How did reducing the employment gender gap impact the US economy? Premise
In the United States, women have been replacing men in the workforce, or rather were from sometime prior to 1976 until the mid-90's. (The general upward trend is from the recent recession, sorry, I'm recycling a graph from another presentation).

Presumably, this occurred when a more qualified woman got a job over a male counterpart as women entered the workforce.
Given that, one would expect the economy to grow substantially as overall productivity rose.
Yet US GDP growth did not appear to outpace the world over that period, since not all the world liberalized their gender roles simultaneously.

Question
Why is that?
Is there a flaw in the reasoning, or were the effects simply not visible at the scale I've looked because the data was too volatile or confounded by external factors.
I'd be interested in any studies that dealt with this topic and offered potential causal mechanisms for breaking the presumed link between (again, the presumed) increased efficiency, and output growth.
Thanks!
Sources:

LNS10000001 - Civilian noninstitutional population, male
LNS11000001 - Civilian labor force, male
LNS10000002 - Civilian noninstitutional population, female
LNS11000002 - Civilian labor force, female
Google
I'm eyeballing that the unemployment rate of man rose by 3% while the rate for woman fall by 13. Clearly not all of those newly working woman replaced man.  

You choose a rather long period with incredible changes to the US economy; The one I think responsible for the effect you saw being the shift from manufacturing to service.

The Situation in 1977 can be seen on Page 10 (4 in the original numbering) of the 1977 Census.
It shows 44% of all employees working in manufacturing and 39% in service (Retail + "Selected services industries".

Contrast that to the 1997 Economics Census (Page 20 or 14) where "Retail Trade" alone employed more people than manufacturing - and Services almost double compared to manufacturing.

That shift favored woman (and probably was only possible due to more woman choosing not be stay-at-home moms) which explains the diminishing employment gap.

(The methodology of those reports has changed considerably so the exact percentage rates can certainly not be compared -- but the shift is so big that the conclusion stands unchallenged)