scholarly journals Petrogenesis of Dacites in a Triassic Volcanic Arc in the South China Sea: Constraints From Whole Rock and Mineral Geochemistry

2022 ◽  
Vol 9 ◽  
Author(s):  
Wu Wei ◽  
Chuan-Zhou Liu ◽  
Ross N. Mitchell ◽  
Wen Yan
Keyword(s):  
Rare Earth ◽  
South China Sea ◽  
Rare Earth Elements ◽  
Partial Melting ◽  
South China ◽  
Volcanic Rocks ◽  
The South China Sea ◽  
South China Block ◽  
The South ◽  
T Values

Triassic volcanic rocks, including basalts and dacites, were drilled from Meiji Atoll in the South China Sea (SCS), which represents a rifted slice from the active continental margin along the Cathaysia Block. In this study, we present apatite and whole rock geochemistry of Meiji dacites to decipher their petrogenesis. Apatite geochronology yielded U-Pb ages of 204–221 Ma, which are identical to zircon U-Pb ages within uncertainty and thus corroborate the formation of the Meiji volcanic rocks during the Late Triassic. Whole rock major elements suggest that Meiji dacites mainly belong to the high-K calc-alkaline series. They display enriched patterns in light rare earth elements (LREE) and flat patterns in heavy rare earth elements (HREE). They show enrichment in large-ion lithophile elements (LILE) and negative anomalies in Eu, Sr, P, Nb, Ta, and Ti. The dacites have initial 87Sr/86Sr ratios of 0.7094–0.7113, εNd(t) values of -5.9–-5.4 and εHf(t) values of -2.9–-1.7, whereas the apatite has relatively higher initial 87Sr/86Sr ratios (0.71289–0.71968) and similar εNd(t) (-8.13–-4.56) values. The dacites have homogeneous Pb isotopes, with initial 206Pb/204Pb of 18.73–18.87, 207Pb/204Pb of 15.75–15.80, and 208Pb/204Pb of 38.97–39.17. Modeling results suggest that Meiji dacites can be generated by <40% partial melting of amphibolites containing ∼10% garnet. Therefore, we propose that the Meiji dacites were produced by partial melting of the lower continental crust beneath the South China block, triggered by the underplating of mafic magmas as a response to Paleo-Pacific (Panthalassa) subduction during the Triassic. Meiji Atoll, together with other microblocks in the SCS, were rifted from the South China block and drifted southward due to continental extension and the opening of the SCS.

Rare Earth Elements Composition and Constraint on the Genesis of the Polymetallic Crusts and Nodules in the South China Sea

2017 ◽  
Vol 91 (5) ◽  
pp. 1751-1766 ◽  
Author(s):  
Yao GUAN ◽  
Xiaoming SUN ◽  
Guiyong SHI ◽  
Xiaodong JIANG ◽  
Hongfeng LU
Keyword(s):  
Rare Earth ◽  
South China Sea ◽  
Rare Earth Elements ◽  
South China ◽  
The South China Sea ◽  
The South ◽  
China Sea

scholarly journals Mesozoic Northward Subduction Along the SE Asian Continental Margin Inferred from Magmatic Records in the South China Sea

Minerals ◽  
2019 ◽  
Vol 9 (10) ◽  
pp. 598 ◽  
Author(s):  
Guanqiang Cai ◽  
Zhifeng Wan ◽  
Yongjian Yao ◽  
Lifeng Zhong ◽  
Hao Zheng ◽  
...  
Keyword(s):  
South China Sea ◽  
Continental Margin ◽  
South China ◽  
Oceanic Lithosphere ◽  
The South China Sea ◽  
The South ◽  
Late Mesozoic ◽  
China Sea ◽  
Depleted Mantle ◽  
T Values

During the Mesozoic, Southeast (SE) Asia (including South China and the South China Sea (SCS)) was located in a transitional area between the Tethyan and Pacific geotectonic regimes. However, it is unclear whether geodynamic processes in the SE Asian continental margin were controlled by Tethyan or paleo-Pacific Ocean subduction. Herein, we report ~124 Ma adakitic granodiorites and Nb-enriched basalts from the Xiaozhenzhu Seamount of the SCS. Granodiorites have relatively high Sr/Y (34.7–37.0) and (La/Yb)N (13.8–15.7) ratios, as well as low Y (9.67–9.90 μg/g) and Yb (0.93–0.94 μg/g) concentrations, typical of adakites. Their Sr/Y and (La/Yb)N values coupled with their relatively low initial 87Sr/86Sr ratios (0.70541–0.70551), relatively high K2O contents (3.31–3.38 wt%), high Th/La ratios (0.33–0.40), negative εNd(t) values (−3.62 to −3.52), and their variable zircon εHf(t) values (−3.8 to +5.2) indicate that these rocks were formed by melting of subducted oceanic crust and sediments. The Nb-enriched basalts show enrichment in high field strength elements (HFSE) and have εNd(t) values of +2.90 to +2.93, as well as relatively low initial 87Sr/86Sr ratios of 0.70341–0.70343, demonstrating that they were derived from a depleted-mantle (DM) source metasomatized by silicate magmas originating from melting of a subducted oceanic lithospheric slab. By combining our findings with data from other Late Mesozoic arc-related magmatic rocks and adakites from the broader study area, we propose a geotectonic model involving subduction of young oceanic lithosphere during the Late Jurassic and northward subduction of the proto-South China Sea (PSCS) along the SE Asian continental margin during the Early Cretaceous. This conceptual model better explains the two-period Mesozoic magmatism, commonly reported for the SE Asian continental margin.

scholarly journals Opening and evolution of the South China Sea constrained by studies on volcanic rocks: Preliminary results and a research design

2011 ◽  
Vol 57 (24) ◽  
pp. 3150-3164 ◽  
Author(s):  
YiGang Xu ◽  
JingXian Wei ◽  
HuaNing Qiu ◽  
HuiHuang Zhang ◽  
XiaoLong Huang
Keyword(s):  
South China Sea ◽  
Research Design ◽  
South China ◽  
Volcanic Rocks ◽  
The South China Sea ◽  
The South ◽  
Preliminary Results ◽  
China Sea

Guadalupian (Permian) onset of subduction zone volcanism and geodynamic turnover from passive- to active-margin tectonics in southeast China

2019 ◽  
Vol 132 (1-2) ◽  
pp. 130-148 ◽  
Author(s):  
Feng-Qi Zhang ◽  
Hong-Xiang Wu ◽  
Yildirim Dilek ◽  
Wei Zhang ◽  
Kong-Yang Zhu ◽  
...  
Keyword(s):  
Rare Earth ◽  
Rare Earth Elements ◽  
South China ◽  
Carbonate Platform ◽  
Passive Margin ◽  
Magma Source ◽  
South China Block ◽  
The South ◽  
Active Margin ◽  
Topographic High

Abstract New stratigraphic, geochemical, and geochronological data from the late Paleozoic depositional record in Anhui Province, China, signal the onset of active-margin magmatism in East Asia. Chert-shale sequences of the Gufeng Formation are part of a Carboniferous–Permian carbonate platform that developed along the passive margin of the South China block. Thin tuffaceous interlayers in these sequences represent distal ash deposits, marking discrete volcanic events. Sensitive high-resolution ion microprobe (SHRIMP) U-Pb zircon dating of the stratigraphically bottom and near-top tuffaceous interlayers has revealed crystallization ages of 270 Ma and 264 Ma, respectively, constraining the time span of subaerial eruptions to ∼6 m.y. during the Guadalupian Epoch. High SiO2 and Al2O3 contents, enrichments in large ion lithophile and light rare earth elements, and depletion patterns of high field strength and heavy rare earth elements indicate a calc-alkaline magma source in an arc setting for the origin of these volcanic tuff deposits. Detrital zircon geochronology of sandstones in the overlying Longtan Formation shows two prominent age populations of 290–250 Ma and 1910–1800 Ma. The former age cluster overlaps with the tightly constrained zircon ages obtained from the Gufeng Formation. The latter age group is compatible with the known magmatic-metamorphic ages from Cathaysia in the South China block, and it points to the existence of a NE-SW–trending topographic high as a major sediment source. We interpret this topographic high and silicic volcanism to represent an Andean-type active margin, developed above a north-dipping paleo-Pacific slab. Our tightly constrained Guadalupian eruption ages indicate the inception of magmatic arc construction and mark a major switch from passive- to active-margin tectonics along SE Asia.

Denudation history of South China block and sediment supply to northern margin of the South China Sea

2009 ◽  
Vol 20 (1) ◽  
pp. 57-65 ◽  
Author(s):  
Yi Yan ◽  
Xiaoqiong Hu ◽  
Ge Lin ◽  
Bin Xia ◽  
Xiaoyong Li ◽  
...  
Keyword(s):  
South China Sea ◽  
South China ◽  
The South China Sea ◽  
Sediment Supply ◽  
South China Block ◽  
The South ◽  
Northern Margin ◽  
China Sea ◽  
History Of

Age and tectonic setting of the East Taiwan Ophiolite: implications for the growth and development of the South China Sea

2016 ◽  
Vol 154 (3) ◽  
pp. 441-455 ◽  
Author(s):  
ROBERT B.-J. HSIEH ◽  
J. GREGORY SHELLNUTT ◽  
MENG-WAN YEH
Keyword(s):  
South China Sea ◽  
South China ◽  
Tectonic Setting ◽  
The South China Sea ◽  
Spreading Ridge ◽  
The South ◽  
China Sea ◽  
Marginal Seas ◽  
Icp Ms ◽  
T Values

AbstractThe South China Sea is one of the youngest marginal seas and understanding its development is important for reconstructing the tectonic evolution of Southeast Asia. The South China Sea is thought to have been actively spreading between 32 Ma and 15.5 Ma. The East Taiwan Ophiolite (ETO) is one of the few preserved remnants of the South China Sea on land and provides an opportunity to investigate the age and the tectonic setting of the accreted easternmost portion. The age of the ETO was obtained by LA-ICP-MSin situzircon U–Pb methods and yielded a mean206Pb–238U age of 14.1±0.4 Ma, suggesting that magmatic activity in the South China Sea continued ~1.5 million years beyond current estimates. Cr-spinel data (Cr no. = 42–54) and depleted εNd(t) values (i.e. +9.1 to +11.4) from the serpentinized peridotites and gabbros and the light rare earth element depleted patterns (La/Yb ≤ 1) of the ETO mafic rocks are consistent with a ridge setting (i.e. N-MORB composition). Therefore, the ETO likely represents the terminal portion of the South China Sea spreading ridge that was sheared off during the northward translation of the Luzon arc.

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