Orciatico lamproitic intrusion

The subvolcanic lamproitic body of Orciatico, near Pisa, emplaced at 4.1 Ma, represents a minor igneous centre of the Tuscan Magmatic Province (Fig.1). This region, during the Neogene, was affected by an extensional stress ?eld responsible for the formation of NNW-SSE horst and graben dissecting the eastward propagating compressional belt of the Northern Apennine.
The igneous activity, dominated by crustal-hybrid products and minor mantle-derived ones (e.g. Orciatico lamproite), followed the migration of the extension from west (14 Ma) to east (0.2 Ma).

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Fig.1: Location of intrusive and extrusive rocks of the Tuscany Magmatic Province. Numbers in parentheses indicate ages (in Ma).





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Fig 2: 3D geological map of Orciatico area.



The Orciatico intrusion (Fig.2) is a laccolith emplaced at the margin of one of the Tuscan Pliocene grabens. The intrusion has a characteristic ovoid-like, subhorizontal tabular shape connected to an elongated subvertical structure to the SE. According to the study of vesicle shape and distribution, the cooling surfaces, and the overall geometry of the body, three main units can be identied:

(1) the subvertical feeding dyke, where flow directions can be well determined;
(2) the connection zone, with a complex structure composed of small stoped blocks of country rock surrounded by lamproite with vesicles paralleling them;
(3) The main body with a remarkable lack of vesicles and cooling surfaces.

The emplacement took place at a depth of about 0.4 km, estimated on the basis of the local stratigraphy and the present mean erosion rate for Italy. The laccolithic body has a length (average ca. 1 km) to thickness (ca. 125 m). The observation of the NNW-SSE subvertical feeding dyke and the mantle origin of the Orciatico lamproite indicate that the NNW-SSE border fault of the graben is connected to lithospheric-scale structures able to rapidly transfer melts from mantle to shallow crustal levels.

The Orciatico lamproite (selagite) have a porphyritic texture with microphenocrysts of olivine (Fo90-75), phlogopite and Al-poor diopside (Al2O3 0.5 wt%) set in a groundmass consisting of the same phases plus sanidine (with feathery texture), glass, and accessory K-richterite, rutile, ilmenite and chromite. Some of the high-MgO olivine crystals show evidence of corrosion and kinking, and are probably xenocrysts resulting from disaggregation of high-pressure ultramafic xenoliths.

Bibliography



• Gˇmez-Izquierdo, B., Caravantes, G., Dini, A., & Rocchi, S. (2008). The laccolithic intrusion of Orciatico (Tuscany). In Geophys. Res. Abstr (p. 10).
• Minissale, A. (2004). Origin, transport and discharge of CO 2 in central Italy. Earth-Science Reviews, 66(1), 89-141.
• Peccerillo, A. (2005). Plio-quaternary volcanism in Italy (Vol. 365). Springer-Verlag Berlin Heidelberg.
• Conticelli, S., et al. (2004): "Petrologic, geochemical, and isotopic characteristics of potassic and ultrapotassic magmatism in Central-Southern Italy: inferences on its genesis and on the nature of mantle sources." Periodico di Mineralogia 73.1: 153-164.


Photo
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Phlogopite (brown) and sanidine (with feathery texture) crystals. Orciatico lamproite, Pisa, Italy. PPL image, 1x (Field of view = 9mm)
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Phlogopite and sanidine (I order gray) crystals. Orciatico lamproite, Pisa, Italy. XPL image, 1x (Field of view = 9mm)
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Phlogopite (brown) and sanidine (with feathery texture) crystals. Orciatico lamproite, Pisa, Italy. PPL image, 1x (Field of view = 9mm)
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Phlogopite (brown) and sanidine (with feathery texture) crystals. Orciatico lamproite, Pisa, Italy. PPL image, 1x (Field of view = 9mm)
orciatico2017(5).jpg

Phlogopite and sanidine (I order gray) crystals. Orciatico lamproite, Pisa, Italy. XPL image, 1x (Field of view = 9mm)
orciatico2017(6).jpg

Phlogopite (brown) and sanidine (with feathery texture) crystals. Orciatico lamproite, Pisa, Italy. PPL image, 1x (Field of view = 9mm)
orciatico2017(12).jpg

Phlogopite (brown), sanidine (with feathery texture) and pyroxene (high relief) crystals. Orciatico lamproite, Pisa, Italy. PPL image, 2x (Field of view = 7mm)
orciatico2017(13).jpg

Phlogopite, sanidine (with feathery texture) and pyroxene crystals. Orciatico lamproite, Pisa, Italy. XPL image, 2x (Field of view = 7mm)
orciatico2017(15).jpg

Phlogopite (brown), sanidine (with feathery texture) and pyroxene (high relief) crystals. Orciatico lamproite, Pisa, Italy. PPL image, 2x (Field of view = 7mm)
orciatico2017(17).jpg

Phlogopite (brown), sanidine (with feathery texture) and pyroxene (high relief) crystals. Orciatico lamproite, Pisa, Italy. PPL image, 2x (Field of view = 7mm)
orciatico2017(18).jpg

Phlogopite (brown), sanidine (with feathery texture) and pyroxene (high relief) crystals. Orciatico lamproite, Pisa, Italy. PPL image, 2x (Field of view = 7mm)
orciatico2017(19).jpg

Phlogopite, sanidine (with feathery texture) and pyroxene crystals. Orciatico lamproite, Pisa, Italy. XPL image, 2x (Field of view = 7mm)
orciatico2017(20).jpg

Phlogopite (brown), sanidine (with feathery texture) and pyroxene (high relief) crystals. Orciatico lamproite, Pisa, Italy. PPL image, 2x (Field of view = 7mm)
orciatico2017(21).jpg

Phlogopite (brown), sanidine (with feathery texture) and pyroxene (high relief) crystals. Orciatico lamproite, Pisa, Italy. PPL image, 2x (Field of view = 7mm)
orciatico2017(22).jpg

Phlogopite (brown), sanidine (with feathery texture) and pyroxene (high relief) crystals. Orciatico lamproite, Pisa, Italy. PPL image, 2x (Field of view = 7mm)
orciatico2017(24).jpg

Phlogopite (brown), sanidine (with feathery texture) and pyroxene (high relief) crystals. Orciatico lamproite, Pisa, Italy. PPL image, 2x (Field of view = 7mm)
orciatico2017(25).jpg

Phlogopite, sanidine (with feathery texture) and pyroxene crystals. Orciatico lamproite, Pisa, Italy. XPL image, 2x (Field of view = 7mm)
orciatico2017(26).jpg

Phlogopite (brown), sanidine (with feathery texture) and pyroxene (high relief) crystals. Orciatico lamproite, Pisa, Italy. PPL image, 2x (Field of view = 7mm)
orciatico2017(27).jpg

Phlogopite (brown), sanidine (with feathery texture) and pyroxene (high relief) crystals. Orciatico lamproite, Pisa, Italy. PPL image, 10x (Field of view = 2mm)
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Phlogopite, sanidine (with feathery texture) and pyroxene crystals. Orciatico lamproite, Pisa, Italy. XPL image, 0x (Field of view = 2mm)
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Phlogopite (brown), sanidine (with feathery texture) and pyroxene (high relief) crystals. Orciatico lamproite, Pisa, Italy. PPL image, 10x (Field of view = 2mm)
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Phlogopite (brown), sanidine (with feathery texture) and pyroxene (high relief) crystals. Orciatico lamproite, Pisa, Italy. PPL image, 10x (Field of view = 2mm)
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Phlogopite (brown), sanidine (with feathery texture) and pyroxene (high relief) crystals. Orciatico lamproite, Pisa, Italy. PPL image, 10x (Field of view = 2mm)
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Phlogopite, sanidine (with feathery texture) and pyroxene crystals. Orciatico lamproite, Pisa, Italy. XPL image, 10x (Field of view = 2mm)
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Skeletal sanidine (with feathery texture) crystals and phlogopite (brown). Orciatico lamproite, Pisa, Italy. PPL image, 20x (Field of view = 1mm)
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Skeletal sanidine (with feathery texture) crystals and phlogopite (brown). Orciatico lamproite, Pisa, Italy. PPL image, 20x (Field of view = 1mm)
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Skeletal sanidine (with feathery texture) crystals. Orciatico lamproite, Pisa, Italy. PPL image, 20x (Field of view = 1mm)
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Skeletal sanidine (with feathery texture) crystals. Orciatico lamproite, Pisa, Italy. PPL image, 20x (Field of view = 1mm)
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Skeletal sanidine (with feathery texture) crystals. Orciatico lamproite, Pisa, Italy. PPL image, 20x (Field of view = 1mm)
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Skeletal sanidine (with feathery texture) crystals. Orciatico lamproite, Pisa, Italy. PPL image, 20x (Field of view = 1mm)
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Skeletal sanidine (with feathery texture) crystals and phlogopite (brown). Orciatico lamproite, Pisa, Italy. PPL image, 20x (Field of view = 1mm)
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Skeletal sanidine (with feathery texture) crystals and phlogopite (brown). Orciatico lamproite, Pisa, Italy. PPL image, 20x (Field of view = 1mm)
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Skeletal sanidine (with feathery texture) crystals and phlogopite (brown). Orciatico lamproite, Pisa, Italy. PPL image, 20x (Field of view = 1mm)
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Skeletal sanidine (with feathery texture) crystals and phlogopite (brown). Orciatico lamproite, Pisa, Italy. PPL image, 20x (Field of view = 1mm)
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Skeletal sanidine (with feathery texture) crystals and phlogopite (brown). Orciatico lamproite, Pisa, Italy. PPL image, 20x (Field of view = 1mm)
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Skeletal sanidine (with feathery texture) crystals and phlogopite (brown). Orciatico lamproite, Pisa, Italy. PPL image, 20x (Field of view = 1mm)
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Skeletal sanidine (with feathery texture) crystals and phlogopite (brown). Orciatico lamproite, Pisa, Italy. PPL image, 20x (Field of view = 1mm)
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Skeletal sanidine (with feathery texture) crystals and phlogopite (brown). Orciatico lamproite, Pisa, Italy. PPL image, 20x (Field of view = 1mm)
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Skeletal sanidine (with feathery texture) crystals. Orciatico lamproite, Pisa, Italy. PPL image, 40x (Field of view = 0,5mm)
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Olivine (altered by green bowlingite), sanidine (colorless) and phlogopite (brown) crystals. Orciatico lamproite, Pisa, Italy. PPL image, 2x (Field of view = 7mm)
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Olivine (altered by green bowlingite), sanidine (colorless) and phlogopite (brown) crystals. Orciatico lamproite, Pisa, Italy. PPL image, 2x (Field of view = 7mm)
orciatico2013(4).jpg

Olivine (altered by green bowlingite), sanidine (colorless) and phlogopite (brown) crystals. Orciatico lamproite, Pisa, Italy. PPL image, 2x (Field of view = 7mm)
orciatico2013(5).jpg

Olivine (altered by bowlingite), sanidine (I order gray) and phlogopite crystals. Orciatico lamproite, Pisa, Italy. XPL image, 2x (Field of view = 7mm)
orciatico2013(7).jpg

Olivine (altered by green bowlingite), sanidine (colorless) and phlogopite (brown) crystals. Orciatico lamproite, Pisa, Italy. PPL image, 2x (Field of view = 7mm)
orciatico2013(8).jpg

Olivine (altered by bowlingite), sanidine (I order gray) and phlogopite crystals. Orciatico lamproite, Pisa, Italy. XPL image, 2x (Field of view = 7mm)
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Olivine (altered by bowlingite), sanidine (I order gray) and phlogopite crystals. Orciatico lamproite, Pisa, Italy. XPL image, 2x (Field of view = 7mm)
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Olivine (altered by bowlingite), sanidine (I order gray) and phlogopite crystals. Orciatico lamproite, Pisa, Italy. XPL image, 2x (Field of view = 7mm)
orciatico2013(11).jpg

Olivine (altered by green bowlingite), sanidine (colorless) and phlogopite (brown) crystals. Orciatico lamproite, Pisa, Italy. PPL image, 2x (Field of view = 7mm)
orciatico2013(12).jpg

Olivine (altered by bowlingite), sanidine (I order gray) and phlogopite crystals. Orciatico lamproite, Pisa, Italy. XPL image, 2x (Field of view = 7mm)
orciatico2013(13).jpg

Olivine (altered by green bowlingite), sanidine (colorless) and phlogopite (brown) crystals. Orciatico lamproite, Pisa, Italy. PPL image, 2x (Field of view = 7mm)
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Olivine (altered by bowlingite), sanidine (I order gray) and phlogopite crystals. Orciatico lamproite, Pisa, Italy. XPL image, 2x (Field of view = 7mm)
orciatico2013(15).jpg

Olivine (altered by green bowlingite), sanidine (colorless) and phlogopite (brown) crystals. Orciatico lamproite, Pisa, Italy. PPL image, 2x (Field of view = 7mm)
orciatico2013(16).jpg

Olivine (altered by green bowlingite), sanidine (colorless) and phlogopite (brown) crystals. Orciatico lamproite, Pisa, Italy. PPL image, 2x (Field of view = 7mm)
orciatico2013(17).jpg

Olivine (altered by green bowlingite), sanidine (colorless) and phlogopite (brown) crystals. Orciatico lamproite, Pisa, Italy. PPL image, 2x (Field of view = 7mm)
orciatico2013(18).jpg

Olivine (altered by green bowlingite), sanidine (colorless, with feathery texture) and phlogopite (brown) crystals. Orciatico lamproite, Pisa, Italy. PPL image, 2x (Field of view = 7mm)
orciatico2013(19).jpg

Olivine (altered by green bowlingite), sanidine (colorless, with feathery texture) and phlogopite (brown) crystals. Orciatico lamproite, Pisa, Italy. PPL image, 2x (Field of view = 7mm)
orciatico2013(20).jpg

Olivine (altered by bowlingite), sanidine (I order gray, with feathery texture) and phlogopite crystals. Orciatico lamproite, Pisa, Italy. XPL image, 2x (Field of view = 7mm)
orciatico2013(22).jpg

Pyroxene (colorless, high relief), sanidine (with feathery texture) and phlogopite (brown) crystals. Orciatico lamproite, Pisa, Italy. PPL image, 10x (Field of view = 2mm)
orciatico2013(23).jpg

Pyroxene (colorless, high relief), sanidine (with feathery texture) and phlogopite (brown) crystals. Orciatico lamproite, Pisa, Italy. PPL image, 10x (Field of view = 2mm)
orciatico2013(24).jpg

Pyroxene (colorless, high relief), sanidine (with feathery texture) and phlogopite (brown) crystals. Orciatico lamproite, Pisa, Italy. PPL image, 10x (Field of view = 2mm)
orciatico2013(25).jpg

Pyroxene (high interference colors), sanidine (with feathery texture) and phlogopite crystals. Orciatico lamproite, Pisa, Italy. XPL image, 10x (Field of view = 2mm)
orciatico2013(26).jpg

Pyroxene (high interference colors), sanidine (with feathery texture) and phlogopite crystals. Orciatico lamproite, Pisa, Italy. XPL image, 10x (Field of view = 2mm)
orciatico2013(27).jpg

Pyroxene (colorless, high relief), sanidine (with feathery texture) and phlogopite (brown) crystals. Orciatico lamproite, Pisa, Italy. PPL image, 10x (Field of view = 2mm)
orciatico2013(25).jpg

Pyroxene (high interference colors), sanidine (with feathery texture) and phlogopite crystals. Orciatico lamproite, Pisa, Italy. XPL image, 10x (Field of view = 2mm)
orciatico2013(26).jpg

Pyroxene (high interference colors), sanidine (with feathery texture) and phlogopite crystals. Orciatico lamproite, Pisa, Italy. XPL image, 10x (Field of view = 2mm)
orciatico2013(27).jpg

Pyroxene (colorless, high relief), sanidine (with feathery texture) and phlogopite (brown) crystals. Orciatico lamproite, Pisa, Italy. PPL image, 10x (Field of view = 2mm)
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Sanidine (with feathery texture) and phlogopite (brown) crystals. Orciatico lamproite, Pisa, Italy. PPL image, 2x (Field of view = 7mm)
orciatico2013a(5).jpg

Sanidine (with feathery texture) and phlogopite (brown) crystals. Orciatico lamproite, Pisa, Italy. PPL image, 2x (Field of view = 7mm)
orciatico2013a(6).jpg

Sanidine (with feathery texture) and phlogopite (brown) crystals. Orciatico lamproite, Pisa, Italy. PPL image, 2x (Field of view = 7mm)
orciatico2013a(3).jpg

Pyroxene (colorless, high relief), sanidine (with feathery texture) and phlogopite (brown) crystals. Orciatico lamproite, Pisa, Italy. PPL image, 10x (Field of view = 2mm)
orciatico2013a(7).jpg

Pyroxene (colorless, high relief), sanidine (with feathery texture) and phlogopite (brown) crystals. Orciatico lamproite, Pisa, Italy. PPL image, 10x (Field of view = 2mm)
orciatico2013a(8).jpg

Pyroxene (colorless, high relief), sanidine (with feathery texture) and phlogopite (brown) crystals. Orciatico lamproite, Pisa, Italy. PPL image, 10x (Field of view = 2mm)
orciatico2013a(9).jpg

Pyroxene (colorless, high relief), sanidine (with feathery texture) and phlogopite (brown) crystals. Orciatico lamproite, Pisa, Italy. PPL image, 10x (Field of view = 2mm)
orciatico2013a(10).jpg

Olivine (altered by green bowlingite), pyroxene (colorless, high relief), sanidine and phlogopite (brown) crystals. Orciatico lamproite, Pisa, Italy. PPL image, 10x (Field of view = 2mm)
orciatico2013a(2).jpg

Olivine (altered by bowlingite), pyroxene, sanidine and phlogopite crystals. Orciatico lamproite, Pisa, Italy. XPL image, 10x (Field of view = 2mm)
orciatico2013a(11).jpg

Olivine (altered by green bowlingite), pyroxene (colorless, high relief), sanidine and phlogopite (brown) crystals. Orciatico lamproite, Pisa, Italy. PPL image, 10x (Field of view = 2mm)
orciatico2013a(12).jpg

Olivine (altered by bowlingite), pyroxene, sanidine and phlogopite crystals. Orciatico lamproite, Pisa, Italy. XPL image, 10x (Field of view = 2mm)
orciatico2013a(13).jpg

Olivine (altered by green bowlingite), pyroxene (colorless, high relief), sanidine and phlogopite (brown) crystals. Orciatico lamproite, Pisa, Italy. PPL image, 10x (Field of view = 2mm)