Norman M. Halden

Professor; Ph.D.University of Glasgow, 1983

 

e-mail: nm_halden@umanitoba.ca

 

 

 

 

 

The Earth is a complex system.  From a geological perspective, different component parts of the system operate at different length and time scales; during the interactions there is feedback between the parts of the system as energy and mass are transferred and redistributed.   Minerals are important because they record the interactions.   The main thrust of my research over the past several years has been to characterize and quantify the distribution of trace elements in zoned minerals in such a way that the patterns of their distribution can be related to environments of mineral growth.   I have directed my efforts in four areas: (1) modelling of trace element oscillatory zoning in minerals from igneous and surficial environments; (2) trace element distribution in layered igneous intrusions; (3) image and microbeam analysis of otolith microchemistry; (4) field-based studies of layered igneous rocks, mineral deposits and deformed sulphide mineralization.

 

Zoning in minerals: In order to understand the significance of oscillatory zoning patterns (OZP) it is important that we develop a quantitative means of describing the patterns as well as a means of linking the chemical and structural information to the optical features.  In this way we will be able to (1) compare zoning patterns in natural minerals and (2) compare natural patterns with the products of numerical models.  This work is needed to set out the framework for considering minerals as dynamical systems.  I have shown, using image and numerical analysis, that it is possible to determine Lyapounov exponents and fractal dimensions for trace‑element oscillatory zoning in minerals. In cases where the exponents are negative this shows that the patterns are chaotic which is a strong indication that the chemical variation is the product of local self-organized processes and chemical feedback operating at the growth interface of the mineral with its environment.   This is distinct from larger-scale changes in the bulk composition of the system.

Environmental studies: Otoliths are the ear bones of teleost (bony) fish, they are made of aragonite and/or vaterite and they are zoned.  Conservation and management of fish stocks require an accurate assessment of (1) the life histories of fish; (2) environmental factors affecting their behaviour and growth, and (3) population stock structure.  Fisheries scientists commonly determine Sr/Ca ratios in this material using EPMA.  This is not the optimum method because of ablation problems and relatively poor sensitivity for Sr; to analyze carbonates without ablation at the low ppm levels desired (~2 - 10 ppm) Proton-Induced X-ray Emission (PIXE) is a more appropriate tool. With the capacity to analyze and map trace elements in minerals I have applied this to a variety of otolith microchemistry problems.

Microbeam studies: For several years I have been working with PIXE (proton-induced X-ray emission) and SPM (scanning proton microprobe) for mineralogical analysis.  2 - 3 MeV µ-PIXE and SPM can be used to analyze and map trace elements (REE, HFSE and LIL) in complexly zoned minerals. These techniques can also be used to map trace elements at grain boundaries. Quantitative data, with detection limits in the low ppm range, is crucial to understanding element partitioning between minerals and their environment. More recently LA-ICP-MS analysis has allowed the analysis of a wider suite of elements to better characterize different environments and growth histories.

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For more information

nm_halden@umanitoba.ca