Clockwise rotation of the Tarim basin driven by the Indian plate impact. Part II*

In the previous article**, data were given on the clockwise rotation of the Tarim Basin at a speed of 0.461° per million years around a virtual axis within the structure. Additional fieldwork and new evidence confirm earlier findings about the asymmetry of the Indo-Asian collision zone. These data are additional arguments in favor of the rotation of the Tarim Basin and lithospheric interactions along the Tarim boundaries. Conclusions are based on detailed geological and geophysical data.


Four profiles crossing Tarim basin and its surrounding mountains
The outcome of the paper is based mainly on four seismic profiles traversing diverse parts of the boundary zones of the Tarim Basin, that is, the XB Line in the north, the KJ Line in the northeast, the BD Line in the east, and the ANTILOPE-I line in the south. The locations of the profiles are shown in Fig. S1 and Fig. 1***. Results of the XB, BD, and ANTILOPE-I lines are published in Zhao et al. [1][2][3]. The KJ line is the most recent profile. Compared with previous profiles, the new data from the KJ line revealed a complex lithospheric configuration of the Tarim Baisin boundaries, which motivated further examination of the plate kinematics and the (clockwise) rotation of the basin. Here we briefly summarize the relevant results of the four profiles, which are closely related to the topic of the present paper. XB line. From the northern margin of the Tarim Basin (TB) (82°52′28″E, 41°02′34″N) to the southern foot hills of the Altay Orogenic Belt (AOB) (86°46′19.2″E, 48°56′00″N), the XB Line is 995 km long and crosses northern part of the Tarim Basin, the Tien Shan Orogenic Belt, the Junggar Basin (JB), and the Altai Orogenic Belt ( Fig.  1 and Fig. S1). During the original study, Zhao et al. [1] obtained a 2D velocity structure by seismic reflection / refraction profiling, a 2D density structure from modeling gravity data, the detailed structure of the crust-mantle transitional zone using wavelet transforms of the deep seismic sounding (DSS) data, and a 2D electrical resistivity structure using magnetotelluric (MT) sounding. They also studied focal mechanisms and tectonic processes. With this comprehensive set of geological and geophysical data, a geodynamic model was obtained for this region ( [1], also shown in Fig. S2). The results suggest that the Tarim Basin subducts northward beneath the Tien Shan orogenic belt, while the Junggar Basin contacts the Tien Shan in a pattern of strike-slip mode (Fig. 2, a and Fig. S2).
Evidence for the northward subduction of the Tarim Basin beneath the Tien Shan orogenic belt can be seen in detail with an example of a shot gather (shot point SP Byblk, located at 218.217 km along the profile). Two Moho reflection phases can be clearly observed (Fig. S3, a) and modeled (Fig. S3, b-d). The upper one is the Moho of the Tien Shan Orogenic Belt, and the lower one is the Moho of the Tarim Basin.
KJ Line. Recently, we have conducted a comprehensive geophysical profile from Korla to Jimsar (KJ line). From the northern margin of the Tarim basin (82°52′28″E, 41°02′34″N) to the southern margin of the Junggar basin (86°46′19.2″E, 48°56′00″N), the profile is 600 km long and crosses the northern margin of the Tarim basin, the Tien Shan, and the southern margin of the Junggar basin (Fig. S1).    We obtained a 2D velocity structure from seismic reflection / refraction profiling, a 2D density structure and 2D geomagnetic intensity structure from joint inversion of the gravity anomaly with the geomagnetic anomaly. In contrast with the XB line, no evidence of crustal underthrusting can be found along the KJ line beneath the northern margin of the Tarim basin. In contrast, the results suggest that the Tarim Basin moves away from the Tien Shan Orogenic belt, and the Junggar Basin subducts southward beneath the Tien Shan orogenic belt, as shown in Fig. 2, b and Fig. S4.
The spatial separation of Tarim Basin and the Tien Shan orogenic belt can be seen in detail in Fig. S5. The shot point SP Hoxud is located at 177 km. Modeling seismic records shows that there exists a gap and dislocation between the Tarim Moho and Tien Shan Moho, implying that the Tarim Basin is moving from the Tien Shan, leaving a lateral gap between the two Mohos.
BD Line. Here we present the results of a 1420-km-long seismic refraction / wide-angle-reflection profile (BD Line) that crosses from NW to SE the northern margin of the Tarim basin, the east central Tarim basin, the Altyn Tagh Range, and the northern Qaidam basin (Fig. 1). The 2D velocity structure along the BD Line as shown in Fig. S6 was obtained from the modeling of the seismic data as mentioned above. The results indicate that the Tarim Basin has subducted beneath the Altyn Tagh Range, as shown in Fig. 2, c and Fig. S7 for detail.  Locations of the shot and the seismic section are indicated in Fig. S4 [3]. A total number of 3476 S receiver functions (including SKS receiver functions from 249 events at epicentral distances of 60-115°).

Результаты полевых исследований
On-Site Research Results

Fig. S6. Crustal and upper-mantle cross-section along the BD line across the east-central Tarim basin, Altyn Tagh Range and Qaidam basin [2]:
a -Tectonic setting and topography; b -Crustal structure derived from the seismic velocity structure using laboratory measurements of seismic velocities for a wide suite of rock types The box marks the location of the seismic section shown in Fig. S5. The respective shot point is highlighted

Соответствующий очаг сейсмического взрыва выделен
In the S receiver function image (Fig. S8), the Moho can be identified along the profile A Moho step can be observed beneath the border from the Tibetan plateau to the Tarim Basin. No evidence of crustal underthrusting can be identified.

GPS Data and strategy
The main part (~55 %) of GPS velocities are from the published solutions of two Chinese national scientific projects, Crustal Movement Observation Network of China (CMONOC-I) and Tectonic and Environmental Observation Network of Mainland China (CMONOC-II) [4]. The detailed GPS observation methods and data processing strategies were introduced by Li et al. [4]. In addition to the GPS velocity data set of 240 stations from CMONOC (around the Tarim Basin but within the territory of China), we merged another published GPS velocity data set of 202 stations (around the western Tarim Basin) from Zubovich et al.
[5] to enhance the density and coverage of GPS stations.
Although the CMONOC velocities and those of another data set are given in Eurasia-fixed reference frames, their frames may differ slightly from each other. As these two data sets shared some stations with the CMONOC data set, we used stations common to the CMONOC data set as "links" to transform all the other velocities into the same reference frame as that for CMONOC by using rigid-body rotations with appropriate angular velocity (Euler vector). After the reference frame transformations, the maximum differences of north and east components of the velocities for the same stations in different data sets are 2.6 and 2.2 mm/yr, respectively; these values are within 2 standard deviations of the velocity components. The final velocities of the common stations are the weighted average of the values from all the data sets in the same Eurasia-fixed reference frame. The combined velocities of 442 GPS stations in a Eurasia-fixed reference frame demonstrate the western Tarim regions are dominated by N-S direction while eastern Tarim moves toward the NE (Fig. 3, a).
In order to highlight the relative motion of Tarim Basin with respect of its surroundings, we used the following strategy to transform the GPS velocity field into a special "Tarim surrounding vicinity fixed reference frame". Firstly, we solved for the angular velocity of rigid-body rotation on Earth sphere that minimized the RMS velocity of all these surrounding stations. Then, by reversely rotating the whole GPS velocity field of the Tarim basin with the above angular velocity, we removed the overall rigid rotation of the surrounding vicinity of the Tarim Basin. This is equivalent to converting the original GPS velocity field relative to the Eurasia-fixed reference frame to the "Tarim surrounding vicinity fixed reference frame".

The geodynamic source of the rotation of the Tarim plate
Tibetan plateau is made up of three plates: the rigid Indian plate in the south, the rigid Asia plate in the north and a giant crush zone -Tibet "plate" sandwiched between the two. The giant crush zone with a horn-like shape facing east is featured high temperature (temperature is higher by ~300° K than both the India plate and Eurasian plate) and low velocity (S wave velocity is lower by 5 % than the two plates on its both sides), and high Sn wave attenuation (on top of the upper mantle the Sn wave almost disappears) and strong seismic anisotropy, hence it must be softer. It can be seen from Fig. S9  between The Indian plate and the Asian plate occurred mainly at the southwest corner of the Tarim Basin, and a torque was generated in the Tarim plate, making the Tarim plate rotate clockwise. To the east, the Tibetan "plate", which is soft between the Indian plate and the Asian plate, has strong internal deformation under the stress background of the south-north compression, transmitting the stress to the west. Therefore, under the impact of the Indian plate, the Tarim plate would rotate clockwise on the one hand and translate from south to north on the other hand.
Eocene and Oligocene mammalian faunas from the Junggar basin and the Mongolian plateau Changes in faunal compositions reveal distinct differences in biological evolution of the Junggar basin nearby the Tarim basin, and the Mongolian plateau, more than 1000 km farther east, but with the same latitude (Fig. S10).
The above arguments in favor of the character of rotation of the Tarim Basin are confirmed by the analysis of the distribution of the Eocene-Oligocene Mammalian fauna. There are data from various sources.

Fig. S9. Plate tectonics of western China
The solid line represents the location of the seismic section. The shaded region highlights the locations of the rigid Tarim plate, the Indian plate, and the giant crush zone (the Tibetan "plate") (the lithospheric mantle) as determined by the seismic wide-angle reflection / refraction profile [1,2], the receiver function [3], and seismic tomography [6].