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Fluid-driven reactions are common in the upper crust, leading to mineral replacement and element redistribution on a kilometer to a micron scale. One common fluid-induced reaction is the chloritization of biotite. Chloritization can lead to the production of multiple phases, such as K-feldspar, titanite, and rutile, depending on local chemistry and fluid composition. Here, we compare different approaches to mass balance calculations using an altered garnet-bearing metapelite collected from Ny Friesland, Svalbard Archipelago, Norway. In the outcrop, amphibolite facies schists are cut by joints that acted as fluid pathways that led to the development of a narrow (~5 cm) alteration zone. Alteration involved the replacement of biotite by chlorite + K-feldspar ± rutile ± titanite. Mass balance calculations based on whole-rock composition and assuming immobile Zr indicate the addition of H2O, Si, Ti, Fe, or Mg and the removal of K or Ca. In contrast, mass balance calculated for the pseudomorphic replacement of Bt by Chl + Kfs ± Rt ± Ttn using X-Ray maps for three focused areas indicates the removal of Si or Ti rather than addition. Moles of product phase and elements gained or lost during this reaction varies between individual areas. This variation suggests that fluid heterogeneity and local chemistry governed the progression of the replacement reaction. All the product phases involved in the biotite breakdown are geochronometers and/or geothermometers, providing new opportunities for the petrochronology of fluid-induced reactions.

The Seve Nappe Complex is a subduction‐related high‐grade metamorphic unit that was emplaced onto the margin of Baltica during Caledonian orogenesis. In this paper, the tectonometamorphic evolution of the Lower Seve Nappe in the Scandinavian Caledonides was characterized with the help of the continuous Collisional Orogeny in the Scandinavian Caledonides (COSC‐1) drill core, using a combination of various P–T estimation techniques based on garnet–quartz mineral pairs (quartz‐in‐garnet and Ti‐in‐quartz [QuiG–TiQ]), conventional thermobarometry and thermodynamic modelling of phase equilibria. This multi‐method approach yields complementary results and delivers critical data to constrain a comprehensive pressure–temperature–deformation–time (P–T–D–t) evolutionary path for the metasedimentary rocks of the Lower Seve Nappe. In the garnetiferous metasedimentary rocks, quartz inclusions in garnet preserve the P–T conditions of three distinct garnet growth stages corresponding to three metamorphic stages Ms1 to Ms3, including prograde and peak metamorphic conditions. Ms1 and Ms2 stages were constrained via quartz inclusions in garnet core and mantle. They are relatively close in the P–T space and could be considered as one single continuous prograde event occurring at epidote–amphibolite facies conditions of 460–520°C and 0.6–0.85 GPa. The growth of the garnet outermost rim defines the Ms3 stage at amphibolite facies conditions of 590–610°C and 1.13–1.18 GPa and corresponds to the peak metamorphic conditions. The microstructural analysis shows that the finite ductile strain pattern of the Lower Seve Nappe results from the superposition of four deformation phases. The initial phase D1 is defined by the S1 foliation that is still preserved as a curved inclusion trail in the garnet core. The D2 phase initiated contemporaneously with garnet core growth and the development of muscovite–biotite–plagioclase S2 foliation. Garnet outermost rim growth marks the end of the prograde path and peak metamorphic conditions. This stage is overprinted by the D3 phase and Ms4 stage associated with the development of the main regional metamorphic and mylonitic fabric S3 associated with C′‐type shear bands along the retrograde path. Ms4 stage, which was constrained using traditional thermobarometric techniques, corresponds to the chemical re‐equilibration of the metasedimentary minerals and occurred under amphibolite facies conditions at ~570–610°C and 0.78–1.00 GPa. The D3 phase is then generally weakly to strongly overprinted by later lower grade deformation D4 phase at greenschist facies conditions (Ms5). 40Ar/39Ar ages of syn‐kinematic white mica and biotite indicate that the final stage of the thrusting of the Lower Seve Nappe and thus the timing of its emplacement onto the Offerdal Nappe occurred at c. 423 Ma. Collectively, these results are consistent with previous estimates of the timing and conditions of metamorphism derived from the Lower Seve Nappe especially in west‐central Jämtland. However, application of QuiG–TiQ thermobarometry demonstrated that quartz inclusions in garnet can preserve different aspects of garnet growth, which are not accessible by traditional methods especially in complex terranes, and therefore provided new significant insights into the Lower Seve prograde evolution. [ABSTRACT FROM AUTHOR]

40Ar/39Ar dating of white mica from foliated metamorphic rocks of the Caledonian orogen of NW Svalbard was performed using the single‐grain fusion technique. Two samples, an augen orthogneiss and a mica schist, were collected from the high‐pressure Richarddalen Complex. Three additional mica schist samples were collected from the tectonically underlying Montblanc Unit. 40Ar/39Ar analysis of white mica separates yielded weighted average 40Ar/39Ar dates of 446.1 ± 1.1, 438.4 ± 1.1, 439.4 ± 1.2, 439.8 ± 1.5 and 439.3 ± 1.0 Ma, with the oldest date provided by the Richarddalen mica schist. The single‐grain fusion 40Ar/39Ar dating was accompanied by geochemical mapping of white mica using a microprobe. We interpret the oldest date as the age of cooling after a Late Ordovician high‐pressure event and the four younger dates to represent the timing of subsequent deformation associated with assembly of a Caledonian nappe stack. [ABSTRACT FROM AUTHOR]

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The juxtaposition of the composite Pearya terrane and the northern Laurentian margin at Ellesmere Island, Nunavut, Canada, has significant ramifications for the Paleozoic tectonic history of the circum-Arctic region. Published tectonic models rely upon interpretation of the subduction-related Kulutingwak Formation as an indicator of Ordovician and/or Silurian accretion (Trettin, 1998). New igneous and detrital zircon U-Pb and Lu-Hf isotopic data from 16 samples collected in the Yelverton Inlet–Kulutingwak Fiord region of northern Ellesmere Island suggest that the Kulutingwak Formation of Trettin (1998) contains structural blocks derived from both the Pearya terrane and Silurian strata associated with the ancestral Laurentian margin. Data from this study demonstrate a complex provenance history for rocks within the Petersen Bay, Kulutingwak Fiord, and Emma Fiord fault zones, with age probability peaks of ca. 470 Ma, 650 Ma, and 960–980 Ma that suggest affinity with the Pearya terrane, and age probability peaks of ca. 1800 Ma and 2700 Ma that indicate connections to the Laurentian margin. The combination of these signatures in Kulutingwak Formation rocks suggests that the Pearya terrane was proximal to the northern Laurentian margin by Late Ordovician time. Silurian and younger strike-slip displacement on the major fault zones resulted in the incorporation of blocks derived from the Pearya terrane basement and Silurian clastic rocks into the Kulutingwak Formation. Silurian displacement along these strike-slip faults, which are integral components of the Canadian Arctic transform system, is recorded by syndepositional deformation structures in the Danish River Formation and prevented the transition from soft to hard collision of the Pearya terrane. The two-stage model for the Pearya terrane—accretion followed by significant translation—provides a process for developing complex steep terrane boundaries with contentious displacement histories that are common in accretionary orogens [ABSTRACT FROM AUTHOR]