You mention AspNetUsers which lead me to https://msdn.microsoft.com/en-us/magazine/dn818488.aspx. This mentions that next to the passwordhash a SecurityStamp GUID is stored. The part you posted after the : is a GUID and unlikely a salt.
On https://www.blinkingcaret.com/2017/11/29...swordhash/ this base64 format is explained.
It looks like your Base64 encoded data is partly the salt and partly the PBKDF2 hash. First byte is for version (yours is Version 2) Next 16 bytes are the salt and the rest is the hash (PBKDF2 with HMAC-SHA1, 128-bit salt, 256-bit subkey, 1000 iterations.)
On https://www.blinkingcaret.com/2017/11/29...swordhash/ this base64 format is explained.
It looks like your Base64 encoded data is partly the salt and partly the PBKDF2 hash. First byte is for version (yours is Version 2) Next 16 bytes are the salt and the rest is the hash (PBKDF2 with HMAC-SHA1, 128-bit salt, 256-bit subkey, 1000 iterations.)