Syn-Magmatic Deformation and Melt Extraction, Alagoinhas Pluton, Borborema Province, Brazil

The outcrop, point 16, 24L 0744256E 9063062N, just south of the village of Alagoinha, south of the Pernambuco Shear Zone. Photographs below show nearly horizontal expsoure but vertical exposures were locally available.

a) Boudinage of porphyritic granite

Figure 1a.	Figure 1b.
Figure 1c. In the bouding neck there is a higher concentration of felsic minerals including feldspar phenocrysts.

Figure 3.	Figure 4a. Boudinage of felsic layer
Figure 4b. Detail of a) showing felsic concentration in neck and bending phenocrysts at margin of boudin.

b) Boudinage and rotation of porphyritic granite in shear zones

Figure 5a. Boudinage of a granitic band trending 060, with dextral shear bands striking E-W in the boudin necks. These allow anticlockwise rotation of the boudins towards 045 (compare to sinistral shearing in Fig. 7) Notice increase in felsic minerals in the boudin neck. Magmatic phenocrysts are oriented parrallel to the shear zone, indicating syn-magmatic shearing. NE is to the rightof the photograph.

Figure 5b. Detail of a). Note how the more felsic shear band on the right-hand-side extends beyond the limit of the granitic layer and merges with another granitic band in the upper part of the photograph. This indicates that the shear band was once mobile and therefore rich in melt (see also Fig. 6 for another example).

Figure 6. Boudinage of foliated diorite. Boudin neck filled with more felsic magmatic rock, interpreted to represent local segregation out of the pores of a crystallizing mush. The boudin neck is an incipient vein that extends beyond the boudin neck area..

Figure 6. Two boundin necks, one adextral shear band trending E-W and the other a simple leucocratic neck with no obvious record of shearing trending 125. This change is interpreted to result from an original curvature in the trend of the granitic band.	Figure 7a. Boudinage of a granitic band trending 350. Boudin necks are sinistral shear zones allowing clockwise rotation of the boudins towards 045 (compare to dextral shearing in Fig. 5). Notice increase in felsic minerals in the boudin neck. NE is to the left of the photograph.
Figure 7b.Detail of a)

c) Shearing of porphyritic granite, syn-magmatic?

Figure 7a. Dextral shearing of porphyritic granite (horizontal exposure). The shear plane is parallel to the granite-diorite contact close to the coin, trending 020, and otherwise the phenocrysts are oriented diagonally across the phtotograph (from lower left to upper right) in a northerly trend.	Figure 7b. Detail of a) showing the dextral shearing (on 020/sv) of the phenocrysts forming S-C fabric.
Figure 8. Phenocrysts arranged in two preferred orientations suggesting dextral shearing.

d) Preferential orientation of irregular leucocratic veinlets and dykes

Figure 9. Irregular leucocratic melt extraction ("leucosomes") with a preferential E-W orientation and irregural fuzzy boundaries. Arrow in scale indicates the main trend of the foliation, and arrow points towards 225 (SW).	Figure 10a. Boudinaged granitic bands on the left-hand-side, parallel to the main foliation (045), and leucocratic bands trending ~E-W, with fuzzy boundaries with the surrounding diorite. Arrow in scale pointing W.
Figure 10b. Detail of a). Note also leucocratic veins in the upper left-hand-side parallel to the main foliation in diorite. Arrow in scale indicates the main trend of the foliation, and arrow points towards 225 (SW)