MATASIETE, Soda Granite Porphyry
PRE-CRETACEOUS ( ? )
State of Nueva Esparta, Venezuela
Author of name: Hess and Maxwell, 1949.
Original reference: Hess and Maxwell, 1949, p. 1861-62.
Original description: ibid.
Hess and Maxwell (1949, p. 1861-62) published the name "Mata Siete" (should be Matasiete) soda granite porphyry for an igneous formation exposed in the Matasiete hills, in the eastern part of Margarita Island. Their description is as follows:
"The rock consists of euhedral to subhedral plagioclase crystals in a matrix of cataclastic (mosaic texture) quartz. Many of the plagioclases are sheared and broken. They exhibit an exceedingly fine polysynthetic albite twinning which suggests an original zoning and are somewhat sericitized. The borders are clear albite, in part at least porphyroblastic, for they include blebs of quartz. Ferro-magnesian minerals, for the most part constitute less than 5 per cent of the rock; the small amounts present are altered to epidote, actinolite or chlorite. Its petrographic feature indicates that the porphyry was intruded at relatively shallow depth". (Hess and Maxwell, 1949, p. 1861-62).
The authors state that it has not been definitely determined, whether the soda granite porphyry originally intruded the Los Robles schist or whether it lies unconformably beneath them; they incline to the latter hypothesis, favored by González de Juana (1947), since no contact metamorphism could be observed along the western margin. A recently active fault along this contact, however, complicates the relations.
González de Juana (1947, p. 694) had already noted the presence of granitic intrusions in the Matasiete and El Tirano hills, and noted that they were undoubtedly older than the ultrabasic intrusions in other parts of the island. He believed that these granites might be related with a post-Tithonian, pre-Urgonian orogeny or with a still earlier orogeny.
References to "granite" in the literature before 1947, are discussed in the article Isla Margarita, "Granite" In.
Frances de Rivero