There are bits that are mutually exclusive in an ical file.
If you specify at TZID property for timezone, it won't work if you also make the time properties Zulu time (i.e. they end in Z).
You need to remove the Z from the end of the date time properties.
This is important for the Google Calendar import to work as well as it must be using the RFC spec.
with the Z at the end, the times are specified to not float (i.e. remain fixed).
On a Google Calendar ical import, you can skip the TZID - and - remove the Zulu time zone spec from the properties and just set the overall timezone of the calendar before the import.
See "FORM #2: DATE WITH UTC TIME" from the link below:
Related RFC link: http://www.kanzaki.com/docs/ical/dateTime.html