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Spotted Dykes: granitic matrix including hornblende phenocrysts with numerous quartz inclusions, and diorite clasts (sample Tng Shyok).

 

Figure 1a-c.

 

Explanation: mixing of intrusive pegmatites with partially molten amphibolite.

 

Index photograph

 

Figure Index

 

Figure 1480. Homogeneous medium grained diorite on the left becoming increasingly spotted due to larger hornblende in the core of leucocratic pockets (just below the coin). Notice also that the boundary of the orange coloured biotite-bearing pegmatite is diffuse against the diorite.. This pattern is interpreted to indicate increasing melt fraction to the right, and a mixing boundary between the pegamtite and the presumably molten leucocratic groundmass of the diorite, see photos 1481 and 1479 for details.

 

Figure 1481 above. Detail of 1480.     Fig. 1479 right. Pegmatite intrusion broken up by coarse spotted diorite with hornblende phenocrysts and leucocratic patches, intepreted to represent melting. See 1470 below for detail of diorite fabric.

Figure 1b.

 

Figure 1470. Incipient formation of spotted diorite due to growth of hornblende phenocrysts and leucocratic patches.

Figure 1486. Better developed in situ melting fabric from another block. Notice small quartz inclusions in phenocrysts.

 

Figure 1473. Pegmatite dyke with irregular, interpenetrating contacts against the spotted diorite in the upper part of the photograph, but sharp boundaries against the regular, more homeogeneous dioirite.

Figure 1474 Detail of pegmatite dykelet into spotted diorite of 1473. Notice intepenetrating boundary and hornblende phenocrysts at the boundary.

 

Figure 1488. Pegmatite dyke (horizontal, top of image) evolving from right to left from an orange pegmatite without mafic minerals, to a groups of 0.5 cm long hornblende grains, to disagreggating the diorite on the left and isolating lens shaped clasts of diorite along pre-existing weakness planes in the matrix of the diorite (could it be along leucocratic melt patches?). Note to the lower right a patchy diorite with an abrupt contact with a homogeneous diorite. The patchy diorite could be a result of in situ melting.

Figure 1491 Detail 1488.