A Strontium Isotopic Investigation of the Bjerkreim--Sokndal Layered Instrusion, Southwest Norway |
| |
Authors: | NIELSEN FRANK M; CAMPBELL IAN H; MCCULLOCH MALCOLM; WILSON J RICHARD |
| |
Institution: | 1STATOIL'S RESEARCH CENTRE POSTUTTAK, N-7004, TRONDHEIM, NORWAY
2RESEARCH SCHOOL OF EARTH SCIENCES, AUSTRALIAN NATIONAL UNIVERSITY GPO BOX 4, 2601 CANBERRA, A.C.T., AUSTRALIA
3GEOLOGISK INSTITUT, AARHUS UNIVERSITET 8000 AARHUS C, DENMARK |
| |
Abstract: | The 230 km2 Proterozoic BjerkreimSokndal layered instrusionhas a monzonoritic bulk composition and comprises a 6 km thick,broadly leuconoritic Layered Series (LS) overlain by unlayeredmangerite and quartz mangerite. In the Bjerkreim lobe the LScomprises six megacyclic units (MCU 0, IA, IB, II, 11 and IV)in a syncline. This lobe is surrounded by migmatitic gneisses;the roof to the instrusion is missing. The mg-number opx, An% and whole-rock initial 87Sr/86Sr isotope ratios (Sr0) displaybroadly parallel trends through MCUs II and III, and into MCUIV, with decreasing mg-number (7558) and An % (5040)accompanying increasing Sr0 (0.70500.7085). This correlationbreaks down in the upper part of MCU IV and mangerite; the quartzmangerite has Sr0 values of 0.7085. Abrupt reversals occur acrossthe MCU boundaries. The LS crystallized on the floor of a periodically replenishedmagma chamber that was continually assimilating country rockgneisses. Strong compositional zoning of the magma developedas a result of repeated replenishments with relatively dense,primitive ferrobasaltic magma (Sr0 = 0.7049) along the floorand the development of extensive buoyant roof melts. Assimilationtook place on a massive scale (up to 50%) in the upper partsof the chamber. KEY WORDS: assimilation; fractional crystallization; hybrid magma; layered intrusion; Sr-isolopes
*Corresponding author. |
| |
Keywords: | |
本文献已被 Oxford 等数据库收录! |
|