Early Paleozoic subduction initiation in the West Proto-Tethys Ocean: Insights from ophiolitic Speik Complex in the Eastern Alps

Abstract

Subduction initiation is a critical part of the plate tectonic system, but its geodynamic process is still poorly understood due to the lack of well-preserved geological records. Based on new zircon U-Pb-Hf isotopic and whole-rock geochemical data, we report the first discovery of a latest Cambrian-Early Ordovician forearc-arc rock sequence in the Eastern Alps. This sequence includes granitic gneisses, amphibolites, and amphibole plagiogneisses from the ophiolitic Speik Complex and Gleinalpe Complex. These rocks exhibit geochemical affinities with typical oceanic plagiogranites, forearc basalts (FABs), and island arc basalts, respectively. The latest Cambrian plagiogranitic protoliths (491 ± 2 Ma) are shearing-type plagiogranites that were formed in the tectonic setting of forearc spreading. The latest Cambrian FABs (496-489 Ma) have similar geochemical compositions and positive ε_Hf(t) values (+2.5 to + 14.9) to the depleted mid-ocean ridge basalts. However, they show depletion in high field strength elements (HFSEs; e.g., Nb, Ta, and Zr) and have relatively low Ti/V ratios. These features suggest that they were derived from a depleted mantle source modified by subducting slab-released components in a forearc environment. The Early Ordovician basaltic protoliths (476-472 Ma) of amphibole plagiogneisses show enrichment in large ion lithophile elements and depletion in HFSEs (e.g. Nb, Ta, Zr, and Hf), implying a mature island arc environment. These metaigneous rocks, along with the coeval boninite-like high-Mg amphibolites near the study area, form a typical rock sequence resembling that of the Izu-Bonin-Mariana (IBM) arc system. The Speik and Gleinalpe complexes document a complete magmatic evolution from subduction initiation to mature arc development within the West Proto-Tethys Ocean. Integrating our new data with published work, we reconstruct the late Ediacaran-early Paleozoic tectonic evolution of the northern Gondwana. During the late Ediacaran-early Cambrian, the rollback of the West Proto-Tethys oceanic plate triggered the separation of the Wechsel-Silvretta-Gleinalpe continental arc from the northern Gondwana. This process led to the formation of the Speik back-arc oceanic basin, a southwestern branch of the West Proto-Tethys Ocean. In the latest Cambrian-Early Ordovician, subduction initiation occurred in the Speik Ocean, which subsequently developed into an intra-oceanic arc system. During the Early Devonian, the Speik Ocean closed and the Wechsel-Silvretta-Gleinalpe continental arc reattached to the Gondwana, as evidenced by the metamorphic event at ca. 400 Ma.

Keywords

Subduction initiation / West Proto-Tethys Ocean / Eastern Alps / Speik Complex / Early Paleozoic

CRediT authorship contribution statement

Qingbin Guan: Writing - original draft, Project administration, Methodology, Investigation, Funding acquisition, Formal analysis, Data curation, Conceptualization. Yongjiang Liu: Writing - review & editing, Supervision, Project administration, Investigation, Funding acquisition. Franz Neubauer: Writing - review & editing, Supervision, Investigation, Conceptualization. Johann Genser: Supervision, Investigation. Ruihong Chang: Methodology, Investigation. Boran Liu: Methodology, Data curation. Sanzhong Li: Supervision, Formal analysis. Qianwen Huang: Methodology, Investigation. Sihua Yuan: Methodology, Investigation, Formal analysis.

Declaration of competing interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgements

We gratefully acknowledge the insightful comments and suggestions of Prof. Chuan-Lin Zhang, Prof. Chen Wu, Prof. Chao Wang, and an anonymous reviewer. We also thank the Associate Editor Sanghoon Kwon for his comments and editorial handling. This study was financially supported by the National Natural Science Foundation of China (Grant Nos. 42272244 and 91755212) and Taishan Scholars (Grant No. ts20190918).

Appendix A. Supplementary data

Supplementary data to this article can be found online at https://doi.org/10.1016/j.gsf.2025.102121.

References

[1] Andersen T., 2002. Correction of common Lead in U-Pb analyses that do not report 204Pb. Chem. Geol. 192, 59-79.

[2] Arculus R.J., Ishizuka O., Bogus K.A., Gurnis M., Hickey-Vargas R., Aljahdali M.H., Bandini-Maeder A.N., Barth A.P., Brandl P.A., Drab L., do Monte Guerra R., Hamada M., Jiang F., Kanayama K., Kender S., Kusano Y., Li H., Loudin L.C., Maffione M., Marsaglia K.M., McCarthy A., Meffre S., Morris A., Neuhaus M., Savov I.P., Sena C., Tepley III F.J., van der Land C., Yogodzinski G.M., Zhang Z., 2015. A record of spontaneous subduction initiation in the Izu-Bonin-Mariana Arc. Nat. Geosci. 8, 728-733.

[3] Bekaert D.V., Turner S.J., Broadley M.W., Barnes J.D., Halld´ orsson S.A., Labidi J., Wade J., Walowski K.J., Barry P.H., 2021. Subduction-driven volatile recycling: a global mass balance. Annu. Rev. Earth Planet. Sci. 49, 37-70.

[4] Bellot N., Boyet M., Doucelance R., Bonnand P., Savov I.P., Plank T., Elliott T., 2018. Origin of negative cerium anomalies in subduction-related volcanic samples: Constraints from Ce and Nd isotopes. Chem. Geol. 500, 46-63.

[5] Black L.P., Kamo S.L., Allen C.M., Aleinikoff C.M., Davis D.W., Korsch R.J., Foudoulis C., 2003. TEMORA 1: a new zircon standard for Phanerozoic U-Pb geochronology. Chem. Geol. 200, 155-170.

[6] Boynton W.V., 1984. Geochemistry of the rare earth elements:meteorite studies. In: HendersonP. (Ed.), Rare Earth Element Geochemistry. Elsevier, pp. 63-114.

[7] Brophy J.G., 2009. La-SiO₂ and Yb-SiO₂ systematics in mid-ocean ridge magmas: implications for the origin of oceanic plagiogranite. Contrib. Mineral. Petrol. 158, 99-111.

[8] Brounce M., Kelley K.A., Cottrell E., Reagan M.K., 2015. Temporal evolution of man-tle wedge oxygen fugacity during subduction initiation. Geology 43, 775-778.

[9] Burda J., Klötzli U., Majka J., Chew D., Li Q.-L.-L., Liu Y., Gawe˛da A., Wiedenbeck M., 2021. Tracing proto-Rheic - Qaidam Ocean vestiges into the Western Tatra Mountains and implications for the Palaeozoic palaeogeography of Central Europe. Gondwana Res. 91, 188-204.

[10] Chang R.H., Neubauer F., Liu Y.J., Yuan S.H., Genser J., Huang Q.W., Guan Q.B., Yu S.Y., 2021. Hf isotopic constraints for the Austroalpine basement evolution of Eastern Alps: Review and new data. Earth-Sci. Rev. 221, 103772.

[11] Chang R.H., Neubauer F., Liu Y.J., Genser J., Guan Q.B., Huang Q.W., Yuan S.H., 2023. Permian to Triassic protolith ages of type locality eclogites in the Eastern Alps: Implications for the opening of the Meliata back-arc basin. Geology 51, 537-542.

[12] Chu N.C., Taylor R.N., Chavagnac V., Nesbitt R.W., Boella R.M., Milton J.A., German C.R., Bayon G., Burton K., 2002. Hf isotope ratio analysis using multicollector inductively coupled plasma mass spectrometry: an evaluation of isobaric interference corrections. J. Anal. at. Spectrom. 17, 1567-1574.

[13] Corfu F., Hanchar J.M., Hoskin P.W.O., Kinny P., 2003. Atlas of Zircon Textures. Rev. Mineral. Geochem. 53, 469-500.

[14] Defant M.J., Drummond M.S., 1993. Mount St. Helens: potential example of the partial melting of the subducted lithosphere in a volcanic arc. Geology 21, 547-550.

[15] Faryad S.W., Hoinkes G., Melcher F., Puhl J., Meisel T., Frank W., 2002. Relics of eclogite facies metamorphism in the Austroalpine basement, Hochgröben (Speik complex). Austria. Mineral. Petrol. 74, 49-73.

[16] Faryad S.W., Hoinkes G., 2004. Complex Growth Textures in a Polymetamorphic Metabasite from the Kraubath Massif (Eastern Alps). J. Petrol. 45, 1441-1451.

[17] Faryad S.W., Hoinkes G., 2006. Reaction textures in Al-rich metabasite; implication for metamorphic evolution of the eastern border of the Middle Austroalpine basement units. Lithos 90, 145-157.

[18] Flagler P.A., Spray J.G., 1991. Generation of plagiogranite by amphibolite anataxis in oceanic shear zones. Geology 19, 70-73.

[19] Floyd P.A., Yaliniz M.K., Goncuoglu M.C., 1998. Geochemistry and petrogenesis of intrusive and extrusive ophiolitic plagiogranites, Central Anatolian Crystalline complex, Turkey. Lithos 42, 225-241.

[20] Forsyth D., Uyeda S., 1975. On the relative importance of the driving forces of plate motion. Geophys. J. Int. 43, 163-200.

[21] Franke W., Cocks L.R.M., Torsvik T.H., 2017. The Palaeozoic Variscan oceans revisited. Gondwana Res. 48, 257-284.

[22] Fu D., Huang B., Johnson T.E., Wilde S.A., Jourdan F., Polat A., Windley B.F., Hu Z. C., Kusky T., 2021. Boninitic blueschists record subduction initiation and subsequent accretion of an arc-forearc in the northeast Proto-Tethys Ocean. Geology 50, 10-15.

[23] Ghatak A., Basu A.R., Wakabayashi J., 2012. Elemental mobility in subduction metamorphism: insight from metamorphic rocks of the Franciscan complex and the Feather River ultramafic belt, California. Int. Geol. Rev. 54, 654-685.

[24] Gillis K.M., Coogan L.A., 2002. Anatectic migmatites from the roof of an ocean ridge magma chamber. J. Petrol. 43, 2075-2095.

[25] Guan Q.B., Liu Y.J., Neubauer F., Li S.Z., Genser J., Yuan S.H., Chang R.H., Huang Q. W., Fang Q.A., 2021. Opening of the West Paleo-Tethys Ocean: New insights from earliest Devonian meta-mafic rocks in the Saualpe crystalline basement, Eastern Alps. Gondwana Res. 97, 121-137.

[26] Guilmette C., Smit M.A., van Hinsbergen D.J.J., et al., 2018. Forced subduction initiation recorded in the sole and crust of the Semail Ophiolite of Oman. Nat. Geosci. 11, 688-695.

[27] Haas I., Eichinger S., Haller D., Fritz H., Nievoll J., Mandl M., Hippler D., Hauzenberger C., 2020. Gondwana fragments in the Eastern Alps: a travel story from U/Pb zircon data. Gondwana Res. 77, 204-222.

[28] Haase K.M., Freund S., Beier C., Koepke J., Erdmann M., Hauff F., 2016. Constraints on the magmatic evolution of the oceanic crust from plagiogranite intrusions in the Oman ophiolite. Contrib. Mineral. Petrol. 171, 46.

[29] Haiss N., 1992. Untersuchungen zur Genese von Plagioklasgneisen im Basiskristallin der Ostalpen (Gleinalm-, ötztal und Sivrettakristallin), Tübinger Geowiss. Arb. Reihe A 10, 1-142.

[30] Handler R., Neubauer F., Hermann S., Dallmeyer R.D., 1999. Silurian-Devonian 40Ar/39Ar mineral ages from the Kaintaleck nappe: evidence for mid-Paleozoic tectonothermal activity in Upper Austroalpine basement units of the Eastern Alps (Austria). Geol. Carpath. 50, 229-239.

[31] Hawkesworth C.J., Cawood P.A., Dhuime B., Kemp T.I., 2017. Earth’s continental lithosphere through time. Annu. Rev. Earth Planet. Sci. 45, 169-198.

[32] Hickey-Vargas R., Yogodzinski G.M., Ishizuka O., McCarthy A., Bizimis M., Kusano Y., Savov I.P., Arculus R., 2018. Origin of depleted basalts during subduction initiation and early development of the Izu-Bonin-Mariana island arc: evidence from IODP expedition 351 site U1438. Amami-Sankaku Basin. Geochim. Cosmochim. Acta 229, 85-111.

[33] Hoinkes G., Koller F., Rantitsch G., Dachs E., Höck V., Neubauer F., Schuster R., 1999. Alpine metamorphism of the Eastern Alps. Schweiz. Mineral. Petrogr. Mitt. 79, 155-181.

[34] Hoskin P.W.O., Schaltegger U., 2003. The composition of zircon and igneous and metamorphic petrogenesis. Rev. Mineral. Geochem. 53, 27-62.

[35] Hou K.J., Li Y.H., Zou T.R., Qu X.M., Shi Y.R., Xie G.Q., 2007. Laser ablation-MC-ICPMS technique for Hf isotope microanalysis of zircon and its geological applications. Acta Petrol. Sin. 23, 2595-2604 (in Chinese with English abstract)

[36] Hu P.Y., Li C., Wu Y.W., Xie C.M., Wang M., Li J., 2014. Opening of the Longmu Co-Shuanghu-Lancangjiang Ocean: constraints from plagiogranites. Chin. Sci. Bull. 59, 3188-3199.

[37] Huang Q.W., Genser J., Liu Y.J., Neubauer F., Yuan S.H., Bernroider M., Guan Q.B., Jin W., Yu S.Y., Chang R.H., 2021. Cambrian-Ordovician continental magmatic arc at the northern margin of Gondwana: Insights from the Schladming complex, Eastern Alps. Lithos 388-389, 106064.

[38] Huang Q.W., Neubauer F., Liu Y.J., Genser J., Guan Q.B., Chang R.H., Yuan S.H., Yu S.Y., 2022. Permian-Triassic granites of the Schladming complex (Austroalpine basement): Implications for subduction of the Paleo-Tethys Ocean in the Eastern Alps. Gondwana Res. 109, 205-224.

[39] Ishizaka K., Yanagi T., 1975. Occurrence of oceanic plagiogranites in the older tectonic zone. Southwest Japan. Earth Planet. Sci. Lett. 27, 371-377.

[40] Ishizuka O., Tani K., Reagan M.K., Kanayama K., Umino S., Harigane Y., Sakamoto I., Miyajima Y., Yuasa M., Dunkley D.J., 2011. The timescales of subduction initiation and subsequent evolution of an oceanic island arc. Earth Planet. Sci. Lett. 306, 229-240.

[41] Ishizuka O., Tani K., Reagan M.K., 2014. Izu-Bonin-Mariana forearc crust as a modern ophiolite analogue. Elements 10 (2), 115-120.

[42] Ishizuka O., Taylor R.N., Umino S., Kanayama K., 2020. Geochemical evolution of arc and slab following subduction initiation: a record from the Bonin Islands, Japan. J. Petrol. 61, egaa050.

[43] Jochum K.P., Weis U., Stoll B., Kuzmin D., Yang Q., Raczek I., Jacob D.E., Stracke A., Birbaum K., Frick D.A., Günther D., Enzweiler J., 2011. Determination of reference values for NIST SRM 610-617 glasses following ISO guidelines. Geostand. Geoanal. Res. 35, 397-429.

[44] 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. Geochem. Geophys. Geosyst. 3, 1074.

[45] Kerrich R., Said N., Manikyamba C., Wyman D., 2013. Sampling oxygenated Archean hydrosphere: Implications from fractionations of Th/U and Ce/Ce* in hydrothermally altered volcanic sequences. Gondwana Res. 23, 506-525.

[46] Koepke J., Berndt J., Feig S.T., Holtz F., 2007. The formation of SiO₂-rich melts within the deep oceanic crust by hydrous partial melting of gabbros. Contrib. Mineral. Petrol. 153, 67-84.

[47] Kohút M., Linnemann U., Hofmann M., Gärtner A., Zieger J., 2022. Provenance and detrital zircon study of the Tatric Unit basement (Western Carpathians, Slovakia). Int. J. Earth Sci. 111, 2149-2168.

[48] Konzett J., Miller C., Armstrong R., Thöni M., 2005. Metamorphic Evolution of Ironrich Mafic Cumulates from the Ötztal-Stubai Crystalline complex, Eastern Alps, Austria. J. Petrol. 46, 717-747.

[49] Koschek G., 1993. Origin and significance of the SEM cathodoluminescence from zircon. J. Microsc. 171, 223-232.

[50] Lesher M.C., Burnham M.O., Keays R.R., Barnes S.J., Hulbert L., 2001. Traceelement geochemistry and petrogenesis of barren and ore-associated komatiites. Can. Mineral. 39, 673-696.

[51] Li S.Z., Zhao S.J., Liu X., Cao H.H., Yu S., Li X.Y., Somerville I., Yu S.Y., Suo Y.H., 2018. Closure of the Proto-Tethys Ocean and Early Paleozoic amalgamation of microcontinental blocks in East Asia. Earth-Sci. Rev. 186, 37-75.

[52] Li W.X., Li X.H., 2003. Rock types and tectonic significance of the granitoids rocks within ophiolites. Adv. Earth. Sci. 18, 392-397.

[53] Li Y.J., Wang G.H., Santosh M., Wang J.F., Dong P.P., Li H.Y., 2020. Subduction initiation of the SE Paleo-Asian Ocean: evidence from a well preserved intraoceanic forearc ophiolite fragment in central Inner Mongolia, North China. Earth Planet. Sci. Lett. 535, 116087.

[54] Liu Y.J., Genser J., Handler R., Friedl G., Neubauer F., 2001. 40Ar/39Ar muscovite ages from the Penninic-Austroalpine plate boundary, Eastern Alps. Tectonics 20, 526-547.

[55] Liu Y.S., Hu Z.C., Gao S., Gunther D., Xu J., Gao C.G., Chen H.H., 2008. In situ analysis of major and trace elements of anhydrous minerals by LA-ICP-MS without applying an internal standard. Chem. Geol. 257, 34-43.

[56] Ludwig K.R., 2003. User’s manual for Isoplot 3.0: a geochronological toolkit for Microsoft Excel. Berkeley Geochronology Center Special Publication 4, 1-70.

[57] Mandl M., Kurz W., Hauzenberger C., Fritz H., Klötzli U., Schuster R., 2018. Pre-Alpine evolution of the Seckau complex (Austroalpine basement/Eastern Alps): Constraints from in-situ LA-ICP-MS U-Pb zircon geochronology. Lithos 296-299, 412-430.

[58] Melcher F., Meisel T., Puhl J., Koller F., 2002. Petrogenesis and geotectonic setting of ultramafic rocks in the Eastern Alps: constraints from geochemistry. Lithos 65, 69-112.

[59] Melcher F., Meisel T., 2004. A metamorphosed early Cambrian crust-mantle transition in the Eastern Alps, Austria. J. Petrol. 45, 1689-1723.

[60] Meschede M., 1986. A method of discriminating between different types of midocean ridge basalts and continental tholeiites with the Nb-Zr-Y diagram. Chem. Geol. 56, 207-218.

[61] Ménot R.P., Peucat J.J., Scarenzi D., Piboule M., 1988. 496 my age of plagiogranites in the Chamrousse ophiolite complex (external crystalline massifs in the French Alps): evidence of a lower Paleozoic oceanization. Earth Planet. Sci. Lett. 88, 82-92.

[62] Miller C., Thöni M., 1995. Origin of eclogites from the Austroalpine ötztal basement (Tirol, Austria): geochemistry and Sm-Nd vs. Rb-Sr isotope systematics. Chem. Geol. 122, 199-225.

[63] Morel M.L.A., Nebel O., Nebel-Jacobsen Y.J., Miller J.S., Vroon P.Z., 2008. Hafnium isotope characterization of the GJ-1 zircon reference material by solution and laser-ablation MC-ICPMS. Chem. Geol. 255, 231-235.

[64] Nandedkar R.H., Ulmer P., Müntener O., 2014. Fractional crystallization of primitive, hydrous arc magmas: an experimental study at 0.7 GPa. Contrib. Mineral. Petrol. 167, 1015.

[65] Neal C.R., Taylor L.A., 1989. A negative Ce anomaly in a peridotite xenolith: evidence for crustal recycling into the mantle or mantle metasomatism? Geochim. Cosmochim. Acta 53, 1035-1040.

[66] Neubauer F., 2002. Evolution of late Neoproterozoic to early Paleozoic tectonic elements in central and southeast European alpine mountain belts: review and synthesis. Tectonophysics 352, 87-103.

[67] Neubauer F., Dallmeyer R.D., Dunkl I., Schirnik D., 1995. Late cretaceous exhumation of the metamorphic Gleinalm dome, Eastern Alps: kinematics, cooling history and sedimentary response in a sinistral wrench corridor. Tectonophysics 242, 79-98.

[68] Neubauer F., Frisch W., 1993. The Austro-Alpine metamorphic basement east of the Tauern window. In: von Raumer, J.F., NeubauerF. (Pre-MesozoicGeology in the Alps.Eds.), Springer, Berlin, pp. 515-536.

[69] Neubauer F., Frisch W., Hansen B.T., 2003. Early Paleozoic and Variscan events in the Austroalpine Rennfeld block, Eastern Alps: a U-Pb zircon study. Jahrb. Geol. Bundesanst. 143 (4), 567-580.

[70] Neubauer F., Frisch W., Schmerold R., Schlöser H., 1989. Metamorphosed and dismembered ophiolite suites in the basement units of the Eastern Alps. Tectonophysics 164, 49-62.

[71] Neubauer F., Handler R., 2000. Variscan orogeny in the Bohemian Massif and Eastern Alps: how do these units correlate? Mitt. Oesterr. Geol. Ges. 92, 35-59.

[72] Neubauer F., Genser J., Handler R., 2000. The Eastern Alps: result of a two-stage collision process. Mitt. Oesterr. Geol. Ges. 92, 117-134.

[73] Neubauer F., Liu Y.J., Chang R.H., Yuan S.H., Yu S.Y., Genser J., Liu B.R., Guan Q.B., 2020. The Wechsel Gneiss complex of Eastern Alps: an Ediacaran to Cambrian continental arc and its Early Proterozoic hinterland. Swiss J. Geosci. 113, 21.

[74] Neubauer F., Liu Y.J., Dong Y.P., Chang R.H., Genser J., Yu S.Y., 2022. Pre-Alpine tectonic evolution of the Eastern Alps: from Prototethys to Paleotethys. Earth-Sci. Rev. 226, 103923.

[75] Pearce J.A., 1982. Trace element characteristics of lavas from destructive plate boundaries. In: ThorpsR.S. (Ed.), Andesites. John Wiley and Sons, New York, pp. 525-548.

[76] Pearce J.A., 1996. A user’s guide to basalt discrimination diagrams. In: WymanD.A. (Ed.), Trace Element Geochemistry of Volcanic Rocks:Applications for Massive Sulphide Exploration. Geological Association of Canada, Winnipeg, pp. 79-114.

[77] Pearce J.A., 2008. Geochemical fingerprinting of oceanic basalts with applications to ophiolite classification and the search for Archean oceanic crust. Lithos 100, 14-48.

[78] Pearce J.A., Robinson P.T., 2010. The Troodos ophiolitic complex probably formed in a subduction initiation, slab edge setting. Gondwana Res. 18, 60-81.

[79] Peccerillo A., Taylor A.R., 1976. Geochemistry of Eocene calc-alkaline volcanic rocks from the Kastamonu area, Northern Turkey. Contrib. Mineral. Petrol. 58 (1), 63-81.

[80] Pirajno F., 2016. A classification of mineral systems, overviews of plate tectonic margins and examples of ore deposits associated with convergent margins. Gondwana Res. 33, 44-62.

[81] Polat A., Hofmann A.W., 2003. Alteration and geochemical patterns in the 3.7-3.8 Ga Isua greenstone belt West Greenland. Precamb. Res. 126, 197-218.

[82] Polat A., Hofmann A.W., Rosing M.T., 2002. Boninite-like volcanic rocks in the 3.7-3.8 Ga Isua greenstone belt, West Greenland: geochemical evidence for intraoceanic subduction zone processes in the early Earth. Chem. Geol. 184, 231-254.

[83] Reagan M.K., Ishizuka O., Stern R.J., Kelley K.A., Ohara Y., Blichert-Toft J., Bloomer S.H., Cash J., Fryer P., Hanan B., Hickey-Vargas R., Ishii T., Kimura J.-I., Peate D.W., Rowe M.C., Woods M., 2010. Fore-arc basalts and subduction initiation in the Izu-Bonin-Mariana system. Geochem. Geophys. Geosyst. 11, 1-17.

[84] Reagan M.K., Heaton D.E., Schmitz M.K., Pearce J.A., Shervais J.W., Koppers A.A.P., 2019. Forearc ages reveal extensive short-lived and rapid seafloor spreading following subduction initiation. Earth Planet. Sci. Lett. 506, 520-529.

[85] Scarrow J.H., Pease V., Fleutelot C., Dushin V., 2001. The late Neoproterozoic Enganepe ophiolite, Polar urals, Russia: an extension of the Cadomian arc? Precambrian Res. 110, 255-275.

[86] Schmid S.M., Fügenschuh B., Kissling E., Schuster R., 2004. Tectonic map and overall architecture of the Alpine orogen. Eclogae Geol. Helv. 97, 93-117.

[87] Schmid S.M., Fügenschuh B., Kounov A., Mat_enco L., Nievergelt P., Oberhänsli R., Pleuger J., Schefer S., Schuster R., Tomljenovic´ B., Ustaszewski K., van Hinsbergen D.J.J., 2020. Tectonic units of the Alpine collision zone between Eastern Alps and western Turkey. Gondwana Res. 78, 308-374.

[88] Schulz B., Bombach K., Pawlig S., Brätz H., 2004. Neoproterozoic to Early-Palaeozoic magmatic evolution in the Gondwana-derived Austroalpine basement to the south of the Tauern Window (Eastern Alps). Int. J. Earth Sci. 93, 824-843.

[89] Song S.G., Bi H.Z., Qi S.S., Yang L.M., Allen M.B., Niu Y.L., Su L., Li W.F., 2018. HP-UHP Metamorphic Belt in the East Kunlun Orogen: Final Closure of the Proto-Tethys Ocean and Formation of the Pan-North-China Continent. J. Petrol. 59, 2043-2060.

[90] Stampfli G.M., Borel G.D., 2002. A plate tectonic model for the Paleozoic and Mesozoic constrained by dynamic plate boundaries and restored synthetic oceanic isochrons. Earth Planet. Sci. Lett. 196, 17-33.

[91] Stern R.J., 2004. Subduction initiation: Spontaneous and induced. Earth Planet. Sci. Lett. 226, 275-292.

[92] Stern R.J., Reagan M., Ishizuka O., Ohara Y., Whattam S., 2012. To understand subduction initiation, study forearc crust: to understand forearc crust, study ophiolites. Lithosphere 4, 469-483.

[93] Stern R.J., Gerya T., 2018. Subduction initiation in nature and models: a review. Tectonophysics 746, 173-198.

[94] Sun S.S., McDonough W.F., 1989. Chemical and isotopic systematics of oceanic basalts:implications for mantle composition and processes. In: SaundersA.D., NorryM.J. (Magmatismin Ocean Basins,Eds.), vol. 27. Geological Society of Special Publication, London, pp. 313-345.

[95] von Raumer J.F., Stampfli G.M., Bussy F., 2003. Gondwana-derived microcontinents—the constituents of the Variscan and Alpine collisional orogens. Tectonophysics 365, 7-22.

[96] von Raumer J.F., Bussy F., Schaltegger U., Schulz B., Stampfli G.M., 2013. Premesozoic alpine basements—their place in the european Paleozoic framework. Geol. Soc. Am. Bull. 125, 89-108.

[97] von Raumer J.F., Stampfli G.M., Arenas R., Martínez S.S., 2015. Ediacaran to Cambrian oceanic rocks of the Gondwana margin and their tectonic interpretation. Int. J. Earth Sci. 104, 1107-1121.

[98] Wang C., Song S.G., Zhao G.C., Allen M.B., Su L., Gao T.Y., Wen T., Feng D., 2023. Calc-Alkaline Plutons in a Proto-Tethyan Intra-Oceanic Arc (Qilian Orogen, NW China): Implications for the Construction of Arc Crust. J. Petrol. 64, egac131.

[99] Wang C., Song S.G., Zhao G.C., Allen M.B., Su L., Ackerman L., Sláma J., Zhang D. H., Wen T., Feng D., Strnad L., 2024. Tracing DUPAL anomaly evolution in the Tethyan-Indian oceanic mantle. Geochim. Cosmochim. Acta 368, 50-63.

[100] Wen T., Song S.G., Wang C., Allen M.B., Dong J., Feng D., Su L., 2022. IBM-type forearc magmatism in the Qilian Orogen records evolution from a continental to an intra-oceanic arc system in the Proto-Tethyan Ocean. Gondwana Res. 110, 197-213.

[101] Whattam S., Stern R.J., 2015. Late cretaceous plume-induced subduction initiation along the southern and eastern margins of the Caribbean: the first documented example with implications for the onset of plate tectonics. Gondwana Res. 27, 38-63.

[102] Whitehead J., Dunning G.R., Spray J.G., 2000. U-Pb geochronology and origin of granitoid rocks in the Thetford Mines ophiolite, Canadian Appalachians. Geol. Soc. Am. Bull. 112, 915-928.

[103] Wiedenbeck M., Alle P., Corfu F., Griffin W.L., Meier M., Oberli F., von Quadt A., Roddick J.C., Spiegel W., 1995. Three natural zircon standards for U-Th-Pb, Lu-Hf, trace element and REE analyses. Geostand. Newsl. 19, 1-23.

[104] Williams I.S., 1998. U-Th-Pb geochronology by ion microprobe. In: McKibbenM. A., ShanksW.C., RidleyW.I. (Applications of Microanalytical Techniques to Understanding Mineralizing Processes.Eds.), Reviews in Economic Geology, vol. 7, pp. 1-35.

[105] Wood D.A., 1980. The application of a Th-Hf-Ta diagram to problems of tectonomagmatic classification and to establishing the nature of crustal contamination of basaltic lavas of the british tertiary volcanic province. Earth Planet. Sci. Lett. 50, 11-30.

[106] Xia L.Q., 2014. The geochemical criteria to distinguish continental basalts from arc related ones. Earth-Sci. Rev. 139, 195-212.

[107] Xu Y.G., Wang Q., Tang G.J., Wang J., Li H.Y., Zhou J.S., Li Q.W., Qi Y., Liu P.P., Ma L., Fan J.J., 2020. The origin of arc basalts: New advances and remaining questions. Sci. China: Earth Sci. 63, 1969-1991.

[108] Yang G.X., Li Y.J., Tong L.L., Wang Z.P., Si G.H., Lindagato P., Zeng R., 2022. Natural observations of subduction initiation: Implications for the geodynamic evolution of the Paleo-Asian Ocean. Geosyst. Geoenviron. 1, 100009.

[109] Yuan S.H., Liu Y.J., Neubauer F., Chang R.H., Genser J., Guan Q.B., Huang Q.W., 2020. Tectonic evolution of Proto-and Paleo-Tethyan in the East Alps. Acta Petrol. Sin. 36, 2357-2382 (in Chinese with English abstract)

[110] Zhang A.K., Tang Y.J., Ying J.F., Ma C., Liu H., 2025. Mantle plume- induced subduction initiation: Mechanisms and implications for plate tectonics. Gondwana Res. 140, 205-228.

[111] Zhang C.L., Zou H.B., Ye X.T., Chen X.Y., 2019. Tectonic evolution of the West Kunlun Orogenic Belt along the northern margin of the Tibetan Plateau: implications for the assembly of the Tarim terrane to Gondwana. Geosci. Front. 10, 973-988.

[112] Zhang Q.C., Li Z.H., Wu Z.H., Chen X.H., Zhang J.E., Yang Y., 2022. Subduction initiation of the western Proto-Tethys Ocean: New evidence from the Cambrian intra-oceanic forearc ophiolitic mélange in the western Kunlun Orogen, NW Tibetan Plateau. Geol. Soc. Am. Bull. 134, 145-159.

[113] Zhu R.X., Zhao P., Zhao L., 2022. Tectonic evolution and geodynamics of the Neo-Tethys Ocean. Sci. China: Earth Sci. 65 (1), 1-24.

[114] Žák J., Svojtka M., Gerdjikov I., Kounov A., Vangelov D.A., 2021. The Balkan terranes: a missing link between the eastern and western segments of the Avalonian-Cadomian orogenic belt? Int. Geol. Rev. 64, 2389-2415.