Download Andean margin

(8)
2
1
The maturity of an orogenic belt will vary
along strike. This is well illustrated by the
collision of Gondwana terrains with Eurasia.
(1) Makran - Andean margin
(2) Himalaya - mature continental collision
(3) N-Australian margin - transition from
intra oceanic to arc-continent collision
Where the arcs contain elements of
Eurasian continental crust rifted away from
their original position by back-arc extension
(arrows) and subduction roll-back
2
Volcanic islands
Non-volcanic
islands
INCIPIENT CONTINENTAL COLLISION
(example from the Australian plate- Banda Arc)
SUNDA - BANDA ARC TOPOGRAPHY
OUTER NON-VOLCANIC ARC-ISLANDS ARE BIGGER IN THE WEST
NIAS
SUNDA - BANDA ARC TOPOGRAPHY
OUTER NON-VOLCANIC ARC-ISLANDS ARE BIGGER IN THE WESTBEFORE THEY ABRUBTLY INCREASE IN SIZE NEAR SUMBA. WHAT ABOUT
TIMOR? ITS RISING VERY FAST! LETS SEE WHAT MAY BE THE REASON
EXTINCT VOLC
SUMBA
SUNDA - BANDA ARC TOPOGRAPHY
OUTER NON-VOLCANIC ARC-ISLANDS ARE BIGGER IN THE WESTBEFORE THEY ABRUBTLY INCREASE IN SIZE NEAR SUMBA. WHAT ABOUT
TIMOR? ITS RISING VERY FAST! LETS SEE WHAT MAY BE THE REASON
EXTINCT VOLC
PLATE BOUNDARY
A NEW PLATE BOUNDARY?
SUMBA
INCIPIENT CONTINENTAL COLLISION
(example from the Australian plate- Banda Arc)
INCIPIENT CONTINENTAL COLLISION
(example from the Australian plate- Banda Arc)
NOTICE:
•THE WADATI-BENIOFF ZONE EARTHQUAKE ZONATION
•THE HIGHLY IRREGULAR SHAPE OF THE AUSTRALIAN
MARGIN (AUSTRALIAN PLATE DOTTED RED)
• BANDA BACK-ARC SEA IAND THE ISLAND ARC ISLANDS
SEPARATE SERAM AUSTRALIA ROM THE MAIN MARGIN
Late Miocene: RAPID SUBDUCTION OF OCEANIC PART
OF THE AUSTRALIAN LITHOSPHERE
PRESENT
Notice that in this model, the Timor
Trough is not the plate boundary,
But a foredeep on the Australian
margin. The polarity of subduction
has flipped and the next scenario is
an Andean margin along northern
Australia!
SCHEMATIC EVOLUTION TO ANDEAN MARGIN
AN ANDEAN MARGIN IS COMMONLY FLOORED BY AN OPHIOLITE COMPLEX
--some ANDEAN MARGIN CHARACTERISTICS:
• Low-angle subduction zones, great distance from trench to active arc.
• Magmatic events produce large composite batholiths, with superunits
and units which individually show mafic to acid (primitive to mature)
compositional trends.
• Very large volumes of magma are emplaced into the crust, and can in
some cases (like the type area) produce crustal thicknesses comparable
to continental collision zones.
• The plutonics are dominated by tonalitic to granodioritic bodies, which
commonly are emplaced as ”permitted” intrusions, i.e. by stoping to
cauldron subsidence mechanisms.
• The volcanoes are dominated by build-up of large strato-volcanoes with
andesitic to rhyolitic compositions.
• Andean margins may be long-lived depending on the width of the ocean
which is subducting.