在聚合性板塊邊界上，增積岩體內的玄武岩，對於該區域的地函特徵、地體演化，以及物質遷移關係提供了關鍵資訊。本研究自臺灣南部的增積岩體，即南中國海岩石圈與菲律賓海岩石圈的聚合邊界，採集19個玄武岩樣本，分析其元素含量以及Sr、Nd、Hf、Pb同位素比值，藉以討論其岩石成因與地體親緣性。所有樣本的燒失量值皆 > 2%，表示受到蝕變作用的影響。稀土元素(REEs)及高場強元素(HFSE)含量與燒失量的相關性顯示這兩群元素未受蝕變作用影響。雖然有數個樣本的Pb濃度偏低，但leached 與un-leached的樣本之Pb同位素比值的差異都低於分析誤差範圍，表示Pb同位素訊號仍具不易遷移的特徵。另外，主要元素的燒失量變異圖顯示Ti和P不易受後期作用影響。藉由Pb、Nd同位素比值以及REE濃度的分佈，可以將本研究的增積岩體玄武岩分為N-MORB、E-MORB與OIB。模擬計算的結果顯示N-MORB-like的樣本來自三個LREE貧瘠程度不同之地函源區。E-MORB-like及OIB-like樣本之地函源區的La含量分別為Hirschman & Stopler (1996)所建議的貧瘠地函成分的3.5及10.8倍；Nd含量則為1.3及2.5倍；Sm含量為1.7及3.6倍。根據地函源區成分的模擬計算，這些玄武岩樣本至少來自六個不同的地函來源，顯示了地函的異質性。這些增積玄武岩，有三種可能的地體親緣性，南中國海海洋地殼，菲律賓海板塊，或者臺灣海板塊。本研究利用Pb, Nd, Hf同位素以及TiO2-P2O5關係作為化學參數，藉以探討其地體親緣性。這些增積玄武岩與所謂的「臺灣海板塊」或者「花東盆地」沒有相關性。基於TiO2-P2O5與eNd – eHf的關係，採集自PL（保力溪）區域的MORB-like樣本增積自南中國海海洋地殼; 而JS（尖山）區域的MORB-like樣本則和菲律賓玄武岩具有關聯性。此外，我們在一個堆晶樣本中觀察到角閃石斑晶，指示此樣本具有來自北呂宋島弧的島弧岩漿成分，推測此樣本來自菲律賓海板塊。受控於體積比例，來自隱沒板塊的剷刮物質主要為N-MORB。增積岩體內的OIB樣本與E-MORB的樣本主要來自上覆的菲律賓海板塊，推測為地勢較高的海底火山與洋島易受侵蝕而進入增積岩體內。因此，建議此等地體親緣性的差異可為隱沒方向之指標，有助於了解古老縫合帶的兩板塊之地體演化史。

Accreted basalts provide critical information on mantle nature, tectonic evolution, and mass transport in convergent boundaries. In this study, nineteen accreted basalts from southern Taiwan on the convergent boundary between South China Sea lithosphere and Philippine Sea plates were analyzed for element concentrations as well as Sr, Nd, Hf, and Pb isotope ratios to investigate their petrogenetic and tectonic significance. All the samples contain > 2% LOI content, reflecting post-magmatic alteration. The invariability of REE and HFSE abundances relative to the LOI content indicates that these two element groups remained intact after magmatic processes. A group of samples show Pb-loss, however, the differences in Pb isotope compositions between the leached and un-leached aliquots are mostly within the analytical uncertainty, reflecting the immobile nature. Also, the LOI variation diagrams of major elements show that Ti and P are immobile during post-magmatic processes. In this study, the Pb and Nd isotope ratios and REE patterns were used to classify the accreted basalts into three groups deriving from the N-MORB, E-MORB, and OIB sources. Model calculations showed derivation of the N-MOEB-like samples from three distinct LREE-depleted mantle sources. Relative to the depleted mantle composition of Hirschman & Stopler (1996), the sources for the E-MORB-like and OIB-like samples were 3.5 and 10.8 times enriched in La, 1.7 and 3.6 times enriched in Nd, and 1.3 and 2.5 times enriched in Sm, respectively. According to the mantle source simulations, it is considered that at least six distinct mantle sources are required for these basalts, showing the scale of heterogeneity. The possible tectonic affinities for the accreted basalts are South China Sea oceanic crust, Philippine Sea plate, or Taiwan Sea plate, and we used Pb, Nd, Hf isotopes as well as TiO2 – P2O5 relationship as the parameters for tracing tectonic affinities. The accreted basalts are not associated with basalts from the so-called “Taiwan Sea Plate” or “Huatung Basin”. Based on the TiO2 – P2O5 and eNd – eHf relationships, it is considered that the MORB-like samples from the PL site were accreted from the South China Sea oceanic crust, whereas those from the JS site were associated with Philippine Sea basalts. Additionally, we found a cumulate sample containing hornblende phenocrysts, indicating an arc component from North Luzon arc, which belongs to the Philippine Sea plate. It, therefore, appears that the materials scraped off the subducting plate are mostly N-MORB due to volumetric prevalence. The dominance of the OIB and E-MORB materials from the overlying Philippine Sea floor in the accretionary prism might be a consequence from preferential erosion of the topographically high seamounts and ocean islands. Accordingly, this tendency is proposed as subduction polarity indicator to add more constraints to tectonic evolution history of ancient convergent zones.

Ali, J. R., Hall, R. 1995. Evolution of the boundary between the Philippine Sea Plate and Australia: palaeomagnetic evidence from eastern Indonesia. Tectonophysics 251, 251–275.
An, W., Hu, X., Garzanti, E., 2017. Sandstone provenance and tectonic evolution of the Xiukang Mélange from Neotethyan subduction to India–Asia collision (Yarlung-Zangbo suture, south Tibet). Gondwana Research 41, 222–234.
Barrier, E., Angelier, J., 1986. Active collision in eastern Tawian, the Coastal Range. Tectonophysics 125, 39–72.
Byrne, T.B., Liu, C.-S., 2002. Geology and geophysics of an arc-continent collision, Taiwan. Geological Society of America Special Paper 358, 211.
Chung, S. -L., Sun, S. -S. 1992. A new genetic model for the East Taiwan Ophiolite and its implications for Dupal domains in the Northern Hemisphere. Earth and Planetary Science Letters 109, 133–145.
DeBari, S.M., Taylor, B., Spencer, K., Fujioka, K., 1999. A trapped Philippine Sea plate origin for MORB from the inner slope of the Izu-Bonin trench. Earth and Planetary Science Letters 174, 183–197.
Eggins, S. M., Woodhead, J. D., Kinsley, L. P. J., Mortimer, G. E., Sylvester, P., McCulloch, M. T., Hergt J.M., & Handler, M. R. 1997. A simple method for the precise determination of≥ 40 trace elements in geological samples by ICPMS using enriched isotope internal standardisation. Chemical Geology 134(4), 311–326.
Escuder-Viruete, J., Friedman, R., Castillo-Carrión, M., Jabites, J., Pérez-Estaún, A., 2011. Origin and significance of the ophiolitic high-P mélanges in the northern Caribbean convergent margin: insights from the geochemistry and large-scale structure of the Río San Juan metamorphic complex. Lithos 127, 483–504.
Flower, M.F.J., Zhang, M., Chert, C.-Y., Tu, K. and Xie, G. 1992. Magmatism in the South China Basin, 2. Post-spreading Quaternary basalts from Hainan Island, south China. Chemical Geology 97, 65–87.
Floyd, P., Winchester, J., 1975. Magma type and tectonic setting discrimination using immobile elements. Earth and Planetary science letters 27, 211–218.
Grove, T.L., Kinzler, R.J., Bryan, W.B., 1992. Fractionation of mid-ocean ridge basalt (MORB). American Geophysical Union, Geophysical Monography 71, 281–310.
Guo, Z., Wilson, M., Zhang, L., Zhang, M., Cheng, Z., Liu, J., 2014. The role of subduction channel mélanges and convergent subduction systems in the petrogenesis of post-collisional K-rich mafic magmatism in NW Tibet. Litos 198–199, 184–201.
Hall, R., Ali, J.R., Anderson, C. D. 1995. Cenozoic motion of the Philippine Sea Plate: Palaeomagnetic evidence from eastern Indonesia. Tectonics 14 (5), 1117–1132.
Hall, R., 2002. Cenozoic geological and plate tectonic evolution of SE Asia and the SW Pacific: computer-based reconstructions, model and animations. Journal of Asian Earth Science 20, 353–431.
Hart, S. R., 1984. A large-scale isotope anomaly in the Southern Hemisphere mantle. Nature 309, 753–757.
Hayes, D. E., Lewis, S.D., 1984. A geophysical study of the Manila Trench, Luzon, Philippines: 1. Crustal structure, gravity, and regional tectonic evolution. Journal of Geophysical Research 89, 9171–9195.
Hickey-Vargas, R., 1991. Isotope characteristics of submarine lavas from the Philippine Sea: implications for the origin of arc and basin magmas of the Philippine tectonic plate. Earth and Planetary Science Letters 107, 290–304.
Hickey-Vargas, R., 1998. Origin of the Indian Ocean-type isotopic signature in basalts from Philippine Sea plate spreading centers: An assessment of localversus large-scale processes. Journal of Geophysical Research 103, 20963–20979.
Hickey-Vargas, R., Savov, I.P., Bizimis, M., Ishii, T., Fujioka, K., 2006. Origin of diverse geochemical signatures in igneous rocks from the West Philippine Basin: implications for tectonic models. In: Christie, D.M., Fisher, C.R., Lee, S.-M., Givens, S. (Eds.), Back-Arc Spreading Systems: Geological, Biological, Chemical and Physical Interactions. America Geophysical Union Geophysical Monograph 166, 287–303.
Hickey-Vargas, R., Bizimis, M., Deschamps, A., 2008. Onset of the Indian Ocean isotopic signature in the Philippine Sea Plate: Hf and Pb isotope evidence from Early Cretaceous terranes. Earth and Planetary Science Letters 268, 255–267.
Hirschmann, M.M., Stolper, E., 1996. A possible role for garnet pyroxenite in the origin of the ‘garnet signature’ in the MORB. Contributions to Mineralogy and Petrology 124, 185–208.
Ho, C., 1986. A synthesis of the geologic evolution of Taiwan. Tectonophysics 125, 1–16.
Huang, C.-Y., Wu,W.-Y., Chang, C.-P., Tsao, S., Yuan, P.B., Lin, C.-W., Xia, K.-Y., 1997. Tectonic evolution of accretionary prism in the arc–continent collision terrane of Taiwan. Tectonophysics 281, 31–51.
Huang, C.-Y., Yuan, P.-B., Lin, C.-W., Wang, T.-K., Chang, C.-P., 2000. Geodynamic processes of Taiwan arc–continent collision and comparison with analogs in Timor, Papua New Guinea,Urals and Corsica. Tectonophysics 325, 1–21.
Huang, C.-Y., Yuan, P.B., Tsao, S.-J., 2006. Temporal and spatial records of active arc–continent collision in Taiwan: a synthesis. Geological Society of America Bulletin 118, 274–288.
Jahn, B. 1986. Mid-ocean ridge or marginal basin origin of the East Taiwan Ophiolite: chemical and isotopic evidence. Contributions to Mineralogy and Petrology 92, 194–206.
Jaques, A.L., Green, D.H., 1980. Anhydrous melting of peridotite at 0 – 15 Kb pressure and the genesis of tholeiitic basalts. Contributions to Mineralogy and Petrology 73, 287–310.
Kempton, P.D., Pearce, J.A., Barry, T.L., Fitton, J.G., Langmuir, C., Christie, D.M., 2002. Sr‐Nd‐Pb‐Hf isotope results from ODP Leg 187: Evidence for mantle dynamics of the Australian‐Antarctic discordance and origin of the Indian MORB source. Geochemistry Geophysics Geosystems 3, 1–35.
Ker, C. -M., Yang, H. -J., Zhang, J., Shau, Y. -H., Chieh, C. -J., Meng, F., Takazawa, E., You, C. –F. 2015. Compositional and Sr–Nd–Hf isotopic variations of Baijingsi eclogites from the North Qilian orogen, China: Causes, protolith origins, and tectonic implications. Gondwana Research 28, 721–734.
Kinzler, R.J., Grove, T.L., 1992a. Primary magmas of mid-ocean ridge basalts, 1, Experiments and methods. Journal of Geophysical Research 97, 6885–6906.
Kinzler, R. J., Grove, T.L., 1992b. Primary magmas of mid ocean ridge basalts, 2, Applications. Journal of Geophysical Research 97, 6907–6926.
Langmuir, C.H., Klein, E.M., Plank, T., 1992. Petrological systematic of mid-ocean ridge basalts: constraints on melt generation beneath mid-ocean ridges. America Geophysical Union Geophysical Monography 71, 183–280.
Lee, C. -S., McCabe, R. 1986. The Banda-Celebes-Sulu basin: a trapped piece of Cretaceous-Eocene oceanic crust? Nature 322, 51–54.
Lee, Y.-H., Chen, C.-C., Liu, T.-K., Ho, H.-C., Lu, H.-Y., Lo, W., 2006. Mountain building mechanisms in the Southern Central Range of the Taiwan Orogenic Belt from accretionary wedge deformation to arc–continental collision. Earth and Planetary Science Letters 252, 413–422.
Lester, R., Mclntosh, K., Van Avendonk, H.J.A., Lavier, L. Liu, C.-S., Wang, T.K., 2013. Crustal accretion in the Minila trench accretionary wedge at the transition from subduction to mountain-building in Taiwan. Earth and Planetary Science Letters 375, 430–440.
Liu, Y. -H., Yang, H. -J., Takazawa, E., Satish-Kumar, M., You, C. -F. 2015. Decoupling of the Lu–Hf, Sm–Nd, and Rb–Sr isotope systems in eclogites and a garnetite from the Sulu ultra-high pressure metamorphic terrane: Causes and implications. Lithos, 234, 1–14.
Liu, C. -C. 2016. Geochemical characteristics and petrogenesis of basalts from Baolai in southern Taiwan. M.S. thesis, National Cheng-Kung University (in Chinese).
Malavieille, J., Molli, G., Genti, M., Dominguez, S., Beyssac, O., Taboada, A., Vitale-Brovarone, A., Lu, C. -Y., Chen, C. -T. 2016. Formation of ophiolite-bearing tectono-sedimentary mélanges in accretionary wedges by gravity driven submarine erosion: Insights from analogue models and case studies. Journal of Geodynamics, 100, 87 –103.
Moore, J.C., Byrne, T., 1987. Thickening of fault zones: a mechanism of mélange formation in accreting sediments. Geology 15, 1040–1043.
Neuman, H., Mead, J., Vitaliano, C.J., 1954. Trace element variation during fractional crystallization as calculated from the distribution law. Geochimica et Cosmochimica Acta 6, 90–99.
Ogata, K., Mutti, E., Pini, G. A., Tinterri, R., 2012. Mass transport-related stratal disruption within sedimentary mélanges: Examples from the northern Apennines (Italy) and south-central Pyrenees (Spain). Tectonophysics 568–569, 185–199.
Pearce, J.A., Kempton, P.D., Nowell, G.M., Noble, S.R., 1999. Hf–Nd element and isotope perspective on the nature and providence of mantle and subduction components in Western Pacific Arc-Basin systems. Journal of Petrology 40, 1579–1611.
Pearce, J.D., Kempton, P.D., Gill, J.B., 2007. Hf–Nd evidence for the origin and distribution of mantle domains in the SW Pacific. Earth and Planetary Science Letters 260, 98–114.
Rayleigh, J.W.S., 1896. Theoretical considerations respecting the separation of gases by diffusion and similar processes. Philosophical Magazine 42, 493–499.
Saccani, E. 2015. A new method of discriminating different types of post-Archean ophiolitic basalts and their tectonic significance using Th-Nb and Ce-Dy-Yb systematics. Geoscience Frontiers 6, 481–501.
Sayit, K., Bedi, Y., Kagan Tekin, U., Cemal Göncüoglu, M., Okuyucu, C., 2017. Middle Triassic back-arc basalts from the blocks in the Mersin Mélange, southern Turkey: Implications for the geodynamic evolution of the Northern Neotethys. Lithos 268–271, 102–113.
Savov, I.P., Hickey-Vargas, R., D'Antonio, M., Ryan, J.G., Spadea, P., 2006. Petrology and Geochemistry of West Philippine Basin Basalts and Early Palau–Kyushu Arc Volcanic Clasts from ODP Leg 195, Site 1201D: Implications for the Early History of the Izu–Bonin–Mariana Arc. Journal of Petrology 47, 277–299.
Shaw, D.M., 1970. Trace element fractionation during anatexis. Geochim. Cosmochim. 34, 237–243.
Sibuet, J.-C., Hsu, S.-K., Le Pichon, X., Le-Formal, J.-P., Reed, D., Moore, G., Liu, C.-S., 2002. East Asia plate tectonics since 15 Ma: constraints from the Taiwan region. Tectonophysics 344, 103–134.
Smith, A.D., Lewis, C., 2007. Geochemistry of metabasalts and associated metasedimentary rocks from the Lushan Formation of the Upthrust Slate Belt, south-central Taiwan. International Geology Review, 49, 1–13.
Stephan, J.F., Blanchet, R., Rangin, C., Pelletier, B., Letouzey, J., Muller, C., 1986. Geodynamic evolution of the Taiwan-Luzon-Mindoro belt since the late Eocene. Tectonophysics 125, 245–268.
Sun, S. -S., McDonough, W. F. 1989. Chemical and isotopic systematics of oceanic basalts: implications for mantle composition and processes. In: Saunders, A.D., Norry, M. J. (Eds.) Magmatism in the Ocean BasinsGeological Society, Special Publication 42, Blackwell Scientific Publications, London, 313–345.
Suppe, J., 1984. Kinematics of Arc-Continent collision, Flipping of subduction, and back-arc spreading near Taiwan. Memoir of the Geological Society of China 6, 21– 33.
Suppe, J., 1988. Tectonics of arc-continent collision on both side of the South China Sea: Taiwan and Mindoro. Acta Geologica Taiwanica 26, 1–18.
Shipboard Scientific Party (2015). Site U1433B. In: Li, C.-F., Lin, J., Kulhanek, D.K., the Expedition 349 Scientists. (Eds.). Proceedings of the International Ocean Discovery Program 349.
Takahashi, T., Shuto, K., 1997. Major and trace element analyses of silicate rocks using X-ray fluorescence spectrometry RIX3000. Rigaku-Denki Journal 28, 25–37 (in Japanese).
Teng, L.-S., Chen, W.-S., Wang, Y., Song, S.-R., Lo, H.-J., 1988. Toward a comprehensive stratigraphic system of the Coastal Range, eastern Taiwan. Acta Geologica Taiwanica 26, 19–35.
Teng, L.-S., 1990. Geotectonic evolution of the late Cenozoic arc–continent collision in Taiwan. Tectonophysics 183, 57–76.
Tsai, C.-H., 2017. Tectonic development and sediment provenances of the Luzon Island and Hengchun Peninsula from detrital zircon analysis. M.S. thesis, National Taiwan University.
Tu, K., Flower, M.F., Carlson, R.W., Xie, G., Chen, C.Y., Zhang, M., 1992. Magmatism in the South China Basin: 1. Isotopic and trace-element evidence for an endogenous Dupal mantle component. Chemical Geology 97, 47–63.
Vervoort, J.D., Patchett, P.J., Blichert-Toft, J., Albarède, F., 1999. Relationships between Lu–Hf and Sm–Nd isotopic systems in the global sedimentary system. Earth and Planetary Science Letters 168, 79–99.
Wood, D.A., Joron, J.-L., Marsh, N.G., Tarney, J., Treuil, M., 1980. Major and trace element variations in basalts from the North Phillipine Sea drilled during Deep Sea Drilling Project Leg 58, a comparative study of back-arc basin basalts with lava series from Japan and mid-ocean ridges. In: Initial Reports of the Deep Sea Drilling Project , U.S. Government Printing Office, Washington, D.C., 873–894.
Workman, R.K., Hart, S.R., 2005. Major and trace element composition of the depleted MORB mantle (DMM). Earth and Planetary Science Letters 231, 53–72.
Yamamoto, Y., Tonogai, K., Anma, R., 2012. Fabric-based criteria to distinguish tectonic from sedimentary mélanges in the Shimanto accretionary complex, Yakushima Island, SW Japan. Tectonophysics 568–569, 65–73.
Yan, Q., Castillo, P., Shi, X., Wang, L., Liao, L., Ren, J., 2015. Geochemistry and petrogenesis of volcanic rocks from Daimao Seamount (South China Sea) and their tectonic implications. Lithos 218–219, 117–126.
Yang, H. -J., Kinzler, R.J., Grove, T.L., 1996. Experiments and models of anhydrous, basaltic olivine-plagioclase-augite saturated melts from 0.001 to 10 kbar. Contributions to Mineralogy and Petrology 124, 1–18.
Yang, H. -J., Sen, G., Shimizu, N., 1998. Mid-ocean ridge melting: constraints from lithospheric xenoliths at Oahu, Hawaii. Journal of Petrology 39, 277–295.
Zhang, X., Yan, Y., Huang, C. -Y., Chen, D., Shan, Y., Lan, Q., Chen, W., Yu, M., 2014. Provenance analysis of the Miocene accretinoary prism of the Hengchun Peninsula, southern Taiwan, and regional geological significance. Journal of Asian Earth Science 85, 26–39.
Zhang, X., Cawood, P.A., Huang, C. -Y., Yan, Y., Santosh, M., Chen, W., Yu, M., 2016. From convegent plate margin to arc-continent collision: Formation of the Kenting melange, Southern Taiwan. Gondwana Research 38, 171–182.
Zindler, A., Hart, S., 1986. Chemical geodynamics. Annual Review of Earth and Planetary Sciences 14, 493–571.