The 131-year-old historic cathedral's spire snapped in half and the building suffered major structural damage in the February 22, 2011 quake, which killed 185 people.
CPT also says the Act did not apply in this case because it was superseded by a Canterbury Earthquake Recovery Authority (Cera) section 38 unsafe building notice, which demanded urgent action.
Earlier this year, Anglican Bishop Victoria Matthews announced plans to deconstruct the cathedral to a safe level of 2-3 metres above the ground in a decision that sparked public protests.
The church trustees have vowed to build a cathedral on the Cathedral Square site, no matter what shape it takes or what any legal outcome is.
They have consistently said they want to build a new structure that is a "combination of the old and the new" while many Cantabrians, including the GCBT, would prefer it to be rebuilt to its original 19th century design.
Mr Ormsby said that the trustees can use the legal powers under the Act only if when it meets the "objectives and purposes" of the trust.
In this case, there was no implicit restriction against deconstruction in the Act, he said.
"The power to develop is clearly wide enough to include partial deconstruction and rebuilding post-earthquakes."
Francis Cooke QC, counsel for GCBT, said the trust was established, with financial backing from the city council and the public, for the original cathedral only.
He argued that the trustees had a legal and moral responsibility to save the building, which was intended to be a cathedral in perpetuity".
"At the outset it was 'a' cathedral, but once it was built it was 'the' cathedral," he said.
Mr Cooke said it was a "symbol of the city" which was trying to reestablish itself after the devastating earthquakes, adding that church and community were intrinsically linked.
Trustees had to consider the wider community of post-disaster Christchurch, and not just their own ecclesiastical interests, when considering the future of its cathedral, he said.
"The cathedral is a public institution. The trustees cannot be free to do what they like," Mr Cooke said.
He said a decision by the trust to use some of its $40 million insurance payout to build the $5m transitional "cardboard" cathedral on a different site amounted to a "breach of trust".
CPT say they do not have the funds available for a maximum retention option, or a replica rebuild, with estimated costs over a five-year build now soaring to $109m plus GST.
Justice Lester Chisholm reserved his decision, which Mr Ormsby said the church hoped would be quick and clear-cut.
"The problem for everyone here is that events have intervened in a way no-one would wish and left a headache for everyone," the judge said.
