Tholeiiteic rocks

The alkaline mafic volcanics are less enriched in silica and more enriched in incompatible trace elements than oversaturated tholeiitic rocks with similar MgO contents. REE show smooth and fractionated patterns (Fig. 9.7). Mantle normalised incompatible element patterns of mafic rocks generally display a small upward convexity with moderate enrichments in Ta and Nb. The large majority of the mafic volcanic rocks exhibit positive spikes of Ba and Pb, which are small or absent in the southern outcrops of Capo Ferrato, Guspini and Rio Girone (Fig. 9.7). Silicic volcanics exhibit a large range of incompatible element concentrations. Sr- and Nd-isotopic... 

The isotopic similarity of some Italian volcanoes, such as Mt. Etna and Iblei, with Na-alkaline and tholeiitic rocks from central and west-... 

Fleming TH, Elliot DH (1988) Iron-rich tholeiitic rocks of the Kirkpatrick Basalt, Beardmore Glacier region. Antarctic J US 23(5) 15-17... 

From late Miocene to present, subaerial arc-volcanic activity (calc—alkali rocks, andesite, tholeiitic and high alumina basalt) started associated with uplift of the Japanese Islands. This volcanic activity is different from that at middle Miocene age. 

Bulk rock geochemistry of the Lac Cinquante deposit shows that the Archean volcanic rocks (both the mafic volcanic flows and the bimodal volcanic suite) are dominantly tholeiitic high-Fe basalts and basaltic andesites. The alternating felsic units in the bimodal suite are dacitic and rhyolitic in composition (Fig. 2). 

Dal Negro A., Carbonin S., Molin G. M., Cundari A., and Piccirillo E. M. (1982). Intracrystalline cation distribution in natural clinopyroxenes of tholeiitic, transitional and alkaline basaltic rocks. In Advances in Physical Geochemistry, vol. 1, S. K. Saxena (series ed.), New York Springer-Verlag. 

The mafic to intermediate and tholeiitic to transitional rocks of the Bousquet Formation are characterized by moderately enriched chondrite-normalized LREE and MREE patterns, flat HREE profiles and negative Nb, Ta, Zr, and Hf... 

All samples plot in the basalt to alkaline basalt fields of the Zr/Ti02 vs. NbA diagram of Pearce (1996) (Fig. 3). The NbA ratios define two distinct groups (1) tholeiitic metavolcanic rocks structurally underlying VMS mineralisation and (2) more alkaline ultramafic cumulates and metavolcanic rocks above VMS... 

Fig. 5. Zr/AbOs vs. Y/AI2O3 plot showing tholeiitic-transitional, transitional, and transitional-calc-alkaline nature of the volcanic rocks that host the Restigouche massive sulfide deposit. Zr/Y boundary ratios for the trends that divide the tholeiitiic-transitional and transitional-calc-alkaline fields are 4.5 and 7, respectively.

The Mount Brittain Formation is made up of tholeiitic-transitional, transitional, and transitional-calc-alkaline dominantly felsic volcanic units and have similar magmatic nature that is recognized elsewhere in felsic volcanic rocks of the BMC. 

Ratios of FeO (total iron expressed as FeO) to MgO versus silica in Mars rocks and soils. A diagonal line separates tholeiitic (TH) from calc-alkaline (CA) rocks tholeiitic magmas are anhydrous and calc-alkaline magmas are hydrous. All the Mars rocks plot in the tholeiitic field, as do GRS data (MgO was calculated from the Mg/Si ratio in Fig. 11.19). TES-derived data plot in the calc-alkaline field, but this is an artifact of alteration. After McSween et al. (2009). 

Sicily (7 Ma to Present) Etna (0.5-Present), Iblei (7-1.5), U-stica (0.75-0.13), Pantelleria (0.3-0.005), Linosa (1-0.5), Sicily Channel seamounts - Stratovolcanoes, diatremes, small plateaux, etc. formed of tholeiitic and Na-alkaline rocks (basanite, hawaiite, trachyte, peralkaline trachyte and rhyolite). 

Tyrrhenian Sea Floor (12 Ma to Present) Comacya (12), Magnaghi (3), Mar-sili (1.8-0), Vavilov, Aceste, Anchi-se, Lametini, Palinuro, older Ponza, etc. - Coexisting intraplate (oceanic tholeiites, Na-transitional and alkaline) and arc-type (arc-tholeiitic, calc-alkaline, potassic) rocks. 

This province consists of central volcanoes, basaltic plateaux and monoge-netic centres composed of tholeiitic to Na-alkaline rocks (basalt to rhyolite, basanite and trachybasalt to phonolite and trachyte). It overlies calc-alkaline rocks of Oligo-Miocene age. 

Rock compositions range from mafic to silicic, and show a calc-alkaline (CA), high-potassium calc-alkaline (HKCA) to shoshonitic (SHO) affinity. A few potassic alkaline rocks with a composition close to the Roman potassic series (KS) occur at Vulcano and Stromboli (e.g. Keller 1982 Francalanci et al. 2004). Arc tholeiites have been dredged along some seamounts (Beccaluva et al. 1982). 

The SiC>2 vs. K2O plot (Fig. 7.8) shows that the Lipari volcanics define a steep increase in K2O from mafic to intermediate rocks, straddling the limits between arc tholeiitic, calc-alkaline and shoshonitic series. Basaltic andesites and andesites have porphyritic textures with phenocrysts of zoned... 

There are several seamounts located to the northwest (Sisifo, Enarete, Eolo) and to the northeast (Lametini, Alcione, Palinuro) of the Aeolian archipelago that define a horseshoe-type pattern around the Marsili basin. Ages range from 1.3 to less than 0.1 Ma. Compositions range from arc-tholeiitic (Lametini and southern Marsili basin), calc-alkaline and F1KCA (Marsili, Sisifo, Eolo, Panarea slope, Palinuro, Stromboli canyon and Alcione) to shoshonitic (Enarete, Eolo, Sisifo, and northern Stromboli slope). Description of rocks from Aeolian seamounts is given in Chap. 9. 

Etna About 0.6 Ma to present - Several coalescing and superimposed stratovolca-noes mostly formed of lavas, spotted with hundreds of cinder cones, cut by three rift zones and by the Valle del Bove depression. Rocks include tholeiitic basalts followed by Na-alkaline rocks (trachybasalts, hawaiites and minor benmoreites and trachytes). 

Iblei 7 to 1.5 Ma - Multicentre district with several monogenetic cones, maars and lava flows formed by both submarine and subaerial activity. Rocks range from tholeiitic basalt to hawaiite, basanite and nephelinite. 

REE patterns are fractionated for all the rocks, but tholeiites show lower La/Yb ratios than alkaline products (Fig. 8.5a). Incompatible element patterns normalised to primordial mantle compositions for mafic rocks are very different from the Aeolian arc and central-southern Italian peninsula. Both tholeiitic and alkaline basalts show a marked upward convexity, with negative spikes of K (Fig. 8.5b). Note, however, that there are also negative anomalies for Hf and Ti, which are uncommon in most Na-alkaline basalts from intraplate settings (e.g. Wilson 1989). Overall, the Etna magmas have been found to be more enriched in volatile components than common intraplate magmas, and water contents up to 3-4 wt % have been found by melt inclusion studies (Corsaro and Pompilio 2004 Pompilio, personal communication). 

---