Question: The Iron Gate breaks up the mountains between Samarkand and a province which is 20 kilometers northwest of what provincial capital?

Related documents: [0]  [DOC] The Iron Gate is a defile between Balkh and Samarkand. It breaks up the mountains which extend from the Hisar range south towards the Amu Darya. In ancient times it was used as the passage between Bactria and Sogdia and was likely of great importance to any power in the region. Its name comes from the belief that an actual gate, reinforced with Iron, stood in the defile. It is located to west from Boysun, Surxondaryo Province. [END] 
[1]  [DOC] Balkh ( ; Persian/Pashto: بلخ‎ "Balkh"; Bactrian: βαχλο, "ẞaxlɔ") is a town in the Balkh Province of Afghanistan, about 20 kilometers northwest of the provincial capital, Mazar-e Sharif, and some 74 km south of the Amu Darya river. It was historically an ancient centre of Buddhism, Islam, and Zoroastrianism and one of the major cities of Khorasan, since the latter's earliest history. [END]  
Answer: Mazar-e Sharif
Mazar-e Sharif