G.A. Belyanin

Geological and taphonomic context for the new hominin species Homo naledi from the Dinaledi Chamber, South Africa

We describe the physical context of the Dinaledi Chamber within the Rising Star cave, South Africa, which contains the fossils of Homo naledi. Approximately 1550 specimens of hominin remains have been recovered from at least 15 individuals, representing a small portion of the total fossil content. Macro-vertebrate fossils are exclusively H. naledi, and occur within clay-rich sediments derived from in situ weathering, and exogenous clay and silt, which entered the chamber through fractures that prevented passage of coarser-grained material. The chamber was always in the dark zone, and not accessible to non-hominins. Bone taphonomy indicates that hominin individuals reached the chamber complete, with disarticulation occurring during/after deposition. Hominins accumulated over time as older laminated mudstone units and sediment along the cave floor were eroded. Preliminary evidence is consistent with deliberate body disposal in a single location, by a hominin species other than Homo sapiens, at an as-yet unknown date. DOI: http://dx.doi.org/10.7554/eLife.09561.001

Response to comments by Nicoli et al. on paper by Belyanin et al. (2012)

The basis of the Nicoli’s et al. (this issue) comment is a critique of the temperature of *1,100 C estimated by Belyanin et al. (2012) from rare Al–Mg-rich mineral assemblages in sample DR19 from the Southern Marginal Zone (SMZ) Limpopo Complex (LC). However, these authors used this critique to promote the argument that UHT conditions are impossible (their terminology) in the SMZ and that Tmax could not have been much higher than 850 C. In the reply, we address major issues highlighted by Nicoli’s et al. (this issue), namely that of biotite stability and dehydration melting of metapelite, and provide new P–T data based on combination of PERPLE_X pseudosection modeling and TWQ conventional thermobarometry for sample DR19. We provide unequivocal evidence that TMax in the SMZ must have been at least 900 C in accordance with the requirement for UHT conditions (e.g., Harley 2008). In fact, higher temperatures could easily have been attained (e.g., Tsunogae et al. 2004). Discussion of the Nicoli’s et al. comments

Corundum + orthopyroxene ± spinel intergrowths in an ultrahigh-temperature Al-Mg granulite from the Southern Marginal Zone, Limpopo Belt, South Africa

Abstract We report the occurrence of unusual lamellar (random and regular subparallel) intergrowths of corundum and symplectic intergrowth of spinel with orthopyroxene in an ultrahigh-temperature Al-Mg granulite from the Southern Marginal Zone of the Limpopo Belt, South Africa. Separate compositions are suggested for the homogenous phase that might have existed prior to the formation of the two types of lamellar intergrowths of corundum with orthopyroxene. In the case of random lamellar corundum + orthopyroxene intergrowth, the estimated precursor composition is similar to Fe-Mg garnet, while, although speculative, an ultrahigh-Al orthopyroxene precursor is suggested to account for the exsolution nature of the unique regular subparallel corundum lamellae in orthopyroxene. Considering that the stability field of Fe-Mg-rich garnet relative to orthopyroxene + corundum extends to lower pressures, the estimated garnet composition (XMg = ~0.65) is most likely stable at low pressures of ~5 kbar. Such low pressures are further supported by the Fe-Mg-rich garnet compositional nature of the pre-spinel-intergrowth orthopyroxene. Given the rare preservation of the mineral assemblages typical of prograde metamorphism in granulite facies rocks, our discovery of corundum lamellar intergrowth with orthopyroxene from an ultrahigh-temperature Al-Mg granulite is unique.

Role of granite intrusions for the formation of ring structures in granulite complexes: Examples from the Limpopo belt, South Africa

Ring structures are cylindrical or sheath folds with concentrically distributed beds, often with granites in the cores. This paper reports structural, petrographic, and petrological evidence for four such structures from the Central Zone of the Limpopo complex, which were formed during granulite exhumation in Neoarchean time (event D2/M2). It was demonstrated that the orientation of linear and planar elements in the rocks are practically identical and independent of the position within the Central Zone. All existing measurements (hundreds for the four structures) project within the same fields in stereograms. The fold axes plunge SW at an angle of ∼40° within the whole area of the Central Zone of the Limpopo complex. This implies that the rocks were metamorphosed and deformed during event D2/M2, which is typical of the Neoarchean stage of the development of the Limpopo granulite complex. Local mineral equilibria and fluid inclusions were studied in a series of key rocks, and P-T paths were derived for them. A gravitation mechanism was substantiated for the ascent of granulites and accompanying granite bodies. The structure of ring complexes was evaluated on the basis of various erosion sections. It was shown that stocklike granite bodies occur at the base of each ring structure. Petrochemical and structural data were used to demonstrate that the granites (2627 Ma) had been derived by the complete or partial melting of the lower parts of the section of Neoarchean (2651 Ma) country rocks. The upwelling of a less dense granite magma synchronously with the exhumation resulted in the helical squeezing of the overlying gneisses. This led to the concentric arrangement of beds and development of a ring structure, a sheath fold containing a granite core in some sections. A preliminary numeric 2D model is considered for the ascent of a granite diapir accompanied by the downwelling of colder and denser country rocks. A better understanding of this process can be gained by 3D numerical simulation.

High-temperature polymetamorphism in the central zone of the Limpopo granulite complex (South Africa): Structural and petrological evidence

The problem of confirmation of HT (hightemperature) metamorphism in Precambrian granulite complexes appeared rather recently. The central zone ofthe Limpopo complex (Fig. 1) is the best polygon forits solution. The results of our investigations demonstrate that gneiss, which underwent deformations (D)and granulite metamorphism (M) in the Neoarchean(D2/M2), was subjected to one more stage of HT metamorphism, but in the Paleoproterozoic (D3/M3).Started from isobaric heating (IH) of rocks in the middle crust, the event D3/M3 was finished with theirdecompression cooling (DC), i.e., exhumation ofrocks from the middle part of the continental crusttowards the surface [2, 4–6, 10]. This evidence wasbased on studies of circular structures, namely sheathfolds. This report contains the first data on analogousphenomena within the shear zones (shift deformations) on a regional scale. The absence of signs of earlier events was suggested in them, but it turned out tobe completely wrong.We studied the regional system of Voorburg–Tshipise shear zones (Fig. 1) where found an outcrop inwhich the structural elements D2/M2 are overprintedby younger D3/M3 structures principally differentfrom the first by foliation and lineation. This is clearlyobserved not only on the projection stereogram forthese elements, but directly in the field as well (Fig. 2).It is evident that overprinted deformations should bealso reflected on paragenetic relationships, becausethey are ductile (deep). For this purpose, we collectedtwo samples on the outcrop with two orientations ofstructural elements. One of them, RB66 (D2/M2),was taken from layers with a relatively steep dip of foliation and southwestern lineation strike reflecting themotion of the material towards the surface with anangle of ~42°. The second sample, RB55 (D3/M3),was taken from the layer of moderate dip (~12 °). Bothsamples have the same mineral composition: garnet(