From floor to roof of a batholith: geology and petrography of the north-eastern Serre Batholith (Calabria, southern Italy)

ABSTRACT We present an original geological map of the north-eastern Serre Batholith (southern Italy), together with new field and petrographic data of its main five granitoid units. Our study provides an overall picture of a c. 13-thick floor-to-roof batholith exposure, focusing on the relationships between the magmatic units, which were sequentially emplaced at depth from c. 23 to c. 6 km, in a time interval from c. 297 Ma to c. 292 Ma. Indeed, this composite and zoned batholith, with its crustal scale exposure and large compositional and structural diversity, is a real natural laboratory where to test models of granitoid magma production and batholith construction. The new geological map and related field and petrographic data provide a valuable addition to the existing knowledge of the Serre Batholith and, at the same time, a new starting point for further in-depth multidisciplinary investigations aimed to better understand its architecture and build-up mechanisms.


Introduction
Mechanisms of granitoid magma ascent and emplacement, leading to the build-up of plutons and batholiths in the middle-upper crust, are still highly debated issues (Cruden & Weinberg, 2018;and references therein).Field studies and mapping activities represent the geological milestone from where to start tackling such issues.In this regard, the rare exposures of entire crustal sections represent natural laboratories that can enable reconstruction of pluton geometry, relationships between different magmatic pulses and their links with the metamorphic basement.In Italy, in addition to the well-known Sesia Magmatic System from the Ivrea Zone -Serie dei Laghi crustal section (Fountain, 1976;Sinigoi et al., 2010;Tavazzani et al., 2017Tavazzani et al., , 2020;;Voshage et al., 1990, and references therein), the late Variscan Serre Batholith in central Calabria also offers such an opportunity to study an important magmatic system from a nearly complete cross section of continental crustal (Caggianelli et al., 2007(Caggianelli et al., , 2013;;Fiannacca et al., 2015;Fiannacca, Ortolano, et al., 2017;Schenk, 1981, 1990, andreferences therein).This batholith, a c. 13 km-thick granitoid complex consisting of compositionally different plutonic units stacked at distinct depth and time, has been mapped by many authors, but mostly sketch maps with very little information about the relationships between the different granitoid units have been published so far (e.g.Caggianelli, 1989;Crisci et al., 1985;Moresi & Paglionico, 1976;Fornelli et al., 1994).Furthermore, some inland areas have never been investigated.In this paper, we report a large set of new field and petrographic data of the main granitoid units that constitute the Serre Batholith, together with an original 1:200,000 scale geological map of its entire north-eastern sector.This is the first time that such details are presented, and for such wide area, providing an overall picture of a crustal-scale floor-toroof batholith exposure.The newly presented data provide a valuable addition to the existing knowledge of this late Variscan complex, and may now represent a new starting point for further in-depth multidisciplinary studies aimed to the general understanding of the architecture and construction mechanisms of post-collisional batholiths.

The Calabria-Peloritani Orogen
The mapped area belongs to the Calabria-Peloritani Orogen (CPO; Figure 1), a fragment of the southern European Variscan Belt (Figure 1) constituted by four tectonically juxtaposed sectors (Sila Massif, Serre Massif, Aspromonte Massif and Peloritani Mountains) mostly represented by c. 300 Ma old basement rocks with a poly-orogenic history (see Cirrincione et al., 2015 for a review).After the main continental collision associated with the amalgamation of Pangea, extensive crustal melting and granitoid magmatism occurred throughout the south Variscan terranes, at c. 320-280 Ma, in a transtensional/transpressional regime that produced a complex pattern of strike-slip shear zones known as the East Variscan Shear Zone, also including the CPO (e.g.Padovano et al., 2012Padovano et al., , 2014)).The final stages of the Variscan orogeny were indeed marked also in the CPO by voluminous felsic magmatism, which gave rise to Sila and Serre composite batholiths in northern and central Calabria together with scattered S-type trondhjemite and granite plutons in southern Calabria and north-eastern Sicily (Fiannacca et al., 2015(Fiannacca et al., , 2019(Fiannacca et al., , 2020;;Fornelli et al., 1994;Rottura et al., 1990).Finally, swarms of felsic to mafic dykes (e.g.Barca et al., 2010;Romano et al., 2011) marked the transition from a late-orogenic to a post-orogenic stage.

The Serre Massif
The Serre Massif represents a tilted, almost continuous and complete cross section of late Variscan continental crust (Figure 2; Angì et al., 2010;Caggianelli et al., 2007;Schenk, 1990).This crustal section consists of three distinct portions, exposed in sequence from the NW to the SE: (a) a lower crustal sector mainly consisting of a basal granulite complex and an overlying migmatite metapelitic complex of c. 3 km and c. 5 km thickness, respectively.The granulite complex is composed of layered metagabbros, felsic granulites with intercalated metabasites and mediumcoarse grained metapelites and semipelites.The metapelitic complex is dominantly made up of biotitic paragneisses, locally garnet-sillimanite bearing, migmatitic paragneisses and intercalated metabasites.

General outline
Geological mapping has been performed on a c. 500 km 2 area at 1:200,000 scale, using the 1:50,000 topographic maps of the Istituto Geografico Militare, and digitalized by means of the ArcGIS® software.The geological map (Main Map) is the result of detailed field surveys of the magmatic units of the study area; from north to south, the mapped area depicts a complete cross section of the Serre Batholith.Field observations were paired with thin-section investigations, with the aim of making a new and refined geological map of the whole north-eastern sector of the Serre Batholith, including a detailed investigation of the relationships between the main magmatic units.(Paglionico et al., 2016), confirming or modifying former geological boundaries.In addition, compared to the above maps, it is to be highlighted that: (a) our map depicts five magmatic units, while Casmez sheets consider all the granitoid rocks as a single unit and, (b) Soverato sheet covers a batholith sector of c. 200 km 2 , much smaller than area mapped in this work, not including two of the main granitoid units and not describing in detail the relationships between them.Finally, several previous studies reporting very precise field observations were also consulted.Bedrock exposure is often poor due to widespread alteration or thick vegetal covers that prevent fruitful field observations; in particular, alteration is typically more intense in inland areas and in two-mica granitoids, porphyritic ones especially.Selected outcrops of well-exposed granitoids from the different magmatic units are shown in Figure 3(a-e).Rocks were mapped taking into account the following compositional and structural criteria: (a) mineral abundances, visually estimated by means of both mesoscopic and microscopic observations; (b) grain size color index and fabric; (c) abundance, size and shape of mafic microgranular enclaves, and (d) size, density and orientation of K-feldspar megacrysts.In this work, we define ''megacrysts'' any crystals that are remarkably larger than the rock grain size.

Migmatitic border zone (MBZ)
The passage from biotite-sillimanite-garnet paragneisses dominating the top of the lower crustal section of the Serre Massif, to the deepest emplaced granitoids of the Serre Batholith is typically marked by a compositionally heterogeneous and discontinuous border zone, c. 1 km wide and 27 km long; here a strong interaction between tonalitic magma and host rocks took place, involving intrusion-related partial melting of the host metapelites and mingling-mixing processes between the produced anatectic magma and the crystallizing tonalites.Similar processes have also been documented in the Capo Vaticano Promontory sector of the batholith (e.g.Clarke & Rottura, 1994).The border zone is mainly represented in the outcrop by: (a) garnet-bearing metapelitic migmatites (Figure 4(a)) with minor augen gneisses and amphibolites and (b) strongly foliated tonalites and quartzdiorites.The latter commonly include strongly stretched mafic microgranular enclaves (Figure 4(b,  c)), or are variably contaminated by garnet-bearing anatectic melt as a consequence of metapelite melting triggered by the emplacement of the tonalitic magma, and affected by intense shearing (e.g.Caggianelli et al., 2000, 2007) (Figure 4(c,d)).Concordant dm-to mthick pegmatitic and discordant mm-to cm-thick aplitic-pegmatitic dykes locally occur.

Amphibole-biotite tonalites (ABT)
This unit comprises strongly to moderately foliated tonalites and minor quartz diorites that, together with strongly to weakly foliated biotite tonalites (BT), represent the oldest and deepest granitoids of the batholith.They crop out extensively over an area of c. 30 km 2 at the north-eastern edge of the Serre Batholith (Squillace area), and in scattered outcrops to the southwest of the main body (Cardinale area).
ABT have a medium grain size (Figure 5 ).Field shear zones, mm-to 30 cm-thick and parallel to the hostrock foliation, commonly occur in these rocks.

Biotite tonalites (BT)
Biotite tonalites and minor quartz-diorites from this unit can be subdivided into strongly to moderately foliated (BT s ) and weakly foliated to unfoliated (BT w ) moving toward the south, i.e. to shallower crustal levels.BT s crop out over an area of c. 50 km 2 to the northeast (Petrizzi-Soverato area), where they are in contact with the ABT and the MBZ, and in a c. 25 km long belt to the southwest (Cardinale area), in contact to the north with the MBZ.Further south, BT w are intruded by the overlying muscovite-biotite porphyritic granitoids (MBPG).BT have a hypidiomorphic texture and a medium grain size, slightly coarsening towards the north (Figures 5(b,c) and 6(b,c)).Major BT components (Figure 6(b,c)) are euhedral-subhedral and rarely zoned plagioclase (c.50%), anhedral to polygonal quartz (c.30%), subhedral biotite plates (c.20%).Ilmenite, allanite, epidote, apatite, titanite and zircon are the accessory minerals.Primary muscovite rarely occurs in the BT w , interleaved with biotite.Evidence of supra-to subsolidus deformation, such as oriented fabric defined by biotite and plagioclase, chessboard extinction in quartz and submagmatic fractures, occur in foliated BT (Figure 7(b,c)).Cmto m-long mafic microgranular enclaves (Figure 8 (c)) vary from strongly to weakly flattened accordingly to host-rock foliation; like in the ABT, size and frequency tend to decrease soutward, i.e. moving to shallower levels, apart from a few outcrops in the proximity of the overlying MBPG, which are characterized by small, but abundant mafic microgranular enclaves.Finally, pegmatitic and aplitic dykes are widespread, occurring with higher frequency toward the roof of the unit and, for the BT from the Cardinale area, also toward the floor.

Muscovite-biotite porphyritic granodiorites and granites (MBPG)
MBPG represent the deep-intermediate level of the Serre Batholith.These rocks also show a rather continuous NE-SW distribution, with irregular width (from c. 0.5-7 km).This unit is bounded to the south and to the east by the overlying two-mica equigranular granodiorites and granites (MBG).They seldom have an oriented fabric marked by rough alignments of K-feldspar megacrysts and biotite plates (Figure 5

Biotite granodiorites (BG)
Biotite granodiorites are the youngest (c., 292 Ma; Fiannacca, Williams et al., 2017, and references therein) and shallowest granitoids of the batholith, intruding the upper crustal metamorphic basement at a depth of c. 6 km (Caggianelli et al., 2000) (Figure 2).Like the underlying magmatic units, the BG unit trends NE-SW, with a maximum width of about 5 km gradually shrinking up to totally disappear to the northeast.BG have an inequigranular medium-coarse grain size and a hypidiomorphic and mainly isotropic structure (Figures 5(f) and 6(f)).A weak oriented fabric is locally observed in areas close to the contact with the metamorphic host rocks.Most samples, from the whole unit, locally exhibit deformation microstructures such as quartz chessboard, core-and-mantle structure in quartz, deformation twins in feldspar and kinked biotite (Fiannacca et al., 2021).BG are made up of wellzoned euhedral-subhedral plagioclase (c.35%), anhedral quartz (c.30%), anhedral K-feldspar (mostly orthoclase, c. 15%), euhedral-subhedral prismatic biotite (c.20%).Biotite is a diagnostic phase in BG, as it typically occurs in euhedral barrel-shaped grains up to 1 cm thick.Very rare hornblende occurs as relicts partially replaced by biotite and fine-grained aggregates (Figure 7(f)).Accessories consist of zircon, apatite, allanite, titanite, ilmenite and rare epidote.Dm-to m-sized mafic microgranular enclaves, usually rounded but locally flattened and stretched, frequently occur (Figure 8(d)).Dm-to m-thick pegmatitic and aplitic dykes, as well as andesite to rhyolite porphyritic dykes, locally cut the BG.

ABT-BT
No primary contact between ABT and BT was detected in the field, because of the widespread vegetal and anthropic covers, together with strong alteration of the outcrops.On the other hand, a quick passage between amphibole-bearing and amphibole-free tonalites has been locally observed in a distance of c. 10 m.In some cases, this sudden passage is due to fault contacts, while in general it might be consistent with primary magmatic relationships, by fractional crystallization of the original tonalitic magma (e.g.Fiannacca et al., 2015;Rottura et al., 1990)  Ortolano, Fazio, et al., 2020;Fazio et al., 2015) and the Serre and Sila Massifs (Curinga-Girifalco Line; Festa et al., 2020;Langone et al., 2006;Schenk, 1990).A physiographic expression of the c.WNW-ESE tectonic lineament is the Catanzaro Through (Brutto et al., 2016;Tansi et al., 2007), also known as Catanzaro Line (Cirrincione et al., 2015;Ortolano, Visalli, et al., 2020), a late Miocene-Quaternary tectonic depression that is considered a key area to understand the tectonic evolution of the entire Mediterranean region (Brutto et al., 2016;and references therein).
ABT and BT share the same strongly foliated structure, with local mylonitic features that provide evidence for syn-shear emplacement of both units.In particular, strong foliation is a feature of the deepest granitoids of the batholith, i.e.ABT-BT from Squillace-Petrizzi area, and BT in the proximity of MBZ in the whole Cardinale area (c.23 and 20 km deep, respectively; Caggianelli et al., 2000).Moving southward, i.e. toward shallower levels of the BT unit, foliation progressively weakens.No significant difference in size and frequency of pegmatitic-aplitic dykes and strongly stretched mafic microgranular enclaves has been observed astride of the mapped ABT-BT boundary.Finally, it is to be highlighted that, despite the batholith floor position of both units, ABT typically underlie BT.

BT-MBPG
Despite extreme alteration of the outcrops, rare exposed contacts clearly document intrusion of the MBPG into the BT, as already reported in several previous studies (Paglionico et al., 2016;and references therein).The contact zones are characterized by interdigitations between the two rock types and by the presence of several rounded to angular BT blocks, up to meter in size, embedded in the MBPG during their emplacement over the tonalite unit (Figure 8  (d)).These zones are often also marked by weak isoorientation of K-feldspar megacrysts, as well as by narrow shear zones developed in the MBPG, both parallel to the contact between the two granitoids; sometimes these shear zones are developed precisely at the magmatic contact.On the other hand, BT from the same contact areas are massive, or show a weak foliation, generally not in accordance with shear zones orientation and MBPG magmatic foliation.

MBPG-MBG
Field observations along several transects crossing the boundary between the two-mica granitoid units, coupled with thin-section investigations, reveal that the MBPG-MBG passage occurs as a transition over an area c. 500 m wide.In particular, this value refers to the eastern boundary of the units (roughly trending N-S), where better outcrop conditions and a more continuous exposure of the studied units occur.Specifically, this transition consists of a progressive decrease in frequency of K-feldspar megacrysts (Figures 3(c) and 8(e)).Moreover, despite no systematic relationship exists between depth and K-feldspar crystal shape or size, being the deepest regions of the unit characterized by K-feldspar in the whole 0.5-12 cm range, the largest megacrysts (> 5-6 cm) do not occur in uppermost levels.Even more significant, quantitative density analysis of 1-6 cm long K-feldspar along the studied transects indicates a gradual drop in K-feldspar megacryst occurrence in about 500 m, moving to the overlying MBG (Figure 8(e)).In particular, considering outcrop windows of 1m 2 , K-feldspar density pass from c. 50 megacrysts/m 2 to c. 20 megacrysts/m 2 in the first 400 m and, more rapidly, from c. 20 megacrysts/m 2 to no occurrence in about 100 m.Based on these findings, and also considering observations from transects across the MBPG-MBG boundaries in the whole mapped area, granitoids the two units can be framed within four categories: MBPG (K-feldspar density>40 megacrysts/m 2 ), mMBPG (mostly MBPG, 40-5 megacrysts/m 2 ), mMBG (mostly MBG, 5-1 megacrysts/m 2 ) and MBG (no megacrysts).This transition might reflect partial homogenization of MBPG granitoids from the unit roof with the freshly emplaced overlying MBG magmas, by crystal mush-magma mixing, or recycling of BMPG granitoids into the younger MBG unit.Similar

MBG-BG
Field observations assisted by thin-section investigations along several transects indicate transitional contacts also between MBG and BG, confirming previous results from Fornelli et al. (1994) and Paglionico et al. (2016).In addition, the transition zone has been carefully characterized in this work and its width quantified in about 1.5 km in the western part of the mapped area, decreasing to the east.The transition from MBG to BG is defined by progressive: (a) muscovite decreasing in abundance and size; (b) biotite noticeably passing from tabular to prismatic crystals, and increasing in abundance and size; (c) decreasing monazite abundance; (d) increasing titanite, allanite and magmatic epidote; (e) K-feldspar passing from microcline to orthoclase.Though, unlike the previous transition, these variations are not regular and simple to quantify.Therefore, these transitional granitoids are here defined MBG/BG to highlight that they are characterized by coexisting MBG-and BG-like features.The gradational contact between MBG and BG is interpreted as previously proposed for the MBPG-MBG transition.Interaction of the uppermost MBG with the overlying BG magmas is also supported by widespread plagioclase disequilibrium features in plagioclase from the transitional MBG, indicative of reaction with a more mafic magma (Fiannacca et al., 2016).

Conclusions
This study presents, for the first time, a geological map of the northeastern late Variscan Serre Batholith at a scale of 1:200,000, providing a floorto roof portrait of the relationships between the different granitoid units making up this c.13 km-thick batholith.
Main findings and related implications arisen from field observations integrated by meso-and microscopic investigations of the main five granitoid units, differing in emplacement depth, composition and age (e.g.Caggianelli et al., 2000;Fiannacca et al., 2015;Fiannacca, Williams, et al., 2017), are here summarized: . Intensity of foliation in strongly to moderately foliated amphibole-biotite tonalites (ABT) and strongly to weakly foliated biotite tonalites (BT), which represent the oldest and deepest mapped granitoids (c.297 Ma; c. 23-20 km deep), increases toward the contact with the lower crustal migmatitic host rocks.A nearly continuous belt of strongly to moderately foliated BT runs from the NE (Petrizzi-Soverato area) to the SW (Cardinale area), where these rocks extend up to c. a 1 km from the migmatite border zone, and then pass upward to weakly foliated to locally unfoliated BT.These structural features, coupled with microstructural evidence of deformation at suprasolidus conditions, are consistent with emplacement of the earliest granitoids along an active shear zone and a minor tectonic influence during solidification of the upper levels of the BT unit.No primary contact between ABT and BT, either sharp or gradational, has been observed in the field.Nevertheless, field, petrographic and previous geochemical work (Fiannacca et al., 2015)  .The contact between MBPG and overlying intermediate-upper seated muscovite-biotite equigranular granodiorites and granites (MBG; c. 295 Ma) is gradational, over a band measured in the eastern part of the unit as c. 500 m wide.Specifically, this transition consists of a progressive decrease in frequency of K-feldspar megacrysts.This may be interpreted to reflect partial homogenization of MBPG granitoids from the roof of the unit with the freshly emplaced MBG magmas by: (a) crystal mush-magma mixing or, (b) recycling of reheated MBPG into the younger MBG magmas. .Lack of visible oriented rock fabric in the whole MBG unit implies negligible shear zone activity during or following magma emplacement.However, all the Serre Batholith granitoids show evidence of deformation at supra-to subsolidus conditions and, furthermore, possible shear zone involvement is suggested by a magnetic foliation detected in the apparently isotropic MBG and overlying BG (Fiannacca et al., 2021; and references therein); .Gradational contacts, over a band wide up to 1.5 km, also occur between the MBG and the overlying biotite granodiorites that make up the batholith roof (BG, c. 292 Ma).As for the MBPG, these gradational contacts suggest that BG magmas interacted with the granitoids from the top of the underlying MBG unit when the latter were likely largely solidified.In addition to magnetic foliation, BG locally show a visible oriented fabric, possibly suggesting a stronger tectonic influence during their emplacement.
On the whole, this study indicates no batholithscale systematic relationship between emplacement depth and age with fabric intensity.On the other hand, a within-unit relationship has been identified in the and BT units, where the most foliated rocks occur at the base of the units, as well as in the MBPG, where evidence of oriented stress occurs close to the contact with underlying BT.MBG and BG show no relationship between type and intensity of deformation with emplacement depth, as also indicated by (Fiannacca et al., 2021), even though foliated BG samples typically come from the top of the BG unit.
This new geological map and related field and petrographic information may now represent a new starting point for further in-depth multidisciplinary investigations of the mechanisms responsible for the build-up of the Serre Batholith.This composite and zoned batholith, with its 13-km of floor-to-roof exposure and large compositional and structural diversity, is indeed a real natural laboratory where to test general models of granitoid magma production and batholith construction, with significant implications on the processes responsible for the compositional and structural evolution of the continental crust.

Software
The map has been drawn using ArcGIS® Pro, and its final assemblage and graphical editing has been realized with CorelDRAW®.

Figure 1 .
Figure 1.(a) Distribution of pre-Alpine basement rocks in western Europe.(b) Distribution of Alpine and pre-Alpine (Variscan and/ or pre-Variscan) basement rocks in the Calabria-Peloritani Orogen and main tectonic lineaments.Modified after Angì et al. (2010; and references therein).
(a)), slightly increasing approaching the border zone, where amphibole crystals up to 2 cm in size locally occur.Texture is generally hypidiomorphic (Figure6(a)).Main assemblage is represented by unzoned to weakly zoned euhedral plagioclase (c.50%), quartz in anhedral crystals or foam aggregates (c.20%, Figure7(a)), biotite aggregates (c.25%, Figure7(a)), and subhedral amphibole (< 5%; hornblende, with rare cummingtonite only close to the metamorphic basement) associated to biotite.Accessories are ilmenite, titanite, allanite, epidote, apatite and zircon.The magmatic foliation, trending NE-SW, parallel to the metamorphic foliation in the underlying migmatites, is more developed close to the MBZ contact; a lineation defined by plagioclase, biotite and amphibole, is also often visible.Supra-to subsolidus deformation microstructures, such as submagmatic microfractures in plagioclase, stretched amphibole, biotite and polygonal quartz aggregates (Figures6(a) and 7(a)), chessboard extinction in quartz and biotite folia wrapped around fractured plagioclase porphyroclasts, commonly occur in these rocks.ABT often contain centimetric to metric mafic microgranular enclaves, which are stretched and flattened on the host rock foliation plane (Figure8(a,b)).Both enclave size and frequency tend to decrease moving to shallower depth.Widespread pegmatitic and, more rarely, aplitic dyke swarms intrude the ABT, mostly in proximity of the border zone(Figures 3(b) and 8(b) 3.6.Muscovite-biotite granodiorites and granites (MBG)MBG represent the intermediate-upper level of the batholith, cropping out along a NE-SW direction and bounded to the south by the overlying biotite granodiorites (BG).A large part of this magmatic unit is covered by forests, where the rocks are mostly exposed as large boulders and tors emerging from the ground level for several meters (Figure3(e)).Rocks have a slightly inequigranular medium grain size and a hypidiomorphic and isotropic texture.Deformation microstructures, described in detail byFiannacca et al. (2021), include local quartz chessboard, stretched mica aggregates wrapping feldspar, deformation twins in feldspar and kinked micas.They are composed by euhedral-

Figure 3 .
Figure 3. Selected granitoid outcrops from different levels of the north-eastern Serre Batholith.(a) Monolith exposure of biotite tonalite from deep batholith levels.(b) Cliff made of amphibole-biotite tonalite from the batholith floor, pervasively intruded by swarm of dm-to m-thick pegmatite dykes.(c) Typical outcrop of well-preserved muscovite-biotite porphyritic granite from the deep-intermediate levels, with 2-3 cm long K-feldspar megacrysts.(d) Tor outcrops of muscovite-biotite equigranular granite from the intermediate-upper crustal levels.(e) River bank exposure of biotite granodiorite from the batholith roof.
. A possible tectonic reworking of the original magmatic relationships in the Squillace-Petrizzi sector of the Serre Batholith is supported by statistics-based geochemical mapping of this area byFiannacca, Ortolano, et al. (2017; and   references therein), indicating an abrupt passage between a more mafic unit to the north and a more felsic unit to the south, along a nearly WNW-ESE direction, c. 3 southward of the present supposed boundary between ABT and BT (e.g,Paglionico et al., 2016; this  work).In fact, this WNW-ESE direction is the same of two main faults that bound to the north and to the south the Squillace-Petrizzi tonalites.Furthermore, this direction coincides with important Alpine tectonic lineaments (Figure1) active since the Paleocene, which were responsible for the juxtaposition of different crustal sectors, such as the Serre and Aspromonte Massifs (Palmi Shear Zone;Prosser et al., 2003;

Figure 7 .
Figure 7. Selected representative petrographic features of the studied granitoids (crossed polars except Figure 5(f)).(a) Oriented fabric defined by alignment of subhedral plagioclase crystals, polygonal quartz aggregates and stretched biotite plates in ABT.(b) Iso-oriented biotite and plagioclase in foliated BT.(c) Submagmatic fracture filled with biotite and epidote in plagioclase from foliated BT.(d) Euhedral microcline from the medium-fine grained matrix of MBPG.(e) Two-mica assemblage in MBG.(f) Partially replaced amphibole in BG.
interpretations have been proposed by Žák and Paterson (2005) and Paterson et al. (2016), respectively to explain gradational contact zones with similar size and features in the Tuolumne Intrusive Complex (Sierra Nevada Batholith).

Figure 8 .
Figure 8. Outcrop-scale features of studied granitoids from the Serre Batholith.(a) Swarm of stretched mafic microgranular enclaves in ABT.(b) ABT cut by discordant aplitic dykelets and 30 cm-thick shear zone parallel to tonalite foliation, also marked by flattened enclaves.(c) Slightly flattened mafic microgranular enclaves in unfoliated BT.(d) three-meter sized tonalite block within MBPG from the BT-MBPG transition zone.MBPG are crossed by a narrow shear zone system.(e) Outcrop of mMBG from the MBPG-MBG transition zone.(f) Globular mafic microgranular enclave in BG.

Table 1 .
Schematic summary of the main petrographic features of the Serre Batholith plutonic units.
not occur in the uppermost unit levels.Matrix consists of rare euhedral (as inclusions in Kfs megacrysts) to anhedral quartz (c.30%), euhedral-subhedral weakly zoned plagioclase (c.20%), euhedral to anhedral microcline (c.15%), euhedral-subhedral biotite (c.7%), and subhedral-anhedral muscovite (c.3%) mainly bordering biotite, K-feldspar or quartz (Figure suggest a genetic link by fractional crystallization, with the ABT likely crystallizing slightly earlier and at slightly deeper levels than BT; .The passage from deep-seated BT and deep-intermediate seated muscovite-biotite porphyritic granodiorites and granites (MBPG; c. 295 Ma) is locally marked by clear intrusive contacts.Rounded to angular blocks of BT in the MBPG indicate that the latter intruded and fragmented the tonalites when they had already achieved a rigid state.Rare oriented fabric marked by alignment of K-feldspar megacrysts and frequent occurrence of narrow shear zones in the MBPG from areas close to the contact with the underlying BT would suggest shear zone activity also during solidification of the basal MBPG; on the other hand, no oriented fabric or narrow shear zones have been observed in the uppermost levels of the MBPG unit;