Timing of Melting in Broken Hill, NSW, Australia

Double Schistosity Hill. Laminated leucogranite folded by F1, and F2, with axial planar S2 garnet-bearing leucosomes.

 

Related pages:
Monument locality: the role of melt in deformation
Diatexite Hill: from metatexite to granite

Interpretation:
a) Laminations in this granite are interpreted to result from syn-D1 intrusion. This is because of local intrusion of granites into S1 planes, and laminations, and K-feldspar orientation parallel to S1.
b) Subsequent development of F1 and S1 indicate solid behaviour of the granite attained after intrusion (Fig. A).
c) The solid granite (or effectively solid with a small melt fraction) was later folded and remelted during F2 (Figs. C and D).
Thus the thermal history of the area can be derived from the history of the granite:
i) Melt is produced at depth and then intruded into the area at subsolidus temperatures (or close to solidus) during D1.
ii) Solidification occurs in an environment of raising temperature.
iii) Temperature rise causes the granite to remelt during D2.

The evolution from D1 to D2 is one of prograde metamorphism, with peak metamorphism achieved during D2.

 

Similar leucosomes on the axial plane of F2 folds can be found at many other localities including the Monument locality