scholarly journals A non–plate tectonic model for the Eoarchean Isua supracrustal belt

Lithosphere ◽  
2020 ◽  
Vol 12 (1) ◽  
pp. 166-179 ◽  
Author(s):  
A. Alexander G. Webb ◽  
Thomas Müller ◽  
Jiawei Zuo ◽  
Peter J. Haproff ◽  
Anthony Ramírez-Salazar
Keyword(s):  
Multiple Scales ◽  
Field Observations ◽  
Plate Tectonic ◽  
Mantle Dynamics ◽  
Tectonic Model ◽  
Tectonic Events ◽  
Tectonic Processes ◽  
Intrusive Rocks ◽  
Supracrustal Belt ◽  
Deformation Event

Abstract The ca. 3.8–3.6-b.y.-old Isua supracrustal belt of SW Greenland is Earth’s only site older than 3.2 Ga that is exclusively interpreted via plate-tectonic theory. The belt is divided into ca. 3.8 Ga and ca. 3.7 Ga halves, and these are interpreted as plate fragments that collided by ca. 3.6 Ga. However, such models are based on idiosyncratic interpretations of field observations and U-Pb zircon data, resulting in intricate, conflicting stratigraphic and structural interpretations. We reanalyzed published geochronological work and associated field constraints previously interpreted to show multiple plate-tectonic events and conducted field-based exploration of metamorphic and structural gradients previously interpreted to show heterogeneities recording plate-tectonic processes. Simpler interpretations are viable, i.e., the belt may have experienced nearly homogeneous metamorphic conditions and strain during a single deformation event prior to intrusion of ca. 3.5 Ga mafic dikes. Curtain and sheath folds occur at multiple scales throughout the belt, with the entire belt potentially representing Earth’s largest a-type fold. Integrating these findings, we present a new model in which two cycles of volcanic burial and resultant melting and tonalite-trondhjemite-granodiorite (TTG) intrusion produced first the ca. 3.8 Ga rocks and then the overlying ca. 3.7 Ga rocks, after which the whole belt was deformed and thinned in a shear zone, producing the multiscale a-type folding patterns. The Eoarchean assembly of the Isua supracrustal belt is therefore most simply explained by vertical stacking of volcanic and intrusive rocks followed by a single shearing event. In combination with well-preserved Paleoarchean terranes, these rocks record the waning downward advection of lithosphere inherent in volcanism-dominated heat-pipe tectonic models for early Earth. These interpretations are consistent with recent findings that early crust-mantle dynamics are remarkably similar across the solar system’s terrestrial bodies.

Eoarchean formation of the Isua supracrustal belt

2020 ◽  
Author(s):  
A Alexander G Webb ◽  
Thomas Müller ◽  
Jiawei Zuo ◽  
Peter Haproff ◽  
Anthony Ramírez-Salazar
Keyword(s):  
Plate Tectonics ◽  
Multiple Scales ◽  
Early Earth ◽  
Plate Tectonic ◽  
Mantle Dynamics ◽  
Change Models ◽  
Fine Grained ◽  
Tectonic Events ◽  
Supracrustal Belt ◽  
Major Shift

<p>A major shift in Earth’s crustal generation processes at ~3.2 to 2.5 Ga has been inferred from mineralogical, geological, and geochemical records, particularly those recorded by fine-grained sediments and zircon crystals. The most common hypothesis to explain this shift is the onset of plate tectonic recycling following some form of hot stagnant lid geodynamics. However, all prior detailed geologic studies of our best-preserved Eoarchean terrane, the ~3.85 - 3.60 Ga Isua supracrustal belt of SW Greenland, interpret this site to record terrane collision within the context of plate tectonics. This represents a significant counterweight to the assumption underpinning the ~3 Ga tectonic-mode-change models, i.e., the idea that early Earth’s record is broadly representative. The Isua belt is divided into ~3.8 and ~3.7 Ga halves, and these have been interpreted as plate fragments which collided by ~3.6 Ga. Here, we examine the evidence used to support plate tectonic interpretations, focusing on 1) reanalysis of prior geochronological results and associated cross-cutting relationships which have previously been interpreted to record as many as eight tectonic events, and 2) new field observations leading to reinterpretation of basic structural relationships. Simpler interpretations of the geochronological and deformation data are viable: the belt may have experienced nearly homogeneous metamorphic conditions and strain during a single deformation event prior to intrusion of ~3.5 Ga mafic dikes. Curtain and sheath folds occur at multiple scales throughout the belt, with the entire belt potentially representing Earth’s largest a-type fold. We propose a new model: two cycles of volcanic burial and resultant melting and TTG intrusion produced first the ~3.8 Ga rocks and then the ~3.7 Ga rocks above, after which the whole belt was deformed and thinned in a shear zone, producing the multi-scale a-type folding patterns. The Eoarchean assembly of the Isua supracrustal belt is therefore most simply explained by vertical-stacking volcanic and instrusive processes followed by a single shearing event. In combination with well-preserved Paleoarchean terranes, these rocks record the waning downward advection of lithosphere inherent in volcanism-dominated heat-pipe tectonic models for early Earth. These interpretations are consistent with recent findings that early crust-mantle dynamics are remarkably similar across the solar system’s terrestrial bodies.</p>

INFLUENCE OF PLATE TECTONIC RE-ORGANISATIONS AND TECTONIC SUBSIDENCE ON THE MESOZOIC STRATIGRAPHY OF NORTHWESTERN AND SOUTHEASTERN AUSTRALIA: IMPLICATIONS FOR SEQUENCE STRATIGRAPHIC ANALYSIS

1995 ◽  
Vol 35 (1) ◽  
pp. 253
Author(s):  
M. I. Ross
Keyword(s):  
Three Dimensional ◽  
Tectonic Subsidence ◽  
Plate Tectonic ◽  
North West ◽  
Sequence Stratigraphic ◽  
Tectonic Model ◽  
Subsidence Rate ◽  
Tectonic Events ◽  
System Tracts ◽  
Lithospheric Stress

Determining and predicting the interplay of plate tectonic events, subsidence, flexure and depositional systems is important in frontier exploration, play concept development, and maturation modelling. A circum-Australian plate tectonic model is here tied to an internally consistent global plate tectonic model to determine the timing and orientation of changes in the lithospheric stress regime induced by plate tectonic changes. One-and three-dimensional geohistory results for the Otway Basin and North West Shelf/Exmouth Plateau are presented, based on an integrated sequence stratigraphic framework. These geohistory results compare the timing and types of changes in subsidence rate to the changes in lithospheric stress due to plate tectonic changes. Changes in tectonic subsidence rate appear to be discrete events related to plate tectonic changes; subsidence events bound major transgressive-regressive facies cycle packages ('supersequences') in a basin. The recognition of sequence system tracts and especially system tract boundaries within a 'supersequence' is enhanced or diminished by processes occurring only during certain phases of the supersequences. Recognition of lowstand systems tracts and sequence boundaries is improved due to erosion during the regressive phase of the supersequence. Conversely, during the transgressive phase of the supersequence, transgressive and highstand system tracts are emphasised and recognition of flooding surfaces improved. Good reservoir sands form during enhanced lowstands, while good source and sealing shales form during enhanced transgressions.In the southeastern Australian Otway Basin, every perturbation of the tectonic subsidence rate during the Late Cretaceous can be correlated directly to a local and/or global plate tectonic event, and each supersequence is bounded by tectonic events. In the North West Shelf/Exmouth Plateau region of Western Australia, the situation is complicated during the Berriasian by uncompensated f lexural load effects related to the rapid formation and filling of multiple Barrow Delta depocentres. Two supersequences correlate to tectonic events, while one supersequence is bounded by a f lexural subsidence event unrelated to regional or global plate tectonic events. Hence not all perturbations of the tectonic subsidence curve are related to tectonic events, and not all supersequences are bound by tectonic events. Without three-dimensional geohistory techniques, it is impossible to isolate the flexural load effects from the effects of plate tectonic events.

Origin of alkali basalts in Iceland: A plate tectonic model

1985 ◽  
Vol 90 (B12) ◽  
pp. 10027 ◽  
Author(s):  
Sigurdur Steinthorsson ◽  
Niels Oskarsson ◽  
Gudmundur E. Sigvaldason
Keyword(s):  
Plate Tectonic ◽  
Alkali Basalts ◽  
Tectonic Model

Geochronology and geochemistry of granite magmatism in Thailand in relation to a plate tectonic model

1979 ◽  
Vol 136 (5) ◽  
pp. 529-537 ◽  
Author(s):  
R. D. Beckinsale ◽  
S. Suensilpong ◽  
S. Nakapadungrat ◽  
J. N. Walsh
Keyword(s):  
Plate Tectonic ◽  
Tectonic Model ◽  
Granite Magmatism
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