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I am deeply interested in how our Earth forms and evolves. During my Ph.D., my research primarily focused on two fundamental aspects of Earth's continental crust: (1) the concentration and distribution of major- and trace-elements in the crust, and (2) the systematics of halogens (F, Cl, Br, and I), a group of volatile elements, in crustal rocks.
By integrating petrological and geochemical constraints derived from diverse crustal rocks (sedimentary, igneous, and metamorphic), I seek to unravel the interactions between the continental crust and other geochemical reservoirs (atmosphere, oceans, and mantle), and to investigate how these interactions have shaped Earth's long-term evolution and habitability.
1. Reassessing the abundances of major and trace elements in the upper continental crust (UCC)
As a product of Earth's differentiation, the continental crust is an important geochemical reservoir, highly concentrated in lithophile and incompatible elements. Characterizing its composition is fundamental to understanding the processes responsible for its formation and to assessing the geochemical exchanges between the crust and other reservoirs (atmosphere, oceans, and mantle). Efforts to determine its average chemical composition began with the emergence of geochemistry in the early 20th century. However, large uncertainties remain in the existing estimates due to the great heterogeneity of crustal rocks (both horizontally and vertically), even for the most accessible part, the UCC.
To provide a more accurate estimate of UCC chemical abundances, my colleagues and I examined elemental relationships in a variety of fine-grained sediments (loess, glacial diamictites, and shales; see figure below), as well as in large datasets of continental igneous rocks. This approach also enables us to systematically assess the sedimentary and magmatic processes involved in the formation and evolution of the continental crust.
Newly analyzed loess samples (this project) and compiled previous fine-grained sedimentary rocks (loess, shales, and glacial diamictites)
Three works related to this project:
a) Han, P.-Y., Chen, K., Rudnick, R.L., Hu, Z.C., Average major element composition of the upper continental crust derived from an integrated study of sedimentary and igneous rocks. (under review)
b) Chen, K., Han, P.-Y., Rudnick, R.L., Guo, J.L., Hu, Z.C., Average trace element composition of the upper continental crust derived from an integrated study of sedimentary and igneous rocks. (under review)
c) Rudnick, R.L., Han, P.-Y., Concentrating Sb in the continental crust (in preparation)
...to be continued...
2. Halogens (F, Cl, Br, and I) in the continental crust
Halogens (F, Cl, Br, and I) are an important group of volatile elements predominantly concentrated on Earth’s surface and they play a critical role in modulating Earth’s habitability. Halogens can also be recycled into the deep Earth via subduction, where they influence magma generation and the transport of ore-forming metals. Despite their importance, the role of the continental crust in Earth's halogen cycle remains poorly explored. To better understand halogen behavior in continental processes such as chemical weathering, biological enrichment, and metamorphic dehydration, I obtained a comprehensive dataset of F-Cl-Br-I concentrations ± Cl isotopes for a series of terrigenous sediments: glacial diamictites, loess, and metasediments (from greenschist- to granulite- facies). These investigations have resulted in three projects for my PhD thesis:
The continental crust is depleted in halogens, indicating extensive degassing during its formation.
More pronounced F depletions in Mesoarchean samples may indicate a more volatile-depleted mantle prior to the onset of global plate tectonics and volatile recycling.
During weathering, Cl is preferentially lost relative to other halogens (F, Br, I), which leads to highly fractionated Br/Cl and I/Cl ratios in terrigenous sediments.
Iodine and Br are strongly concentrated in terrigenous, organic-rich sediments, and these enriched halogens likely source from the ocean, with their fluxes modulated by climate fluctuations.
Loess samples exhibit Br/Cl and I/Cl ratios indistinguishable from marine organic matter.
Mixing models suggest that >80–90% of loess originates from crystalline bedrocks, with <10–20% derived from halogen- and organic-rich sedimentary cover.
Unlike the other halogens (F, Br, I), whose concentrations gradually decrease in metasediments from amphibolite- to granulite- facies, Cl shows elevated concentrations in granulite-facies samples.
This Cl enrichment may result from Cl-rich fluids released from underplating magmas.
Such fluids may be widespread in the lower continental crust and play a key role in high-grade metamorphism and deep-crustal anatexis.
Three works related to this project:
a) Han, P.-Y., Rudnick, R.L., He, T., Marks, M A.W., Wang, S.J., Gaschnig, R.M., Hu, Z.C. (2023). Halogen (F, Cl, Br, and I) concentrations of the upper continental crust through time as recorded in ancient glacial diamictite composites. Geochimica et Cosmochimica Acta, 341, 28–45. doi.org/10.1016/j.gca.2022.11.012
b) Han, P.-Y., Rudnick, R.L., Hu, Z.C., Marks, M.A.W., He, T., Chen, K., Halogen (F, Cl, Br, and I) enrichments on the continental surface: a perspective from loess. Geochemical Perspective Letters, 32, 52–57. doi.org/10.7185/geochemlet.2442
c) Han, P.-Y., Husing, M., Barnes, J.D., Marks, M.A.W., He, T., Bea, F., Hu, Z.C., Rudnick, R.L., Halogen behavior during high-grade metamorphism and partial melting in the deep continental crust (Ivrea Zone, NW Italy). (under review)
...to be continued...
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