Structural Geology

Question

A geologist mapped an area along the shoreline with well outcrops. Metasandstones and metapelites have been suffered from deformation. Faults, folds are formed and dykes are intruded to these rocks. Please use different stereonets for each measurements.

Bedding: 172/28; 215/66; 240/15; 158/40; 141/84; 279/28; 190/18; 147/60

Bedding with flute casts: 147/60 (bedding) – 136/59 (flute cast!); 172/28 – 132/22; 190/18 – 140/11

Cleavage: 286/51; 293/53; 285/56; 292/50

Faults and slickensides: 126/55 (Fault plane) – 119/55 (slickensides); 130/60 – 124/60; 121/64 – 112/64; 284/60 – 277/64

Dykes: 130/84; 286/88; 288/90

With these measurement; please answer questions:

e) What type of faults are they and what sense of movement do the slickensides indicate?

f) In approximately which direction was the palaeocurrent flowing as given by the restored flute marks?

g) Were the dykes, folds, faults and cleavage all formed under the same deformation? If not, which set of structures came first?

h) From all the information available write a detailed geological history.

Answer 1

Using B for Bedding:

B1

B2

B3

B4

B5

B7

B8

Plane joining poles

Axial plane

Line (T/P) = 352/07

Plane (S/D) = 082/83

e) Normal faults and conjugate dip faults. Along the dip direction.

f) N136E - N140E

g) No. The folds and cleavage came first.

h) Deposition of pelite sediments takes place. Current action and turbulence form flute casts. Then sandstone is deposited along with flute casts in metasandstone. The closing basin metamorphoses the sediments. The cleavages form, and then an extensional regime develops from a convergent collision that forms normal faults. Because of extension, decompression melting and intrusion of basalt dikes occur.