Ancient xenocrystic zircon in young volcanic rocks of the southern Lesser Antilles island arc

Yamirka ROJAS-AGRAMONTE*, Ian S. WILLIAMS, Richard ARCULUS, Alfred KRÖNER, Antonio GARCÍA-CASCO, Concepción LÁZARO, Stephan BUHRE, Jean WONG, Helen GENG, Carlos Morales ECHEVERRÍA, Teresa JEFFRIES, Hangqian XIE, Regina MERTZ-KRAUS

*Corresponding author for this work

Research output: Journal PublicationsJournal Article (refereed)peer-review

29 Citations (Scopus)

Abstract

The Lesser Antilles arc is one of the best global examples in which to examine the effects of the involvement of subducted sediment and crustal assimilation in the generation of arc crust. Most of the zircon recovered in our study of igneous and volcaniclastic rocks from Grenada and Carriacou (part of the Grenadines chain) is younger than 2 Ma. Within some late Paleogene to Neogene (~ 34–0.2 Ma) lavas and volcaniclastic sediments however, there are Paleozoic to Paleoarchean (~ 250–3469 Ma) xenocrysts, and Late Jurassic to Precambrian zircon (~ 158–2667 Ma) are found in beach and river sands. The trace element characteristics of zircon clearly differentiate between different types of magmas generated in the southern Lesser Antilles through time. The zircon population from the younger arc (Miocene, ~ 22–19 Ma, to Present) has minor negative Eu anomalies, well-defined positive Ce anomalies, and a marked enrichment in heavy rare earth elements (HREE), consistent with crystallization from very oxidized magmas in which Eu 2 + was in low abundance. In contrast, zircon from the older arc (Eocene to mid-Oligocene, ~ 30–28 Ma) has two different REE patterns: 1) slight enrichment in the light (L)REE, small to absent Ce anomalies, and negative Eu anomalies and 2) enriched High (H)REE, positive Ce anomalies and negative Eu anomalies (a similar pattern is observed in the xenocrystic zircon population). The combination of positive Ce and negative Eu anomalies in the zircon population of the older arc indicates crystallization from magmas that were variably, but considerably less oxidized than those of the younger arc. All the igneous zircon has positive εHf(t), reflecting derivation from a predominantly juvenile mantle source. However, the εHf(t) values vary significantly within samples, reflecting considerable Hf isotopic heterogeneity in the source. The presence of xenocrystic zircon in the southern Lesser Antilles is evidence for the assimilation of intra-arc crustal sediments and/or the recycling and incorporation of sediments into the magma sources in the mantle wedge. Most likely however, primitive magmas stalling and fractionating during their ascent through the Antilles crust entrained ancient zircon. This is evidence by the geochemistry of the study samples, which is inconsistent with any involvement of partially melted subducted sediment. Paleogeographic reconstructions show that the old zircon could derive from distant regions such as the Eastern Andean Cordillera of Colombia, the Merida Andes, and the northern Venezuela coastal ranges, transported for example by the Proto-Maracaibo River precursor of the Orinoco River.

Original languageEnglish
Pages (from-to)228-252
Number of pages25
JournalLithos
Volume290-291
Early online date17 Aug 2017
DOIs
Publication statusPublished - Oct 2017
Externally publishedYes

Bibliographical note

YRA thanks Bob Stern for suggesting fieldwork in Grenada to “hunt” for old zircons” and Jesús Máximo and Kathrin Abraham for help and support during fieldwork. Liqin Zhou and Xiao-Chao Che provided the zircon CL images, Chun Yang prepared perfect zircon mounts, and Jianhui Liu and Zhiqing Yang made sure that the SHRIMP II instrument in Beijing was in excellent operating condition. Jianfeng Gao of Nanjing University provided an unpublished Excel-based program to construct the Hf evolution diagrams of Fig. 10 .

Funding

This study was supported by Deutsche Forschungsgemeinschaft (DFG) grants KR590/85-1 to AK and RO4174/2-1 to YRA, and Spanish MINECO grants CGL2015-65824 and CGL2012-36263 and University of Granada research program (CIC) to AGC and CLC. This research also received support from the SYNTHESYS Project ( http://www.synthesys.info /) which is financed by the European Community Research Infrastructure Action under the FP7 “Capacities” Program, the Intra-University Research Support Program of Mainz University (Universitätsinterne Forschungsförderung (FoFö). We thank two anonymous reviewers who helped to improve the manuscript and Prof. Sun (editor of LITHOS) for handling our publication.

Keywords

  • Th disequilibrium
  • Carriacou-Petite Martinique
  • Crustal assimilation
  • Grenada
  • Lesser Antilles
  • Zircon xenocryst

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