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Taiwan (Lithology (Central Ranges ('Proto-Taiwan' - accreted…
Taiwan
Taiwan Situation
Sits at interface between 2 SZs opposing orientation
= unfeasible tectonics
∴
Must be a tear beneath Taiwan
i.e. mega-scale rupture cutting through lithosphere
to bring plates back into alignment
2 SZs
Eurasian plate subducts Phillipine Sea Plate (PSP)
Luzon Arc
Philippine Sea Plate subducts Eurasian Plate
Ryuku Arc
Subduction around Taiwan
Slab sediments dehydrate as subducts & heated
Dehydration melting of mantle
∴ arc magmatism on overlying mantle wedge
Phillipine Sea Plate
Moving NW @ 80 mm/yr
Taiwan Structure
Essentially Taiwan = pile of
accreted sediments & granite intrusions
Most of mountains = exhumed sediments
Orogenic Front
Delineated by shallow earthquakes
Compressional equakes = shallow (orogenesis)
Extensional equakes = deep
(in North Taiwan --> backarc ext)
Taiwan Seismicity
West Coast
less seismicity (away from orogenesis)
Central Ranges
'Dead Zone'
Where orogen = thickest in accretionary wedge to S
East Coast
Lotsa seismicity
Shallow equakes assoc w orogenesis
Taiwan Uplift
Fast mountain building
= confined to East Taiwan
(Expect S region will get involved in uplift as system migrates S with time)
Lithology
Ilan Plain
Associated with back-arc extension of Ryuku Arc
= Low topography on Nmost Taiwan
Coastal Ranges
(E)
Basinal material obducted & accreted onto Taiwan margin ~ 700 ka
Intercalated w some Luzon Arc material
Central Ranges
'Proto-Taiwan' - accreted fragment Chinese margin
Schist backbone
Much older (~170 Ma)
Smost Tip
(Henchung Pen)
Accretionary wedge
sediments accumulate as cover on downgoing slab = bulldozed off during collision
assoc with Eurasia subducting PSP
+
Carbonates accumulate
Western Foothills
< 70 Ma
Coastal Plain
(W)
Unconsolidated modern sediments
(Plio-Pleistocene)
Taiwan Tectonics
North: Active extension
Middle: Active collision
South: Unaffected by active tectonics 'pootling about'
Suture
Exists btwn Coastal Range & Central Range
≈ Area of low topography
Nobody knows exact location
covered by modern topog
little surface expression
Hueshan Range
= flower structure formed btwn W foothills & Central Range
∴ no high temps