Ordovician zircons as detrital markers in the Ötztal Nappe (Austroalpine, Italy)

<p>The Austroalpine Ötztal Nappe shows pervasive Eoalpine and local Variscan high-pressure metamorphism and deformation in its southeastern end, which obscure pr<span>i</span>or structures. We used magmatic and detrital zircon U-Pb dating by laser ablation ICP-MS to identify the precursor units of the Ötztal Nappe and the relationships among them.</p><p>Magmatic protolith dating of granitoid othogneisses in the Ötztal basement yielded Ordovician ages (450 – 470 Ma). The zircons of the Ordovician magmatism are important markers in the detrital zircon record. The paragneisses of the Ötztal basement, in which the Ordovician granitoids intruded, show no Ordovician zircons. The partly calcareous metasediments of the Schneeberg Complex and the Laas Series record some Ordovician detrital zircons. While the Schneeberg Complex is in tectonic contact to the Ötztal Nappe (Klug & Froitzheim, subm.), the Laas Series is the post-Ordovician sedimentary cover of the Ötztal basement. A Permo-Triassic basal metasandstone of the Brenner Mesozoic shows next to a strong Ordovician zircon age population some Variscan and Permo-Triassic zircons.</p><p>Zircon dating allowed to identify pre-Ordovician basement with Ordovician intrusions covered by post-Ordovician-pre-Variscan and Permo-Mesozoic sediments. This supports the concept of a non-tectonic unity in the southeastern Ötztal Nappe outside of the Schneeberg Complex.</p><p> </p>

Supplemental Material: Petrogenesis of Ordovician granitoids in Western Kunlun, NW Tibetan Plateau: Insights into the evolution of the Proto-Tethys Ocean

Table S1: Zircon U-Pb ages of igneous rocks in the Western Kunlun orogenic belt; Table S2: Results of whole-rock major- (wt%) and trace-element (ppm) data from the three intrusions; Table S3: Zircon U-Pb age of the three intrusions; Table S4: Zircon Hf isotope compositions of the three intrusions; Table S5: Whole-rock Sr-Nd-Pb isotope compositions of the three intrusions; Table S6: Representative analyses of feldspar, amphibole, and pyroxene from the Aqiang and Yutian intrusions; Table S7: Bulk partition coefficients used for trace-element modeling in Figure 14; Figure S1: CL images of zircons showing internal textures and ages of 206Pb/238U (Ma).

Supplemental Material: Petrogenesis of Ordovician granitoids in Western Kunlun, NW Tibetan Plateau: Insights into the evolution of the Proto-Tethys Ocean

Table S1: Zircon U-Pb ages of igneous rocks in the Western Kunlun orogenic belt; Table S2: Results of whole-rock major- (wt%) and trace-element (ppm) data from the three intrusions; Table S3: Zircon U-Pb age of the three intrusions; Table S4: Zircon Hf isotope compositions of the three intrusions; Table S5: Whole-rock Sr-Nd-Pb isotope compositions of the three intrusions; Table S6: Representative analyses of feldspar, amphibole, and pyroxene from the Aqiang and Yutian intrusions; Table S7: Bulk partition coefficients used for trace-element modeling in Figure 14; Figure S1: CL images of zircons showing internal textures and ages of 206Pb/238U (Ma).

Detrital zircon U–Pb ages of the Palaeozoic Natal Group and Msikaba Formation, Kwazulu-Natal, South Africa: provenance areas in context of Gondwana

The Natal Group and Msikaba Formation remain relatively poorly understood with regards to their provenance and relative age of deposition; a much-needed geochronological study of the detrital zircons from these two units was therefore undertaken. Five samples of the Durban and Mariannhill Formations (Natal Group) and the Msikaba Formation (Cape Supergroup) were obtained. A total of 882 concordant U–Pb ages of detrital zircon populations from these units were determined by means of laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS). Major Neoproterozoic and secondary Mesoproterozoic detrital zircon age populations are present in the detrital zircon content of all the samples. Smaller contributions from Archean-, Palaeoproterozoic-, Cambrian- and Ordovician-aged grains are also present. Due to the presence of a prominent major population of 800–1000 Ma zircons in all the samples, late Stenian – Tonian ancient volcanic arc complexes overprinted by Pan-African metamorphism of Mozambique, Malawi and Zambia, along with areas of similar age within Antarctica, India and Sri Lanka, are suggested as major sources of detritus. The Namaqua–Natal Metamorphic Complex is suggested as a possible source of minor late Mesoproterozoic-aged detritus. Minor populations of Archean and Palaeoproterozoic zircons were likely sourced from the Kaapvaal and Grunehogna Cratons. Post-orogenic Cambrian – Lower Ordovician granitoids of the Mozambique Belt (Mozambique) and the Maud Belt (Antarctica) made lesser contributions. In view of the apparent broad similarity of source areas for the Natal Group and Msikaba Formation, their sedimentation occurred in parts of the same large and evolving basin rather than localized in small continental basins, and the current exposures merely represent small erosional relicts.

Detrital zircon populations in quartzites of the Krkonoše–Jizera Massif: implications for pre-collisional history of the Saxothuringian Domain in the Bohemian Massif

Age spectra of detrital zircons from metamorphosed quartzites of the Krkonoše–Jizera Massif in the northeastern part of the Saxothuringian Domain were obtained by U–Pb laser ablation inductively coupled plasma mass spectrometry dating. The zircon ages cluster in the intervals of 450–530 Ma and 550–670 Ma, and show individual data between 1.6 and 3.1 Ga. Zircons in the analysed samples are predominantly of Cambrian–Ordovician and Neoproterozoic age, and the marked peak at c. 525–500 Ma suggests a late Cambrian maximum age for the sedimentary protolith. Detritus of the quartzites probably originated from the erosion of Cambrian–Ordovician granitoids and their Neoproterozoic (meta)sedimentary or magmatic country rocks. The lack of Neoproterozoic (meta)sedimentary rocks in the central and eastern part of the Krkonoše–Jizera Massif suggests that the country rocks to voluminous Cambrian–Ordovician magmatic bodies were largely eroded during the formation of early Palaeozoic rift basins along the southeast passive margin of the Saxothuringian Domain. The detrital zircon age spectra confirm the previous interpretation that the exposed basement, dominated by Neoproterozoic to Cambrian–Ordovician granitoids, was overthrust during Devonian–Carboniferous subduction–collision processes by nappes composed of metamorphosed equivalents of the uppermost Cambrian–Devonian passive margin sedimentary formations. Only a negligible number of Mesoproterozoic ages, typically from the Grenvillian event, supports the interpretation that the Saxothuringian Neoproterozoic basement has an affinity to the West African Craton of the northwestern margin of Gondwana.