Minimal Cenozoic Denudation of the Central Tibetan Plateau Revealed by low-Temperature Thermochronology
Abstract
Low-temperature thermochronologic data from crystalline rocks across central Tibet reveal mostly limited denudation and cooling since the Late Cretaceous - Early Eocene. Apatite fission-track analysis of the mid- Cretaceous Bange granite in the north-central Lhasa terrane indicates slow cooling since crystallization with a model age of ~62 Ma. Orthogneisses of the Amdo basement, located ~200 km northeast of the Bange granite along the Bangong suture, record pooled fission track ages of 72-74 Ma and coupled with K-feldspar Ar40/Ar39 data, suggest slow denudation since rapid exhumation during the Early Cretaceous Lhasa- Qiangtang collision. North of the Amdo basement ~100 km, an ~67 Ma granite from the Tanggula Shan in the central Qiangtang terrane yielded an apatite fission track age of ~53 Ma, despite being located in a region of relatively high relief (~1500 m) and active E-W rifting. These ages are similar to older fission track ages from the eastern Tibetan plateau, which fall in a range from 60-100 Ma. Cooling data from K-feldspar Ar40/Ar39 diffusion modeling from the northern Lhasa terrane in central and westernmost Tibet are also consistent, generally revealing Cretaceous episodes of rapid cooling followed by slow cooling in the Tertiary. Cretaceous-Eocene rapid cooling followed by slow cooling is also a characteristic of parts of the southern Lhasa terrane where there is a widely preserved angular unconformity beneath the Tertiary volcanic Linzizong Formation. Some areas of Tertiary upper-crustal exhumation are indicated by K-feldspar diffusion modeling and mid-Tertiary shortening and basin development in the north-central Lhasa terrane and the development of narrow, E-W trending Tertiary nonmarine basins in central Tibet. In general, however, the data suggest a relatively low-relief landscape characterized much of the present-day Tibetan Plateau prior to the Indo-Asian collision and shortening in Tibet in response to the Indo-Asian collision resulted in only minor exhumation. The lack of early-mid Tertiary rapid cooling in the interior of the plateau is evidence against the northward and eastward migration of a high-elevation margin, as the current margins show evidence of mid-late Tertiary cooling. The initiation of slow-cooling periods immediately follow episodes of relatively rapid cooling and major upper crustal shortening, which leads to the possibility that the crust was thick and the elevation high when the low-relief surface landscape developed.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2006
- Bibcode:
- 2006AGUFM.T43E..06G
- Keywords:
-
- 1140 Thermochronology;
- 8038 Regional crustal structure;
- 8102 Continental contractional orogenic belts and inversion tectonics;
- 8108 Continental tectonics: compressional;
- 8175 Tectonics and landscape evolution