Projects / Mag.I.C. / Geology of Macau

Scientific overview · last update Mar 2021

Geology of Macau

Geographic evolution, tectonics, seismicity and Mesozoic magmatism of the Macao Special Administrative Region

Location 22°10′N 113°33′E · Pearl River Delta
Area ~30 km²
Setting Cathaysia Block · SE China
Related project Mag.I.C. (FDCT 043/2014/A1)

Setting

Macao, a Special Administrative Region (MSAR) of the People’s Republic of China since 1999, lies on the western side of the Pearl River Delta and is bordered by Guangdong to the north and the South China Sea to the east and south. The territory covers about 30 km² and consists of the Macao Peninsula, linked by an isthmus to Guangdong, and the islands of Taipa and Coloane, now connected by landfill forming the CoTai Strip.

Geographic evolution of Macao

Animated topographic and administrative map of Macao from 1555 to 2011
Figure 1 — Topographic and administrative map of Macao since 1555 until 2011 (Bourrichon 2010).

Macao Peninsula was originally an island, connected sporadically with mainland China at the north by a sandbar that gradually turned into a narrow isthmus. Successive land reclamation transformed the geography of Macao over the last centuries. Taipa and Coloane are now linked through CoTai and form one island, connected by three bridges to the Macao peninsula and via a tunnel to a small area of Hengqin Island (Ilha da Montanha / Ilha de Dom João) under MSAR administration. In November 2017, eastern Macao was connected to Hong Kong and Zhuhai through the Hong Kong–Zhuhai–Macao Bridge (HKZMB).

Original islands of Macao

Tectonic evolution

Before the Mesozoic (~251 Ma), the territory of Macao was submerged and the terrains of South China were drifting from the southern to the northern hemisphere. Only in the Mesozoic (≈252–66 Ma) was southeastern China affected by granitic plutonism of the Indosinian (Triassic) and Yanshanian (Jurassic–Cretaceous) orogenies, overprinting earlier events in the South China Fold Belt (SCFB; Quelhas et al., 2021a).

South China is a craton bordered by the North China Block, the Tibetan Plateau, Indochina and the Philippine Sea Plate. It comprises two major terranes juxtaposed along the Jiangshan–Shaoxing Fault Zone: the Yangtze Block and the Cathaysia Block, where Macao is located. Cathaysia is made of NE- to NNE-trending crustal slices with depleted-mantle model ages from Paleoproterozoic to Mesoproterozoic.

Principal tectonic units of SE China and Cathaysia Block
Figure 2 — Principal tectonic units of SE China (after Pirajno & Bagas, 2002; Kusky et al., 2007).

Seismic activity

Macao is relatively distant from major plate boundaries (Eurasia–Philippines, Eurasia–Australia) and is therefore intraplate, which explains why seismic activity is less strong and frequent than in Taiwan or Japan. Most seismicity relates to the Southeast Coastal Seismic Belt of China, linked to relative motion between the Sunda and Eurasia plates and absorbed by coastal faults.

Macao lies within the NE-trending Lianhuashan Fault Zone, between the Shenzhen Fault (north) and the Haifeng Fault (south). Small-magnitude earthquakes are frequent along the SCSB; Guangdong records on average more than 10 events of M>2 per month. Historic moderate–strong events felt in or near Macao include Honghai Bay (M 6.0, 1991), Yangjiang (M 6.4, 1969), Heyuan (M 6.1, 1962), Nanao (M 7.3, 1918), Mo Dao Men adjacent to Macao (M 5.5, 1905) and the Dangan Islands (M 5.8, 1874).

Macao is a zone of low to moderate seismic risk. Distant interplate events (e.g. Taiwan Strait, M 5.7 in 2018 and M 7.3 in 1994) may also be felt and present an additional tsunamigenic hazard.

Petrology, geochemistry and geochronology

Macao (~30 km²) is composed of granitic intrusions of the Southeast China Magmatic Belt (SCMB) in the SE Cathaysia Block. This belt hosts large volumes of Mesozoic magmatic rocks (over 90% granitic and equivalent volcanic rocks with minor basalts), covering nearly 200 000 km² in SE China.

Distribution of Mesozoic granitic and volcanic rocks on the Cathaysia Block
Figure 7 — Mesozoic granitic and volcanic rocks on the Cathaysia Block (Quelhas et al., 2020).

U–Pb zircon geochronology shows two main intrusive phases: Macao Group I (MGI) between 164.5 ± 0.6 and 162.9 ± 0.7 Ma, and Macao Group II (MGII) between 156.6 ± 0.2 and 155.5 ± 0.8 Ma. Younger dacite dykes were dated at 150.6 ± 0.6 Ma and <120 Ma. The suite was incrementally assembled over ~9 Ma, with a ~6 Ma gap between pulses.

Distribution of two granite groups in Macao
Figure 8 — Distribution of MGI and MGII granites and geochronology sample sites.
Timing of magmatic pulses in Macao and Hong Kong
Figure 9 — Timing of magmatic pulses in Macao and Hong Kong.
Sm/La vs Lu/Ho diagram for Macao granites
Figure 10 — Sm/La vs. Lu/Ho diagram for Macao granites (Quelhas et al., 2020).

Inheritance patterns indicate antecrysts (165–180 Ma) and inherited zircons from Precambrian to Phanerozoic sources; the oldest ages suggest Proterozoic and possibly late Archaean crustal sources (~2.4 Ga and possibly 2.9 Ga).

Zircon images from Macao magmatic rocks
Figure 11a — Zircon images.
Histogram of inherited zircon ages
Figure 11b — Inherited zircon age histogram.

Macao granites are mainly high-K calc-alkaline metaluminous to weakly peraluminous I-type granites with variable fractionation. Isotope and major-element compositions and model ages indicate partial melting of infracrustal medium- to high-K basaltic Proterozoic protoliths, mixed to some degree with mantle-derived magmas.

Tectono-magmatic evolution

Association of Jurassic I-type granites with basaltic/gabbroic rocks, syenites and A-type granites with intraplate chemical features indicates an extensional regime rather than an active margin. Adiabatic decompression melting of the asthenosphere produced mafic magmas that underplated the Moho and triggered lower-crustal melting. Jurassic Macao granites are interpreted as products of intraplate extension related to break-off and foundering of a previously flat Paleo-Pacific slab beneath Eurasia.

Two-stage tectono-magmatic evolution of Macao part 1
Figure 12a–b — Jurassic magmatism and flat-slab foundering.
Two-stage tectono-magmatic evolution of Macao part 2
Figure 12c — Return to normal subduction (150–110 Ma).

Younger dacite dykes record Late Yanshanian (Cretaceous) magmatism with more arc-like signatures, marking a change from intraplate granitic magmatism to re-established normal subduction-related processes in this part of SE China.

Geological maps of Macao

Geological map of Macao with magmatic ages from MagIC
Figure 13 — Geological map of Macao with lithologies and ages (Quelhas et al., Journal of Maps, 2021; MagIC project).

The new trilingual (English, Chinese, Portuguese) geological map was produced during the Mag.I.C. project (FDCT 043/2014/A1) and published in the Journal of Maps (Quelhas et al., 2021). Reproduction for commercial purposes is prohibited; please acknowledge the source.

Earlier geological sketch map of Macao
Earlier geological sketch of Macao (historical mapping tradition).

Before this map, the main official document was Ribeiro et al. (1992): Carta Geológica de Macau at 1:5000 and memoir (Serviços Geológicos de Portugal / LNEG). Earlier contributions include Carrington da Costa (1944), Lemos (1963), Carrington da Costa & Lemos (1964) and Marques (1988).

Key publications

See also the full MagIC outputs on the Mag.I.C. project page. Mag.I.C.

Content adapted from the MagIC research programme and the former ISE/USJ “Geology of Macau” overview (updated Mar 2021). Contributors included Ágata A. Dias, João Mata, Pedro Quelhas, Varon Lou, Ricardo Borges, Pedro Costa and Luísa Ribeiro, with additional input from Wenhong Qiu and Yafei Wu.

Contact: Ágata Alveirinho Dias

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