Exploration Insights May 2020 | Page 24

Exploration Handbook | 25
Borel, 2002; Hochard, 2008; Vérard et al. 2015; Vérard, 2019).
Isochron
Mid-ocean
ridge
Continent-Ocean
boundary
Active margin
Intra-oceanic
subduction
Geodynamic
units
Continental
crust
© 2020 Halliburton
Oceanic crust
Plate
Figure 3> Schematic representation of plate model components including geodynamic units, continents/terranes and plates. The
linework is composed of plate boundaries (e.g active margin, and mid-ocean ridge), continent-ocean boundaries (e.g. active margin,
and passive margin) and other important features (e.g. isochrons).
THE BASIS OF A PLATE MODEL
Each polygon component of the plate model ‘map’ is called a geodynamic unit (GDU). A GDU is a
portion of the Earth’s lithosphere that has had a discrete evolution through geological time. Each GDU
is attributed with rotation poles describing its movement to its paleo-positions back through geological
time. This information can be read by plate reconstruction software, such as GPlates, PaleoGIS, and
QuickPlates ® online application.
In this approach, the plate model is built around reference
reconstructions. These are key time slices for which global
plate tectonic frameworks are created, including GDU
positions, plate boundaries, and oceanic crust (consumed
and extant). Plates in their entirety (continental and oceanic
portions) are then moved from one reference reconstruction to
the next one, conserving a globally consistent plate boundary
network, while respecting the addition or consumption
of lithosphere and triple junctions. Between reference
reconstructions, the evolution of the plate boundaries has to be
consistent with the motion of plates, and must reflect a valid
geodynamic scenario that respects physical and geometrical
rules (Fowlers, 2004; Vérard, 2019).
“ Each polygon component of
the plate model ‘map’ is called
a geodynamic unit (GDU). A
GDU is a portion of the Earth’s
lithosphere that has had a
discrete evolution through
geological time. ”
The integration of large datasets, allowing for absolute and
relative plate positioning methods, combined with a globally
consistent plate boundaries framework and a dual control
approach, are essential conditions for higher accuracy and
confidence in plate tectonic models. This is particularly true
the further back you go in geological time, as data quality and
availability decreases.
The quality of the plate model is often associated with the level of detail in the subdivision of GDUs,
and the precision of the associated poles of rotation. The quality also depends on how well the GDU
positions have been constrained, which is related to the amount, variety, and precision of the data used.
PLATE MODEL CONSTRAINTS
Plate positions can be difficult to track back using observational methods alone, so vast multi-
disciplinary datasets are synthesized and integrated, using concepts from different fields of
geosciences. The challenge for the modeler is to understand the absolute position, the relative position,
and the geodynamic context of each GDU.
Absolute position with respect to a fixed mantle frame of reference generally relies on proxies, such as
paleo-magnetic data or temperature-sensitive biostratigraphic markers. These enable an estimate to be
made of the paleo-latitude of a GDU at a certain time, but without a direct constraint on paleo-longitude
(Torsvik, 2019). Hotspots are considered as fixed mantle points (O’Neil et al., 2005; Ivanov, 2007).
Subducted paleo-ocean slabs, imaged by tomography, indicate where oceans once existed. These two
methods only provide support for absolute plate positioning as far back as the last 300 million years
(van der Meer et al., 2010; 2018).
The relative plate (GDU) position and its geodynamic context are assessed using multi-disciplinary
proxies from sedimentology, stratigraphy, structural geology, geochronology, and geochemistry. These
data are integrated, while obeying plate tectonic concepts, such as plate buoyancy, mantle physics,
ocean spreading, and subduction rates, to determine the GDU positions with respect to each other, and
to support the modeling of a globally consistent and closed plate boundary network.
A globally consistent plate boundary network exists in a few plate tectonic models, including the
Neftex ® Plate Model. Where present, it allows a geoscientist to go one step further into true plate
modeling (as opposed to continental drift), and impose a “dual control” on the model (e.g. Stampfli and
© 2020 Halliburton
Figure 4> Building a robust plate tectonic model from data and regional knowledge is just the starting point for understanding the
wider Earth system, enabling advanced predictions of the occurrence of natural resources through time and space.
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