40 Ar/ 39 Ar geochronology and Pb isotopic evidence for the role of ridge subduction in generating orogenic gold mineralization in the Otago Schist Belt, New Zealand
Notice bibliographique
Résumé
Orogenic gold mineralization in the Otago Schist Belt (OSB) of South Island, New Zealand, occurs as synto late tectonic veins and disseminations in brittle-ductile shear zones (e.g., Hyde-Macraes, Rise&Shine), as well as in late and posttectonic fissure veins. Gold is hosted within lower to upper greenschist facies metaclastic rocks of the Otago Schist that comprise part of a long-lived (Triassic to mid-Cretaceous) accretionary complex that developed along the active margin of Gondwana. Orogenic gold mineralization in the OSB is thought to have formed from fluids produced during prograde dehydration reactions within the Otago Schist at depth that also liberated and mobilized S and metals (including Au). Ar/Ar dating of muscovite within veins at the Macraes Mine (Hyde-Macraes shear zone) and the Glenorchy District yield ages in the range of 135-141 Ma, and are interpreted to represent the age of veining. Previous Ar/Ar dating of muscovite from the Rise&Shine shear zone and several late gold-bearing fissure veins elsewhere in the OSB suggest ages for that mineralization of ~101-106 Ma. Pb isotopic analyses of 48 sulphide separates from all of the various styles of gold mineralization within the OSB define two distinct clusters: a less radiogenic cluster of analyses that includes samples from Macraes and Glenorchy, and a more radiogenic cluster that includes samples from the Rise&Shine shear zone and other veins that have yielded younger Ar/Ar ages. Together the age and Pb isotopic data suggests that gold mineralization in the OSB formed during two discrete and relatively short-lived pulses, at ~135-141 Ma and ~101-106 Ma. The highly episodic nature of the gold mineralization argues that hydrothermal activity that produced orogenic gold mineralization in the OSB was not simply part of a steadystate process related to the normal development of an accretionary complex, but rather was related to specific tectonic events that affected the wedge. Age and geochemical studies of the associated arc complex suggest that a ridge subduction event occurred under the OSB at ~135-140 Ma, and reconstructions of probable plate motions in the region appear to require a younger ridge subduction event at ~100 Ma. We suggest that gold mineralization in the OSB was related to two discrete ridge subduction events, analogous to gold mineralization in the Chugach accretionary complex in southern Alaska. Zircon U-Pb age discordance and trace element alteration due to deep, post-impact flow: Implications for planetary chronology D.E. MOSER, W.J. DAVIS, S. REDDY, R.L. FLEMMING AND R.J. HART Dept. of Earth Sciences, Univ. of Western Ontario, London, Ontario, Canada N6A 5B7 (desmond.moser@uwo.ca) Geological Survey of Canada, 601 Booth St., Ottawa, Canada, K1A 0E8 (bidavis@NRCan.gc.ca) Dept. of Applied Geology, Curtin University of Technology, GPO Box U1987, Perth, WA 6845, Australia (s.reddy@curtin.edu.au) iThemba labs, Johannesburg, South Africa (hart@tlabs.ac.za)
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Comment cette classification a été obtenuedéplier
Prédiction distillée sur la base complète
Imitation des enseignantsNi prévalence calibrée, ni vérité terrain. Validation humaine à venir. Apprise à partir de 10 348 étiquettes directes de Codex et de 10 348 étiquettes directes de Gemma. Le mode candidate est l'union des têtes enseignantes seuillées; le consensus est leur intersection. Ces sorties portent le statut machine_predicted_unvalidated et ne sont ni des étiquettes humaines ni des étiquettes directes de modèles de pointe.
Scores Codex et Gemma par catégorie
| Catégorie | Codex | Gemma |
|---|---|---|
| Métarecherche | 0,001 | 0,000 |
| Méta-épidémiologie (sens strict) | 0,000 | 0,000 |
| Méta-épidémiologie (sens large) | 0,000 | 0,000 |
| Bibliométrie | 0,000 | 0,000 |
| Études des sciences et des technologies | 0,000 | 0,000 |
| Communication savante | 0,000 | 0,000 |
| Science ouverte | 0,001 | 0,000 |
| Intégrité de la recherche | 0,000 | 0,000 |
| Charge utile insuffisante (le modèle a refusé de juger) | 0,000 | 0,000 |
Scores machine (provisoires)
Les deux têtes enseignantes du modèle étudiant, lues sur ce travail. Un score ordonne la base pour la relecture; il n'affirme jamais une catégorie, et le statut de validation accompagne chaque rangée tel quel.
Scores de référence d'un modèle non mature (critères de maturité non atteints, 7 itérations). Un score ordonne; il n'affirme jamais une catégorie.
score_only:v0-immature-baseline · tel quel depuis la passe de notation : score_only signifie que le nombre peut ordonner les travaux, et qu'aucune étiquette de catégorie n'en découleClassification
machine, non validéePrédiction automatique; un appel candidat d’une seule tête enseignante, pas un consensus.
Le détail, modèle par modèle et score par score, se trouve en fin de page sous « Comment cette classification a été obtenue ».