Early Permian Tarim Large Igneous Province in northwest China

Tarim Large Igneous Province (TLIP) is the second Late Paleozoic LIPs in China after the recognition of Emeishan LIP, and is a hot research topic in geosciences. On the basis of the analysis of research history about TLIP, this paper summarizes the research result during last twenty years and suggests the key research area in the future. The residual distribution range of TLIP is up to 250000 km², and the largest residual thickness is 780 m. The eruption of basalt happened during 290–288 Ma and belongs to LIPs magmatic event with fast eruption of magma. The lithological units of the TLIP include basalt, diabase, layered intrusive rock, breccia pipe mica-olivine pyroxenite, olivine pyroxenite, gabbro, ultramafic dyke, quartz syenite, quartz syenite porphyry and bimodal dyke. The basalt and diabase of TLIP exhibit OIB-like trace element patterns and enrichment of LILE and HFSE, and mainly belong to high TiO₂ series. There is an obvious difference in isotope among the basalt from Keping and the basalt and dibase from the northern Tarim Basin. The basalt from Keping with negative ? _Nd and high REE value derives from enriched mantle, and the diabase and basalt from the northern Tarim Basin with positive ? _Nd and low REE value are related to depleted mantle. The crust uplifting in the Early Permian and the development of picrite and large scale dyke and formation of large scale V-Ti-Magnetite deposit in Wajilitag area support the view that the TLIP is related to mantle plume. The TLIP has a temporal-spatial relationship with Permian basic to ultra-basic igneous rock, which is distributed widely in Central Asia, and they represent a tectono-magmatic event with very important geodynamic setting. This paper also suggests that the deep geological process, the relation with mantle plume, mineralization, the relation with environmental change and biological evolution, and the geodynamics of the TLIP will be the key research topics in the future.     

Origin of Icelandic basalts: A review of their petrology and geochemistry

The petrology and geochemistry of Icelandic basalts have been studied for more than a century. The results reveal that the Holocene basalts belong to three magma series: two sub-alkaline series (tholeiitic and transitional alkaline) and an alkali one. The alkali and the transitional basalts, which occupy the off-rift volcanic zones, are enriched in incompatible trace elements compared to the tholeiites, and have more radiogenic Sr, Pb and He isotope compositions. Compared to the tholeiites, they are most likely formed by partial melting of a lithologically heterogeneous mantle with higher proportions of melts derived from recycled oceanic crust in the form of garnet pyroxenites compared to the tholeiites. The tholeiitic basalts characterise the mid-Atlantic rift zone that transects the island, and their most enriched compositions and highest primordial (least radiogenic) He isotope signature are observed close to the centre of the presumed mantle plume. High-MgO basalts are found scattered along the rift zone and probably represent partial melting of refractory mantle already depleted of initial water-rich melts. Higher mantle temperature in the centre of the Iceland mantle plume explains the combination of higher magma productivity and diluted signatures of garnet pyroxenites in basalts from Central Iceland. A crustal component, derived from altered basalts, is evident in evolved tholeiites and indeed in most basalts; however, distinguishing between contamination by the present hydrothermally altered crust, and melting of recycled oceanic crust, remains non-trivial. Constraints from radiogenic isotope ratios suggest the presence of three principal mantle components beneath Iceland: a depleted upper mantle source, enriched mantle plume, and recycled oceanic crust.The study of glass inclusions in primitive phenocrysts is still in its infancy but already shows results unattainable by other methods. Such studies reveal the existence of mantle melts with highly variable compositions, such as calcium-rich melts and a low-¹⁸O mantle component, probably recycled oceanic crust. Future high-resolution seismic studies may help to identify and reveal the relative proportions of different lithologies in the mantle.     

Geochemistry of ophiolite cherts from the Qinling orogenic belt and implications for their tectonic settings

Since the 1980s, one of the important progresses in the study of the Qinling orogenic belt is marked by findings of numerous ophiolite zones[1—4]. On the basis of the former orogenic models of the Paleozoic colli-sional orogeny[1,5,6] and the Mesozoic collision[7—9], another orogenic evolution model from the Paleozoic subduction-collision along the Shangdan suture to the Mesozoic final collision orogeny along the Mianle suture[3,10], including the relicts of the Jining orogeny, has been pr…     

Indian Ocean-MORB-type isotopic signature of Yushigou ophiolite in North Qilian Mountains and its implications

Many researchers have focused on the tectonic evolution of North Qilian Mountains (NQM) since the 1970s[1―7]. However, the tectonic affinity of the an- cient oceanic mantle in early Paleozoic remains in de-bate. Three general explanations for it have been pro- posed. The first one suggests that the ancient ocean was a part of Proto-Tethys, and the tectonic evolution of NQM should be regarded as a portion of the562 Science in China: Series D Earth Sciences Tethyan tectonic domain[1]. …     

扬子地块古生代大地构造演化及古地磁学研究综述

本文简要地论述了扬子地块古生代大地构造研究现状，扬子与华夏地块之间的华南裂谷盆地于奥陶纪初发生收缩，直到加里东末期基本封闭，古生代扬子地块与华北地块之间的秦岭海槽以拉张为主，扬子地块西缘古生代期间处于相对稳定的构造环境，古生代末进入特提斯构造域，发生活化。     

Petrogenetic model of the Permian Tarim Large Igneous Province

Over the last two decades great strides have been made in characterizing the spatial distribution, time sequence,geochemical characteristics, mantle sources, and magma evolution processes for various igneous rocks in the Early Permian Tarim Large Igneous Province(TLIP). This work has laid a solid foundation for revealing the evolutionary processes and genetic models of large igneous provinces(LIPs). This study systematically demonstrates the two-stage melting model for the TLIP based on our previous research work and predecessor achievements, and highlights the two types of magmatic rocks within the TLIP.The two-stage melting model suggests that the formation of the TLIP is mantle plume related. The early hot mantle plume caused the low-degree partial melting of the lithosphere mantle, while in the later stage, the plume partially melted due to adiabatic uplift and decompression. Therefore, this model carries signatures of both the "Parana" and "Deccan" models in terms of mantle plume activity. During the early stage, the mantle plume provided the heat required for partial melting of sub-continental lithosphere mantle(SCLM), similar to the "Parana Model", while later the plume acted as the main avenue for melting, as in the "Deccan Model". Basalts that erupted in the first stage have higher 87Sr/86 Sr, lower 143Nd/144 Nd ratios, and are enriched in large ion lithophile elements and high field strength elements, indicating a possible origin from the enriched continental lithosphere mantle,similar to the Parana type geochemical features. The basic-ultrabasic intrusive rocks in the second stage exhibit lower 87Sr/86 Sr,higher 143Nd/144 Nd ratios relative to the basalts, consistent with the involvement of a more depleted asthenospheric material,such as a mantle plume, similar to the Deccan type geochemical features. The first stage basalts can be further subdivided into two categories, i.e., Group 1 and Group 2 basalts. Group 2 basalts have lower 87Sr/86 Sr and higher 143Nd/144 Nd ratios than Group 1 basalts, and lie between compositions of the Group 1 basalts and second stage magmatism. Group 2 basalts may be the intermediate component of the TLIP, and the whole TLIP is the result of plume and lithosphere interaction. Developing this petrogenetic model for the TLIP aids in comprehensively understanding its magmatism and deep geological and geodynamic processes. Furthermore, this work enriches the theories describing the origin of large igneous province and mantle plume activity.     

Zircon U-Pb and geochemical analyses for leucocratic intrusive rocks in pillow lavas in the Danfeng Group,north Qinling Mountains,China

Field observation showed that there are many irregular leucocratic intrusive rocks in pillow lavas in the Danfeng Group in the Xiaowangjian area, north Qinling orogenic belt. Photomicrographs indicated that the protoliths of those altered leucocratic intrusive rocks are dioritic rocks. Geochemical analyses showed that pillow lavas have a range of SiO2 from 47.35% to 51.20%, low abundance of TiO2 from 0.97% to 1.72%, and percentages of MgO (MgO#=41―49). Chondrite-normalized REE patterns of pillow lavas are even, indicative of a weak differentiation between LREE and HREE (La/YbN=1.52―0.99). N-MORB-normalized trace element abundances showed that pillow lavas are enriched in incompatible elements (e.g., K, Rb, and Ba). Leucocratic intrusive rocks in pillow lavas have a wide range of SiO2 from 53.85%―67.20%, low abundances of TiO2 from 0.51%―1.10%, and MgO (MgO#=40―51), and higher percentages of Al2O3 (13.32%―16.62%) and concentration of Sr (342-539 μg/g), ratios of Na2O/K2O (2―7) and Sr/Y (17―28). Chondrite-normalized REE patterns of leucocratic intrusive rocks showed highly differentiation between LREE and HREE (La/YbN=12.26―19.41). N-MORB-normalized trace element abundances showed that leucocratic intrusive rocks are enriched in incompatible elements (e.g., K, Rb, and Ba), and significantly depleted in HFSE (e.g., Nb, Ta, Zr and Ti), indicative of a relationship to subduction. Isotopically, leucocratic intrusive rocks have a similar εNd(t) ( 7.45― 13.14) to that of MORB ( 8.8― 9.7), which indicates that those leucocratic intrusive rocks sourced from depleted mantle most likely. SHRIMP U-Pb analyses for zircon showed that those leucocratic intrusive rocks were formed at 442±7 Ma, yielding an age of subduction in the early Paleozoic in the north Qinling orogenic belt.     

Characteristics of the mantle source region of sodium lamprophyres and petrogenetic tectonic setting in northeastern Hunan,China

~~Characteristics of the mantle source region of sodium lamprophyres and petrogenetic tectonic setting in northeastern Hunan,China~~     

North Qinling Paleozoic granite associations and their variation in space and time: Implications for orogenic processes in the orogens of central China

Integrated zircon U-Pb dating and whole rock geochemical analyses have been carried out for two typical S-and I-type granitoids in the north Qinling. Zircon dating by SIMS of the Piaochi S-type grani- toids yields an emplacement age of 495±6 Ma. The granitoids show whole-rock εNd(t)=-8.2--8.8, zircon εHf(t)=-6―-39. The Huichizi I-type granitoids have emplacement ages of 421±27 Ma and 434±7 Ma es- tablished by LA-ICP-MS and SIMS methods, respectively. Their whole-rock εNd(t)=-0.9-0.9 and zircon εHf(t)=-11-8....     

Geochemistry of the E-MORB type ophiolite and related volcanic rocks from the Wushan area,West Qinling

The mafic-ultramafic assemblages, which thrustthrust into the Wushan-Tangzang boundary fault as some blocks and outcropped in the Yuanyangzhen, Lijiahe, Lubangou and Gaojiahe area, consist mainly of meta-peridotites, gabbros and basalts. The meta-peridotites are characterized by high SiO₂ and MgO contents, low ΣREE, as well as their chondrite-normalized rare earth element patterns show some similarities to that of middle oceanic meta-peridotite. The basalts from the Yuanyangzhen, Lijiahe and Lubangou area are characterized by relatively high TiO₂ content, low Al₂O₃ content and Na₂O>>K₂O. Above all, it is the slight enrichment or flat REE distribution patterns and the unfractionated in HFS elements in the primitive-normalized trace elements distribution patterns that indicate these basalts are similar to that of the typical E-MORB. In comparison, the basalts from the Gaojiahe section are featured by depletion in Nb and Ta contents and enrichment in Th content which show that these were derived from an island-arc setting. From studies of the regional geology, petrology, geochemistry, geo-chronology and all above evidence, it can be suggested that the mafic-ultramafic rocks from the Wushan area are mainly dismembered E-MORB type ophiolite, which represent the fragments of the lithosphere of the Early-Paleozoic Qinling ocean. It is preferred that these rocks were formed in an initial mid-ocean ridge setting during the beginning stage of the oceanic basin spreading. This ophiolite together with the Gaojiahe island-arc basalts shows that there exists an ophiolitic mélange along the Wushan-Tangzang boundary fault, and marks the suture zone after the closure of the Qinling ocean in early Paleozoic.

     

A re-appraisal of the use of trace elements to classify and discriminate between magma series erupted in different tectonic settings

The hygromagmatophile element composition of basic lavas from several tectonic environments are compared with the estimated composition of the primordial mantle. The observed variations are used to subdivide mid-ocean ridge basalts (MORB) into two main types according to the tectonic character of the ridge segment from which they were erupted. Ridge segments with positive residual gravity, depth and heat flow anomalies erupt E-type MORB which are predominantly enriched in the more hygromagmatophile elements, but also include magma types which are depleted in most of these elements. Both enriched and depleted E-type MORB can be distinguished from the basalts erupted at normal ridge segments (N-type MORB) by their La/Ta ratios (in E-type MORB La/Ta ～10, in N-type MORB La/Ta is ～15) and by Hf/Ta ratios (in E-type MORB Hf/Ta> 7, in N-type MORB Hf/Ta> 7). E-type MORB can be distinguished from the basalts erupted at ocean islands by their higher Hf/Ta ratios (>2). A Th-Hf-Ta triangular diagram is used to discriminate between the different ocean floor basalts as well as those erupted at destructive plate margins, which are depleted in Ta and Nb. This diagram can also distinguish between silicic lavas from the different tectonic environments as well as identifying lavas that have been contaminated with continental crust.     

Basement control on dyke distribution in Large Igneous Provinces: Case study of the Karoo triple junction

Continental flood basalts consist of vast quantities of lava, sills and giant dyke swarms that are associated with continental break-up. The commonly radiating geometry of dyke swarms in these provinces is generally interpreted as the result of the stress regime that affected the lithosphere during the initial stage of continental break-up or as the result of plume impact. On the other hand, structures in the basement may also control dyke orientations, though such control has not previously been documented. In order to test the role of pre-dyke structures, we investigated four major putative Karoo-aged dyke swarms that taken together represent a giant radiating dyke swarm (the so-called “triple-junction”) ascribed to the Jurassic Karoo continental flood basalt (> 3 × 10⁶ km²; southern Africa). One of the best tests to discriminate between neoformed and inherited dyke orientation is to detect Precambrian dykes in the Jurassic swarms. Accordingly, we efficiently distinguished between Jurassic and Precambrian dykes using abbreviated low resolution, ⁴⁰Ar/³⁹Ar incremental heating schedules.Save-Limpopo dyke swarm samples (n = 19) yield either apparent Proterozoic (728–1683 Ma) or Mesozoic (131–179 Ma) integrated ages; the Olifants River swarm (n = 20) includes only Proterozoic (851–1731 Ma) and Archaean (2470–2872 Ma) dykes. The single age obtained on one N–S striking dyke (1464 Ma) suggests that the Lebombo dyke swarm includes Proterozoic dykes in the basement as well. These dates demonstrate the existence of pre-Karoo dykes in these swarms as previously hypothesized without supporting age data. In addition, aeromagnetic and air-photo interpretations indicate that: (1) dyke emplacement was largely controlled by major discontinuities such as the Zimbabwe and Kaapvaal craton boundaries, the orientation of the Limpopo mobile belt, and other pre-dyke structures including shear zones and (2) considering its polygenetic, pre-Mesozoic origin, the Olif ants River dyke swarm cannot be considered part of the Karoo magmatic event.This study, along with previous results obtained on the Okavango dyke swarm, shows that the apparent “triple junction” formed by radiating dyke swarms is not a Jurassic structure; rather, it reflects weakened lithospheric pathways that have controlled dyke orientations over hundreds of millions of years. One consequence is that the “triple-junction” geometry can no longer be unambiguously used as a mantle plume marker as previously proposed, although it does not preclude the possible existence of a mantle plume. More generally, we suggest that most Phanerozoic dyke swarms (including triple junctions) related to continental flood basalts were probably controlled in part by pre-existing lithospheric discontinuities.     

Lithospheric composition and structure beneath the northern margin of the Qinling orogenic belt——On deep-seated xenoliths in Minggang region of Henan Province

Swarms of mafic-intermediate volcaniclastic bodies occur in the Minggang region of Henan Province, a tectonic boundary between the North Qinling and the North China Block, and emplaced at (178.31±3.77) Ma. These volcanic rocks are subalkaline basaltic andesites and contain abundance of lower crust and mantle xenoliths. Thus this area is an ideal place to reveal the lithospheric composition and structure beneath the northern margin of the Qinling orogenic belt. Geochemical data indicate that these mafic granulites, eclogites and metagabbros have trace elemental and Pb isotopic characteristics very similar to those rocks from the South Qinling Block, representing the lower part of lower crust of the South Qinling which subducted beneath the North China Block. Talcic peridotites represent the overlying mantle wedge materials of the North China Block, which underwent the metasomatism of the acidic melt/fluid released from the underlying lower crust of the South Qinling Block. Deep tectonic model proposed i     

东秦岭陆壳反射地震剖面

河南省叶县一邓州的反射地震剖面给出了秦岭地壳构造模型．东秦岭深部构造可分为３个区域：华北克拉通、扬子克拉通和秦岭碰撞缝合带．华北克拉通是稳定的地壳；扬子地壳要比稳定的华北地壳更具流变性质，有多层滑脱，至少可分辨出４个滑脱面：陡岭滑脱面、武当滑脱面、扬子滑脱面和地壳底部滑脱面；秦岭碰撞缝合带宽约１００ｋｍ，向南倾，倾角约１５°，地壳结构呈菱形块体样式．秦岭地区的上部地壳为巨型推覆构造，可分为北秦岭和南秦岭两个推覆体，各由主推覆体和前缘叠瓦扇组成．前印支期，秦岭地壳向南俯冲，秦岭古生代海盆闭合．在碰撞的后期，秦岭下部地壳向扬子作Ａ型俯冲，而上部地壳则发生大规模由北向南的推覆。     

Lithospheric composition and structure beneath the northern margin of the Qinling orogenic belt

Swarms of mafic-intermediate volcaniclastic bodies occur in the Minggang region of Henan Province, a tectonic boundary between the North Qinling and the North China Block, and emplaced at (178.31±3.77) Ma. These volcanic rocks are subalkaline basaltic andesites and contain abundance of lower crust and mantle xenoliths. Thus this area is an ideal place to reveal the lithospheric composition and structure beneath the northern margin of the Qinling orogenic belt. Geochemical data indicate that these mafic granulites, eclogites and metagabbros have trace elemental and Pb isotopic characteristics very similar to those rocks from the South Qinling Block, representing the lower part of lower crust of the South Qinling which subducted beneath the North China Block. Talcic peridotites represent the overlying mantle wedge materials of the North China Block, which underwent the metasomatism of the acidic melt/fluid released from the underlying lower crust of the South Qinling Block. Deep tectonic model proposed in this paper is that after the Late Paleozoic South Qinling lithosphere subducted northward and decoupled, the upper part of the lithosphere emplaced under the North Qinling and the lower part continuously subducted northward under the North China Block. In Early Mesozoic, the North Qinling Block obducted northward and the North China Block inserted into the Qinling orogenic belt in a crocodile-mouth shape.     

Bundelkhand mafic dykes, Central Indian Shield: Implications for the role of sediment subduction in Proterozoic crustal evolution

Abstract The Archean to Paleo–Proterozoic Bundelkhand massif basement of the central Indian shield has been dissected by numerous mafic dykes of Proterozoic age. These dykes are low‐Ti tholeiites, ranging in composition from subalkaline basalt through basaltic‐andesite to dacite. They are enriched in light rare earth elements (LREE), large ion lithophile elements (LILE) and depleted in high field strength elements (HFSE: Nb, P and Ti). Negative Sr anomaly is conspicuous. Nb/La ratios of the dykes are much lower compared with the primitive mantle, not much different from the average crustal values, but quite similar to those of continental and subduction related basaltic rocks. Bulk contamination of the mantle derived magma by crustal material is inadequate to explain the observed geochemical characteristics; instead contamination of the mantle/lithospheric source(s) via subduction of sediment is a better proposition. Thus, in addition to generating juvenile crust along the former island arcs, subduction processes appear to have influence on the development of enriched mantle/lithospheric source(s). The Bundelkhand massif basement is inferred to represent subduction related juvenile crust, that experienced lithospheric extension and rifting possibly in response to mantle plume activities. The latter probably supplied the required heat, material (fluids) and extensional environment to trigger melting in the refractory lithospheric source(s) and emplacement of the mafic dykes. Proterozoic mafic magmatic rocks from Bundelkhand, Aravalli, Singhbhum and Bastar regions of the Indian shield and those from the Garhwal region of the Lesser Himalaya display remarkably similar enriched incompatible trace elements characteristics, although limited chemical variations are observed in all these rocks. This may indicate the existence of a large magmatic province, different parts of which might have experienced similar petrogenetic processes and were probably derived from mantle/lithospheric source(s) with similar trace element characteristics. The minor, less enriched to depleted components of the Jharol Group of the Aravalli terrane and those from the Singhbhum terrane may represent protracted phases of rifting, that probably caused thinning and mobilization of the lithosphere, facilitating the eruption/emplacement of the asthenospheric melts (with N‐ to T‐types mid‐oceanic ridge basalts signatures) and deposition of deep water facies sediments in the younger developing oceanic basins. In contrast, Bundelkhand region did not experience such protracted rifting, although dyke swarms were emplaced and shallow water Bijawar Group and Vindhyan Supergroup sediments were deposited in continental rift basins. All these discrete Proterozoic terranes appear to have experienced similar petrogenetic processes, tectonomagmatic and possibly temporal evolution involving subduction processes, influencing the lithospheric source characteristics, followed by probably mantle plume induced ensialic rifting through to the development of oceanic basins in the Indian shield regions and their extension in the Lesser Himalaya.     

Petrogenesis of Songshugou dunite body in the Qinling orogenic belt,Central China: Constraints from geochemistry and melt inclusions

The chemical variation of the Earth’s mantle rocks has been interpreted to reflect multiple episodes of partial melting. With the increasing of melt generation and extraction, the readily molten minerals and incompatible elements decrease in the residual mantle peridotite. The present-day gladiate of the Earth, however, cannot cause mantle batch melting[1], nor 40% partial melting that allows pyroxenes to be completely dissolved into melt and forms dunite[2,3]. Recent studies show that mantl…     

Origin of Late Permian Emeishan basaltic rocks from the Panxi region (SW China): Implications for the Ti-classification and spatial–compositional distribution of the Emeishan flood basalts

Basalts and a mafic dyke collected from the city of Panzhihua show characteristics of high-Ti and low-Ti Emeishan basalts respectively. The dyke yielded a SHRIMP zircon U–Pb mean age of 261 ± 5 Ma making it contemporaneous with the eruption of Emeishan basalts. The basalts have I_Sr ranging from 0.7059 to 0.7062 with εNd_(T) ranging from ?1.1 to + 0.7 whereas the dyke has I_Sr ranging from 0.7056 to 0.7064 with εNd_(T) ranging from + 0.3 to + 0.5. Trace element modeling shows that the two rock types can be generated by different degrees of partial melting from the same garnet-bearing source. Assimilation of crustal material is required in order to produce the depletion of some trace elements (e.g. Nb and Ta) of the dyke however crustal assimilation is not required to produce the basalts. Trace element modeling and isotopic data of the Emeishan basalts suggest that, in general, the high- and low-Ti basaltic rocks are likely derived from the same source and represent different degrees of partial melting with or without crustal assimilation. The location and geological relationships of the ‘high-Ti’ basalts indicate they erupted relatively early and within the central part of the ELIP, casting doubt on the previous spatial–compositional distribution of the Emeishan basalts.     

嵊泗岛辉绿岩墙群的侵位方式:来自磁组构的证据

岩墙磁组构能反映岩浆的侵位方式.中国东部嵊泗岛广泛发育了晚白垩世辉绿岩岩墙群.我们对其中8条不同走向岩墙进行了采样,沿岩墙两边部及横跨岩墙剖面获得共273个独立定向岩芯样品.岩石磁学分析表明辉绿岩的主要携磁矿物为多畴贫钛磁铁矿,可能含少量磁赤铁矿.各条岩墙的磁组构均具有低的各向异性度Pj＜1.2,且主轴的空间方位各不相...     

Hydrothermal alteration and tectonic evolution of an intermediate- to fast-spreading back-arc oceanic crust: Late Ordovician Solund-Stavfjord ophiolite, western Norway

Abstract The Solund‐Stavfjord ophiolite complex (SSOC) in western Norway represents a remnant of the Late Ordovician oceanic lithosphere, which developed in an intermediate‐ to fast‐spreading Caledonian back‐arc basin. The internal architecture and magmatic features of its crustal component suggest that the SSOC has a complex, multistage sea floor spreading history in a supra‐subduction zone environment. The youngest crustal section associated with the propagating rift tectonics consists of a relatively complete ophiolite pseudostratigraphy, including basaltic volcanic rocks, a transition zone between the sheeted dyke complex and the extrusive sequence, sheeted dykes, and high‐level isotropic gabbros. Large‐scale variations in major and trace element distributions indicate significant remobilization far beyond that which would result from magmatic processes, as a result of the hydrothermal alteration of crustal rocks. Whereas K₂O is strongly enriched in volcanic rocks of the extrusive sequence, Cu and Zn show the largest enrichment in the dyke complex near the dyke–volcanic transition zone or within this transition zone. The δ¹⁸O values of the whole‐rock samples show a general depletion structurally downwards in the ophiolite, with the largest and smallest variations observed in volcanic rocks and the transition zone, respectively. δ¹⁸O values of epidote–quartz mineral pairs indicate 260–290°C for volcanic rocks, 420°C for the transition zone, 280–345°C for the sheeted dyke complex and 290–475°C for the gabbros. The ⁸⁷Sr/⁸⁶Sr isotope ratios show the widest range and highest values in the extrusive rocks (0.70316–0.70495), and generally the lowest values and the narrowest range in the sheeted dyke complex (0.70338–0.70377). The minimum water/rock ratios calculated show the largest variations in volcanic rocks and gabbros (approximately 0–14), and generally the lowest values and range in the sheeted dyke complex (approximately 1–3). The δD values of epidote (?1 to ?12‰), together with the δ¹⁸O calculated for Ordovician seawater, are similar to those of present‐day seawater. Volcanic rocks experienced both cold and warm water circulation, resulting in the observed K₂O‐enrichment and the largest scatter in the δ¹⁸O values. As a result of metal leaching in the hot reaction zone above a magma chamber, Zn is strongly depleted in the gabbros but enriched in the sheeted dyke complex because of precipitation from upwelling of discharged hydrothermal fluids. The present study demonstrates that the near intact effect of ocean floor hydrothermal activity is preserved in the upper part of the SSOC crust, despite the influence of regional lower greenschist facies metamorphism.