What Is Older Granite That Intruded Or Gneiss

The granite gneiss is relatively coarse grained streaky gray or pink and composed principally of quartz feldspar biotite and hornblende.

What is older granite that intruded or gneiss.

The gneiss is older because it had to exist before it was intruded by the granite. Has pronounced phacoidal texture. Which is older and why. Was probably an intrusive magma with gradational contacts or a mobilized component of the metasomatic microcline augen gneiss.

The rock in the lower hill in the foreground is gneiss and migmatite of the the highly metamorposed and intruded skagit gneiss complex part of the chelan mountains terrane. Granite intruded into mafic dikes which in turn cross cut granite. Similar to alaskite gneiss but with more than 3 dark minerals. You go to mount rushmore and see a blob of what appears to be black granite in that beautiful white gneiss.

Massive fine grained phases discordantly intrude massive coarse grained phases which are concordant with the older augen gneiss. All these rock types can be observed at close hand along trails in these areas. Sterling igneous suite granite gneiss pale pink to gray medium grained granite gneiss commonly with small porphyroclasts of microcline orthoclase. The oldest components of the gneiss are between 3 500 and 3 100 ma in age but later at around 2 600 ma after most deformation and metamorphism had ceased the gneiss was intruded by several large bodies of granite which have not been metamorphosed.

The golden horn granite is different from the older plutonic rocks of the north cascades crystalline core the golden horn rock is a true granite with a high amount. 8 10 37 table pl. Compositions range from quartz monzonite to granite. Mt crawford granite gneiss hypothesis 4 the granitic gneiss is an early delamerian granite intruded during or just before the first phase of delamerian deformation similar to the rathjen gneiss.

The presence of two generations of granitic rocks in the gneiss domes he examined led eskola to suggest that the gen eral condition for gneiss dome formation is the superposition of two orogenic events. Interpreted as having been intruded into original grenville series. A gently sloping contact between the granite and the older overlying gneiss and schist can be seen in cliffs along canyons east of the continental divide where also light colored pegmatite veins extend in all directions through the gneiss and schist. Composition is granite with generally less than 3 dark minerals.

It differs from enclosing layered gneisses in its coarser texture lack of layering.