Piedra Parada, Chubut, Argentina

 

Piedra Parada Caldera

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A small andesite body is fed by a dyke and forms a 10x5x5m blob into a soft tuff layer underneath a lahar. The andesite intrudes the lahar which remained unconsolidated at that point.

Figure 1a)Contact of the andesite blob with layered tuff at the base.	Figure 1b) Irregular contact of the andesite blob with the top lahar in orange colours.
Figure 1c) The merging of a foliated andesite dyke with the curved, foliated margin of the andesite.	Figure 1d) The merging of a foliated andesite dyke with the curved, foliated margin of the andesite.
Figure 1e) Wispy andesite (unvesiculated) within vesiculated andesite.	Figure 1f) Wispy andesite (unvesiculated) within vesiculated andesite.
Figure 1g) Wispy andesite (unvesiculated) within vesiculated andesite.	Figure 1h) Irregular intrusive andesite dyke into lahar, showing sediment was still soft.
Figure 1i) Irregular intrusive andesite dyke into lahar, showing sediment was still soft.	Figure 1j) Contact between lahar and underlying tuff.

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Cryptodome

Google Earth image of cryptodome. Photos shown here are from the east side of the dome, looking west.

Figure 2a) Cryptodome.

Figure 2b) South tip of the cryptodome.	Figure 2c) North tip of the cryptodome.
Figure 2d) Base of dome: hyaloclastite.	Figure 2f) Hyaloclastite intruded/interlayered by a sill of greenish cryptocrystalline rhyolite.
Figure 2g) Interlayered hyaloclastite and green sill.	Figure 2h) Interlayered hyaloclastite and green sill. Notice angular blocks of both greenish rhyolite and cream-coloured ones.
Figure 2i) Interlayered hyaloclastite and green rhyolites at the south tip of the dome.

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Fiamme in Barda Colorada ignimbrite.

Figure 3a) Fluidal lapilli-shaped clasts. Note a 1cm rim of orange altered clast, with a narrow rim of zeolite. The matrix is not rheomorphic.	Figure 3b) Same but notice the internal texture of the clast, with dark elongated blebs in an orange matrix.
Figure 3c) Same but notice the internal texture of the clast, with dark elongated blebs in an orange matrix. Interpretation: the clasts froze before	Figure 3d) Same.
Figure 3e) In other blocks of ignimbrites, similar fiamme/clasts are angular.	Figure 3f) Rectantular clast, but the edges are feathery and grade with the matrix of the ignimbrite.
Figure 3g) Non-flattened clast centre but the margins are both flattened and feathery mixed with ignimbrite matrix.	Figure 3h) Rectantular clast, with internal foliation defined by small stretched blobs of dark material in a light brown matrix.
Figure 3i) Irregular fiamme? clast with a mafic core and light brown rim.	Figure 3j) Irregular fiamme? with internal foliation defined by small stretched blobs of dark material in a light brown matrix and feathery contacts.
Figure 3k) Rheomorphic ignimbrite with delicate stretched, flattened fiamme.	Figure 3l) Rheomorphic ignimbrite with delicate stretched, flattened fiamme.
Figure 3m) Rheomorphic ignimbrite with delicate stretched, flattened fiamme.	Figure 3n) Rheomorphic ignimbrite with delicate stretched, flattened fiamme.

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Photomicrographs of ignimbrite

Petrography.htm