Return subclass of return object in override of abstract method

Question

I am porting a portion of Google Gson (Java) to C#. The public abstract class JsonElement defines the following:

public abstract JsonElement deepCopy();

which can be easily translated into C#:

public abstract JsonElement DeepCopy();

The public final class JsonArray (public sealed class in C#), which extends JsonElement, defines the following:

@Override
public JsonArray deepCopy() {
    //irrelevant code
}

which I attempted to translate into C#:

public override JsonArray DeepCopy()
{
    //irrelevant code
}

However, this produces an error:

'JsonArray.DeepCopy()': return type must be 'JsonElement' to match overridden member 'JsonElement.DeepCopy()'

How do I work around this?