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Description:
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Mesozoic tectonic inversion in the Neuquen Basin of west -central Argentina
produced two main fault systems : (1 ) deep faults that affected basement and syn -rift
strata where preexisting faults were selectively reactivated during inversion based on
their length and (2 ) shallow faults that affected post -rift and syn -inversion strata . Normal
faults formed at high angle to the reactivated half -graben bounding fault as a result of
hangingwall expansion and internal deformation as it accommodated to the shape of the
curved footwall during oblique inversion . Contraction during inversion was initially
accommodated by folding and internal deformation of syn -rift sedimentary wedges ,
followed by displacement along half -graben bounding faults . We suspect that late during
inversion the weight of the overburden inhibited additional fault displacement and
folding became the shortening -accommodating mechanism .
A Middle Jurassic inversion event produced synchronous uplift of inversion
structures across the central Neuquen Basin . Later inversion events (during Late
Jurassic , Early Cretaceous , and Late Cretaceous time ) produced an "inversion front" that advanced north of the Huincul Arch . Synchroneity of fault reactivation during the
Callovian inversion event may be related to efficient stress transmission north of the
Huincul Arch , probably due to easy reactivation of low -dip listric fault segments . This
required little strain accumulation along "proximal" inversion structures before
shortening was transferred to more distal structures . Later inversion events found harderto -
reactivate fault segments , resulting in proximal structures undergoing significant
inversion before transferring shortening .
The time between the end of rifting and the different inversion events may have
affected inversion . Lithosphere was probably thermally weakened at the onset of the
initial Callovian inversion phase , allowing stress transmission over a large distance from
the Huincul Arch and causing synchronous inversion across the basin . Later inversion
affected a colder and more viscous lithosphere . Significant strain needed to accumulate
along proximal inversion structures before shortening was transferred to more distal
parts of the basin .
Timing of inversion events along the central Neuquen Basin suggest a megaregional
control by right -lateral displacement motion along the Gastre Fault Zone , an
intracontinental megashear zone thought to have been active prior to and during the
opening of the South Atlantic Ocean . |