SGTSG 2022 King Island
Structure in the Strait
22nd - 24th November 2022
Expression of Interest for pre-conference Fieldtrip 19-20 November 2022, Departing / Returning Melbourne CBD
Costs TBA subject to confirmation of site access and likely participation numbers.
Please send expressions of interest to Ross Cayley (Geological Survey of Victoria) at : firstname.lastname@example.org by 23rd September 2022.
Expressions of interest are sought for a 2-day pre-conference field trip to examine probable northern extensions of Proterozoic King Island geology in Central Victoria. The excursion will depart Melbourne CBD early on Saturday 19th November and return to Melbourne on the evening of Sunday 20th.
Depending on numbers, travel by minibus will be provided. Overnight accommodation is anticipated to be in Cowes on Phillip Island. There are a range of extra-curricular activities available on the island with wildlife viewing a highlight.
The geological reasons why this excursion will be cool:
The bedrock geology of King Island continues northeast beneath Bass Strait as a prominent sub-sea topographical feature – the King-Island-Mornington High. Greater context of the Proterozoic geology of King Island is revealed by geophysics, particularly aeromagnetic data (figure 1) which shows the weakly magnetic Mesoproterozoic Surprise Bay and Fraser formations – schist and quartzite – to be bracketed by northerly-trending tracts of highly magnetic, probable Ediacaran-age mafic igneous rocks to the west and east.
The western magnetic tract continues north from King Island to beneath Cape Otway in Victoria (Figure 1), northeast of which probable Proterozoic-age amphibolite (derived from the Ceres Gabbro; see VandenBerg et al., 2000) is exposed at Barrabool Hills west of Geelong (A on Figure 1). These high-grade metamorphic rocks are yet to be reliably dated but are a very poor match for surrounding Victorian Palaeozoic successions. The metamorphic and structural character of these rocks are a much better match for (and lie directly north along-strike from) strongly regionally metamorphosed Mesoproterozoic amphibolites found within the Fraser Formation on King Island, for example north of Pegarah Road.
The eastern magnetic tract is exposed on the eastern coastline of King Island as the Skipworth Subgroup (Upper Grassy Group), a thick ~570 Ma package of mafic volcanics. These rocks can be traced northeast in magnetic data along the King Island-Mornington High to Phillip Island (B on Figure 1) where they are exposed in Kitty Millers Bay as the Phillip Island Metabasalt (Henry & Birch, 1992). The wider context of these rocks with Victorian Palaeozoic geology is obscured beneath Cainozoic basalt but the metabasalt on Phillip Island contains a northeast-striking penetrative cleavage that lies parallel to the magnetic tract and several of the Phillip Island dolerites are low in titanium and closer in composition to tholeiitic and picritic basalt of the King Island Upper Grassy Group. These rocks all lie on common magnetic trends, and the structural fabrics in the basalts are aligned too.
These are the two sites that we intend to visit in the excursion.
A minimum Cambrian age for the context of these rocks within Central Victorian continental crust is given by a Late Cambrian unconformity beautifully exposed at Waratah Bay (C – Figure 1) and at other sites inland which, together with the aeromagnetic data, was the inspiration for the Selwyn Block concept – western Tasmania/King Island Proterozoic continental crust extending north beneath Central Victoria (imaged in seismic reflection data – D in Figure 1).
Day 1, Saturday 19th November 2022:
The plan is to drive to Phillip Island (~2.5 hour drive) from a Melbourne CBD pickup point departing early (~7:30 am) Saturday morning. We plan to spend ~4 hours in and around Kitty Miller Bay (including a lunchbreak). We should be on the rocks at ~10:00 am on a falling tide. Low tide is at 13.23. There is an old shipwreck on the beach (Shipwreck SS Speke - Location & Trail Kitty Miller Bay, Phillip Island (phillipislandpoint.com.au)).
In the late afternoon will travel the short distance to Cowes for an early dinner and to check in to our overnight accommodation.
The non-geological reasons why this excursion will be cool:
Post-dinner entertainment will include the option of visiting the World Famous Phillip Island Fairy Penguins Parade (https://www.penguins.org.au/attractions/penguin-parade/). There is an Australian Fur Seal colony nearby (on Seal Rock; more than 25,000 seals at times). Bring a good pair of binoculars
Day 2, Sunday 20th November 2022:
On Sunday morning we will travel to Barrabool Hills via the Port Phillip Ferry that links Sorrento and Queenscliff (https://www.searoad.com.au/Prices-Timetable/Ferry-Timetable). Dolphins surfing the ferry wake is a common feature of this pleasant voyage. After several hours on the rocks at Barrabool Hills we will travel to Geelong for lunch. The return to the Melbourne CBD late Sunday afternoon marks the conclusion of the pre-conference excursion.