The Outcrops of this pluton, described below, include examples of the country rock surrounding the complex, intrusion mechanism, shearing of plutonic rocks as well as different mingling processes and textures.
Northwest and west of the Santa Angélica Intrusive Complex (SAIC), a granodioritic gneiss (Estrela Batholith, G1 suite) crops out, extending northwards until the Guaçui Lineament (Fig. 2). This rock-type has a coarse-grained homogeneous augen texture with an amphibolite-facies metamorphic foliation (D1) (Bayer, et al., 1986). In the contact zone with the SAIC (G5 suite), this D1 foliation was deformed plastically together with microdioritic dikes from the intrusion (Bayer, 1987; Wiedemann et al., 1997).
At the southeastern border of the SAIC, the internal marginal zone is made up of an almost continuous ring of coarse-grained granite (Granite I, analysis SA4.1, Table 1), showing strong magmatic flow-structure parallel to the border (Wiedemann et al., 1997). In this Outcrop, the earlier flow-structure of the granite is gently undulated and overprinted by a second ductile foliation. The quarry is at the very contact between the gneiss and granite I. Blocks showing this contact can be seen. Sills of the granite intrude the enclosing gneiss lit par lit (Fig. 18). The contacts are sharp but irregular and produce an injection migmatite. The schistosity of the gneiss is chaotically folded and partially melted, with clear separation of leucosome and melanosome. Strongly deformed basic enclaves can be observed in the granite.
This is a region of homogeneous gabbro-norites and gabbro-diorites. In the homogeneous dark matrix, K-feldspar xenocrysts may be found as drops together with granitic schlieren.
The composition of clinopyroxene in the gabbros shows small variations in the fields of salite and augite. Orthopyroxene is mostly hypersthene (Schmidt-Thomé, 1987). A single analysis of pigeonitic composition is probably due to several submicroscopic exsolution lamellae of cpx in opx. Exsolution of ilmenite is also common in pyroxene. Secondary amphibole after pyroxenes are mostly edenitic hornblende with higher Si- and Mg-contents than the quartz poikilitic magnesium hastingsitic hornblende from the megacrysts and matrix. The TiO2-content of biotite reaches levels up to 3.56% and MgO up to 13.82% (Schmidt-Thomé, 1987). A characteristic microfabric of these gabbros is the coalescence of plagioclase crystals in synneusis (Wiedemann, et al., 1986). This could be a sign for an abrupt lowering of crystallization temperature which stopped further magma mixing. Apatite, as fine acicular needles, is a common accessory mineral. No olivine has been found. See Table 1, SA2.1 for chemical analysis.
In this region, mingling of magmas, from microscopic to metric scales, is exposed (Fig. 20). Different corrosion stages of feldspars, differently mantled feldspar and quartz xenocrysts are noteworthy (Fig. 21). Granitic schlieren mingle with the basic magma producing a pillow network. Local mixing originates intermediate rocks of granodioritic composition (Table 2, chemical analyses: SA 2.1; SA2.2; SA 3.1; SA 3.2; SA 3.3).
Seven Outcrops of the Castelo Complex are described below. They reveal the nature of this inversely zoned, mingled pluton and the nature of its contacts with country rock gneisses. In this complex, a porphyritic, fine-grained sphene monzogranite (granite II), very similar to the granite II of Santa Angélica, crops out in the border region, in contact with the enclosing gneisses. It forms most of the matrix of a thick agmatic border. It consists of rafts of the enclosing gneisses in a granite-II matrix and suggests stoping. This granite II may also intrude the border gneisses as lit par lit sills or discordantly, as dykes along shear zones (Fig. 24).
From the BR-262 take the asphalt road Venda-Nova-Cachoeiro do Itapemirim, shortly after the small village of São Paulino (on the tographic IGBE map) take the country road to Alto Santa Clara.
A coarse-grained granodiorite is intruded by several dikes of a porphyritic granite giving rise to net-veined structure. The megacrysts consist of K-feldspars. Gradation between granite and granodiorite may also be observed.
This is the core of the intrusion, dominated by coarse-grained diorite. Shrinkage cracks (Hibbard and Watters, 1985) formed during solidification are intruded by granite. Walking along the river, there are local changes in the diorite grain size, tending to a finer texture due to the contact with coarse-grained granite. The contact is characterized by a frozen layer of mingled microdiorite and granitic schlieren (Fig. 25).
A very interesting Outcrop of Granites I and II in close proximity showing:
magmatic banding of granite I and II with foliation parallel to the margins of the intrusion;
feldspar megacryst imbrication and deformation due to viscous magmatic flow;
discordant contact between a syn-intrusive microdioritic dike showing strong magmatic foliation and a coarse-grained granite I (Figure 32). This is a hybrid monzodiorite with a glomeroporphyritic texture, with hornblende + biotite + apatite + ilmenite + magnetite clots surrounded by a titanite rim. Poikilitic hornblende contains biotite, opaque minerals, acicular apatite and sphene. Strongly zoned plagioclase grains are randomly dispersed in the very fine-grained diorite matrix;
zone of different layers of the two granites (I and II) in sub-parallel contact with less evolved elongated magma blobs (pillow-like structure) of diorite to granodiorite, in different degrees of mixing with the granites. Presence of xenocrysts of corroded quartz and mantled feldspars in the mafic pillows. Under the microscope, common acicular apatite indicates rapid cooling during crystallization.
Figure 32. Castelo Complex
Discordant contact between a synintrusive microdioritic dike, showing strong flow deformation at the border, and coarse-grained granite.
The most usual minerals are: andesine, augite, hornblende, sphene, apatite and zircon. Occasionally, quartz content increases, mostly as corroded xenocrysts surrounded by mafic minerals and the rock becomes a quartz diorite. K-feldspar is rare; augite may be replaced by hornblende or by biotite, accompanied by exsolution of ilmenite and Ti-magnetite, parallel to the 001 cleavage of the augite. Less frequently the diorite may contains small amounts of subhedral opx.
Most of the magma-mingling features seen in Santa Angélica are also present in Castelo. However, here granite mingles with dioritic and granodioritic magmas, showing similar quartz xenocrysts with mafic aureoles and mantled feldspars, like those from Santa Angélica. Coarse-grained granite forms a net-veined structure with the microdiorite. At the bottom of a small waterfall, spotted fine-grained granite, rich in surmicaceous enclaves, which are aligned parallel to the magmatic flow, crops out. Going up hill, differently shaped enclaves are embedded in a porphyritic granite (type-II). Pillow-like structures of different types can be observed:
fine-grained microdioritic;
medium grained dioritic showing different hybridization degree with the granite;
local more homogeneous hybridization between granite and diorite originating granodioritic portions;
spotted textures (Hibbard, 1995) and granitic schlieren in the microdiorite;
A fine-grained granite, similar to the Santa Angélica granite II, typically Outcrops close to the contact of the pluton with the country rock. This same granite also forms layers in the coarse-grained granite I, towards the center of the structure. The foliation is always parallel to the pluton margin. This granite is occasionally porphyritic with microcline megacrysts in a monzogranitic matrix. The accessory minerals are titanite, zircon, apatite, magnetite, ilmenite, pyrite, chalcopyrite and allanite. Gradational contacts between diatexitic rocks, from the enclosing gneisses, and this granite are common. Ghost structures from the gneisses are possible evidence for the anatetic origin of this granite. Surmicaceous enclaves parallel to magmatic foliation are also common.
Close to Outcrop 19, very homogeneous coarse-grained granite, with well-developed magmatic flow given by K-feldspars megacrysts, crops out. Enclaves with intermediate to basic compositions are stretched and deformed, parallel to the main flow direction. Sphene is the most common accessory mineral.
Spotted textures are a common feature for mafic rocks of the Castelo Complex. This texture is formed by a glomeroporphyritic aggregate of mafic minerals (pyroxenes and/or amphibole and biotite clots) in a microdioritic matrix. Xenocrysts of quartz surrounded by a mafic aureole are often present in this unit. Biotite concentrations may be observed at the contact between the granitic schlieren and the microdiorite. Analyses of similar rocks in Table 1: Ca 1.1 and Ca 1.2.
The Pedra Azul Complex crops out in the center-southern region of Espírito Santo. This inversely zoned pluton is formed by contrasting lithofacies grading from quartz diorite to syenogranite (Costa Nascimento et al., 1996; Fig. 23). Inside the pluton, a medium-grained monzogranite forms the highest peaks as well as the lower border regions, forming the magmatic envelope of the structure. Several portions of tonalitc to granodioritc compositions were mapped towards the center of the structure. Evidence for magma mingling processes are sharp contacts between coarse- and fine-grained contrasting lithotypes, acicular apatite grains in mafic pillows, mantled and corroded feldspars, corroded / embayed biotite and other mineral instability textures.
A fine- to medium-grained paragneiss megaxenolith can be observed in the monzogranite. At the contact between the xenolith and the granite, partial melting is evidenced by intrusive lit-par-lit interfingering. The local partial melting of the xenolith also produced aplitic veins that intrude the granite.
A layered structure, formed by stretched pillow-like tonalitic/granodioritic enclaves (Figure 33) can be followed over one hundred meters. Felsic coarse-grained granitic schlieren and veins surround and/or intrude the enclaves.
Figure 33. Tonalitic/granodioritic enclaves
Layered structure formed by stretched pillow-like tonalitic/granodioritic enclaves or layers and medium-grained granite. Pedra Azul Pluton.
Coarse-grained monzogranite, showing large feldspar crystals aligned along a NW-SE magmatic flow trend.
Mixed zone characterized by a net-veined/pillow-like structure. Tonalitic/granodioritic pillow-like and angular enclaves are chaotically distributed and wrapped by felsic medium- grained monzogranitic veins. Pegmatite veins is the last intrusive event.
This Outcrop is characterized by several types of autholitic and xenolithic enclaves, showing variable shapes and dimensions, and different assimilation degrees. The matrix is a medium- to coarse- grained rock. Some enclaves have clear reaction borders, grading from diffuse to sharp contacts. A very interesting feature is the presence of bimodal enclaves diorite/granodiorite, probably formed during the mingling process. The irregular distribution of the enclaves points toward a local turbulent magmatic flow.
In this stop, an exotic ocellar texture can be observed in the fine-grained syenogranite. This rock consists of rounded leucocratic ocelli, wrapped by a mesocratic biotitic rim. The ocelli are essentially sphene-centered aggregates of microcline and quartz, with minor amounts of allanite. Microcline, quartz, biotite, plagioclase and accessory phases (zircon, allanite, opaque minerals and fluorite) form the matrix.