In the Ladakh'Zanskar area, two groups of ophiolites document closure of the Neo-Tethys Ocean during India Asia convergence. They are localized north of the Indus Suture Zone and in South Ladakh, respectively. The South Ladakh group includes the Spontang ophiolite, with both crustal and mantle units, the Nidar ophiolite, with mainly crustal units, and the small Karzog ophiolite, with abundant chromitites and gabbros. The mafic rocks of the three South Ladakh ophiolites are tholeiites with similar compositions, displaying slight LREE depletion relative to HREE and enrichment in LILE relative to REE and HFSE. They are also characterized by a low Y content (<20 ppm) and a Ti/V ratio between 10 and 20. Such chemical features and similarity imply that these ophiolites were derived from the same N-MORB-like mantle source slightly enriched in LILE during a metasomatic event in a supra-subduction zone setting. We suggest the South Ladakh ophiolites are relics of an intra-oceanic arc. According to 39Ar/40Ar dating on amphiboles from both Spontang and Nidar mafic rocks, this arc developed at around 110 130 Ma. The associated ultramafic rocks show a decoupling between LREE and LILE (both enriched relative to abyssal peridotites) and HREE (which decrease from lherzolites to harzburgites). This contrasting behavior reflects the depletion of residues during partial melting and subsequent metasomatism in a supra-subduction zone setting. REE modeling indicates that the Spontang and Nidar lherzolites could not have been the source of the mafic rocks because their partial melting would have produced magmas more depleted in LREE. The South Ladakh ophiolites are clearly distinct from the northern ophiolites and require the existence of another north-dipping subduction zone. Thus, the closure of the Neo-Tethys was not accommodated by a single but by two subduction zones in the Ladakh'Zanskar area and from Oman to Tibet, respectively.
Maheo, G., Bertrand, H., Guillot, S., Villa, I., Keller, F., Capiez, P. (2004). The South Ladakh ophiolites (NW Himalaya, India): An intra-oceanic tholeiitic arc origin with implication for the closure of the Neo-Tethys. CHEMICAL GEOLOGY, 203(3-4), 273-303 [10.1016/j.chemgeo.2003.10.007].
The South Ladakh ophiolites (NW Himalaya, India): An intra-oceanic tholeiitic arc origin with implication for the closure of the Neo-Tethys
VILLA, IGOR MARIA;
2004
Abstract
In the Ladakh'Zanskar area, two groups of ophiolites document closure of the Neo-Tethys Ocean during India Asia convergence. They are localized north of the Indus Suture Zone and in South Ladakh, respectively. The South Ladakh group includes the Spontang ophiolite, with both crustal and mantle units, the Nidar ophiolite, with mainly crustal units, and the small Karzog ophiolite, with abundant chromitites and gabbros. The mafic rocks of the three South Ladakh ophiolites are tholeiites with similar compositions, displaying slight LREE depletion relative to HREE and enrichment in LILE relative to REE and HFSE. They are also characterized by a low Y content (<20 ppm) and a Ti/V ratio between 10 and 20. Such chemical features and similarity imply that these ophiolites were derived from the same N-MORB-like mantle source slightly enriched in LILE during a metasomatic event in a supra-subduction zone setting. We suggest the South Ladakh ophiolites are relics of an intra-oceanic arc. According to 39Ar/40Ar dating on amphiboles from both Spontang and Nidar mafic rocks, this arc developed at around 110 130 Ma. The associated ultramafic rocks show a decoupling between LREE and LILE (both enriched relative to abyssal peridotites) and HREE (which decrease from lherzolites to harzburgites). This contrasting behavior reflects the depletion of residues during partial melting and subsequent metasomatism in a supra-subduction zone setting. REE modeling indicates that the Spontang and Nidar lherzolites could not have been the source of the mafic rocks because their partial melting would have produced magmas more depleted in LREE. The South Ladakh ophiolites are clearly distinct from the northern ophiolites and require the existence of another north-dipping subduction zone. Thus, the closure of the Neo-Tethys was not accommodated by a single but by two subduction zones in the Ladakh'Zanskar area and from Oman to Tibet, respectively.
I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
