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| 2. |
- Andersson, Joel B.H., et al.
(författare)
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U-Pb zircon-titanite-apatite age constraints on basin development and basin inversion in the Kiruna mining district, Sweden
- 2022
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Ingår i: Precambrian Research. - : Elsevier. - 0301-9268 .- 1872-7433. ; 372
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Tidskriftsartikel (refereegranskat)abstract
- To constrain the tectonothermal evolution of the type locality for iron oxide-apatite deposits, we have obtained U-Pb zircon, titanite, and apatite age data for the Kiruna mining district in northernmost Sweden. The results indicate that the host basin initiated in an overall extensional regime as indicated by the deposition of alluvial conglomerates and greywackes. A volcanic intercalation in a conglomerate unit northwest of the Luossavaara iron oxide-apatite deposit yields a U-Pb zircon age of 1887 ± 3 Ma representing the timing of the earliest Orosirian volcanism in the central Kiruna mining district coinciding with the onset of basin development. In-situ analysis of titanite on hydrothermally altered fracture planes within a cataclastic fault damage zone (c. 270 m from the fault core system associated to the Luossavaara iron oxide-apatite deposit) yields complex U-Pb data. Applying a strict discordance filter yields a 207Pb/206Pb age of 1889 ± 26 Ma. The age implies that the fault probably has a syn-volcanic origin and that syn-volcanic faults may have played an important role during iron ore emplacement. The mineralized basin was subsequently buried and metamorphosed under upper greenschist-facies conditions and later tectonically exhumed and cooled below the apatite closure temperature at 1805 ± 26 Ma indicated by apatite from the Nukutus iron oxide-apatite deposit. Basin inversion is temporally constrained by syn-tectonic titanite as part of sodic-calcic + Fe + Cl hydrothermal alteration along a brittle-ductile reverse shear zone to the east of the study area. Titanite grains that show sector and oscillatory zoning yield an age of 1812 ± 3 Ma, which we interpret as the onset of basin inversion. Homogeneous (relatively unzoned) titanite in the same sample yields an age of 1802 ± 8 Ma, tentatively indicating that the tectonothermal activity lasted up to c. 20 m.y.
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| 3. |
- Barnes, C. J., et al.
(författare)
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Using Th-U-Pb geochronology to extract crystallization ages of Paleozoic metamorphic monazite contaminated by initial Pb
- 2021
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Ingår i: Chemical Geology. - : Elsevier. - 0009-2541 .- 1872-6836. ; 582
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Tidskriftsartikel (refereegranskat)abstract
- Geochronology of Th-rich minerals is advantageous as it allows use of three isotopic systems (i.e., Pb-206/U-238, Pb-207/U-235, and Pb-208/Th-232) for accurate data assessment. The Pb-208/Th-232 system is especially advantageous in cases where the dated mineral includes an initial Pb component, as Pb-208/Th-232 is the least sensitive to the effects of initial Pb amongst the three systems. This benefit is demonstrated with monazite from a white mica schist of the Tsakkok Lens, Scandinavian Caledonides, where three distinct generations of Paleozoic monazite (Mnzsingle bondI, Mnz-II, Mnz-III) are recognized and dated using laser ablation inductively coupled mass spectrometry. The generations are interpreted to represent monazite crystallization in high-pressure conditions (Mnzsingle bondI), followed by lower-pressure monazite growth (Mnz-II), and likely dissolution-reprecipitation of the pre-existing monazite (Mnz-III). The results are compared in Tera-Wasserburg, Wetherill, and Th-U-Pb concordia space for each monazite generation. In both Tera-Wasserburg and Wetherill space, the data are all discordant and indicate an initial Pb component in the monazite. The trend and magnitude of discordance due to initial Pb in Mnz-I and Mnz-II is generally controlled by UO2 content of the monazite, with higher UO2 equating to greater radiogenic Pb and a dampening of the initial Pb effect, which is most prominent in the Pb-207/U-235 system. For the same generations, initial Pb discordance of Pb-206/U-238 versus Pb-208/Th-232 is less apparent due to the insensitivity of Pb-208/Th-232. Mnz-III does not follow the initial Pb trends, likely due to disturbance of the chemical and isotopic systems during recrystallization. Additional discordance in Mnz-I and Mnz-II, which is not related to initial Pb, is recognized and increases with actinide content. The additional discordance may be due to Pb-mobilization in Mnz-I and Mnz-II domains and is revealed when utilizing the( 208)Pb/Th-232 system due to its insensitivity to initial Pb effects. Consequently, relying only on the U-Pb systems can lead to significant initial Pb overcorrections in Tera-Wasserburg or Wetherill concordia space and to calculations of erroneously young concordia dates. The Th-U-Pb concordia method, incorporating all three systems, does not require an initial Pb correction and, therefore, can account for the additional discordance. The Th-U-Pb concordia dates are interpretated as accurate crystallization ages for Mnz-I (484.7 +/- 1.1 Ma, MSWD: 1.4) and Mnz-II (474.7 +/- 1.2 Ma, MSWD: 1.9). The timing for Mnz-III formation is not well-resolved as it formed via result of dissolution-reprecipitation of the pre-existing monazite, likely under lower amphibolite- to greenschist-facies conditions.
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| 4. |
- Barnes, Christopher J., et al.
(författare)
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Zircon and monazite reveal late Cambrian/early Ordovician partial melting of the Central Seve Nappe Complex, Scandinavian Caledonides
- 2022
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Ingår i: Contributions to Mineralogy and Petrology. - : Springer. - 0010-7999 .- 1432-0967. ; 177:9
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Tidskriftsartikel (refereegranskat)abstract
- The Seve Nappe Complex (SNC) comprises continental rocks of Baltica that were subducted and exhumed during the Caledonian orogeny prior to collision with Laurentia. The tectonic history of the central SNC is investigated by applying in-situ zircon and monazite (Th-)U-Pb geochronology and trace element analysis to (ultra-)high pressure (UHP) paragneisses in the Avardo and Marsfjallet gneisses. Zircons in the Avardo Gneiss exposed at Sippmikk creek exhibit xenocrystic cores with metamorphic rims. Cores show typical igneous REE profiles and were affected by partial Pb-loss. The rims have flat HREE profiles and are interpreted to have crystallized at 482.5 +/- 3.7 Ma during biotite-dehydration melting and peritectic garnet growth. Monazites in the paragneiss are chemically homogeneous and record metamorphism at 420.6 +/- 2.0 Ma. In the Marsfjallet Gneiss exposed near Kittelfjall, monazites exhibit complex zoning with cores enveloped by mantles and rims. The cores are interpreted to have crystallized at 481.6 +/- 2.1 Ma, possibly during garnet resorption. The mantles and rims provide a dispersion of dates and are interpreted to have formed by melt-driven dissolution-reprecipitation of pre-existing monazites until 463.1 +/- 1.8 Ma. Depletion of Y, HREE, and U in the mantles and rims compared to the cores record peritectic garnet and zircon growth. Altogether, the Avardo and Marsfjallet gneisses show evidence of late Cambrian/early Ordovician partial melting (possibly in (U)HP conditions), Middle Ordovician (U)HP metamorphism, and late Silurian tectonism. These results indicate that the SNC underwent south-to-north oblique subduction in late Cambrian time, followed by progressive north-to-south exhumation to crustal levels prior to late Silurian continental collision.
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| 5. |
- Boethius, Adam, et al.
(författare)
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Assessing laser ablation multi-collector inductively coupled plasma mass spectrometry as a tool to study archaeological and modern human mobility through strontium isotope analyses of tooth enamel
- 2022
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Ingår i: Archaeological and Anthropological Sciences. - : Springer Science and Business Media LLC. - 1866-9557 .- 1866-9565. ; 14:5
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Tidskriftsartikel (refereegranskat)abstract
- To evaluate the possibility of obtaining detailed individual mobility data from archaeological teeth, the strontium isotope ratios on 28 human teeth from three separate Early-Mid Holocene, Swedish, foraging contexts (Norje Sunnansund, Skateholm and Västerbjers) were analysed through laser ablation. The teeth/individuals have previously been analysed using traditional bulk sampled thermal ionisation mass spectrometry. To validate the conclusions regarding the archaeological teeth, a tooth from a modern man with a known background was also analysed. The result shows that all of the teeth display less than 0.4% discrepancy between the mean values of the laser ablation profiles and the previously published bulk data and 25 (89%) of the teeth display less than a 0.2% discrepancy. By calculating linear and polynomial trendlines for each ablated tooth, it was possible to illustrate a strong correlation for the transition pattern between the measurements when following a chronological sequence from the tip to the cervix. Such correlations were not reproduced when the data sequence was randomized. The analyses show that the chronologically sequenced ablation data fit with a transition between local bioavailable strontium regions, that the measurements do not fluctuate between extremes and that their values are not caused by end-member mixing. This indicates an increasing data resolution when reducing strontium isotope ratio averaging time by minimizing the sampling area. The results suggest strontium incorporation in human teeth can be measured on an ordinal scale, with a traceable chronological order to enamel mineralization when sampled from tip to cervix at an equal distance from the surface. Micro-sampling enamel is considered a valid method to assess prehistoric, but not modern, human mobility; laser ablation technology increases the amount of information obtained from a single tooth while rendering minimal damage to the studied specimen.
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| 6. |
- Boethius, Adam, et al.
(författare)
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Diachronic forager mobility : untangling the Stone Age movement patterns at the sites Norje Sunnansund, Skateholm and Västerbjers through strontium isotope ratio analysis by laser ablation
- 2022
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Ingår i: Archaeological and Anthropological Sciences. - : Springer Science and Business Media LLC. - 1866-9557 .- 1866-9565. ; 14:9
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Tidskriftsartikel (refereegranskat)abstract
- Strontium isotope ratios in human teeth from the three Swedish prehistoric Stone Age hunter-fisher-gathering societies Norje Sunnansund (Maglemose), Skateholm (Ertebølle) and Västerbjers (Pitted Ware Culture) were analysed with laser ablation to produce data on both individual movement patterns and societal mobility trends. The analyses of teeth from both Skateholm and Västerbjers displayed homogeneous ratios and corresponding mobility patterns, while the data from Norje Sunnansund showed larger variances with heterogenous strontium ratios and varied inter-individual mobility patterns. Correlation with the bioavailable baseline suggests that the size of the geographical areas, where human strontium ratios could have originated, was roughly comparable for all three sites. The teeth measurements were reflected within a 50-km radius of the surrounding landscape and the 25–75% data quartile matched with distances between 3 and 30 km from the sites, suggesting limited mobility ranges among aquatically dependent foragers from southernmost Sweden. By applying ethnographic analogies and site-specific contextual inferences, the results suggest that mobility ranges at Norje Sunnansund were likely not delimited by neighbouring group territories. This changed over time and an increasing territorialisation of the landscape may have influenced movement patterns and caused restrictions to the foraging activities at both Skateholm and Västerbjers.
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| 7. |
- Boethius, Adam, et al.
(författare)
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Mesolithic Scandinavian foraging patterns and hunting grounds targeted through laser ablation derived 87Sr/86Sr ratios at the Early-Mid Holocene site of Huseby Klev on the west coast of Sweden
- 2022
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Ingår i: Quaternary Science Reviews. - : Elsevier BV. - 0277-3791 .- 1873-457X. ; 293
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Tidskriftsartikel (refereegranskat)abstract
- Mobility is one of the most fundamental aspects of a foraging society. Since prehistoric mobility is often difficult to identify in the archaeological record, our understanding is largely based on comparison with ethnographic communities. In recent years the application of 87Sr/86Sr isotope analysis has, however, greatly broadened our knowledge of mobility in the past. Despite this, few studies have been undertaken on faunal remains to explore their mobility patterns and infer human exploitation patterns with more precision. In this contribution we sampled 28 mammal teeth from three different occupation phases at the Early to Mid-Holocene coastal site of Huseby Klev, Sweden. We first established the local baseline for seven geographical areas in the region surrounding Huseby Klev. Then, by applying laser ablation-multi collector-inductively coupled plasma-mass spectrometry to the selected teeth, we identified the likely origins of a range of terrestrial and marine fauna, and the possible human mobility patterns required in their exploitation. Overall, our results demonstrate that the prehistoric communities inhabiting Huseby Klev undertook both short- and long-distance forays for the exploitation of particular species. By relating inferences on hunting grounds, derived from strontium isotope data, to zooarchaeological evidence from the site and ethnographic human mobility patterns, we establish and discuss the prerequisites for landscape utilization. Lastly, we demonstrate that glacial meltwater may have temporally affected the local oceanic Sr ratios – suggesting significantly increased soil and bedrock weathering may influence the Sr values in aquatic ecosystems and, consequently, should be considered in such regions and at times of melting glaciers. By applying the method to additional sites and assemblages in the future, our understanding of prehistoric mobility will be greatly enhanced.
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| 8. |
- Caton, Summer A., et al.
(författare)
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Evolution of the sources of TTG and associated rocks during the Archean from in-situ 87Sr/86Sr isotope analysis of apatite by LA-MC-ICPMS
- 2022
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Ingår i: Lithos. - : Elsevier BV. - 0024-4937 .- 1872-6143. ; 428-429
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Tidskriftsartikel (refereegranskat)abstract
- Radiogenic isotopes provide an important means towards elucidating Archean crustal evolution. The global Hf and Nd isotope record of Archean crustal fragments has been instrumental to unveiling the history of ancient crustal growth and differentiation. The Rb-Sr system could provide valuable complementary constraints in this regard, as this system is particularly sensitive to magmatic fractionation processes, and the chemical and isotopic evolution of magma sources. Application of this system has so far been complicated, however, by its susceptibility to isotope re-equilibration or alteration of the Rb/Sr parent-daughter ratio. In-situ Sr isotope analysis of primary igneous minerals with very low Rb/Sr, such as apatite, provides a new means to determine the initial 87Sr/86Sr (87Sr/86Sri) values for igneous rocks directly. In this study, we apply in-situ Sr isotope analysis of apatite by LA-MC-ICPMS to tonalite-trondhjemite-granodiorite (TTG) rocks and end-member sanukitoids from Archean cratons worldwide. The 87Sr/86Sri values of sanukitoids are relatively radiogenic, supporting the model in which such rocks are formed by flux melting of a mantle strongly enriched by metasomatism, possibly by slab-derived fluids. The 87Sr/86Sri values for TTGs formed between 3.72 and 3.45 Ga are generally radiogenic, indicating aged amphibolite sources. The 87Sr/86Sri values of younger TTGs are systematically lower and were derived from mafic sources that had an average age of ≤0.2 Gyr. This evolution matches with observations from Hf isotopes for TTGs of similar age and indicates a systematic change in the nature or efficiency of TTG crust formation during the Paleoarchean. In-situ Sr isotope analysis of apatite provides a useful method to uncover the Sr record of the early continental crust, and enables constraints on local source evolution and the general two-step evolutionary process of Archean crust formation.
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| 9. |
- Cutts, Jamie, et al.
(författare)
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Two‐Stage Cooling and Exhumation of Deeply Subducted Continents
- 2019
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Ingår i: Tectonics. - 0278-7407 .- 1944-9194.
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Tidskriftsartikel (refereegranskat)abstract
- The burial and exhumation of continental crust during collisional orogeny exert a strong controlon the dynamics of mountain belts and plateaus. Constraining the rates and style of exhumation of deeply buried crust has proven difficult due to complexities in the local geology and thermochronometric methods typically used. To advance this field, we applied trace‐element and U‐Pb laser ablation inductively coupled plasma mass spectrometry analyses to rutile from eclogite and amphibolite samples from the Western Gneiss Complex of Norway—an archetypal continental (ultra)high‐pressure (UHP) terrane. Peak temperature and timing of midcrustal cooling were constrained for samples collected along a subduction‐ and exhumation‐parallel transect, using Zr‐in‐rutile thermometry and U‐Pb rutile geochronology, respectively. Peak temperatures decrease from 830 °C in the UHP domain to 730 °C at the UHP‐HP transition, remain constant at 730 °C across most of the terrane, and decrease to 620 °C at the eclogite‐out boundary. U‐Pb results show that most of the terrane cooled through 500 °C at 380–375 Ma except for the lowest grade region, where cooling occurred approximately 20 million years earlier. The results indicate that exhumation was a two stage process, involving (1) flexural rebound and slab flattening at depth combined with foreland‐directed extrusion, followed by (2) synchronous cooling below 500 °C across the, by then, largely flat‐lying Western Gneiss Complex. The latter implies and requires relatively homogeneous mass removal across a large area, consistent with erosion of an overlying orogenic plateau. The Caledonides were at near‐equatorial latitudes at the time. A Caledonian paleo‐plateau thus may represent a so far unrecognized factor in Devonian and Carboniferous atmospheric circulation and climate forcing.
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| 13. |
- Piličiauskienė, Giedrė, et al.
(författare)
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The Origin of Late Roman Period-Post-Migration Period Lithuanian Horses
- 2022
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Ingår i: Heritage. - : MDPI AG. - 2571-9408. ; 5:1, s. 332-352
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Tidskriftsartikel (refereegranskat)abstract
- In this paper, we present the 87Sr/86Sr data of 13 samples from horses from six Lithuanian burial sites dating from the 3rd to the 7th C AD. Alongside these data, we also publish the bioavailable 87Sr/86Sr data of 15 Lithuanian archaeological sites, based on 41 animals which enabled the construction of a reliable baseline for the Southeast Baltic area. The 87Sr/86Sr values partially confirmed the hypothesis that the unusually large horses found in Late Roman Period to Post-Migration Period burials are of non-local origin. Of the three non-local horses identified, two were among the largest specimens. However, the overlap of bioavailable 87Sr/86Sr data across different European regions does not permit us to establish whether the non-local horses originated from other areas in Lithuania or from more distant regions. With regards to the 87Sr/86Sr data, the place of origin of the non-local horses could be Southern Sweden. This encourages discussions on the possible directions of migration and compels us to rethink the current models that posit South and Central Europe as the main sources of migration. The results of the 87Sr/86Sr, δ13C, and δ15N analyses demonstrate that horses buried in the same cemetery had different mobility and feeding patterns. Differences could be due to the different function and sex of the horses as well as the lifestyle of their owners. The most sedentary horses were pregnant mares, while the extremely high δ15N of three horses may reflect additional fodder and probably a better diet.
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| 14. |
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| 15. |
- Sun, Xiaole, et al.
(författare)
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Stable silicon isotopic compositions of the Lena River and its tributaries : Implications for silicon delivery to the Arctic Ocean
- 2018
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Ingår i: Geochimica et Cosmochimica Acta. - : Elsevier BV. - 0016-7037 .- 1872-9533. ; 241, s. 120-133
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Tidskriftsartikel (refereegranskat)abstract
- Silicon isotope values (delta Si-30(DSi)) of dissolved silicon (DSi) have been analyzed in the Lena River and its tributaries, one of the largest Arctic watersheds in the world. The geographical and temporal variations of delta Si-30(DSi) range from +0.39 to +1.86% with DSi concentrations from 34 to 121 mu M. No obvious patterns of DSi concentrations and delta Si-30(DSi) values were observed along over 200 km of the two major tributaries, the Viliui and Aldan Rivers. In summer, the variations of DSi concentrations and delta Si-30(DSi) values in the water are either caused by biological uptake by higher plants and phytoplankton or by mixing of water masses carrying different DSi concentrations and delta Si-30(DSi) values. DSi in tributaries from the Verkhoyansk Mountain Range seems to be associated with secondary clay formation that increased the delta Si-30(DSi) values, while terrestrial biological production is likely more prevalent in controlling delta Si-30(DSi) values in Central Siberian Plateau and Lena Amganski Inter-River Area. In winter, when soils were frozen, the delta Si-30(DSi) values in the river appeared to be controlled by weathering and clay formation in deep intrapermafrost groundwater. During the spring flood, dissolved silicate materials and phytoliths were flushed from the upper thawed soils into rivers, which reset delta Si-30(DSi) values to the values observed prior to the biological bloom in summer. The results indicate that the Si isotope values reflect the changing processes controlling Si outputs to the Lena River and to the Arctic Ocean between seasons. The annual average delta Si-30(DSi) value of the Lena Si flux is calculated to be +0.86 +/- 0.3 parts per thousand using measured delta Si-30(DSi) values from each season. Combined with the estimate of + 1.6 +/- 0.25 parts per thousand for the Yenisey River, an updated delta Si-30(DSi) value of the major river Si inputs to the Arctic Ocean is estimated to be + 1.3 +/- 0.3 parts per thousand. This value is expected to shift towards higher values in the future because of the impacts from a variety of biological and geochemical processes and sources under global warming.
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| 18. |
- Tual, Lorraine, et al.
(författare)
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Rapid, paced metamorphism of blueschists (Syros, Greece) from laser-based zoned Lu-Hf garnet chronology and LA-ICPMS trace element mapping
- 2022
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Ingår i: Chemical Geology. - : Elsevier. - 0009-2541 .- 1872-6836. ; 607
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Tidskriftsartikel (refereegranskat)abstract
- Unravelling the timing and rate of subduction-zone metamorphism and H2O release requires linking time to the compositional changes of petrogenetic indicator minerals in blueschists and eclogites. Garnet is a key mineral in this regard, as it forms by, and records, H2O-releasing mineral reactions that can be linked to pressure and temperature conditions. These can be placed in time using chronology. Bulk-or multi-grain ages are the norm in garnet chronology. While these ages provide important and precise time constraints on reactions across both facies, the duration, rates and style of growth???crucial parameters in the petrological and geochemical evolution of subducting oceanic crust???remain unconstrained. Domain dating, i.e., dating of individual growth zones, is necessary to investigate these aspects, but is generally impeded in ???common???-sized garnet grains due to sample size requirements. To overcome these limitations, we use a low-loss micro-sampling by laser cutting combined with Lu-Hf chronology. We used this approach to precisely date multiple growth zones in a 1-cm garnet grain from glaucophane-bearing micaceous schist of the Cycladic Blueschist Unit (CBU), Syros Island, Greece. The analysis was combined with major- and trace-element mapping (EPMA, LA-ICPMS) to investigate garnet petrogenesis. Garnet core and mantle zones are chemically comparable and identical in age within 0.1 Myr precision (2??), indicating an initial growth pulse at 51.8 ?? 0.1 Ma (MSWD = 1.13). The two rim zones, which are chemically distinct, were resolvably younger at 51.3 ?? 0.2 Ma (MSWD = 0.67). Integrated with compositional data, these age constraints provide a time-resolved record of extremely fast, pulsed garnet growth and fluidrelease reactions, such as chloritoid breakdown. These reactions can be considered near-instantaneous on subduction time scales, indicating that re-equilibration far outpaces changes in pressure and temperature conditions. The analysed sample is associated with the upper-subunit of the CBU with oceanic affinities, which does not share the last part of the prograde history with the rest of the CBU, i.e., the margin sub-unit. We interpret our sample as a sliver that became attached to the base of the ophiolitic sub-unit and was thrusted onto the lower margin unit at high-pressure. Beyond providing insights into the timing of subduction-zone processes, our new protocol for zoned garnet Lu-Hf geochronology of ???common-sized??? garnet opens new possibilities for constraining the causes and rates of garnet growth and the pace of tectonic processes in general.
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| 19. |
- Walczak, Katarzyna, et al.
(författare)
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Late Neoproterozoic extended continental margin development recorded by the Seve Nappe Complex of the northern Scandinavian Caledonides
- 2022
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Ingår i: Lithos. - : Elsevier. - 0024-4937 .- 1872-6143. ; 416
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Tidskriftsartikel (refereegranskat)abstract
- The Scandinavian Caledonides comprise nappe stacks of far-travelled allochthons that record the opening and closure of the Iapetus Ocean, culminating with the collision of Baltica and Laurentia. The Seve Nappe Complex (SNC) of the Scandinavian Caledonides comprises relics of the outermost Baltoscandian passive margin that were subducted to mantle depths during ocean closure. Subduction of these rocks overprinted much of the Neoproterozoic record for Iapetus Ocean formation, and as a result, much of the work conducted in the SNC has focused solely on the Caledonian orogenic history.& nbsp;In this study, we combined petrological and geochronological work to expand the knowledge about the Neoproterozoic metamorphic history of the Baltoscandian margin in the understudied Vaivancohkka-Salmmecohkat region of the northern Scandinavian Caledonides. The work focused on rocks that belong to the upper gneiss unit, which constitutes part of SNC in the region. The unit comprises migmatitic paragneisses and garnet-mica schist containing metamafic bodies. U-Pb zircon and Th-U-total Pb monazite dating of the migmatitic paragneiss yielded consistent age of metamorphism in 602 +/- 5 Ma and 599 +/- 3 Ma, respectively. A similar U-Pb age of 604 +/- 8 Ma was obtained for the zircon from the leucocratic vein transecting the amphibolite within the studied gneiss. Interestingly, no Caledonian ages were identified. Likewise, no evidence for high or ultra-high pressure conditions was found, neither in the gneisses/schists nor in the metamafic rocks. Petrographic observations and calculated metamorphic P-T conditions indicate that rocks belonging to upper gneiss unit underwent upper-amphibolite facies metamorphism in a melt stability field; 8.0-10.5 kbar at 750-790 degrees C.& nbsp;Since the studied rocks underwent high-grade metamorphism in the Ediacaran and lack obvious evidence for Caledonian high-pressure metamorphism, the studied part of the SNC offers an extraordinary insight into the Late Neoproterozoic history of the hot, extended Baltoscandian margin.
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