Sci Research

SCIENCE CHINA

Earth Sciences

RESEARCH PAPER June 2012 Vol.55 No.6: 926 939

doi: 10.1007/s11430-012-4402-7

EW-trending uplifts along the southern side of the central segment

of the Altyn Tagh Fault, NW China: Insight into the rising

mechanism of the Altyn Mountain during the Cenozoic

WU Lei1,2, XIAO AnCheng1,2*, WANG LiQun3, MAO LiGuang1,2, WANG Liang4,

DONG YouPu1,2 & XU Bo1,2

1

Department of Earth Sciences, Zhejiang University, Hangzhou 310027, China;

2

Research Center for Structures in Oil & Gas Bearing Basins, Ministry of Education, Hangzhou 310027, China;

3

Research Center of Qinghai Oilfield Company, PetroChina, Dunhuang 736200, China;

4

Beijing Geological Survey, Beijing 102206, China

Received June 7, 2011; accepted December 30, 2011; published online April 12, 2012

The Altyn Tagh Fault and the Altyn Mountain define respectively the tectonic and geographical northern edges of the Tibetan

Plateau, and figure prominently in the growth and rising mechanism of the plateau. The rhombus-shaped Altyn Mountain has

long been thought to have an intimate relation with the Altyn Tagh Fault; however, its formation mechanism remains unclear

and debatable. In this paper, we focus on the EW-trending uplifts in the Altyn Mountain, and investigated three Cenozoic

sedimentary sections in the vicinity of the EW-trending uplifts located along the southern side of the central segment of the

Altyn Tagh Fault. Magnetostratigraphy and pollen analysis were used to constrain ages of the sediments. Clast composition of

conglomerate and paleocurrents obtained from clast imbrications were applied to determine the provenance. We also estab-

lished a geological section parallel to the Altyn Tagh Fault on sedimentary facies across the northwestern Qaidam Basin. The

results indicate that these en-echelon EW-trending uplifts formed as early as ca. 36 Ma and were preferred to be under the con-

trol of basal shear of the Altyn Tagh Fault in the middle-lower crust, symbolizing the early uplift of the Altyn Mountain during

the Cenozoic. Left-slip along the Altyn Tagh Fault occurring during the Miocene and afterwards displaced and altered these

uplifts, shaping the Altyn Mountain to its present fabric.

Northern Tibetan Plateau, Altyn Tagh Fault, Altyn Mountain, EW-trending uplift, Qaidam Basin

Citation: Wu L, Xiao A C, Wang L Q, et al. EW-trending uplifts along the southern side of the central segment of the Altyn Tagh Fault, NW China: Insight

into the rising mechanism of the Altyn Mountain during the Cenozoic. Sci China Earth Sci, 2012, 55: 926 939, doi: 10.1007/s11430-012-4402-7

Rise of the Tibetan Plateau is one of the most prominent timing, mechanism and stress dissipation of the Tibetan

tectonic events during the Cenozoic, and has been exerting uplift [11 16].

The Cenozoic uplift of the Altyn Mountain is commonly

enormous impacts on regional and global tectonics, sedi-

interpreted as the result of left-slip movement along the

mentation, climate and magmatism [1 9]. The Altyn Tagh

ATF [17 22]. Different from other linear mountains caused

Fault (ATF) and the Altyn Mountain define respectively the

by strike-slip faults worldwide, the Altyn Mountain is

tectonic and geographical northern edges of the Tibetan

rhombus-shaped and varies greatly in width along strike

Plateau (Figure 1(a)), and hold a key for constraining the

with minimum

corresponding ATF, however, extends straightly without

*Corresponding author (email: ********@***.***.**)

Science China Press and Springer-Verlag Berlin Heidelberg 2012 earth.scichina.com www.springerlink.com

927

Wu L, et al. Sci China Earth Sci June (2012) Vol.55 No.6

obvious bends. DEM map shows that the Altyn Mountain is Altyn Mountain was the western extension of the Qilian

made up of three types of uplifts (Figure 1(b)): 1) Mountain based on correlation of UHP/HP metamorphic

NEE-trending uplift, parallel to the extension of and con- belts in their northern and southern parts [27 31]; and 4) the

fined to a narrow zone (ca. 20 km wide) across the ATF, Altyn Mountain has experienced oroclinal bending along

and resulting obviously from transpression and friction the ATF around a vertical axis [32]. All of these opinions,

induced by left-slip movement along the ATF; 2) EW- however, are ambiguous when referred to the rising mecha-

trending uplifts, 25 40 km wide, 40 150 km long, and nism of the Altyn Mountain as well as its relation with the

en-echelon configured at the both sides of the ATF; and 3) activity of the ATF.

NE-trending uplifts, situated mainly in the southwestern The Qaidam Basin is the largest sedimentary basin inside

Altyn Mountain with many NE-trending faults oblique to the Tibetan plateau, and accumulated thick terrestrial sedi-

the ATF. The NEE-trending uplift cut obviously the other ments during the Cenozoic, which are subdivided into eight

two, indicating that it formed later. This is corroborated by units, i.e., Lulehe Formation (LLH), lower part of the

the previous studies on apatite fission-track ages which are Xiaganchaigou Formation (LXG), upper part of the Xiagan-

100 m. Conglomerate clasts decrease in

4 and 5(a)). Horizontal beddings are well developed. The

size while sandstone increases from a minor component to

stratum even comprises more than 100 m thick calcareous

dominance upward through the upper part of the SY, repre-

mudstone in the upper part in the Borelhole Chaishen 3,

senting a braided river setting at the time. The SZG un-

about 6 km east of the section (Figure 3). These features are

929

Wu L, et al. Sci China Earth Sci June (2012) Vol.55 No.6

Figure 4 Lithology, sedimentary facies, paleocurrents, clasts composition and magnetostratigraphy in the Ganchaigou section. Magnetostratigraphic result

is cited from adjacent Xichagou section [33].

conformably overlies the SY, and is dominated by massive glomerate in the UXG, SG, XY, SY, and SZG using the

conglomerate again with average clast size 35 40 mm. Un- gravel-count method. The result shows that these clasts

deformed incompact Holocene pebbles rest at the topmost contain 61% conglomerate and sandstone (non-quartz sand-

of the section (Figure 4). stone), 36% quartzite, quartz sandstone and phyllite, and

We also measured in detail the clast composition of con- merely 3% granite, gneiss, and siliceous rock (Figure 4).

930 Wu L, et al. Sci China Earth Sci June (2012) Vol.55 No.6

Figure 5 Lithological pictures mentioned in this paper. (a) and (b) From the Ganchaigou section; (c) (h) from Hongsanhan No.1 section; (i) (k) from the

Heishiqiu section. (a) Red fluvial mudstone and siltstone in the LXG; (b) massive conglomerate in the UXG; (c) brown and grey-green lacustrine mudstone

and a normal fault with related growth sequences in the LXG; (d) wave-ripples in the LXG; (e) boundary between the LXG and UXG, showing the initial

deposition of conglomerate; (f) erosion surface filled up by fine-grained conglomerate in the UXG; (g) mud-cracks and its sketch map in the SG; (h)

boulder-grained conglomerate in the XY; (i) conglomerate in Unit 1; (j) fluvial conglomerate and sandstone in Unit 3; (k) boundary between Unit 4 and Unit

5. Sizes of the white semi-rectangles in (b) and (i) are 1 m 1 m.

Through regional correlation, we interpret that these clasts tostratigraphic study on the Xichagou section, about 6 km

were all derived from the Ahati uplift and the Altyn Moun- east of our measured section, and assigned the ages of the

tain to the north: the conglomerate is from the Lower Cre- LXG, UXG, SG, XY, SY, and SZG to > 36, 36 29.3,

taceous rocks; the sandstone is identical with the lithology 29.3 23.8, 23.8 15, 15 7.2, and

Contact this candidate