Magma Mixing Within Migmatitic Source: Kangaroo Island, South Australia

 

Migmatitic terranes are usually overly complex. This page is part of a concerted effort to understand them, which includes a) understanding deformation during melting (Lindsay Ward, Honours Thesis), b) comparison with dewatering structures in sediments indicative of melt extraction from source, c) and this page on mxing of different magmas in source, and transfer of material between magma pulses through remobilization of earlier magmatic pulses. This page covers in PART I:

a) original magma formed from separation from diatexite,

b) intrusion of porphyritic magma into diatexite leading to mingling,

c) mingling of diatexites and of magmas,

d) more on mingling,

e) hibridized original magma mixed with porphyritic magma,

 

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PART I. Multiple magma interaction in source

a) Original magma formed from separation from diatexite

Figure 1a) Separation of grey magma from schollen-rich section.	1b) Magma separating from restite-rich source and dragging and stretching some of it.

 

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b) Intrusion of porphyritic magma into diatexite leading to mingling

 

Figure 1c) Intrusion of pegmatitic dykes into diatexite, the branch that is nearly parallel to the main foliation in migmatite is relatively straight, but the branch that cuts across foliation (bottom of photo) is irregular with tall protrusions parallel to foliation.	Figure 1d) Detail of previous one. Notice a number of leucocratic patches in the grey di atexite, which we suggest may have originated from disrupted sections of the intrusions.
Figure 1e) Detail of the contact between the two branches. They have slightly different textures suggesting that they could be two separate intrusions that do not quite merge at the contact. Notice how the horizontal dyke wraps around the solid schollen in the diatexite.	Figure 1f) Detail of the tip of dyke showing how it peters out into the diatexite on the lower left and how it has the same appearance as the two layer parallel lenses above, suggesting that they are linked.

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c) Mingling of diatexites and of magmas,

 

Figure 1) On the same outcrop as previous two photographs, a more intensely foliated, lighter grey diatexitic magma intrudes the darker grey resident one.	Figure 1) Mingling between two distinct magmas at Six Mile Lagoon: grey magma rich in small schollen or biotite clots remnants from separation from diatexite, with crenulated complex margins with a lighter porphyritic granite
Figure 1) Mingling between two distinct magmas at Six Mile Lagoon: grey magma rich in small schollen or biotite clots remnants from separation from diatexite, with crenulated complex margins with a lighter porphyritic granite.	Figure 1) Detail

 

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d) Disruption of diatexite by inflowing magma,

 

Figure 1) Disruption of	Figure 1) Detail
Figure 1) Stretching and intrusion of diatexite within porphyritic magmatic rock.	Figure 1) Detail of stretching of a diatexite within a hybrid porphyritic magmatic rock.

 

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e) Hibridized original magma mixed with porphyritic magma

 

 

Figure 1c) Similar to Fig. 1a except that the magma-rich part (right) is comprised of two .	Figure 1d) Detail 1c showing lenses of coarse-grained light granites in more homogeneous finer-granite.
Figure 1e) Flow bands rich in schlieren from source inside grey granite with lenses of porphyritic granite.	1f) Same.

 

 

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