『Abstract
Mineral deposits associated with continental collision are abundant
in many orogenic systems. However, the metallogenesis of collisional
orogens is often poorly understood, due to the lack of systematic
studies on the genetic links between collisional processes and
ore formation in collisional orogenic belts. This paper reviews
the key metallogenic settings and resultant collision-related
ore deposits in the Tibetan Orogen, created by Indo-Asian collision
starting in the early Cenozoic. The resulting synthesis leads
us to propose a new conceptual framework for Tibetan metallogenic
systems, which may aid in deciphering relationships among ore
types in other comparable collisional belts. This framework includes
three principal metallogenic epochs in the Tibetan orogen, and
metallogenesis in: (1) a main-collisional convergent setting (〜65-41
Ma); (2) a late-collisional transform structural setting (〜40-26
Ma); and (3) a post-collisional crustal extension setting (〜25-0
Ma), each forming more than three distinct types of ore deposits
in the Tibetan orogen.
The main-collisional metallogenesis took place in a convergent
setting, i.e., a collisional zone, characterized by collision-related
crustal shortening and thickening, associated syn-peak metamorphism
and two distinct magmatic series (Paleocene-Eocene crust-derived
low-fO2 granitoids generated by crustal anatexis
and Eocene high-fO2 granitoids formed by
MASH processes at the base of the Tibetan crust). Metallogenesis
during this period formed Sn-W-rare metal deposits related to
the low-fO2 granitoids, skarn-hosted Cu-Au
polymetallic deposits related to high-fO2
granitoids, and orogenic-type Au deposits formed by CO2-dominant
metamorphic fluids.
Late-collisional metallogenesis occurred mainly in a transform
structural setting dominated by Cenozoic strike-slip faulting,
shearing, thrust systems, and associated potassic magmatism in
eastern Tibet, and formed the most economically-significant metallogenic
province in the orogen. Four significant ore-forming systems are
recognized in the transform zone: porphyry Cu-Mo-Au systems associated
with potassic adakitic melts and controlled by Cenozoic strike-slip
faults; orogenic-type Au systems related to large-scale left-slip
ductile shearing; REE-bearing systems associated with lithospheric
mantle-derived carbonatite-alkalic complexes; and Zn-Pb-Cu-Ag
systems related to basinal brines and controlled by Cenozoic thrust
structures and subsequent strike-slip faults developed in the
Tertiary foreland basin.
Post-collisional metallogenesis occurred in a crustal extension
setting, characterized by lithospheric mantle thinning or delamination
at depth, crustal shortening at a lower structural level and synchronal
extension at shallower levels. The resulting ore-forming systems
include: (1) porphyry Cu-Mo ore systems related to high-K adakitic
stocks derived from the newly-formed thickened mafic lower-crust;
(2) vein-type Sb-Au ore systems controlled by the south Tibetan
detachment system (STDs) and the metamorphic core complex or thermal
dome intruded by leucogranite intrusions; (3) hydrothermal Pb-Zn-Ag
ore systems controlled by the intersections of N-S-striking normal
faults with E-W-trending thrust faults; and (4) spring-type Cs-Au
ore systems related to geothermal activity driven by partial melting
of the upper crust. Associated ore deposits lie mostly within
the mid-Miocene Gangdese tectono-magmatic belt, in which the scavenging
role of fluids derived from evolved magma systems or dewatering
of rift basins, and finally discharging at intersections of the
orogen-transverse and -parallel faults are extremely important
for formation of the low-temperature hydrothermal deposits.
Based on the synthesis of deposits in the Tibetan orogen and
comparison with the metallogenesis of other orogenic systems,
a more complete classification for these collision-related deposits
can be proposed.
Keywords: Geodynamics; Collisional process; Metallogenesis; Collision-related
deposits: Tibetan Orogen』
1. Introduction
2. Tectonic framework of the Tibetan Orogen
3. Tectono-magmatic evolution of the collisional orogen
3.1. Main-collisional period (65-41 Ma)
3.2. Late-collisional period (40-26 Ma)
3.3. Post-collisional period (25 Ma to present)
4. Metallogenesis of the Tibetan collisional orogen
4.1.Metallogenesis in the main-collisional convergent setting
4.2. Metallogenesis in late-collisional transform setting
4.2.1. Orogenic-type Au ore system
4.3. Metallogenesis in post-collisional extension setting
4.3.1. Porphyry Cu-Mo ore system
4.3.2. Sb-Au ore systems
4.3.3. Vein-type Pb-Zn-Ag ore system
5. Classification of collision-related deposits and comparison
with global examples
Acknowledgments
References