Constraints and deception in the isotopic record; the crustal evolution of the west Musgrave Province, central Australia

Christopher L. Kirkland, R. Hugh Smithies, Ailsa J. Woodhouse, Heather M. Howard, Michael T.D. Wingate, Elena A. Belousova, John B. Cliff, Rosanna C. Murphy, Catherine V. Spaggiar

Constraints and deception in the isotopic record; the crustal evolution of the west Musgrave Province, central Australia

The Hf and Nd isotopic evolution of the Musgrave Province, central Australia, is used to constrain the timing of crust formation and lithospheric organisation of Proterozoic Australia. The dataset from this region challenges two widely held tenets of Hf and Nd isotope systematics, namely; that crust formation events can only be identified as periods when crystallisation ages correspond to model ages, and that linear Hf evolution arrays away from depleted mantle (along crustal Lu/Hf or Sm/Nd slopes) reflect reworking of the same source.
 Hf isotopes in Musgrave Province zircon crystals indicate two major crust formation events at c. 1900 Ma and at 1600–1550 Ma. Although no juvenile rocks or crystals are known from c. 1900 Ma, radiogenic addition into the crust at this time is required to account for consistent Nd and Hf evolution patterns, which show no indication of an initially heterogeneous source. Oxygen isotopes in zircon grains confirm that much of the c. 1900 Ma Hf isotopic signal is not compromised by mixtures. Furthermore, the correspondence between mantle extraction and the commencement of reworking of Archean material supports new crust generation at c. 1900 Ma and a coupling between lower and upper crustal processes. The c. 1900 Ma timing of juvenile addition is dissimilar to that in the Albany–Fraser and Arunta Orogens and may reflect continental arc development on the margin of a southern continent.
 The general Hf isotopic evolution trend of the Musgrave Province apparently reflects reworking from a dominant c. 1900 Ma source with some additional unradiogenic and radiogenic input through time. However, in the 1220–1050 Ma interval this apparent isotopic evolution contrasts with geological observations that indicate input of voluminous mantle-derived material. Intracontinental rifts and other regions with sustained very-high temperature crustal recycling processes generate magmatic provinces with extreme HFSE enrichment. This can have a profound influence on isotopic evolution trends, suppressing typical juvenile addition patterns. Isotopic mixture modelling indicates that a significant volume of mantle derived material can be accommodated within HFSE enriched magmas without diverging isotopic signatures from apparent reworking trends. In the Musgrave Province, the crust had become so HFSE enriched during the prolonged Musgrave Orogeny (1220–1150 Ma) that it was insensitive to mantle input, which is estimated to have been as much as 85% during this event

Buried but preserved: The Proterozoic Arubiddy Ophiolite, Madura Province, Western Australia

We describe a previously unidentified Proterozoic ophiolite complex situated in the Madura Province in southeastern Western Australia. The Madura Province is almost entirely covered by Mesozoic to Cenozoic basin rocks but new basement drillcores have revealed oceanic crustal assemblages that record continental marginal basin formation followed by oceanic subduction and basin closure. The Pinto Basalt has E-MORB/OIB chemical affinity and ?Nd(1600 Ma)from 2.54 to +3.3. It formed by mantle upwelling beneath extending crust in an ocean-continent transition zone and must be considerably older than c. 1389 Ma adakite that intrudes it. The Sleeper Camp Formation comprises mafic metavolcaniclastic schist intruded by metadolerite and plagiogranite veins. Zircon crystals from the metavolcaniclastic schist yield a dominant age component and maximum depositional age of 1536 ± 13 Ma. The metadolerite and plagiogranite veins have zircon crystallization ages of 1479 ± 8 Ma and 1471 ± 5 Ma, respectively. Interlayered basalt and sediments of the Malcolm Metamorphics have a maximum depositional age of c. 1470 Ma and were metamorphosed at 1315 ± 11 Ma. The mafic rocks from both units are tholeiitic, with MORB-like HFSE ratios that point to a depleted mantle source similar to N-MORB, but with trace element patterns that indicate subduction enrichment. V/Ti ratio trends suggest the Sleeper Camp Formation marks oceanic subduction initiation at c. 1479 Ma. The progression to oceanic arc formation is recorded by the Malcolm Metamorphics after c. 1470 Ma, and the Haig Cave Supersuite from 1415 to 1389 Ma. The majority of these rocks occur within the hanging wall of the Rodona Shear Zone and were structurally emplaced above the continental margin of the West Australian Craton between 1389 and 1330 Ma during oceanic arc–continent collision, forming the Arubiddy Ophiolite Complex. The occurrence of oceanic crustal assemblages behind the accreted ophiolite complex frozen by the emplacement of voluminous 1192–1125 Ma Moodini Supersuite ferrogabbros and granites demonstrates that continental collision did not occur between the West Australian and South Australian Cratons. The preservation of rocks of oceanic affinity behind ophiolites could be a hallmark of other Proterozoic terranes that have escaped full continent-continent collision

Competitive testing of the WHO 2010 versus the WHO 2017 grading of pancreatic neuroendocrine neoplasms: Data from a large international cohort study

Background: The World Health Organization (WHO) and the American Joint Cancer Committee (AJCC) modified the grading of pancreatic neuroendocrine neoplasms from a three-tier (WHO-AJCC 2010) to a four-tier system by introducing the novel category of NET G3 (WHO-AJCC 2017). Objectives: This study aims at validating the WHO-AJCC 2017 and identifying the most effective grading system. Method: A total of 2,102 patients were enrolled; entry criteria were: (i) patient underwent surgery; (ii) at least 2 years of follow-up; (iii) observation time up to 2015. Data from 34 variables were collected; grading was assessed and compared for efficacy by statistical means including Kaplan-Meier method, Cox regression analysis, Harrell's C statistics, and Royston's explained variation in univariable and multivariable analyses. Results: In descriptive analysis, the two grading systems demonstrated statistically significant differences for the major category sex but not for age groups. In Cox regression analysis, both grading systems showed statistically significant differences between grades for OS and EFS; however, no statistically significant difference was observed between the two G3 classes of WHO-AJCC 2017. In multivariable analysis for the two models fitted to compare efficacy, the two grading systems performed equally well with substantially similar optimal discrimination and well-explained variation for both OS and EFS. The WHO-AJCC 2017 grading system retained statistically significant difference between the two G3 classes for OS but not for EFS. Conclusions: The WHO-AJCC 2017 grading system is at least equally performing as the WHO-AJCC 2010 but allows the successful identification of the most aggressive PanNET subgroup. Grading is confirmed as probably the most powerful tool for predicting patient survival