A new approach to understanding the origin of Fuerteventura, Canary Islands (Spain): A U-Pb, Hf and O isotope and minor- and trace- element detrital zircon study

• Author / Creator

  Sagan, Madisen

• The Canarian Archipelago contains seven islands proximal to the African continent and High Atlas Mountains. The origin and magmatic evolution of these islands has been a contentious issue for several decades. This particular archipelago is unique because three of the islands (Fuerteventura, La Palma, La Gomera) have been reported to contain uplifted portions of the intrusive complex, potentially exposing the earliest phases of the islands growth. In order to better understand Fuerteventura’s early magmatic history, we have conducted a U-Pb, Hf and O isotope and minor- and trace-element detrital zircon study of sand samples from three locations proximal to the intrusive complex. A U-Pb and geochemical study of detrital zircons is an efficient method to evaluate the early growth history of the island since most of the uplifted complex consists of zircon-bearing rocks (syenite, nepheline syenite, gabbro, anorthosite, carbonatite). The Hf and O isotope study helps to develop an understanding of the magma source of these intrusive rock units and evaluate the role of lithospheric contamination during the magmatic activity. A total of 260 zircon grains were analyzed using in-situ U-Pb Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA-MC-ICPMS). The U-Pb detrital zircon ages from this study range from the Early Oligocene to Early Pliocene (33.7-3.8 Ma), with results exhibiting four prominent age peaks at 4.4, 16.8, 21.1, and 25.5 Ma. A total of 149 single detrital zircon grains were analyzed for their trace-element content using a New Wave UP-213 laser ablation workstation coupled with a Thermo Scientific iCAP-Q Quadrupole Inductively Coupled Plasma Mass Spectrometer (LA-ICPMS) to subdivide the zircons based on probable magma provenance to further develop our understanding of the islands magmatic evolution. The main distinguishing geochemical features of the detrital zircons are their Ti and Y concentrations, along with the magnitude of the Eu/Eu* anomaly. Using these geochemical criteria, the detrital zircons analyzed from this study indicate the following provenance: 51% syenite, 36% anorthosite/gabbro, 7% nepheline syenite, and 5% carbonatite. A subset of the mounted grains (n=133) were analyzed for their hafnium isotope composition using a Laser Ablation Split Stream (LASS) technique. The new zircon Hf isotopic data can be divided into three distinct groups: a predominant zircon suite with εHfi values ranging from +7.5 to +10.4, a more ‘depleted’ population ranging from +10.6 to +15.2, and a more ‘enriched’ population ranging from -0.2 to +7.0. The zircon εHf values are relatively consistent (+7.5 to +10) in the early part of Fuerteventura’s magmatic history from 34-20 Ma, but an abrupt change occurs at ~20 Ma, where these younger zircons display εHf variation reflecting both depleted and enriched isotopic signatures. The depleted signature discontinues after an apparent hiatus from 14.5- 6.5 Ma, while the enriched signature is observed to persist into the Late-Miocene to Pliocene samples. A total of 191 oxygen isotope (18O/16O) spot compositions were measured on 91 detrital zircon grains using a Cameca IMS 1280 multicollector ion microprobe. The oxygen isotope data exhibit two distinct populations. The first group, representing 12% of the sample population, resembles the mantle-like oxygen field (+5.3 ± 0.3‰) with δ18O values ranging from 5.00-5.48‰, the second group representing the remaining 88% of the population, records low δ18O values (3.27- 4.99‰) that are below the zircon mantle field, representing 88% of the sample population. Low δ18O values provide evidence for high temperature rock-water alteration in the source region of these magmas, suggesting an origin for some magmas by melting or assimilation of hydrothermally altered oceanic crust.There are several new features of Fuerteventura’s magmatic history revealed from this study: 1) there are four peaks of magmatic activity (25.7, 21.0, 16.7, 4.4 Ma), 2) Oligocene detrital zircons (33.7-24.4 Ma) dominate the northern part of the complex, 3) magmatic activity in general youngs from north to south, 4) a previously unrecognized period of Late Miocene and Early Pliocene intrusive rocks (6.5-3.8 Ma) must exist in the central part of the island, 5) zircon Hf isotope data require at least three mantle source endmembers to explain the generation of Fuerteventura’s magmatic activity, including an enriched, depleted , and HIMU-plume component, and 6) low δ18O values of some detrital zircons suggest the involvement of hydrothermally altered oceanic crust in the origin of many Fuerteventura magmas.

• Subjects / Keywords

  • oxygen isotope
  • geochronology
  • detrital zircon
  • Canary Islands
  • hafnium isotope
  • Hf
  • U-Pb isotope
  • trace element study
  • Fuerteventura
  • geology

• Graduation date

  Spring 2019

• Type of Item

  Thesis

• Degree

  Master of Science

• DOI

  https://doi.org/10.7939/r3-grvd-5s14

• License

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