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Contents:
a) The Nature of the Contact
b) Main Rock Types
c) Inside the Batholith: Structures and Rock Types
d) Hbl-Granites: Anatexis of Gabbros

 

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a) Nature of Contact

 

Figure 1. Contact between metamorphic rocks of the Pangong Range and the Karakoram Baholith. The contact is partly covered by alluvial material related to previous stages of evolution of the Shyok valley. The contact is apparently dipping at low angle (~30 degrees) inwards to the mountain (NE). The real contact however is ~60 degrees, and the gentler planes are related to dextral-thrusts. The country rocks grade from greenschist facties to amphibolite facies as the contact with the Batholith is approached. The density of intrusive sills/dykes increases markedly close to the contact.

 

Figure 2a)  Thrust planes on the wall SW of Rongdo village, dipping ~30 NE.

Figure 2b)  Gently NE-dipping dextral thrusts on greenschist facies rocks. Notice steep foliation in between thrust planes and a late lamprophyre dyke intruding the thrust plane. Looking NW. See lamprophyre dyke in Google Earth at N34 25' 16.5" E77 48' 53.2" cross-cutting granite.

Figure 2c)  Detail of a moderately dipping quartz-siderite vein in NE-dipping dextral-thrust.

 

Figure 2d) Steep foliation is schist with a strong lineation dipping gently NW, indicative of oblique dextral shearing pre-dating gently dipping shear zones.

Figure 3a) Intense intrusions marking the contact with the batholith and dipping steeply NE. Scale 100-200m in the vertical.

Figure 3b)  Detail of intrusions (looking NW).

 

Figure 4a, b) Contact exposed in a valley NW of the Rongdo valley approaching Satti. In all three valleys investigate (Satti, Rongdo and this unnamed one) the contact is characterized by intense steepening in the topography.

 

Figure 4c, d) Fracture zones that control the valleys that cut into the batholith.

 

b) Main rock types: the bulk of the country rocks is comprised of metamorphosed and sheared igneous rocks (diorites-granodiorites) itnerpreted to represent igneous rocks contemporanerous with the 80-60Ma Muglib and Tirit calc-alkaline granitoids. These are interlatyered with metasedimentary rocks (generally schists).

 

Figure 5a) Mylonitic, amphibolite-facies biotite and amphibole rich gneiss itnerpreted to have been a diorite

Figure 5b Mylonitic, and folded biotite-gness with epidote growth in the vicinity of quartz veins. Asymmetry of folds indicate dextral thrusting.

Figure 5c) Mylonitic, banded gneisses interpreted to represent a deformed calc-alkaline intrusive sequence.

 

Figure 6a) Epidotized rock around folded quartz veins.

Figure 6b) Ms-schist with garnets in transition between greenschist and amphibolite facies areas approaching the batholith contact.

 

Figure 6c) Granite dyke folded and snapped during dextral shearing.

Figure 6d) Irregular contact between intrusive leucogranite and folded gneiss.

 

Figure 6e) Quartz vein in Bt-schist surrounded by an alteration halo characterized by Hbl and Ep. This is in the transition between greenschist and amphibolite facies and indicates that quartz veining and fluid influx was associated with prograde metamorphism.

 

c) Inside the Batholith: Structures and Rock Types

Figure 7a) Back thrust inside the batholith. Looking SE.

Figure 7b) Detail of (a).

 

Figure 8a) PREPARE LINE DRAWING Granodiorite xenolith with mafic enclaves (left of the hammer) cut by different phases of leucogranite. The xenolith is interpreted as the older phase of calc-alkaline magmatism contemporaneous with the Ladakh Batholith to the S and to the Muglib and Tirit plutons both along strike. Furthermore, this is interpreted to represent a preserved version of the sheared/mylonitic country rocks to the batholith.

Figure 8b) Detail of (a).

 

d) Hbl-granites: anatexis of gabbros.

Figure 9a) Gabbroic enclave, rounded and surrounded by Hbl-rich leucogranite. Enclave to the right is partly disaggregated by leucogranites, and enclave on the left has porphyritic Hbl. Hbl-leucogranite associated with gabbroic rocks can be related to anatexis of gabbroic rocks of the Muglib batholith recorded in Tangtse-Muglib area.

Figure 9b) Detail of (a).

 

Figure 10a) Granite in contact with gabbro. Granite has large poikilitic Hbl, whilst the gabbro generally with smaller Hbl, has a melanocratic layer enriched in larger Hbl in contact with granite. Very similar relations have been documented in Muglib during anatexis of gabbros.

Figure 10b) Gabbro with leucocratic patches around Hbl porphyroblasts. Leucocratic patches are linked continuously with the external leucogranite.