Red mountains and crescent bays of Freycinet Peninsula, Tasmania

Map, Freycinet Peninsula Circuit, Freycinet, Freycinet Peninsula, Tasmania, Australia, hiking, bushwalking, outline, location, distance

Map of Freycinet Peninsula (Circuit) – Tasmania, Australia (© State of Tasmania)

Intro: Freycinet Peninsula is arguably the most popular tourist destination in Tasmania. Just look on any pamphlet for the island state and you will more than likely find a photo of the stunning (and appropriately named), Wineglass Bay. What makes Freycinet so beautiful can be traced back to the geology and geomorphology of the area. I recently did a multi-day hike along the Peninsula (i.e., the Freycinet Peninsula Circuit), which consists of a counterclockwise circuit, starting from Coles Bay and ending at Mt. Amos. In this post I will share some of the insights in the glowing red mountains and sparkling blue beaches that make this place so alluring.

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Hazard’s Beach (left) and Wineglass Bay (right) from the top of Mt. Graham – Freycinet Peninsula, Tasmania, Australia

Science Spiel: Glowing mountains and wine glass shaped beaches (Geology, Geomorphology)

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Just another wallaby (they are everywhere!) hanging out by an outcrop of red granite at Hazard’s Beach – Freycinet Peninsula, Tasmania, Australia

Freycinet Peninsula is composed of large granite bodies. They are Devonian in age, and are a striking difference to the other main geological units that comprise most of Tasmania (i.e., the young, prominent Jurassic dolerite and the old, deformed Precambrian quartzite). There are two major types of granites, I-type and S-type. They are classified this way in regards to their molten source being either igneous (I) or sedimentary (S). The I-type granites are enriched in sodium and calcium, and have the mineral hornblende. S-type granites are depleted in sodium but enriched in aluminum, they typically have the minerals muscovite, biotite, corundum and garnet. On the Freycinet Peninsula, granites are mostly S-type, and they range from equigranular to porphyritic, with large K-feldspar crystals (Groves, 1967). In fact, the K-feldspar-rich composition of the granites is what gives them their characteristic red appearance, which appears to be amplified when the sunset light hits Mt. Amos and the Hazards mountains. Granites here are also more radioactive than other granites in Australian, due to significant amount of U and Th. This isn’t, however, a contributing factor to the famous red glow at sunset!

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Prominentc red glow of the Hazards and Mt. Amos granite mountains at sunset at Freycinet National Park – Tasmania, Australia

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Cartoon showing how the Freycinet granites formed, and then got uplifted and eroded (Parks Tasmania, 2016)

These granites have curved, domal surfaces which is a characteristic feature of granites called “onion skin” weathering (e.g., sugarloaf in Rio de Janeiro). This is caused by exfoliation from elastic expansion and contraction of the rock, which causes outer slabs “skin” of the rock to fall off, which exposes fresher surfaces that haven’t been discoloured yet due to weathering processes. Pre-existing joints and faults also get weathered out more easily, which aids in making and defining the rounded boulders.

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Brilliant blue water on an granite beach near Cooks Beach – Freycinet, Tasmania

Beside the rocks, the other remarkable landscape of Freycinet is the white sand, blue water, crescent-shaped beaches. Some of the most popular are Hazard’s Bay and Wineglass Bay. Bays are semi-enclosed bodies of water, commonly in a crescent shape (hence the characteristic “wineglass” shape), with calmer water than the surrounding ocean. This is due to headlands on either side of the Bay which reduces wind and blocks and refracts waves into the bay. The beautiful white sand that composes the beaches can also be attributed to the granite rocks, as the most of the quartz sand grains likely came from erosion of the quartz-rich granite bodies.

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The famous Wineglass-shaped Wineglass Bay of Freycinet Peninsula (view from the top of Mt. Freycinet) – Tasmania, Australia

Final Thoughts: While the mountains at Freycinet aren’t as rugged as those in the southwest of Tasmania, the domal-shaped granites definitely hold their own magical allure. It isn’t a surprise why Freycinet is regarded as one of the must-see places in Tasmania. Freycinet National Park is easily accessible driving from Hobart, with only a short hike to the lookout of Wineglass Bay. I, however, also highly recommend the Freycinet Peninsula Circuit 3-day hike. Both are great ways to experience (and hopefully appreciate) the granite mountains and crescent-shaped beaches that define this place!

-Stephanie

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Hiking group photo, from the top of Mt. Freycinet, with Wineglass Bay in background – Freycinet, Tasmania

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View (looking south) of Schouten Island from the top of Mt. Freycinet – Tasmania, Australia

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Wineglass Bay, looking toward Mt. Amos – Freycinet Peninsula, Tasmania, Australia

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Mapping with drones

Intro: An exciting part of being a PhD student is being surrounded by new ideas and technology that pushes forward your field of study. On an undergraduate geology field trip to Freycinet National Park, Tasmania, I was part of a team in conjunction with our new TMVC hub (i.e. ARC Industrial Transformation Research Hub, Transforming the Mining Value Chain) at the University of Tasmania, to teach the undergraduate students geological mapping. What was different about this was that we integrated high-resolution photographs taken from an aerial drone with a mapping technique used in mineral exploration and ore deposit studies. Are exercise took place on a beautiful outcrop near Bluestone Bay, Freycinet Peninsula, Tasmania, Australia.

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An aerial done (UAV) with a student mapping in the background – Freycinet Peninsula, Tasmania, Australia

Science Spiel: Mapping and drones

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First published geological map, by William Smith in 1815

Geology is very much an observational-based science. While many branches of the science focus on observation on a microscopic scale, it is critical to first understand what the bigger picture is. The best way to record these observations is by creating a geological map of the rocks you are interested in. In fact, it was just the 200th anniversary of the first ever geological map by William Smith in 1815. The technique of geological mapping hasn’t changed a whole lot since then, but new technologies like Unmanned Aerial Vehicles (UAVs; i.e. drones) are being used to create the most detailed 3-D photos of the outcrops ever.

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Undergraduate students observing the UAV (i.e. drone) in action.

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Dr. Roach fly a UAV to capture a 3-D photograph of the outcrop

On a recent field trip for the 2nd year geology undergraduate students, we went to Freycinet Peninsula, on the east coast of Tasmania, to teach them about the rocks that make up the peninsula, and how to do geological mapping. One of the professors in the Geology department at the University of Tasmania, Dr. Michael Roach, has been very active with capturing 3-D spatially referenced geological outcrops. The main purpose is to have a representation of key geological outcrops for teaching to students (check out www.AusGeol.org for a virtual library of Australia’s geology). The UAV was flown over the area ahead of time so we had the high-resolution maps ready to deploy.

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High-resolution photograph, obtained from a drone (UAV), for the base layer of geological map

Bridging the Old with the New

A small area was chosen for detailed mapping, with a high-resolution photograph as a base layer. Instead of just mapping the usual rock units (lithotypes) and structures (…which are beautiful, note the fault offsetting the pink dyke in the centre of the photo…), we also mapped hydrothermal alteration and mineralization. This is very important when it comes to mineral exploration, as the hydrothermal fluids that create veins and alter rocks over a wide area are usually associated with (or are the same) hydrothermal fluids that cause mineralization and ore deposition (i.e. gold, copper). A colour-coated mapping style was used, known as “Anaconda” mapping, which basically is mapping of different alteration assemblages (Einaudi, 1997).

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Example legend for mapping hydrothermal veins and alteration

That is, if a hydrothermal fluid passed through or nearby a rock, the original minerals will because altered with depletion or addition of different elements. These are visible in the rocks, as when you look at primary minerals their properties (i.e. colour, hardness, appearance, etc.), differ from what they originally were.

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Teaching alteration mapping at Freycinet, Tasmania, Australia

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A geology student mapping on the outcrop at Freycinet Peninsula, Tasmania, Australia

Final Thoughts: For the interest of future students doing this exercise I shouldn’t reveal the final geological map, but there were some good-looking maps by the students and lots of enthusiasm to go around (a good chunk coming from us, the demonstrators…). The aid of a high-resolution base layer makes mapping prominent geological features fantastic, and it allows you to keep thinking about the big picture while you take your hand lens, hammer and notebook out to understand the details. Mapping alteration and veins systematically in the field allows you to start to see the more prospective areas on the map while you are still on the ground, and have a better understanding of the prospective areas associated with hydrothermal fluid flow. Overall it was a successful exercise in integrating an old technique with new technology, something that will no doubt be used going forward!

-Stephanie

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An Unmanned Aerial Vehicle (i.e. UAV) flying over a geological outcrop and taking 3-D spatially referenced photos

What is the Tessellated Pavement

Tasmania, Australia, Travel, Geology, Adventure, Blog, Rocks, Tessellated Pavement, Joints, How did it form, formation, what is, explore, outdoors, Tasman Peninsula, Eaglehawk Neck, Photography, Tassie, nature, science, geoscience, cool rock formations, salt water, ocean, sea, shore, coast, location, mapIntro: Sometimes it is hard to believe certain rock formations are natural… and this is definitely the case with a place in Tasmania called the Tessellated Pavement. It is named this due to the tessellated (i.e. tiled-like) appearance of the rocks along the water. This little tourist spot is near Eaglehawk Neck, on the way to the famous Tasman Peninsula, and only about an hour drive from Hobart. Not only is the Tessellated Pavement a spectacular sight (and photographer’s dream), but it also is a unique geological phenomenon…

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Overview of the Tessellated Pavement at Eaglehawk Neck – Tasmania, Australia

 

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Myself (for scale) at the Tessellated Pavement at Eaglehawk Neck – Tasmania, Australia

Science Spiel: Cracks and salt (Geology, Geomorphology)

The rock that comprises the Tessellated Pavement is mostly siltstone that formed in the Permian (about 300 million years ago), by sediments that accumulated on a relatively low-lying area. The sediments eventually got compacted and lithified to form the solid siltstone. Local stresses at the Earth’s surface then caused the siltstone to crack and fracture in certain directions, this is called jointing.  There are three mains sets of joints; ENE, NNW, and NNE. The fact that they are mutually cross-cutting without off-set each other is a key observation that tells you the joints formed at the same time.The way they criss-cross each other is what creates the tiled-like appearance.

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Joints of the Tessellated Pavement at Eaglehawk Neck – Tasmania, Australia

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Joints of the Tessellated Pavement at Eaglehawk Neck – Tasmania, Australia

But wait, the story doesn’t end there… time and water also played (and continue to play) a role in creating this site.

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Tessellated Pavement at Eaglehawk Neck – Tasmania, Australia

The rocks are currently on an intertidal seaward platform, and thus years and years of erosion (i.e. since sea levels stabilised in the area ~6000 year ago), has exaggerated the tessellation appearance (Leaman, 2001). The constant action of the salt water splashing over and partly covering the rocks with changing tides has lead to the accumulation and percolation salt water on the rocks, particularly within the joint. As the water gets evaporated by the sun, salt crystals forms and as they grow they exert pressure on the rocks causing rocks and joints to flake away and be more susceptible to erosion.

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Cartoon of how salt crystals enhance erosion and the appearance of the Tessellated Pavement (modified from Parks Tasmania, 2016)

The salt crystallization mostly occurs in the joints, however, water that pools on the top of the rocks furthest away from the ocean dries the fastest and salt crystallization is more intense on the rock surface there, causing the depressed, or “pan-like” tiles.

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“Pan-like” tiles of the Tessellated Pavement at Eaglehawk Neck – Tasmania, Australia

The opposite occurs for rocks closer to the water, and therefore only the joint really are visibly depressed, creating the “loaf-like” tiles (Banks et al., 1986; Leeman, 2001).

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“Loaf-like” tiles of the Tessellated Pavement at Eaglehawk Neck – Tasmania, Australia

Final Thoughts: The Tessellated Pavement is a stunning sight that sparks curiosity of visitors. The reason I checked it out is that actually a friend of mine asked me what it was, as it looked man-made to her! Jointing in rocks is not an uncommon thing, but the special circumstances with salt crystal formations and increased erosion really enhanced this pattern. I would highly recommend stopping by this neat place on the way to the Tasman Peninsula, I hope it sparks your curiosity about rocks as well!

-Stephanie

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Curious (?) about the Tessellated Pavement at Eaglehawk Neck – Tasmania, Australia

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Tessellated Pavement at Eaglehawk Neck – Tasmania, Australia

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Tessellated Pavement at Eaglehawk Neck – Tasmania, Australia

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Rare minerals of Tasmania and where to find them

Intro: There are some people, known as mineral collectors, that hunt for the most unique and beautiful mineral specimens in the world… and Tasmania has two of these world renowned and highly sought-after minerals in our own backyard; crocoite and stichtite.

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Crocoite sample at mineral fair from the Adelaide mine in Dundas -Tasmania, Australia

Minerals are naturally occurring substances that make up rocks. Geologists (specifically mineralogists) study and admire them, however, their beauty is admired by far more than just these specialists. These rare and highly prized minerals, specifically crocoite, are found (almost) exclusively here in Tasmania. Luckily one of my friends at the university, a German experimental petrologist, is also an avid mineral collector. He got us access to visit the Adelaide Mine in the Dundas district, near the town of Zeehan in western Tasmania. The Adelaide Mine, as well as other mines in the Dundas area, are the key localities for the best crocoites samples! In this post I will attempt to explain a bit more about these beautiful minerals, how they formed, and where to find them.

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Entrance to the Adelaide mine for crocoite samples – Dundas, Tasmania, Australia

 

Science Spiel: Red, green and purple (Geology, MineralogyOre Deposit Geology)

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Crocoite [PbCrO4]

Crocoite is a rare lead chromate [PbCrO4] and arguably the most famous mineral from Tasmania. It has beautiful elongated, hollow, prismatic to acicular crystals that are bright orange and red. The name comes from the Greek name for saffron, and it isn’t hard to imagine why! Crocoite has a beautiful vitreous lustre, but this is lost once exposed to UV light (i.e. sunlight).

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Geological cross-section through the crocoite-bearing gossans (i.e. the crocoite mines) in Dundas, Tasmania, Australia (after Bottrill and Baker, 2008)

How crocoite forms is still a bit enigmatic, however, simply put it basically forms when a hydrothermal fluid rich in chrome (Cr), that was likely leached and oxidized from the surrounding chrome-rich ultramafic rocks in the area, encounters a hydrothermal fluid rich in lead (Pb). When these two Cr- and Pb-rich hydrothermal fluids meet, or when the Pb-rich hydrothermal fluid encounters the Cr-rich hostrock, crocoite forms (Bottrill and Baker, 2008). The mineral crocoite occurs with Pb-Zn-Ag sulfide veins in siderite and ankerite faults zones, but commonly the crocoite grows in open-space cavities and vugs within the surrounding rocks in areas that have been largely altered to clays and gossans (Bottrill and Baker, 2008).

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Crocoite in a large vug within the Adelaide mine in Dundas – Tasmania, Australia

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Stichtite (purple) in serpentine (green) from Tasmania, Australia

Stichtite is a beautiful purple magnesium hydroxycarbonate [Mg6Cr2CO3(OH)16·4H2O] that was first discovered here in Tasmania, near the town of Zeehan, in 1981 (Twelvetrees, 1914). It has a waxy luster and is generally within Cambrian-aged serpentine as small disseminations that have replaced chromite/magnesiochromite (Bottrill, 2001). The bright green mineral serpentine forms when high temperature and pressure rocks from the earth’s mantle rich in the mineral olivine, interact with lower temperature fluids. This interaction happens when the mantle-derived rocks are obducted or thrusted to the earth’s surface, and they chemically react with lower temperature fluids to hydrate and produce the mineral serpentine. The light purple mineral stichtite is intertwined with serpentine and also comes from the chemical reaction of mantle-derived minerals, such as chromite, with alkaline lower temperature fluids. As a geologist, I always think mineral specimens are beautiful natural, however, stichtite in serpentine is very frequently polished to highlight the green and purple contrasting colours.

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Stichtite (purple) in serpentine (green) from Tasmania, Australia

Where do you find these minerals in Tasmania?

The Dundas district, near Zeehan, is where the majority of the stichtite and crocoite are found. Most of the good sites are private mines, with only some open to the general public. For the stichtite in serpentine samples, some key localities are Serpentitne Hill, Nevada Creek and Stichtite Hill. For crocoite samples, the key mines are Adelaide mine, Dundas Extended mine, Red Lead mine, as well as others (Bottrill, 2001).

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Locations of crocoite and stichtite mines and outcrops in western Tasmania, Australia (after Bottrill, 2001). Highlighted crocoite mines are 1: West Comet and Dundas Extended mines; Crocoite: 2: Adelaide mine; 3 Red Lead mine; Stichtite outcrops and mines are 4: Stichtite Hill; 5: Platt and Kosminsky mines; 6: Comet-Maestries mines; 7: South Comet mine. Highlighted stichtite outcrops and mines are 1: West Comet and Dundas Extended mines; 9: Nevada Creek; 11: Serpentine Hill (Tunnel Hill).

For more information, check out this .pdf guide from Mineral Resources Tasmania (http://www.mrt.tas.gov.au/mrtdoc/dominfo/download/UR2001_08/UR2001_08.pdf),

and if you are interested in minerals of Tasmania I recommend this book as well (http://www.mrt.tas.gov.au/portal/a-catalogue-of-the-minerals-of-tasmania).

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Driving to the Adelaide crocoite mine – Dundas, Tasmania

As mentioned above, most of these are private, but if you are keen and ask nicely you might get access to a mine tour, such as the kind folks at Adelaide mine did for us!

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Inside the Adelaide crocoite mine – Dundas, Tasmania

Final Thoughts: I usually try and collect an interesting rock or mineral from the place I travel to, and I personally think this is the best type of souvenir as it is unique and a little natural piece of the place. If you want something from Tasmania, I can’t think of a better item than a beautiful mineral that is uniquely from the westcoast of Tassie! It was quite the adventure going out to the westcoast and mines themselves, and just a superb experience to be able to go into the Adelaide mine and see the large vugs and cavities where the minerals have grown in situ. I don’t think you have to be a geologist or specialist to appreciate these beautiful minerals of Tasmania.

 -Stephanie

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Crocoite in a vug within the Adelaide mine in Dundas – Tasmania, Australia

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Morning reflections of a little Silurian siltstone and fine-grained sandstone island on Lake Burbury, Tasmania

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A geological oddity; orbicular granites of Tasmania

Tasmania, Australia, West Coast, Travel, Geology, Adventure, Blog, Granite, UST, Orbicules, unidirectional solidification textures, tourmaline, quartz, aplite, feldspar, cavities, slushy texture, magmatic, hydrothermal, textures, rocks, explore, outdoors, Trial Harbour, Granville Harbour, Zeehan, Western Tassie, Tassie, nature, science

Orbicular granite near Trial Harbour – Tasmania, Australia

Intro: Tasmania sure does pack-a-punch when it comes to geological oddities. One of the strangest I would argue is the bizarre spotted granites on the west coast. Clustered within certain areas of the granite are orbs containing tourmaline, quartz and other minerals. The sight of them is spectacular, and their formation is still enigmatic! We ventured over to the west coast to sample and map these in more detail, as one of the PhD students in my department is doing his thesis attempting to unravel their mystery. I don’t have all the answers (maybe he will soon), but I will attempt explain a bit more about theses wonderful but odd features in this post.

Tasmania, Australia, West Coast, Travel, Geology, Adventure, Blog, Granite, UST, Orbicules, unidirectional solidification textures, tourmaline, quartz, aplite, feldspar, cavities, slushy texture, magmatic, hydrothermal, textures, rocks, explore, outdoors, Trial Harbour, Granville Harbour, Zeehan, Western Tassie, Tassie, nature, science

Heemskirk granite on the coast near Trial Harbour – Tasmania, Australia

Tasmania, Australia, West Coast, Travel, Geology, Adventure, Blog, Granite, UST, Orbicules, unidirectional solidification textures, tourmaline, quartz, aplite, feldspar, cavities, slushy texture, magmatic, hydrothermal, textures, rocks, explore, outdoors, Trial Harbour, Granville Harbour, Zeehan, Western Tassie, Tassie, nature, science

Orbicular granite near Trial Harbour – Tasmania, Australia

Science Spiel: Odd Orbicules (Geology)

The northeast and west coast of Tasmania contain large granite batholiths around ~360 million years old. One of the largest ones is called the Heemskirk granite, and it is exposed along the shore at Trial and Granville Harbour, near the town of Zeehan in western Tasmania. This is where we went to see these strange features. It is also interesting to mention that another aspect to these granites is their common association with tin and tungsten ore deposits (Kitto, 2009).

Tasmania, Australia, West Coast, Travel, Geology, Adventure, Blog, Granite, UST, Orbicules, unidirectional solidification textures, tourmaline, quartz, aplite, feldspar, cavities, slushy texture, magmatic, hydrothermal, textures, rocks, explore, outdoors, Trial Harbour, Granville Harbour, Zeehan, Western Tassie, Tassie, nature, science

Location and Trial and Granville Harbour, and geological map of the Heemskirk granite in western Tasmania, Australia

Granites form from the solidification of felsic magma deep within the crust. Within the granite various processes take place, most of which earth scientist still don’t have a full understanding of. One of these processes is the generation of magmatic liquids and volatiles within the magma, which subsequently get released around the edges of the magma and result in hydrothermal veins and alteration. It is rare to see this transition from magmatic to hydrothermal conditions, but luckily there are some spectacular outcrops in Tasmania that exhibit features that are attributed to this enigmatic transition.

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Folded UST band with parallel smaller UST band, near Granville Harbour – Tasmania, Australia

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Formation of unidirectional solidification textures

Unidirectional solidification textures (USTs), well-exposed at Granville Harbour, are formed by the downward growth of prismatic crystals, usually quartz or feldspar, at the roof of a crystallizing magma (Shannon et al., 1982; Kirkham and Sinclair, 1988). Is it thought that they form from the buoyant hydrothermal fluid that migrates to the top of the magma chamber. Eventually pressure builds up and the seal is breached and this results in melt and (possible metal-bearing) fluids to escape, and then rapid cooling and devolitisation of the magma, resulting in fine grained aplite layers between the UST layers. These fractures get sealed up soon after, and then another layer of UST forms, thus repeating the processes.

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Quartz USTs near Granville Harbour – Tasmania, Australia

Tasmania, Australia, West Coast, Travel, Geology, Adventure, Blog, Granite, UST, Orbicules, unidirectional solidification textures, tourmaline, quartz, aplite, feldspar, cavities, slushy texture, magmatic, hydrothermal, textures, rocks, explore, outdoors, Trial Harbour, Granville Harbour, Zeehan, Western Tassie, Tassie, nature, science

Myself by a planar layer of quartz USTs near Granville Harbour – Tasmania, Australia

Other magmatic-hydrothermal transition features are giant pegmatite pods and veins, vein-dykes, miarolitic cavities and orbicules!

Tasmania, Australia, West Coast, Travel, Geology, Adventure, Blog, Granite, UST, Orbicules, unidirectional solidification textures, tourmaline, quartz, aplite, feldspar, cavities, slushy texture, magmatic, hydrothermal, textures, rocks, explore, outdoors, Trial Harbour, Granville Harbour, Zeehan, Western Tassie, Tassie, nature, science

Tourmaline and quartz crystals within a cavity in the Heemskirk granite near Granville Harbour – Tasmania, Australia

Tasmania, Australia, West Coast, Travel, Geology, Adventure, Blog, Granite, UST, Orbicules, unidirectional solidification textures, tourmaline, quartz, aplite, feldspar, cavities, slushy texture, magmatic, hydrothermal, textures, rocks, explore, outdoors, Trial Harbour, Granville Harbour, Zeehan, Western Tassie, Tassie, nature, science

Orbicular granite near Trial Harbour – Tasmania, Australia

Tasmania, Australia, West Coast, Travel, Geology, Adventure, Blog, Granite, UST, Orbicules, unidirectional solidification textures, tourmaline, quartz, aplite, feldspar, cavities, slushy texture, magmatic, hydrothermal, textures, rocks, explore, outdoors, Trial Harbour, Granville Harbour, Zeehan, Western Tassie, Tassie, nature, science

Tourmaline cavity

Orbicules are spectacularly exposed near Trial Harbour. They are very spherical, round and consist of dominantly tourmaline and quartz. They look like chickenpox within the granite, which is why I sometimes refer to this as a diseased rock! The orbicules aren’t the only odd round features with tourmaline and quartz, there are patches and spherical cavities with well-developed tourmaline crystals and quartz, and commonly potassium feldspar alteration rim at the edges.

Tasmania, Australia, West Coast, Travel, Geology, Adventure, Blog, Granite, UST, Orbicules, unidirectional solidification textures, tourmaline, quartz, aplite, feldspar, cavities, slushy texture, magmatic, hydrothermal, textures, rocks, explore, outdoors, Trial Harbour, Granville Harbour, Zeehan, Western Tassie, Tassie, nature, science

Orbicules with K-feldspar alteration rims, in the Heemskirk granite near Trial Harbour – Tasmania, Australia

How do they form? Again, this is still enigmatic! But a couple theories are that these represent bubbles of volatiles and/or melt coalescing near the roof of an intrusion, or by nucleation and outward growth of crystals within the melt.

Tasmania, Australia, West Coast, Travel, Geology, Adventure, Blog, Granite, UST, Orbicules, unidirectional solidification textures, tourmaline, quartz, aplite, feldspar, cavities, slushy texture, magmatic, hydrothermal, textures, rocks, explore, outdoors, Trial Harbour, Granville Harbour, Zeehan, Western Tassie, Tassie, nature, science

Orbicular granite near Trial Harbour – Tasmania, Australia

Final Thoughts: As I mentioned at least half a dozen times, these really are odd rocks. Granites are a very common rock type in the geological record, but rarely do they exhibit these magmatic-hydrothermal transition features as we can see exposed within the Heemskirk granite on the west coast of Tasmania. Being able to see these beautifully USTs and orbicules allows a unique opportunity to think about and study what the processes are that take place within a crystallizing magma. The west coast of Tasmania is also a stunning place to explore, in case you needed another reason besides the rocks!

-Stephanie

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Tasmania, Australia, West Coast, Travel, Geology, Adventure, Blog, Granite, UST, Orbicules, unidirectional solidification textures, tourmaline, quartz, aplite, feldspar, cavities, slushy texture, magmatic, hydrothermal, textures, rocks, explore, outdoors, Trial Harbour, Granville Harbour, Zeehan, Western Tassie, Tassie, nature, science, sunset

Sunset near Granville Harbour – Tasmania, Australia

Tasmania, Australia, West Coast, Travel, Geology, Adventure, Blog, Granite, UST, Orbicules, unidirectional solidification textures, tourmaline, quartz, aplite, feldspar, cavities, slushy texture, magmatic, hydrothermal, textures, rocks, explore, outdoors, Trial Harbour, Granville Harbour, Zeehan, Western Tassie, Tassie, nature, science

Folded quartz UST, near Granville Harbour – Tasmania, Australia

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