Incompatible element

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

Characterization of mesostasis areas in mare basalts: constraining melt compositions from which apatite crystallizes

Abstract: Crystallization of major silicate and oxide phases from basaltic melts produces late-stage liquids whose chemical compositions differ from the initial melt. These chemically evolved liquids crystallize phases in the interstitial mesostasis regions in lunar basaltic rocks. Enrichment of incompatible elements, including volatiles such as OH, F, Cl, is characteristic of these late-stage liquids and encourages growth of accessory phases including apatite [Ca5(PO4)2(F,Cl,OH)]. Apatite is the main volatile bearing crystalline phase in lunar rocks. It starts crystallizing after ~95% melt solidification in typical mare basalts, but could crystallize earlier, after ~85-90% solidification in KREEP basalts. Using the OH contents of apatites, several researchers have calculated water contents for parental magmas. These calculated parental magma water contents can then be used to estimate a range of values for water in the mantle source regions of mare basalts [e.g.,2-6]. Therefore, a better characterization of the mesostasis areas, and of the melts in which apatite forms, is paramount to gain further insights and constraints on water in the lunar interior, especially because important parameters such as partitioning of volatiles between late-stage melts and apatite remain poorly constrained.

Geochronological and geochemical study on the Yulong porphyry copper ore belt in eastern Tibet, China

Abstract: The Yulong copper belt, along part of the Red River-Ailao Shan fault system and its northwestern extension in eastern Tibet, consists of five porphyry pipes that contain a total copper resource of over 8 million tons. The porphyries are characterized by high alkali content (K2O+Na2O > 6%), K2O/Na2O > 1, and marked negative Ti, Ta and Nb anomalies on mantle-normalized incompatible element diagrams. U-Th-Pb laser ICP-MS dating of zircons from the Yulong porphyries showed that they were emplaced over a 4.3 Ma period and that they Young systematically from northwest to southeast as follows: Yulong, 41.2 +/- 0.2Ma; Zalaga, 38.5 +/- 0.2Ma; Mangzong, 37.6 +/- 0.2 Ma; Duoxiasongduo, 37.5 +/- 0.2Ma; and Malasongduo, 36.9 +/- 0.4 Ma. We suggest that the source of the shoshonites was lower crust that was pushed into the mantle by the compressive component of transpressional movement on the adjacent Tuoba-Mangkang fault and that the compositional variation in the porphyries is due to mixing between magmas of different composition, generated by different degrees of partial melting of a heterogeneous source region.

Geochemistry and petrogenesis of forearc peridotites, ODP Leg 125

Abstract: ODP Leg 125 recovered peridotites from Conical Seamount in the Mariana forearc and Torishima Forearc Seamount in the Izu-Bonin forearc. The peridotites recovered comprise about 95% harzburgites and about 5% dunites, which are variably serpentinised (mostly 60-100%). The Leg 125 peridotites represent some of the first extant peridotites recovered from a forearc selling. A detailed petrographic, mineral and bulk-rock chemical study of the peridotites has been undertaken in order to elucidate information about melting and fluid processes in the forearc mantle wedge. The harzburgites are highly refractory in terms of their mineralogy and geochemistry. They have low modal clinopyroxene, highly magnesian olivine (Mg# = 91.1-93.6) and orthopyroxene (Mg# = 91.6-93.2) and chrome-rich spinels (Cr# = 60-80) and very low incompatible element contents (Ti 20%). The Ti concentrations in the clinopyroxene indicate that the harzburgites are residues to -25% fractional melting. However, petrographic and other geochemical information show that the Leg 125 harzburgites have had a complicated melting and enrichment history. Many samples have olivine fabrics which are interpreted as having formed beneath a spreading ridge. Orthopyroxenes have lobate grain boundaries often associated with fresh olivine neoblasts. This texture is interpreted as showing the incongruent melting of orthopyroxene, a process which happens at low pressures (-3 kb) and high water pressures. These two types of textures indicate that the peridotites have had a two stage melting history. Moreover, the V concentrations in the clinopyroxenes can be explained by -15% partial melting at low oxygen fugacities (FMQ-1), followed by 5- 10% melting at high oxygen fugacities (FMQ+1). Oxygen thermobarometry calculations are in accordance with the peridotites last equilibrating under oxygen fugacities of greater than FMQ+1.The bulk-rocks have chondrite-normalised REE patterns showing extreme U-shapes with [La/Sm](_N) ratios in the range 5.03-250.0 and [Sm/Yb](_N) ratios in the range 0.05 to 0.25; several samples have possible small positive Eu anomalies. On extended chondrite-normalised plots the bulk-rocks also show enrichments in Sr and Zr relative to their neighbouring REEs and are enriched in LREE, Rb, Cs, Ba, Sm, and Eu relative to abyssal peridotites. Covariation diagrams based on clinopyroxene data show that Sr, Ce, Nd, Sm, Eu and Zr are enriched in the clinopyroxenes and that the enrichment took place during or after melting. The enrichment component is most likely a melt derived from the underlying subduction zone. A multistage melting and enrichment model is proposed for the peridotites where they first melt 10-15% beneath a spreading ridge. The resulting depleted spinel Iherzolite is enriched and then melted again 10- 15% above the subduction zone to produce the spatially associated boninites. A final enrichment event takes place during and after this melting event to produce the characteristic trace element enrichments in the Leg 125 peridotites.