The Mishnah in Brachot 1:2 tells us that:
הַקּוֹרֵא מִכָּאן וְאֵילָךְ לֹא הִפְסִיד, כְּאָדָם הַקּוֹרֵא בַתּוֹרָה:
If one recites [Shema] later than this (The third hour), he has not lost out, [but rather is] like one who reads the Torah.
The reason we are allowed to say shema in tefilla after the sof ziman kiriat shema is because it counts as limud torah. What is the halacha, however, if You miss the sof ziman for kiriat shema on Tisha B'av, since you are not allowed to learn Torah on that day, so it can't count as limud Torah?