Diverse protolith ages for the Mindoro and Romblon Metamorphics (Philippines): Evidence from single zircon U–Pb dating

Abstract

Within the north-eastern part of the Palawan Continental Terrane, which forms the south-western part of the Philippine archipelago, several metamorphic complexes are exposed that are considered to be rifted parts of the Asian margin in South-East China. The protolith age(s) and correlations of these complexes are contentious. The largest metamorphic complex of the Palawan Continental Terrane comprises the Mindoro Metamorphics. The north-eastern part of this metamorphic complex has recently been found to be composed of protoliths of Late Carboniferous to Late Permian protolith age. However, meta-sediments exposed at the westernmost tip and close to the southern boundary of the exposure of the Mindoro Metamorphics contain detrital zircons and with U-Pb ages, determined by LA-ICP-MS, in the range 22-56 Ma. In addition, zircons as young as 112 Ma were found in a sample of the Romblon Metamorphics in Tablas. As the youngest detrital zircons provide an upper age limit for the time of deposition in metasediments, these results suggest that the Mindoro and Romblon Metamorphics comprise protoliths of variable age: Late Carboniferous to Late Permian in NE Mindoro; Eocene or later in NW Mindoro; Miocene at the southern margin of the Mindoro metamorphics; and Cretaceous or later on Tablas. The presence of non-metamorphic sediments of Late Eocene to Early Oligocene age in Mindoro (Lasala Formation), which are older than the youngest metasediments, suggests that metamorphism of the young meta-sediments of Mindoro is the result of the collision of the Palawan Continental terrane with the Philippine Mobile Belt in Late Miocene. Similarities of the age spectra of zircons from the Eocene to Miocene metamorphics with the Eocene to Early Miocene Lasala Formation suggest that the protoliths of the young metamorphics may be equivalents of the Lasala Formation or were recycled from the Lasala Formation.

Cretaceous–Palaeogene sedimentary evolution of the South China Sea region: A preliminary synthesis

“…We favour the palaeogeographic scenario that the Palawan Continental Terrane was once conjugated to the northeastern South China Sea region (Hall, ; Taylor & Hayes, ) rather than the southern Pearl River Mouth Basin (Sibuet et al, ), based on the evidence that the zircon age signatures of the Cretaceous–Eocene strata from these two areas are largely comparable (Shao, Cao, et al, ) and that the Eocene Palawan Continental Terrane and northeastern South China Sea region were dominated by a marine environment, contrasting to the continental facies in the southern Pearl River Mouth Basin (Knittel et al, ; Q. Li, Wu, Zhang, Shu, & Shao, ; Shao et al, ). Accordingly, prior to the oceanic spreading, the Reed Bank adjacent to the Palawan Continental Terrane was more likely located near to the Dongsha Uplift than the Macclesfield Bank‐Xisha Islands (Paracel Islands; Barckhausen et al, ; Wei et al, ) because of the already developed hemipelagic environment in the Eocene Reed Bank (Yao et al, ) and the comparable patterns of the lower structural layers (i.e., Mesozoic sequences) beneath both Dongsha Uplift and Reed Bank (Schlüter et al, ; Y. Wang et al, ).…”

“…We favour the palaeogeographic scenario that the Palawan Continental Terrane was once conjugated to the northeastern South China Sea region (Hall, 2002;Taylor & Hayes, 1983) rather than the southern Pearl River Mouth Basin (Sibuet et al, 2016), based on the evidence that the zircon age signatures of the Cretaceous-Eocene strata from these two areas are largely comparable and that the Eocene Palawan Continental Terrane and northeastern South China Sea region were dominated by a marine environment, contrasting to the continental facies in the southern Pearl River Mouth Basin (Knittel et al, 2017;Q. Li, Wu, Zhang, Shu, & Shao, 2016;Shao et al, 2016).…”

“…More specifically, the depressions in the northern Pearl River Mouth Basin were characterized by the massive fluvial facies, because of the birth of small-scale Palaeo-Pearl River confirmed by seismic data and detrital provenance analysis Pang et al, 2009;, whereas the southern part of the Pearl River Mouth Basin and farther south to the continental-oceanic boundary mainly deposited the deltaic-lacustrine-littoral-neritic facies, where sediments were supplied from multiple provenance areas and potential influences from local uplifts are readily observable (C. Liu, Clift, et al, 2017;Shao et al, 2016; In the Palawan Continental Terrane, the deposition of turbiditic Panas Formation continued into the Late Eocene with their metamorphic equivalents of Pandian Formation forming during the Late Eocene to Early Oligocene. Meanwhile, the Late Eocene to Early Oligocene deep marine sequence, Lasala Formation, was developed in Mindoro, and noteworthily, its composition and provenance signatures are comparable to those of the Panas Formation (Concepcion et al, 2012;Knittel et al, 2017). The sedimentary facies of the Late Eocene to Early Oligocene Reed Bank are not significantly different from those of the Early-Middle Eocene age, only with an expansion of littoral floodplain and deltaic facies in the northwest (Yao et al, 2012).…”

“…In the Palawan Continental Terrane, the deposition of turbiditic Panas Formation continued into the Late Eocene with their metamorphic equivalents of Pandian Formation forming during the Late Eocene to Early Oligocene. Meanwhile, the Late Eocene to Early Oligocene deep marine sequence, Lasala Formation, was developed in Mindoro, and noteworthily, its composition and provenance signatures are comparable to those of the Panas Formation (Concepcion et al, ; Knittel et al, ). The sedimentary facies of the Late Eocene to Early Oligocene Reed Bank are not significantly different from those of the Early–Middle Eocene age, only with an expansion of littoral floodplain and deltaic facies in the northwest (Yao et al, ).…”

Hf isotopes from Palawan Continental Terrane, Philippines-clues to the evolution of sediment sources

“…Dating of detrital zircons extracted from sediments in Palawan, Tablas, Mindoro, and Panay has further established the link between the sedimentary rocks exposed in the PCT and potential sediment sources in SE China (Walia et al 2012(Walia et al , 2013Suggate et al 2014;Knittel et al 2017) as many zircons have Precambrian ages. While rocks of Precambrian age form the basement of SE China, rocks of Precambrian age are not known in the Philippine archipelago.…”