Incompatible element

About: Incompatible element is a research topic. Over the lifetime, 2420 publications have been published within this topic receiving 154052 citations.

The Scenic Rim of Southeastern Queensland, Australia: A History of Mid Cenozoic Intraplate Volcanism

Abstract: Intraplate volcanism was widespread in southeastern Queensland during the mid Cenozoic, leaving a legacy of variably eroded volcanoes and rugged topography known locally as "The Scenic Rim". These plume-derived volcanoes provide a detailed record of northward Australian plate velocity, and indicate a major slowdown commencing at 26 Ma and persisting until 23 Ma, correlated with initial collision of the massive Ontong Java plateau with the northern subduction margin of the Australian plate. Despite traversing over 36 km of continental crust, trace element and isotopic signatures indicate little or only minor contamination for most units, with the exception of rhyolites formed during the period of slow plate velocity. Nevertheless, the thick continental crust allowed magmas to stall and fractionate during ascent, often producing highly evolved rocks (e.g., comendites) containing extreme concentrations of incompatible elements, including >2000 ppm Zr. Meanwhile, isotopic and trace element results from mafic units are consistent with melting and mixing of depleted upper mantle and an EM1-like source. Alkaline mafic eruptions also often contain abundant upper mantle and lower crustal xenoliths, providing excellent samples of these otherwise inaccessible regions. Denudation has produced good exposures of the subsurface magmatic architecture, a variety of landscapes, and diverse wildlife habitats; as a result many of the volcanoes are contained in National Parks, including the World Heritage listed Gondwana Rainforests of Australia.

Miocene Olivine Leucitites in the Hoh Xil Basin, Northern Tibet: Implications for Intracontinental Lithosphere Melting and Surface Uplift of the Tibetan Plateau

Abstract: The generation of Miocene–Pliocene post-collisional magmatic rocks in northern Tibet was coeval with surface uplift, meaning that understanding the petrogenesis of these rocks should provide clues to the mechanism of uplift of the Tibetan Plateau. However, the nature of the source(s) of Miocene–Pliocene post-collisional rocks is unresolved, especially for potassic–ultrapotassic rocks. This study focuses on 16 Ma olivine leucitites in the Hoh Xil Basin of northern Tibet, which display the lowest SiO 2 (43·4–48·8 wt%) contents of all Miocene–Pliocene magmatic rocks in northern Tibet and have high MgO (4·85–8·57 wt%) contents and high K 2 O/Na 2 O (>1) ratios. Whole-rock geochemical compositions suggest that the olivine leucitites did not undergo significant fractional crystallization or crustal assimilation. All samples are enriched in large ion lithophile elements relative to high field strength elements, and they exhibit uniform whole-rock Sr–Nd isotope [( 87 Sr/ 86 Sr) i = 0·7071–0·7077 and eNd(t) = −3·1 to −3·9] and olivine O isotope (5·8–6·6 ‰, mean of 6·2 ± 0·2 ‰, n = 21) compositions. We propose that the olivine leucitites were derived by low-degree partial melting of phlogopite-lherzolite in garnet-facies lithospheric mantle. Given the tectonic evolution of the Hoh Xil Basin and adjacent areas, we suggest that southward subduction of Asian (Qaidam block) lithosphere after India–Asia collision transferred potassium and other incompatible elements into the lithospheric mantle, forming the K-enriched mantle source of the Miocene–Pliocene potassic–ultrapotassic rocks. Removal of lower lithospheric mantle subsequently induced voluminous Miocene–Pliocene magmatism and generated >1 km surface uplift in the Hoh Xil Basin.