ERTH3104 Virtual Field Trip to New England Orogen
Stop name: Cotley Creek site of Tia Granodiorite
Location: ~10 km west of the Oxley Highway along the Tia Diggings Road (then turn north into the Cotley Road). The best exposure is at the Cotley Creek, which is dry most of the time. Watch out for snakes!
Coordinates: 31°12'10.75"S, 151°45'40.49"E
What to see: This is a classic location for S-type granite in the New England Orogen. This outcrop is a part of the Tia granodiorite (~300 Ma) within the Hillgrove Suite.
Additional data:
A petrographic thin section for an S-type granite sampled at this location (19S01 at Thin section collection). Hint on what to do: compare I-type and S-type granites with thinsection photos.
A U-Pb geochronogic dataset and CL images (the end of this page) for a batch of zircons collected from this outcrop (Click to download the Excel data file). Hint on what to do: intepret these ages into a brief magmatic history.
Field photo from this site
(Photo by R. Zhou)
Two-mica granite (an S-type granite)
(Photo by J. Aitchison)
Granite landscape - Tor
Tors develop in areas where granites (general) dominate.
Tors form as weathering preferentially works along the joints.
(Illustration by S. Marshak)
Exfoliation
Exfoliation is another type of common weathering for granites. It takes place during the unroofing of these deeply burried rocks.
(Above) Cathodoluminescence (Cl) images of zircon. Zircon are from a granite sample taken from the Tia granodiorite. U/Pb ages were measured at the spots labelled with laser abaltion techniques. You are provided with the U-Pb age data for these zircon. Click to download the Excel data file. What could you tell about the timing of magmatism with these data?