Incompatible element

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

Physicochemical processes involved in Cenozoic volcanism in eastern China

Abstract: Eastern China is a Cenozoic composite volcanic rock province, where volcanic rocks of the tholeiite series, calc-alkali series, Hy-norm-bearing olivine basalt series, Na-alkali series and K-alkali series coexist. Eastern China is separated into the northern and southern volcanic rock regions by the Changzhou-Yueyang old deep fault. Magma generation and magmatic activities in the northern region were controlled by the mantle uplift and old deep faults. These old deep faults were revived and some of them were changed into a multiple rift system due to back-arc expansion. The Bohai Sea depression is situated at the intersection of the Lujiang-Tancheng-Shenyang-Mishan and Zhangjiakou-Tianjin uplift belts of the upper mantle. Eogene (71.5-28.5 Ma) tholeiites largely occur in the central part of the mantle uplift; the well developed Neogene (23.8-2.6 Ma) alkali olivine basalts are distributed in the outer lane of the former and the Quaternary (1.48 Ma-recent) peralkali volcanic rocks are far away from them. In the southern region magma generation and magmatic activities were controlled mainly by plate subduction and three sets of old deep faults. Studies of incompatible elements and REE show that the degree of enrichment of incompatible elements and LREE increases with decreasing age, increasing source depth and decreasing degree of partial melting of the upper mantle. This presumably is an indication of a rapid uplifting and then waning magmatic hearth with gradually decreasing temperature, accompanied with down-cutting of the lithospheric faults. We call such a process “a reverse process of magma generation”. And the opposite process of the magmatic evolution of the East African rift in Kenya can be called “a positive process of magma generation”.

Geochemical constraints on cumulate textured Ti-rich Al-depleted Komatiites from Chotanagpur Gneissic Complex, Eastern India

Abstract: For the first time occurrence of Ti rich Al depleted ultramafic cumulates having komatiitic signature in the northwestern fringe of Chotanagpur Gneissic Complex is presented. These rocks exhibit intrusive relationship with metasedimentary rocks and metaultramafites. Geochemically they are characterized by Mg# 79.1–91.60, high TiO2 (1.29–1.54 wt%), significantly low Al2O3/TiO2 and (Gd/Yb)n >1. Major oxides, trace and REE content suggest low degree of fractional crystallization and lesser degree of partial melting. These Al depleted komatiites are characterized by high concentration of incompatible elements than most suites of Barberton type komatiites. High Ti content suggests less degree of majorite garnet melting, leaving behind garnet in the restite. The rock shows higher Ti/Sc (190),Ti/V (22), Zr/Y (3), Zr/Sc (4), V/Sc (8), Zr/Sm (28) and Zr/Hf (47) ratios than primitive mantle and REE distribution pattern shows gentle slope from LREE to HREE in most samples pointing towards mantle metasomatism and crustal contamination during emplacement. The observed chemical characteristics indicate derivation of komatiite from an enriched mantle source and represent plume activity in an extensional tectonic regime of intracratonic setting.

Geochemical characteristics of Permian basalt from Hutiaoxia and Jin'an area of the Emeishan Large Igneous Province and constraints on their source region

Abstract: The geochemical characteristics of picrite and basalt that we discovered recently in Hutiaoxia and Jin'an area show that the primitive-mantle normalized incompatible element diagrams and Sr,Nd-Pb isotopic ratios are similar to those of OIB and Lijiang picrite,all of which display an enrichment of lithophile element( LILE) and relative depletion of high field strength element( HFSE) associated with an absence of Nb,Ta and Ti negative anomalies All these observations suggest little lithosphere or crustal material contamination of uplifting magma With the Klein and Langmuir method( 1987),the MgO content of the Hutiaoxia's and Jin'an's primary magma are 15 81% ~ 20 89% and 8 06% ~ 13 84% respectively Mantle temperature of both are 1493 ~ 1611℃ and 1055 ~ 1474℃ respectively These mantle temperatures are lower than Shiman picritic melting temperature( 1630 ~ 1680℃),and a little higher than mantle temperature of normal asthenosphere Thus,the axis of the Emeishan mantle plume should be located beneath the Lijiang County Town,Yunnan Province

Geochemistry of the Mantle

Abstract: The degree to which the mantle can be considered chemically uniform depends partly on the scales at which phenomena are analyzed. Many key geophysical observations (e.g., seismic velocities) relate to scales of 10–100 km. A key result discussed in Chapter 1 is that at these scales, the overall pyrolite composition derived for the upper mantle is capable of explaining the essential features of the distribution of seismic velocities and density with depth throughout the transition zone and lower mantle to depths of about 2700 km, when the effects of known phase transformations are taken into account. In particular, there is no convincing evidence requiring the existence of any major radial chemical zoning in the mantle,1 e.g., a substantial increase of the FeO/MgO ratio in the lower mantle. This suggests that the pyrolite upper mantle composition might be applicable throughout the entire mantle. At the very least, this would be a reasonable assumption in attempting to estimate the bulk composition of the mantle.