Speaker: Dr. Daniel Pastor Galán
Talk Title: Becoming a supercontinent
Time: Feb 25th, 10:30-11:30
Location: Room 213, Department of Geosciences, NTU
The Earth has written its own history in thousands of rock pages, the geological record, which contains evidence of the evolution and interactions of continents, oceans, atmosphere, and biosphere. Despite the rock archive is really dismembered, scattered and hidden in remote places or deeply buried, gathering the pieces together is our only opportunity to reveal the history of our planet, our history. Sometimes struck by punctual catastrophes, secular changes have shaped most Earth history: crustal growth and loss, biogeochemical cycles, global mantle circulation, long-term secular changes in sea-level, major variations in the geomagnetic field, global climate changes, mass extinctions… There is an emerging consensus that plate tectonics force lithospheric plates to amalgamating supercontinents in a quasi-periodic cycle, forming rigid super-plates with limited lithosphere-mantle interactions in their cores. The supercontinent cycle has been linked to most of the episodic global changes that shaped Earth History and to the distribution of natural resources. Despite their potential importance, however, many of these proposed links are, to date, permissive rather than proven.
Pangea, the most recent supercontinent, provides our best opportunity to evaluate supercontinent assembly and dispersal. Tectonic reconstructions assume Pangea being a single and stable superplate from 320 to 200 Ma representing an absolute minimum of 25% of Earth's area. However, the hypothesis of a long-lived Pangean superplate faces too many contradictions: plate kinematics do not fit with such timing, it is unclear the which oceans where involved and how and magmatic response, there are contradictions between petrological and structural constraints, the geodynamics driving this formation are absolutely unclear. However, there are silver linings, a thorough work in structural geology, paleomagnetism, geochronology and tectonic modeling suggest that Pangea was much less stable than previously thought and during a shorter time. Also, its formation produced a large plate tectonic reorganization which, in turn triggered its own break up.