A comparison of detrital U–Pb zircon, ~(40)Ar/~(39)Ar hornblende, ~(40)Ar/~(39)Ar biotite ages in marine sediments off East Antarctica: Implications for the geology of subglacial terrains and provenance studies

摘要

U–Pb ages of detrital zircon grains have provided an extraordinary tool for sedimentary provenance work, given that they are ubiquitous, resistant to damage and weathering, and that the U–Pb age records the crystallization age of the mineral. Although not as widely used, ~(40)Ar/~(39)Ar dating of detrital hornblende and biotite grains can also serve as powerful sedimentary provenance tools, particularly in situations where chemical weathering is minor (e.g., Antarctica). Certain natural biases exist among these mineral chronometers (e.g., abundance in different rock types, durability during abrasion, resistance to dissolution) that determine the extent to which they are found in sedimentary deposits. Additionally, the ~(40)Ar/~(39)Ar systems in hornblende and biotite have lower closure temperatures for thermally activated diffusion (~500 °C and ~300 °C, respectively). Thus, for areas that have experienced a polymetamorphic history, such as East Antarctica, combining these approaches can provide added detail to provenance studies. In this studywe provide a comparison of the detrital U–Pb zircon, ~(40)Ar/~(39)Ar hornblende and ~(40)Ar/~(39)Ar biotite age populations from 28 glacial-diamict and glacial-marine sediment core samples located around East Antarctica (55°W to 163°E). We present 3370 new detrital age measurements of U–Pb zircon, ~(40)Ar/~(39)Ar hornblende, and ~(40)Ar/~(39)Ar biotite, in conjunction with previously published data from some of the same core sites, as well as 78 U–Pb zircon ages measured on dispersed zircons from five ice-rafted debris (IRD) layers recovered at ODP Site 1165. Our data indicate that detrital U–Pb zircon, ~(40)Ar/~(39)Ar hornblende and ~(40)Ar/~(39)Ar biotite ages faithfully document the onshore geology of source areas within East Antarctica, as expressed in their respective age populations. In addition, a number of previously unknown age populations are recorded by the combined thermochronometers. Assuming an East Antarctic provenance, this approach helps to identify otherwise hidden geologic provinces. Previously unrecognized age populations include Archean ~(40)Ar/~(39)Ar hornblende and biotite ages in Dronning Maud Land; 1200–1300 Ma ~(40)Ar/~(39)Ar hornblende ages in the Weddell Sea; ~1560 Ma population of U–Pb zircons from the Wilkes Land margin; and Grenvillian (1000–1200 Ma) U–Pb zircon ages from the Adélie/George V Land margin.