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The Wellington Region of New Zealand has a foundation of Torlesse Greywacke rocks, that make up the Tararua and Rimutaka Ranges, that go from Wellington in the south to the Manawatu Gorge, where they are renamed as the Ruahine Ranges, and continue further north-northeast, towards East Cape. To the west of the Tararua Ranges are the Manawatu coastal plains. To the east of the Ruahine Ranges is the Wairarapa-Masterton Basin, then the Eastern Uplands that border the eastern coast of the North Island from Cape Palliser to Napier. To the east of the North Island is the Hikurangi Trough, a collision zone between the Pacific Plate and the Australian Plate. The Pacific Plate is being subducted under the Australian Plate, compressing the Wellington Region, and causing the North Island Fault System, and a series of SSW-NNE trending basins and ranges, including the Tararua and Rimutaka Ranges, and the Wairarapa-Masterton Basin. Successively newer rocks have been accreted to the east coast. The Wellington Region is prone to major earthquakes, the biggest in historical times being the magnitude 8.2 1855 Wairarapa earthquake. ==Basement rocks== All basement rocks beneath the Wellington Region belong to the Torlesse Composite Terrane. They are largely composed of Greywacke (hardened sandstone and mudstone), but also contain Chert, and Pillow lavas. In the Wellington Region, the Torlesse Composite Terrane is composed of two subterranes, the Rakaia Terrane (late Triassic to early Jurassic, 230-180 Ma), to the west of the Ruahine Ranges, and the Pahau Terrane (late Jurassic to early Cretaceous, 180-100 Ma), to the east. Major faults such as the Wellington Fault and Wairarapa Fault lie close to the boundary between the terranes. At the boundary between these two terranes, is the Esk Head Belt, a 20 km wide melange of rocks, broken and deformed by earthquakes along the fault lines near the boundary. Further to the east of the Wairarapa-Masterton Basin, are successively younger Cretaceous (140-65 Ma) sandstones and mudstones (sometimes called the Waioeka Terrane), that can be regarded as part of the Torlesse Composite Terrane. There seems to be some disagreement on where to place the boundary between basement rocks and overlying rocks, and the decision seems to be based on the degree of induration. In the east, even younger and softer sandstones and mudstones occur. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Geology of the Wellington Region」の詳細全文を読む スポンサード リンク
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