Melt Flow, Transposition and Breakup of Enclaves in Delamerian Migmatites, Kangaroo Island, South Australia

 

Coastal outcrops on the south coast of Kangaroo Island expose the interaction between deformation and migmatization of rocks of the Kanmantoo Group. This page is an extract of the best field evidence for magma flow and channeling which is associated with transposition of early formed foliation/layering and disruption of the psammite-pelites of the Kanmantoo Group. Part I focus on general channeling, Part II expands part I to demonstrate transposition, and Part III the disaggregation of blocks.

 

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Part I. Flow and channeling of magma in diatexite

Figure 1a) Schollen with asymmetric shape indicative of dextral shearing and broken up in situ.	Figure 1b) Channels converging upwards.	Figure 1c) Channels funneling upwards and stretching schollen.

Figure 1 CENTRAL) Field sketch of sheared diatexite in Six Mile Lagoon. a) Dextral shearing on N60-70E of schollen preserved in magma-rich diatexite, b)Funnel-shaped N-directed channels draining magmas from same diatexite a few meters to the right (East) of (a). This outcrop has therefore two parallel processes occurring simultaneously during anatexis: dextral shearing on N70E and melt extraction through channels trending N-S. Boxes mark details shown on photographs.

Figure 1d) Sheared and broken up trailing edge of schollen.	Figure 1e) Flow asymmetry at the side of a larger schollen to the right.	Figure 1f) Flow asymmetry around a schollen indicative of dextral shearing.

 

 

 

 

 

 

Figure 1c) Channel.	1d) Inside a channel with well-defined channel parallel seams.
Figure 1e) Channel.	1f) Inside a channel with well-defined channel parallel seams.
Figure 1) Enclaves swimming in granite, aligned parallel to well-defined seams that are continuous over 1-2m.	1) Straight seam bounding sharply the margin of an enclave.
Figure 1) Channel.	Figure 1) Detail of previous.
Figure 2a) Magma-rich diatexite with seams in amongst enclaves.	Figure 2b) A quartz clast inside a single seam that splits into two to wrap around it, suggesting that the seam marked the boundary of a magma channel and the clast had been carried in the magma.
Figure 4a) Channel of magma cutting through banded migmatite. This channel feeds into a local irregular magmatic body of 20x10m across.	FIgure 4b) Channel detail of a).
Figure 3a) Enclaves swimming in granite, aligned parallel to well-defined seams that are continuous over 1-2m.	Figure 3b) Straight seam bounding sharply the margin of an enclave.

 

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Part II. Transposition of early layering by magma flow.

 

 

 

 

Figure 5a) Block of layered psammite block inside banded migmatite transposed in D1 trending NW-SE/steeply.	FIgure 5b) Detail of margin of psammmite block in a.
Figure 6a) Rootless D1 folds in D1 transposed zone trending NW-SE/steeply.	FIgure 6b) same
Figure 7a)	FIgure 7b) D1 thrusts (horizontal planes) overprinting pre-exisiting steep D1 foliation (vertical plane).
Figure 8a) Intense magma channels around a lithon.	FIgure 8b) D1 thrusts overprinting pre-exisiting steep D1 foliation (vertical plane).

 

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Part III. Breakup of psammite blocks.

 

Figure 9a) Block broken up in migmatite into smaller blocks along main magma channel orientation.	FIgure 9b) Same, not extruded block on the upper right corner.

 

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