How to interpret two clauses separated by a semicolon, then followed with a colon

I can't say I know in what sense you mean a colon applies to a preceding clause, so I'm not sure I can entirely answer your question. But I think there are some assumptions and terminological confusion in it that should be addressed. You probably know these things, but just to keep terminology straight:

• Sentences are groups of words which work together to complete a thought and can therefore stand and on their own; sentences begin with a capitalized word and end with terminal punctuation: period, question mark, or exclamation point--not a colon or semicolon.

  Groups of words which are grammatical and semantic equivalents of sentences but are only part of a sentence are called independent clauses. They must be punctuated correctly, usually separated from each other with a semicolon or a comma and coordinating conjunction. The independent clauses in a sentence should work together to completely address a single topic. What comes after a colon should be even more closely related to the preceding clause; its structure can vary.

  Sentences and independent clauses are both statements.

Following your schematic example, substituting "statement" for "sentence," statement 1 and statement 2 are independent clauses separated by a semicolon; whatever comes after the colon specifically fulfills, exemplifies, or supplements a thought broached in statement 2 and can have various grammatical forms: a single word, a phrase, or an independent clause begun with a capitalized word.