Incompatible element

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

Across-arc geochemical variation of Quaternary lavas in West Java, Indonesia: Mass-balance elucidation using arc basalt simulator model

Abstract: The Sunda Arc of Indonesia developed along the convergent margin between the Eurasian and the Australian Plates More than 100 Quaternary volcanic centers occur along the arc The West Java Arc is a segment of the Sunda Arc in which more than 10 volcanic centers are located, corresponding to the 120 to 200 km depth contours of the Wadati–Benioff zone The geochemistry of 207 Quaternary lavas from six centers across the arc was investigated The lavas range from basalt to dacite Incompatible element abundances increase from the volcanic front to the rear-arc in response to a change from low-K to high-K suites Nd–Sr isotope compositions of the basalts scatter between mid-ocean ridge basalt (MORB) source mantle and Indian Ocean sediment (SED) compositions, with volcanic front low-K basalts having more radiogenic Nd than the rear-arc basalts It is suggested that mixing between slab-derived fluids mainly from the SED and melt from MORB source mantle played a significant role in determining the geochemistry of the West Java basalts Incompatible element patterns in primitive mantle normalized multi-element plots are almost identical across the arc, except for greater inclination and weaker positive Sr spikes in the rear-arc basalts This suggests a lower degree of partial melting in the rear-arc mantle, accompanied by change in SED fluid composition between the volcanic front and the rear-arc The latter is confirmed by fluid-fluxed melting model calculations using multiple trace elements and Nd and Sr isotopes All the West Java Arc lavas require deficit of Sr from the slab SED This may occur due to selective breakdown of Sr-rich hydrous silicate minerals, such as zoisite, at shallower depths before the SED component reaches the depth of dehydration effective for magma genesis The rear-arc basalts need further Sr deficits along with lesser fluid These features are commonly observed in many arc basalts, and are likely attributable to the same mechanism

Formation and composition of the Late Cretaceous Gangdese arc lower crust in southern Tibet

Abstract: Arc lower crust plays a critical role in processing mantle-derived basaltic melts into the intermediate continental crust, yet can only be studied indirectly or in exposed arc sections. Compared with the relatively well-studied oceanic arc sections (e.g., Kohistan and Talkeetna), the composition and formation mechanisms of continental arc lower crust remain less clear. Here we present a geochronological and geochemical study on the Lilong Complex and the Wolong granitoids from the Gangdese arc deep crustal section in southern Tibet. The Lilong Complex is composed of the early (85–95 Ma) mafic-intermediate sequence and late (85–86 Ma) ultramafic sequence. The Lilong crustal section exposed crustal depth extending from ~ 42 to 17 km based on the geobarometry. The mafic-intermediate sequence is a damp (low H2O) igneous differentiation sequence characterized by the subsequent appearance of pyroxene → plagioclase → amphibole → biotite. The ultramafic sequence represents a wet igneous differentiation sequence composed of olivine → pyroxene → amphibole → plagioclase. The 74–84 Ma Wolong granitoids were formed by fractional crystallization of wet magma and intra-crustal assimilation. Calculated seismic properties of the Gangdese deep arc crust are comparable to the average continental crust at a similar depth. The average composition of the Gangdese arc lower crust is basaltic andesite with SiO2 of ~ 54 wt%. The highly incompatible elements in the Gangdese arc lower crust are systematically higher than those of the oceanic arc and are comparable with the estimates of lower continental crust, suggesting continental arc magmatism significantly contributes to the formation of continental crust.

Re-Os isotope characteristics of postorogenic lavas: Implications for the nature of young lithospheric mantle and its contribution to basaltic magmas

Abstract: Re-Os isotopes have been measured on postorogenic potassic lavas from the Tibetan Plateau, the Betic domain of southeastern Spain, and the Colorado Plateau of the southwestern United States. Previous work has established that these lavas were all derived from parts of the subcontinental lithospheric mantle that had undergone metasomatic enrichment in incompatible elements, following various degrees of melt depletion. Cratonic depleted subcontinental lithospheric mantle peridotites typically have subchondritic 187 Os/ 188 Os; however, the postorogenic lavas are characterized by radiogenic 187 Os/ 188 Os ratios (0.139‐0.559). Simple modeling shows that only very large degrees of melt depletion (>25%‐30%) can lower source Re/Os ratios sufficiently to permit timeintegrated development of subchondritic 187 Os/ 188 Os ratios. Such processes may have been largely restricted to the older Precambrian, and the peridotite component of the postorogenic lavas source was probably depleted by <25%. The more radiogenic values may reflect increasing contributions from metasomatic components or possibly crustal contamination. Our findings imply the need for caution in the use of Os isotopes as a diagnostic tracer of subcontinental lithospheric mantle contributions to lavas erupted through younger Proterozoic and Phanerozoic lithosphere.