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The Geology of Hong Kong (Interactive On-line)
Mafic and intermediate dykes - mnd

Mafic and intermediate dykes - mnd

Stratigraphy: Mafic and intermediate intrusive rocks cut many plutonic and volcanic lithologies and are divided into two main groups: an older group with an age of approximately 146 million years before present, and a younger group with ages ranging from approximately 108 to 75 million years before present.

Distribution:The older group of dykes is mainly associated with the Lantau Dyke Swarm in the northern Lantau Island, Ma Wan and Tsing Yi. The younger group is widespread throughout eastern, central and western Hong Kong.

Lithology: The older group of dykes is dominantly high-K calc-alkaline basaltic andesites to dacites, whereas the younger group is shoshonitic in composition and includes a number of calc-alkaline lamprophyres.

Mafic dykes

(Mafic dykes, eastern Po Toi)