Whole-Rock Geochemical Dataset of Late Variscan Intrusive Rocks from the Serre Batholith (Calabria, Southern Italy)

1. Summary

Whole-rock chemical data for plutonic rocks, including major, minor, and trace elements, are fundamental for constraining the origin of intrusive magmas and the geodynamic context of their generation and emplacement (e.g., [1]). In this regard, the Serre Carboniferous-early Permian composite batholith [2], exposed in in the Serre Massif of central Calabria (southern Italy; Figure 1a), has been of great interest to magmatic petrologists since the 1970s, as evidenced by the extensive geochemical data reported in numerous research papers [3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24].

The present study presents a publicly available chemical dataset of intrusive rocks from the composite Serre batholith. This dataset is intended for use in fundamental research on magma evolution as well as applied geological investigations, such as the interaction between plutonic rock bodies and their hosted groundwater systems (e.g., [25]).

Within the tilted late Variscan continental crustal block exposed in the Serre Massif (e.g., [26,27]), nearly tabular rock granitoids bodies constitute the Serre batholith, which occupies the intermediate crustal level [28]. The emplacement and construction of this plutonic stack occurred between approximately 305 and 292 Ma (e.g., [21,29]) at depths ranging from roughly 20 to 7 km [28], between the lower and upper continental crust (Figure 1b). Overall, the stratigraphy of the Serre batholith is geometrically characterized, from the bottom (in the northern area), upward (in the southern portion), by plutonic bodies dominated by: tonalites and quartz-diorites (i.e., Squillace-Petrizzi and Cardinale units–5 in Figure 1a,b), coarse- to medium-grained granodiorites, granites, and monzogranites (i.e., Sant’Andrea Apostolo dello Ionio/Serre unit–4 in Figure 1a,b), granites and granodiorites with K-feldspar megacrysts (i.e., Isca sullo Ionio unit–3 in Figure 1a,b); and fine-grained, strongly peraluminous granites (i.e., Cittanova unit–2 in Figure 1a,b) (Figure 1a,b) [30,31]. These main plutonic units were subsequently intruded by porphyritic dikes during the late Permian [18].

At the base of the batholith, a migmatitic border zone (migmatitic unit 8 in Figure 1a,b) developed within high-grade metasedimentary host rocks [9]. During regional metamorphism, these metasediments-predominantely metapelites, metarenites, and metagreywakes underwent granulite-facies conditions and partial melting (migmatitic paragneisses metamorphic unit 9 in Figure 1a,b) [16]. The resulting melts were removed from the source rocks, contributing to the growth of the Serre batholith, while the remaining fractions were trapped within the metasediments to forme leucosomes. Notably, these leucosomes do not represent the exact in-situ complements to the adjacent melanosomes [15,32]. At the roof of the batholith, magmas intruded phyllites and greenschists- to amphibolite-facies paragneisses; here, contact metamorphism produced a broad aureole characterized by the growth of biotite, andalusite, and cordierite (metamorphic units 6 and 7 in Figure 1a,b) (e.g., [33,34]).

2. Data Description

A total of 74 samples were collected from the various intrusive bodies of the exposed Serre batholith, as well as from leucosomes within the high-grade metasediments. The WGS84 geographic coordinates for each sample, along with their predominant lithotype and the related lithostratigraphic unit (as in Figure 1a,b), are provided in Table 1. Sampling locations can be also displayed in Google Earth opening the file as in Geographic Data S1, i.e., Samples_Serre.kmz.

Whole-rock chemical analyses, which constitute the dataset of the present paper, is available in the Database S1 as a Excel file, i.e., Geochemistry_Samples_Serre.xlsx.

The petrographic and structural characteristics of the granitoids are described below.

Concordant and discordant leucosomes are scattered within the deep crustal migmatitic rocks. Their composition ranges from leuco-tonalite to granite, depending on the host rocks and the presence of xenocrysts such as sillimanite, biotite, garnet and/or orthopyroxene. The melt composition is reflected by quartz, plagioclase, K-feldspar, biotite, and muscovite [15,32].

Coarse-grained granodiorites are characterized by large biotite clusters. They contain quartz, plagioclase, K-feldspar, and biotite; the granodioritic varieties exhibit higher proportion of plagioclase and resorbed actinolite-hornblende. Frequently, these rocks host microgranular mafic enclaves containing Mg-hornblende. They show a calc-alkaline and meta-luminous character [14].

Medium-grained muscovite granitoids exhibit a calc-alkaline, peraluminous character, as indicated by the presence of muscovite alongside quartz, K-feldspar, plagioclase, and biotite [9,14].

K-feldspar megacryst granitoids are characterized by large orthoclase crystals, measuring up to 5-6 cm, which are occasionally mantled by oligoclase-plagioclase. Their composition varies from granodiorite to granites; locally, they are calc-alkaline and may contain muscovite and rare microgranular biotite-bearing enclaves [7,8].

Peraluminous fine-grained granites display a fine-grained texture with a pervasive presence of muscovite and metamorphic xenoliths. They frequently contain cordierite, andalusite, garnet, and fibrolite dispersed in a matrix consisting of quartz, K-feldspar, and plagioclase [4,13,14].

Hypabyssal rocks in Permian dikes show porphyritic textures, with phenocrysts of amphibole, biotite, quartz, plagioclase, and K-feldspar. Their composition ranges from andesite to dacite.

3. Methods

Chemical analyses of granitoid samples were performed using X-ray fluorescence (XRF), except for Fe²⁺ and LOI. Samples were first reduced to powder in a planetary grinder equipped with agate jars and subsequently prepared as pressed pellets using polyvinyl alcohol as a binder.

Major and trace element concentrations in whole-rock samples were determined using a Philips PW1480/10 automatic spectrometer. For major elements, a Cr anti-cathode tube operating at 50 kV and 30 mA was used. Trace elements Ni, Cr, V, Ce, La, and Ba were detected using a W anti-cathode tube powered at 60kV and 45mA, while Rb, Sr, Y, Zr, and Nb were analyzed with a Rh anti-cathode tube operating at 60 kW and 45 mA. Fluorescence intensities were converted into oxides weight percentages of or trace elements concentrations (ppm) using a computational program based on the matrix effect correction method proposed by [37,38]. Two reference standards (AGV-1 of USGS-U.S.A. and NIM-G of NIM-South Africa) were used: precision is better than 5% for all elements, except for Ce, La and, Ba, for it is better than 10%.

Rare earth elements (REE) were measured at the CRPG laboratory in Nancy (France) using a Jobin Yvon^TM JY70 inductively coupled plasma mass spectrometry (ICP-MS). For the BR standard, the laboratory reports a relative standard deviation (RDS) of less than 6% for all REE excluding Lu, based on 25 repeated analyses; for Lu, an RSD of 16% is reported.

FeO contents (where available) was measured volumetrically by titration with N/10 KMnO₄.

Loss of Ignition (LOI) was determined by calcination in a furnace at 900 °C.; the obtained values were subsequently corrected to occount for the oxidation of FeO to Fe₂O₃.

For a subset of samples, major and trace elements were determined by lithium metaborate/tetraborate fusion followed by ICP-MS at Actlabs laboratory (Canada).