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Introduction Avascular necrosis (AVN) is a serious complication of treatment for developmental dysplasia of the hip. There is ongoing controversy regarding AVN and its influence on hip development following medial open reduction (MOR). Purpose The aim of our study was to (1) determine the long-term prevalence of AVN following MOR, (2) evaluate hip development after MOR, and (3) identify predictors of AVN and radiographic outcome at skeletal maturity after MOR. Methods A retrospective cohort analysis of 60 patients (70 hips) who underwent MOR with a mean follow-up of 10.83 years (5.23–16.74) was conducted. AVN was recorded according to Bucholz and Ogden classification and radiographic outcome based on Severin grading. AVN and hip morphology related to length of follow-up were evaluated. Chi-squared and t-tests were used to identify relationships between AVN and other variables. Logistic regression was used to assess predictors of AVN and Severin outcome. Results The rate of clinically significant AVN (types 2–4) following MOR was 32.9 % with type 2 accounting for 82.6 % of these cases. While early acetabular development was satisfactory, long-term outcome was unsatisfactory in 26 % of cases with AVN (vs 8.7 % of cases without AVN). A higher rate of AVN was identified when hips were immobilized in ≥60° of abduction postoperatively. A higher rate of poor Severin outcome was identified in hips with AVN. Conclusions Our findings suggest that there is a high rate of AVN and unsatisfactory long-term outcome following MOR. AVN remains a significant concern following MOR surgery for developmental dysplasia of the hip that may not be apparent until long-term evaluation.

Detrital mica ages in the Southern Uplands range from 458 to 502 Ma. The evidence favours a source in a basement which was part of an arc complex to the north rather than from the Dalradian block which also has mica ages of this range. No Grenville ages have yet been recorded. Detrital volcanic clasts dispersed from the south have cooling ages of 560 and 530 Ma indicating that they did not come from a contemporary arc, but an older arc terrane of uncertain affinities.

Early Proterozoic tholeiitic lavas and sills were emplaced during the initial phase of extension of the intra-cratonic Cuddapah Basin, southern India. Ar-40-Ar-39 laser-fusion determinations on phlogopite mica,from the Tadpatri Fm mafic-ultramafic sill complex, constrain the age of the initial phase of extension and volcanism in the basin at 1.9 Ga. Despite their Early Proterozoic age, the igneous rocks are unmetamorphosed, undeformed and remarkably fresh. They exhibit a wide range in MgO contents (4-28 wt %) and have undergone varying degrees of accumulation or crystal fractionation. Variable La/Nb ratios (1.2-3.7) and epsilon(Nd) values (1 to -10) suggest that some, but not all, of the mafic rocks have been affected by crustal contamination. This appears to have taken place in magma chambers at similar to9 kbar, i.e. the base of the continental crust. Forward modelling of major and trace elements (Fe and Nd) and inverse modelling of rare earth elements suggest that the primary Cuddapah melts were generated by similar to10-15% partial melting of a lherzolite mantle source. This corresponds to a mantle Potential temperature of similar to1500degreesC. The thickness of the mechanical boundary layer predicted by the geochemical modelling is 70 km with a minimum initial lithospheric thickness of 120 kin. This corresponds to a stretching factor of 1.6-1.8. Richter's (1988) secular cooling model for the Earth predicts that, at 1.9 Ga, the ambient mantle had a potential temperature of similar to1500degreesC (i.e. similar to200degreesC hotter than Phanerozoic mantle). If the cooling model is correct then Proterozoic lithospheric stretching and mantle melting beneath the intra-cratonic Cuddapah Basin could have been caused by passive rather than active rifting.

During the Cambrian-Ordovician the paleo–Pacific margin of Gondwana underwent a rapid transition from a site of convergent deformation (Delamerian-Ross orogeny) to one of sedimentation during which the thick turbiditic sequences of the adjacent basal Lachlan fold belt were deposited. Laser-probe 40 Ar- 39 Ar data show that the synkinematic (523–486 Ma), mid-crustal I- and S-type granites and metamorphic country rocks of the Delamerian fold belt were rapidly cooled at 490–485 Ma, coincident with the intrusion of a suite of high-level, postkinematic A-type granites and gabbros (ca. 497–481 Ma). 40 Ar- 39 Ar data on detrital muscovites from the basal sections of the Lachlan fold belt provide information on exhumation rather than cooling but yield an age pattern (507–480 Ma) identical to that of the Delamerian fold belt, demonstrating that this was the source of the sediments. The combined data require that some 15 km of exhumation occurred very rapidly (∼ 5–15 mm ·yr −1 ), coincident (as implied by overlapping ages) with the cessation of convergent deformation and partial melting to form the postkinematic magmas. This scenario implies a causative link, which we infer to have been convective removal of lithospheric mantle following orogenic thickening. The model is analogous to the Tertiary uplift of the India-Asia orogen, which provided the sediment source for the Bengal fan. Our results suggest that similar processes were important in the evolution of mountain belts at least as far back as the early Phanerozoic.

THE Tibetan plateau has had a central role in the development of recent models for the mechanics of mountain belts1,2 and Cenozoic global climate change3. The present elevation and extensional deformation of the plateau probably result from uplift owing to convective thinning of the underlying lithospheric mantle1,2. An age for the uplift would provide a valuable constraint on these models; but because recently proposed indicators of uplift are all climate-dependent, they are equivocal, possibly reflecting global cooling rather than regional uplift4. Here we present new geochemical data on post-mid-Miocene lavas from the plateau, which show that the lavas were derived from the lithospheric mantle. Simple thermal arguments indicate that the generation of such magmas also necessitates thinning of the lithospheric mantle. Thus volcanism is coincident with uplift, providing a climate-independent means of dating the onset of uplift. Dating by the laser 40Ar/39Ar technique places the beginning of this volcanism, and therefore the time of uplift of the Tibetan plateau, at 13 Myr ago.

Controversy exists over whether east-west extension in southern Tibet is related to plateau uplift or to the accomodation of plate boundary forces. Relationships between the onset of extension, plateau uplift, and the thermal state of the lithosphere are critical to this debate. We present new data on postcollisional, north-south-trending dikes in southern Tibet. Their ages range from 18.3 ± 2.7 Ma to 13.3 ± 0.8 Ma, and define the onset of regional east-west extension in southern Tibet. Dikes are compositionally indistinguishable from postcollisional lavas in southern Tibet, being either ultrapotassic, having a source in the subcontinental lithospheric mantle, or calc-alkaline with a dominantly crustal origin. The ultrapotassic dikes demonstrate that east-west extension and subcontinental lithospheric mantle-derived magmatism were temporally and spatially linked, supporting models that relate the latest phase of plateau uplift to subcontinental lithospheric mantle thinning. Thus, the onset of extension by 18.3 ± 2.7 Ma represents the time at which the potential energy of the plateau exceeded convergent boundary forces. This places a new age limitation on the attainment of high elevation in southern Tibet, with implications for models that relate Cenozoic monsoon intensification to plateau uplift.

Some of the many problems associated with the acquisition and interpretation of K-Ar isotope data for authigenic illites in porous sandstone lithologies are discussed. Difficulties arise from a lack of critical awareness of the assumptions made in deriving a K-Ar age of illite formation. Calculations are presented which imply that where sustained reservoir temperatures are high (> 150°C), erroneously low K-Ar ages could result from diffusive Ar loss. Very low levels of detrital contamination with other K-bearing minerals cause further difficulties. Even non-K-bearing contaminants may have a marked effect on apparent ages of illite ‘separates’. However, if considerable care is exercised during separation, the contamination problem is not intractable. The potential of the K-Ar technique to specify temporal development of the characteristics of reservoir rocks suggests that analytical refinements and basic experimental parameters are worth pursuit. Hypothetical examples of depth-age profiles are discussed in the context of their relevance to the timing and nature of hydrocarbon charging of reservoirs.

Structural analysis of remotely sensed images of Eritrea, guided by the common presence of a mid-Oligocene datum at the base of flood basalt at different elevations, helps to piece together the Tertiary history of the western flank of the Red Sea basin. Many of the Tertiary faults are reactivated shear zones in the Pan-African basement, the most important Tertiary fault at the foot of the Red Sea Escarpment marking the site of a pre-Tertiary boundary between andesitic island-arc crust and deeper, perhaps older granitoid migmatites. The initiation of extensional sedimentary basins in Eritrea clearly followed volcanism, as did doming and uplift. This sequence lends some support to active mantle upwelling as the primary tectonic impetus, specifically to massive melting simultaneous with plume impact with the lithosphere. The coincidence of major Tertiary extensional faults with zones of mid-crustal to lower-crustal silicic basement may indicate that active mantle processes were focused by zones of Theologically weak lithosphere, as postulated by Dixon et al. (1989).

New 40Ar39Ar analyses of borehole samples from the Parana-Etendeka continental flood basalt province provide critical evidence of eruption rates in unexposed regions. When combined with surface samples, the new data clarify the duration of this major volcanic province. New ages from both surface and borehole samples confirm a 10–12 million year duration of magmatism, which post-dates the Tithonian mass extinction, and provide a unique 3-dimensional picture of the spatial and temporal eruption of the lava pile. Chemically defined magma types are diachronous and the onset of magmatism occurred 500–1000 km inland, migrating southeast towards the incipient South Atlantic ocean. Calculated eruption rates increased from 0.03 km3 yr−1 between 138 and 135 Ma, through 0.13 km3 yr−1 between 135 and 133 Ma, to 0.21 km3 yr−1 between 133 and 131 Ma, supporting the notion that the rate of magmatism increased with time and proximity to the developing South Atlantic. After 131 Ma the continental eruption rates dropped dramatically to 0.01 km3 yr−1, presumably because rifting had occurred, and eruption centred in the oceanic Rio Grande Rise with eruption rates of around 0.3–0.5 km3 yr−1. Given the available constraints on the potential temperature of the plume, thickness of the continental lithosphere and degrees of extension through time, predicted melt production rates within the plume seriously underestimate the calculated eruption rates on the continent. However, the eruption rates can be reconciled if melting occurred by conductive heating of volatile-enriched mantle. The diachronous nature of the magma types supports the idea that melting occurred over a wide area and that the different magma types reflect different source regions rather than the temporal evolution of magmas from a single source. Given that 10 million years is appropriate to the timescales for conductive heating above the mantle plume, it is suggested that these distinct source regions were located within the lithospheric mantle, consistent with geochemical studies.

Metamorphic rocks may be exhumed to the surface either by isostatic rebound, uplift and erosion or tectonically via thrusting or extension. The latter mechanism is particularly important in the Himalayas where a large extensional detachment system appears to be responsible for very fast unroofing at ∼20 Ma. Here we present the results of a laser argon study of micas and quartz aimed at investigating the thermal response of an orogenic belt to such extension. The data, when combined with existing constraints on the prograde evolution, lead to a uniquely complete thermal history for a metamorphic belt. Laser argon data are reported for quartz and micas from semi-pelitic metamorphic rocks from the Zanskar Himalayas, NW India. The samples derive from three traverses extending from low-grade rocks near the detachment to high-grade rocks in the core of the belt. Most samples demonstrably contain no excess component and the ages of muscovite and biotite show a correlation with distance from the extensional detachment. The ages themselves as well as the difference between the muscovite and biotite ages both increase as the detachment is approached. Muscovite and biotite ages from within the shear zone date deformation associated with extension at 20–25 Ma. The remaining data are most readily interpreted in terms of early slow cooling of the lower grade rocks near the detachment in response to erosional denudation before the detachment became active. Rocks in the core of the orogen were still heating at this time. Later fast cooling of the high-grade rocks in the core of the belt ensued when the extensional regime became active. Simple heat-transfer calculations based on the distance of the high-grade rocks from the fault and the argon ages of their micas provide further constraints on the timing of extension and suggest that the fault first moved 23–25 Ma ago and that it abruptly terminated metamorphism in the core of the metamorphic belt. Our analysis of the thermal history suggests that cooling and exhumation rates determined from metamorphic belts beneath extensional detachments will often be minima.