Metamorphosed ultramafic and mafic lithoclasts and detrital minerals from sandstones of clastic ophiolitic deposits of the Rassokha terrane: a setting of formation of the Chersky range ophiolites

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Abstract

Ophiolite-derived clastic rocks of the Rassokha terrane in the Chersky Range of the Verkhoyansk−Kolyma folded area were studied to obtain representative characteristics of the eroded source metamorphosed ultramafic and mafic rocks, to gain an insight into the possible geodynamic setting in which the protoliths of these rocks were formed, and to identify the possible source of the eroded material. The composition of lithoclasts and detrital minerals of the serpentinite and listwanite sandstones suggests that their source was composed of serpentinite, chloritite, listwanite, and dolomite rocks and that this source was proximal. Prior to the source erosion, the ultramafic and mafic rocks were metamorphosed and recrystallized, listwanite was formed, and the ultramafic rocks were tectonically disintegrated and combined with units of carbonate rocks (dolomite). Ultramafic rocks from lithoclasts experienced allochemical metamorphic retrogression during at least the latest stage of their serpentinization in a nonoceanic setting, where also the listwanite was formed. The Late Neoproterozoic ophiolites of the collisional belt of the Chersky Range were the most probable source for the protoliths of the clastic material. The protoliths of the ophiolite rock were probably formed in a backarc setting. Considered together with the published ages, our data indicate that relics of suprasubduction oceanic lithosphere of the Neoproterozoic basin occurred in the Chersky Range.

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About the authors

G. V. Ledneva

Geological Institute, RAS

Author for correspondence.
Email: ledneva@ginras.ru
Russian Federation, Moscow

B. A. Bazylev

V.I. Vernadsky Institute of geochemistry and analytical chemistry, RAS

Email: ledneva@ginras.ru
Russian Federation, Moscow

S. N. Sychev

Geological Institute, RAS; St. Petersburg State University; A.P. Karpinsky Russian Geological Research Institute

Email: ledneva@ginras.ru

Institute of Earth Sciences

Russian Federation, Moscow; St. Petersburg; St. Petersburg

A. V. Rogov

Gold Mining LLC

Email: ledneva@ginras.ru
Russian Federation, Yakutsk

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Supplementary files

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2. Fig. 1. Position of the ophiolite massifs of the Chersky Ridge and the study area on the tectonic zoning scheme of the Verkhoyansk-Kolyma folded region (Parfenov et al., 2001), modified according to (Sokolov et al., 2010) and simplifications. 1 - Verkhoyansk fold-and-thrust belt; terranes: 2 - passive continental margin; 3 - cratonic (Omolon); 4 - island-arc; 5 - turbidite; 6 - turbidite foot of the continental margin (shale belt); 7 - accretionary wedge, composed mainly of oceanic sediments; 8 - accretionary wedge, mainly turbidite (Polousno-Debinsky); 9 – ophiolite massifs, including the Munilkan terrane: MUY – Uyandinsky (Kalgynsky), MMU – Munilkansky, MKY – Kabytygassky, MIN – Indigirsky (Uchchinsky), MGA – Garbynyinsky, MUV – Uvyazkinsky; 10 – thrusts; 11 – strike-slip faults; 12 – faults. OVR – Rassokhinsky and adjacent Omulevsky (OVO) and Arga-Tassky (AG) terranes.

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3. Fig. 2. Rocks of the ophiolite-clastic sequence from the Rassokha River basin: (a) alternation of layers and lenses of dolomite rocks (light beige) with serpentinite siltstones (dark greenish-gray); (b) grayish-green serpentinite sandstones and gravelstones with rubble and small pebbles of differently colored dolomite rocks; (c) interlayer of boulder-pebble conglomerates in serpentinite sandstone, pebbles and boulders are composed of dolomite rocks; (d) listvenite sandstone with pinkish pebbles of dolomite rocks.

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4. Fig. 3. Serpentinite sandstone (sample 1099/4) (a, b) and listvenite sandstone (sample 1099/1) (c, d). (a) – in transmitted light; (b) – in polarized light; (c, d) – in secondary scattered electrons (BSE). Fragments in (a, b): 1 – serpentinites, 2 – chloritites, 3 – dolomite rocks, 4 – chrome spinels and magnetites. Fragments in (c, d) and other figures: Ds – dolomite rocks, List – listvenites. The analyzed lithoclasts (here and in other figures) are numbered (see Suppl. 2, ESM_1.xls).

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5. Fig. 4. Post-sedimentary recrystallization in sandstones. BSE images: (a–c) development of euhedral magnetite in clasts and in the matrix of serpentinite sandstones; (d) rim of ferrodolomite at the contact of a dolomite clast with the matrix of serpentinite sandstone; (e) ferrodolomite cementing small dolomite clasts in listvenite sandstone; (e) recrystallization of dolomite in isolated areas and at the contact with albite, dolomite clast in listvenite sandstone. Abbreviations of minerals here and below are according to (Warr, 2021), mineral generations (here and in other figures) are characterized in the text. The analyzed grains of chrome spinels (here and in other figures) are numbered (see Suppl. 2, ESM_2.xls).

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6. Fig. 5. Grains of chrome spinels in serpentinite sandstones.

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7. Fig. 6. Compositions of restitic and chromitite chrome spinels from sandstones: (a) primary (all studied samples); (b–d) primary, partially recrystallized, and metamorphic in individual samples. Generations of chrome spinels: 1 – primary restitic (Spl1res), 2 – primary chromitite (Spl1chr-te); 3 – partially recrystallized (Spl2), 4 – partially recrystallized, specific for listvenites (Spl2a); 5 – metamorphic (Spl3); 6 – chrome spinels from harzburgites of the Munilkan massif (Oxman, 2000); Fields of compositions of primary chrome-spinels from: 7 – restitic peridotites of the MOR (Dick, Bullen, 1994), 8 – harzburgites of fore-arc basins (Ishii et al., 1992), 9 – harzburgites of Oman ophiolites (LeMée et al., 2004), 10 – chromitites of Oman ophiolite massifs (Rollinson, Adetunji, 2013, 2015). Solid and dotted arrows show typical trends in the composition of spinels during partial and complete recrystallization, respectively.

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8. Fig. 7. Compositions of silicates from fragments of serpentinites and chloritites. 1 – chlorites (Chl1, Chl4); 2 – chlorites (Chl2, Chl3); 3 – chlorites (Chl5); 4 – talc; 5 – talc-chlorite; 6 – serpentines (lizardite and antigorite); 7 – Fe-lizardites; 8 – talc + serpentine(?); 9 – serpentine + chlorite(?). Lz, Atg, Tlc, Chl (unfilled diamonds) – ideal compositions of minerals; for chlorites, the number of Si atoms in the formula is given in brackets when recalculated to 18O. Solid lines limit the field of talc-chlorite compositions.

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9. Fig. 8. Compositions of serpentines: 1 – antigorites, 2 – lizardites, 3 – Fe-lizardites.

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10. Fig. 9. Fragments in serpentinite sandstone, sample 1099/4; BSE (a–g, e) and in polarized light (d). (a) serpentinite fragment of indeterminate structure; (b) serpentinite fragment with pseudo-loop structure; (c) serpentinite fragments with different structures; (d–f) serpentinite fragment with signs of pseudomorphic replacement of primary silicates.

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11. Fig. 10. Chloritite fragments and their individual grains in serpentinite sandstones; BSE. (a–c) massive fragments, (d) schistose fragment, (d) ilmenite grain with local magnetite overgrowth rim, (e) rounded titaniferous magnetite grain with lamellae of silicate minerals, (g) apatite grain.

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12. Fig. 11. Compositions of chlorites: 1 – high-alumina magnesian chlorites (Chl1), 2 – low-alumina magnesian chlorites (high-chromium) (Chl2), 3 – low-alumina magnesian chlorites (low-chromium) (Chl3), 4 – moderate-magnesian chlorites (Chl4), 5 – ferrous chlorites (Chl5).

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13. Fig. 12. Rock fragments and detrital minerals in listvenite sandstone (sample 1099/1). (a–c) rounded listvenite fragments with ferrodolomite rims, (d) different generations of chrome-spinel in a grain with a fuchsite framing, (d) a grain of chrome-spinel with a fuchsite pseudomorph by an euhedral inclusion of primary silicate, (e) an aggregate of millerite and polydymite in cement, (g) rutile segregations in replaced ilmenite, (h) grains of zircon, metamorphic chrome-spinel, and fuchsite (Fuch) in cement.

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14. Fig. 13. Dolomite compositions: 1, 2 – serpentinite sandstones: 1 – central areas of dolomite fragments (Dol1), 2 – rims of fragments, small grains in the matrix, inclusions in magnetite (Dol2); 3–5 – listvenite sandstones: 3 – central areas of dolomite fragments (Dol3), 4 – listvenites (Dol4), 5 – rims around listvenite fragments, recrystallized areas of dolomite rock fragments, veinlets in cement and in dolomite rock fragments (Dol5).

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15. Fig. 14. Compositions of metamorphic chrome spinels. Sample 1099/1 is a listvenite sandstone, the other samples are serpentinite sandstones. The line connects the compositions measured in one grain.

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16. Supplementary 1: Geological, tectonic position and age of the ophiolithoclastite sequence
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17. Supplementary 2: ESM_1.xls – Mineral associations and lithoclast sizes; ESM_2.xls – Average compositions of chrome spinels; ESM_3.xls – Compositions of serpentines, chlorites, and talc; ESM_4.xls – Compositions of micas (fuchsites); ESM_5.xls – Compositions of carbonates; ESM_6.xls – Average compositions of accessory minerals; ESM_7.xls – Compositions of sulfides.
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