Syntectonic mobility of supergene nickel ores of New Caledonia (Southwest Pacific). Evidence from faulted regolith and garnierite veins.

International audienceSupergene nickel deposits of New Caledonia that have been formed in the Neogene by weathering of obducted ultramafic rocks are tightly controlled by fracture development. The relationship of tropical weathering and tectonic structures, faults and tension gashes, have been investigated in order to determine whether fractures have play a passive role only, as previously thought; or alternatively, if brittle tectonics was acting together with alteration. From the observation of time-relationship, textures, and mineralogy of various fracture fills and fault gouges, it may be unambiguously established that active faulting has play a prominent role not only in facilitating drainage and providing room for synkinematic crystallisation of supergene nickel silicate, but also in mobilising already formed sparse nickel ore, giving birth to the very high grade ore nicknamed "green gold"

Stress Field Interactions Between Overlapping Shield Volcanoes : Borehole Breakout Evidence From the Island of Hawai'i, USA

Acknowledgments: This PTA2 borehole investigation was funded by the International Continental Scientific Drilling Program (ICDP) and by VMAPP (Volcanic Margin Petroleum Prospectivity) project (VBPR/DougalEARTH/TGS) in collaboration with the Humu'ula Groundwater Research Project. D. A. J. and S. P. are partly funded through a Norwegian Research Council Centres of Excellence project (project number 223272, CEED). We thank Marco Groh for the logging operations. We thank two anonymous reviewers for the comments and suggestions. We are particularly grateful to the Associate Editor Mike Poland for his valuable comments and his critical review that greatly improved the manuscript.Peer reviewedPublisher PD

Note on analysis of quartz grain dimensions in foliated greywackes

Quarzkorn-Abmessungen aus Grauwacken wurden auf ein internes Referenzsystem (reference aspect ratio, RAR) bezogen und mit Hilfe der linearen Regressionsanalyse der reduzierten Hauptachse (reduced major axis, RMA) ausgewertet. Das verwendete statistische Verfahren unterscheidet im Gegensatz zur Methode der kleinsten Quadrate nicht zwischen abhängigen und unabhängigen Variablen. Die Anwendung der RMX-Methode in Verbindung mit den RAR-Meßwerten kann sehr hilfreich für Vergleiche innerhalb geschieferter Grauwacken sein, bei denen unterschiedliche Prozesse in Korngrößenbereich wirksam waren wie etwa Drucklösung und Festkörper-Rotation. Die RAR/RMA-Analyse erfaßt Kornregelungen und ist daher auch einsetzbar für die Klassifikation von Schieferungen. Darüber hinaus wird die Anwendung der RAR/RMA-Analyse für die Bestimmung der Deformation diskutiert. Robin strain-Werte werden mit arithmetischen und harmonischen Mittelwerten der RAR-Analyse verglichen. Es zeigt sich, daß das arithmetische Mittel des RAR ein vernünftiges Maß für die longitudinale Deformation darstellt. Quartz grain dimensions, measured parallel to an internal reference system (reference aspect ratio, RAR), were analyzed using the »reduced major axis« (RMA) linear regression analysis. In contrast to least-squares analysis, this statistical technique does not distinguish between dependent and independent variables. Application of the RMA analysis in conjunction with RAR values can be most useful for comparisons between foliated greywackes in which different grain scale processes, such as pressure solution and rigid-body rotation, were active. The RAR/RMA analysis reflects grain alignment and is therefore also useful for cleavage classification. In addition to the above, the application of RAR/RMA analysis for the determination of strain is discussed. Robin strains are compared with the arithmetic and harmonic means from RAR's and it is concluded that the arithmetic mean RAR produces a reasonable estimate of longitudinal strain in these rocks. Les dimensions des grains de quartz, mesurés parallèlement à un système de référence interne (»reference aspect ratio«: RAR) ont été traitées par la méthode de la régression linéaire (»reduced major axis«: RMA). Contrairement à la méthode des moindres carrés, cette technique statistique ne fait pas de distinction entre les variables dépendantes et indépendantes. L'application de ce type de méthode s'avère très utile à la comparaison de grauwackes schisteuses dans lesquelles les dimensions des grains peuvent être la conséquence de processus différents, tels que la dissolution (pressure solution) et la rotation. L'analyse RAR/RMA traduit l'alignement des grains et peut, de ce fait, être utilisée aussi à l'appréciation du type de schistosité. D'autre part, l'auteur discute l'application de l'analyse RAR/RMA à la détermination de la déformation finie. Si on compare les déformations »Robin« aux moyennes arithmétique et harmonique des RAR, on peut conclure que les moyennes RAR arithmétiques fournissent une estimation raisonnable de la déformation longitudinale. Помимо интернациона льной системы RAR, разме ры зерен кварца анализи ровали с помощью регр ессивного анализа «Изменение о сновных осей» — RMA. В отличие от анализа ме тодом наименьшего кв адратов, при названном статис тическом методе разл ичия между зависимыми и не зависимыми переменн ыми не учитываются. Компл ексное применение RAR иPeer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/47848/1/531_2005_Article_BF01821068.pd