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G฀EOLOGY฀OF฀HONG฀KONG฀AND฀THE฀CAPE฀D'AGUILAR฀MARIN E฀RESERV E฀ m w฀Th e฀geology฀of฀Hong฀Kong฀ In orde r t o understan d th e roc k formation s see n i n both th e Cap e d'Aguila r Marin e Reserv e an d thos e i n Hong Kon g a s a whole , i t i s necessar y t o conside r th e geological history of the region, in particular its setting in terms of plate tectonics . The surfac e o f th e eart h i s spli t int o a numbe r o f rigid plates which mov e around it s surface o n the mobil e mantle beneath . Radioactiv e deca y an d hea t fro m th e cooling cor e provid e th e hea t sourc e whic h set s u p th e convection cell s within the mantle, and i t is these whic h cause this motion. Plates consist most often o f both dens e oceanic crus t and les s dense continental rock s which ar e broadly graniti c i n composition . A s the y move , plate s interact i n either on e o f two main ways . At constructiv e plate margins , tw o plate s mov e i n opposit e directions . Magma well s u p int o th e ga p betwee n them , producin g new oceanic crust. At destructive plate margins, two plates move toward s on e another . I n thi s case , wher e ther e i s dense oceanic crust on the leadin g edge of one plate, thi s will subduct belo w the les s dense continental roc k of th e other plate . Whe n thi s happens , th e descendin g plat e melts as it heats up within the mantle, producing magm a which the n rise s t o th e surfac e t o for m volcanoes . I t i s along thes e subductio n zone s that earthquake s ar e ofte n generated, cause d by the friction betwee n th e two plates. When tw o continenta l block s collide , neithe r i s dens e enough t o b e subducte d an d th e tw o masse s effectivel y fuse. Hong Kon g i s locate d o n th e souther n edg e o f th e large Eurasian Plate . This situatio n place s i t clos e t o tw o destructive plat e margins : on e t o th e sout h wher e th e Indian/Australian Plat e i s pushin g northwar d int o th e Eurasian Plate, and to the east where the Philippine Plat e is ploughing westward s int o th e Eurasia n Plate . I t i s thi s latter interaction which has produced the chain of volcanic islands which mak e up the Philippines . It i s clear that Hon g Kong has long occupied suc h a dynamic positio n o n th e globe . Geological map s o f Asi a appear ver y complex . Muc h o f Chin a i s compose d o f relatively small 'slivers' of ill-matched geology which have been brought togethe r by plate movement. I t is clear tha t these ar e isolate d terrains , effectivel y 'mini-continents' , which hav e move d togethe r an d fuse d a s th e area s o f intervening ocea n floor hav e been subducted . Most of the rocks which make up Hong Kong's solid geology are the result of magmatic activity which took place in the region during the Mesozoic (the era of earth's history, when the dinosaurs reigned and which lasted from 250-6 5 Mya), althoug h ther e ar e som e olde r sediment s i n th e northwest and northeast (Strang e and Shaw 1986). During the Mesozoic , Hon g Kon g wa s subjecte d t o intens e an d prolonged igneou s activity. Such activity resulted from it s v Figure 2. A, the solid geology of the Cape d'Aguilar Marine Reserve. th e marine reserve. 1, Indian tree pipit {Anthus hodgsoni); 2, Chinese Inset B, a table of the relative ages of...

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