BlackRock's iShares unit operates exchange-traded funds that track dozens of indexes from well-known benchmarking outfits like Standard & Poor's and MSCI. Now, the investment manager wants to create some of those benchmarks itself.

The iShares family, which controls slightly less than half the $1 trillion invested in US ETFs, filed late Thursday with the Securities and Exchange Commission for clearance to offer iShares ETFs that track potential proprietary BlackRock indexes, something it has never done before.