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This study presents new field and microstructural constraints into the batholith architecture and supra- to subsolidus evolution of late Variscan granitoids at Capo Vaticano Promontory, part of the ∼13 km-thick Serre Batholith in southern Italy. A field survey, assisted by petrographic analyses, produced the first geological map of the area (1:140,000 scale), detailing magmatic unit relationships and their petro-structural features. A migmatitic border zone (MBZ) marks the transition from lower-crustal paragneisses to the deepest emplaced granitoids. The oldest, deepest granitoids are strongly to moderately foliated amphibole-biotite tonalites and quartz diorites, transitioning to biotite tonalites and quartz-diorites (BT), which can be subdivided into strongly to moderately foliated (BTs) and weakly foliated to unfoliated (BTw). Clear intrusive contacts mark the passage from BTw to overlying weakly foliated-unfoliated porphyritic muscovite-biotite granodiorites and granites (PMBG). The study also revealed: a) a northern sector with a continuous batholith cross-section and b) a southern sector with an irregular distribution of the magmatic units due to post-Variscan tectonics. Microstructures document late Variscan deformation starting at suprasolidus conditions (e.g., quartz chessboard patterns and submagmatic fractures in plagioclase) and evolving through progressively high- to low-temperature subsolidus stages (e.g., feldspar bulging, quartz recrystallization, mica kinking) for all the magmatic units. Continuous supra- to subsolidus deformation associated with a well-developed fabric suggests tectonic control on the emplacement and cooling of early tonalites/quartz diorites, while the emplacement of the porphyritic granitoids has occurred during waning tectonic activity stages in the framework of the post-collisional evolution of the south-western Variscan Belt.

The Cornubian Batholith (SW England) is an archetypal Variscan rare metal granite with potential for Li-mica mineralization. We present a petrographic, trace element and multivariate statistical study of micas from the Cornubian Batholith granite series and related hydrothermally altered units to assess the role of magmatic vs subsolidus processes and of fluxing elements (F and B) on the Li cycle during the evolution of the system. The mica types are as follows: (1) magmatic, which include Fe-biotite, protolithionite I and phengite-muscovite from the most primitive granites, and zinnwaldite I from more fractionated lithologies; (2) subsolidus, which encompass high-temperature autometasomatic Li-micas and low-temperature hydrothermal muscovite-phengite. Autometasomatic species include protolithionite II, zinnwaldite II and lepidolite, which were observed in the most fractionated and hydrothermally altered units, and occur as replacements of magmatic micas. Low-temperature hydrothermal Li-poor micas formed via alteration of magmatic and autometasomatic micas or as replacement of feldspars, and albeit occur in all studied lithologies they are best represented by the granite facies enriched in metasomatic tourmaline. The evolution of micas follows two major trends underlining a coupling and decoupling between the Li(F) and B fluxes. These include as follows: (1) a Li(F)-progressive trend explaining the formation of protolithionite I and zinnwaldite I, which fractionate Li along with Cs, Nb and Sn during the late-magmatic stages of crystallization, and of zinnwaldite II and lepidolite forming from the re-equilibration of primary micas with high-temperature Li-B-W-Tl-Cs-Mn-W-rich autometasomatic fluids; (2) a Li(F)-retrogressive trend explaining the low-temperature hydrothermal muscovitization, which represents the main Li depletion process. Trace element geochemistry and paragenesis of late muscovite-phengite support that muscovitization is a district-scale process that affected the upper parts of the granite cupolas through acidic and B(Fe-Sn)-saturated hydrothermal fluids associated with metasomatic tourmalinization, which were mixed with a low Eh meteoric component.

Continental arcs are the sites of production of continental crust, but the origin of these magmatic systems is not well understood. Although a number of processes have been suggested to be important, the role of water migrating from slab to surface during subduction has been underappreciated. Directly below the Moho, hot (approximately 1,100 °C), hydrous basaltic magmas fractionate as they cool to the regional geotherm at 750 to 800 °C, ultimately solidifying as mafic underplates. Cooling and fractionation cause water to exsolve and ascend, triggering fluid-fluxed melting of overlying mafic underplates and other crust. Melting of prior mafic underplates buffers temperatures and generates the voluminous, juvenile low-K magmas of Cordilleran batholiths. These granitoid magmas comprise a low-temperature slurry of melt and residue, and recrystallize into silicic mush during adiabatic ascent. Such hydrous mushes are intermittently infused by hotter, more mafic magmas, which hybridize and facilitate ascent and, potentially, eruption. Fluid-fluxed melting overcomes many of the general petrological and geochemical problems associated with models dominated by fractional crystallization. The role of water during repeated episodes of mafic underplating is critical to generate the juvenile granitoid infrastructure of the continents.Migration of water from the slab to the surface during subduction is highlighted as a key process in the formation of continental crust.

Although the voluminous granitoids that constitute the upper crust of the Sierra Nevada batholith (California) have been investigated in detail, comparatively few studies focus on the origin of mafic bodies at similar crustal levels. Here, we present field and petrographic observations, geochronology, and geochemistry of the Hidden Lakes mafic complex in the central-eastern Sierra Nevada batholith. Our results show that the complex comprises norites, gabbros, monzondiorites, and monzonites that record fractional crystallization of a hydrous (~ 3 wt% H2O), non-primitive basalt within the upper crust (0.3 GPa) at c. 95–96 Ma. To quantitatively model the generation of the observed lithologies, we construct a two-stage polybaric crystallization model based on cumulate and melt-like bulk-rock compositions. In the first step, we model fractionation of a primitive, mantle-derived basalt at > 30 km depth, generating dominantly pyroxenite cumulates. The evolution of the derivative melt (67% of melt mass remaining) is then modeled to fractionate at 12 km depth to produce the observed lithologies within the Hidden Lakes mafic complex. Extension of this model to higher-silica melt compositions (> 65 wt% SiO2) replicates observed granodiorite compositions in the batholith, suggesting that polybaric crystallization could be an important process for the generation of arc granitoid melts. The depth of differentiation in continental arcs is debated, as field observations indicate abundant lower crustal fractionation while experimental data suggest that high-pressure crystallization of hydrous basalts cannot produce the non-peraluminous granitoid compositions observed in continental arc batholiths. Our model supports polybaric differentiation as one potential mechanism to resolve this inconsistency.

Despite the first-order importance of crystallisation–differentiation for arc magma evolution, several other processes contribute to their compositional diversity. Among them is the remelting of partly crystallised magmas, also known as cumulate melting or ‘petrological cannibalism’. The impact of this process on the plutonic record is poorly constrained. We investigate a nepheline-normative dyke suite close to the Blumone gabbros, a large amphibole-gabbro unit of the Tertiary Southern Alpine Adamello igneous complex. The compositions of the studied dykes are characterised by low SiO 2 (43–46 wt. %), MgO (5.0–7.2 wt. %), Ni (18–40 μg/g), and high Al 2 O 3 (20.2–22.0 wt. %) contents. Phenocrystic plagioclase in these dykes exhibits major, trace, and Sr isotope compositions similar to Blumone cumulate plagioclase, suggesting a genetic link between the nepheline-normative dykes and the amphibole-gabbro cumulates. We tested this hypothesis by performing saturation experiments on a nepheline-normative dyke composition in an externally heated pressure vessel at 200 MPa between 975 and 1100 °C at fO 2 conditions close to the Ni–NiO buffer. Plagioclase and spinel are near-liquidus phases at and above 1050 °C, contrasting with the typical near-liquidus olivine ± spinel assemblage in hydrous calc-alkaline basalts. The alkaline nature of the dykes results from the abundance of amphibole in the protolith, consistent with melting of amphibole-gabbro cumulates. We modelled the heat budget from the repeated injection of basaltic andesite into a partly crystallised amphibole-gabbro cumulate. The results of this model show that no more than 7% of the cumulate pile reaches temperatures high enough to produce nepheline-normative melts. We propose that such nepheline-normative dykes are a hallmark of hydrous cumulate melting in subvolcanic plumbing systems. Therefore, ne-normative dykes in arc batholiths may indicate periods with high magma fluxes.

The high-K, calcalkaline granitic rocks of the 370 Ma, post-orogenic Harcourt batholith in southeastern Australia have I-type affinities but are mildly peraluminous and have remarkably radiogenic isotope characteristics, with 87Sr/86Srt in the range 0.70807 to 0.714121 and εNdt in the range − 5.6 to − 4.3. This batholith appears to be a good example of magmas that were derived through partial melting of distinctly heterogeneous source rocks that vary from intermediate meta-igneous to mildly aluminous metasedimentary rocks, with the balance between the two rock types on the metasedimentary side. Such transitional S-I-type magmas, formed from mainly metasedimentary source rocks, may be more common than is generally realised. The Harcourt batholith also contains mainly granodioritic igneous microgranular enclaves (IMEs). Like their host rocks, the IMEs are peraluminous and have rather radiogenic isotope signatures (87Sr/86Srt of 0.71257–0.71435 and εNdt of − 7.3 to − 4.3), though some are hornblende-bearing. Origins of these IMEs by mixing a putative mantle end member with the host granitic magma can be excluded because of the variability in whole-rock isotope ratios and, for the same reason, the IME magmas cannot represent quench cumulates (autoliths) from the host magmas. Less abundant monzonitic to monzosyenitic IMEs cannot represent accumulations of magmatic biotite and/or alkali feldspar because K-feldspar is absent, and there is no co-enrichment of K2O and FeO + MgO, nor can they be mixtures of anything plausible with the host-rock magma. The granodioritic IMEs probably originated through high degrees of assimilation of a range of crustal materials (partial melts?) by basaltic magmas in the deep crust, and the monzonitic IMEs as melts of enriched subcontinental mantle. Such enclave suites provide little or no information on the chemical evolution of their host granitic rocks.

Granite is one of the most important components of the continental crust on our Earth; it thus has been an enduring studied subject in geology. According to present knowledge, granite shows a great deal of heterogeneity in terms of its texture,structure, mineral species and geochemical compositions at different scales from small dike to large batholith. However, the reasons for these variations are not well understood although numerous interpretations have been proposed. The key point of this debate is whether granitic magma can be effectively differentiated through fractional crystallization, and, if so, what kind of crystallization occurred during the magmatic evolution. Although granitic magma has high viscosity because of its elevated SiO2 content, we agree that fractional crystallization is effectively processed during its evolution based on the evidence from field investigation,mineral species and its chemical variations, and geochemical compositions. These data indicate that crystal settling by gravitation is not the only mechanism dominating granitic differentiation. On the contrary, flow segregation or dynamic sorting may be more important. Accordingly, granite can be divided into unfractionated, fractionated（including weakly fractionated and highly fractionated） and cumulated types, according to the differentiation degree. Highly fractionated granitic magmas are generally high in primary temperature or high with various volatiles during the later stage, which make the fractional crystallization much easier than the common granitic melts. In addition, effective magmatic differentiation can be also expected when the magma emplaced along a large scale of extensional structure. Highly fractionated granitic magma is easily contaminated by country rocks due to its relatively prolonged crystallization time. Thus, granites do not always reflect the characteristics of the source areas and the physical and chemical conditions of the primary magma. We proposed that highly fractionated granites are an important sign indicating compositional maturity of the continental crust, and they are also closely related to the rare-elemental（metal） mineralization of W,Sn, Nb, Ta, Li, Be, Rb, Cs, REEs, etc.

Exposures of arc crustal sections represent rare opportunities to directly evaluate lower crustal magmatic processes and their link to arc products in the middle and upper crust. Within the southernmost Sierra Nevada batholith, the Bear Valley Intrusive Suite (BVIS) exposes a contemporaneously constructed ~ 30 km thick intrusive suite, and thus is ideal for this type of examination. Here we present detailed petrography and mineral major and trace element data for the BVIS. The deepest exposed portion of the BVIS (8–9 kbars) is composed of heterogeneous mafic igneous intrusions of olivine metagabbro, olivine-hornblende orthopyroxenite, olivine-bearing hornblende norite, hornblende norite, hornblende gabbronorite, hornblendite and hornblende gabbro. Shallower crustal intrusions (3–7 kbars) are comparatively homogeneous and dominated by hypersthene-bearing and hypersthene-free tonalites. Using amphibole-plagioclase geothermometry, we show that the mafic lower crustal intrusions crystallized over a wide temperature range from 850 to 1070 °C, highlighting mafic igneous fractionation during isobaric cooling in the lower crust of the Sierran arc, while tonalitic liquids were emplaced at temperatures < 800 °C in the middle and upper crust. Calculated trace element melt compositions in equilibrium with amphibole in lower crustal gabbros are similar to measured tonalite bulk compositions and support the generation of tonalites through fractionation of the observed gabbros. Further, petrography and mineral chemistry suggest multiple distinct crystallization sequences recorded in the different types of gabbro, requiring the presence of coexisting parental melts with contrasting compositions and H2O contents. Using available experimental data, we develop a model by which mixing of variably fractionated dry and wet magmas with similar viscosities followed by crystallization-differentiation in the deep crust to explain the formation of uniform tonalitic melts at shallower crustal levels in the BVIS. This process also explains the unusual predominance of orthopyroxene in the BVIS, and the limited aluminum enrichment compared to experimental differentiation sequences of hydrous basalts. Considering the similar geochemical characteristics of intermediate and felsic igneous rocks from the Sierra Nevada batholith and the Cascades, mixing magmas of variable H2O contents in the lower crust represents a viable petrological process to produce SiO2-rich liquids that may be more common than previously recognized.

The formation, storage, and evolution of granitic magmas are fundamental processes driving the growth of continental crust. While traditionally attributed to crystal fractionation in high‐melt fraction magma chambers, the model invoking low‐melt fraction crystal mushes has gained wide acceptance. However, the chemical and textural impacts of crystal mush rejuvenation remain elusive and the precise petrological record is relatively poorly studied. The rapakivi K‐feldspar identified in the early Eocene monzogranitic porphyry of the Caina intrusive complex, Gangdese batholith, is an ideal candidate for investigating these issues, as feldspar can record clues to magmatic processes. Field survey, optical and mineral flake scanning observations, X‐ray fluorescence analysis, in situ Sr and mineral Sm‐Nd isotopic analyses, TESCAN integrated mineral analysis, electron probe microanalysis, and three‐dimensional crystal shape modeling were performed on the collected samples. K‐feldspars can be divided into three types based on chemical zonation: normal, reverse, and oscillatory zoning crystals. Varying isotopic signatures between the K‐feldspar and associated mantle suggest that the rapakivi texture originated in heterogeneous magmatic pulse recharge. Crystal shape modeling of the plagioclase chadacryst, mantle, and matrix plagioclase, combined with compositions, indicates that mantle plagioclase originated from the quenching of recharge magmas. We propose a model for the formation of rapakivi K‐feldspar and the rejuvenation of crystal mush. Repeated hot magma pulses recharged the mush, triggering magma convection and thermal perturbations. This process enabled the prolonged growth of K‐feldspar megacrysts, which were subsequently capped by plagioclase, resulting in the formation of the rapakivi texture.

The origin of the wide range of sulfur isotope compositions (i.e., δ 34 S) measured in arc rocks remains debated. While the observed δ 34 S variability has been attributed to slab-related fluids that flux the sub-arc mantle, others have argued that it primarily reflects crustal-derived processes by some combination of magmatic differentiation, country rock assimilation, and/or degassing. Here, we present new whole rock sulfur isotopes for the Late Cretaceous Bear Valley Intrusive Suite (BVIS) that represents a continuous arc crustal section in the southern Sierra Nevada Batholith, exposing lower crustal mafic cumulates and cogenetic mid-upper crustal tonalites. Our data reveal a range of δ 34 S-depleted values (–1.2 to − 5.1‰) for the BVIS with overlapping δ 34 S between mafic cumulates and tonalites. Complementary δ 34 S measurements of structurally concordant metasedimentary pendants indicate δ 34 S-depleted values (–11.5 to − 5.2‰) for deep metasedimentary rocks compared to δ 34 S-enriched values (+ 1.6 to + 6.4‰) for shallower ones. Quantitative mixing models suggest that assimilation of crustal-derived sulfur from metasedimentary rocks in the lower crust can account for the δ 34 S-depleted values in the BVIS, whereas assimilation of shallower ones is unlikely. Sulfur degassing modelling indicates that the range of δ 34 S-depleted values observed within mid-upper crustal tonalites can be reproduced by degassing  ~60–80% of the initial melt sulfur at f O 2  ≤ FMQ + 1 with initial H 2 O content of 10–12 wt%. Finally, the identical ranges of δ 34 S values within the tonalites and mafic cumulates argue for limited sulfur isotope fractionation related to magmatic sulfide immiscibility. Although assimilation, magma degassing and sulfide immiscibility are not mutually exclusive during crustal magmatic processes, field, thermal and geochemical evidence favor lower crustal-derived sulfur assimilation as the primary mechanism to explain the range of δ 34 S- depleted values within the mafic cumulates, which are ultimately inherited by the derivative tonalitic melts. Overall, this study emphasizes that deep crustal magmatic processes can severely influence the early δ 34 S evolution of arc magmas.