Lithostratigraphy of the Mesoproterozoic Twakputs Gneiss

The Twakputs Gneiss is a garnetiferous, K-feldspar megacrystic, biotite granite-granodiorite orthogneiss. It represents a major unit in the Kakamas Domain of the Mesoproterozoic Namaqua-Natal Metamorphic Province extending about 250 km between Riemvasmaak in South Africa and Grünau in southern Namibia. The Twakputs Gneiss occurs as foliation-parallel, sheet-like bodies tightly infolded together with granulite-facies paragneisses into which it intrudes along with a variety of other pre-tectonic granite and leucogranite orthogneisses. These rocks were subsequently intruded by late-tectonic garnet-leucogranites, granites and charnockites. The Twakputs Gneiss is a distinctive unit characterised by large ovoid to elongate megacrysts of twinned perthitic K-feldspar, set in a coarse-grained matrix of garnet, biotite, quartz and feldspar. It contains a penetrative foliation defined by the alignment of K-feldspars and streaks of biotite that developed during the main phase D2 of the Namaqua Orogeny (~1.2 to 1.1 Ga). The foliation and an accompanying elongation lineation are more intensely developed along lithological contacts, especially at the margins of the mega-scale F3 domes and basins that refold the regional fabrics. U-Pb zircon dating of the Twakputs Gneiss has yielded concordia ages of between ~1192 and 1208 Ma. Whole-rock geochemistry shows consistent major, trace and REE elemental trends, and thus reflect chemical variability from a single fractionating magma. The Twakputs Gneiss has a granitic to granodiorite composition and is strongly peraluminous. The geochemistry and the ubiquitous presence of garnet and pelitic xenoliths indicate an S-type granite protolith. The Twakputs Gneiss is the most voluminous and widespread member of the Eendoorn Suite which comprises seven textural variants of garnetiferous, K-feldspar-megacrystic granitoid orthogneiss of the same age.

Newly Discovered Tuff in the Lower Shaximiao Formation in Yunyang, Chongqing, Southwestern China and Its Constraint on the Burial Age of the Yunyang Dinosaur Fauna

The Shaximiao Formation is one of the important Mesozoic burial horizons of dinosaur fossils in the Sichuan Basin. Although a large number of research results on the stratigraphic age of the Shaximiao Formation have been published, the age and division of the Shaximiao Formation are still controversial. To a certain extent, this affects the precise constraints on the burial age of the dinosaur fauna in Yunyang, Chongqing. In this study, the newly discovered tuff intercalation in the Lower Shaximiao Formation in Pu'an Township, Yunyang County, Chongqing City, was taken as the research object, and its lithology and formation age were determined using thin section identification, X-ray diffraction (XRD), scanning electron microscopy (SEM), and U-Pb zircon dating. The field observations and thin section microscopic characteristics of the rocks reveal that the clay rock intercalation has a typical sedimentary tuff structure, which is altered lithic tuff. The SEM imaging and XRD results indicate that it has a typical tuff mineral composition. The U-Pb zircon dating shows that the weighted average age of the newly discovered tuff is 174.8 ± 2.4 Ma, and the burial age of the dinosaur fossils is estimated to be 174.7 ± 2.4 Ma based on the sedimentation rate and the thickness of the stratum. Key words: Sichuan Basin; Shaximiao Formation; Yunyang Dinosaur Fauna; Tuff; Burial Age

Supplemental Material: Migmatite and leucogranite in a continental-scale exhumed strike-slip shear zone: Implications for tectonic evolution and initiation of shearing

Analytical methods of Zircon U–Pb geochronology, Major and trace elemental geochemistry, EBSD and cathodoluminescence (CL) analysis and EPMA methodology, Figure S1 present that deformed leucogranite with ductile structures. Figure S2 show Structures of zircons from foliated leucogranites and migmatite. Tables S1–S6 show sample locations, results of zircon dating and geochemistry.

Supplemental Material: Migmatite and leucogranite in a continental-scale exhumed strike-slip shear zone: Implications for tectonic evolution and initiation of shearing

Analytical methods of Zircon U–Pb geochronology, Major and trace elemental geochemistry, EBSD and cathodoluminescence (CL) analysis and EPMA methodology, Figure S1 present that deformed leucogranite with ductile structures. Figure S2 show Structures of zircons from foliated leucogranites and migmatite. Tables S1–S6 show sample locations, results of zircon dating and geochemistry.

Magma flux of silicic supereruptions from the Afro-Arabian large igneous province

The Main Silicics phase of the Afro-Arabian large igneous province preserves some of the largest volcanic eruptions on Earth, with six units totaling >8,600 km3 dense rock equivalent (DRE). The large volumes of rapidly emplaced individual eruptions present a case study for examining the tempo of generation and emplacement of voluminous silicic magmas. We use high-precision 206Pb/238U zircon dating to differentiate individual eruption ages and show that the largest sequentially dated eruptions occurred within a timeframe of 48 ± 34 kyr (29.755 ± 0.023 Ma to 29.707 ± 0.025 Ma), yielding a maximum magma flux of 3.09 x 10-1 km3/yr for 4,339 km3 DRE and making this sequence the highest known flux of silicic volcanism on Earth. The Main Silicics phase of volcanism occurred within a timeframe of 130 ± 150 kyr (29.80 ± 0.80 Ma to 29.67 ± 0.13 Ma), yielding a maximum magma flux of 3.05 x 10-2 km3/yr. We also provide a robust tie-point for calibration of the geomagnetic polarity timescale by integrating recalculated 40Ar/39Ar data with our high-precision 206Pb/238U ages to yield new constraints on the duration of the C11n.1r Subchron.