Abstract
The Yanshanian Orogeny consists of Jurassic to Cretaceous compressional-extensional cycles related to the subduction of the Paleo-Pacific Ocean beneath East Asia. Numerous granitic plutons were emplaced across southeast China at distinct intervals over a period of ~100 million years that migrate from the interior to the coast. A key region to help constrain the secular evolution of granitic magmatism related to the Yanshanian Orogeny is the Peal River estuary as three distinct Mesozoic magmatic belts congregate. The islands of Taipa and Coloane, Macau Special Administrative Region, are located along the western bank of the Pearl River estuary and are composed of spessartine-bearing biotite leucogranite. In situ zircon geochronology yielded Late Jurassic weighted-mean 206Pb/238U ages of 160.0 ± 2.0 Ma and 161.5 ± 2.0 Ma that correlate to the late Early Yanshanian Orogeny. Inherited zircons of Middle Triassic to Middle Jurassic age were also identified. The rocks are peraluminous, ferroan, calc-alkalic to calcic and classify as post-collisional granite. Geochemical modeling indicates that the chemical variability of the rocks is related to hydrous fractional crystallization under reducing conditions (dFMQ -1) at ~7 km depth. The Sr-Nd isotopes (ISr = 0.71156 to 0.72477; eNd(t) = -7.9 to –8.6), zircon Hf isotopes (eHf(t) = -3.8 to -8.8), incompatible trace element ratios, and whole rock composition indicate that the parental magma was derived primarily from a sedimentary source. It is likely that the islands of Taipa and Coloane form a coherent plutonic complex that may be a member of larger batholith that extends across the Pearl River estuary to Hong Kong. The emplacement of the leucogranites is attributed to decompressional melting associated with a period of crustal relaxation or tensional plate stress that occurred during the transition from low angle subduction to high angle subduction of the Paleo-Pacific plate.
Highlights
We present in situ zircon U-Pb geochronology and Hf isotopes, mineral chemistry, whole rock geochemistry, and whole rock Sr-Nd isotopes on a collection of rocks from the Mesozoic granitic islands of Taipa and Coloane, Macau Special Administrative Region
Analysis of three crystals shows that the garnet is spessartine (Supplementary Table S1)
The spessartine-bearing biotite leucogranites from Taipa and Coloane were emplaced during the Late Jurassic (Oxfordian) period of the Yanshanian Orogeny
Summary
The Mesozoic Era was a critical time in the lithotectonic development of East and Southeast Asia (Zhou and Li, 2000; Wu, 2005; Metcalfe, 2006; Zhou et al, 2006; Li et al, 2013; Shellnutt et al, 2013; Wang et al, 2013; Xu et al, 2016; Dong et al, 2018; Rossignol et al, 2018). The Early Triassic Indosinian Orogeny marks the collision between the rifted terranes of Tethyan Gondwana (e.g., Indochina, Simao) and the southern SCB (Metcalfe, 2006; Wang et al, 2013; Liu et al, 2018; Rossignol et al, 2018); in the northern SCB, the Early to Middle Triassic Qinling-Dabie orogenic belt marks the initial stages of the collision between the SCB and the North China Block (NCB) (Wu and Zheng, 2013; Dong and Santosh, 2016); and, in the east, the Early Jurassic to Late Cretaceous Yanshanian Orogeny is related to compressional-extensional cycles caused by the westward subduction of the Paleo-Pacific Ocean (Wu, 2005; Zhou et al, 2006; Li and Li, 2007; Shu et al, 2009; Dong et al, 2018). The eastward migration of magmatism may be related to an increase in dip angle of the westward subducting Paleo-Pacific Ocean over time (Zhou and Li, 2000; Li and Li, 2007; Jiang et al, 2009; Li et al, 2012; Zhu et al, 2014; Zuo et al, 2017)
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