1 - Cochin University of Science and Technology
1 - Cochin University of Science and Technology
1 - Cochin University of Science and Technology
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l<br />
<strong>of</strong> joints (horizontal <strong>and</strong> oblique). Near Malampuzha dam<br />
site, the exposed biotite - hornblende gneisses shows minor<br />
displacement in N 60 0 E direction (Fig. 13).<br />
Mainly stromatic (layered) in structure, the migmatitic<br />
gneisses <strong>of</strong>ten grade into surreitic (dilatational <strong>and</strong><br />
scho I I en varieties (Mehnert, 1968; Ashworth, 19851. Since,<br />
molten <strong>and</strong> unmolten portions <strong>of</strong> these irregularly layered<br />
rocks can stil I be distinguished petrographically, these are<br />
broadly categorised as metatexites.<br />
Amphibolites are localised within the gneisses <strong>and</strong> occur<br />
as medium - to coarse - grained xenolithic masses <strong>of</strong> various<br />
sizes <strong>and</strong> shapes. Rarely, some fine-grained schistose types<br />
are also observed. Intricately permeated by granitic<br />
material, these lenticular, discontinuous patches pass<br />
imperceptibly into migmatitic gneisses (Fig. 14, 151.<br />
quite<br />
These<br />
enclaves are generally dark <strong>and</strong> <strong>of</strong>ten show boudinage (F i g.<br />
161. Some <strong>of</strong> these enclaves located within the hornblende<br />
biotite migmatitic gneiss, measure upto 40 to 75 cm in length<br />
<strong>and</strong> 10-15 cm in width <strong>and</strong> <strong>of</strong>ten pinch out along<br />
within outcrop I eve 1. Near Pulamparapudur<br />
foliation<br />
locality,<br />
amphibolite patches in migmatitic gneisses attain a maximum<br />
width <strong>of</strong> 10 m which get progressively reduced to small er<br />
patches towards the eastern extremity <strong>of</strong> the quarry, due to<br />
progressive transformation <strong>of</strong> amphibole to biotite.<br />
Amphibolite b<strong>and</strong>s <strong>of</strong> 2-3 m thickness showing weathering<br />
effects are also seen. Some <strong>of</strong> the b<strong>and</strong>s show displacement