Metamorphic soles are key petrotectonic units that offer valuable insights into the processes governing ophiolite emplacement on continental margins (obduction). In this work, we have investigated the metamorphic sole of the Pindos ophiolite in northwestern Greece. In the studied locality, the sole is sandwiched between mantle peridotites and pillow lavas of N-MORB affinity. Our study focuses on two lithologies from the metamorphic sole: a garnet-mica schist (metapelite) and a mafic amphibolite. Kinematic indicators from the garnet-mica schists are consistent with top-to-the-NE shearing of the Pindos ophiolite on the Pelagonian zone. Petrographic and textural evidence, geothermometry results (Fe Mg garnet-biotite exchange and paragonite-muscovite solvus thermometry), and phase-equilibria modelling bracket the upper-limit of metamorphism at amphibolite-facies conditions (630 ± 20 °C and 1.1 ± 0.2GPa). Moreover, Quartz-in-Garnet (QuiG) barometry yields a pressure of ∼1.2GPa for 630 °C demonstrating the equilibration of garnet inclusions at high-pressure conditions. New 40 Ar/ 39 Ar dating results from syn -kinematic muscovite from the metapelite and amphibole from the amphibolite indicate an apparent minimum age of 164.16 ± 0.37 Ma and a consistent age plateau at 165.5 ± 0.73 Ma respectively. Notably, the amphibole exhibits no evidence of argon loss. The muscovite age, by contrast, should be considered a minimum apparent age due to the potential influence of argon diffusion. Finally, U Pb geochronology of garnet was dominated by inclusions and did not result in a meaningful age. The measured ages imply cooling rates for the Pindos metamorphic sole ranging from 60 to 625 °C/Ma. • Kinematic indicators show a top-to-the-NE obduction of the Pindos ophiolite. • The studied metapelite from the sole experienced upper-amphibolite-facies conditions. • Phase equilibria, geothermobarometry and elastic barometry show P: 1.1 ± 0.2GPa and T: 630 ± 20 °C • The metamorphic sole indicates rapid cooling from 550 to 400 °C with cooling rates between 60 and 625 °C/Ma. • Such cooling rates indicate the occurrence of fast, transient processes during ophiolite emplacement.

Here we investigate the genesis of the Moho transition zone (MTZ), sandwiched between mantle and crustal rocks of the Samail ophiolite, through a petrological and geochemical study of cores taken by the Oman Drilling Project (Oman DP). The MTZ drilled, comprises a 150 m-thick dunite horizon that is practically pure dunite in the upper 90 m but cut by several gabbroic intrusions in the lower part. The dunite is nearly completely altered to serpentinite, with only Cr-spinel as the relict primary phase. We interpret the entire MTZ as having formed through reactive interactions between MORB melts and shallow mantle peridotite. The key process is the dissolution of orthopyroxene and concomitant precipitation of olivine during porous flow of ascending MORB melts. In the lower part of the MTZ, evolution trends in Cr-spinel chemistry are absent, precluding crystal fractionation processes. Instead, the presence of relict clino- and orthopyroxene in the serpentinized dunites, exhibiting characteristic mantle deformation, associated with elevated “spoon”-shaped bulk REE patterns, are interpreted as signatures of replacive dunites formed by MORB/harzburgite interaction. In contrast, relict spinels of the upper pure dunite zone at the top of the MTZ show systematic compositional variations with depth, interpreted to have resulted from differentiation of a primitive MORB melt. Although spinel compositions are well correlated with incompatible element concentrations, including Ti and V, there is very poor or non-existent correlation of compatible elements, such as Ni and Cr. These are diagnostic signatures of “reactive fractionation” according to Collier and Kelemen (2010) , where compatible element concentrations are buffered by diffusive interaction with the surrounding harzburgite, whereas the decreasing magma mass leads to the accumulation of incompatible elements in the remaining melt. This upper dunite zone could correspond to the “missing cumulates”, necessary to model the evolution of the Oman bulk crust, which shows a too-evolved composition, assuming it was formed from a typical primitive parental MORB. • Providing a detailed description of the Oman crust-mantle transition zone based on spinel chemistry. • Combining replacive and cumulative dunite origin models. • Solving the “missing cumulate problem”. • Providing a conclusive model for the crust-mantle transition zone at mid-ocean ridges.

Enclaves in plutonic and volcanic rocks serve as pivotal indicators of magmatic processes and magma dynamics, offering valuable insights into the evolution of igneous systems. This study investigates the structural, textural, and geochemical characteristics of mafic and felsic enclaves in the Triassic, continental rift-related Ditrău Alkaline Massif (Eastern Carpathians, Romania), aiming to elucidate their origin and relationship with the host rock which belongs to the Tarnița Complex. Overlapping whole-rock geochemical as well as amphibole and plagioclase compositions strongly suggest the cognate origin of the different lithologies. The mafic enclaves are characterised by sharp contacts and fine-grained igneous textures, implying rapid crystallisation along the margins of the magma batches. Side-wall cumulates were fragmented, transported and dispersed in the partially solidified host magma by convective currents. Felsic enclaves represent fragments of previously crystallised felsic roof cumulates and felsic rock fragments as well as loosely packed crystal mush fragments. The study emphasises the dynamic nature of the studied magma reservoir in the Ditrău Alkaline Massif, where convective magma flow and injections of replenishing magma batches played a crucial role in the formation and distribution of the enclaves. • Rocks in the Tarnița Complex, Ditrău Alkaline Massif bear various types of enclaves. • Texture and geochemistry of the enclaves reveal magma chamber processes. • All types of felsic and mafic enclaves are genetically linked to their host rock. • Magma flow and convection led to enclave formation and (re-)distribution.

New geochronological, whole-rock, and zircon geochemical data for diorite and andesite porphyries from the Kennon Cu–Au porphyry deposit located in the Black Mountain intrusive complex, in the Baguio Mineral District in the Benguet Province, Northern Luzon, Philippines, are presented to evaluate ore-forming processes. The U–Pb geochronological data indicate that diorite and andesite porphyries were emplaced synchronously at ∼3.36 to 3.10 Ma, coinciding with the mineralization event driven by the fertile Pliocene magmatism related to the subduction of the Scarborough ridge along the Manila Trench. Whole-rock and zircon geochemistry show moderate to high degrees of magmatic fractionation, as reflected in Nb/Ta, Zr/Hf, and Rb/Sr ratios, along with zircon Dy/Yb, Hf, and Th/U values. Zircon trace element characteristics, including Ce 4+ /Ce 3+ ratios (>300), Eu/Eu ⁎ (>0.4), and (Ce/Nd)/Y (>0.01), indicate high oxygen fugacity and water content, supported by the presence of magnetite, hornblende, and apatite in samples. Crystallization temperatures ranging from 726 to 835 °C and oxygen fugacity values (ΔFMQ +0.99 to +1.17) calculated from zircon trace element data fall within the typical range of intrusion-related Au deposits. Furthermore, the combination of the oxygen fugacity and whole-rock Fe content places it in the Cu field. These results demonstrate that high oxidation states and elevated water contents typically associated with primitive magmas can coexist with significant fractionation in mid-crustal, hydrous, oxidized magma chambers. • U–Pb dating shows Kennon porphyries emplaced during Pliocene mineralization. • Zircon and whole-rock data reveal high f O 2 , H 2 O, and magma fractionation. • Kennon orebody is a fertile, oxidized, hydrous system linked to Cu–Au deposits.

Rapakivi granites from the late Paleoproterozoic Suomenniemi Complex (south-eastern Finland) experienced pervasive localised metasomatism via interaction of high-temperature, oxidising peralkaline fluids and granite along dyke-like zones, resulting in the formation of episyenite bodies. To constrain the timing and conditions of episyenite formation, we combine in-situ U Pb zircon, U Pb and Lu Hf apatite, and U Pb titanite geochronology with petrography and mineral chemistry from four episyenite bodies. Zircon yields U Pb ages coeval with crystallisation of the ca. 1644 Ma granite, preserving the igneous protolith age, whereas U Pb ages from hydrothermally modified zircon (1635.1 ± 2.7 Ma; 1627.8 ± 6.3 Ma) and apatite (1611.6 ± 9.5 Ma; 1630 ± 19 Ma), along with hydrothermal titanite (1603 ± 43 Ma; 1623 ± 30 Ma) record younger ages, reflecting variable degrees of disturbance of the U Pb system and indicating that episyenite formation post-dated granite emplacement. Apatite Lu Hf ages (1648 ± 30 Ma; 1643 ± 41 Ma) and some titanite U Pb ages (1646 ± 12 Ma; 1642 ± 62 Ma) overlap with the host granite but their large uncertainties preclude confident attribution to either magmatic crystallisation or subsequent metasomatism. Collectively, these data indicate that episyenitisation postdated granite emplacement and was likely driven by regional thermal perturbations linked to the emplacement of the ~1630 Ma Wiborg Batholith. Petrographic and mineral chemistry analyses of zircon, apatite, and titanite indicate that hydrothermal alteration of the protolith was highly variable, both between episyenite bodies and even over small metre-scale intervals within individual bodies. This is evident in zircon, where different areas of high intensity hydrothermal alteration under high temperature and oxidising conditions resulted dissolution and reprecipitation of zircon. Apatite in the host granite was likely recrystallised during episyenitisation, as evidenced by textural modification and younger U Pb ages. Titanite is an accessory mineral found exclusively within the episyenite bodies and is absent in the surrounding granite protolith. It commonly occurs as inclusions in mafic mineral aggregates or as rims around Fe Ti oxides (magnetite, ilmenite), suggesting a hydrothermal origin associated with episyenitisation and crystallisation under oxidising conditions. Variations in the major (Al, Fe, Ti, F) and trace element (light REE, Nb) chemistry of titanite and Zr-in-titanite thermometry (660–875 °C) further indicate differences in hydrothermal fluid composition and temperatures during titanite formation across different episyenite bodies. These findings, along with the overlapping ages of hydrothermal titanite and the host protolith, suggest that the episyenites in the Suomenniemi Complex formed by fluid-rock interaction, either shortly after consolidation of the main granite sequence of the complex and/or during subsequent regional rapakivi granite magmatism. Thus, resolving the timing of episyenite formation is crucial for understanding fluid-assisted alteration of granitic systems, identifying potential fluid sources, and assessing their geochemical evolution and metallogenic potential. • Episyenites in the Suomenniemi granite formed due to hydrothermal alteration. • Zircon, apatite, titanite ages show episyenites formed shortly after the granite. • Zircon records alteration by oxidising fluids via dissolution–reprecipitation. • Hydrothermal titanite tracks fluid temperature and alteration intensity. • Hydrothermal alteration shows local variability between episyenite bodies.