Interplay between oceanic subduction and continental collision in building continental crust

Area of Science:

• Geology
• Tectonics
• Petrology

Background:

• Continental crust generation involves oceanic subduction and continental collision.
• The Gangdese continental crust in Tibet formed during Mesozoic subduction and Cenozoic India-Asia collision.

Purpose of the Study:

• To investigate the two-stage process of continental crust formation in collision zones.
• To understand the chemical evolution of juvenile continental crust.

Main Methods:

• Analysis of continental arc magmatism.
• Geochemical studies of crustal composition.
• Tectonic modeling of convergence rates and slab dynamics.

Main Results:

• Continental arc magmatism initiated with fractional crystallization, forming cumulates and medium-K calc-alkaline suites.
• Around 70 Ma, remelting of the lower crust produced more potassic compositions, linked to accelerated India-Asia convergence.
• Slab breakoff led to deceleration, high heat flow, and melting at the arc's base.

Conclusions:

• A two-stage process of accumulation and remelting drives chemical maturation of continental crust.
• This process enhances crustal stratification in collision zones.
• Understanding these mechanisms is key to deciphering continental crust evolution.