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The Geology of Hong Kong (Interactive On-line)
Luk Keng Quartz Monzonite - Kcl

The Luk Keng Quartz Monzonite (Table 6.4 ) crops out in two places on the southeastern margin of the Lantau Caldera. A major outcrop occurs at the type locality of Luk Keng and smaller outcrops are found at Fan Lau and Cha Kwo Chau. The monzonite is typically fine grained and dominantly contains subhedral megacrysts of orthoclase (7–10 mm) with subordinate, concentrically-zoned plagioclase phenocrysts (3–5 mm). The matrix mostly comprises plagioclase, quartz, and biotite with trace amounts of zoned allanite, zircon, titanite, apatite and Fe-oxide.

The contact with older intrusive units is not exposed although at Fan Lau, a double enclave relationship confirms that the monzonite post-dates the Lantau Granite (Plate 6.19).

An absolute age for the Luk Keng Quartz Monzonite has yet to be determined. However, field relationships at Fan Lau indicate that it is older than the Tong Fuk Quartz Monzonite (see below), while petrography and geochemistry suggest that it belongs to the same magmatic phase as the Mount Davis Formation (Chapter 5).