogenesis of this enigmatic rock unit. In the ore bed, apatite forms nodules or is found in phosphatic (phoslithoclasts) and sulphide clasts. In the latter, the replacement of organic matter and sulphides by apatite microspherules suggests a microbially mediated phosphogenesis. Enrichment in middle rare earth elements emphasizes the role played by Fe-oxyhydroxides and organic matter in element scavenging. Moderately reducing conditions are supported by a lack of Ce and Eu anomalies. The trace element signature of apatite and its initial 87Sr/86Sr (0.7032-0.7190), which is -for a group of analyses -well below the signature of Lower Cambrian seawater, points to some contribution from mafic rock-sourced hydrothermal brines. This effectively explains the exceptional enrichment of Ni and PGE in the sulphides. Seawater remains, however, the preferred source for other elements such as P and Mo.
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| 4. |
- Jian, W., et al.
(författare)
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Late Triassic Au-Mo mineralization in the Xiaoqinling region and a genetic connection to carbonatitic magmatism
- 2022
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Ingår i: Ore Geology Reviews. - : Elsevier BV. - 0169-1368. ; 145
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Tidskriftsartikel (refereegranskat)abstract
- The southern margin of the North China craton hosts a number of quartz vein-style deposits of the unusual AuMo ore spectrum, including the Dahu deposit in the Xiaoqinling region. Pristine euhedral monazite and rutile crystals from the Dahu Au-Mo mineralized veins yield LA-ICP-MS weighted mean 206Pb/238U ages of 212.1 +/- 1.7 Ma (1 s, MSWD = 1.13) and 209.7 +/- 2.7 Ma (2 s, MSWD = 1.7), respectively. These ages point to a Late Triassic gold mineralization event in the Xiaoqinling region, aside from the regionally well-recognized Early Cretaceous gold mineralization event. Tectonic setting, mineral association, elemental and isotopic signatures, and fluid characteristics of the Dahu deposit suggest that the Late Triassic Au-Mo mineralization represents a carbonatiteassociated hydrothermal system, with ore fluids exsolved from a late-stage carbonatite system. Mineralogically, the Dahu deposit is enriched in hydrothermal minerals common to carbonatite systems, such as carbonates, sulfates, and REE minerals. Trace element and isotope compositions of vein minerals also show similarities to those of carbonatites. Monazite displays a pronounced LREE-enriched and smooth pattern (no Eu anomaly), with epsilon Nd(t) values ranging from -14.9 to -13.3. Rutile is characterized by high Nb concentrations (6 to 18 wt%) and extremely high Nb/Ta ratios of 236 to 2044. Fluid inclusions in the Dahu Au-Mo mineralized veins and the regionally distributed coeval carbonatites are all dominated by low to moderate salinity H2O-CO2 fluids that contain sulfates as trapped solids/daughter minerals. Our study suggests that the southern margin of the North China craton has potential for the exploration of polymetallic hydrothermal mineralization related to hidden carbonatites.
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| 5. |
- Richter, M., et al.
(författare)
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Assessment of Five Monazite Reference Materials for U-Th/Pb Dating Using Laser-Ablation ICP-MS
- 2019
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Ingår i: Geosciences. - : MDPI AG. - 2076-3263. ; 9:9
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Tidskriftsartikel (refereegranskat)abstract
- Monazite is a common accessory phosphate mineral that occurs under a wide range of pressure and temperature conditions in sedimentary, metamorphic and igneous rocks. Monazite contains high amounts of Th and U, rendering single monazite grains suitable for in-situ U-Th/Pb dating using laser ablation inductively-coupled mass spectrometry (LA-ICP-MS). Two key aspects of monazite dating that are critical for accurate age data with maximum precision are (i) optimized instrumental conditions to minimize analytical scatter and (ii) a well characterized reference material to ensure the accuracy of the obtained aged. Here, we analyzed five monazite reference materials (USGS 44069, 94-222, MAdel, Moacir and Thompson Mine Monazite) for their U-Th/Pb ages using LA-ICP-MS technique and applied a variety of laser spot diameters and repetition rates to find the best operational conditions to achieve accurate age data while maintaining maximum precision. We find that a spot diameter of 10 mu m and a repetition rate of 10 Hz yield the most precise ages with a deviation of +/- 2.0% from their respective high-precision U/Pb literature age data. Ages were reproduced in three different LA-ICP-MS laboratories using these parameters. Each reference material was tested for its suitability as a matrix-matched age reference material. For this, a rotating, iterative approach was adopted in which one reference monazite was used as calibration reference material against all others, which were treated as unknowns. The results reveal that USGS 44069, 94-222, Thompson Mine Monazite and MAdel all agree with their respective calculated ages and ID-TIMS reference ages and thus are suggested as suitable calibration reference materials. Moacir, however, appears slightly older than previously suggested (up to 4%), thus, caution is advised here when using Moacir as reference material for U-Th/Pb LA-ICP-MS dating in the absence of further absolute age calibration.
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| 6. |
- Rösel, Delia, et al.
(författare)
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Interpretation and significance of combined trace element and U–Pb isotopic data of detrital rutile: a case study from late Ordovician sedimentary rocks of Saxo-Thuringia, Germany
- 2019
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Ingår i: International journal of earth sciences. - : Springer Science and Business Media LLC. - 1437-3254 .- 1437-3262. ; 108:1, s. 1-25
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Tidskriftsartikel (refereegranskat)abstract
- The U–Pb age and trace element composition of detrital rutile provide information about the metamorphic history of the source region that cannot be constrained by traditional U–Pb dating of detrital zircon. Previous provenance investigations focussed on only one of these methods. Based on a large LA-ICP-MS trace element and U–Pb isotopic dataset of detrital rutile and U–Pb isotopic data of detrital zircon from late Ordovician sedimentary rocks of Saxo-Thuringia, Germany, this paper discusses the application and significance of combining these methods in provenance investigations. U–Pb age spectra from the detrital zircons analysed show multiple age components (multimodal age spectra) in all samples. This is in contrast with the detrital rutile data, as only one sample yielded a multimodal U–Pb age distribution. Multimodal age spectra of detrital rutile are most likely preserved in sediments from (large) catchment areas with complex geological histories. They may also be related to specific sedimentation events, such as glacial washout during the retreat of large ice shields (e.g. the Hirnantian glaciation of Gondwana). Unimodal age spectra are however not restricted to small catchment areas, if the provenance region is characterized by a pervasive thermal overprint such as the Pan-African orogeny throughout Gondwana. Unimodal age distributions may further consist of overlapping age cluster detectable by different trace element composition of the detrital rutile grains. The combined U–Pb age and trace element data from detrital rutile grains demonstrate that rutile sourced from metapelitic rocks yield reliable and precise U–Pb ages. In contrast, detrital rutile classified to be of metamafic origin generally has too low uranium concentrations to be dated reliably by LA-ICP-MS. Detrital rutile records low- to medium-grade metamorphic events in the source region and therefore has the potential to better constrain the maximum depositional age of sedimentary rocks in comparison to U–Pb dating of detrital zircon.
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| 7. |
- Rösel, Delia, et al.
(författare)
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LA-ICP-MS/MS Single-Spot Rb-Sr Dating
- 2022
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Ingår i: Geostandards and Geoanalytical Research. - : Wiley. - 1639-4488 .- 1751-908X. ; 46:2, s. 143-168
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Tidskriftsartikel (refereegranskat)abstract
- Due to developments in reaction cell technologies, it is now possible to collect large Rb-87/Sr-86 and Sr-87/Sr-86 data sets using LA-ICP-MS/MS. Until now, LA-ICP-MS/MS Rb-Sr ages were constrained using conventional isochrons on a contiguous set of Rb-Sr data. In this contribution, we present a straightforward procedure on how to measure, calculate and validate Rb-Sr ages from individual laser spots even from detrital grains devoid of context. This approach does not only allow provenance studies of detrital micas, but also furthermore opens the opportunity to produce age maps with unprecedented spatial resolution, both for zoned single crystals and targeting different textural domains. The main challenge for calculating single-spot Rb-Sr ages is the estimation of the initial Sr-87/Sr-86 composition, if it cannot be constrained through analysis of a paragenetic phase. In this case, we propose to use a range of geologically relevant initial Sr-87/Sr-86 compositions rather than one fixed value: (1) 0.703 +/- 0.003 (for mantle derived magmatic rocks), (2) 0.715 +/- 0.015 (for evolved magmatic rocks) and (3) 0.730 +/- 0.030 (for crustal rocks). Modelling shows that the Sr-87/Sr-86 ratio of the targeted material delineates the accuracy and precision of single-spot Rb-Sr ages. If the measured Sr isotopic composition is sufficiently radiogenic [Sr-87/Sr-86 of > 1.0 for scenario (1) to > 4.5 for scenario (3)], the calculated age and its uncertainty are not significantly influenced by the initial Sr-87/Sr-86 composition. Using Mica-Mg as the primary reference material, single-spot Rb-Sr dating was tested on biotite (Mount Dromedary, La Posta, McClure Mountain), muscovite (Hogsbo) and a nano-powder tablet (Mica-Fe) that we further propose using as secondary reference materials for Rb-Sr geochronology.
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| 8. |
- Sorokina, E. S., et al.
(författare)
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Sapphire-bearing magmatic rocks trace the boundary between paleo-continents: A case study of Ilmenogorsky alkaline complex, Uralian collision zone of Russia
- 2021
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Ingår i: Gondwana Research. - : Elsevier BV. - 1342-937X. ; 92, s. 239-252
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Tidskriftsartikel (refereegranskat)abstract
- Metamorphic gem corundum (mainly ruby) deposits are robust indicators of continent-continent collision processes. However, a systematic link of primary magmatic blue sapphire occurrences to orogenic belts is less understood. An example is the Ilmenogorsky alkaline complex, within the Ilmen Mountains region and part of the Uralian orogenic belt. The mobile belt is a product of the collision among Kazakhstania, Laurussia, and Siberia continents prior to the closure of the Paleo-Uralian ocean and formation of the Laurasia supercontinent (330-250 Ma). It is believed that the alkaline complex became included into the separate SysertskIlmenogorsk microcontinent with unconstrained borders, when sandwiched between Kazakhstania and Laurussia during that collision. Paleo-reconstructions illustrate that magmatic and metasomatic sapphire deposits linked to alkaline magmatism trace the natural boundary of the "lost" microcontinent with a high precision. The syenite pegmatites of alkaline complex carried unusually large corundum-blue sapphire megacrysts that have recorded the multi-stage development of the Ilmenogorsky complex. The deposits were formed at about 275-295 Ma ago as reconstructed by in situ LA-ICP-MS U-Pb zircon dating. This formation stage corresponds to a broader continental collision process followed by the formation of Uralian orogeny in the area of the Ilmenogorsky complex. One pegmatite deposit, the "298" mine, is characterized by the occurrence of unusually large corundum megacrysts. The analyses of Rb-Sr isotopic system in the rocks from this deposit revealed two isochrons at 249 +/- 2 Ma and 254 +/- 22 Ma implying a late stage modification of original pegmatites. The timing of this stage corresponds to the limited post-collision stretching time. Hence, corundum-blue sapphire studied from magmatic (syenites) and metasomatic rocks linked to alkaline rocks in Uralian orogen suggests as a promising indicator for constraining the timing of continent-to-continent collision processes. (c) 2021 International Association for Gondwana Research. Published by Elsevier B.V. All rights reserved.
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