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Assimilation of peridotite in zoned calc-alkaline plutonic complexes: The Artel Amur mining company provided us with open access to drill core topp from — m depth into the metasomatic domain, which allowed detailed observations of the mineralogy of the glimmerite and clinopyroxenite veins and their wall-rocks Fig.
This clearly indicates that the Mg-number—Ni covariation in dunites is governed by melt—rock interaction rather than by fractional crystallization. The other distinct and economically valuable feature of Kondyor is the high concentration of platinum-group elements PGE in the eroded tip, and lower concentrations in the remaining metasomatic zone.
New foliation and lineation measurements in dunite obtained as part xomal this study are consistent with previous studies Gurovich et al. Stereonet projection of dyke orientations equal area, lower hemisphere.
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In the models presented here, strong pressure gradients in the crust favour propagation of melts outward from the magmatic channel so that the emplacement work is minimized: Large, poikiloblastic crystals of chromite are rare. Conversely, because it is partitioned into pyroxene preferentially to olivine, Cr may be substantially enriched during olivine-forming reactions Godard et al.
In subduction-related environments, it could be responsible for magmatic arc splitting e. Parental magma composition of the Main Zone of the Bushveld Complex: Hornfels xenoliths also occur in the centre of the ultramafic body. In addition, the absence of dunite or pyroxenite dikes in the country rocks argues against simple magmatic intrusion, even if the contact metamorphic aureole indicates that the Kondyor ZUC intruded the upper crust up to c. Peripheral gabbros have higher Al, and lower Mg and Ca contents than the rim clinopyroxenites Table 3.
Email alerts New issue alert. Second, although showing strong similarities in their trace-element signature, all rim pyroxenites and wehrlites are distinguished from intrusive and vein pyroxenites by much lower abundance of incompatible trace elements Fig. Acceptable shortcomings of model kofz concern the attitude of the body subvertical in Kondyor and inclined in the modelthe internal rock distribution, the synformal final shape and the rim plutons.
Other constraints were the preservation of basement slivers around the peridotite body, a narrow thermal aureole around it and slightly asymmetrical, concentric zoning with a fluid-rich medial zone. In detail, however, the rim wehrlites and clinopyroxenites differ in having less enriched, or even depleted, contents of the most incompatible elements Rb to LREE relative to HREE. This idea is consistent with the conclusions of Davies et al.
Subduction-related ZUCs form linear belts and are surrounded by large gabbroic bodies e.
Methods of determining the rheological properties of magmas at subliquidus temperatures. Mineral lineation trajectories are concentric Fig. Deep-seated partial melts migrating upward tend to dissolve the pyroxene component of percolated peridotites and crystallize olivine, leading to the formation of olivine-rich rocks Kelemen, Structures and petrotextures of the ultrabasic cores of ring massifs in the Russian Far East.
Zoned ultramafic complexes ZUCs consist of relatively small bodies that expose a dunite core surrounded by successive shells of wehrlite—pyroxenite, hornblendite and, in some cases, felsic rocks e. The existence of deformed cpx aggregates in the transitional, cpx-bearing dunites indicates that the Kondyor ZUC was pervasively percolated by melt and still deforming at high temperature when the pyroxenite rim was initiated.
The strong enrichments in Rb, Cs and Ba in several vomal are clearly related to the presence of phlogopite. In turn, the buoyancy of the upwelling body may be increased by partial melt produced along with olivine Kelemen, The wehrlite K2 exhibits a high-temperature porphyroclastic texture with a tendency to develop tabular olivine grains Fig.
We envisaged the following scenario. The high field strength elements HFSE: The transition from dunite to pyroxenite is gradual over several centimetres to a few tens of metres and shows textural evidence for replacement of domla dunite by pyroxenite.
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For most elements, the composition of the nephelinite syenite sample K21 lies on an extrapolation of the clinopyroxenite—gabbro trends towards low Mg-number and Ca values, and high Al, Na, K and incompatible trace-element contents. Such reactions were probably involved in the formation of the Kondyor rim pyroxenites. Partially molten mantle material has a much lower viscosity than the surrounding solid mantle e.
As such, the petro-structural data support the interpretation of a high-temperature mantle intrusion triggered by fluid pressure channelized in the core and associated hydrofracturing. Murray, ; Burg et al. Pt—Fe nuggets derived from clinopyroxenite—dunite massifs, Russia: Ultramafic and mafic rocks follow the extruded and eroded lower crustal spine and intrude the upper crust up to near-surface conditions within c.
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The classical relationships close to foliation and  close to lineation imply that the slip system was  Odmal relationships between lithologies. The offset from the dunite array is subtle for wehrlites but more significant for pyroxenites and related gabbros or syenites see below that define a positive correlation markedly distinct from that shown by the dunites.
The ultramafic rocks are subdivided into three subconcentric lithologies, from core to rim: Clinopyroxenite veins are phlogopite—richterite clinopyroxenites. However, they are distinguished by a much finer-grained, fluidal texture and the lack of patent metasomatism in their wall-rocks, suggesting that they represent hypovolcanic dykes intruded after substantial cooling of the ultramafic host.
A case study from the East African Rift. Detection limits obtained by long-term analyses of chemical blanks have been given by Ionov et al. Overall, the rim wehrlites and clinopyroxenites are intermediate between the dunites and the intrusive clinopyroxenites of the metasomatic domain in most of their incompatible-element contents, except for the highly incompatible elements Rb, Ba, Th and U that overlap the dunite composition Fig.
The code colour gop specific rock types is given in Fig. In such a case, subvertical emplacement minimizes the mechanical work during dommal. Time kyr is given in the figures. The inclusions are of coarser-grained, darker gabbro, which suggests comagmatism. The LPO could not be measured because of the large grain size 5—10 mm.