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The Geology of Hong Kong (Interactive On-line)
Chi Ma Wan Granite - Kcc

The Chi Ma Wan Granite (Table 6.4) forms a subcircular, biotite monzogranite pluton centred on the Chi Ma Wan Peninsula on the eastern side of Lantau Island. The granite extends south and east to the islands of Shek Kwu Chau and Cheung Chau respectively (Figure 6.5). The Chi Ma Wan Granite intrudes the Lantau Granite and East Lantau Rhyodacite dykes at Chi Ma Wan. However, on Cheung Chau, the granitoid is cut by rhyolite dykes suggesting a coeval phase of dyke emplacement.

The Chi Ma Wan Granite is dominantly equigranular and medium grained (Plate 6.17). In thin section, mesoperthite is the dominant alkali feldspar although sparse microcline is also present. Subhedral plagioclase is strongly concentrically zoned. Brown biotite is the dominant mafic mineral. Accessory minerals include zircon, titanite, allanite, apatite and Fe-oxide.

U–Pb single zircon geochronology has established an age of 143.7 ± 0.3 Ma which is considered to be an upper limit on the age of crystallization of the rock (Davis et al., 1997).