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Heavitree Gap - EarthCache
A simple EarthCache to bring you here and to highlight the landform that has been formed over the millions of years
This cache is almost a driveby and answerable even while traveling onboard the Ghan!
The Heavitree Gap, or Ntaripe in the Arrernte language, is a water gap in the MacDonnell Ranges of Central Australia and was an important sacred site for the Arrernte people.
It is the southern entrance to the city of Alice Springs and in addition to the Todd River it carries the main road and rail access to the South.
The sandy trail of the Todd River is an ancient river system that is between 300 and 350 million years old and was able to cut through a mountain range forming a 'gap' through the range as it was being formed. The Todd is like other Central Australian rivers including the Finke and the Hale which were created at a time when the land was going through a major building period known as the Alice Springs Orogeny.
The Alice Springs Orogeny was centered in an area that had previously been a marine sedimentary basin, and involved the thrusting up of the underlying metamorphic and igneous rocks. It was an event beginning approximately 450 million years ago and concluding about 300 million years ago, and it involved less than 100 km of distributed shortening responsible for the formation of the MacDonnell Ranges area.
The river at that time had enough energy to keep pace with the mountain building phase and it was able to incise down through the rocks that were rising underneath it and it ended up cutting out its gorges and gaps through those ancient mountain ranges which are now just remnants of their former magnificent selves and just as over time the MacDonnell Ranges have slowly diminished in size, so too has the Todd River reduced in flow.
Heavitree Gap contains an excellent exposure of an unconformity between the Hevitree Quartzite and Early Proterozoic Sadadeen Range gneiss , one of the metamorphic rocks of the Arunta Inlier .
The underlying gneiss, which rather looks like a granite was metamorphosed about 1750 million years ago, is separated by an uneven southward dipping unconformity from the overlying 9 metre thick siltstone bed, the oldest member of the Heavitree Quartzite. The siltstone and the overlying quartzite are the oldest (about 850 Million years old) of the preserved sediments deposited by a shallow sea which flooded much of central Australia after a long period of erosion.
Questions to log this EarthCache
Q1 Describe the Layers and which direction do they run
Q2 What colours do you see in the rock and describe the texture of the rock?
Q3 In you own words decribe what the Alice Springs Orogeny was
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