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  • 1. Batki, Aniko
    et al.
    Pal-Molnar, Elemer
    Dobosi, Gabor
    Skelton, Alasdair
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Petrogenetic significance of ocellar camptonite dykes in the Ditrau Alkaline Massif, Romania2014In: Lithos, ISSN 0024-4937, E-ISSN 1872-6143, Vol. 200, p. 181-196Article in journal (Refereed)
    Abstract [en]

    Camptonite dykes intrude the rift-related Mesozoic igneous body of the Ditrau Alkaline Massif, Eastern Carpathians, Romania. We present and discuss mineral chemical data, major and trace elements, and the Nd isotopic compositions of the dykes in order to define their nature and origin. The dykes are classified as the clinopyroxene-bearing (camptonite-I) and clinopyroxene-free (camptonite-II) varieties. Camptonite-I consists of aluminian-ferroan diopside phenocrysts accompanied by kaersutite, subordinate Ti-rich annite, albite to oligoclase and abundant calcite-albite ocelli. Camptonite-II comprises K-rich hastingsite to magnesiohastingsite, Ti-rich annite, albite to andesine, abundant accessory titanite and apatite, and silicate ocelli filled mainly with plagioclase (An(4-34)). Age-corrected Nd-143/Nd-144 ratios vary from 0.51258 to 0.51269. The high epsilon(Nd) values of +4.0 to +6.1 which are consistent with intra-plate composition, together with light rare earth element (LREE), large ion lithophile element (LIE) and high field strength element (HFSE) enrichment in the camptonites is ascribed to the formation of small melt batches of a metasomatised sub-lithospheric mantle source. The presence of an asthenospheric 'high mu' ocean island basalt (HIMU-OIB)-type mantle component in the source region has also been revealed. A 1-4% degree of partial melting of an enriched garnet Iherzolite mantle source containing pargasitic amphibole followed by fractionation is inferred to have been involved in the generation of the camptonites. They are deduced to be parental melts to the Ditrau Alkaline Massif.

  • 2.
    Bender, Hagen
    et al.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Glodny, Johannes
    Ring, Uwe
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Absolute timing of Caledonian orogenic wedge assembly, Central Sweden, constrained by Rb-Sr multi-mineral isochron data2019In: Lithos, ISSN 0024-4937, E-ISSN 1872-6143, Vol. 344, p. 339-359Article in journal (Refereed)
    Abstract [en]

    Multi-mineral Rb-Sr isochron ages for mylonites of the Caledonian nappe pile (Jamtland, Sweden) constrain the orogenic evolution of the central Scandinavian Caledonides. An age of 437.8 +/- 3.9 Ma from a metamorphic leucosome in the central nappe stack dates crystallization of migmatized gneiss. Thirteen isotopic ages derived from mylonites across all structural levels are between 434.6 +/- 6.9 Ma and 426.3 +/- 3.1 Ma. These results, complemented by a dense network of kinematic field data, are interpreted to reflect the timing of protracted top-to-the-ESE general shear under decreasing amphibolite- to upper-greenschist-facies conditions across all nappes. Three samples, derived from the top, middle and bottom of the nappe pile, yield additional deformation ages between 416.0 +/- 3.6 Ma and 410.1 +/- 3.0 Ma. These ages are interpreted to represent post-assembly imbrication of the nappe stack under decreasing metamorphic conditions. The new tectonochronologic data are consistent with a tectonic model that explains nappe stacking in Jamtland by three stages of ESE-directed in- and out-of-sequence thrusting. In the first stage, postdating earlier subduction-exhumation of the high-grade metamorphic Seve Nappe Complex, the latter was emplaced in-sequence in the lower/mid-crust above nappes in its footwall (foreland) at c. 430 Ma. This event is related to the collision of Baltica with an island arc. Concurrently at c. 430 Ma, determined by paleogeography and structurally unrelated to the first stage, second-stage out-of-sequence thrusting emplaced the Kali Nappe Complex atop the developing nappe stack during final Baltica-Laurentia collision. Eventually, imbrication and exhumation of the composite Jamtland nappe stack in the uppermost middle crust during the third stage at c. 414 Ma was caused by continuous underthrusting of Baltica beneath Laurentia. This three-stage thrust model reflects the complex interactions of Baltica-arc-Laurentia collisions that were accommodated by two merging subduction zones.

  • 3.
    Bender, Hagen
    et al.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Glodny, Johannes
    Ring, Uwe
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Stephens, Michael B.
    Absolute timing of Caledonian orogenic wedge assembly, central Sweden, constrained by Rb-Sr multi-mineral isochron dataIn: Lithos, ISSN 0024-4937, E-ISSN 1872-6143Article in journal (Refereed)
  • 4. Jarrar, Ghaleb H.
    et al.
    Stern, Robert J.
    Theye, Thomas
    Yaseen, Najel
    Pease, Victoria
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Miller, Nathan
    Ibrahim, Khalil M.
    Passchier, Cees W.
    Whitehouse, Martin
    Neoproterozoic Rosetta Gabbro from northernmost Arabian–Nubian Shield, south Jordan: Geochemistry and petrogenesis2017In: Lithos, ISSN 0024-4937, E-ISSN 1872-6143, Vol. 284-285, p. 545-559Article in journal (Refereed)
    Abstract [en]

    An Ediacaran mafic intrusion of south Jordan is a distinctive appinitic igneous rock with a possibly unique texture, characterized by spherical clots up to 40 mm in diameter composed of amphibole cores from which plagioclase euhedra radiate; we call it the Rosetta Gabbro. It is exposed as a small (ca. 750 m(2)) outcrop in the Neoproterozoic basement of south Jordan. A second outcrop of otherwise similar gabbro is located about 400 m to the north of the Rosetta Gabbro, but it lacks the distinctive texture. The Rosetta Gabbro could represent a magma pipe. It intrudes the Aqaba Complex (similar to 600 Ma) granitoids and metasediments of the Janub Metamorphic Complex (633-617 Ma). The gabbro is an 01- to QZ tholeiite with the following chemical characteristics: SiO2 = 46.2-47.8 wt.%; Al2O3 = 16.4-17.7 wt.%, TiO2 = 1.70-2.82 wt.%, Na2O = 1.27-2.83 wt.%. K2O = 0.82-1.63 wt.%; Mg# 58-63; Sigma REE = 70-117 ppm; La/Yb similar to 6 to 8; and Eu/Eu* = 1.05-1.2. The investigated gabbro has the geochemical features of a continental flood tholeiitic basalt emplaced in a within-plate tectonic setting. Two varieties of amphiboles are found: 1) large, 3-5 mm, brown ferri-titanian-tschermakite K0.09Na0.28) (Na020Ca1.80) (Mn0.04Fe1.13+Mg2.34Fe0.902+Ti029Al0.22)(Al-1.Si-85(6.15))O-22(OH)(1.95) of the calcic amphibole group which is riddled with opaques; and 2) acicular yellowish-light green ferrian-magnesiohomblende (K0.04Na0.153)(Ca1.755Na0245) (Fe(0.66)(3+)Mn(0.01)Fe(1.01)(2+)mg(3.03)Ti(0.06)Al(0.22))(Al1.03Si6.97)O-22(OH)1.95. Scattered flakes of phlogopite also occur. Tabular radiating plagioclase (An(64-79)) are complexly twinned, with broad lamellae that show no zoning. Laser-ablation ICP-MS analyses of amphibole and plagioclase reveal considerable variation in trace element abundance, in spite of more subtle major element variations except for TiO2 in amphibole. The REE in the amphibole shows an order of magnitude variation with a concave-downward pattern and a positive Eu anomaly Eu/Eu* = 0.6-2, though far less pronounced compared to the Eu/Eu* = 5-45 of plagioclase. The 3D dandelion-like texture of the rosettas is broadly similar to "Chrysanthemum Stone", which is a diagenetic growth in sedimentary rock, but we can find no description of similar textures in igneous rocks. The formation of the rosettas is thought to reflect loss of magmatic water resulting in supersaturation of plagioclase, which grew rapidly around amphibole and may havelloated in the magma. This implies magmatic evolution in shallow (10 to 12 km deep) crust where temperatures were nevertheless in the range of ca. 750 to 900 degrees C.

  • 5.
    Kleine, Barbara I.
    et al.
    Stockholm University, Faculty of Science, Department of Geological Sciences. University of Iceland, Iceland.
    Pitcairn, Iain K.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Skelton, Alasdair D. L.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Mineralogical controls on metamorphic fluid flow in metabasaltic sills from Islay, Scotland2016In: Lithos, ISSN 0024-4937, E-ISSN 1872-6143, Vol. 248, p. 22-39Article in journal (Refereed)
    Abstract [en]

    In this study we show that mineralogy was the primary control of metamorphic fluid flow in the well-studied metabasaltic sills in the SW Scottish Highlands. Here, basaltic sills have been partially carbonated by H2O-CO2 fluids at greenschist facies conditions. This has led to mineral zonation with carbonate-poor sill interiors separated from carbonate-rich sill margins by reaction fronts. Although deformation set the stage for metamorphic fluid flow in the SW Scottish Highlands by causing the preferred alignment of mineral grains, metamorphic fluid flow was not coupled with active deformation but occurred later utilizing the pre-existing mineral alignment as a means of accessing the sill interiors. The sills which were studied were partially carbonated with well-preserved reaction fronts. They were selected because (atypically for the SW Scottish Highlands) they are mineralogically heterogeneous making them ideal for a study of mineralogical controls of metamorphic fluid flow. Their mineralogical heterogeneity reflects chemical heterogeneity arising from magmatic flow differentiation and spilitization, which occurred before greenschist facies metamorphism. Magmatic flow differentiation resulted in parts of the sill containing large crystals with no preferred alignment. Large (up to 3 cm) plagioclase phenocrysts were concentrated in the sill interior whereas large (up to 1 cm) amphibole (after pyroxene) grains formed cumulate layers close to the sill margins. These large randomly oriented crystals were replaced by an interface-coupled dissolution-precipitation mechanism. Replacement is constant volume and with hydration and carbonation affecting the cores of these minerals while the rims are remained intact and unaltered. This finding points to intro-granular metamorphic fluid flow. In contrast inter-granular metamorphic fluid flow was facilitated by mineral alignment on different scales. Pre-metamorphic spilitization, produced layers of epidote called segregations, whereas regional deformation caused preferred alignment mainly of amphibole and chlorite. Epidote undergoes a series of volume changes during greenschist facies metamorphism. This created porosity which produced preferred pathways for metamorphic fluids affecting the advancement of fluid-driven reaction fronts. Preferred alignment of amphibole and chlorite also affected the advancement of reaction fronts. In this case, fluid flow was preferentially parallel to the foliation. In both cases, inter-granular metamorphic fluid flow utilized a pre-existing fabric albeit on different scales. These results show intra-granular metamorphic fluid flow in unfoliated rock and inter-granular metamorphic fluid flow in foliated rock. In both cases metamorphic fluid flow occurred after deformation controlled by pre-existing mineralogical heterogeneities, such as grain composition and shape anisotropy as well as preferred alignment of mineral grains.

  • 6. Petersson, Jesper
    et al.
    Fallick, Anthony E.
    Broman, Curt
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Eliasson, Thomas
    Imprints of multiple fluid regimes on episyenites in the Bohus granite, Sweden2014In: Lithos, ISSN 0024-4937, E-ISSN 1872-6143, Vol. 196, p. 99-114Article in journal (Refereed)
    Abstract [en]

    A number of episyenite occurrences within the Neoproterozoic Bohus granite, southwestern Sweden, were investigated in order to elucidate their genesis and past associated fluid regimes. Fluid inclusion microthermometry and O-H isotope systematics integrated with information from detailed mineralogy reveal a paragenetic succession within individual episyenites, including: (1) albitization of plagioclase, accompanied by dissolution of quartz, with a vuggy feldspathic reservoir rock as a result; (2) resumed infilling and replacement of igneous Fe-Ti-phases by various phyllosilicates (muscovite, chlorite and/or illite) +/- hematite assemblages and quartz, due to rift-related reactivation and (3) sporadic argillitic alteration and precipitation of fracture calcite. Although sparse owing to later overprinting, there are a few remnants that provide arguments for the involvement of meteoric water, shifted to a more O-18-rich composition, during the initial stage of dissolution and albitization. The main vug-filling phase is proposed to be associated with the ingress of surface-derived fluids with negative delta O-18 values, during the regional thermal anomaly accompanying the development of the nearby Permo-Carboniferous Oslo Rift at similar to 250 Ma The fluids involved during this event show consistently a marked, but variable O-18-depletion and resemble the modern-day shield brines, with modal salinities of 11-24 wt.% NaCl eq., low NaCl/(NaCl + CaCl2) weight ratios and no discernible CO2. Even though no P-T path can be defined for this phase, the fluid pressure can be restricted to 03-0.8 kbar and temperature to 160-280 degrees C, assuming a sedimentary overburden of similar to 3 km. An overall variability in the delta O-18 and delta D data can mainly be ascribed to (1) precipitation from fluids affected by isotopic exchange with the host rock and/or sedimentary overburden under highly variable water/rock ratios, and to some extent with (2) varying degrees of partial re-equilibration during subsequent hydrothermal interaction at lower temperatures, as emphasized by the presence of fluid inclusions of suspected secondary origin in quartz.

  • 7.
    Pitcairn, Iain K.
    et al.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Skelton, Alasdair D. L.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Wohlgemuth-Ueberwasser, Cora C.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Mobility of gold during metamorphism of the Dalradian in Scotland2015In: Lithos, ISSN 0024-4937, E-ISSN 1872-6143, Vol. 233, p. 69-88Article in journal (Refereed)
    Abstract [en]

    Mobility of Au and related metals during metamorphism has been suggested to be the source of metals enriched in orogenic Au deposits. This study investigates the mobility of Au, As, and Sb during metamorphism of the Dalradian metasedimentary rocks of Scotland. The metamorphic processes in the Dalradian of Scotland are extremely well studied, and the terrane is an ideal area to investigate mobility of these metals. Our results show that of the 25 major and trace elements analysed, only Au, As, Sb, S and volatile contents as shown by loss on ignition (LOI) values show systematic variation with the metamorphic grade of the samples. Average Au concentrations decrease from 1.1 +/- 0.55 ppb and 0.72 +/- 0.34 ppb in chlorite and biotite zone rocks down to 0.4 +/- 0.22 ppb and 034 +/- 0.13 ppb in kyanite and sillimanite zone rocks. Average As concentrations decrease from 4.8 ppm (range 0.5 to 17.8 ppm) and 1.96 +/- 1.9 ppm in chlorite and biotite zone rocks down to 0.24 +/- 0.15 ppm and 0.2 +/- 0.12 ppm in kyanite and sillimanite zone rocks. Average Sb concentrations decrease from 0.18 +/- 0.15 ppm and 0.11 +/- 0.10 ppm in chlorite and biotite zone rocks down to 0.04 +/- 0.02 ppm in both kyanite and sillimanite zone rocks. Sulphur and LOI concentrations also show significant decreases. Mass balance calculations indicate that compared to chlorite and biotite zone samples, sillimanite zone samples have an average mass loss of 62 +/- 14%, 94 +/- 4% and 74 +/- 14% for Au, As, and Sb respectively. Every 1 km(3) of chlorite-biotite zone mixed psammitic-pelitic protolith rock that is metamorphosed to sillimanite zone conditions would release 1.5 t Au, 8613 t As, 270 t Sb, and 1.02 Mt S. The mobility of these elements is strongly controlled by the paragenesis of sulphide minerals. Pyrite, sphalerite, galena and cobaltite (as well as gersdorffite) decrease in abundance with increasing metamorphic grade in the Dalradian metasedimentary rocks. A critical aspect of the sulphide paragenesis is the transition of pyrite to pyrrhotite. This transition is complete by mid greenschist facies in the Loch Lomond samples but is more gradual at Glen Esk occurring between biotite and sillimanite zones. The Au, As, and Sb content of the sulphide assemblage also decreases with increasing metamorphic grade, and we suggest that this is a controlling factor on the mobility of these metals from the Dalradian metasedimentary rocks during metamorphism. Chlorite may be an important host mineral for As in the greenschist fades rocks. Breakdown of chlorite indirectly drives the mobility of Au, As, and Sb, as this produces the bulk of metamorphic fluid that drives transition between pyrite and pyrrhotite. We suggest that there is potential for significant undiscovered mineralisation in the Central and SW Highlands of Scotland. However, as the total mass of gold mobilised is lower than observed in other metasedimentary terranes such as the Otago and Alpine Schist's, New Zealand, very efficient fluid focussing and trapping mechanisms would be required to form large deposits in the Dalradian of Scotland.

  • 8. Rosenbaum, Gideon
    et al.
    Menegon, Luca
    Glodny, Johannes
    Vasconcelos, Paulo
    Ring, Uwe
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Massironi, Matteo
    Thiede, David
    Nasipuri, Pritam
    Dating deformation in the Gran Paradiso Massif (NW Italian Alps): Implications for the exhumation of high-pressure rocks in a collisional belt2012In: Lithos, ISSN 0024-4937, E-ISSN 1872-6143, Vol. 144, p. 130-144Article in journal (Refereed)
    Abstract [en]

    The Gran Paradiso massif, situated in the internal part of the Western Italian Alps, records a complex tectono-metamorphic history involving high-pressure metamorphism and subsequent exhumation during retrograde metamorphism. The exact timing of deformation and, consequently, the geodynamic evolution of this part of the Western Alps is still debated and is addressed here by the application of Rb/Sr geochronology, Ar-40/Ar-39 step heating and Ar-40/Ar-39 total fusion dating techniques. Geochronological results are presented from shear zone samples in the core of the Gran Paradiso massif (Piantonetto Valley). and in the area closer to the contact with the overlying Piedmont ophiolitic domain (south and southwest of Pont Valsavarenche). The shear zones operated during crustal thinning and exhumation of the Gran Paradiso massif. Ar-40/Ar-39 step heating results from shear zones in the Piantonetto Valley show acceptable plateau ages that are interpreted to represent two events of mica growth. Similar ages, and an additional younger age cluster, are recognised in the Ar-40/Ar-39 total fusion analyses, indicating that specific cleavage domains operated at 39.2 +/- 0.2, 36.5 +/- 0.6 and 33.3 +/- 0.4 Ma. P-T pseudosections show a progressive decrease in metamorphic conditions during deformation, suggesting that the age of incipient exhumation and the related deformation in the Piantonetto Valley is equal to or older than 39.2 +/- 02 Ma. In the Pont area, the last increments of deformation in a top-to-W shear zone postdate 36.6 +/- 0.6 Ma (Rb/Sr mineral data), whereas the present-day top-to-W contact of the Gran Paradiso massif with the overlying Piedmont domain is dated at 41.2 +/- 1.1 Ma (Rb/Sr multi-mineral isochron age). We propose a model that considers exhumation of the Gran Paradiso nappe at 41-34 Ma. During this period, the nappe was coupled with the Zermatt-Saas zone, forming an extruding wedge. The kinematics associated with this wedge involved top-to-W shearing within the Gran Paradiso nappe (e.g. Pont area shear zones) and top-to-E shearing at the top of the extruding wedge (e.g. Orco shear zone). Subsequent deformation (after similar to 34 Ma) was characterised by coaxial strain involving orogenic-scale backfolding and backthrusting.

  • 9. Vuorinen, Jaana Hode
    et al.
    Hålenius, Ulf
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Nb-, Zr- and LREE-rich titanite from the ALnö alkaline complex: Crystal chemistry and its importance as a petrogenetic indicator2005In: Lithos, ISSN 0024-4937, E-ISSN 1872-6143, Vol. 83, no 1-2, p. 128-142Article in journal (Refereed)
    Abstract [en]

    Titanite occurs as an accessory phase in melteigite, ijolite and nepheline syenite from the Alnö alkaline intrusion and is typically associated with Ti-andradite and calcite±perovskite. Titanite from 7 samples was investigated using microanalytical techniques including EMPA, 57Fe Mössbauer spectroscopy, powder X-ray diffractometry and FTIR-spectroscopy. A common feature of the analysed titanite is high amounts of Nb2O5 (up to 7.3 wt.%), ZrO2 (up to 2.8 wt.%) and LREE2O3 (up to 3.9 wt.%), and significant amounts of Al2O3+Fe2O3 (up to 4.3 wt.%). Important substitutions are consequently (i) 2[7]Ca→[7]Na++[7]LREE3+, (ii) [7]Ca2++[6]Ti4+[7]LREE3++[6](Al, Fe3+), (iii) 2[6]Ti4+[6]M5++[6](Al, Fe3+). Zr is most likely accommodated into the structure through simple direct isovalent octahedral substitution for Ti, contrasting with other proposed, more complex models for Zr-incorporation in titanite. Stoichiometric calculations indicate all iron to be present as Fe3+ but 57Fe Mössbauer analyses show a small fraction (10%) of ferrous iron to be present as well. FTIR-spectroscopy indicate 0.14–0.26 wt.% H2O in the investigated titanites and X-ray diffraction data yield cell parameters close to the ideal synthetic end-member values. Chondrite normalised LREE patterns for the analysed titanites show (Ce+Pr)N>LaN similar to patterns reported from other occurrences and enrichment factors are typically in the order of 103–104. Comparison of whole rock Nb-, Zr- and LREE-contents with variations in modal amounts of trace element enriched titanite shows a significant effect which needs to be addressed when modeling magma evolution. The use of the prv–ttn assemblage for estimating silica-activity during crystallization of silica undersaturated alkaline rocks is discussed.

  • 10.
    Zhang, Wen
    et al.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Pease, Victoria
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Wu, Tairan
    Zheng, Rongguo
    Feng, Jicheng
    He, Yuankai
    Luo, Hongling
    Xu, Cao
    Discovery of an adakite-like pluton near Dongqiyishan (Beishan, NW China) - Its age and tectonic significance2012In: Lithos, ISSN 0024-4937, E-ISSN 1872-6143, Vol. 142, p. 148-160Article in journal (Refereed)
    Abstract [en]

    The Dongqiyishan granitic pluton is exposed in the Eastern Beishan area, in the central part of the Southern Central Asia Orogenic Belt. SIMS U-Pb zircon dating indicates that the Dongqiyishan pluton was emplaced at 356 +/- 2 Ma. Geochemically the pluton is calc-alkaline and characterized by high SiO2 (> 65%), Al2O3 (mostly > 15%), Na2O/K2O ratios (1.3-3.9) and Sr (generally > 400 ppm). Samples display positive to weakly negative Eu anomalies (delta(Eu) = 0.81-2.32). low HREE, Y and Yb (Y < 18 ppm, Yb < 1.9 ppm), are enriched in LREE, LILE (Rb, Ba, Sr, U, and K), Zr, and Hf, and depleted in HFSE. They have relatively low epsilon(Nd)(t) values (-2.9-+ 0.6) and relatively high (Sr-87/Sr-86)(i) ratios (0.70581-0.70749). Together, these geochemical traits suggest an adakite-like composition that reflects melting of subducted oceanic crust and the involvement of older continental material. Assimilation and fractional crystallization (AFC) modeling requires significant crustal assimilation to modify an initial MORB-derived andesitic melt to produce the hybrid granitic melt, e.g. - the Dongqiyishan pluton. A back-arc basin to the south (represented by the Yueyashan-Xichangjing ophiolitic belt) closed before the Early Carboniferous Dongqiyishan adakite-like pluton was emplaced into the Silurian volcanic arc. Closure of the back-arc basin potentially provides the continental component seen in the isotopic signature of the Dongqiyishan pluton and required by the AFC modeling. Post-Ordovician flattening of the subducting slab together with crustal thickening from closure of the back-arc basin, led to the formation of a tightly coupled subducting slab and lower crust which resulted in the formation of Dongqiyishan adakite-like pluton. The Dongqiyishan pluton is consistent with southward subduction (represented by the Xiaohuangshan ophiolitic belt) and indicates that oceanic crust was still being produced in the Paleo-Asian Ocean during the Early Carboniferous. Adakite-like granitic rocks may be more abundant than previously thought in the Beishan region.

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