Incompatible element

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

Mapping a hidden terrane boundary in the mantle lithosphere with lamprophyres.

Abstract: Lamprophyres represent hydrous alkaline mantle melts that are a unique source of information about the composition of continental lithosphere Throughout southwest Britain, post-Variscan lamprophyres are (ultra)potassic with strong incompatible element enrichments Here we show that they form two distinct groups in terms of their Sr and Nd isotopic compositions, occurring on either side of a postulated, hitherto unrecognized terrane boundary Lamprophyres emplaced north of the boundary fall on the mantle array with eNd -1 to +16 Those south of the boundary are enriched in radiogenic Sr, have initial eNd values of -03 to -35, and are isotopically indistinguishable from similar-aged lamprophyres in Armorican massifs in Europe We conclude that an Armorican terrane was juxtaposed against Avalonia well before the closure of the Variscan oceans and the formation of Pangea The giant Cornubian Tin-Tungsten Ore Province and associated batholith can be accounted for by the fertility of Armorican lower crust and mantle lithosphere

Petrogenesis and thermobarometry of the 50 Ma rapakivi granite-syenite Acapulco intrusive: Implications for post-Laramide magmatism in southern Mexico

Abstract: The Acapulco intrusion is a composite pluton that belongs to the coastal batholithic belt of southern Mexico, intruding the Xolapa metamorphic complex and cropping out in the neighboring area of Acapulco city. The Acapulco intrusion has been considered as an anomaly based on its age, which contrasts with the surrounding plutons and the general age trend from the coastal batholithic belt and corresponds to an Eocene–Oligocene age. It ranges in composition from granite (sensu stricto) to syenite and diorite. The most distinctive characteristic of the Acapulco intrusion is the rapakivi texture developed in the granites, which are characterized by biotite, amphibole, allanite, and fl uorite as distinctive minerals, plus titanite, zircon, and apatite as accessory phases. Geochemically, the Acapulco intrusion varies from metaluminous to peraluminous, and displays the distinctive signatures of arc-related magmas. The studied rocks show strong negative Sr, Ba, and Eu anomalies, coupled with incompatible element enrichments and high Ga/Al ratios, which are typical characteristics of A-type granites that underwent strong plagioclase fractionation from a formerly metaluminous magma. Initial isotopic ratios ( 87 Sr/ 86 Sr from 0.7035 to 0.7100, and eNd from +5.50 to +1.78) indicate a range from depleted mantle compositions to compositions consistent with crustal contamination by continental crust, particularly from the surrounding Xolapa Complex. U-Pb geochronology in zircons by laser ablation–inductively coupled plasma–mass spectrometry (LA-ICP-MS) established crystallization ages of 49.40 ± 0.40 Ma, 50.20 ± 1.0 Ma, 50.42 ± 0.39 Ma, and 50.56 ± 0.39 Ma for different lithologies of the Acapulco intrusion. These geochronological data, together with previous published works, confi rm that post-Laramide plutonism between 50 and 60 Ma is widespread in the southern continental margin of Mexico as a major magmatic event. Finally, new thermobarometric determinations established emplacement conditions of ~700 °C at 8–10 km depth (2.08–2.8 kbar), indicating an exhumation rate of ~0.21 km/m.y. between 50 and 20 Ma, which is slower than the previous estimated rate of 0.44 km/m.y. These results call for a review on models suggesting fast and/or slow exhumation of the southern Mexico coastal batholitic belt.

Mantle-crust interaction generating the Wuping granites: evidenced from Sr-Nd-Hf-U-Pb isotopes.

Abstract: Detailed petrologic, geochemical and Sr-Nd-Hf-U-Pb isotopic researches indicate that the Wuping granitic complex consist mainly of biotite granite and garnet-bearing granite with different formation age and petrogenesis. LA-ICPMS zircon U-Pb dating results show that biotite granite formed at 161. 4 Ma and garnet-bearing granite did at ca. 113 Ma. Biotite granites are characterized by moderate enrichment of most incompatible elements and middle REE fractionation. These rocks exhibit lower initial 87Sr/86Sr ratios (0. 710) and higher eNd(t) value (-2. 6 - -5.7), similar to typical I-type calc-alkaline granites. In comparison with the isotopic compositions of nearby basement metamorphic rocks, the present study indicates that biotite granites resulted from the mixing of the melt generated from the partial melting of Proterozoic basement metamorphic rocks and juvenile mantle-derived liquids. Variable Hf isotopic compositions of zircons (eHf(t) = -3.6 --10.8) strongly support this conclusion. Garnet-bearing granites are featured by high Si, Al, Na, K, Nb, Ta, Y and HREE concentrations, low P, Sr, Ba, LREE, Zr and Hf concentrations. They have low (La/Yb)n, Zr/Hf and Nb/Ta ratios and high Rb/Sr ratio, suggesting strongly differentiated geochemical characteristics. Their initial 87Sr/86Sr ratios 0.710, eNd(t) is -7.1, and Hf isotopic compositions of zircons are relatively homogeneous and much low with an average eHf(t) of-9.7, indicating little or a little contribution of mantle-derived compositions. Combined with extremely high HREE contents, the study suggests that the parental magma of garnet-bearing granite was likely produced by re-melting of garnet-rich restites of a previous melting. Consequently, Mesozoic granites with different geochemical features in Nanling area were formed by variable extent of crust-mantle interaction.

Continental Flood Basalts and Rifting: Geochemistry of Cenozoic Yemen Volcanic Province

Abstract: Rift formation is a crucial topic in global tectonics. The Yemen rift-related area is one of the most important provinces, being connected to the rifting processes of the Gulf of Aden, the Red Sea and Afar Triangle. In this paper, a review of the Yemen volcanic province and its relations with the Red Sea rifting are presented. Tertiary continental extension in Yemen resulted in the extrusion of large volumes of effusive rocks. This magmatism is divided in the Oligo-Miocene Yemen Trap Series (YTS) separated by an unconformity from the Miocene-Recent Yemen Volcanic Series (YVS). Magmas of the YTS were erupted during the synrift phase and correlate with the first stage of sea-floor spreading of the Red Sea and the Gulf of Aden (30 - 15 Ma), whereas the magmas of the YVS were emplaced during the post rift phase (10 - 0 Ma). A continental within plate character is recognized for both the YTS and YVS basalts. The YTS volcanic rocks are contemporaneous with, and geochemically similar to, the Ethiopian rift volcanism, just as the volcanic fields of the YVS are geochemically alike to most of the Saudi Arabian volcanics. YTS and YVS have analogous SiO2 ranges, but YVS tend to have, on average, higher alkalis and MgO contents than YTS. Fractional crystallization processes dominate geochemical variations of both series. Primitive magmas (MgO > 7.0%) are enriched in incompatible elements and LREEs with respect to primitive mantle, but YVS are more enriched than YTS. To first order, the different geochemical patterns agree with different degrees of partial melting of an astenospheric mantle source: 25% - 30% of partial melting for YTS and 10% - 3% for YVS. Secondly, the higher degree of enrichment in incompatible elements of YVS reflects also greater contribution of a lithospheric mantle component in their source region.