Graduation Year

2024

Document Type

Dissertation

Degree

Ph.D.

Degree Name

Doctor of Philosophy (Ph.D.)

Degree Granting Department

Geology

Major Professor

Jeffrey Ryan, Ph.D.

Committee Member

Aurelie Germa, Ph.D.

Committee Member

Zachary Atlas, Ph.D.

Committee Member

Tobias Höfig, Ph.D.

Keywords

Crust, Enrichment, Mantle, Melt, Mixing, Subduction

Abstract

In this dissertation, I have characterized the geochemical signatures of the South China Sea (SCS) igneous basement and marine sediments with the intent to examine the results in the context of the understanding the origin and evolution of the SCS oceanic mafic crust, the type of sediments found in the SCS, and finally their impact on the composition of the island arc lavas within the northern Luzon Arc. This dissertation research has three main objectives:

  1. Examining the origin, composition, and evolution of the SCS mid-ocean ridge basalt (MORB), as well as the preexisting crustal rocks recovered near the continent-ocean transition zone, and out to the relict ocean ridge, to scrutinize the geochemical changes of the SCS ocean floor basalts over the approximately 17 million years of spreading and 15 million years post-spreading.
  2. Analyzing the compositional signatures of the seafloor sediments of the Pearl River Mouth Basin, as compared to a range of the compositional averages for marine sediments globally, and creating a composite to represent the continentally derived marine sediments entering the Manila Trench.
  3. Investigating the connections between these subducting igneous basement rocks with marine sediments of the SCS and the geochemical signatures of lavas from the Luzon Arc, to better understand the subduction and mantle source mixing influences that have led to the island arc basalts (IAB) of the Luzon Strait and northern Luzon Island.

My new geochemical data were collected via Inductively Coupled Plasma-Mass Spectrometry (ICP-MS) and ICP-Optical Emissions Spectrometry (OES) at the University of South Florida on both the igneous basement and marine sediment samples recovered during the International Ocean Discovery Program (IODP) Expeditions 367 and 368 while aboard the JOIDES Resolution in 2017. These results build upon existing data to create a larger view of the SCS-Luzon Arc system. Comparing these new data to existing compositions for MORBs and global sedimentary materials highlights significant differences between the SCS crust and sediments and the crust and sediment compositions that are being subducted into trenches worldwide.

These findings show that the SCS sediments and igneous basement differ compositionally from the crust and sediments encountered in both adjacent ocean and marginal basins, and from the global composites for ocean crust and marine sediments that are commonly used in subduction zone studies. These differences must be considered when attempting to model the melting and mixing phenomena within the mantle sources for the Luzon Arc. This study underscores the importance of considering individual arc systems' complexities to understand arc magmatism globally.

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