Paul H. Wrote:
-------------------------------------------------------
> Hi, I have just gotten back from visiting family
> in Eugene,
> Oregon. Arrived at 6:30 AM this morning and took a
> long nap.
> That having been stated, one paper concerning the
> geology
> of the Inca fortress of Sacsayhuamán, Peru, is:
>
> Spencer, J.E., 1999. Geologic continuous casting
> below
> continental and deep-sea detachment faults and at
> the striated
> extrusion of Sacsayhuaman, Peru. Geology, 27(4),
> pp.327-330.
> [pubs.geoscienceworld.org]
>
> This articles states that this outcrop, called "El
> Rodadero",
> consists of "hypabyssal andesite". "Hypabyssal"
> simply
> means that this plutonic rock was emplaced and
> solidified
> at depths of less than 2 km (1,2 m) within the
> crust. In
> this case, the proposed environment of intrusion /
> emplaced
> is within oceanic crust in association with an
> active core
> metamorphic complex.
>
> A discussion of what a metamorphic core complex
> is
> can be found in "Chapter 13: Metamorphic Core
> Complexes
> and Related Features" at
> [www.idahomuseum.org]
>
> A later paper is:
>
> Spencer, J.E., Ohara, Y. and Titley, S.R., 2008.
> Magmatic
> and tectonic continuous casting in the
> circum-Pacific
> region. Arizona Geological Society Digest, 22,
> pp.31-53.
> [www.geo.arizona.edu]
>
> It turns out that this "andesitic" rock is more
> properly
> called a "diorite porphyry containing augite" /
> "hypabyssal
> diorite". The "andesite" designation likely is the
> result
> of changing terminology and the loosey goosey
> usage of
> geologic terminology by various authors.
>
> This plutonic diorite porphyry intruded into a
> gray,
> fossiliferous limestone of Late Jurassic or
> Cretaceous
> age. The limestone underlies the stonework of
> Saqsaywaman. The limestone was metamorphosed
> by contact with hot, dioritic magma during its
> intrusion.
>
> Other Papers about the geology of Sacsayhuaman
> are:
>
> Ericksen, G.E., and Muessig, S., 1986. Comment and
> Reply on June 1985 Geology cover: Comment and
> Reply.
> Geology, 14(1), pp.91-92.
>
> Feininger, T., 1978, The extraordinary striated
> outcrop
> at Saqsaywaman, Peru. Geological Society of
> America
> Bulletin, v. 89, p. 494–503.
>
> Gabelman, J.W., 1967, Structure and origin of El
> Rodadero, Cuzco, Perú: Boletín de la Sociedad
> Geológica del Peru: v. 40, p. 25-54.
>
> Gregory, H.E., 1914, The Rodadero (Cuzco, Peru)—
> A fault plane of unusual aspect. American Journal
> of
> Science, 4th ser., v. 37, p. 289-298.
>
> Marocco, R. and García-Zabaleta, F., 1974. Estudio
> geológico de la región entre Cuzco y Machu Picchu.
> Bulletin de l’Institut Français d’Études Andines,
> 3(2),
> pp.1-27.
> [www.persee.fr]
>
> Marocco, R., and Feininger, T., 1980. The
> extraordinary
> striated outcrop at Saqsaywaman, Peru. Comment and
> Reply: Geological Society of America Bulletin, v.
> 91,
> part 1, p. 251–252.
> [pubs.geoscienceworld.org]
>
> As far as the types of rocks used to build
> Saqsaywaman,
> I have had little luck finding a detailed
> accounting of the
> subject. The best that I have found so far is:
>
> J. Cárdenas, V. Carlotto, V. Cano, T. Flores, M.
> Oviedo
> Estudio geológico y geodinámico de los baluartes
> en
> el sitio arqueológico de saqsaywaman-Cusco.
> instituto
> geológico minero y metalúrgico (INGEMMET) y
> universidad nacional San Antonio abad del Cusco
> First Report (2009)
> [hdl.handle.net]
> [repositorio.ingemmet.gob.pe]
>
> I am still translating text. So far, from what I
> have
> translated, the carved stones used to build the
> structure are composed of "limestone".
>
> Yours,
>
> Paul H.

Thanks for the extensive information on that question!