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Geochemistry and age of seamounts in the West Pacific: mantle processes and petrogenetic implications
TANG Limei, DONG Yanhui, CHU Fengyou, CHEN Ling, MA Weilin, LIU Yonggang
2019, 38(1): 71-77. doi: 10.1007/s13131-019-1371-0
Keywords: 40Ar/39Ar ages, geochemistry, magmatic evolution, basalts, West Pacific
Research on seamounts provides some of the best constraints for understanding intraplate volcanism, and samples from seamounts reveal crucial evidence about the geochemical makeup of the oceanic mantle. There are still many seamounts in the West Pacific Seamount Province (WPSP) that have not been studied, meaning their ages and geochemistry remain unknown. A better understanding of these seamount trails and their evolutionary history, investigated with age and geochemistry data, will enable better understanding of the geological processes operating underneath the Pacific Ocean Plate. Here, new 40Ar/39Ar ages and trace element and Sr-Nd-Pb isotopic data for seven basalt rocks from four seamounts in the WPSP are provided. Chemically, these rocks are all Oceanic Island Alkali basalt (OIA type); analysis of olivine phenocrysts shows that the magmas experienced strong olivine fractionation and changed from olivine + plagioclase to olivine + plagioclase + clinopyroxene cotectic during their evolution. Rare earth element (REE) patterns and a spider diagram of the samples in this study show OIB (Ocean Island Basalt) like behavior. The range of 87Sr/86Sr values is from 0.704 60 to 0.706 24, the range of 206Pb/204Pb values is from 18.241 to 18.599, and the range of 143Nd/144Nd values is from 0.512 646 to 0.512 826; together, these values indicate magma sources ranging from EMI to EMⅡ. Finally, new 40Ar/39Ar age data show that these seamounts formed at ~97 and ~106 Ma, indicating that some may have undergone the same formation processes as seamounts in the eastern part of the Magellan Seamount Trail, but other seamounts likely have different origins.
Geochemistry and environment evolution of Core E in the Laizhou Bay since last stage of Middle Pleistocene
Han Deliang, Yu Hongjun, Li Guanbao
2001(3): 391-399.
Keywords: Laizhou Bay, last stage of Middle Pleistocene, geochemistry, paleo-environment, element strata
Geochemistry analysis has been done on Core E (37°07'N,118°55'E; depth:82.1 m) taken from the Laizhou Bay in 1994.Nine kinds of invariable elements,15 kinds of microelements and the content of lime carbonate are measured by means of ICP.The results indicate that most of the in variable elements and microelements in Core E show significant changes in the boundary stratotype,and the ratios between elements (Mn/Fe,Sr/Ba,Ti/Al) in particular.So they can be used as characteristic indicator to stratigraphic division of Quaternary.The changes of invariable elements are primarily con trolled by the host minerals,and they mainly indicate the provenance as well as the sedimentation and depositional environment.Several elements,such as Fe,Al,Ca,Mg,Mn and Ti,are very sensitive to the provenance and environment.The distribution of microelements differs in four depositional periods:last stage of Middle Pleistocene,last interglacial period,last glacial period and Recent epoch,and espe cially in the "cold period" and "warm period".The loops in the cycle curves of the most microelements correspond with the sand bed sediments,among which there are six sand units representing "warm period" sediments,and one representing "cold period" sediments.The carbonate is on the high side in the aeolian silt sediments formed in the glacial lowering of sea level in Core E,but on the low side in the transgressive sand beds formed in the interglacial period.The content variation of carbonate has a direct bearing on the grain size and the styles of sediments,and is a good indicator to the climate,environment and stratigraphic division.
Mineralogy and geochemistry of hydrothermal sulphide from a submarine volcanic high at 18°36.4'S Central Lau Spreading Center, Southwest Pacific
Durbar Ray, Anil L. Paropkari
2023, 42(5): 93-101. doi: 10.1007/s13131-022-2121-2  Published:2023-05-25
Keywords: Central Lau Spreading Center, hydrothermal sulphide, mineralogy, geochemistry
We report the mineralogy and geochemistry of hydrothermal sulphide from the crater of a volcanic high near 18°36.4′S of the Central Lau Spreading Center. During 1990s, that volcanic structure was reported active and sulphide samples were collected by MIR submersible. A section of a chimney-like structure from the crater-floor was studied here. The Fe-depleted sphalerites, and Co-depleted pyrites in that chimney were similar to those commonly found in low to moderate temperature (<300℃) sulphides from sediment-starved hydrothermal systems. Bulk analyses of three parts of that chimney section showed substantial enrichment of Zn (18%–20%) and Fe (14%–27%) but depletion of Cu (0.8%–1.3%). In chondrite-normalized rare earth element-patterns, the significant negative Ce-anomalies (Ce/Ce*=0.27–0.39) and weakly positive Eu-anomalies (Eu/Eu*=1.60–1.68) suggested sulphide mineralisation took place from reduced low-temperature fluid. The depleted concentration of lithophiles in this sulphide indicates restricted contribution of sub-ducting plate in genesis of source fluid as compared to those from other parts of Lau Spreading Centre. Uniform mineralogy and bulk composition of subsamples across the chimney section suggests barely any alteration of fluid composition and/or mode of mineralisation occurred during its growth.
Geochemistry of some major chemical composition in marine sediments of the Haitan Island
Yang Huihui, Chen Lan
1999(1): 127-135.
Keywords: Sediments, geochemistry, Haitan Island
Zircon U-Pb geochronology, Hf isotopes, and geochemistry constraints on the age and tectonic affinity of the basement granitoids from the Qiongdongnan Basin, northern South China Sea
Lijun Mi, Xiaoyin Tang, Haizhang Yang, Shuchun Yang, Shuai Guo
2023, 42(3): 19-30. doi: 10.1007/s13131-022-2078-1  Published:2023-03-25
Keywords: Qiongdongnan Basin, basement granitoids, geochemistry, U-Pb and Hf isotopes, Paleo-Pacific Plate subduction
Studies in the northern South China Sea (SCS) basement remain important for understanding the evolution of the Southeast Asian continental margin. Due to a thick cover of sediments and scarce borehole penetration, little is known about the age and tectonic affinity of this basement. In this study, an integrated study of zircon U-Pb geochronology, Hf isotopes, and whole-rock major and trace elements on seven basement granitoids from seven boreholes of Qiongdongnan Basin has been carried out. New zircon U-Pb results for these granitoids present middle-late Permian ((270.0±1.2) Ma; (253±3.4) Ma), middle to late Triassic ((246.2±3.4) Ma; (239.3±0.96) Ma; (237.9±0.99) Ma; (228.9±1.0) Ma) and Late Cretaceous ages ((120.6±0.6) Ma). New data from this study, in combination with the previous dataset, indicates that granitoid ages in northern SCS basement vary from 270 Ma to 70.5 Ma, with three age groups of 270–196 Ma, 162–142 Ma, and 137–71 Ma, respectively. Except for the late Paleozoic-Mesozoic rocks in the basement of the northern SCS, a few old zircon grains with the age of (2708.1±17) Ma to (2166.6±19) Ma provide clues to the existence of the pre-Proterozoic components. The geochemical signatures indicate that the middle Permian-early Cretaceous granitoids from the Qiongdongnan Basin are I-type granites formed in a volcanic arc environment, which were probably related to the subduction of the Paleo-Pacific Plate.
Tephra records from abyssal sediments off western Sumatra in recent 135 ka: evidence from Core IR-GC1
QIU Zhongyan, HAN Xiqiu, JIN Xianglong, WANG Yejian, ZHU Jihao
2014, 33(12): 75-80. doi: 10.1007/s13131-014-0568-5
Keywords: geochemistry, glass shards, youngest Toba tuff, abyssal sediment
Three volcanic ash layers were identified in a deep-sea Core IR-GC1 from the north-eastern Indian Ocean, adjacent to western Indonesian arc. They were dominated by glass shards with minor mineral crystals, such as plagioclase, biotite, and hornblende. According to the morphology and major element compositions of the representative glass shards, combined with the δ18O-based age, it is suggested that ash Layer A is correlated to the youngest Toba tuff (YTT), Layer B is supposed to be associated with a new eruption of Toba caldera in an age of 98 to 100 ka. Ash Layer C is different the geochemistry characteristics than those of Layer A and Layer B, suggesting that Layer C was not originated from Toba but registered another volcanic eruption event.
Geological comparative studies of Japan Arc System and Kyushu-Palau Arc
YAN Quanshu, SHI Xuefa
2011(4): 107-121. doi: 10.1007/s13131-011-0134-3
Keywords: Japan arc system, Kyushu-Palau ridge (KPR), Philippine sea plate (PSP), Tectonic evolution, geochronology, geochemistry
Based on the published data of structure geology, geochronology, petrology and isotope geochemistry, the authors of this paper have conducted studies on the tectonic evolution history of Japan arc system and Kyushu-Palau ridge (KPR). The studies show that the initial Japan arc system was resulted from the subduction of ancient Pacific plate beneath Eurasian Plate in Permian. It was part of an Andean-type continental volcanic arc which occurred in the offshore in the east of Asian during late Mesozoic era. The formation of tertiary back-arc basin (Japan Sea) resulted in the fundamental tectonic framework of the present arc system. Since Quaternary the system has been lying at E-W compression tectonic setting due to the eastward subduction of Amur Plate. It is expected that Japan arc system will be juxtaposed with Asian continent, which is similar to the present Taiwan arc system. The origin of Philippine Sea Plate (PSP) is still in debate. Some studies argued that it is a trapped oceanic crust segment, while the others insisted that it is a back-arc basin accompanied with ancient IBM arc. However, it is all agreed that the tectonic evolution of PSP started since 50 Ma, i.e., PSP has drifted from the site around equator at 50 Ma to the present site, and the subduction of PSP along Nankai trough-Ryukyu Trench beneath the Japan arc system during 6-2 Ma led to the formation of the present Ryukyu arc system. Of the PSP, the KPR has been found with the oldest rocks formed at 38 Ma. Combining with its geochemical characteristics of oceanic arc tholeiite, it is suggested that KPR is an intraoceanic volcanic arc, more specifically, a relic arc (i.e., rear arc of the ancient IBM) after rifting of ancient IBM. In addition, Amami-Daito province is of arc tectonic affinity, but has been affected by mantle plume. Therefore, based on their respective tectonic evolution history and geochemical characteristics of rock samples, it is inferred that there is no genetic relationship between Japan arc system and KPR. It is noted that rocks reflecting continental crust basement feature have been collected on the northern tip of KPR, which may be related to the process of KPR accreting on Japan arc, but the arc-continent accretion process are still at initial stage of modern continental crust accretion model. However, due to the scarcity of data of the northern tip of KPR, crustal structure of this location and its adjacent Nankai trough need to be further constrained by geophysical studies in the future.
Geological characteristics of the Nankai Trough subduction zone and their tectonic significances
Jie Zhang, Ling Chen, Zihua Cheng, Limei Tang
2020, 39(10): 81-95. doi: 10.1007/s13131-020-1663-4  Published:2020-10-25
Keywords: Nankai Trough, subduction zone, velocity structure, gravity modeling, geochemistry, petrology, slab melting, geological effect
The Nankai Trough subduction zone is a typical subduction system characterized by subduction of multiple geological units of the Philippine Sea Plate (the Kyushu-Palau Ridge, the Shikoku Basin, the Kinan Seamount Chain, and the Izu-Bonin Arc) beneath the Eurasian Plate in the southwest of Japan. This study presents a geophysical and geochemical analysis of the Nankai Trough subduction zone in order to determine the features and subduction effects of each geological unit. The results show that the Nankai Trough is characterized by low-gravity anomalies (–20 mGal to –40 mGal) and high heat flow (60–200 mW/m2) in the middle part and low heat flow (20–80 mW/m2) in the western and eastern parts. The crust of the subducting plate is 5–20 km thick. The mantle composition of the subducting plate is progressively depleted from west to east. Subduction of aseismic ridges (e.g., the Kyushu-Palau Ridge, the Kinan Seamount Chain, and the Zenisu Ridge) is a common process that leads to a series of subduction effects at the Nankai Trough. Firstly, aseismic ridge or seamount chain subduction may deform the overriding plate, resulting in irregular concave topography along the front edge of the accretionary wedge. Secondly, it may have served as a seismic barrier inhibiting rupture propagation in the 1944 Mw 8.1 and 1946 Mw 8.3 earthquakes. In addition, subduction of the Kyushu-Palau Ridge and hot and young Shikoku Basin lithosphere may induce slab melting, resulting in adakitic magmatism and the provision of ore-forming metals for the formation of porphyry copper and gold deposits in the overriding Japan Arc. Based on comparisons of their geophysical and geochemical characteristics, we suggest that, although the Izu-Bonin Arc has already collided with the Japan Arc, the Kyushu-Palau Ridge, which represents a remnant arc of the Izu-Bonin Arc, is still at the subduction stage characterized by a single-vergence system and a topographic boundary with the Japan Arc.
Geochemistry and zircon U-Pb ages of the Oligocene sediments in the Baiyun Sag, Zhujiang River Mouth Basin
Rui Sun, Ming Ma, Kai Zhong, Xiayang Wang, Zhao Zhao, Shuai Guo, Xingzong Yao, Gongcheng Zhang
2021, 40(2): 123-135. doi: 10.1007/s13131-020-1628-7  Published:2021-04-02
Keywords: weathering degree, lithology of parent rock, provenance, element geochemistry, zircon U-Pb ages, Baiyun Sag
In this study, element geochemistry and zircon chronology are used to analyze the Oligocene sediments in the Baiyun Sag, Zhujiang River Mouth Basin. The experimental results are discussed with respect to weathering conditions, parent rock lithologies, and provenances. The chemical index of alteration and the chemical index of weathering values of mudstone samples from the lower Oligocene Enping Formation indicate that clastic particles in the study area underwent moderate weathering. Mudstone samples exhibit relatively enriched light rare earth elements and depleted heavy rare earth elements, “V”-shaped negative Eu anomalies, and negligible Ce anomalies. The rare earth element distribution curves are obviously right-inclined, with shapes and contents similar to those of post-Archean Australian shale and upper continental crust, indicating that the samples originated from acid rocks in the upper crust. The Hf-La/Th and La/Sc-Co/Th diagrams show this same origin for the sediments in the study area. For the samples from the upper Enping deltas, the overall age spectrum shows four major age peaks ca. 59–68 Ma, 98–136 Ma, 153–168 Ma and 239–260 Ma. For the Zhuhai Formation samples, the overall age spectrum shows three major age peaks ca. 149 Ma, 252 Ma and 380 Ma. The detrital zircon shapes and U-Pb ages reveal that during Oligocene sedimentation, the sediments on the northwestern margin of the Baiyun Sag were supplied jointly from two provenances: Precambrian-Paleozoic metamorphic rocks in the extrabasinal South China fold zone and Mesozoic volcanic rocks in the intrabasinal Panyu Low Uplift, and the former supply became stronger through time. Thus, the provenance of the Oligocene deltas experienced a transition from an early proximal intrabasinal source to a late distal extrabasinal source.
Chemical composition of sediments from the subducting Cocos Ridge segment at the Southern Central American subduction zone
Renjie Zhao, Quanshu Yan, Haitao Zhang, Yili Guan, Xuefa Shi
2022, 41(1): 58-75. doi: 10.1007/s13131-021-1920-1  Published:2022-01-10
Keywords: subducting sediments, IODP Expedition 344, geochemistry, Southern Central American subduction zone
Subducted sediments play an important role in the magmatism at subduction zones and the formation of mantle heterogeneity, making them an important tracer for shallow crustal processes and deep mantle processes. Therefore, ascertaining the chemical compositions of different subduction end-members is a prerequisite for using subducted sediments to trace key geological processes. We reports here the comprehensive major and trace element analyses of 52 samples from two holes (U1414A and U1381C) drilled on the subducting Cocos Ridge segment at the Southern Central American (SCA) subduction zone during Integrated Ocean Drilling Program (IODP) Expedition 344. The results show that the SCA subducting sediments contain 51% (wt%) CaCO3, 27% (wt%) terrigenous material, 16% (wt%) opal, and 6% (wt%) mineral-bound H2O+. Compared to the global trenches subducting sediment, the SCA subducting sediments are enriched in biogenic elements (Ba, Sr, and Ca), and depleted in high field strength elements (Nb, Ta, Zr, Hf, and Ti) and alkali elements (K, Rb, and Cs). Meanwhile, the sediments in this area were affected by the carbonate crash event, which could have been caused by a ~800 m rise in the carbonate compensation depth at 11 Ma in the Guatemala Basin. The reason for the sedimentary hiatus at Hole U1381C may be the closure of the Panama Isthmus and the collision between the Cocos Ridge and the Middle America Trench. In addition, the sediments from the subducting Cocos Ridge segment have influenced the petrogenesis of volcanic lavas erupted in the SCA.
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