Use "<<<" to start *and end* the blockquote (not ">>>")
This is before the blockquote
<<<
<nowiki>
this is blockquote text
note the SAME sequence is used to start and end the blockquote.
</nowiki>
<<<
This is after the blockquote
Note that in TWClassic, the blank line before the <<< is will be displayed as literal text (an actual blank line)... you can safely omit the blank line if you don't want the whitespace; however, in TW5, the blank line preceding the "<<<" is needed so the blockquote syntax won't be treated as "inline mode" content rather than being recognized as the start of "block mode" content. The blank line is not actually displayed.
enjoy,
-e
Eric Shulman
TiddlyTools / ELS Design Studios