| 1. |
- Cornell, David H., 1948, et al.
(författare)
-
A new chronostratigraphic paradigm for the age and tectonic history of the Mesoproterozoic Bushmanland Ore District.
- 2009
-
Ingår i: Economic Geology. ; 104, s. 385-404
-
Tidskriftsartikel (refereegranskat)abstract
- The four giant stratiform Cu-Pb-Zn-Ag base metal deposits of the Bushmanland Ore District have long been regarded as Paleoproterozoic sedimentary-exhalative deposits formed in a continental basin at about 1650 Ma and overlying the Achab Gneiss, an approximately 2.0 Ga basement complex, with no known Archean crustal history. The supracrustal sequence was thought to include the Hoogoor 'pink' metavolcanic gneiss at the base and the ore-bearing metaquartzites to be unconformably overlain by the 1650 Ma Koeris Formation. All the supracrustals were regarded as predating the 1200 to 1000 Ma Namaqua-Natal orogenic cycle. In this work we present ion probe and laser ablation zircon dating of xenocrystic, magmatic, detrital and metamorphic zircon which leads to fundamental changes in our understanding of the age and tectonic history of the Bushmanland Ore District. The Bushmanland base metal deposits are not older than 1650 Ma as entrenched in the literature, but younger than the 1285 ± 14 Ma detrital zircons found within the ore horizon at Gamsberg. The ore is probably older than the 1198 ±10 and 1154 ± 18 Ma detrital zircons found in the unconformably overlying Koeris Formation, and most likely older than the 1130 ± 35 Ma Koeris Formation metabasalts. The existence of an Archean crustal component in the Bushmanland Ore District has now been established by detrital zircon ages and by Sm-Nd model ages. However no outcrops of Archean rocks have yet been found. The Bushmanland Group metasediments were derived largely from 1850 to 2100 Ma Paleoproterozoic rocks, which probably reflects their provenance in the Richtersveld Subprovince to the north. However they also contain Mesoproterozoic detrital zircon which constrains their minimum age. The Bushmanland Ore District metasediments conform to the same chronostratigraphic and tectonostratigraphic pattern as recently established at Bitterfontein to the southwest. An older group represented by the Bushmanland Group and including the sedimentary-exhalative Cu-Pb-Zn-Ag ores, formed before, but within 80 Ma of, the main collision event at 1200 Ma. A younger group, represented by the Koeris Formation, formed after the main collision at about 1130 Ma. The older group should thus have experienced an early collision-related D1 folding event and metamorphism, whereas the younger group should show only D2-D3 and M2-M3 metamorphism, between 1130 and 1000 Ma. This prediction should be tested against more structural observations. The 1204 ± 11 Ma Aroams Gneiss is now recognised as the oldest known granitoid in the Bushmanland Ore District, in agreement with other recently published ion probe data. However it probably does not represent basement to the older metasediments. The Achab Gneiss, previously thought to be about 2000 Ma old and the polydeformed basement, is dated by our published 1166 ± 13 and 1163 ± 11 Ma concordia ages for magmatic emplacement. The Aroams Gneiss is confirmed to belong to the 1200 Ma syn-collisional Little Namaqualand Suite documented in the Okiep Copper District to the west. The 30 Ma younger Achab and Hoogoor Gneisses may be grouped in the Aggeneys Suite. Microbeam zircon dating has established a new chronostratigraphic paradigm for the geological history of the Bushmanland Ore District, however many issues related to ore formation and the deformation history remain to be resolved.
|
|
| 2. |
|
|
| 3. |
- Cornell, David H., 1948, et al.
(författare)
-
Reply to comments by Mc Clung, C.R., Gutzmer, J., Beukes, N.J, on: A new chronostratigraphic paradigm for the age and tectonic history of the Mesoproterozoic Bushmanland Ore District.
- 2009
-
Ingår i: Economic Geology. - 0361-0128. ; 104, s. 1282-1285
-
Tidskriftsartikel (refereegranskat)abstract
- We were pleased and encouraged by the congratulations expressed in the first paragraph of our friend McClung et al.’s (2009) comment. However, as we read further, we found that not all was rosy. We were dismayed to discover that we had made a lot of mistakes and in the end, all we had achieved was to add to the confusion about the origin of the Bushmanland ore district!
|
|
| 4. |
- Cornell, David H., 1948, et al.
(författare)
-
Zircon dating reveals an Archaean crust beneath the Kalahari sand.
- 2008
-
Ingår i: Annual Meeting Mineralogical Network, Natural History Museum, University of Oslo, June 2008. ; abstracts
-
Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Continents are subdivided into structural provinces based on the age of the last orogeny or major magmatic event which imprinted the structural fabric on the bedrock. These first-order subdivisions are important in understanding how the continents were assembled. The continuity and boundaries of provinces such as the Namaqua-Natal Province in Southern Africa have been established, however adjoining Kheis province which lies almost entirely under the Tertiary to Recent Kalahari sands, has thus far defied attempts to understand its age and geological history. A foreland thrust complex developed in 1.92 Ga redbeds at Olifantshoek (Fig. 1a) was postulated by Cornell et al. 1998. However the much younger 1.2 Ga to 1.1 Ga Sinclair Sequence volcanic and plutonic rocks exposed in the same area suggest that the Kheis Province could have experienced an Andean-type orogeny at ~1.2 Ga. Thus Moen (1999) suggested that much of the Kheis Province was coeval with and belonged to the ~1.2 Ga Namaqua-Natal Province. At Rietfontein on the eastern margin of the Kheis, tillites of the Permian Dwyka Group, were found to contain abundant cobble-sized clasts of crystalline bedrock. Bearing in mind the generally westward transport directions for the Dwyka Ice sheet (Fig. 1a), these exposures were investigated to see if they contained information about what lies under the Kalahari. These granotoid cobbles are badly weathered, but we succeeded in dating them using an ion probe and laser ablation ICPMS, by the U-Pb method. The data is largely discordant, reflecting ancient lead loss at the time of glaciation. Nevertheless we find compelling evidence that Archean and 2.0 Ga (Bushveld Complex age) granitic crust exists beneath the Kalahari. We also failed to find any evidence for the existence of younger granitic crust or high-grade metamorphic terranes. The published concepts of the Kheis Province as either a 1900 - 1750 Ma collisional orogen, or an extension of the 1200 Ma Namaqua Province find no support in our data. The possibility of Archean and Bushveld-aged rocks occuring as basement beneath the Kalahari has important implications for diamond, base and precious metal prospecting in the western Kalahari in South Africa, Botswana and Namibia. These possibilities should be tested by drilling with geophysical control, the last such campaign having been completed in Botswana in 1984.
|
|
| 5. |
- Dahlman, S., et al.
(författare)
-
Expanding the donor pool: lung transplantation with donors 55 years and older
- 2006
-
Ingår i: Transplant Proc. - 0041-1345. ; 38:8, s. 2691-3
-
Tidskriftsartikel (refereegranskat)abstract
- The scarcity of donor organs is one of the major limitations to lung transplantation. This has led to a progressive expansion of criteria for donor selection in lung transplantation. This study evaluated the outcome of recipients of lungs from donors >/=55 years. We performed a retrospective analysis of 212 consecutive lung transplantations. Recipients were divided into two groups, those receiving lungs from donors >/=55 years (older donor group) and those receiving lungs from donors <55 years (younger donor group). Recipient baseline characteristics, time in the intensive care unit (ICU), early mortality, and long-term survival (Kaplan-Meier) were compared between the groups. Forty-one donors (19%) were >/=55 years. Mean recipient age in the older donor group was higher than in the younger donor group (52 +/- 8 vs. 47 +/- 12 years; P = .015). Indication for transplantation did not differ between the groups. ICU stay was comparable between the two groups (6 +/- 12 vs. 7 +/- 11 days; P = .64). Actual 30-day mortality (10.8% vs. 6.4%; P = .32), 1-year mortality (17.1 vs. 19.6%; P = .50), and cumulative long-term survival (65% and 62% at 5 years, P = 1.00) did not differ between the older and younger donor group. This study indicated that transplantation of lungs from selected donors aged >/=55 years did not impair short-or long-term results. The use of lungs from elderly donors may help to increase the number of donor organs for lung transplantation.
|
|
| 6. |
|
|
| 7. |
- Hamnegård, Carl-Hugo, 1954, et al.
(författare)
-
Effect of lung volume reduction surgery for emphysema on diaphragm function
- 2006
-
Ingår i: Respir Physiol Neurobiol.. ; 150:2-3
-
Tidskriftsartikel (refereegranskat)abstract
- Preoperative prediction of a successful outcome following lung volume reduction surgery (LVRS) for emphysema is imperfect. One mechanism could be improvement in respiratory muscle function yet controversy exists regarding the magnitude and mechanism of such an improvement. Therefore, we measured diaphragm strength in 18 patients before and after LVRS. Mean (S.D.) FRC fell from 6.53 to 5.40l (p=0.0001). Mean sniff transdiaphragmatic pressure increased from 76 to 87cmH(2)O (14%, p<0.03) and mean twitch transdiaphragmatic pressure (Tw Pdi) increased by 2.5cmH(2)O at 3 months (12%, p=0.03). There was a highly significant increase in twitch esophageal pressure (Tw Pes) (60%, p<0.0001), which was maintained at 12 months (46% increase, p=0.0004). No change was observed in quadriceps twitch tension in nine subjects in whom it was measured. After LVRS the ratio Tw Pes:Tw Pdi increased from 0.24 to 0.37 at 3 months (p=0.0003) and 0.36 at 12 months (p=008). Low values of Sn Pdi, Sn Pes, Tw Pes and a high RV/TLC ratio were the preoperative variables most predictive of improvement in shuttle walking distance. We conclude that LVRS improves diaphragm function primarily by alteration of lung volume. Patients with poor diaphragm function and high RV/TLC ratio preoperatively are most likely to benefit from the procedure.
|
|
| 8. |
- Kemp, Tony, et al.
(författare)
-
Concurrent Pb-Hf isotope analysis of zircon by laser ablation multi-collector ICP-MS, with implications for the crustal evolution of Greenland and the Himalayas
- 2009
-
Ingår i: Chemical Geology. - : Elsevier BV. - 0009-2541. ; 261:3-4, s. 244-260
-
Tidskriftsartikel (refereegranskat)abstract
- Abstract in UndeterminedThe in situ Lu-Hf isotope analysis of zircon by laser ablation has emerged as a high-calibre tool for tackling magmatic and crustal evolution. The strength of the approach lies with the ability to target specific zircon growth domains identified by imaging, and thus to unravel polyphase crystallisation histories. However, due to the volume of material being sampled during analysis there remains the possibility of ablation-induced mixing between Hf from domains of different age. Inaccurate Hf isotope ratios and spurious geological interpretations could result. One approach to this problem involves dating the same volume of material analysed for Hf isotopes by concurrently measuring (207)Pb/(206)Pb ratios during ablation [Woodhead,J.D., Hergt,J.M.. Shelley, M., Eggins, S., Kemp, R. 2004. Zircon Hf-isotope analysis with an excimer laser, depth profiling, ablation of complex geometries, and concomitant age estimation. Chemical Geology 209,121-135.]. This paper explores the viability of this dual analysis by investigating complex zircons from three different geological contexts, detrital zircons in sedimentary rocks, inherited zircons in granites, and zircons in metamorphosed Eo-Archaean TTG gneisses from Greenland. The implications of the Greenland data for Archaean crustal evolution are discussed in the light of published solution zircon Hf isotope datasets from these gneisses. A case study of detrital zircons from modern river sands in the Himalayas highlights the potential of the technique for providing a rapid, cost-effective picture of crustal evolution that should complement regional bulk rock studies.
|
|
| 9. |
|
|
| 10. |
|
|
| 11. |
|
|
| 12. |
|
|
| 13. |
|
|
| 14. |
- Wierup, Per, et al.
(författare)
-
Moderate mitral regurgitation in patients undergoing CABG--the MoMIC trial.
- 2009
-
Ingår i: Scandinavian cardiovascular journal. - : Informa UK Limited. - 1651-2006 .- 1401-7431. ; 43:1, s. 50-6
-
Tidskriftsartikel (refereegranskat)abstract
- BACKGROUND: The presence of mild to moderate ischemic mitral regurgitation (IMR) marks a significantly reduced long-term survival and increased hospitalizations due to heart-failure. However, it is common practice in many institutions to refrain from repairing the mitral valve in these patients. There are no available conclusive data to support this practice, and thus there is a need for an adequately powered randomized trial. STUDY DESIGN: The Moderate Mitral Regurgitation In Patients Undergoing CABG (MoMIC) trial is the first international multi-center, large-scale study to clarify whether moderate IMR in CABG patients should be corrected. A total of 550 CABG patients with moderate IMR are to be randomized to treatment of either CABG alone or CABG plus mitral valve correction. The primary end point is a composite end point of mortality and rehospitalization for heart failure at five years. The inclusion and randomization of patients started in February 2008. IMPLICATION: If correction of moderate IMR in CABG patients proves to be the superior strategy, most patients should be treated accordingly.
|
|
| 15. |
- Wierup, Per, et al.
(författare)
-
The prevalence of moderate mitral regurgitation in patients undergoing CABG.
- 2009
-
Ingår i: Scandinavian cardiovascular journal : SCJ. - : Informa UK Limited. - 1651-2006 .- 1401-7431. ; 43:1, s. 46-9
-
Tidskriftsartikel (refereegranskat)abstract
- OBJECTIVE: The aim of this study was to determine the prevalence of moderate ischemic mitral regurgitation (IMR) in the contemporary CABG population. We also aimed to correlate the effective regurgitant orifice area (ERO) of any regurgitant mitral valve in patients with coronary artery disease with the semiquantitative integrated scale of IMR. DESIGN: From March 15 through June 15, 2006, 510 consecutive CABG patients in three tertiary centres were included in the study. All patients showing any sign of mitral regurgitation (MR) at the referring hospital underwent a preoperative transthoracic echocardiographic estimation of the degree of MR using the integrated scale (1-4) and ERO. RESULTS: IMR was found in 141 patients (28%). The prevalence of moderate 2+ or worse IMR was 4% (95% CI; 2.5-6.1%) and the ERO corresponding to 2+ IMR or more ranged from 5 to 30 mm(2). Fourteen patients had an ERO between 15-30 mm(2). CONCLUSIONS: According to our study, patients with moderate IMR, defined as an ERO between 15-30 mm(2), account for only 2.7% (95% CI; 1.5-4.7%) of a non-emergency CABG population.
|
|
