Incompatible element

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

The Geochemistry of Feldspar-Free Volcanic Rocks.

Abstract: Highly silica-undersaturated magmas which form feldspar-free volcanic rocks have been erupted at some time on most continents and in all major ocean basins. In this study 488 oceanic and continental feldspar-free volcanic rocks have been analyzed for major and trace elements. The results are presented in a new compilation covering five continents and three oceans. This type of volcanism is associated with intraplate volcanic activity and occurs within extensional tectonic regimes in continental areas or as late-stage, post-erosional volcanism on oceanic islands. It is restricted almost entirely to the continental circum-cratonic Proterozoic lithosphere and to the margins of ocean basins where the Phanerozoic oceanic lithosphere is older. The magmas responsible for oceanic (OIN) and continental (CON) nephelinites are dominated by asthenosphere-derived melts. Nephelinitic rocks are enriched in elements which partition strongly into carbonate melts. Small silicate melt fractions may have been enriched by a carbonate precursor liquid derived by 0.1 % melting of the same source, the carbonate addition being ca. 10% for GIN and up to 20% for CON. K and Rb variation in OIN and CON indicate derivation from amphibole. (ca. 2%)Tgamet Iherzolite sources by carbonate-silicate liquid mixing. Amphibole is residual at small degrees of partial melting but consumed before larger degrees of melting appropriate to most OIB are reached. In a few somewhat K-enriched sources phlogopite is indicated. OIN are characterised by HIMU and EMI trace-element ratios but amphibole implies shWlow sources rather than the deep mantle location proposed for the HIMU component. OIN and CON are enriched in carbonate-phobic incompatible elements. This may be the result of remobilization of asthenosphere-derived melts from the base of the lithosphere. Continental lithosphere involvement is also indicated by the greater variability of CON in incompatible element compositions. Potassic rocks from the Western Rift (WR) and New South Wales (NSW) are extremely enriched in incompatible elements. This may be evidence of metasomatised lithospheric mantle involvement in magma genesis. Carbonate liquids are involved in most WR magmas but not in NSW magmas where H20 -rich fluids are indicated. Phlogopite (probably with amphibole) dominates both sources. Olivine-poor nephelinites (COP) are also enriched in incompatible elements but have similar normalised profiles to OIN and CON. COP may be derived by liquid immiscibility from highly carbonated asthenospheric magmas and are related to CON by two-stage silicate-carbonate liquid partitioning effects, crystal fractionation, and contamination by lithospheric mantle.

Petrogenesis of macrocrystic and aphanitic intrusions in Mesoproterozoic diamondiferous pipe 2 kimberlite, Wajrakarur kimberlite field, eastern Dharwar craton, southern India

Abstract: Mesoproterozoic Pipe 2 kimberlite intruding granitic gneisses in the Wajrakarur Kimberlite Field (WKF) of Eastern Dharwar craton, southern India, is one of the first discovered pipes from this field. The two different intrusions belonging to coherent facies are observed in this kimberlite which are texturally distinct i.e., macrocrystic (with abundant macrocrysts) as well as aphanitic (devoid of or very fewer macrocrysts). Petrographic observations give evidence of presence of veined metasomatic mantle in the source region. Distinct geochemical variation is observed between macrocrystic (Mg# 75.4-76.6, SiO 2 : 34.3-35.4 wt%, MgO: 18.7-20.4 wt%) and aphanitic samples (Mg# 74.7-75.5, SiO 2 : 30.4-31.8 wt%, MgO: ∼21 wt%), furthermore aphanitic samples are relatively more enriched in trace and rare earth elements. Geochemical studies point out that aphanitic and macrocrystic varieties of Pipe 2 kimberlite to be products of the same mantle source but have experienced different evolutionary histories. The inferred primary magma of Pipe 2 kimberlite (for both aphanitic and macrocrystic) is suggested to have a composition of ∼33 wt% SiO2, Mg# ∼75.6 and ∼460 ppm Ni. Pipe 2 primary magma can be derived by using forward melting model assuming ∼1% partial melting of a source enriched in light REE by a factor of ∼11 x chondrite and almost chondritic heavy REE with 2% residual garnet. Differences between aphanitic and macrocrystic varieties in their chondrite normalized REE abundance patterns can be explained by about 5% crystal fractionation of primary magma and not by variations in the degree of partial melting. The primitive mantle normalized trace element patterns exhibit significant negative K, Sr, P, Ti and Hf anomalies that are interpreted to be characteristic of the primary magma. Combined petrology and whole rock geochemistry including compatible and incompatible element abundances and their ratios confirm that Pipe 2 kimberlite intrusions are archetypal Group I kimberlites similar to other kimberlites of EDC and not lamproites.

Geochemical characteristics,chronology and the significance of Laqing copper polymetallic skarn deposit,Bange county,Tibet

Abstract: Laqing deposit located in the south of Bangong Lake-Nujiang suture is a skarn type copper-riched polymetallic depositThe intrusive rock is well-developed in the mining district,the monzogranite is closely related to mineralizationThis paper is based on the data of zircon LA-ICP-MS U-Pb datingThe age of monzogranite is 11424Ma ±087Ma,which imply Laqing deposit was formed in the late Early CretaceousThe geochemistry results show A/CNK value is near 115～117 and A/NK value is 153 ～159The rock which is ultraluminum type belongs to high-K calc-alkaline seriesLaqing rock is enriched in HREE and depleted in LREE,negative Eu is not obviousIn the spider diagram of trace elements,big ion incompatible elements Rb,K,Pb and Ti are rich,and Nb,Ti are poorThe R1-R2 and Rb-(Yb+Nb) diagrams imply the monzogranite formed in the continental crust collision environmentAccording to regional geology and ore deposit geology data,it is considered that the deposit formed in the background of the Gangdese and the Qiangtang continental crust collision

Hydrated Peridotite-Basaltic Melt Interaction Part II: Fast Assimilation of Serpentinized Mantle by Basaltic Magma

Abstract: The most abundant terrestrial lavas, mid-ocean ridge and ocean island basalt (MORB and OIB), are commonly considered to be derived from a depleted MORB-mantle component (DMM) and more specific, variably enriched mantle plume sources. However, findings of oceanic lavas and mafic cumulates issued from melts, enriched in chlorine and having a radiogenic 87Sr/86Sr ratio, can be attributed to an interaction between the asthenosphere-derived melts and lithospheric peridotite variably hydrated due to penetration of hydrothermal water down to and below Moho level. To constrain mechanisms and rates responsible for the interaction, we report results of 15 experiments of reaction between serpentinite and tholeiitic basaltic melt at 0.2 - 1.0 GPa and 1250 - 1300°C. Results show that the reaction proceeds via a multi-stage mechanism: (i) transformation of serpentinite into Cr-rich spinel-bearing harzburgite (Fo92-95 mol.%) containing pore fluid, (ii) partial melting and dissolution of the harzburgite assemblage with formation of interstitial hydrous melts (up to 57 – 60 wt% of SiO2 contents at 0.5 GPa pressure), and (iii) final assimilation of the Cr-rich spinel-bearing harzburgite/dunite and formation of hybrid basaltic melts with 12 – 13 wt.% of MgO and elevated Cr (up to ~500 ppm) and Ni (up to ~200 ppm) contents. Assimilation of serpentinite by basaltic melt may occur under elevated melt/rock ratios (>2) and may lead to chromitite formation. We show that hybrid magmas produced by the progressive assimilation of serpentinized lithospheric mantle may be recognized by high Mg-numbers and high Cr and Ni contents of olivine and pyroxenes, an excess of SiO2, H2O and halogens in the melts, and some unusual isotopic composition (e.g., radiogenic 87Sr/86Sr, non-mantle δ18O). Our experiments provide evidence that MORB and high-Mg-Cr orthopyroxene-rich cumulates depleted in incompatible elements can be produced from common mid-ocean ridge basaltic melts modified by reaction with hydrated lithospheric peridotite. We established that the rate of assimilation of serpentinized peridotite is controlled by silica diffusion in the reacting hydrous basaltic melt. Our study challenges traditional interpretation of the variations in MORB and OIB chemical and isotopic composition in terms of deep mantle plume source heterogeneities or/and degrees of partial melting.