Friday, 24 September 2010

Deformation in the Desert field trip 2007

Today I read a post by Anne over at Highly Allochthonous on some major flooding she witnessed on her trip to Alice Springs in 2000. This reminded me of my one trip to Alice Springs (it wasn’t flooding when I was there). Since my trip pre-dates my starting this blog, I thought I’d share with you the write-up I did for friends and family.

The below was written on 14 July 2007.

I just returned from the "Deformation in the Desert" Conference, held in Alice Springs, Northern Territory, Australia, sponsored by the Geological Society of Australia Specialist Group in Tectonics and Structural Geology.

The highlight of the conference was the five-day pre-conference field trip (photos below) which looked at the Palaeozoic tectonothermal evolution of the Irindina Province of the eastern Arunta Region. The trip started out in Alice Springs, headed south through the Heavitree Quartzite Gap (the ridge is a wall just south of town, the rocks steeply dipping, with a couple of gaps where the "rivers" cut through--though how you can call a waterless stream course a river, I don't know). From there we took the sealed (read: "paved" if you happen to speak American) road east and thence north into the Strangways and Hearts Range metamorphic complex. As soon as we turned north we were on dirt roads, and stayed on them for most of the rest of the trip.

Each day saw us rise before the sun so as to have breakfast before hitting the road. We stopped at many interesting outcrops, and at each stop the trip leader would show us the map, remind us of the geology at the last stop, tell us about the current stop, and then let us know what the next stop held in store for us. By the end of the trip I had a good understanding of the geology of the region! There were just about 40 people on the trip, including the catering group. They took good care of us, feeding us well (even us fussy eaters with special dietary requirements), and provided "swags" for each of us--a sleeping bag, mattress, pillow and water-proof canvas cover for the lot. We slept each night on the sands of (dry) creek beds, under the stars. There was no rain, nor any clouds (nor would any have been expected), making the camp sites safe enough, though in rainy seasons (once every several years) flash floods would be a problem (see above mentioned post by Anne).

The conference itself was held in Alice Springs and, unlike the conference I attended in Melbourne the year before, had only one track of sessions, so there was never a problem deciding which talk to attend--we simply attended all of them! Most of the talks were interesting, quite a number were very, very well presented, and only one was bad.

Stop 1: Ross River Gorge

Stop 2: Bitter Springs Formation, view to the east

Stop 3 Arumba Sandstone

Stop 3B Ross River syncline

Stop 5 Strangways Metamorphic Complex, with lovely garnets (800C, 6Kbars)

Stop 6: fold in mylonite zone

Stop 7: Argument Gorge, mylonite zone

Stop 7: stretching lineations on mylonite surface (this was the first time I'd seen a good exposure of a mylonite, and suddenly everything I'd been reading about them made so much more sense!

Stop 9: garnet rich boudin (some exceed 1.5 cm)--I liked this stop!

Stop 9, garnet showing sense of shear

Stop 9: mafic layer + garnet sand

Stop 10: near Lizzy creek, view north to the Hearts Range

Stop 11: an old mica mine in a pegmatite dike. Note huge sheets of mica that still litter the ground

Stop 12 Bruna Granitic Gneiss--view to the east

Stop 13: Mt. Ruby garnet zone in amphibolite from the Hearts Range Metaigneous complex

Stop 14: Indiana Granite Hill. We climbed this one.
Us, at the top of Indiana Granite Hill (stop 14)

Stop 16: Huckitta Creek, Intense strain zone
Stop 16: folding
Stop 16: more of the intense strain

Stop 17: Large fold
Stop 17: large deformed pegmatite dike to the right of the above fold. Note boudins in the layers of the fold limb

Stop 19: fold in gneiss
Stop 19: view to the east

Stop 20: Bruna granitic gneiss:
Stop 20 garnet-rich metapelite:

Stop 20: a mylonite zone in gneiss. Note that the mylonite contains garnet, the gneiss does not.
Stop 21: a mica and garnet rich layer in gneiss:
Stop 21: folding in gneiss:

There was also a mid-conference filed trip--a one day trip to the west of Alice Springs, driving on sealed roads the entire time (in large tourist-style air conditioned busses). The person who sat next to me happened to have been from Tasmania, and graduated years ago from UTAS before moving to the mainland to do geology there. Needless to say we had some very pleasant discussions about the uni we both attended.
The rocks on the mid-confluence trip weren't as pretty (they hadn't been sufficiently deformed to show the pretty folding or nice minerals that we saw on the five day trip), but they were still nice, and we actually saw a few waterholes (one 30 feet deep) which stay wet year-round, despite the fact that the rest of the river course is dry.
Mid conference trip stop 1: looking west at the Arumba Sandstone
Mid-conference trip, stop 2 Elery water hole (and folding of the rocks)

Mid-conference trip Stop 3: anticline in Heavitree quartzite
Mid-conference trip Stop 3 Heavitree quartzite repeated above thrust fault
Mid Conference trip stop 3: Ormiston Gorge (with some nice folding showing)
Mid Conference trip stop 4: Mt. Saunders
Mid conference trip, stop 5: The waterhole at Glen Hellen Gorge

Note: all above photo captions were taken straight from the file names of the photo, I didn't have to look for my field notes from the trip today--I had the sense to give the photos meaningful names, including stop numbers and sometimes even P/T data promptly after taking them.

1 comment:

Roads said...

Thanks for this. My first ever job as a professional geologist was three months in an iron mine in Western Australia.

There were two competing theories around the development of Banded Iron Formation at the time. Did the layering record sedimentary (or climatic) cyclity, or was it a produced by diagenetic effect?

As a fresh-eyed undergraduate of one full year's study behind me, I can remember asking my boss:

'But how can you work effectively, when you're still not sure how the BIF formed?'

'Aw, no worries, Roads,' came the honest and thoroughly practical reply. 'We just dig the f*#@!£% stuff out.'

Lesson learned.