Radiometric age dating of detrital zircons is highly advantageous for analysis of the depositional environment and to identify source areas. Aiming at the uplift and denudation of the surrounding ranges, LA ICP-MS U-Pb analysis has been performed on zircon grains from a conglomerate collected at the Lower Pliocene of Mazartagh, which is in the center of the Tarim basin, Xinjiang (新疆), China. A wide range of ages mainly falling into three groups was yielded: 200–500, 800–1 100, and 1 800–2 000 Ma. Zircon features principally indicate magmatic origin. According to the comparison between the analyzed zircons with those from surrounding orogenic belts, the younger grains are mainly related to the west while the older ones are to the regions more eastward. The variations might imply the W-E propagation tectonic activation and uplift of the surrounding orogenic belts. The west segment uplifted and was denuded firstly, driven by the approximate W-E height difference, upon the denudation, transportation and deposition, acting as the source of young zircons analyzed. With the eastward spreading of tectonic movement, the segment more to the east rose, the meridional relief increased rapidly and began to control the flow direction, then more zircons joined in the Pliocene in Mazartagh. It is difficult to definitely explain the source of grains with similar values to that from the Altyn Mountain region, more detailed data and chronological ages with higher precision will be helpful for making more credible conclusion.
The collision between India plate and Eurasia continent 55 Ma ago caused the convergence between Southwest Tienshan and Pamirs tectonic systems, and conclusions by other researchers also suggest that the convergence will continue. Studies on the collision between these systems are helpful to the knowledge of the history and the tendency of the in-land tectonics since Cenozoic and are important in science and the real world as for environment changes, resources and energy reform, and forecast of earthquakes. For this reason, by means of digital modeling, on the basis of crustal shortening rate, crustal motion rate and data of physical properties of rocks, with the help of the FE (finite element) theory-based marc software, the United States, we address on the tendency of the convergence in this area in almost 10 Ma and draw a conclusion that the converged borders move northward and stretch southeast. The Southwest Tienshan will move more slowly and suffer less deformation than the Pamirs-West Kunlun (昆仑) system. The Pamirs-West Kunlun system will rotate counterclockwise while moving northward and extending westward.
Geometry analysis of the Hongsanhan (红三旱) Section in the northwestern Qaidam basin illustrates the typical growth strata in the Xiaganchaigou (下干柴沟) Formation. The age and sedimentation rates of the Xiaganchaigou and the Shangganchaigou (上干柴沟) formations were determined by the high-resolution magnetostratigraphy. This result shows that the growth strata began to form at ca. 38.0 Ma and increased sedimentation rates occurred at ca. 37.0 Ma. The uplift of the Tibetan plateau before the Eocene–Oligocene boundary is confirmed, which enables us to better understand the relationship between climatic changes and the tectonic uplift. This uplift event could have resulted in the regional drying by blocking the moisture and contributed to the Eocene–Oligocene boundary global cooling event due to the declining atmospheric CO2 concentrations by increased weathering of the mountains.
The Karakorum Fault zone(KFZ)plays an important role in understanding the formation,evolvement and deformation of the Tibetan Plateau.The high-T dextral shearing metamorphic rocks,e.g.,mylonites or mylonitized gneisses-granites,locally crop out along the southeastern part of the KFZ in the Ayila Ri’gyüRange area.The SHRIMP U-Pb dating of the syn-kinematic crystallized zircons indicates that the initial age of the KFZ is^27 Ma,~10 Ma older than previous results.The extensive high-T dextral shearing along the KFZ started at least at 27-20 Ma,accompanied by the syn-kinematic emplacement of leuco-granites.Deformation and concomitant fluid circulation during shearing most likely occurred as early as at 25-13 Ma.The KFZ probably grew from southeast to northwest along the fault as a result of continuous convergence between the India plate and Eurasia plate.
