How to make parentheses bigger (to fit the size of an expression inide of them) in an R plot label? -

for example. consider code

plot(rnorm(10), xlab = na, ylab = na) mtext(side=1, expression( paste("log"["10"], ( frac( "x","y") ) )))  

i make parentheses in expression larger, fit size of expression inside them. note expression more complicated in actual script, minimal reproducible example captures essence of problem.

from demo pointed out @pascal, answer use bgroup

mtext(side=1, expression( paste("log"["10"], bgroup("(", frac( "x","y"), ")" ) )))