Geochemical Study of Detrital Apatite in Sediment from the Southern Okinawa Trough: New Insights into Sediment Provenance

Hu Hu,Chen Chen,Yin Yin,Li Li,Qi Qi,Zeng Zeng,Fang Fang,Zhu Zhu

doi:10.3390/min9100619

Abstract

Detrital apatite is a promising accessory mineral for reliable fingerprinting of the protolith composition of detrital sediment. Here, we present the geochemical compositions of detrital apatites from four sections of a high-resolution (~140 cm/kyr) sedimentary archive from the southern Okinawa Trough (SOT) for constraining sediment source rock types and establishing changes in provenance. A series of diagrams based on the geochemical data show that apatites in Section 1 derived mainly from mafic/intermediate rocks, while apatites in the three younger sections largely originated from mafic/intermediate rocks and acid rocks. Further, the four sections included a few contributions of apatites from alkaline rocks and metamorphic rocks. Through a comprehensive analysis of controlling factors and regional stratigraphy in the study area, we concluded that sediments in the SOT are the weathering/erosion products of sedimentary and meta-sedimentary rocks in the western and northeastern Taiwan Island, with ultimate sources containing a wide variety of rock types. The sediment from rivers in eastern Taiwan did not significantly contribute to deposition in the SOT. Apatites in Sections 2–4 showed strong geochemical similarity but differed from those in Section 1, indicating that the types of weathered/eroded sedimentary rocks in the weathering profile of river drainage basins of Taiwan Island changed in Section 2 (2010–1940 cal. yr BP) and have remained stable since then.

Highlights

The mineralogical and geochemical characteristics of sedimentary archives from lakes, deltas, and marginal seas have long been used for studying the source-to-sink pathways of terrigenous sediments in response to variations in climate and environment in the geological past [1,2,3,4,5,6]
Detrital apatite is a promising candidate for fingerprinting changes in sediment provenance, mainly because (1) apatite is a common accessory mineral in most igneous, metamorphic, and sedimentary rocks [20,24,25,26]; (2) apatite generally contains a wide range of trace elements substituting on both cation and anion sites, which may exert dominant control over the geochemical behavior of trace components like Mn, Y, Sr, U, Th, and rare earth elements (REEs) in melts and magmatic fluids [8,20]; (3) the geochemical composition of apatite depends on source rock types and is unlikely to change with weathering, transport, and even burial diagenesis [20,21,27,28,29]
Four sections from the bottom to top of Core S3 were chosen for apatite separation

Summary

Introduction

The mineralogical and geochemical characteristics of sedimentary archives from lakes, deltas, and marginal seas have long been used for studying the source-to-sink pathways of terrigenous sediments in response to variations in climate and environment in the geological past [1,2,3,4,5,6]. The geochemical analysis of heavy minerals such as apatite, garnet, rutile, clinopyroxene, zircon, and magnetite has provided much better constraints on sediment provenance, since their varietal characteristics are mainly inherited from source rocks and their compositions are specific to certain parageneses [8,14,18,19,20,21,22,23] Among these heavy minerals, detrital apatite is a promising candidate for fingerprinting changes in sediment provenance, mainly because (1) apatite is a common accessory mineral in most igneous, metamorphic, and sedimentary rocks [20,24,25,26]; (2) apatite generally contains a wide range of trace elements substituting on both cation and anion sites, which may exert dominant control over the geochemical behavior of trace components like Mn, Y, Sr, U, Th, and rare earth elements (REEs) in melts and magmatic fluids [8,20];

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Discussion

Conclusion