​​​​​Orogenic Architecture and Crustal Growth 

from Accretion to Collision

IGCP 662
Leaders
Aims and background
Aims:
      Orogens can generally be grouped as accretionary, collisional and intracratonic (Fig.1, Cawood et al., 2009). However, most orogens are composite and develop from accretionary to collisional and possibly to intracratonic tectonic environments (Fig. 2). The major aims are: (1) to characterise differences in crust formation and architecture between  accretionary and collisional orogens; (2) to establish criteria to (semi-) quantitatively describe orogenic development through evaluation of the relative proportions of juvenile vs. reworked crust; and (3) to better understand the role of orogenic compositions in metallogenesis (see detailed working plan).

Fig. 1. Classification of orogen types into three interrelated end-members (Cawood et al.,2009).
 Previous work：
       The above questions and aims are based on previous work, including research bythe proposers, in some typical orogens, such as the CAOB, the Tibetan Plateau, and the Central China Orogenic System (CCOS; Fig. 2).

Fig.2 Tectonic framework of Asia showing major orogens and various oceanic basins (Modified from Li, 2008).
     Four ICGP Projects (420, 473, 638, and 592) and many other projects have been carried out on the CAOB. These studies mainly focused on (1) accretionary orogenic processes (e.g., Şengör et al., 1993); (2) isotopic mapping and evaluation of continental growth (e.g., Kovalenko et al., 2004; Kröner et al., 2017); and (3) metallogenesis. The proposers took part in all the above ICGP Projects, as leaders or regional leaders, and have made significant contributions (see vitae of proposers).
     Abundant research was carried out on the Himalaya orogenic belt in the Tibetan Plateau, including that of the proposers (e.g. China National 973 programs, and key projects of NSFC and ICGP600, 2011-2015, led by Zengqian Hou). Hou and his team focused on the collisional architecture and main ore deposit systems. They applied Hf inzircon isotopic mapping in imaging the lithospheric architecture and crustal growth of the Lhasa terrane.
     Relevant studies were also performed on the CCOS, one of the main orogenic belts in Asia. This is a composite orogen (e.g., Guowei Zhang and Yongfei Zheng’ groups). Tao Wang’s group undertook Nd-Hf isotopic mapping of granitoids in the western CCOS and defines three isotopic provinces (e.g., Wang et al., 2015).
Rationale
   Most previous studies on orogens focused on one specific orogenic system. This new project will undertake comparative studies on two typical orogens (CAOB and Tethyan orogen), as well as other relevant orogens. This may result new concepts and approaches. Isotopic mapping makes it possible to semi-quantitatively assess the volume of continental growth. It will therefore be applied in comparative studies of orogens. Additionally, the new project will establish a new platform for wide cooperative studies of orogens.

Bibliography (some references of the proposers are in section 8.10 Vitae of proposers)
1. Cawood, P.A., Kröner, A., Collins, W.J. et al. 2009. Accretionary Orogens through Earth history. In: Cawood, P.A., Kröner, A. (Eds.), Earth Accretionary Systems in Space and Time. Geol. Soc.(Lond.) Spec. Publ. 318, 1–36.
2. Kovalenko, V. I., Yarmolyuk, V. V., Kovach, V. P. et al. 2004. Isotopic provinces, mechanism of generation and sources of the continental crust in the Central Asian mobile belt: geological  and isotopic evidence. Journal of Asian Earth Sciences, 23, 605-627.
3. Kröner, A., Kovach, V., Alexeiev, D., et al. 2017. No excessive crustal growth in the Central Asian Orogenic Belt: Further evidence from field relationships and isotopic data. Gondwana  Research, 50, 135-166.
4. Şengör, A. M. C., Natal'in, B. A., Burtman, V. S., 1993. Evolution of the Altaid tectonic collage and Palaeozoic crustal growth in Eurasia. Nature 364, 299-307.