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Origin and emplacement of the ultramafic rocks of the Emigrant Gap area, California. Variations in final shapes and internal geometry of intrusions with varying numerical model parameters Table 5. 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.
Although the bulk composition of the SMSR is ultramafic, the melt composition depends on the degree of melting and thus varies between mafic and ultramafic. The distinctive feature of Kondyor is its nearly perfect circular columnar shape, which may additionally reflect the absence of far-field stresses in the crust.
These numerical conditions limit the parameter space for Kondyor-like models. We envisaged the following scenario. This is confirmed by varying the initial cohesion of the upper crust compare models kofh and kofz; Models 1 and 11 in Table 5 ; Fig.
Close mobile search navigation Article navigation. Interpretation of SKS-wave using samples from the subcontinental lithosphere. Part I, phase relations, the origin of calc-alkaline magma series, and the formation of discordant dunite. View large Download slide. However, Ni does not show the drastic drop observed in olivines of clear igneous origin at a given Mg-number e.
However, the textural and petro-structural characteristics of the ultramafic rocks indicate that the Kondyor dunite was emplaced at the final stage as a solid mass, such that magma pressure cannot be invoked to explain doming of the regional sedimentary basement.
The flat foliation suggests that the present level of erosion exposes the domal top of the intrusion, and that the synformal structure could result from internal sagging. Textures and fabrics of peridotite nodules from kimberlite at Mothae, Thaba Putsoa and Kimberley. A odmal of their occurrence and chemical fop and speculations on their petrogenesis.
Citing articles via Web of Science This variation is coupled with a textural change from fine-grained textures reminiscent of mantle tectonites cpx-bearing dunites and wehrlites with olivine flames to coarse-grained cumulate textures clinopyroxenitesthrough poikiloblastic, replacive textures wehrlites.
It is worth noting that, because of the strong dependence of orthopyroxene stability on pressure Kelemen,the reactivity of peridotite—melt systems is likely to be enhanced by translithospheric mantle upwelling, as long as primary pyroxene is not reacted out and the mantle body is not conductively cooled to subsolidus temperatures.
The slip system is the common with  close to lineation and close to foliation; the marked  maximum probably results from large subgrain rotations, with  as the external rotation axis. Instabilities triggered by the accumulation of volatile-rich melt forced the dunite into the crust as a translithospheric diapir.
Among the dykes that cut the dunites, the koswites and the hornblende gabbros are compositionally comparable with the clinopyroxenites of the metasomatic domain and the peripheral ring gabbros and syenites, respectively Table 3. The peripheral intrusions of diorite and monzodiorite and subordinate alkaline gabbros and granodiorites contain xenoliths of Kondyor pyroxenites Fig.
These intrusions were sampled by drilling to m depth in the 655 centre of the ZUC Orlova, Cross-cutting field relationships indicate that the usually steeply dipping clinopyroxene dykes are older than the syenitic, pegmatitic dykes Fig.
Lower continental crust formation through focused flow in km-scale melt conduits: The wehrlite K2 exhibits a high-temperature porphyroclastic texture with a tendency to develop tabular olivine grains Fig.
These models had, however, important caveats concerning the depth that molten rocks reach, the shape rather than a funnel and depth of emplacement. Thin section and fabric of the K2 wehrlite GPS: Irvine, ; Veksler et al. The Ni content of the dunites is notably lower than that of both cumulates from primary mantle melts and residual mantle rocks left domzl melt extraction.
Conversely, because it is partitioned into pyroxene preferentially to olivine, Cr may be substantially enriched during olivine-forming reactions Godard et al. Asymmetrical zoning is a result of models kofm and kofp Models 6 and 9 Table 5 ; Fig. Rim pyroxenites were formed by a dommal peritectic reaction, implying the existence of at least a small, conductive thermal gradient around the dunite body while the latter was still at near-solidus temperature conditions.
They are similar to the Aldan Shield lamproites with respect to REE, but doma distinctive features for the other elements; that is, lower HIE abundances Rb—Tamore pronounced negative anomalies of Zr and Hf, and slightly negative anomalies of Sr, instead of positive anomalies.
Channel spreading is a rapid event 10—20 kyr. Changes in these two parameters significantly affect both the final model geometry and the emplacement depth Table 4Fig. Lamproites and other potassium-rich igneous rocks: 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.