Zircon Xenocrysts from the Shaka Ridge Record Ancient Continental Crust: New U-Pb Geochronological and Oxygen Isotopic Data

Abstract

Over the past two decades, a significant number of discoveries of ancient zircon xenocrysts in ocean-floor magmatic rocks have been reported. These findings provide compelling evidence for the presence of ancient continental crust within young oceanic lithosphere. Almost all finds of ancient zircon xenocrysts within oceanic crust are from the Mid-Atlantic Ridge. For other localities, however, similar data are very limited. This report presents the first age determinations (U-Pb, SHRIMP-II) and isotope-geochemical data (oxygen, trace and rare earth elements) for zircon xenocrysts from gabbro-diorites of the Shaka Ridge, in the vicinity of the Shaka fracture zone, near the western end of the Southwest Indian Ridge. The work is based on a study of bottom rock material dredged during expeditionary research on the R/V “Akademik Fedorov” (Russia) in 2016. The U-Pb isotope system of the zircon xenocrysts recorded a crystallization age of ∼2.8 Ga at an upper discordia intercept and an age of ∼600 Ma interpreted as the timing of a superimposed thermal event at a lower discordia intercept. The zircon xenocrysts show geochemical signatures of magmatic origin, i.e., fractionated REE distribution spectra with an increase in chondrite-normalized values from light to heavy REE, positive Ce anomalies and negative Eu anomalies, and high Th/U ratios (0.59–7.77). In discrimination diagrams based on a series of inter-element relationships, zircon compositions fall into the fields of zircons from rocks of continental crust, mostly granitoids. The Li content of the zircons is high (1.8 ppm–50 ppm), adding further evidence to their derivation from rocks of continental crust. During their residence within young oceanic crust, the zircon xenocrysts experienced alterations under the influence of submarine high-temperature hydrothermal fluids, which selectively affected the distribution of trace elements in the zircons and reduced the δ¹⁸O values to 1.75‰–3.15‰. The presence of obviously older zircons in Shaka gabbro-diorites clearly demonstrates the presence of ancient continental fragments and their recycling into the mantle at the western end of the Southwest Indian Ridge.

Keywords

zircon / U-Pb geochronology / oxygen isotopes / trace elements / rare earth elements / Shaka Ridge / South Atlantic / Southwest Indian Ridge

References

Aranovich L Y, Zinger T F, Bortnikov N S, . Zircon in Gabbroids from the Axial Zone of the Mid-Atlantic Ridge, Markov Deep, 6°N: Correlation of Geochemical Features with Petrogenetic Processes. Petrology, 2013, 21(1): 1-15.

Ashwal L D, Wiedenbeck M, Torsvik T H. Archaean Zircons in Miocene Oceanic Hotspot Rocks Establish Ancient Continental Crust beneath Mauritius. Nature Communications, 2017, 8: 14086

Balashov Y A, Skublov S G. Contrasting Geochemistry of Magmatic and Secondary Zircons. Geochemistry International, 2011, 49(6): 594-604.

Ballard J R, Palin M J, Campbell I H. Relative Oxidation States of Magmas Inferred from Ce(IV)/Ce(III) in Zircon: Application to Porphyry Copper Deposits of Northern Chile. Contributions to Mineralogy and Petrology, 2002, 144(3): 347-364.

Bau M, Dulski P. Comparing Yttrium and Rare Earths in Hydrothermal Fluids from the Mid-Atlantic Ridge: Implications for Y and REE Behaviour during Near-Vent Mixing and for the Y/Ho Ratio of Proterozoic Seawater. Chemical Geology, 1999, 155(1/2): 77-90.

Bea F, Bortnikov N, Montero P, . Zircon Xenocryst Evidence for Crustal Recycling at the Mid-Atlantic Ridge. Lithos, 2020, 354/355 105361

Belousova E A, Griffin W L, O’Reilly S Y. Zircon Crystal Morphology, Trace Element Signatures and Hf Isotope Composition as a Tool for Petrogenetic Modelling: Examples from Eastern Australian Granitoids. Journal of Petrology, 2006, 47(2): 329-353.

Belousova E A, Griffin W L, O’Reilly S Y, . Igneous Zircon: Trace Element Composition as an Indicator of Source Rock Type. Contributions to Mineralogy and Petrology, 2002, 143(5): 602-622.

Belyatskii B V, Levskii L, Trukhalev A I, . Precambrian Granite-Gneiss from the Mid-Atlantic Ridge (26°N): A U-Pb and Sm-Nd Isotopic Study. Geochemistry International, 1997, 35(8): 770-773

Bindeman I. Oxygen Isotopes in Mantle and Crustal Magmas as Revealed by Single Crystal Analysis. Reviews in Mineralogy and Geochemistry, 2008, 69(1): 445-478.

Black L P, Kamo S L, Allen C M, . Improved ²⁰⁶Pb/²³⁸U Microprobe Geochronology by the Monitoring of a Trace-Element-Related Matrix Effect; SHRIMP, ID-TIMS, ELA-ICP-MS and Oxygen Isotope Documentation for a Series of Zircon Standards. Chemical Geology, 2004, 205(1/2): 115-140.

Bortnikov N S, Sharkov E V, Bogatikov O A, . Finds of Young and Ancient Zircons in Gabbroids of the Markov Deep, Mid-Atlantic Ridge, 5°54′-5°02.2′N (Results of SHRIMP-II U-Pb Dating): Implication for Deep Geodynamics of Modern Oceans. Doklady Earth Sciences, 2008, 421 859-866.

Bortnikov N S, Silantyev S A, Bea F, . U-Pb Dating, Oxygen and Hafnium Isotope Ratios of Zircon from Rocks of Oceanic Core Complexes at the Mid-Atlantic Ridge: Evidence for the Interaction of Contemporary and Ancient Crusts in the Spreading Center of the Ocean Floor. Doklady Earth Sciences, 2019, 489(2): 1396-1401.

Bouvier A S, Ushikubo T, Kita N T, . Li Isotopes and Trace Elements as a Petrogenetic Tracer in Zircon: Insights from Archean TTGs and Sanukitoids. Contributions to Mineralogy and Petrology, 2012, 163(5): 745-768.

Bröcker M, Löwen K, Rodionov N. Unraveling Protolith Ages of Meta-Gabbros from Samos and the Attic-Cycladic Crystalline Belt, Greece: Results of a U-Pb Zircon and Sr-Nd Whole Rock Study. Lithos, 2014, 198/199: 234-248.

Cheng H, Zhou H Y, Yang Q H, . Jurassic Zircons from the Southwest Indian Ridge. Scientific Reports, 2016, 6: 26260

Corfu F, Hanchar J M, Hoskin P W O, . Atlas of Zircon Textures. Reviews in Mineralogy and Geochemistry, 2003, 53(1): 469-500.

Dokukina K A, Kaulina T V, Konilov A N, . Archaean to Palaeoproterozoic High-Grade Evolution of the Belomorian Eclogite Province in the Gridino Area, Fennoscandian Shield: Geochronological Evidence. Gondwana Research, 2014, 25(2): 585-613.

Douglass J, Schilling J G, Fontignie D. Plume-Ridge Interactions of the Discovery and Shona Mantle Plumes with the Southern Mid-Atlantic Ridge (40°–55°S). Journal of Geophysical Research: Solid Earth, 1999, 104(B2): 2941-2962.

Eiler J M. Oxygen Isotope Variations of Basaltic Lavas and Upper Mantle Rocks. Reviews in Mineralogy and Geochemistry, 2001, 43(1): 319-364.

Fedotova A A, Bibikova E V, Simakin S G. Ion-Microprobe Zircon Geochemistry as an Indicator of Mineral Genesis during Geochronological Studies. Geochemistry International, 2008, 46(9): 912-927.

Finch R J, Hanchar J M. Structure and Chemistry of Zircon and Zircon-Group Minerals. Reviews in Mineralogy and Geochemistry, 2003, 53(1): 1-25.

Fisher R L, Sclater J G. Tectonic Evolution of the Southwest Indian Ocean since the Mid-Cretaceous: Plate Motions and Stability of the Pole of Antarctica/Africa for at Least 80 Myr. Geophysical Journal International, 1983, 73(2): 553-576.

Frey F A, Weis D, Borisova A Y, . Involvement of Continental Crust in the Formation of the Cretaceous Kerguelen Plateau: New Perspectives from ODP Leg 120 Sites. Journal of Petrology, 2002, 43(7): 1207-1239.

Fu B, Mernagh T P, Kita N T, . Distinguishing Magmatic Zircon from Hydrothermal Zircon: A Case Study from the Gidginbung High-Sulphidation Au-Ag-(Cu) Deposit, SE Australia. Chemical Geology, 2009, 259(3/4): 131-142.

Geisler T, Schleicher H. Improved U-Th-Total Pb Dating of Zircons by Electron Microprobe Using a Simple New Background Modeling Procedure and Ca as a Chemical Criterion of Fluid-Induced U-Th-Pb Discordance in Zircon. Chemical Geology, 2000, 163(1/2/3/4): 269-285.

Georgen J E, Lin J, Dick H J B. Evidence from Gravity Anomalies for Interactions of the Marion and Bouvet Hotspots with the Southwest Indian Ridge: Effects of Transform Offsets. Earth and Planetary Science Letters, 2001, 187(3/4): 283-300.

Gregory R T, Taylor H P Jr.. An Oxygen Isotope Profile in a Section of Cretaceous Oceanic Crust, Samail Ophiolite, Oman: Evidence for δ¹⁸O Buffering of the Oceans by Deep (>5 km) Seawater-Hydrothermal Circulation at Mid-Ocean Ridges. Journal of Geophysical Research: Solid Earth, 1981, 86(B4): 2737-2755.

Grimes C B, John B E, Cheadle M J, . On the Occurrence, Trace Element Geochemistry, and Crystallization History of Zircon from in situ Ocean Lithosphere. Contributions to Mineralogy and Petrology, 2009, 158(6): 757-783.

Grimes C B, John B E, Kelemen P B, . Trace Element Chemistry of Zircons from Oceanic Crust: A Method for Distinguishing Detrital Zircon Provenance. Geology, 2007, 35(7): 643-646.

Grimes C B, Ushikubo T, John B E, . Uniformly Mantle-Like δ¹⁸O in Zircons from Oceanic Plagiogranites and Gabbros. Contributions to Mineralogy and Petrology, 2011, 161(1): 13-33.

Grimes C B, Wooden J L, Cheadle M J, . “Fingerprinting” Tectono-Magmatic Provenance Using Trace Elements in Igneous Zircon. Contributions to Mineralogy and Petrology, 2015, 170(5/6): 46

Hinton R W, Upton B G J. The Chemistry of Zircon: Variations within and between Large Crystals from Syenite and Alkali Basalt Xenoliths. Geochimica et Cosmochimica Acta, 1991, 55 11 3287-3302.

Hoskin P W O. Trace-Element Composition of Hydrothermal Zircon and the Alteration of Hadean Zircon from the Jack Hills, Australia. Geochimica et Cosmochimica Acta, 2005, 69(3): 637-648.

Hoskin P W O, Schaltegger U. The Composition of Zircon and Igneous and Metamorphic Petrogenesis. Reviews in Mineralogy and Geochemistry, 2003, 53(1): 27-62.

Jochum K P, Dingwell D B, Rocholl A, . The Preparation and Preliminary Characterisation of Eight Geological MPI-DING Reference Glasses for in-situ Microanalysis. Geostandards and Geoanalytical Research, 2000, 24(1): 87-133.

Geochemistry, Geophysics, Geosystems, 2006, 7(2

Kamenetsky V S, Maas R, Sushchevskaya N M, . Remnants of Gondwanan Continental Lithosphere in Oceanic Upper Mantle: Evidence from the South Atlantic Ridge. Geology, 2001, 29 3): 243-246.

Kirkland C L, Whitehouse M J, Slagstad T. Fluid-Assisted Zircon and Monazite Growth within a Shear Zone: A Case Study from Finnmark, Arctic Norway. Contributions to Mineralogy and Petrology, 2009, 158(5): 637-657.

Korolev N M, Melnik A E, Li X H, . The Oxygen Isotope Composition of Mantle Eclogites as a Proxy of Their Origin and Evolution: A Review. Earth-Science Reviews, 2018, 185 288-300.

Kostitsyn Y A, Belousova E A, Bortnikov N S, . Zircons in Gabbroids from the Axial Zone of the Mid-Atlantic Ridge: U-Pb Age and ¹⁷⁶Hf/¹⁷⁷Hf Ratio (Results of Investigations by the Laser Ablation Method). Doklady Earth Sciences, 2009, 429: 1305

Kostitsyn Y A, Belousova E A, Silant’ev S A, . Modern Problems of Geochemical and U-Pb Geochronological Studies of Zircon in Oceanic Rocks. Geochemistry International, 2015, 53(9): 759-785.

Kostitsyn Y A, Silantyev S A, Anosova M O, . Age of Plutonic Rocks from the Vema Fracture Zone (Central Atlantic) and Nature of Their Mantle Sources. Geochemistry International, 2018, 56(2): 89-110.

Kremenetskiy A A, Gromalova N A, Skolotnev S G, . Sources of Magmatic Rocks from the Deep-Sea Floor of the Arctic Ocean and the Central Atlantic: Evidence from Data on the U-Pb Age, Hf Isotopes, and REE Geochemistry of Zircons. Doklady Earth Sciences, 2018, 481(1): 852-856.

le Roux P J, le Roex A P, Schilling J G, . Mantle Heterogeneity beneath the Southern Mid-Atlantic Ridge: Trace Element Evidence for Contamination of Ambient Asthenospheric Mantle. Earth and Planetary Science Letters, 2002, 203(1): 479-498.

Leontev V I, Skublov S G, Shatova N V, . Zircon U-Pb Geochronology Recorded Late Cretaceous Fluid Activation in the Central Aldan Gold Ore District, Aldan Shield, Russia: First Data. Journal of Earth Science, 2020, 31(3): 481-491.

Li X H, Long W G, Li Q L, . Penglai Zircon Megacrysts: A Potential New Working Reference Material for Microbeam Determination of Hf-O Isotopes and U-Pb Age. Geostandards and Geoanalytical Research, 2010, 34(2): 117-134.

Lin, J., Dick, H. J., Schouten, H., et al., 2001. Evidence for Off-Axis Volcanic Relicts of the Bouvet Hotspot and Its Interaction with the Southwest Indian Ridge. (2022-01-12). https://ui.adsabs.harvard.edu/abs/2001AGUFM.T31D..10L/abstract

Lin, J., Georgen, J. E., Dick, H., 2003. Ridge-Hotspot Interactions at Ultra-Slow Spreading Conditions: Bouvet/Marion Hotspot and the SW Indian Ridge. InterRidge Symposium and Workshop: Ridge-Hotspot Interaction: Recent Progress and Prospects for Enhanced International Collaboration, September 8–10, 2003, Brest. 30

Ludwig K R. Squid 1.02: A User’s Manual, 2001, Berkeley: Berkeley Geochronological Center Special Publication, 19 2

Ludwig K R. Isoplot 3.00: A Geochronological Toolkit for Microsoft Excel, 2003, Berkeley: Berkeley Geochronology Center Special Publication, 71 4

McDonough W F, Sun S S. The Composition of the Earth. Chemical Geology, 1995, 120(3/4): 223-253.

Michard A, Albarède F. The REE Content of some Hydrothermal Fluids. Chemical Geology, 1986, 55(1/2): 51-60.

Middlemost E A K. Naming Materials in the Magma/Igneous Rock System. Earth-Science Reviews, 1994, 37(3/4): 215-224.

Norton I O, Sclater J G. A Model for the Evolution of the Indian Ocean and the Breakup of Gondwanaland. Journal of Geophysical Research: Solid Earth, 1979, 84(B12): 6803-6830.

Pilot J, Werner C D, Haubrich F, . Palaeozoic and Proterozoic Zircons from the Mid-Atlantic Ridge. Nature, 1998, 393(6686): 676-679.

Rocholl A B E, Simon K, Jochum K P, . Chemical Characterisation of NIST Silicate Glass Certified Reference Material SRM 610 by ICP-MS, TIMS, LIMS, SSMS, INAA, AAS and PIXE. Geostandards and Geoanalytical Research, 1997, 21(1): 101-114.

Rodionov N V, Belyatsky B V, Antonov A V, . Comparative in-situ U-Th-Pb Geochronology and Trace Element Composition of Baddeleyite and Low-U Zircon from Carbonatites of the Palaeozoic Kovdor Alkaline-Ultramafic Complex, Kola Peninsula, Russia. Gondwana Research, 2012, 21(4): 728-744.

Rumyantseva N A, Vanshteyn B G, Skublov S G. Petrochemical Features of Tholeiites from the Shaka Ridge (South Atlantic). Journal of Mining Institute, 2021, 248 223-231.

Sauter, D., Cannat, M., 2010. The Ultraslow Spreading Southwest Indian Ridge. In: Rona, P. A., Devey, C. W., Dyment, J., eds., Geophysical Monograph Series. American Geophysical Union, Washington D. C. 153–173. https://doi.org/10.1029/2008gm000843

Sharkov E V, Bortnikov N S, Bogatikov O A, . Mesozoic Zircon from Gabbronorites of the Axial Mid-Atlantic Ridge, 6°N, Markov Deep. Doklady Earth Sciences, 2004, 397(5): 654-657

Shulyatin O G, Belyatsky B V, Kremenetsky A A. Geochemical and Geochronological Studies of Polychronic Zircons in Igneous Rocks from the Mid-Atlantic Ridge and Some Features of Its Structure. Regional Geology and Metallogeny, 2019, 77: 11-19.

Skolotnev S G, Bel’tenev V E, Lepekhina E N, . Younger and Older Zircons from Rocks of the Oceanic Lithosphere in the Central Atlantic and Their Geotectonic Implications. Geotectonics, 2010, 44(6): 462-492.

Tang G Q, Li X H, Li Q L, . Deciphering the Physical Mechanism of the Topography Effect for Oxygen Isotope Measurements Using a Cameca IMS-1280 SIMS. Journal of Analytical Atomic Spectrometry, 2015, 30(4): 950-956.

Torsvik T H, Amundsen H, Hartz E H, . A Precambrian Microcontinent in the Indian Ocean. Nature Geoscience, 2013, 6(3): 223-227.

Ushikubo T, Kita N T, Cavosie A J, . Lithium in Jack Hills Zircons: Evidence for Extensive Weathering of Earth’s Earliest Crust. Earth and Planetary Science Letters, 2008, 272(3/4): 666-676.

Valley J W, Kinny P D, Schulze D J, . Zircon Megacrysts from Kimberlite: Oxygen Isotope Variability among Mantle Melts. Contributions to Mineralogy and Petrology, 1998, 133(1/2): 1-11.

Valley J W, Lackey J S, Cavosie A J, . 4.4 Billion Years of Crustal Maturation: Oxygen Isotope Ratios of Magmatic Zircon. Contributions to Mineralogy and Petrology, 2005, 150(6): 561-580.

Watson E B, Wark D A, Thomas J B. Crystallization Thermometers for Zircon and Rutile. Contributions to Mineralogy and Petrology, 2006, 151(4): 413-433.

Wiedenbeck M, Allé P, Corfu F, . Three Natural Zircon Standards for U-Th-Pb, Lu-Hf, Trace Element and REE Analyses. Geostandards and Geoanalytical Research, 1995, 19(1): 1-23.

Wiedenbeck M, Hanchar J M, Peck W H, . Further Characterisation of the 91500 Zircon Crystal. Geostandards and Geoanalytical Research, 2004, 28(1): 9-39.

Williams I S. U-Th-Pb Geochronology by Ion Microprobe. Applications of Microanalytical Techniques to Understanding Mineralizing Processes. Society of Economic Geologists, 1998, 7: 1-35.

Xu H J, Zhang J F. Zircon Geochronological Evidence for Participation of the North China Craton in the Protolith of Migmatite of the North Dabie Terrane. Journal of Earth Science, 2018, 29(1): 30-42.

Zhao Y, Zheng J P, Xiong Q. Zircon from Orogenic Peridotite: an Ideal Indicator for Mantle-Crust Interaction in Subduction Zones. Journal of Earth Science, 2019, 30(3): 666-678.