TTGs (IMAGE) University of British Columbia Caption The building blocks of the first continents are comprised of three types of granitoid rocks—tonalite, trondhjemite and granodiorite (TTG). Credit Jaana Halla Usage Restrictions Credit must be given to the creator. License CC BY Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.