Petrography and Geochemistry of the Leucocratic Rocks in the Ophiolites from the Pollino Massif (Southern Italy)

: In the Tethyan realm, leucocratic rocks were recognized as dikes and layers outcropping in the ophiolitic rocks of the Western Alps, in Corsica, and in the Northern Apennines. Several authors have suggested that the origin of leucocratic rocks is associated with partial melting of cumulate gabbro. Major and trace elements composition and paragenesis provided information about the leucocratic rocks genetic processes. This research aims at disclosing, for the ﬁrst time, the petrographical and geochemical features of Timpa delle Murge leucocratic rocks, Pollino Massif (southern Italy), in order to discuss their origin and geodynamic signiﬁcance through a comparison with other Tethyan leucocratic rocks. These rocks are characterized by high amounts of silica with moderate alumina and iron-magnesium contents showing higher potassium contents than plagiogranites, due to plagioclase alteration to sericite. Plagioclase fractionation reﬂects negative Eu anomalies indicating its derivation from gabbroic crystal mushes. The chondrite normalized REEs patterns suggest the participation of partial melts derived from a metasomatized mantle in a subduction environment. The results reveal some similarities in composition with other Tethyan leucocratic rocks, especially those concerning Corsica and the Northern Alps. These new data provide further clues on the origin of these leucocratic rocks and the Tethyan area geodynamic evolution.


Introduction
The petrography and the geochemistry of leucocratic rocks outcropping in the Pollino Massif ophiolitic sequence were analyzed. The origin of leucocratic rocks has been much debated since these rocks can provide important constraints on the evolution of the Earth's continental lithosphere [1].
It is important to note that geochemical data of some major oxides (SiO 2 , TiO 2 , Na 2 O) and especially trace elements (Sr, Nb, Y, and REEs) are useful in order to distinguish between these different processes which led to the formation and evolution of granitoid rocks [11,12].
It is important to note that geochemical data of some major oxides (SiO2, TiO2, Na2O) and especially trace elements (Sr, Nb, Y, and REEs) are useful in order to distinguish between these different processes which led to the formation and evolution of granitoid rocks [11,12].
The purpose of this paper is to characterize, for the first time, with a petrographic and geochemical study, the leucocratic rocks of the ophiolitic rocks of the North Calabria Unit of the Pollino Massif, southern Italy. We also compare these rocks with those of Western Alps [15], Northern Apennines [16,17], and other Tethyan regions such as Turkey [18], Cyprus [1], Serbia [19], and Oman [20,21], in order to provide new constraints on the origin of these rocks within the general framework of the geodynamic evolution of the Tethyan realm.
The Liguride Complex includes, from bottom to top, the Northern Calabrian Unit, the Frido Unit, and the Crystalline Metamorphic Units [35,36]. The Northern Calabrian Unit consists of a pelitic matrix with blocks of ophiolitic rocks, pelagic sediments, and turbiditic successions [37]. The pelitic matrix is not foliated because the Northern Calabrian Unit is not affected by any orogenic metamorphism [28]. This unit shows sea-floor alteration [28] and any evidence of orogenic metamorphism. The Frido Unit consists of low-grade phyllites, calc-schists, and meta limestones with associated ophiolitic rocks [38]. Slivers of continental crust [24,25,31,36,37,39,40] occur in this unit. The association of continental crust slivers with ophiolites is commonly reported in ophiolite-bearing units of the Alpine-Apennine orogenic system [36]. The slivers of continental crust together with ophiolites have been involved in the subduction process responsible for the formation of the Liguride accretionary wedge [36]. Ophiolites of the Northern Calabrian Unit outcrop in the Timpa delle Murge and Timpa di Pietrasasso area [41]. In the Timpa delle Murge area ophiolites are composed of serpentinites, gabbro cumulates [39,[42][43][44], and are associated with leucocratic rocks, forming a volumetrically minor part of an ophiolitic sequence ( Figure 2). They are stratigraphically overlain by pillow lavas, hyaloclastites, and diabases. Serpentinites are characterized by a pseudomorphic texture and miloniticcataclastic structures.  [26]).
The Liguride Complex includes, from bottom to top, the Northern Calabrian Unit, the Frido Unit, and the Crystalline Metamorphic Units [35,36]. The Northern Calabrian Unit consists of a pelitic matrix with blocks of ophiolitic rocks, pelagic sediments, and turbiditic successions [37]. The pelitic matrix is not foliated because the Northern Calabrian Unit is not affected by any orogenic metamorphism [28]. This unit shows sea-floor alteration [28] and any evidence of orogenic metamorphism. The Frido Unit consists of low-grade phyllites, calc-schists, and meta limestones with associated ophiolitic rocks [38]. Slivers of continental crust [24,25,31,36,37,39,40] occur in this unit. The association of continental crust slivers with ophiolites is commonly reported in ophiolite-bearing units of the Alpine-Apennine orogenic system [36]. The slivers of continental crust together with ophiolites have been involved in the subduction process responsible for the formation of the Liguride accretionary wedge [36]. Ophiolites of the Northern Calabrian Unit outcrop in the Timpa delle Murge and Timpa di Pietrasasso area [41]. In the Timpa delle Murge area ophiolites are composed of serpentinites, gabbro cumulates [39,[42][43][44], and are associated with leucocratic rocks, forming a volumetrically minor part of an ophiolitic sequence ( Figure 2). They are stratigraphically overlain by pillow lavas, hyaloclastites, and diabases. Serpentinites are characterized by a pseudomorphic texture and milonitic-cataclastic structures. The intrusive complex of the ophiolitic sequences of the Northern Calabrian Unit is a minor part of the ophiolites from the Calabria-Lucania area and occurs as bodies not exceeding 1 km 3 in volume [2]. Figure 2. Geological schematic map of sampled area (Timpa delle Murge). Scale 1:10,000 (modified after [44]).
Field observations indicate that the studied leucocratic rocks typically occur as flaps at the pseudo stratigraphic contact between gabbroic and basaltic bodies of the ophiolitic sequence of Timpa delle Murge. They appear in limited strips, and are medium to coarse grained, a few tens of meters thick and are light gray in color. The texture is massive and heterogeneous; quartz and plagioclase crystals can be identified in hand specimens (Figure 3).  The intrusive complex of the ophiolitic sequences of the Northern Calabrian Unit is a minor part of the ophiolites from the Calabria-Lucania area and occurs as bodies not exceeding 1 km 3 in volume [2].
Field observations indicate that the studied leucocratic rocks typically occur as flaps at the pseudo stratigraphic contact between gabbroic and basaltic bodies of the ophiolitic sequence of Timpa delle Murge. They appear in limited strips, and are medium to coarse grained, a few tens of meters thick and are light gray in color. The texture is massive and heterogeneous; quartz and plagioclase crystals can be identified in hand specimens ( Figure 3). The intrusive complex of the ophiolitic sequences of the Northern Calabrian Unit is a minor part of the ophiolites from the Calabria-Lucania area and occurs as bodies not exceeding 1 km 3 in volume [2]. Figure 2. Geological schematic map of sampled area (Timpa delle Murge). Scale 1:10,000 (modified after [44]).
Field observations indicate that the studied leucocratic rocks typically occur as flaps at the pseudo stratigraphic contact between gabbroic and basaltic bodies of the ophiolitic sequence of Timpa delle Murge. They appear in limited strips, and are medium to coarse grained, a few tens of meters thick and are light gray in color. The texture is massive and heterogeneous; quartz and plagioclase crystals can be identified in hand specimens (Figure 3).

Materials and Methods
For this work, 16 samples of unweathered leucocratic rocks were collected at Timpa delle Murge. The specimens are leucocratic rocks of the Timpa delle Murge ophiolitic sequence, found in contact between gabbroic and basaltic bodies.
Petrographic and microstructural observations were carried out with a transmitted light microscope. Whole rock major (SiO 2 , Al 2 O 3 , Fe 2 O 3 , MnO, MgO, CaO, Na 2 O, K 2 O, TiO 2 , P 2 O 5 ) and trace elements (Sc, Be, V, Ba, Sr, Y, Zr, Cr, Co, Zn, Ga, Ge, Rb, Nb, Ag, Sn, Cs, Hf, Ta, W, Tl, Pb, Th, U, REE) contents of the 16 samples were measured by using an inductively coupled plasma mass spectrometer (ICP-MS) at the Activation Laboratories (Ancaster, Canada) after sample powders digestion using a four acid attack. A 0.25 g sample was firstly digested using hydrofluoric acid, then using a nitric and perchloric acids mixture, before being heated in several ramping cycles using precise programmer-controlled heating that took the samples to incipient dryness. When the incipient dryness was obtained, the samples were brought back into solution using aqua regia and then they were analyzed with Varian ICP-OES and PerkinElmer ICP-MS instruments. Total loss on ignition (LOI) values were gravimetrically estimated after overnight heating at a temperature of 950 • C. Precision and accuracy are generally within 10%. Whole-rock mineralogy of samples was determined by X-ray powder diffraction (XRPD) at the Department of Sciences, University of Basilicata, Potenza, Italy, using a Siemens D5000 diffractometer with Cu-Kα radiation and a 40 kV, 32 mA, and 0.02 • (2θ) step size setup.

Petrography
The samples consist of leucocratic rocks and show equigranular, medium to coarse grained texture ( Figure 4). The texture ranges from hypidiomorphic granular consertal (Figure 4a), where the boundaries between the quartz crystals are interdigitated and wedged together indicating simultaneous growth of the crystals, to granophyric, with vermicular intergrowths between quartz and plagioclase ( Figure 4b). Coleman and Donato [45] suggest that the granophyric texture is a primary magmatic feature in granitic rocks. The mineral assemblage consists of quartz, plagioclase, and minor amounts of K-feldspar and secondary muscovite and generally these rocks show accessory minerals such as zircon, apatite, epidote, and opaque minerals [46,47]. Mafic minerals are primary biotite and secondary chlorite. Plagioclase crystals are euhedral and show deformation twins as well as an ondulose extinction and have albitic composition (Figure 4c). Quartz crystals show undulose extinction and incipient dynamic recrystallization along their boundaries, as shown by subgrains, new grains, and deformation lamellae ( Figure 4d). K-feldspar is not interstitial since it is euhedral with tabular prismatic habit, often Carlsbad twinned with orthoclase. Muscovite forms tabular crystals associated with epidote and quartz and show undulose extinction and ductile deformations until two generations of muscovite are present. The first type of muscovite is igneous and forms large crystals with euhedral habit associated with epidote and quartz and shows undulose extinction and ductile deformations. The second type consists of small crystals associated with chlorite ( Figure 4e). Biotite is present as brownish to greenish flakes, and contains zircon, apatite, and secondary epidote. Sericite and saussurite occur as secondary phases replacing plagioclase. Chlorite is present as pseudomorphs after biotite with inclusions of apatite, zircon, and opaques ( Figure 4f). These rocks have undergone considerable deformation associated with metamorphic events, as clearly indicated by the microstructures observed in the major minerals as the simplectites that form as a breakdown product of K-feldspar during retrograde metamorphism.  Since mafic minerals do not exceed 10%, these rocks are classified, according to some authors [48][49][50] as trondhjemites, also evidenced in the Ab-An-Or triangular diagram (  The presence of chlorite, mica, and epidote crystals shows that these rocks are a result of metasomatism, probably related to fluid circulation near spreading centers [51]. Since mafic minerals do not exceed 10%, these rocks are classified, according to some authors [48][49][50] as trondhjemites, also evidenced in the Ab-An-Or triangular diagram ( Figure 5). Since mafic minerals do not exceed 10%, these rocks are classified, according to some authors [48][49][50] as trondhjemites, also evidenced in the Ab-An-Or triangular diagram (  The presence of chlorite, mica, and epidote crystals shows that these rocks are a result of metasomatism, probably related to fluid circulation near spreading centers [51]. The presence of chlorite, mica, and epidote crystals shows that these rocks are a result of metasomatism, probably related to fluid circulation near spreading centers [51].

Trace Elements
Regarding trace elements (Table 1)

Geochemical Features and Genetic Interpretation
The Na 2 O content in analyzed leucocratic rocks is consistent with those of mid-ocean ridge basalts (MORB) as defined by Silantyev et al. [52] (≤8.0 wt.%). However, the relatively high potassium content indicates that the studied rocks experienced a secondary alteration that is testified by the muscovite/sericite occurrence [53].
The SiO 2 vs. Na 2 O+K 2 O diagram [48,54] (Figure 6a) indicates that the studied samples may be classified as sub-alkaline in composition characterized by Na 2 O values from 4.59 to 5.08 wt.% which matches the high modal abundance of plagioclase with albitic composition observed in these rocks.

Geochemical Features and Genetic Interpretation
The Na2O content in analyzed leucocratic rocks is consistent with those of mid-ocean ridge basalts (MORB) as defined by Silantyev et al. [52] (≤8.0 wt.%). However, the relatively high potassium content indicates that the studied rocks experienced a secondary alteration that is testified by the muscovite/sericite occurrence [53].
The SiO2 vs. Na2O+K2O diagram [48,54] (Figure 6a) indicates that the studied samples may be classified as sub-alkaline in composition characterized by Na2O values from 4.59 to 5.08 wt.% which matches the high modal abundance of plagioclase with albitic composition observed in these rocks.   Trace element contents were normalized to MORB composition defined by Pearce et al. [57]. Figure 8 shows that the analyzed rocks have high content of K and Ba of about 10 times the MORB, Rb and Th of about 70-80 times those of MORB, enrichments in Ta, Nb, Ce, P, Zr, Hf, Sm, between 1 and 10 times the MORB, and depletions in Sr, Y, and Yb compared to the MORB. The depletion in Sr resulting from Figure 8 may indicate fluid leaching but may alternatively be interpreted as the result of trondhjemites fractionation retained in gabbroic mushes, and thus related to the negative Eu anomaly (Figure 9) [58]. The relative enrichment in K and Rb depends on the presence of K-feldspar whereas the moderate negative Ba anomaly may be due to the low degree of alteration of the samples [51,59].  Trace element contents were normalized to MORB composition defined by Pearce et al. [57]. Figure 8 shows that the analyzed rocks have high content of K and Ba of about 10 times the MORB, Rb and Th of about 70-80 times those of MORB, enrichments in Ta, Nb, Ce, P, Zr, Hf, Sm, between 1 and 10 times the MORB, and depletions in Sr, Y, and Yb compared to the MORB. The depletion in Sr resulting from Figure 8 may indicate fluid leaching but may alternatively be interpreted as the result of trondhjemites fractionation retained in gabbroic mushes, and thus related to the negative Eu anomaly (Figure 9) [58]. The relative enrichment in K and Rb depends on the presence of K-feldspar whereas the moderate negative Ba anomaly may be due to the low degree of alteration of the samples [51,59].  Trace element contents were normalized to MORB composition defined by Pearce et al. [57]. Figure 8 shows that the analyzed rocks have high content of K and Ba of about 10 times the MORB, Rb and Th of about 70-80 times those of MORB, enrichments in Ta, Nb, Ce, P, Zr, Hf, Sm, between 1 and 10 times the MORB, and depletions in Sr, Y, and Yb compared to the MORB. The depletion in Sr resulting from Figure 8 may indicate fluid leaching but may alternatively be interpreted as the result of trondhjemites fractionation retained in gabbroic mushes, and thus related to the negative Eu anomaly (Figure 9) [58]. The relative enrichment in K and Rb depends on the presence of K-feldspar whereas the moderate negative Ba anomaly may be due to the low degree of alteration of the samples [51,59].  Chondrite normalized REEs patterns (Figure 9, normalization values from [60]) lack anomalies in Ce for all samples (Ce/Ce* median = 0.97). In contrast, negative Eu anomalies were observed for all samples with a median of 0.61 and a range of 0.47-0.68, consistent with fractional crystallization of plagioclase from precursor highly crystalline crystal mushes [59]. The role of plagioclase fractionation is clearly evident in the increasing depletion of Eu during magma evolution from gabbroic to plagiogranite as occurs in many arc and rift-related granites rocks [17]. In Table 1, further fractionation indices such as (La/Yb)ch and (Gd/Yb)ch were calculated exhibiting median values 52.17 and 6.93, respectively. The resulting chondrite normalized REEs patterns are very similar for all studied samples showing, in particular, a major enrichment in light over heavy REEs. The LREEs concentrations (about 100 La) are higher than those of the HREEs by almost two orders of magnitude. The light and middle REEs (La-Tb) show less variation between samples than the heavy REE (Dy-Lu). The homogeneous chondrite normalized REEs patterns of the leucocratic rocks of Timpa delle Murge exhibit higher (La/Yb)ch values with depletion of MREEs and HREEs with respect to those of other Tethyan plagiogranites ( Figure 9). This REEs pattern is typical of leucocratic and granitoid rocks such as tonalites and trondhjemites suggesting we are in the presence of differentiated rocks that originated by mantle partial melting in a subduction environment, in agreement with what was reported, for instance, by [10][11][12]14]. The (Gd/Yb)ch values indicate that other phases (such as amphibole and/or garnet) were fractionated pointing to an origin in a thickened continental crust.
A comparison among the samples of Timpa delle Murge with those of several Tethyan realm plagiogranites of ophiolitic complexes [1,11,12,17,19,21,42,52,61], was made. These rocks are characterized by SiO2 contents showing a median between 65 and 70 wt.%, Al2O3 with a median of about 15 wt.%, Fe2O3 in the 0 to 5-6 wt.% range, Na2O ranging from 3 to 10 wt.%, K2O from 0 to 4 wt.% and MgO in the 0-7 wt.% range (Table  1). Furthermore, Figure 10 displays a box and whiskers plot for major oxides for both the analyzed samples from Timpa delle Murge as well as for other Tethyan plagiogranites. Chondrite normalized REEs patterns (Figure 9, normalization values from [60]) lack anomalies in Ce for all samples (Ce/Ce* median = 0.97). In contrast, negative Eu anomalies were observed for all samples with a median of 0.61 and a range of 0.47-0.68, consistent with fractional crystallization of plagioclase from precursor highly crystalline crystal mushes [59]. The role of plagioclase fractionation is clearly evident in the increasing depletion of Eu during magma evolution from gabbroic to plagiogranite as occurs in many arc and rift-related granites rocks [17]. In Table 1 (Figure 9). This REEs pattern is typical of leucocratic and granitoid rocks such as tonalites and trondhjemites suggesting we are in the presence of differentiated rocks that originated by mantle partial melting in a subduction environment, in agreement with what was reported, for instance, by [10][11][12]14]. The (Gd/Yb) ch values indicate that other phases (such as amphibole and/or garnet) were fractionated pointing to an origin in a thickened continental crust.
We extended our comparison to the ternary AFM diagram (Figure 11a) [15,17]. There is a considerable difference among the plagiogranites, in particular regarding the relative abundances of FeO Tot   A further comparison was made by using the normative triangular An-Ab-Or diagram ( Figure 11b) for Timpa delle Murge leucocratic rocks from the Tethyan area which are located in Serbia, Turkey, and Cyprus [1,[18][19][20][21]. In general, the values of An in all the considered rocks from the Tethyan realm are very variable and range from ≈ 10 to ≈60%, with lower values observed in the Timpa delle Murge leucocratic rocks and Sjenica ophiolitic belt plagiogranites (Serbia) whereas higher values are relative to some samples of the Oman Northern ophiolites belt and Troodos ophiolites (Cyprus). Figure 12 shows a Y-Nb binary diagram with data for the studied samples and plagiogranites from other areas [13,14,18,51,57,62]. The compositions of the studied rocks fall within the Volcanic arc and Syn-Collisional Granites field. In particular, the Nb concentrations of the studied samples from leucocratic rocks of Timpa delle Murge, are higher than those of most other Tethyan plagiogranites, in fact, they are comparable only with some samples of the Corsica, showing higher Nb content, and part of Tuscanian plagiogranites complexes, which, however, fall into the Ocean Ridge Granites field. In contrast, Y contents are consistently lower than those of all other considered plagiogranites. A further comparison was made by using the normative triangular An-Ab-Or diagram ( Figure 11b) for Timpa delle Murge leucocratic rocks from the Tethyan area which are located in Serbia, Turkey, and Cyprus [1,[18][19][20][21]. In general, the values of An in all the considered rocks from the Tethyan realm are very variable and range from ≈10 to ≈60%, with lower values observed in the Timpa delle Murge leucocratic rocks and Sjenica ophiolitic belt plagiogranites (Serbia) whereas higher values are relative to some samples of the Oman Northern ophiolites belt and Troodos ophiolites (Cyprus). Figure 12 shows a Y-Nb binary diagram with data for the studied samples and plagiogranites from other areas [13,14,18,51,57,62]. The compositions of the studied rocks fall within the Volcanic arc and Syn-Collisional Granites field. In particular, the Nb concentrations of the studied samples from leucocratic rocks of Timpa delle Murge, are higher than those of most other Tethyan plagiogranites, in fact, they are comparable only with some samples of the Corsica, showing higher Nb content, and part of Tuscanian plagiogranites complexes, which, however, fall into the Ocean Ridge Granites field. In contrast, Y contents are consistently lower than those of all other considered plagiogranites.
A further comparison was made by using the normative triangular An-Ab-Or diagram ( Figure 11b) for Timpa delle Murge leucocratic rocks from the Tethyan area which are located in Serbia, Turkey, and Cyprus [1,[18][19][20][21]. In general, the values of An in all the considered rocks from the Tethyan realm are very variable and range from ≈ 10 to ≈60%, with lower values observed in the Timpa delle Murge leucocratic rocks and Sjenica ophiolitic belt plagiogranites (Serbia) whereas higher values are relative to some samples of the Oman Northern ophiolites belt and Troodos ophiolites (Cyprus). Figure 12 shows a Y-Nb binary diagram with data for the studied samples and plagiogranites from other areas [13,14,18,51,57,62]. The compositions of the studied rocks fall within the Volcanic arc and Syn-Collisional Granites field. In particular, the Nb concentrations of the studied samples from leucocratic rocks of Timpa delle Murge, are higher than those of most other Tethyan plagiogranites, in fact, they are comparable only with some samples of the Corsica, showing higher Nb content, and part of Tuscanian plagiogranites complexes, which, however, fall into the Ocean Ridge Granites field. In contrast, Y contents are consistently lower than those of all other considered plagiogranites.

Tectonic Setting
Pearce et al. [57] classified granites based on their tectonic environment into volcanic arc granites (VAG), syn-collisional granites (syn-COLG), within plate granites (WPG), and oceanic ridge granites (ORG). This classification is based on discriminating elements such as Rb, Y, and Nb. In the Nb vs. SiO 2 diagram the Timpa delle Murge leucocratic rock fall into the VAG+COLG+ORG field ( Figure 13).

Tectonic Setting
Pearce et al. [57] classified granites based on their tectonic environment into volcanic arc granites (VAG), syn-collisional granites (syn-COLG), within plate granites (WPG), and oceanic ridge granites (ORG). This classification is based on discriminating elements such as Rb, Y, and Nb. In the Nb vs. SiO2 diagram the Timpa delle Murge leucocratic rock fall into the VAG+COLG+ORG field ( Figure 13). Tectonic environment, for trondhjemites, is that of volcanic arc granites (VAG), as reported in Figure 9; in fact, Ta and Nb anomalies, relative to Th and Ce, are diagnostic of volcanic arc environments [54,63,64]. Furthermore, enrichments in K, Rb, Ba, and Th relative to Nb and Zr and depletions in Y are typical of volcanic arc granites [53].
The significant enrichment in Th is indicative of subduction zones [65,66]. The analyzed samples show Th/Y ratios between 0.89 and 1.7, much higher than that of MORB which is 0.03 [14]; this could indicate enrichment of magma with fluids or melts separated from the subducting plate [66,67].
Finally, enrichment in LILE and depletion in HFSE is interpreted as a consequence of subduction [68,69]. Magma composition is related to the interaction between the subducting plate and the mantle. The low Ti and Zr rates of the samples suggests low depths partial melting which, in turn, indicates low crustal thickness. Interaction of subducting plate and mantle induces change in magma composition and low concentration of elements coming from the mantle indicates a depleted mantle source [14]. In the analyzed leucocratic rocks, the lower concentration of mantle-derived elements, such as Nb, Ti, Y, and Yb, relative to the normalized compositions, evidence, in fact, a depletion of mantle in these components [14].
The origin of plagiogranites is mainly associated with two very different processes which are the fractional crystallization from a gabbroic source [70], and/or the partial melting of metasomatized gabbros [8,10]. The petrographic and the geochemical features of the Timpa delle Murge leucocratic rocks, suggest a model involving a rifting stage in a Tectonic environment, for trondhjemites, is that of volcanic arc granites (VAG), as reported in Figure 9; in fact, Ta and Nb anomalies, relative to Th and Ce, are diagnostic of volcanic arc environments [54,63,64]. Furthermore, enrichments in K, Rb, Ba, and Th relative to Nb and Zr and depletions in Y are typical of volcanic arc granites [53].
The significant enrichment in Th is indicative of subduction zones [65,66]. The analyzed samples show Th/Y ratios between 0.89 and 1.7, much higher than that of MORB which is 0.03 [14]; this could indicate enrichment of magma with fluids or melts separated from the subducting plate [66,67].
Finally, enrichment in LILE and depletion in HFSE is interpreted as a consequence of subduction [68,69]. Magma composition is related to the interaction between the subducting plate and the mantle. The low Ti and Zr rates of the samples suggests low depths partial melting which, in turn, indicates low crustal thickness. Interaction of subducting plate and mantle induces change in magma composition and low concentration of elements coming from the mantle indicates a depleted mantle source [14]. In the analyzed leucocratic rocks, the lower concentration of mantle-derived elements, such as Nb, Ti, Y, and Yb, relative to the normalized compositions, evidence, in fact, a depletion of mantle in these components [14].
The origin of plagiogranites is mainly associated with two very different processes which are the fractional crystallization from a gabbroic source [70], and/or the partial melting of metasomatized gabbros [8,10]. The petrographic and the geochemical features of the Timpa delle Murge leucocratic rocks, suggest a model involving a rifting stage in a subduction setting, where the ophiolitic gabbros intruded the continental crust ( Figure 14). This scenario promotes the partial melting and generation of crustal derived melts producing rocks of trondhjemite composition [71]. subduction setting, where the ophiolitic gabbros intruded the continental crust ( Figure  14). This scenario promotes the partial melting and generation of crustal derived melts producing rocks of trondhjemite composition [71].

Conclusions
The Timpa delle Murge ophiolitic sequence in the Northern Calabrian Unit is part of the Liguride Complex in the Pollino Massif and, for the first time, a petrographic and geochemical study were carried out on leucocratic rocks occurring in these ophiolitic sequences. These ophiolites do not show any subduction related high-pressure metamorphism whereas the presence of gabbros and leucocratic suggests that the Northern Calabrian Unit experienced an intrusive activity that can be classified as subduction related.
The petrographic features of the analyzed samples showed a consertal hypidiomorphic granular structure. The observed mineralogical assemblage consists of plagioclase, quartz, feldspar, muscovite, biotite, and secondary chlorite. Their color index (M) is less than 10, in fact, the mafic minerals present are biotite and chlorite. These leucocratic rocks are classified as trondhjemites, in accordance with the IUGS classification.
Leucocratic rocks of Timpa delle Murge show high amounts of silica (SiO2) with moderate alumina (Al2O3) and iron-magnesium (FeO-MgO) contents. Overall, the geochemical constrains, including both major oxides and trace elements are consistent with those from Western Alps, Northern Apennines, Turkey, Cyprus, Serbia, and Oman. The analyzed samples have higher potassium contents than the plagiogranites related to MORBs, this can be due to a partial plagioclase alteration to sericite. The Ab-An-Or ternary diagram shows that the analyzed leucocratic rocks fall within the trondhjemitic field and have subalkaline features, consistent with a possible differentiation from a tholeiitic gabbroic source mixed with crustal melts.
Spider diagrams exhibit compositional features which are consistent with fractional crystallization from a mafic magma as observed by several authors (Borsi et al. [16], Köksal et al. [18], and Milovanovic et al. [19]). The role of plagioclase fractionation is clearly evidenced by Eu depletion in an evolution from plagioclase-rich crystal mushes. Compositional data qualify these rocks as trondhjemites formed in a volcanic arc environment during continental extension as already observed for the Pollino Massif ophiolitic gabbros.

Conclusions
The Timpa delle Murge ophiolitic sequence in the Northern Calabrian Unit is part of the Liguride Complex in the Pollino Massif and, for the first time, a petrographic and geochemical study were carried out on leucocratic rocks occurring in these ophiolitic sequences. These ophiolites do not show any subduction related high-pressure metamorphism whereas the presence of gabbros and leucocratic suggests that the Northern Calabrian Unit experienced an intrusive activity that can be classified as subduction related.
The petrographic features of the analyzed samples showed a consertal hypidiomorphic granular structure. The observed mineralogical assemblage consists of plagioclase, quartz, feldspar, muscovite, biotite, and secondary chlorite. Their color index (M) is less than 10, in fact, the mafic minerals present are biotite and chlorite. These leucocratic rocks are classified as trondhjemites, in accordance with the IUGS classification.
Leucocratic rocks of Timpa delle Murge show high amounts of silica (SiO 2 ) with moderate alumina (Al 2 O 3 ) and iron-magnesium (FeO-MgO) contents. Overall, the geochemical constrains, including both major oxides and trace elements are consistent with those from Western Alps, Northern Apennines, Turkey, Cyprus, Serbia, and Oman. The analyzed samples have higher potassium contents than the plagiogranites related to MORBs, this can be due to a partial plagioclase alteration to sericite. The Ab-An-Or ternary diagram shows that the analyzed leucocratic rocks fall within the trondhjemitic field and have subalkaline features, consistent with a possible differentiation from a tholeiitic gabbroic source mixed with crustal melts.
Spider diagrams exhibit compositional features which are consistent with fractional crystallization from a mafic magma as observed by several authors (Borsi et al. [16], Köksal et al. [18], and Milovanovic et al. [19]). The role of plagioclase fractionation is clearly evidenced by Eu depletion in an evolution from plagioclase-rich crystal mushes. Compositional data qualify these rocks as trondhjemites formed in a volcanic arc environment during continental extension as already observed for the Pollino Massif ophiolitic gabbros.