Incompatible element

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

Trace element compositions of rocks and minerals from the Chilas Igneous Complex, Kohistan, northern Pakistan

Abstract: ...... The Kohistan terrane in the western Himalayan region is considered as a Cretaceous island-arc sequence sandwiched between the Asian and Indian continental crusts. It is a 300-kmlong plutonic body that extends parallel to the general trend of the Kohistan terrane. Rocks of this complex are petrographically and compositionally similar to plutonic xenoliths found in island arcs (Khan et al. 1989). We report geochemical data of rocks and minerals in the Chilas Complex and discuss the melt compositions and magmatism in middle to lower arc crust. The Chilas Complex is well exposed along the Indus and Swat Rivers. Most of the complex consists of generally homogeneous gabbronorite, pyroxene diorite and pyroxene quartz diorite, and these are called as the Main facies rocks. Some of the rocks were re-equilibrated under granulite facies conditions at 750-850 °C and 6-8 kbar (Swat valley, Jan and Howie 1980). Rocks with layered structure are also found in the Chilas Complex, which often occur in km-scale masses. Some of the masses are abundant in peridotites associated with layered gabbroic rocks (ultramafic-mafic association), which are deduced to be crystal accumulates. One of the bodies of the ultramaficmafic association, Thak body just to the east of Chilas town, shows excellent outcrops. This body is included in the Main facies rocks, and consists of cyclic units of layered cumulate rocks, which is classified into olivine-dominant cumulate (dunite-wehrlite), plagioclase-dominant cumulate (troctolite-gabbronorite) and pyroxene-dominant cumulate (websterite-clinopyroxenite). Hornblende and spinel are often included in the rocks. Mg values of the pyroxenes and An content of plagioclase are high in these cumulative rocks, but systematic change of major chemical composition of the minerals are not recognized through the Thak body. In addition, one gabbronorite mass along the Indus River (Basehri body) is characterized by well-developed rhythmic layering, and most of the layers were overturned. The Basehri body is intruded by the Main facies rocks, which is considered as crystal cumulate from the magma of the Main facies. Main facies rocks of the Chilas Complex have the characteristics of subduction-related calc-alkaline magmas with depletion of Nb relative to other incompatible elements (Khan et al. 1989). The concentrations of K2O, Y, Zr, Th and rare earth elements (REE) in the Main facies rocks are positively correlative with SiO 2 content. In the chondrite-normalized diagram, the light REE are enriched relative to heavy REE in the rocks, and the REE patterns are slightly concave upward. The chemical variation of the most of the Main facies rocks can be explained by a weak segregation of melt and early-formed crystals composed of plagioclase, clinopyroxene and orthopyroxene. The major element compositions of the rocks from the Thak body show the wide variation reflecting accumulation of earlystage crystals. Rocks are generally poor in REE and other incompatible elements, implying the separation of the melt and crystals are effective. Even the gabbroic rocks without olivine are still poor in REE and other incompatible elements relative to the Main facies rocks. REE concentrations of the layered rocks of the Basehri body are generally lower than those of the Main facies rocks. For characterization of magmas of these layered rocks, trace element compositions of clinopyroxene and plagioclase are determined by ICP-MS after mineral separation. Clinopyroxene fractions from wehrlite and websterite, and whole-rock sample of clinopyroxenite in the Thak body have REE, Ba, Nb, Sr and Zr concentrations similar to each other. The clinopyroxenite and the clinopyroxene from websterite have weak negative Eu anomaly and REE concentrations slightly higher than the clinopyroxene from wehrlite. The clinopyroxene from a plagioclase-rich part of the layered gabbronorite of the Basehri body shows the REE concentrations 3-5 times higher than clinopyroxenes from the Thak body, with clear negative Eu anomaly. Plagioclase fractions from a troctolite in the Thak body and from the plagioclase-rich rock of the Basehri body have REE concentrations with positive Eu anomalies, and they have similar Sr concentrations although the plagioclase from the troctolite are poor in most of the incompatible elements. The melts calculated from the clinopyroxenes of the pyroxene- and olivine-dominant cumulates in the Thak body are enriched in light REE relative to heavy REE, showing chemical characteristics closer to calc-alkaline or high-alumina basalt magmas in island arcs rather than depleted island-arc tholeiites. The calculated melts have REE, Sr and Zr concentrations similar to the Main facies rocks. The melts calculated from the plagioclase fractions have Sr, Ba and Rb concentrations similar to the Main facies rocks. These data suggest a possibility that the original magmas of the cumulates of the Thak body and the magma of the Main facies were derived from common or similar source materials, in spite of large petrographic variations. Trace element abundances in clinopyroxene and plagioclase from the Basehri body may have been affected by subsolidus equilibration, and also affected by a small amount of trapped melt.

The discovery of alkaline basaltic pyroclastic rocks in original Heilongjiang Group of Yilan area and its geodynamic significance

Abstract: In this paper,a set of pyroclastic rocks was discovered in the original Heilongjiang Group of Yilan area.They are composed of debris and fine-grained pyroclastics.The debris is in the lenticular and flame forms,whereas the fine-grained pyroclastics have been highly deformed.With similar composition,they are comprised of sodium amphibole,albite,epidote and minor amounts of chlorite;nevertheless,there is an obvious difference between them in mineral content and mineral characteristics.Geochemical characteristics of pyroclastic rocks suggest that the debris belongs to alkaline basalt,with its LREE/HREE ratio between 3.87 and 4.24,its(La/Yb)n between 7.20 and 8.12,its Eu/Eu ratio between 1.03 and 1.09,and its REE distribution partition curve being of the right-oblique type.Compared to things of MORB,the trace elements of pyroclastics are more enriched in such incompatible elements as Sr,K,Rb and Ba.Yb is slightly lower than that in MORB.In the Zr-Zr/Y diagram and TiO2-MnO×10-P2O5×10 diagram,points of all samples are plotted in the oceanic-island basalt and interpolated area.It is considered that pyroclastics are alkaline basalts formed in an ocean island environment within the oceanic plate.Before the complete coagulation of these oceanic-island alkaline basalts,the hotspot in the oceanic plate became active again and broke the previously-formed alkaline basalts into plastic-semiplastic debris,which was then cemented by pyroclastics.The pyroclastics are ocean island type pyroclastics formed by "off-axis volcanism" within the oceanic plate.This discovery has provided some new clues to the paleotectonic environment and to the determination of tectonic attributes of the original Heilongjiang Group.

Distribution of Incompatible Trace Elements between the Constituents of Mantle Spinel Peridotites: Inversion of ICP-MS Data

Abstract: Minerals of the Earth's upper mantle have crystal structures notoriously unfavourable to large ion lithophile elements (LILE, such as K, Rb, Cs, Ba, Th, U), and to some extent to the high field strength elements (HFSE, such as Nb and Ta). Several authors have suggested that, in the convective mantle and the lower lithosphere, these 'highly incompatible elements' are dominantly concentrated in small fractions of partial melt. These melts would be volatile-rich and rather similar in composition to kimberlites and/or carbonatitic magmas (McKenzie, 1989). Alternatively, at shallow depth (lithosphere), the small volume melts could be silica-rich (Schiano and Clocchiatti, 1994; Kelemen et al., 1995). In the lithospheric mantle, LILE and HFSE may also be concentrated in accessory minerals such as amphibole, phlogopite, apatite and titanates, in fluidderived inclusions trapped in minerals, or along grain boundaries (e.g. Zindler and Jagoutz, 1988). Among the predominant rock-forming minerals, only clinopyroxene is considered to play a significant role as a host for incompatible elements. However, very few high-quality are available to constrain these assumptions. Minerals such as orthopyroxene, olivine and spinel have rarely been analysed, and the importance of fluid/melt inclusions and grain boundaries as reservoirs of trace elements remains controversial. For this reason, some important issues such as the behaviour and distribution of the ItFSE in the upper mantle are still a matter of debate. The aim of this paper is to provide quantitative estimates of the distribution of lithophile trace elements between the various constituents of spinel peridotites from the East African Rift. Predominant and accessory minerals were separated in 12 mantle xenoliths from Mega (Sidamo region, South-Eastern Ethiopia). The samples range in composition from fertile, cpx-rich lherzolites to refractory harzburgites Dipartimento di Scienze della Terra e Geologico-Ambientali, Universitg di Bologna, Piazza di Porta S. Donato I, Bologna 140127, Italy

Oxygen Fugacity of the Upper Mantle of Mars. Evidence from the Partitioning Behavior of Vanadium in Y980459 (Y98) and other Olivine-Phyric Shergottites

Abstract: Using partitioning behavior of V between olivine and basaltic liquid precisely calibrated for martian basalts, we determined the redox state of primitive (olivine-rich, high Mg#) martian basalts near their liquidus. The combination of oxidation state and incompatible element characteristics determined from early olivine indicates that correlations between fO2 and other geochemical characteristics observed in many martian basalts is also a fundamental characteristic of these primitive magmas. However, our data does not exhibit the range of fO2 observed in these previous studies.. We conclude that the fO2 for the martian upper mantle is approximately IW+1 and is incompatible-element depleted. It seems most likely (although clearly open to interpretation) that these mantle-derived magmas assimilated a more oxidizing (>IW+3), incompatible-element enriched, lower crustal component as they ponded at the base of the martian crust.

Mantle fluid and its role in gold ore forming process _taking jiapigou gold field for example

Abstract: Mantle fluid is a system majorly composed of C H O,and riched in H,CO 2,CH 4,H 2S,H 2O and incompatible elements(K,P,Li,etc.)with some metallic oxides.The composition of the mantle fluid varies with depth,lithology and physical chemical conditions.The mantle fluids are mainly derived from mantle plumes,MORB and arc areas.According to some research results of mantle fluid,the probable metallogenic modes and mechanisms of mantle fluid are summed,and the genetic relationship between the mantle fluid and the large gold deposit field is explained by some examples. Magmatic structural activities and regional metamorphic characteristics indicate that the mantle activeties are frequent and strong in Jiapigou area.The fluid characteristics related to Au mineralization are the same as those of mantle fluid.