Abstract
A composite lamprophyre dyke from the Central Bohemian Dyke Swarm (Czech Republic) shows both indications of magma free flow (normal magnetic fabric with magnetic foliation and lineation parallel to the dyke plane) as well as those of forcefully driven magma movement (intermediate and inverse magnetic fabrics with magnetic foliation perpendicular to the dyke plane). The overall characteristics of the magnetic parameters across the dyke indicate the existence of at least two slightly differing parts that probably represent two magma pulses. The marginal part of the dyke is formed by kersantite, while toward the axial part, the composition gradually changes to spessartite, and obtains an increasing degree of amphibolization. The rocks of the dyke are inhomogeneous, both compositionally and structurally. It is likely that some portions of ascending magma were more viscous than the others, and the magnetic minerals in the more viscous magma portions may have oriented according to their longer dimensions perpendicular to the dyke, creating an inverse fabric. The lengthening perpendicular to the dyke was compensated by the vertical escape of neighboring more fluid magma, creating a normal magnetic fabric. The frequent oblique magnetic fabrics may represent transitions between the above two mechanisms.
Highlights
The magnetic fabric of igneous dykes has been intensely investigated because their creation and propagation signify important mechanisms of mass transport within the Earth’s crust and the upper mantle
A question arises: how it is possible that the magma movement in one dyke shows indications of both free flow and forceful intrusion? One explanation of this phenomenon assumes that the central, marginal, and rim parts represent different injections undergoing different mechanisms of magma movement
The Anisotropy of Anhysteretic Magnetic Remanence (AAMR) in the measuring configuration used is controlled by the mineral(s) that can be magnetized anhysteretically and subsequently demagnetized before changing the magnetizing direction, which is probably represented by low-Ti titanomagnetite
Summary
The magnetic fabric of igneous dykes has been intensely investigated because their creation and propagation signify important mechanisms of mass transport within the Earth’s crust and the upper mantle. In the free flow of magma within the dyke, the large surfaces of magnetic minerals orient approximately parallel to the dyke, while the longer dimensions orient parallel to the magma flow direction In a forceful intrusion, the large surfaces of magnetic minerals orient approximately perpendicular to the dyke, and the longer dimensions orient parallel to the dyke plane [11,15,16], giving rise to the intermediate or Type II magnetic fabric with an approximately perpendicular orientation of magnetic foliation to the dyke plane and magnetic lineation parallel to the dyke [11,12]. A question arises: how it is possible that the magma movement in one dyke shows indications of both free flow (normal magnetic fabric in central parts) and forceful intrusion (intermediate magnetic fabric in marginal and rim parts)? The results were combined with detail petrological and geochemical analyses
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
