Geology Reference
In-Depth Information
First, in the Terra Nova Bay area of Northern Victoria Land, tafoni and cavernously-
weathered forms are well developed in coarse-grained granites and metasedimentary
rocks (Figure 4.11A). The area is extremely dry and cold (see Table 3.1). Thin sections of
the weathered bedrock indicate that physical disintegration is associated with the prefer-
ential fracturing of quartz minerals while softer feldspar minerals remain relatively intact
(Figure 4.11B). It has been hypothesized that micro-cracks, formed in the quartz minerals
at the time of magma cooling, permit penetration and subsequent freezing of gas-liquid
intrusions at sub-zero temperatures (French and Guglielmin, 2000). The salt is provided
by snowmelt and acts to lower the freezing point. Disintegration is further helped by the
increasing brittleness of quartz at low temperature, and case hardening accentuates the
unusual morphology by providing a hardened outer shell. Thus, the process is best
(A)
(B)
Figure 4.11. Cavernous weathering in coarse-grained monzogranite, Terra Nova Bay area, North-
ern Victoria Land, Antarctica. (A) Taffoni-weathered boulder. Backpack for scale. (B) Thin section
photo of tafoni-weathered monzogranite viewed under cross-polarized light. The photo dimensions
cover 8 mm. The photo shows a highly fractured quartz mineral (left) and a largely unfractured
microcline mineral (right). A large void separates the two minerals and smaller voids are present
within the quartz mineral.
Search WWH ::




Custom Search