The Dike of Magma EarthCache
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This Earthcache can be found along a gorge hike that is 1.3 kms
long and drops 460m from beginning to end and takes about 5 hours
to complete, but only if you have made prior arrangements with
either "Die Bosman", "Fish Eagle" or " GPS Storm".
Alternatively you can access the cache from the bottom via the
railway maintenance road without permission (See 'Bottom' at
additional waypoints).
But beware... the walk up is a very difficult 260m.
The area in which the dike is found is an erroded gorge where the
soil has been washed away completely to expose the granite
batholith (Large intrusive masses of granite). Towering on either
side of the small gorge are huge granite boulders and dome like
batholiths.
The boulders sizes range from about 1m to up to 15-20m diameters,
and have been rounded through spheroidial weathering and errosion.
The dike is not easy to miss and is a clear example of the less
dense and more fluid basaltic magma that can rise into cracks of
weakness in the surrounding granite.
The gorge in which this dike is found is only one of many that
funnels rain water from the plateu above into the Crocodile valley
that is carved out of the countryside by the Crocodile river
below.
Below is a more descriptive explanation of Dikes.
The dike is a body of rock that cuts across the layers of its
surroundings. Most dikes are made of magma, but sediments can form
dikes too.
An igneous dike is molten basaltic magma that rises through and
cuts across existing layers of basalt. Igneous dikes are common in
many bodies of plutonic or highly metamorphosed rock, where molten
or fluid materials have invaded pre-existing rock formations.
What defines a dike is that it cuts across the bedding planes of
the rock it intrudes. When an intrusion cuts along the bedding
planes, it is called a sill. In a simple set of flat-lying rock
beds, dikes are vertical and sills are horizontal. In tilted and
folded rocks, dikes and sills may be tilted too.
The true three-dimensional shape of a dike is not exposed at sites
like these, but we can show that dikes must be thin, flat tongues
or lobes. Clearly they intrude along the plane of least resistance,
where rocks are relatively in tension, so dike orientations give us
clues to the local dynamic environment at the time they formed.
Commonly dikes are oriented in line with local patterns of
jointing.
In order to claim a find you need to send us an e-mail telling
us the following:
1) What Colour is the dike.
2) What is the approximate thickness of the dike on the thickest
side, and
3) Tell us what rock you think is on either side of the
dike.
Additional Hints
(No hints available.)
Treasures
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