In Situ Geochemical Compositions of the Minerals in Basaltic Rocks from the West Philippine Basin: Constraints on Source Lithology and Magmatic Processes

Abstract Since the early Cenozoic, the West Philippine Basin (WPB) and the whole Philippine Sea Plate (PSP) has undergone a complex geological evolution. In this study, we presented K-Ar ages, in situ trace element, and major element compositions of minerals of basalts collected from the Benham Rise and the Central Basin Fault (CBF) in the WPB, to constrain their magmatic process and regional geological evolution. Olivine phenocrysts and microlites in the alkali basalts (20.9 Ma) from the Benham Rise have forsterite (Fo) contents of 56.90%–76.10% and 53.13%-66.41%, respectively. The clinopyroxenes in the tholeiites (29.1 Ma) from the CBF is predominantly diopside and augite, and it is depleted in light rare earth elements (LREEs) (LaN/YbN=0.13–3.40) and large-ion lithophile elements (LILEs). The plagioclases in the basalts from both of the Benham Rise and the CBF are predominantly labradorite and andesine, with a minor amount of bytownite, and it is enriched in LREEs, Ba, Sr, and Pb and exhibits strong positive Eu anomalies. However, there exist obvious differences in plagioclase compositions between these two tectonic sites. The source lithology of the Benham Rise basaltic rocks could be garnet pyroxenite, and yet that of the CBF could be spinel-lherzolite. The calculated mantle potential temperature beneath the Benham Rise is 1439°C–1473°C, which is significantly higher than that beneath the CBF (1345°C–1381°C), suggesting there existed thermal anomaly beneath the Rise during basaltic magmatism. This study also calculated the temperature and pressure of the clinopyroxenes and plagioclases, which have been used to indicate magmatic processes. Finally, we suggest that the Benham Rise basaltic rocks may be related to a mantle plume (e.g., the Oki-Daito mantle plume), and the CBF was once located in a back-arc spreading center behind an active subduction zone. The extinction of the Oki-Daito mantle plume activity might be at about 20.9 Ma, and cessation of the back-arc spreading of WPB was at about 29.1 Ma or younger.

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Basalt from the Extinct Spreading Center in the West Philippine Basin: New Geochemical Results and Their Petrologic and Tectonic Implications

Minerals ◽

10.3390/min11111277 ◽

2021 ◽

Vol 11 (11) ◽

pp. 1277

Author(s):

Zhengxin Yin ◽

Weiping Wang ◽

Liang Chen ◽

Zhengyuan Li ◽

Qiang Liu ◽

...

Keyword(s):

Mantle Source ◽

Spreading Center ◽

Isotopic Data ◽

The West ◽

Mafic Rocks ◽

West Philippine Basin ◽

Mantle Reservoir ◽

Back Arc ◽

Parental Melts ◽

Ocean Ridge

We present geological, bulk-rock geochemical and Sr–Nd–Hf isotopic data for mafic rocks from the West Philippine Basin (WPB). These mafic rocks comprise pillow basalts characterized by a vesicular structure. The mid-ocean ridge basalt (MORB)-normalized trace element patterns of basalts from the study area display depletions in Nb. In addition, the chondrite-normalized lanthanide patterns of basalts from the WPB are characterized by significant depletions in the light lanthanides and nearly flat Eu to Lu segments. The investigated rocks have initial 87Sr/86Sr ratios (87Sr/86Sr(i)) of 0.703339–0.703455 and high εNd(t) values (8.0 to 8.7). Furthermore, basalts from the WPB have 176Hf/177Hf ratios that range from 0.28318 to 0.28321 and high εHf(t) from 15.2 to 16.3. Semi-quantitative modeling demonstrates that the parental melts of basalts from the study area were derived by ~20% adiabatic decompression melting of a rising spinel-bearing peridotite source. The Sr–Nd–Hf isotopic compositions of basalts from the WPB indicate that their parental magmas were derived from an upper mantle reservoir possessing the so-called Indian-type isotopic anomaly. Interpretation of the isotopic data suggests that the inferred mantle source was most likely influenced by minor inputs of a sediment melt derived from a downgoing lithospheric slab. Collectively, the petrographic and geochemical characteristics of basalts from the study area are analogous to those of mafic rocks with a back-arc basin (BAB)-like affinity. As such, the petrogenesis of basalts from the WPB can be linked to upwelling of an Indian-type mantle source due to lithospheric slab subduction that was followed by back-arc spreading.

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Geochemical characteristics of back-arc basin lower crust and upper mantle at final spreading stage of Shikoku Basin: an example of Mado Megamullion

Progress in Earth and Planetary Science ◽

10.1186/s40645-021-00454-3 ◽

2021 ◽

Vol 8 (1) ◽

Author(s):

Norikatsu Akizawa ◽

Yasuhiko Ohara ◽

Kyoko Okino ◽

Osamu Ishizuka ◽

Hiroyuki Yamashita ◽

...

Keyword(s):

Isotope Composition ◽

Spreading Center ◽

Chemical Compositions ◽

Olivine Gabbro ◽

Pb Isotope ◽

Shikoku Basin ◽

Source Mantle ◽

Evolutional Process ◽

Back Arc

AbstractThis paper explores the evolutional process of back-arc basin (BAB) magma system at final spreading stage of extinct BAB, Shikoku Basin (Philippine Sea) and assesses its tectonic evolution using a newly discovered oceanic core complex, the Mado Megamullion. Bulk and in-situ chemical compositions together with in-situ Pb isotope composition of dolerite, oxide gabbro, gabbro, olivine gabbro, dunite, and peridotite are presented. Compositional ranges and trends of the igneous and peridotitic rocks from the Mado Megamullion are similar to those from the slow- to ultraslow-spreading mid-ocean ridges (MOR). Since the timing of the Mado Megamullion exhumation corresponds to the very end of the Shikoku Basin opening, the magma supply was subdued and highly episodic, leading to extreme magma differentiation to form ferrobasaltic, hydrous magmas. In-situ Pb isotope composition of magmatic brown amphibole in the oxide gabbro is identical to that of depleted source mantle for mid-ocean ridge basalt (MORB). In the context of hydrous BAB magma genesis, the magmatic water was derived solely from the MORB source mantle. The distance from the back-arc spreading center to the arc front increased away through maturing of the Shikoku Basin to cause MORB-like magmatism. After the exhumation of Mado Megamullion along detachment faults, dolerite dikes intruded as a post-spreading magmatism. The final magmatism along with post-spreading Kinan Seamount Chain volcanism were introduced around the extinct back-arc spreading center after the opening of Shikoku Basin by residual mantle upwelling.

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In Situ LA-ICP-MS Analysis of Minerals Hosted by Late Cenozoic Basaltic Rocks from Thailand

Minerals ◽

10.3390/min9070446 ◽

2019 ◽

Vol 9 (7) ◽

pp. 446 ◽

Cited By ~ 1

Author(s):

Long Yuan ◽

Quanshu Yan ◽

Xuefa Shi ◽

Haitao Zhang ◽

Xijun Liu

Keyword(s):

Mantle Plume ◽

Inductively Coupled Plasma ◽

Potential Temperature ◽

Geodynamic Setting ◽

Late Cenozoic ◽

Basaltic Rocks ◽

Southern Vietnam ◽

Icp Ms ◽

Hainan Mantle Plume

Shortly after the cessation of seafloor spreading, intraplate magmatism affected large areas in the South China Sea (SCS) region. The origin and geodynamic setting of the post-spreading volcanism is still in debate, for many previous studies have focused on petrogenesis and mantle source of the late Cenozoic basalts from the SCS region. In this study, we obtained in situ major element compositions (by using Electron microprobe analysis—EMPA) and trace element compositions (by using laser ablation inductively coupled plasma mass spectrometry— LA-ICP-MS) for minerals (clinopyroxenes (Cpx), plagioclases (Pl), and olivines (Ol)) hosted by late Cenozoic basaltic rocks from Thailand. The results showed that the olivines had forsterite contents between 60.12% and 84.74%. Clinopyroxene were diopside and augite, and they were enriched in light rare earth elements (LREEs) (LaN/YbN = 1.93–4.27) and depleted in large-ion lithophile elements (LILEs). Mineral compositions (mainly based on clinopyroxene) confirmed that these late Cenozoic basaltic rocks were of an intraplate affinity and were similar to contemporaneous basaltic fields in the SCS region (Southern Vietnam, Northern Hainan, and SCS seamounts). Plagioclases were predominantly labradorite, with a few andesine and bytownite, and they were enriched in LREEs and Ba, Sr, and Pb, and most of them exhibited strong positive Eu anomalies. The source lithology of Thailand basaltic rocks could be garnet pyroxenite. The mantle potential temperature beneath Thailand is in the range of 1448–1467 °C, which can be comparable to those beneath Southern Vietnam and Northern Hainan, indicating the Thailand basaltic rocks could be produced by the Hainan mantle plume. In addition, the crystallization temperature of clinopyroxenes (1145–1214 °C) and plagioclase (1067–1133 °C) and their composition characteristics indicate that the magmatic processes have a conspicuous characteristic of fast rate of magma upwelling. Thus, we proposed that the deep geodynamic setting of Thailand late Cenozoic basaltic rocks is similar to those of the whole SCS region, and Hainan mantle plume plays a significant role in the petrogenesis of these basaltic rocks.

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The West Philippine Basin: An Eocene to early Oligocene back arc basin opened between two opposed subduction zones

Journal of Geophysical Research Atmospheres ◽

10.1029/2001jb001706 ◽

2002 ◽

Vol 107 (B12) ◽

pp. EPM 1-1-EPM 1-24 ◽

Cited By ~ 114

Author(s):

Anne Deschamps ◽

Serge Lallemand

Keyword(s):

Subduction Zones ◽

The West ◽

West Philippine Basin ◽

Early Oligocene ◽

Back Arc

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Propagators and ridge jumps in a back-arc basin, the West Philippine Basin

Terra Nova ◽

10.1111/j.1365-3121.2008.00824.x ◽

2008 ◽

Vol 20 (4) ◽

pp. 327-332 ◽

Cited By ~ 11

Author(s):

Anne Deschamps ◽

Ryuichi Shinjo ◽

Takeshi Matsumoto ◽

Chao-Shing Lee ◽

Serge E. Lallemand ◽

...

Keyword(s):

The West ◽

West Philippine Basin ◽

Back Arc

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Abstract: The West Siberian Bazhenov Petroleum System In Situ": Geological Evolution and Generation-Accumulation Efficiency"

AAPG Bulletin ◽

10.1306/e4fd38e7-1732-11d7-8645000102c1865d ◽

1999 ◽

Vol 83 ◽

Author(s):

LOPATIN, NIKLOLAY, and TAMARA EMETS

Keyword(s):

Petroleum System ◽

The West ◽

Geological Evolution ◽

Accumulation Efficiency

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Separation of Gagua Rise from Great Benham Rise in the West Philippine Basin during the Middle Eocene

Scientific Reports ◽

10.1038/s41598-021-01330-2 ◽

2021 ◽

Vol 11 (1) ◽

Author(s):

Yi-Ching Yeh ◽

Jing-Yi Lin ◽

Shu-Kun Hsu ◽

Ching-Hui Tsai ◽

Ching-Min Chang

Keyword(s):

Middle Eocene ◽

Spreading Rate ◽

Spreading Center ◽

The West ◽

West Philippine Basin ◽

Swath Bathymetry ◽

History Of ◽

Free Air Gravity ◽

The Right ◽

Multichannel Seismic Data

AbstractThe West Philippine Basin (WPB) has started opening at ~ 58 Ma and ceased spreading at ~ 33 Ma, developing a fast spreading (~ 44 mm/yr half-spreading rate) magmatic episode between 58 and 41 Ma and the second amagmatic episode between 41 and 33 Ma. The occurrence of the first stage of spreading is closely related to the Oki-Daito mantle plume and related Benham Rise (BR) and Urdaneta Plateau (UP) activity. To the east of the Luzon–Okinawa Fracture Zone (LOFZ), BR was the most active volcanism from 48 to 41 Ma. The geomagnetic ages on both sides of the LOFZ have been determined; however, their causal relationship and evolution in the WPB remain unclear. In this study, we performed integrated analyses of multichannel seismic data and swath bathymetry data for the area to the west of the LOFZ. To the west of the LOFZ, the Gagua Rise (GR), is identified by a high residual free-air gravity anomaly, volcanic seamount chains and an overlapping spreading center. The GR is located at magnetic isochrons C20/C22 (50 to 44 Ma) and shows a thick oceanic crust of at least 12.7 km. We first propose an oceanic plateau named Great Benham Rise (GBR) which includes GR, UP and BR. We infer that the GR was a portion of the GBR since ~ 49 Ma and was separated from the GBR at ~ 41 Ma by the right-lateral LOFZ motion. Later, the relict GBR magmatism only continued in the area to the east of the LOFZ. Overall, the GBR dominates the spreading history of the WPB.

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Zircon Petrochronology of the Kişladaǧ Porphyry Au Deposit (Turkey)

Economic Geology ◽

10.5382/econgeo.4864 ◽

2021 ◽

Author(s):

Luca Paolillo ◽

Massimo Chiaradia ◽

Alexey Ulianov

Keyword(s):

Wall Rock ◽

Western Anatolia ◽

Deposit Formation ◽

Porphyry Deposit ◽

Porphyry Deposits ◽

High K ◽

Magmatic Processes ◽

Back Arc ◽

Tectonic Environments

Abstract Porphyry deposits typically occur in subduction-related arcs but have more recently also been described in postsubduction, collisional to extensional back-arc settings. These different tectonic environments not only might imply different genetic processes but also seem to result in different metal endowments (e.g., Au rich versus Cu rich). It is therefore relevant, also for exploration purposes, to understand the magmatic processes involved in porphyry formation in these different tectonic environments. This study focuses on the Kişladaǧ porphyry Au (17.4 Moz) deposit in western Anatolia, which is centered on a series of porphyritic monzonite stocks of high-K calc-alkaline to shoshonitic affinity and formed in a continental rifting environment. With 17.4 Moz of Au, Kişladaǧ is of global metallogenic importance and hence a good example for studying the genetic processes associated with porphyry deposits in extensional back-arc settings. We herein combine a comprehensive set of new zircon textural observations, in situ zircon trace element and Hf isotope data, and previously published zircon geochronology to study the magmatic processes associated with porphyry deposit formation at Kişladaǧ. We show that mafic rejuvenation of a slowly crystallizing (between ~15.8 and 14.9 Ma) magma reservoir below Kişladaǧ immediately preceded porphyry deposit formation. Zircon trace elements and geochronology suggest a longer and deeper evolution for the early fertile magmas compared to the later infertile magmas. Magma evolution at Kişladaǧ was accompanied by crustal wall-rock assimilation. Whole-rock Nd and Sr radiogenic isotopes show that increasing asthenosphere-derived melt input under accelerated regional extension caused a loss in fertility of the system over time.

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