Basement Rocks:
Are hard, crystalline rocks which were injected into the Earth’s crust in a molten state, there to cool slowly over thousands of years are widespread in Fiordland. They are the oldest rocks in the area and form the “basement” or foundation of younger layers of sedimentary rock such as conglomerate, limestone, sandstone and coal. According to their minerals and crystals size they are named:
Gabbro: dark green, heavy rock with almost no pale minerals.
Dunite: olive-green rock make up almost entirely of the mineral olivine.
Ultramafic rock: rich in magnesium and iron minerals and poor in silica;
Pegmatite: very coarse crystals (up to 5 cm) of pink or white feldspar, grey quartz and black or white mica. Occurs in veins.
Granite: pink or pale speckled rock with same minerals as pegmatite but smaller crystals.
Diorite: black and white speckled rock usually darker than granite.
Gneiss: rock like granite or diorite but with bands or layer rather than random speckles.
Dull, rusty-red rocks which can be found on your path are gabbro and dunite, with coarse crystals which are easily seen on weathered surfaces. The first outcrops on the track to Mt Luxmore are made of ultramafic boulders cemented together to form “conglomerate”. Near the summit of Mount Luxmore’s eastern peak the conglomerate contains fossils of sea shells – most are species found on rocky seashores, such as paua or abalone. In the past 30 million years the whole area has been uplifted from sea level to its present height.
Soils developed on ultramafic rock often have high concentrations of magnesium and nickel, and very low levels of plant nutrients. This limits plant growth and the vegetation is usually very sparse. Here the soils are not only poor but stony and shallow because of slow soil development, erosion, and down-slope movement.
On the northern side of Mount Luxmore, the track sidles into a small glacially eroded cirque with a steep headwall, and many small tarns. Rock wrens may be seen flitting across the boulder fields and alpine grasshoppers of many sizes and colours are abundant in summer.
Below the western peak of Mount Luxmore, rusty ultamafic rocks give way to types of gneiss, granite and diorite which are seen along the main track to the Forest Burn Shelter and beyond. A side-track leads to the Mount Luxmore Summit for the high point of the walk and wonderful views on a fine day.
Please make your way up there and answer the following questions:
- At GZ please have a closer look and describe the stone's structure, minerals and crystals size.
- Which colour can be found within the stone structure?
- Based on your findings for Q1/2 what basement rock did you discover?
- (Optional): Take a photo of yourself, your GPS or just the view showing Te Anau or with bad weather conditions the trick station in the clouds.
Please log your find at the same time as your email me your answers. However, if your answers are incomplete or wrong you will be asked to provide more details. If this is not provided the log will be deleted.
Additional Information - Kepler Track:
The Kepler Track is one of the newer tracks in New Zealand, being completed in December 1988. The track was built to relieve pressure off the nearby and very popular Routeburn and Milford Tracks. It has now become popular and is now one of the "Great Walks" of New Zealand. The Track makes a 60 km (37 mile) loop "tramp" through some great scenery in Fiordlands National Park. Walking the loop usually take three to four days. From the Mount Luxmore hut, the Kepler track zigzags up onto the upper slopes of Mount Luxmore, towards the eastern peak.