Page 330 - Global Tectonics

OROGENIC BELTS 313

(a) 47
47
TIBET
50–54
50–54 32 N
38
38
Delhi 20 70–85 37 28 N
70–85
20
37
37
37
55–65
55–65
44
44
Depression
36
29
29 36
23 25
23
25
20
51 20
51
36
36
Forebulge 45
45
45–49
20
20 Jabalpur 54 45–49 29 38 24 N
29 38
54
46
35
9 9 46 35 Udaypur
40–44
11
11 40–44
20 N
INDIA
Depression
4 4 3 3 10
10
4 4
72 E 76 E 80 E 84 E 88 E 92 E 96 E
(b) Flexural
Depression forebulge Himalaya
Indian ~40m 450m Ganges TIBET
Ocean Latur Plain
R R T T 4 km
Indian Plate R T T R R 20 km
SW R R R R R Great Thrust R R NE
Jabalpur R R
R reverse faulting (compressional) earthquakes Udaypur R neutral axis
R
T normal faulting (tensile) earthquakes R
Figure 10.18 (a) Earthquake focal mechanism solutions in India and southern Tibet (modified from Jackson et al.,

2004, with permission from the Geological Society of America). Numbers represent depths. Black solutions are from
events that occur within the Indian craton, light gray solutions are at depths of 10–15 km. Depths highlighted by a box
are Moho depths from receiver function studies. Ellipse in Tibet is the high velocity anomaly imaged by Tilmann et al.

(2003) and shown in Plate 9.4 (bottom) (between pages 244 and 245). (b) Schematic cross-section showing flexure of

Indian lithosphere as it is underthrust to the north beneath Tibet (modified from Bilham, 2004). At the crest of the
flexural bulge the surface of the Indian plate is in tension (T) and its base is in compression (R).

Paleozoic and Mesozoic sedimentary rock of Tethyan land-propagating fold-thrust system. At depth, each of
origin. These rocks have been thrust southward for a three main thrusts of the system merges downward
distance exceeding 100 km. The unit includes migmatite into a common décollement called the Main Himalayan

and amphibolite grade metamorphic rocks intruded by Thrust (Fig. 10.20). Seismic reflection and velocity pro-
light-colored granitic bodies of Miocene age called leu- fi les (Zho et al., 1991; Nelson et al., 1996) show that the
cogranite (Hodges et al., 1996; Searle et al., 1999). The décollement continues beneath the Greater Himalaya
migmatite and leucogranite have originated by the where it disappears beneath southern Tibet amid a zone
partial melting of the lower crust beneath Tibet (Le of weak reflectivity thought to represent a zone of par-

Fort et al., 1987) and are absent north of the Greater tially molten rock (Section 10.4.5).
Himalaya. Bounding the top of the thrust stack at the surface
The progressive decrease in the age of thrusting is a system of normal faults that form the South Tibetan
from north to south within the Himalaya defines a fore- Detachment System (Burchfi el et al., 1992). The basal