Detrital zircon sources in the Ordovician metasedimentary rocks of the Moroccan Meseta: Inferences for northern Gondwanan passive-margin paleogeography

ABSTRACT Detrital zircon U-Pb geochronology has been widely used to constrain the pre-Carboniferous geography of the European and, to a lesser extent, the Moroccan Variscides. The latter have been generally considered as part of a long-lasting passive margin that characterized northern Gondwana from Ordovician to Devonian time, and was subsequently involved in the late Paleozoic Variscan orogeny. We report detrital zircon ages for three Early to Late Ordovician samples from the Beni Mellala inlier in the northeastern part of the Western Moroccan Meseta in order to discuss the temporal evolution of the sources of sediments in this region. The detrital zircon spectra of these samples, characterized by two main populations with mean ages of 630–610 Ma and 2170–2060 Ma, are typical of Cambrian–Devonian rocks from the Moroccan Variscides and confirm their link to the West African craton. A minor Stenian–Tonian population (peak at ca. 970 Ma) suggests the influence of a distant and intermittent NE African source (Sahara metacraton), which was probably interrupted after Ordovician time. Our data support previous interpretations of the Moroccan Meseta (and the entire northern Moroccan Variscides) as part of the northern Gondwana passive margin. The main sources of these sediments would have been the West African craton in the western regions of the passive margin (Moroc- can Meseta and central European Paleozoic massifs), and the Arabian-Nubian Shield and/or Sahara metacraton in the eastern areas (Libya, Egypt, Jordan, central and NW Iberian zones during Paleozoic time), where the 1.0 Ga detrital zircon population is persistent throughout the Ordovician–Devonian time span.

Evaluating preservation bias in the continental growth record against the monazite archive

Most recent models of continental growth are based on large global compilations of detrital zircon ages, which preserve a distinctly episodic record of crust formation over billion-year timescales. However, it remains unclear whether this uneven distribution of zircon ages reflects a true episodicity in the generation of continental crust through time or is an artifact of the selective preservation of crust isolated in the interior of collisional orogens. We address this issue by analyzing a new global compilation of monazite ages (n >100,000), which is comparable in size, temporal resolution, and spatial distribution to the zircon continental growth record and unambiguously records collisional orogenesis. We demonstrate that the global monazite and zircon age distributions are strongly correlated throughout most of Earth history, implying a link between collisional orogenesis and the preserved record of continental growth. Our findings support the interpretation that the continental crust provides a preservational, rather than generational, archive of crustal growth.

U-Pb Detrital Zircon Ages and Geochemical Features of the Jingxing Formation, (Qamdo Basin, Tibet: Implications): Inferences for the Metallogenic Model of the East Tethys Evaporite

Qamdo basin is located between the suture zone of Jinsha River (Ailao Mountains) and that of Ban Gong Lake (Nujiang) in the eastern Tethys. Part of the Jingxing Formation is deposited in the southwest of the basin. In this study, two profiles were investigated from the north and south of Qamdo basin. The characteristics of detrital zircon LA-ICP-MS U-Pb age, and the main and trace elements of sandstone were analyzed. The characteristics of major and trace elements showed that the tectonic setting of the study area is mainly composed of a relatively stable active continental margin and a passive continental margin, showing characteristics of a continental island arc. The weathering degree of Jingxing Formation in the Qamdo area is lower than that in the Lanping-Simao area, which may be closer to the origin. The age distribution characteristics of detrital zircon grains indicate that the Qiangtang Block, Youjiang basin, and Yangtze area jointly constitute the provenance of the Qamdo-Lanping-Simao basin. Both basins may be part of a large marine basin with unified water conservancy connection before evaporite deposition. Metamorphic seawater from the Qamdo basin may migrate to the Lanping-Simao basin and even the Khorat basin, where evaporite was deposited.

U–Pb ages of detrital zircons in Cretaceous–Paleogene/Neogene kaolins within Eastern Dahomey and Niger Delta Basins (Nigeria) as provenance indicators

Detrital zircon grains within four (4) deposits including two (2) Cretaceous and two (2) Paleogene/Neogene kaolins in Nigeria were analysed using U–Pb LA-SFICP-MS to determine their provenance. The zircon textures were dominated by xenocrystic cores and oscillatory zoning in the Cretaceous and Paleogene/Neogene kaolins, respectively. The Th/U ratios obtained for the detrital zircon grains within the kaolins were predominantly within known values for rocks with magmatic origin. The age populations obtained for the detrital zircon grains were dominated by values from 529 to 978 Ma within the Neoproterozoic, followed by values from 1754 to 2497 Ma of the Paleoproterozoic. Detrital zircon ages obtained between 553.2 ± 6.2 and 583.5 ± 2.0 Ma represent part of the minimum provenance ages for the primary minerals that were kaolinised. The Cretaceous–Paleogene/Neogene kaolins were derived from parent rocks of Eburnean and Pan African ages within the Western and Northern Nigeria Basements.