You can use FROM_TZ to form a TIMESTAMP WITH TIME ZONE value by combining a TIMESTAMP and a TIME ZONE. Next, use SYS_EXTRACT_UTC to convert it into UTC Time.
SQL> select from_tz(timestamp'2013-02-03 14:05:53','05:30'),
sys_extract_utc(from_tz(timestamp'2013-02-03 14:05:53','05:30'))
from dual;
FROM_TZ(TIMESTAMP'2013-02-0314:05:53','05:30') SYS_EXTRACT_UTC(FROM_TZ(TIMESTAMP'2013-02-0314:05:53','05:30'))
------------------------------------------------- -----------------------------------------------------------------
03-FEB-13 02.05.53.000000000 PM +05:30 03-FEB-13 08.35.53.000000000 AM