Webinar – South American Structural Geology. AusIMM South West branch.
Date: Tuesday 23rd, February 2021. Time: 12:00pm – 2:00pm AWST, 12.00pm – 2.00pm (UTC+08:00)
Illustrated Abstract
South America has some of the most diverse geology and mineralisation on Earth. This paper is an introduction to the South American continent evolution and is based on ultra-detailed, but broad scale research of the South American lithosphere from the surface to 2,900 km depth.
This is the first South American research to use ultra-detailed Landsat, topography, magnetics, gravity and seismic tomography. This great increase in detail enables lithospheric geological structures to be clearly seen in plan and section enabling a 3 D model to be made of the continent (see top figure). It also enables the lithosphere/crust and mineralisation timing relationships to be observed.
Thus, this research is able to give a much more accurate model of the continent’s evolution than the current hypotheses based on very coarse lithospheric and surface data.
South America has a series of cratons at the surface up to 3.6 billion years old. The lithosphere obviously would be older. There are huge ring structures up to 8,000 km diameter which form the nucleus of the continent (see figure below).
The strongest ring structure on Earth sits under the centre of the Pacific Ocean. I suspect that this is where the Mars sized planet hit Earth to form the moon. We can also see the impact of this ring structure at the core-mantle boundary at 2,850 km deep. This is still Earth’s hugest heat source and probably drives the Pacific Plate Tectonism.
Plate Tectonics and Earth’s evolution rethink needed – The current Plate Tectonics theory suggests that South America progressively accreted over the last 4 billion years. This current hypothesis suggests that the Sao Francisco craton was part of the oldest small, thin, original continent (Vaalbara) which formed 3.8 billion years ago.
The most startling observation in this latest research is that the mantle under Africa and South America has brittle deformation right down to the limits of detailed seismic tomography at the Core Mantle Boundary at 2,850 km depth. This study shows that the lithosphere down to at least 600 km depth formed during the Late Heavy Bombardment from 4.1 to 3.8 billion years ago (see top and next figure).
Thus, the original South American super-continent has remained an unbroken continent up to the present era. It originated as part of an Earth-wide thick lithosphere. It has survived over the last 4 billion years despite the action, firstly from vertical tectonics and then Plate Tectonics which commenced perhaps 2.7 billion years ago. It shows many generations of brittle deformation to this depth with no evidence of widespread ductile deformation required by the current Plate Tectonics theory. Thus the plumes as shown on current plans and sections cannot free-flow up through this brittle solid lithosphere (see top and next figure).
This requires a complete change to the mechanism of Plate Tectonics, from a free-flowing world-wide drifting of accreting thin surface continents to an original rigid earth being progressively broken up. It will be interesting for us to try and discover the mechanism of how this new Plate Tectonics regime can operate.
Structure – Another far-reaching discovery is the discovery of a 4 billion-year-old immovable barrier extending from the surface to the core and from South America to Alaska. The Andes separates totally different east/west lithospheric morphologies and is where this barrier lies (see top and next figure).
The broad structural geology of South America is a pop-up structure. South America is getting pushed by the Asia-African plate to the west at 25 mm per year but it is also getting pushed eastward by the Pacific plate which moves at about 40 mm a year. That’s a total compression of about 65 mm a year, or about a metre every 15 years. The only way this pressure can release itself is upwards. Hence there are large subvertical compression and orthogonal dilation flat fractures under South America extending to the core (see top and next figure).
Mineralisation – this lower pressure under South America to the core allows for heat and fluid release (see top figure).
South America is a rich source of minerals. The main mining fields are located on ring structures and linears observed from the surface to the limits of detailed tomographic plan data at 200 km depth.
The mechanism and source of the fluid for most mineralisation may have been discovered by this research. The fluid source is suggested to be from passive resorption of the lithosphere by heat from as far down as the core. This fluid then flows up vertical linear and ring structures to the surface scavenging and depositing minerals along its path. I have defined these structures down to 2,850 km depth (see top figure).
My research shows that this mechanism also occurs in Australia, North America, China and Fennoscandia. This suggests a close connection between deeply buried LHB impact structures, world girdling linears and mineralisation.
Once this relationship has been firmly established, and acted upon for mineral and energy targeting, a leap forward will have been made in exploration understanding and success.
The webinar will be available from the AusIMM and I will be posting the webinar notes and figures on this website as a series of papers.
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