The maturity of an orogenic belt will vary

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(7)
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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 oseanic to arc-continent
collision Where the arcs contain elements of
Eurasian continetal crust rifted away from their
original position by back-arc extension (arrows)
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INCIPIENT CONTINENTAL COLLISION (example from the
Australian plate- Banda Arc)
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SUNDA - BANDA ARC TOPOGRAPHY OUTER NON-VOLCANIC
ARC-ISLANDS ARE BIGGER IN THE WEST
NIAS
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SUNDA - BANDA ARC TOPOGRAPHY OUTER NON-VOLCANIC
ARC-ISLANDS ARE BIGGER IN THE WEST- BEFORE THEY
ABRUBTLY INCREASE IN SIZE NEAR SUMBA. WHAT ABOUT
TIMOR? ITS RISING VERY FAST! LETS SEE WHAT MAY
BE THE REASON
EXTINCT VOLC
SUMBA
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SUNDA - BANDA ARC TOPOGRAPHY OUTER NON-VOLCANIC
ARC-ISLANDS ARE BIGGER IN THE WEST- BEFORE 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
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INCIPIENT CONTINENTAL COLLISION (example from the
Australian plate- Banda Arc)
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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

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Late Miocene RAPID SUBDUCTION OF OCEANIC PART OF
THE AUSTRALIAN LITHOSPHERE
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PRESENT
Notice that in this model, the Timor Trough is
not the plate boundary, But a fordeep on the
Australian margin. The polarity of subduction has
flipped and the next scenario is an Andean margin
along northern Australia!
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SCHEMATIC EVOLUTION TO ANDEAN MARGIN
AN ANDEAN MARGIN IS COMMONLY FLOORED BY AN
OPHIOLITE COMPLEX
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• --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.