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) (7)

INCIPIENT CONTINENTAL COLLISION (example from the Australian plate- Banda Arc) Volcanic islands Non-volcanic islands

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 WEST- BEFORE THEY ABRUBTLY INCREASE IN SIZE NEAR SUMBA. WHAT ABOUT TIMOR? ITS RISING VERY FAST! LETS SEE WHAT MAY BE THE REASON SUMBA EXTINCT VOLC

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

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 INCIPIENT CONTINENTAL COLLISION (example from the Australian plate- Banda Arc)

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 fordeep 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 --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.