Fidelity Investments is winding down a fund that had more than $3 billion in assets last year, with the Boston-based money manager citing an overlap in holdings of other funds used in its target-date products to explain the rare move.

The Fidelity Series 100 Index Fund is one of about 30 funds that make up the target-date portfolios in the Fidelity Freedom Funds. It had $3.5 billion in assets late last year, but money managers at Fidelity have been winding down its assets in recent months.

The Fidelity Freedom 2060 Fund, for example, has 9 different funds that hold shares of iPhone maker Apple Inc , including the Series 100 Index Fund, according to Fidelity disclosures.

At the end of May, the Series 100 Index Fund's largest holding was Apple, which accounted for nearly 7 percent of its assets, according to disclosures with the U.S. Securities and Exchange Commission.

"The management team felt that the combination of other series funds would achieve the desired portfolio characteristics, and have been reducing exposure to Series 100 Index," Fidelity spokesman Adam Banker said on Thursday.

The Series 100 Index Fund accounted for only 0.02 percent of the assets in the Fidelity Freedom 2020 Fund at the end of July. Fidelity's investor website no longer provides information on the Series 100 Index Fund.