The D-loop in tRNA contains the modified nucleotide dihydrouridine. It is composed of 7 to 11 bases and is closed by a Watson Crick base pair. The TψC-loop (generally called the T-loop) contains thymine, a base usually found in DNA and pseudouracil (ψ). The D-loop and T-loop form a tertiary interaction in tRNA.
Reference: Holbrook,S.R., J.L.Sussman, R.W.Warrant, and S.H.Kim. 1978. Crystal-Structure of Yeast Phenylalanine Transfer-RNA.2. Structural Features and Functional Implications. JMB 123:631-660.