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 it is bordered by Guangdong to the north and the South China Sea to the east and south (geographic coordinates: 22°10′N 113°33′E).
The territory covers an area of around 30km2 and consists of the Macao Peninsula itself, linked through an isthmus to the Guangdong province, and the islands of Taipa and Coloane, which are now connected by landfill forming the CoTai Strip.
Macao Peninsula was originally an island, connected sporadically with mainland China at the north by a sandbar that gradually turned into a narrow isthmus. The successive land reclamation transformed the geography of Macao along the last centuries (see animated Figure 1). Currently, Taipa and Coloane islands are linked through an area designated by CoTai and together they form just one island. This island (Coloane – CoTai – Taipa) is connected, through three bridges, to Macao peninsula, at north, and via a tunnel to one small area in the Hengqin island (also called as Ilha de Dom João and Ilha da Montanha) at west, which is now under control of MSAR as enforced by a Macanese-Chinese agreement. In November 2017, the eastern part of Macao was connected to Hong Kong and Mainland China (Zhuhai) through the world’s longest sea bridge (HKZMB; 港珠澳大桥).
List of original islands of Macao:
Just on the Mesozoic Era (the Age of the Dinosaurs, which spans from about 252 Ma ago to about 66 Ma ago) the Southeastern China region (Cathasya block), where Macao is localized, was affected by granitic plutonism generated during the Indosinian (Triassic Period) and Yanshanian orogenies (Jurassic-Cretaceous Periods), overprinting all previous events in the South China Fold Belt (SCFB).
From a geological perspective, South China is a craton surrounded by the North China craton in the north, the Tibetan Plateau in the west, the Indochina terrain in the southwest and the Philippine Sea Plate in the east (see figure).
Southeast China is composed of two major tectonic crustal terranes, juxtaposed along a tectonically complex zone. These two terranes are (1) the Yangtze terrane and (2) the Cathaysia (or Huanan) terrane, where Macao is positioned. The latter is composed of the amalgamation of NE- to NNE-trending narrow crustal slices characterised by isotope signatures and TDM (depleted-mantle model ages), ranging in age from Paleoproterozoic (dominant) to Mesoproterozoic (e.g. Fletcher et al., 2004; Li et al., 2007; Liu et al., 2009; Sewell et al., 2000).
(a) Principal tectonic units of SE China (from Pirajno and Bagas, 2002). Several northeast-trending fault zones traverse the South China Fold Belt (SCFB), including the Jiangshan–Shaoxing and the Yuao–Macao fault zones, both of which constitute major crustal-scale structures. The Jiangshan–Shaoxing Fault Zone marks, as suggested by Shen (1999) as a continent–continent subduction zone and Sewell (1992) refers to the Yuao–Macao fault zone as a deep crustal boundary; (b). Principal geological units from China; (c) Tectonic map of Asia (Kusky et al., 2007)
As consequence of these events in South China, large volumes of Mesozoic granitic rocks occupy an estimated area of circa 135000 km2 (Zhou et al., 2006) and thus this is an ideal region to study granitic rocks and their petrogenetic processes and to constrain the evolution of crustal sectors. The major plutonic events from Southeast China seem to have about 160Ma and are geochemically described as I-type (and A-Type).
Although various tectonic models have been proposed to explain this granitic plutonism (e.g., Gilder et al., 1991; Zhou and Li, 2000; Li and Li, 2007; Sewell et al., 1992; Zhou and Li, 2000), there is no consensus on its causal mechanism.
Faulting: It seems to exist two main faulting systems: ENE-WSW and NW-SW and two secondary systems: NE-SW and NS to NNE-SSW. The NW-SE system is consistent with the orientation of the structures of southern China, namely the fault zone of Shenzhen-Wuhua.
Petrology, Geochemistry and Geochronology of Magmatic Rocks of Macau
Macao is composed by granites (dominant lithology), which are intruded by a variety of dykes and veins ranging from acid to intermediate and mafic compositions (aplites, dacites and basalts) and quartz veins.Different granitic facies occur in the three main areas of Macao – Macao Peninsula, Taipa and Coloane. Despite our observations of variable petrographic and geochemical characteristics (Dias, 2015, Quelhas, 2016, 2107 and 2018), two dominant groups of granitoids were defined: porphyritic biotite granites (LaN/YbN = 2.05 – 11.83 and zircon saturation temperatures TZr = 727 – 835ºC ) and non-porphyritic garnet-bearing biotite granites (LaN/YbN = 0.12-1.2 and TZr = 697 – 735ºC). A smaller group is composed by fine-grained granites with or without biotite. In some regions, centimetric to metric mafic enclaves (monzogranitic and tonalitic compositions) were also observed into the granite outcrops (Quelhas et al, 2016, 2017 and 2018).
Macau granites are in general calc-alkaline metaluminous to weakly peraluminous I-type granites with different degrees of fractionation, ranging from quartz monzodiorite, through monzogranite, syenogranite to alkali feldspar granite. These rocks were the result of a complex magmatic evolution involving fractional crystallization and late-stage fluid-melt interactions. Isotopic data (Sr, Nd, Pb and Hf) indicates that these granites were likely derived from Paleoproterozoic to Mesoproterozoic crustal protolith(s) with minor addition of mantle-derived magmas (Dias et al, 2016; Quelhas et al, 2017 and 208).
In Macao, Mesozoic granitic magmatism has occurred during Mesozoic ages between 162-164 million years ago (Mesozoic Era; Middle Jurassic period), similarly to neighbouring territories. However, high precision TIMS U-Pb zircon dating (Quelhas, in preparation) suggest that some areas of Macau and Taipa are younger and have crystallized around five million years later (Mesozoic Era; Upper Jurassic period). Finally, dykes represent a distinctly younger magmatic event which has cut the previous granites around 153 to 120 million years ago (Mesozoic Era; from the Upper Jurassic to the end of the lower Jurassic period).
These magmatic pulses record a temporal evolution of magma compositions indicative of a transition from a subduction-related to an extension-related tectonic regime consistent with the tectonic-magmatic evolution of southwestern China.
Note: A representative collection of rock samples of Macau and the geological map can be found in the USJ Library (@ Ilha Verde Campus; address: https://www.usj.edu.mo/en/libraries/).
For further information about the geology of Macau, please contact the Institute of Science and Environment (http://www.ise.usj.edu.mo/contacts/). PI: Professor Ágata Dias
In the new geological map of Macau, all data was updated and new data was obtained during field trips and petrographic and geochemical studies performed along the MagIC project. The work was carried out using geographic information software. In this new version, information is provided in English, Chinese and Portuguese. This map is freely available to all through this website, however, it’s source should be acknowledged (@Geology of Macau, ISE website, USJ, Macau) and reproduction for any commercial purposes is forbidden. Currently, only a low-quality map can be downloaded, however, a high-resolution version will be available after its final publication.
Previous Geological Maps of Macau
Before the new map, the complete official document reporting the geology of Macao was published by Ribeiro et al. (1992). The document consists of the Macao Geological Map (“Carta Geológica de Macau”) at a scale of 1:5000 and an accompanying memoir (Ribeiro et al., 1992), edited by the Serviços Geológicos de Portugal.
The first published works describing the Geology of the Macao territory and its main lithologies date from the mid of the XX century (Carrington da Costa, 1944; Carrington da Costa and Lemos, 1964; Lemos, 1963) which also produced the first draft of a geological map of Macao. Later, Marques (1988) also contributed to the knowledge of Macao’s geology with a study strongly focused on geotechnical analyses. Here, relevant stratigraphic sections were presented through the study of cores collected in the territory.
The new Geological map of Macao is now available in hard copy and in GIS format. It is the first one since 1992. Macao territory had been mapped more extensively and in greater detail during the MagIC project. – for example, the new map present more petrografic informations about the different type of magmatic rocks outcropping in the territory and includes the age of the different lithologies. These work had also been fundamental for the advances in scientific knowledge on the geology Macau and SE China. Please properly cite this map if using it in derivative work: Dias, A; Quelhas, P, Mata, J; Borges, R and Lou, V. (2019) Geologic Map of Macao, MagIC project .Institute of Science and Environment, University of Saint Joseph, Macao.
note: the map and a representative sample collection is available for consultation in the USJ Library
This work was carried out as part of “MagIC” – Petrology and Geochemistry of Igneous Rocks from Macao: Implications for the Crustal Evolution of Southern China / 项目: 澳门火成岩之岩石学与地球化学—对华南地壳演化的影响), Reference no. 043/2014/A1, financed by Science and Technology Development Fund from Macau (FDCT – Fundo para o Desenvolvimento das Ciências e da Tecnologia).
Team members: Agata Dias (Principal Investigator), João Mata (scientific member), Pedro Quelhas (doctoral student) and Varon Lou and Ricardo Borges (research assistants)