Journal of Volcanology and Geothermal Research
Relatively rapid emplacement of dome-forming magma inferred from strain analyses: The case of the acid Latian dome complexes (Central Italy)
Introduction
The area of southern Tuscany and northern Latium, from Rome to Mt. Amiata along the Tyrrhenian margin of the Apennine chain, was the site of complex geological processes during the Neogene (Fig. 1). Due to the post-orogenic extensional processes occurring at the back of the eastward-migrating Apennine fold-and-thrust belt, the area experienced repeated subsidence episodes with the development of a series of marine and continental sedimentary basins (Ambrosetti et al., 1978, Barberi et al., 1994). Local subsidence alternated with periods of differential uplift (Baldi et al., 1974, Marinelli et al., 1993, Barberi et al., 1994). Since the Pliocene, intense volcanic activity affected the area as a result of crustal extension with a space-time migration from west to the east (Innocenti et al., 1992, Serri et al., 1993, Jolivet et al., 1998). Such migration of the locus of volcanic activity was associated with important changes in the nature of the erupted magmas. Initially, volcanic activity was characterized by crustal metasomatized acidic magmas. Eruptive activity during this phase built a series of volcanic edifices, mainly cryptodomes. Beginning in the Late Pleistocene, magmatism changed to a more alkali-potassic composition derived from the mantle (Civetta et al., 1978, Serri et al., 1991, Serri et al., 1993, Peccerillo, 1999, Conticelli et al., 2002).
This work investigates the acidic volcanic complexes of Latium focusing on the relationship between the volcanic substratum and magma body emplacement. The role of regional extension on the rise and emplacement of laccoliths is also investigated.
Section snippets
Structure of the basement
Motivated by the prospecting of a geothermal energy resource, the structure of the basement along the Tyrrhenian sector of central Italy was studied during the 1980's by means of geophysical surveys and exploration drilling (Buonasorte et al., 1987, Barberi et al., 1994). The studies revealed that the thickened fold and thrusted pre-volcanic substratum of this area is composed of Mesozoic–Cenozoic limestones and siliciclastic turbidite deposits (locally known as flysch units). These basement
Dome complexes
In this section, the important volcanological and structural aspects of the acid dome complexes are summarized. Emphasis is given on the role of related laccolith intrusions to the formation of domes.
Methodology
To estimate the magmatic strain rate induced by the emplacement of these magmatic bodies in the shallow crust, and in order to compare it with the tectonic strain rate estimated for this area during Pliocene times, the methodology proposed by Acocella and Rossetti (2002) for the Mt. Amiata intrusion was followed. Their methodology may be applied to the laccolith intrusions related to the Latian dome complexes, considering that the regional geological conditions are the same in this area of
Discussion
Several assumptions were used in calculating the magmatic strain rate, such as the constant rate of pluton filling and geometry of the feeder conduit (L/w = 103). In order to obtain the minimum time of pluton infilling, the maximum value of Q = 30 m3 s− 1 estimated from both TDC and CDC was used. These choices are supported by field evidence of conduit geometry from the TDC where a maximum width of about 10 m can be estimated.
The calculated magmatic strain rate is larger than the tectonic strain
Concluding remarks
Calculations suggest that the dome complexes experienced a very rapid evolution. This is supported by field evidence, that do not show relevant interruptions in volcanic activity and significant compositional changes in the volcanic products related to the extrusion of the domes (de Rita et al., 1997, Cimarelli and de Rita, 2006). Similarly to the Latian shallow intrusions in the Amiata and Larderello volcanic areas (Acocella and Rossetti, 2002), the magmatic strain rates of the CDC, TDC appear
Acknowledgements
We would like to thank the reviewers S.A. Alaniz-Alvarez and Y. Wada for providing helpful and thoughtful comments to the draft version of the paper. Careful revision by A.M.F. Lagmay and C. Corazzato helped improving the final version of the manuscript.
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