Supplemental Material: Ordovician–Silurian back-arc silicic magmatism in the southernmost Appalachians

Sample Preparation and Geochemical Analysis Methodology; Table S1: Major oxide percentages for metaigneous rocks of the Wedowee-Emuckfaw-Dahlonega basin; Table S2: Measured isotope ratios and normalized U-Pb ages calculated without 204Pb Correction; Table S3: Lu-Hf isotope analyses; Table S4: Latitude-longitude (WGS84), geologic unit, and age information for samples analyzed as part of this project.

Supplemental Material: Ordovician–Silurian back-arc silicic magmatism in the southernmost Appalachians

Sample Preparation and Geochemical Analysis Methodology; Table S1: Major oxide percentages for metaigneous rocks of the Wedowee-Emuckfaw-Dahlonega basin; Table S2: Measured isotope ratios and normalized U-Pb ages calculated without 204Pb Correction; Table S3: Lu-Hf isotope analyses; Table S4: Latitude-longitude (WGS84), geologic unit, and age information for samples analyzed as part of this project.

Supplemental Material: Ordovician–Silurian back-arc silicic magmatism in the southernmost Appalachians

Sample Preparation and Geochemical Analysis Methodology; Table S1: Major oxide percentages for metaigneous rocks of the Wedowee-Emuckfaw-Dahlonega basin; Table S2: Measured isotope ratios and normalized U-Pb ages calculated without 204Pb Correction; Table S3: Lu-Hf isotope analyses; Table S4: Latitude-longitude (WGS84), geologic unit, and age information for samples analyzed as part of this project.

Supplemental Material: Ordovician–Silurian back-arc silicic magmatism in the southernmost Appalachians

Sample Preparation and Geochemical Analysis Methodology; Table S1: Major oxide percentages for metaigneous rocks of the Wedowee-Emuckfaw-Dahlonega basin; Table S2: Measured isotope ratios and normalized U-Pb ages calculated without 204Pb Correction; Table S3: Lu-Hf isotope analyses; Table S4: Latitude-longitude (WGS84), geologic unit, and age information for samples analyzed as part of this project.

The birth of the Alps: Ediacaran to Paleozoic accretionary processes and crustal growth along the northern Gondwana margin

New whole-rock geochemical and coupled U–Pb and Lu–Hf LA-ICP-MS zircon data of metasedimentary rocks of the Austroalpine, South Alpine and Penninic basement domains are presented, to disentangle the pre-Variscan tectonic evolution of the proto-Alps. The studied units seem to record distinct stages of protracted Late Ediacaran to Carboniferous tectonosedimentary processes prior to the Variscan collision. In the case of Austroalpine and South Alpine units, nevertheless, no major differences in terms of provenance are observed, since most detrital zircon samples are characterized by a major Pan-African peak. Their detrital zircon spectra record a provenance from the northeastern Saharan Metacraton and the Sinai basement at the northern Arabian-Nubian Shield, being thus located along the eastern Early Paleozoic northern Gondwana margin, whereas sources located further west are inferred for the Penninic Unit, which might have been placed close to the Moldanubian Unit of the Bohemian Massif. In any case, it is thus clear that the Alpine basement remained in a close position to the Gondwana mainland at least during the Early Paleozoic. The Late Ediacaran to Silurian tectonic evolution, which includes Cadomian and Cenerian tectonometamorphic and magmatic processes, seem thus to record a continuum related to a retreating-mode accretionary orogen, with diachronous back-arc basin opening and possibly discrete compressional/transpressional pulses linked to changes in subduction zone dynamics. On the other hand, it is inferred that the Alpine basement essentially comprises Pan-African metasedimentary and subordinate metaigneous rocks, possibly with very few Early Neoproterozoic relics. This basement was significantly reworked during the protracted Paleozoic orogenic evolution, due to anatexis and/or assimilation by mantle-derived juvenile magmatism.

Deciphering the Vássačorru Igneous Complex within the Seve Nappe Complex, Scandinavian Caledonides

<p>The Seve Nappe Complex (SNC) of the Scandinavian Caledonides comprises Neoproterozoic sedimentary and igneous rocks that experienced high-pressure metamorphism and deformation during subduction and exhumation. Fieldwork was conducted in the Kebnekaise region in northern Sweden, focusing on the Aurek metagabbro and the Vistas metaigneous rocks within the Vássačorru Igneous Complex (VIC), hosted within SNC metasediments. Field observations show that the Aurek metagabbro is locally sheared with well-defined foliation and lineation. In contrast, the Vistas metaigneous rocks, consisting of both granite and gabbro bodies, are only locally foliated. Furthermore, the granite is intruded by ENE-WSW striking dolerite and rhyolite dykes that parallel the local foliation, and are weakly deformed, whereas a NNE-SSW striking syenite dyke is observed in a portion of undeformed gabbro.</p><p>The Aurek metagabbro mineral assemblages consist of garnet, amphibole, plagioclase, biotite, chlorite, and pyroxene. The Vistas gabbro and dolerite dyke both consist of plagioclase, pyroxene, and amphibole. The Vistas granites and rhyolite dyke include quartz, feldspar, biotite, muscovite, ± garnet, and the syenite dyke contains feldspar, plagioclase, pyroxene, amphibole, quartz, and biotite. The Vistas metaigneous rocks generally show primary igneous assemblages.</p><p>Bulk rock chemistry shows that the Aurek and Vistas gabbros, and the Vistas dolerite dyke, are classified as tholeiites. For the Aurek gabbros, Th/Yb of 0.06-1.86 and Nb/Yb of 0.11-5.14 indicate that they have N-MORB to E-MORB compositions, with possible crustal input. The Vistas gabbro (Th/Yb of 0.09 and Nb/Yb of 1.15) and the dolerite dyke (Th/Yb of 0.12 and Nb/Yb of 0.66) also suggest such trend. The Vistas granites, rhyolite, and syenite dyke all have calc-alkaline composition. Trace elements confirm volcanic arc affinity for the granites and the syenite dyke (Nb: 3.1-5.9 ppm, Rb: 116.5-177.5 ppm, Y: 12.9-18.0 ppm, Ta: 0.3-0.4 ppm, Yb: 2.04-3.19 ppm), whereas the rhyolite dyke (Nb: 38.2 ppm, Rb: 247.8 ppm, Y: 72.6 ppm, Ta: 2.8 ppm and Yb: 12.62 ppm) reflects a within plate setting.</p><p>Combining the field relationship with geochemistry of the studied metaigneous rocks, we tentatively propose that the VIC is composed of three pulses of magmatism: (1) mafic MORB magmatism represented by the gabbros, emplaced in an extensional regime; (2) felsic calc-alkaline magmatism represented by granites and syenite, emplaced in an active continental margin environment; and (3) bimodal within-plate magmatism or crustal assimilation in a volcanic arc represented by dolerite and rhyolite dykes. However, the only existing age is from U-Pb zircon dating of the Vistas granite, which yielded 845±14 Ma (Paulsson & Andreasson, 2002). Further zircon U-Pb geochronology will be conducted to obtain ages of the various lithologies of the VIC to better understand temporal relationships and to link the VIC with tectonic events in the Scandinavian Caledonides.</p><p>This study was supported by the National Science Centre (Poland) grant no. 2019/33/B/ST10/01728 to J. Majka.</p><p>References</p><p>Paulsson, O., Andreasson, P.-G., 2002. Attempted break-up of Rodinia at 850 Ma: Geochronological evidence from the Seve-Kalak Superterrane, Scandinavian Caledonides. J. Geol. Soc. 159, 751–761. https://doi.org/10.1144/0016-764901-156</p>

Permian Hydrothermal Alteration Preserved in Polymetamorphic Basement and Constraints for Ore-genesis (Alpi Apuane, Italy)

The reconstruction of the polymetamorphic history of basement rocks in orogens is crucial for deciphering past geodynamic evolution. However, the current petrographic features are usually interpreted as the results of the metamorphic recrystallization of primary sedimentary and/or magmatic features. In contrast, metamorphic rocks derived by protoliths affected by pre-metamorphic hydrothermal alterations are rarely recognized. This work reports textural, mineralogical and geochemical data of metasedimentary and metaigneous rocks from the Paleozoic succession of the Sant’Anna tectonic window (Alpi Apuane, Tuscany, Italy). These rocks were recrystallized and reworked during the Alpine tectono-metamorphic event, but the bulk composition and some refractory minerals (e.g., tourmaline) are largely preserved. Our data show that the Paleozoic rocks from the Alpi Apuane were locally altered by hydrothermal fluids prior to Alpine metamorphism, and that the Permian magmatic cycle was likely responsible for this hydrothermal alteration. Finally, the Ishikawa Alteration Index, initially developed for magmatic rocks, was applied to metasedimentary rocks, providing a useful geochemical tool for unravelling the hydrothermal history of Paleozoic rocks, as well as a potential guide to the localization of hidden ore deposits in metamorphic terranes.

TETGAR_C: a three-dimensional (3D) provenance plot and calculation tool for detrital garnets

<p>We present a new interactive MATLAB-based visualization and calculation tool (TETGAR_C) for assessing the provenance of detrital garnets in a four-component (tetrahedral) plot system (almandine–pyrope–grossular–spessartine). The chemistry of more than 2,600 garnet samples was evaluated and used to create various subfields in the tetrahedron that correspond to calc-silicate rocks, felsic igneous rocks (granites and pegmatites) as well as metasedimentary and metaigneous rocks of various metamorphic grades. These subfields act as reference structures facilitating assignments of garnet chemistries to source lithologies. An integrated function calculates whether a point is located in a subfield or not. Moreover, TETGAR_C determines the distance to the closest subfield. Compared with conventional ternary garnet discrimination diagrams, this provenance tool enables a more accurate assessment of potential source rocks by reducing the overlap of specific subfields and offering quantitative testing of garnet compositions. In particular, a much clearer distinction between garnets from greenschist-facies rocks, amphibolite-facies rocks, blueschist-facies rocks and felsic igneous rocks is achieved. Moreover, TETGAR_C enables a distinction between metaigenous and metasedimentary garnet grains. In general, metaigneous garnet tends to have higher grossular content than metasedimentary garnet formed under similar P–T conditions.</p>