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Wang, K.L., Chung, S.L., Chen, C.H., Shinjo, R., Yang, T.F. and Chen, C-H., 1999. Post collisional magmatism around northern Taiwan and its relation with opening of the Okinawa Trough. Tectonophysics, 308, 363-376. Abstract

Wang, K.L., Chen, C.H., Chung, S.L., Lin, L.H., Lo, C.H., Yang, T.F. and Lee, H.Y., 2000. Filed occurrence, 40Ar/39Ar dating and petrochemical features of volcanic rocks in Mienhuayu off NE Taiwan. J. Geol. Soc. China, 43, 247-266. Abstract

Chung, S.L., Wang, K.L., Crawford, A.J., Kamenetsky, V.S., Chen, C.-H., Lan, C.Y. and Chen, C.H., 2001. High-Mg potassic rocks from Taiwan: Implications for the genesis of orogenic potassic lavas. Lithos, 59, 153-170.

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Wang, K.L., O'Reilly, S.Y., Griffin, W.L., Chung , S.L., and Pearson, N.J. Proterozoic mantle lithosphere beneath the extended margin of the South China Block: in situ Re-Os evidence. Geology, 31, 709-712. Abstract

Wang, K.L., Chung , S.L., O'Reilly, S.Y., Sun, S.-s., Shinjo, R. and Chen, C.H. Geochemical constraints for the genesis of post-collisional magmatism and the geodynamic evolution in the northern Taiwan region. Journal of Petrology, in revision.

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Wang, K.L., Chung, S.L., Shinjo, R., Chen, C.H., Yang, T.F. and Chen, C-H., 1997. Post-collisional magmatism around northern Taiwan and its relation with opening of the Okinawa Trough. Int'l Conf. and Sino-Amer. Symp. on TEA, Chungli, Program and Abstracts, p.151-152.

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Wang, K.L., Chen, C.H., Chung, S.L., Chen, C-H. and Yang, T.F., 1998. Geochemical characteristics and geological significance of volcanic rocks from Mienhuayu off NE Taiwan. Program with abstracts, 1998 Annual Meeting of Geological Society of China, p106. (in Chinese)

Wang, K.L., Chung, S.L., Shinjo, R., Chen, C.H., Yang, T.F. and Chen, C-H., 1998. Post-collisional magmatism around northern Taiwan and its relation with opening of the Okinawa Trough. Supplement to EOS, Transactions, v.79, N24, W109 pp.

Wang, K.L., Chung, S.L. and Chen, C-H., 1999. Geochemical constraints on the petro-genesis of the Northern Taiwan Volcanic Zone (NTVZ): A three-component model.1999 Annual Meeting of Geological Society of China, p.147-149. (in Chinese)

Wang, K.L., Chung, S.L. and Chen, C.H., 1999. Post-collisional magmatism in the Northern Taiwan Mountain Belt. Supplement to EOS, Transactions, v.80, N46, F1041.

Wang, K.L., Chung, S.L. and Chen, C.H., 2000. Geochemical and Sr-Nd isotopic systematics of post-collisional magmatism around northern Taiwan: Implications for the subduction component and mantle enrichment processes. EOS, Transactions, v.81, N22, WP177.

Wang, K.L., Chung, S.L. Chen, C.H., and Chen, C.-H., 2000. Geochemical constraints on the petrogenesis of high-Mg basaltic andesites from the Northern Taiwan Volcanic Zone and their geodynamic significance. Goldschmidt 2000, Journal of Conference Abstracts v. 5 (2), 1067.

Lo, C.H., Chung, S.L., Lee, T.-Y., Wang, K.L., and Wu, C. T., 2000. Cenozoic magmatism and rifted basin evolution around the Taiwan Strait, SE China continental margin. (Abstract) EOS, Transactions, v.81, N22, F1111.

Wang, K.L., O’Reilly, S.Y., Griffin, W.L., Chung, S.L. and Juang, W.S., 2003. Geochemical characteristics of mantle xenoliths from Penghu Islands, Taiwan Straits, SE Asian margin. 8th International Kimberlite Conference, Program with Abstract, p139.

Wang, K.L.,  O’Reilly, S.Y., Griffin, W.L., Chung , S.L., and Pearson, N.J. Proterozoic mantle lithosphere beneath the extended margin of the South China Block: in situ Re-Os evidence. Accepted abstract for the 13th Goldschmidt Conference (September 2003)

Abstracts:

Post collisional magmatism around northern Taiwan and its relation with opening of the Okinawa Trough

Being part of an active mountain belt formed by oblique collision of the Luzon arc with Asia, northern Taiwan and offshore islets mark with a series of latest Pliocene-Quaternary volcanoes whose eruptions have been conventionally ascribed to westward propagation of the Ryukyu volcanic arc. On the basis of new geochemical data, along with supporting geologic and geophysical evidence, we propose instead that this young volcanism resulted from post-collisional lithospheric extension in the northern Taiwan mountain belt and the mantle source regions involved in the melt generation have been significantly modified by the nearby Ryukyu subduction-related processes. Magmas thus produced through the northeast to the southwest in the Northern Taiwan Volcanic Zone (NTVZ) vary from low-K to calc-alkaline and then shoshonitic compositions. Such a spatial geochemical variation, characterized by southwestward increase in enrichments of the potassium and incompatible trace elements, runs subparallel to the southwestern part of the present-day Ryukyu Trench. The geochemical variation that can be explained by southwestward decrease in degrees of partial melting of the mantle sources reconciles with a southwestward-weakening extensional regime observed in the NTVZ. The post-collisional extension in northern Taiwan, furthermore, might have played a role in reactivation of opening in the middle Okinawa Trough, and gave way to its rapid southwestward propagation with associated development of the Ryukyu subduction zone west of ~124˚E. This nascent subduction, in turn, resulted in abundant submarine volcanoes which delineate an embryo volcanic front along the southern margin of the Trough. Therefore, the southwestern Okinawa Trough is not a “fore-arc” basin as had been previously alleged, but represents an “atypical” back-arc basin which developed broadly synchronously or prior to its arc-trench system in this particular collsion/extension/subduction tectonic environment.

Filed occurrence, 40Ar/39Ar dating and petrochemical features of volcanic rocks in Mienhuayu off NE Taiwan

Mienhuayu, a volcanic islet off NE Taiwan, is located in the central part of the Northern Taiwan Volcanic Zone (NTVZ). In this study, we first conducted a detailed field investigation which reveals that the islet is composed dominantly of subaerial mafic lava flows and scoria deposits. 40Ar/39Ar dating on a whole-rock sample from a lava flow indicates that the volcanic activity started as early as 2.6 Ma, in good accordance with the time proposed for the onset of extensional collapse of the northern Taiwan mountain belt. Volcanic rocks from the Mienhuayu are generally hypocrystalline, showing porphyritic texture with high-Mg olivine (Fo _ 80~81), bronzite (En _ 79~82) and labradorite (An _ 58~66) as major phenocryst phases in a glassy matrix. They are uniform in the whole-rock composition marked by apparently higher magnesium (i.e., MgO _ 5.9~8.1 wt.%, Mg-value _ 56~62) relative to silica contents (SiO2 _ 52.7~54.5 wt.%), a feature that may be observed in either silica-saturated melts from the intraplate extension environment or high-Mg andesites commonly from the fore-arc settings. In the incompatible element variation diagram, although the Mienhuayu volcanic rocks exhibit moderate enrichments in the large ion lithophile and light rare earth elements and lead, they do not display depletions in the high field strength elements as other NTVZ volcanic rocks. The Mienhuayu volcanic rocks, moreover, show geochemical affinities to the Miocene (~23-9 Ma) intraplate tholeiitic basalts from NW Taiwan and contemporaneous (~13 Ma), extension-related high-Mg andesites from the Iriomote-jima, southern Ryukyu. We therefore suggest that, in comparison to other NTVZ volcanics whose generation requires a subduction-modified, lithospheric mantle source, the Mienhuayu magmas originated from an ascended asthenospheric mantle which had been subtly affected by adjacent Ryukyu subduction zone processes. This asthenosphere upwelling could have been achieved in the beginning of post-collisional lithospheric extension in the northern Taiwan mountain belt during Plio-Pleistocene time.

Geochemical constrain on the petrogenesis of high-Mg basaltic andesites from the northern Taiwan volcanic zone and their geodynamic significance

The Northern Taiwan Volcanic Zone (NTVZ) is a Late Pliocene-Quaternary volcanic field that occurred as a result of extensional collapse of the northern Taiwan mountain belt. We report here mineral compositions, major and trace element and Sr-Nd isotope data of high-Mg basaltic andesites from the Mienhuayu, a volcanic islet formed at ~2.6 Ma in the central part of the NTVZ. The rocks are hypocrystalline, showing porphyritic texture with Mg-rich olivine (Fo_81-80), bronzite (En_82-79) and plagioclase (An_66-58) as major phenocryst phases. They have uniform whole-rock compositions, marked by high magnesium (MgO_5.9~8.1 wt.%, Mg-value_ 0.6) relative to accompanying silica contents (SiO2_52.8~54.5 wt.%). The high-Mg basaltic andesites contain the highest TiO2(~1.5 wt.%) and lowest K2O (~0.4 wt.%) among the NTVZ volcanic rocks. In the incompatible element variation diagram, these Mienhuayu magmas exhibit mild enrichments in large ion lithophile (LILE) and light rare earth elements (LREE), coupled with an apparent Pb positive spike. They do not display depletions in high field strength elements (HFSE), a feature observed universally in the other NTVZ volcanics. The high-Mg basaltic andesites have rather unradiogenic Nd (eNd_+5.1~7.2) but apparently elevated Sr (87Sr/86Sr_0.70435~0.70543; leached values) isotope ratios. Their overall geochemical and isotopic characteristics are similar to mid-Miocene (~13 Ma) high-Mg andesites from the Iriomote-jima, southern Ryukyus, Japan. Despite these magmas have lower LILE and LREE enrichments and Pb positive spike, their °ßintraplate-type°® incompatible element variation patterns are comparable to those of extension-induced Miocene intraplate basalts emplaced in the Taiwan-Fujian region. Therefore, we interpret the Mienhuayu magmas as silica-saturated melts derived from decompression melting of the ascended asthenosphere that had been subtly affected by the adjacent Ryukyu subduction zone processes. This interpretation is consistent with the notion that in the northern Taiwan mountain belt post-orogenic lithospheric extension started in Plio-Pleistocene time.

Proterozoic mantle lithosphere beneath the extended margin of the South China block: In situ Re-Os evidence

The Os isotope compositions of sulfides in mantle xenoliths from the Penghu Islands, Taiwan Strait, reveal the presence of Proterozoic subcontinental lithospheric mantle (SCLM) beneath the highly extended southeast margin of the South China block. Both TRD model ages for individual sulfides and model ages estimated from the initial 187Os/188Os ratios of Re-Os mixing lines require that some volumes of the SCLM formed prior to 2.3–1.9 Ga. Later events in the SCLM may be recorded by TRD model ages of 1.5–1.2 Ga and ca. 0.9 Ga. The events recognized in the SCLM are consistent with those known in the crust of the mainland South China block. The sulfide Os isotope data show that Proterozoic lithosphere beneath the South China block has survived the extensive Mesozoic Yanshanian magmatism on the continental margin and has not been delaminated even during the severe lithospheric extension that led to the subsidence of the Taiwan Strait.