Hi,
it seems that nothing provides tcl >= 8.6.7 needed by tk-8.6.7-1.1.aarch64:

orion:~ # zypper dup --no-allow-vendor-change
Loading repository data...
Reading installed packages...
Computing distribution upgrade...

Problem: nothing provides tcl >= 8.6.7 needed by tk-8.6.7-1.1.aarch64
 Solution 1: keep obsolete tk-8.6.6-1.4.aarch64
 Solution 2: break tk-8.6.7-1.1.aarch64 by ignoring some of its dependencies

Choose from above solutions by number or cancel [1/2/c] (c): 

orion:~ # cat /etc/os-release 
NAME="openSUSE Tumbleweed"
# VERSION="20170831"
ID=opensuse
ID_LIKE="suse"
VERSION_ID="20170831"
PRETTY_NAME="openSUSE Tumbleweed"
ANSI_COLOR="0;32"
CPE_NAME="cpe:/o:opensuse:tumbleweed:20170831"
BUG_REPORT_URL="https://bugs.opensuse.org"
HOME_URL="https://www.opensuse.org/"

orion:~ # uname -a
Linux orion 4.12.9-1-default #1 SMP Fri Aug 25 07:08:45 UTC 2017 (f2ab6ba)
aarch64 aarch64 aarch64 GNU/Linux

Thank you.

-- Emiliano